Constraints on Language: Aging, Grammar and Memory

Constraints on Language: Aging, Grammar, and Memory This page intentionally left blank. Constraints on Language: Ag...

Author: Susan Kemper | Reinhold Kliegl

47 downloads 1630 Views 2MB Size Report

This content was uploaded by our users and we assume good faith they have the permission to share this book. If you own the copyright to this book and it is wrongfully on our website, we offer a simple DMCA procedure to remove your content from our site. Start by pressing the button below!

Report copyright / DMCA form

DOWNLOAD PDF

Constraints on Language: Aging, Grammar, and Memory

This page intentionally left blank.

Constraints on Language: Aging, Grammar, and Memory

edited by

Susan Kemper University of Kansas and

Reinhold Kliegl University of Potsdam

Kluwer Academic Publishers New York/Boston/Dordrecht/London/Moscow

eBook ISBN: Print ISBN:

0-306-46902-2 0-7923-8526-8

©2002 Kluwer Academic Publishers New York, Boston, Dordrecht, London, Moscow All rights reserved No part of this eBook may be reproduced or transmitted in any form or by any means, electronic, mechanical, recording, or otherwise, without written consent from the Publisher Created in the United States of America Visit Kluwer Online at: and Kluwer's eBookstore at:

http://www.kluweronline.com http://www.ebooks.kluweronline.com

CONTENTS

List of Contributors

vii

Preface

xi Susan Kemper

Part 1: Constraints on Language: Aging

1

Language Production and Aging

3

1.

Deborah M. Burke

2.

Working Memory and Spoken Language Comprehension: 29 The Case for Age Stability in Conceptual Short-Term Memory Arthur Wingfield and Patricia A. Tun

3.

Discourse Processing and Aging: Resource Allocation As a Limiting Factor

53

Elizabeth A. L. Stine-Morrow and Lisa M. Soederberg Miller

Part 2: Constraints on Language: Memory

77

4.

79

Limitations on Syntactic Processing Susan Kemper and Karen A. Kemtes

v

vi

5.

Verbal Working Memory Capacity and On-Line Sentence Processing Efficiency in the Elderly

107

Gloria Waters and David Caplan

6.

Testing Age Invariance in Language Processes

137

Reinhold Kliegl, Ulrich Mayr, Martina Junker, and Gisbert Fanselow

Part 3: Constraints on Language: Grammar 7.

Processing Difficulty and Principles of Grammar

169 171

Gisbert Fanselow, Reinhold Kliegl, and Matthias Schlesewsky

8.

Parsing and Memory

203

Lyn Frazier

Part 4: Constraints on Language: Neuroscience

225

9.

227

Working with Limited Memory: Sentence Comprehension in Alzheimer's Disease Daniel Kempler, Amit Almor, Maryellen C. MacDonald, and Elaine S. Andersen

10.

Memory or Aging? That's the Question: An Electrophysiological Perspective on Language

249

Thomas C. Gunter, Sandra H. Vos, and Angela D. Friederici

11.

Age Effects on the Functional Neuroanatomy of Syntactic Processing in Sentence Comprehension

283

David Caplan and Gloria Waters

Concluding Observations

299

Reinhold Kliegl and Susan Kemper

Index

309

LIST OF CONTRIBUTORS

Dr. Amit Almor Department of Psychology University of Southern California Los Angeles, Ca 90089 [email protected] Dr. Elaine S. Andersen Department of Linguistics University of Southern California Los Angeles, Ca 90089 [email protected] Dr. Deborah M. Burke Department of Psychology Pomona College Claremont, CA 917 11 [email protected] Dr. David Caplan Neuropsychology Laboratory Department of Neurology Massachusetts General Hospital Boston, MA 021 14 [email protected] Dr. Gisbert Fanselow Department of Linguistics and Innovationskolleg "Formal Models of Cognitive Complexity" University of Potsdam Potsdam D14469 Germany [email protected] vii

viii

Dr. Angela Friederici Max Planck Institute for Cognitive Neuroscience Stephanstrasse la Leipzig D-04103 Germany [email protected] Dr. Lyn Frazier Department of Linguistics University of Massachusetts Amherst, MA 01003 [email protected] Dr. Thomas C. Gunter Max Planck Institute for Cognitive Neuroscience Stephanstrasse la Leipzig D-04103 Germany [email protected] Martina Junker Department of Psychology and Innovationskolleg "Formal Models of Cognitive Complexity" University of Potsdam Potsdam D14469 Germany [email protected] Dr. Susan Kemper Gerontology Center 4089 Dole University of Kansas Lawrence, KS 66045 [email protected] Dr. Daniel Kempler Department of Otolaryngology School of Medicine and the Leonard Davis School of Gerontology University of Southern California Los Angeles, CA 90089 [email protected]

ix

Dr. Karen Kemtes Volen National Center for Complex Systems Brandeis University Waltham, MA 02254 [email protected] Dr. Reinhold Kliegl Department of Psychology and Innovationskolleg "Formal Models of Cognitive Complexity" University of Potsdam Potsdam D14469 Germany [email protected] Dr. Maryellen C. MacDonald Departments of Psychology and Linguistics University of Southern California Los Angeles, CA 90089 [email protected] Dr. Ulrich Mayr Department of Psychology and Innovationskolleg "Formal Models of Cognitive Complexity" University of Potsdam Potsdam D14469 Germany [email protected] Dr. Lisa Soederberg Miller Department of Psychology Brandeis University Waltham, MA 02254 [email protected] Dr. Matthias Schlesewsky Department of Linguistics and Innovationskolleg "Formal Models of Cognitive Complexity" University of Potsdam Potsdam D14469 Germany [email protected]

x

Dr. Elizabeth Stine-Morrow Department of Psychology University of New Hampshire Durham, NH 03824 [email protected] Dr. Patricia A. Tun Department of Psychology and Volen National Center for Complex Systems Brandeis University Waltham, MA 02454 [email protected] Dr. Sandra H. Vos Max Planck Institute for Cognitive Neuroscience Stephanstrasse la Leipzig D-04103 Germany [email protected] Dr. Gloria Waters Department of Communication Disorders Boston University 635 Commonwealth Ave. Boston, MA 02215 [email protected] Dr. Arthur Wingfield Department of Psychology and Volen National Center for Complex Systems Brandeis University Waltham, MA 02254 [email protected]

PREFACE Susan Kemper

A debate about the role of working memory in language processing has become center-most in psycholinguistics (Caplan & Waters, in press; Just & Carpenter, 1992; Just, Carpenter, & Keller, 1996; Waters & Caplan, 1996). This debate concerns which aspects of language processing are vulnerable to working memory limitations, how working memory is best measured, and whether compensatory processes can offset working memory limitations. Age-comparative studies are particularly relevant to this debate for several reasons: difficulties with language and communication are frequently mentioned by older adults and signal the onset of Alzheimer's dementia and other pathologies associated with age; older adults commonly experience working memory limitations that affect their ability to perform everyday activities; the rapid aging of the United States population has forced psychologists and gerontologists to examine the effects of aging on cognition, drawing many investigators to the study of cognitive aging. Older adults constitute ideal population for studying how working memory limitations affect cognitive performance, particularly language and communication. Age-comparative studies of cognitive processes have advanced our understanding of the temporal dynamics of cognition as well as the working memory demands of many types of tasks (Kliegl, Mayr, & Krampe, 1994; Mayr & Kliegl, 1993). The research findings reviewed in this volume have clear implications - for addressing the practical problems of older adults as consumers of leisure timereading, radio and television broadcasts, as targets of medical, legal, and financial documents, and as participants in a web of service agencies and volunteer activities. Older adults are often the recipients of "elderspeak," an insulting and patronizing form of address which is intended to enhance older adults' comprehension (Kemper, 1992; Kemper, Finter-Urczyk, Ferrell, Harden, & Billington, in press); yet elderspeak, by conveying a sense of disrespect, may offend older adults, reducing intergenerational contact and thereby indirectly contributing to older adults' cognitive and social decline (Ryan, Giles, Bartolucci, & Henwood, 1986). Effective strategies for enhancing older adults' comprehension must be developed xi

xii

which will minimize processing demands without relying on "baby talk." Broadcasts and texts targeted at older adults must be adapted to slower information processing rates and reduced working memory capacity if older adults are to continue to be informed and engaged. The chapters in this volume examine what is known about memory, aging, and grammar in order to better understand how such constraints affect language and communication. PLAN

OF THE

BOOK

The contributors to this volume fall into three clusters: (1) Leading cognitive aging researchers with special expertise in language production and comprehension (Kemper, Burke, Kliegl, Stine-Morrow, Waters, Wingfield); (2) Syntacticians concerned with developing performance-based models of language (Frazier and Fanselow); (3) Neuroscientists studying language processing (Gunter, Caplan, Kempler). These researchers adopt a variety of methodological approaches to the study of language processing including psycholinguistic investigations of comprehension and production, psychometric studies of the component processes of reading and of individual differences, neuroimaging studies of linguistic function, and neurolinguistic investigations of pathologies of language. Research populations including young and older adults, older adults with dementia and other age-related diseases, and speakers of English and German. The first set of chapters draws upon recent research in cognitive aging to consider how language production and comprehension are constrained by aging. Studies of normal aging adults offer a unique opportunity to study the role of working memory in language processes. Each chapter focuses on a different aspect of language processing and explores how the architecure of cognition affects language processing. In Chapter 1, Burke draws upon Node Structure Theory in order to consider how asymmetries in language production and perception can arise from limitations of phonological access. She presents new evidence from experimental and naturalistic studies of verbal fluency, word finding, name retrieval, and spelling that highlight how constrains on phonological access can affect older adults. In Chapter 2, Wingfield and Tun focus on studies of spoken language perception to consider the role of working memory and the role of compensatory mechanisms in language processing. In Chapter 3, Stine-Morrow and Soederberg Miller consider how time as a limited resource can affect older adults' reading comprehension. They use regression techniques to decompose the reading process, discovering how some components may be disadvantaged by slower processing whereas other components of reading may be advantaged by slower processing. The chapters in Section 2 focus on syntactic processing. Kemper and Kemtes in Chapter 4 review recent research on the effects of working memory limitations on language processing with an emphasis on syntactic processing. In Chapter 5, Waters and Caplan consider whether there are significant individual differences in working memory, how they best might be measured, and the extent to which such individual differences affect on-line language processing. In Chapter 6, Kliegl and his colleagues investigate how syntactic factors interact to affect older adults' processing of complex constructions. Like the other contributors to this section, they argue that

xiii

some aspects of language processing are age-invariant whereas others are agevarying. Kliegl et al. also provide a detailed tutorial on alternative experimental paradigms for investigating age invariance in language processing. The contributors in Section 2 identify a mosaic of age-spared versus age-impaired language processes at lexical - sentence - and discourse levels of analysis; age-spared processes appear to be buffered from working memory whereas age-varying processes are dependent on working memory. The third set of chapters offer insights from contemporary models of syntax. Both contributors seek to define which aspects of language are subject to working memory constraints and which are buffered from working memory limitations. In Chapter 7, Fanselow and his colleagues, working from a Minimalist perspective, consider parallels between formal grammatical theory and the operation of the human syntactic parser. They argue that grammars avoid postulating movement operations in the same way that human parsers do. Drawing upon linguistic arguments as well as experimental studies, they consider the costs of movement operations in both German and English. In Chapter 8, Frazier also draws upon linguistic arguments as well as experimental studies of reading to examine how sentence complexity as well as discourse factors can affect comprehension. The final set of chapters draws on neuroscience studies of language processing to examine how working memory may be affected by aging and, in turn, affect language processing. In Chapter 9, Kempler and his colleagues draw on comparative studies of healthy older adults and adults with probable Alzheimer's dementia. They show how Alzheimer's dementia selectively impairs semantic processes, including word retrieval and word comprehension, while sparing basic syntactic processes. In Chapter 10, Gunter and his colleagues from the MPI in Cognitive Neurosciences present evidence for age-related working memory limitations on syntactic processing from a study of event-related potentials (ERPs) measured during a sentence reading task. The effects of syntactic complexity on the pattern of ERPs varied with age and working memory capacity, providing further insight into the role of working memory in syntactic parsing. In Chapter 11, Caplan and Waters look at how the use of positron emission tomography (PET) can help to resolve questions concerning the neurological localization of language processing. They suggest that aging may affect language processing at the level of neurological organization and localization. Kliegl and Kemper provide a summary discussion of issues raised by these chapters in their Conclusion. ORIGINS

OF THE

BOOK

This book is based on a workshop sponsored by the Merrill Advanced Studies Institute and the Research Training Program in Communication and Aging at the University of Kansas. The workshop was held March 25 - 29, 1998 in Sedona, AZ. Participation was limited to the senior contributing authors (Burke, Wingfield, Waters, Stine-Morrow, Kliegl, Fanselow, Frazier, Gunter, Kempler, and Caplan) plus a small group of students and faculty from the University of Kansas. We thank Mabel Rice, the Director of the Merrill Advanced Studies Institute and University Distinguished Professor, for her support and encouragement, Meredith Porter for her

xiv

excellent arrangements, and Diane Filion, Ruth Herman, Mary Lee Hummert, Karen Kemtes, Joan McDowd, Melanie Morgan, Laureen O’Hanlon, Pam Saunders, Dick Schiefelbusch, Shari Speer, and Steve Schroeder for their spirited participation and assistance with the workshop. The Research Training Program in Communication and Aging is supported by a grant from the National Institute on Aging, T32 AG000226.

xv REFERENCES

Caplan, D., & Waters, G. S. (in press). Verbal working memory and sentence comprehension. Behavioral and Brain Sciences. Just, M. A., & Carpenter, P. A. (1992). A capacity theory of comprehension: Individual differences in working memory. Psychological Review, 99, 122149. Just, M. A., Carpenter, P. A., & Keller, T. A. (1996). The capacity theory of comprehension: New frontiers of evidence and arguments. Psychological Review, 103, 773-780. Kemper, S. (1994). Elderspeak: Speech Accommodations to older adults. Aging and Cognition, 1, 17-28. Kemper, S., Finter-Urczyk, A., Ferrell, P., Harden, T., & Billington, C. (in press). Using Elderspeak with Older Adults. Discourse Processes. Kliegl, R., Mayr, U., & Krampe, R. Th. (1994). Time-accuracy functions for determining process and person differences: An application to cognitive aging. Cognitive Psychology, 26, 134-164. Mayr, U., & Kliegl, R. (1993). Sequential and coordinative complexity: Age-based processing limitations in figural transformations. Journal of Experimental Psychology: Learning, Memory, and Cognition, 19, 1297-1320. Ryan, E. B., Giles, H., Bartolucci, G., & Henwood, K. (1986). Psycholinguistic and social psychological components of communication by and with the elderly. Language and Communication, 6, 1-24. Waters, G. S., & Caplan, D. (1996). The capacity theory of sentence comprehension: Critique of Just and Carpenter (1992). Psychological Review, 103,761-772.

This page intentionally left blank.

Part 1

CONSTRAINTS ON LANGUAGE: AGING

This page intentionally left blank.

1

LANGUAGE PRODUCTION AND AGING Deborah M. Burke

When older adults are asked to identify problems in their daily cognitive functioning, certain aspects of language production are at the top of their list. They rate word finding failures and tip of the tongue experiences (TOTs) as their most severe cognitive problems, and the ones most affected by aging (Rabbitt, Maylor, McInnes, Bent & Moore, 1995; Ryan, See, Meneer & Trovato, 1994; Sunderland, Watts, Baddeley, & Harris, 1986). Although older adults’ complaints focus on word retrieval failures, younger adults believe that older adults suffer general declines in their ability to produce effective language (Giles, Coupland & Wiemann, 1992; Ryan & Laurie, 1990). In this chapter, we investigate whether aging affects language production in only specific functions, or across the board. This question is important for evaluating two different types of theories of cognitive aging: informationuniversal and information-specific theories. We focus on word retrieval, reviewing empirical evidence that sheds light on the nature of age-related changes in production processes during adulthood. This evidence suggests an asymmetric effect of aging on different aspects of production, and we discuss the implications of this pattern for the two classes of theory. Changes in language production in old age carry practical as well as theoretical significance, because language production is a critical component of interpersonal communication. If aging impairs production, this may disrupt interpersonal communication, contributing to social isolation. Moreover, people use language production in their everyday interactions as an index of intellectual functioning. Impaired word production, for example, may negatively affect both self-evaluation of cognitive ability and evaluation by others (e.g., Ryan et al., 1994). Negative selfappraisal may promote withdrawal from social interaction, and negative appraisal by others may promote the use of simplified speech to older adults, which appears to further erode their self-evaluation of cognitive functioning (Cohen, 1994; Kemper, Othick, Warren, Gubarchuk, & Gerhing, 1996; Hummert, 1994; Ryan et al., 1994). This downward spiral linked to impaired production highlights the practical 3

4

Figure 1. A sample of nodes in the semantic and phonological systems representing the common nouns mausoleum and mortuary. Many nodes have been left out to simplify the figure. The arrows indicate the spread of priming, top-down, when nodes are activated during production. significance of identifying age-related changes in language production and the underlyingmechanisms. MODELS OF WORD PRODUCTION

There is considerable agreement about the production processes that allow us to name an object or produce a word in spontaneous speech. Probably the best specified and most popular production models are interactive activation models, a type of connectionist model with excitatory and inhibitory connections among representational units. A vast network of pathways connecting representational units is organized into a semantic system which represents word meanings and a phonological and orthographic system which represent word sounds and spellings, respectively (e.g., Burke, MacKay, Worthley, & Wade, 1991; Dell, 1986; Dell, Burger & Svec, 1997; Griffin & Bock, 1998; Harley, 1993; Levelt, 1989; MacKay,

5

1987; MacKay & Abrams, 1998; Stemberger, 1985). Production begins with activation of conceptual units and the spread of excitation through the network, priming semantically appropriate lexical representations which prepares them for activation (retrieval). Phonological representations corresponding to a lexical unit are primed, but temporal aspects of this priming are model-dependent. In some models selection of the lexical unit is completed before access to phonology (e.g., Levelt et al., 1991). In other models, phonological priming occurs during lexical selection so that priming from phonological nodes affects lexical selection in an interactive process (e.g., Dell et al., 1997; Harley, 1993; MacKay, 1987). Interactive activation models vary on specific features; we delineate one model which provides a framework for understanding word production in old age. Figure 1 illustrates aspects of the semantic, lexical and phonological representation of two words, mausoleum and mortuary according to MacKay’s (1987) interactive activation model, Node Structure Theory. The organization of representations or nodes is hierarchical with semantic representations connecting to a lexical node for each word, and lexical nodes connecting to phonological nodes. Note that phonological and semantic nodes are also shared with other words with these components. For example, lexical nodes for mausoleum and mortuary connect to some of the same phonological nodes because they share the phonemes /mo/, and to some of the same semantic nodes because they share an association with death. As shown by the arrows in Figure 1, excitation of semantic features of mausoleum would spread to mortuary, and excitation of phonological components of mausoleum would spread to mortuary. This interactive activation process will explain characteristics of word retrieval failures that we take up below. Activation of a node causes retrieval of the information it represents (MacKay, 1982, 1987). A node is activated if its priming level reaches a critical difference above other nodes in the same domain, a selection rule that makes retrieval sensitive to the priming level of competing nodes (e.g., Wheeldon & Monsell, 1994). The strength of connections between nodes determines the rate and amount of priming transmitted between them and is an important determinant of what information in memory becomes available. Recency and frequency of node activation strengthen connections, whereas aging weakens connections, thereby decreasing the transmission of priming (Burke et al., 1991; MacKay & Burke, 1990). WORD PRODUCTION IN OLD AGE

There is considerable empirical evidence that word production processes are impaired for older adults, consistent with their self reports’ of increased word finding failures. In a review of 25 studies of the effects of aging on picture naming, the majority of studies reported that older adults produced fewer correct names than young adults (Goulet, Ska & Kahn, 1994). In their spoken discourse, older adults produced more pronouns and ambiguous references compared to young adults when describing a memorable experience (Ulatowska, Hayashi, Cannito & Fleming, 1986), a picture (Cooper, 1990), a video (Heller & Dobbs, 1993), or retelling a story (Pratt, Boyes, Robins & Manchester, 1989). This age difference reflects the greater

6

difficulty that older adults have in retrieving the appropriate nouns (but see Glosser & Deser, 1992). Speech disfluencies such as filled pauses, repetitions and hesitations increase with age and may indicate word retrieval difficulties (Cooper, 1990; Kemper, 1992a). A clear case of word finding difficulty is the TOT state in which a person is temporarily unable to produce a word although they are absolutely certain that they know it. In the words of William James (1890), a TOT is “... a gap that is intensely active. A sort of wraith of the name is in it...making us at moments tingle with the sense of our closeness” (p.251). The gap does hold the meaning of the word, allowing rejection of wrong words. What is missing from the gap is the complete phonology of the word, although partial phonological information or related words may come to mind. Older adults report more naturally occurring TOTs during everyday life than young adults (Burke et al., 1991) and more TOTs induced in the laboratory using definitions of rare words (e.g., Burke et al., 1991; Rastle & Burke, 1996) or pictures of rare objects (e.g., a bellows, a yoke) (Brown & Nix, 1996) or pictures of famous people (Maylor, 1990b). While filling out a family tree, older adults also reported a greater proportion of TOTs for the names of members of their extended family than young adults (Burke & Austin, 1999). Interestingly, partial information and alternate words occur during a TOT less frequently for older than young adults (Burke et al., 1991; Cohen & Faulkner, 1986; Maylor, 1990a). Older adults’ word retrieval failures do not seem to be caused by a deficit in formulating the idea to be expressed or in activating appropriate semantic information because studies consistently demonstrate age constancy in conceptual knowledge and its retrieval. For example, on the WAIS vocabulary test participants describe the meaning of presented words. Performance shows little change in adulthood, at least into the 70’s (e.g., Salthouse, 1982, 1988). Similarly, young and older adults produce comparable scripts for common activities (e.g., Light & Anderson, 1983), similar responses for word associations (e.g., Burke & Peters, 1986; Howard 1979; Lovelace & Cooley, 1982) and the same properties of nouns whose meaning is biased by sentence context (Burke & Harrold, 1988; Light, Valencia-Laver, & Zavis, 1991). These findings support the conclusion reached in a number of thorough reviews of the literature: Semantic processes are unaffected by aging (Kemper, 1992b; Light, 1991; MacKay & Abrams, 1996; MacKay & Burke, 1990; Tun & Wingfield, 1993). The locus of older adults’ word finding deficits would seem to be in retrieval at the lexical or phonological level. THEORIES OF AGE-RELATED PRODUCTION FAILURES

There are two theories that have been advanced to explain word production failures and their increase in old age. The Transmission Deficit model extends the Node Structure Theory and postulates that TOTs are caused by insufficient transmission of priming from lexical nodes to phonological nodes (Burke & MacKay, 1997; Burke et al., 1991; MacKay & Burke, 1990). A node is activated only if its accumulation of priming reaches a criteria1 level. If connection strength weakens to the point that transmission of priming to a target node is inadequate to raise its priming to this level, a retrieval failure or error will occur. TOTs occur when connections to

7

Figure 2. Lateral inhibition between lexical units is illustrated for mausoleum and mortuary. The broken line indicates lateral inhibition produced by a lexical unit in proportion to its level of excitation. phonological nodes become too weak to transmit adequate priming. Under the Transmission Deficit model, recency and frequency of node activation strengthen connections so that rare words or words not used recently should be most susceptible to TOT, as observed (Burke et al., 1991; Harley & Brown, 1998). Aging weakens connections so that older adults should produce more TOTs than young adults, as observed (e.g., Burke et al., 1991). The Transmission Deficit theory is an information-specific theory because the type or structure of language units determines whether or not there are aging effects. The functional effect of transmission deficits depends on the architecture of the memory system. Transmission deficits are more likely to involve nodes with one-onone connections, such as phonological nodes which have one-to-one connections with lexical nodes (see Figure 1). In contrast, transmission of priming from semantic nodes to lexical nodes is aided by the many connections that Iink related concepts and produce summation of priming at lexical nodes, making transmission deficits unlikely (see Laver & Burke, 1993). An alternative account of TOTs postulates inhibition as the mechanism underlying TOTs, capturing the phenomenology of an alternate word “blocking” access to the target word. Retrieval fails because another word, related to the target word and more available, blocks or inhibits the target word (e.g., Jones, 1989; Reason & Lucas, 1984; Woodworth, 1938). Within a connectionist model, this occurs through lateral inhibitory connections between lexical nodes, as shown in

8

e.g., Harley, 1993; McClelland & Rumelhart, 1981; Stemberger, 1985. For example, excitation of the lexical node for mausoleum would produce inhibition of related but incorrect words such as mortuary. If, however, mortuary had accumulated more priming than mausoleum, its higher levels of excitation would lead to inhibition of the intended word mausoleum. This inhibition explanation is relevant to age differences via the Inhibition Deficit model proposed by Hasher and Zacks (1988). They argued that inhibitory processes become less efficient in old age so that older adults are less able to

Figure 3. An example of the sequence of verbal cues and pictures in the primed competitor paradigm. Participants produced a response to each stimulus.

9

suppress irrelevant information which impedes retrieval of target information. Word retrieval failures occur because, for example, “...older adults might have trouble when trying to remember the names of acquaintances to make introductions, not because of the loss of access to the relevant memories, but because irrelevant ones are likely to be activated as well, which slows retrieval of the target memories” (Zacks & Hasher, 1994, p. 259). In Figure 2, inhibition of mortuary by the intended word mausoleum would be impaired in older adults, increasing the competition from mortuary for retrieval and increasing the probability that a TOT would occur because an alternate word, mortuary, would be produced, blocking retrieval of the target word. The Inhibition Deficit model is an information-universal theory because the mechanism underlying aging effects, namely, inhibition, is independent of the type or structure of language units being processed. Thus, inhibition deficits would have widespread effects on language production, allowing selection of incorrect information at the level of a lexical item, causing TOTs, but also at a higher, semantic level, causing the intrusion of irrelevant thoughts into discourse. For example, older adults are hypothesized to be less able to inhibit irrelevant ideas at a semantic level and this should drive their narratives or conversations off-topic and produce inappropriate comments and anecdotes (Arbuckle & Gold, 1993; Zacks & Hasher, 1994). WORD PRODUCTION, SEMANTIC COMPETITORS AND INHIBITION DEFICITS

Under the Inhibition Deficit model, older adults’ word retrieval deficits reflect their reduced ability to inhibit irrelevant words which compete for retrieval with the correct word, slowing or preventing its production. We tested this explanation in a series of experiments using a primed competitor paradigm in which recent production of a word increases its competition with a correct word in a subsequent picture naming task (Vitkovitch & Humphreys, 1991; Vitkovitch, Humphreys & Lloyd-Jones, 1993; Wheeldon & Monsell, 1994). Words likely to compete with the correct name of a picture are words for objects sharing physical and semantic attributes with the pictured object; such words would be primed along with the correct name in early stages of processing the picture, but additional processing should allow the correct name to be selected over the competitors. Wheeldon and Monsell (1994) demonstrated that prior production of competitors for a picture name made them more available when the picture was presented, slowing production of the correct picture name. This semantic competitor effect on naming latency reflects the interference of the competitors with retrieval of the correct lexical unit. Note that when semantically similar prime words precede a target picture by a brief interval (e.g., about one second), picture naming is speeded, a semantic priming effect attributed to spreading semantic activation from the prime word to the target (e.g., Lupker, 1988). Under conditions, however, where primes and targets are semantically similar and occur at intervals of several seconds, short-lived semantic facilitation has dissipated and naming is slowed (Kroll & Curley, 1988; Wheeldon & Monsell, 1994).

10

Under the Inhibition Deficit hypothesis, older adults are less able to inhibit irrelevant information so their picture naming should be slowed more than young adults’ by competitors. There are no published data on competitor effects on older adults’ production. Interestingly, however, in speech perception, there were no age differences in the effect of a strong competitor on word recognition in sentences (Stine & Wingfield, 1994). Loveless and Burke (1999) reported three experiments in which young and older adults saw a series of alternating verbal cues and pictures and responded to each stimulus as quickly and accurately as possible with the appropriate one word name (see Figure 3). Verbal cues and pictures were selected that elicited correct responses from young and older adults in pilot testing, and thus naming errors were rare. The verbal cues were constructed to elicit an unrelated word or a word that named an object that was semantically and physically similar to a picture, and thus likely to be a competitor for picture naming. The semantic competitor effect is calculated by subtracting naming latency for a target picture (e.g., cake in Figure 3) when a prior trial presented a verbal cue eliciting an unrelated prime word (dice), from target naming latency when a prior trial presented a verbal cue eliciting a semantically similar prime word (pie). In Experiment 1, two filler trials intervened between the verbal cue for a similar or unrelated prime word and the target picture as shown in Figure 3. Naming latency for target pictures was slower after production of semantically similar prime words (e.g., competitors) compared to unrelated words for 20 young and 30 older

Figure 4. The primed competitor effect for young and older adults in Experiments 1-3 (Loveless & Burke, 1999). The competitor effect is the difference (in milleseconds) between picture naming latency in the unrelated prime condition and the primed competitor condition.

11

adults. Figure 4 shows the primed competitor effect for this experiment in the first panel. Although older adults were slower than young adults overall, there was no statistically significant age difference in the slowing produced by the primed competitor. Indeed, the competitor effect was about half as large in absolute terms for old as for young adults. This raised the possibility that the semantic competitor slowed target retrieval through inhibition of the target and this effect was slightly weaker in older adults because of inhibition deficits. This possibility, however, garnered no support in two subsequent experiments. In Experiment 2, we attempted to increase the competitor effect, especially for older adults, by having participants process the competitor twice before picture naming. The logic is that recent processing of a word strengthens its lexical and phonological connections, increasing its availability for production. By creating two opportunities for processing the competitor, we hoped to increase its availability beyond that in the primed competitor condition of Experiment 1, thereby increasing the competitor effect, especially for older adults. Prior to the verbal cue and picture naming tasks, 21 young and 21 older adults rated the pleasantness of half of the semantically similar prime words (competitors) that were then cued in the subsequent naming task. As shown in the middle panel of Figure 4, the competitor effect was greater than in Experiment 1, but this cannot be attributed to the double processing, because the competitor effect was comparable with single and with double processing. Indeed, there was no increase in the competitor effect from the pleasantness rating task, perhaps because it did not require production of the competitor (see Small, Hultsch & Masson, 1995). The competitor effect was statistically significant for both young and older adults and the magnitude of the competitor effect did not differ by age. In Experiment 3, we attempted to strengthen the competitor effect by eliminating some competitor-picture pairs with relatively low physical similarity that had been used in the first experiment. In all other respects the experiment followed Experiment 1. As can be seen in Table 1, the competitor effect was almost double that in Experiment 1 for both young and older adults, suggesting that competition is related to the physical similarity of the competitor and target. Again there was no age interaction with the competitor effect. The results of these experiments are quite clear: There is no evidence that older adults are more disrupted than young adults by competing but incorrect words in word retrieval. Recent production of a competitor slowed naming, but the effect was comparable across age in three experiments. These findings are contrary to the Inhibition Deficit model, because older adults displayed no sign of a deficit or inefficiency in suppressing irrelevant information (competitors) during retrieval. According to this model, inhibition is the process responsible for suppressing competing but incorrect words in naming; the results suggest this process is maintained in old age. When the competitor effect is considered within a connectionist model with lateral inhibition, the prediction for age effects is quite different from that based on the Zacks and Hasher (1994) notion that irrelevant information slows retrieval until it is inhibited. In connectionist models, inhibition causes interference as well as ending interference. That is, inhibition is emitted from a node in proportion to the

12

node’s level of excitation (e.g., McClelland & Rumelhart, 1981; Stemberger, 1985). The primed competitor achieves relatively high levels of excitation early in the processing of the picture, because of its recently strengthened connections, and would emit inhibition that would slow excitation of the target. If inhibition is impaired in old age, older adults would be affected by competitors. This prediction also is inconsistent with the findings. The primed competitor effect can be explained without invoking inhibition. Under the NST, which has no lateral inhibition, a node is activated if its priming level reaches a critical difference above the priming levels of other nodes in the same domain. Thus, a criteria1 difference between the priming level of the lexical node for the target and the priming level of the lexical node for the competitor must be reached before the target lexical node can be activated. The recent production of the competitor will strengthen its connections increasing the transmission of priming to its lexical node during early processing of the picture. The increased level of priming for the competitor increases the amount of priming that the target must accumulate to achieve the critical difference, thereby delaying target activation and production of the correct name (e.g., Vitkovitch, Humphreys, & Lloyd-Jones, 1993; Wheeldon & Monsell, 1994). The literature on repetition priming effects suggests that recent generation of a word increases availability of the word for production to the same extent across age in production tasks such as category exemplar generation (e.g., Light & Albertson, 1989; Maki & Knopman, 1996) or general knowledge questions (e.g., Rastle & Burke, 1996; Small et al., 1995; see Fleischman & Gabrieli, 1998 for a review). Within the NST framework, this suggests that activation strengthens connections for existing representations in a similar way for young and older adults (MacKay & Burke, 1990). Thus, in the competitor priming paradigm, recent production increases transmission of priming to the competitor to the same extent in young and older adults. Why is there no indication of transmission deficits in older adults? For example, a deficit in transmission of priming to the lexical node for the target, but not the recently activated competitor, would increase the competitor effect in older adults. This effect is not predicted because the functional effect of transmission deficits depends on the architecture of the relevant connections and nodes. The competitor effect occurs at a lexical level where converging connections from semantic representations summate at lexical nodes (see Figure 1), compensating for a transmission deficit in any single connection (see Laver & Burke, 1993 for full exposition of this argument). WORD PRODUCTION, PHONOLOGICAL PRIMING AND TRANSMISSION DEFICITS

Under the Transmission Deficit model, TOTs occur when semantic information activates a lexical node but at least some phonological information remains inaccessible because deficits in the transmission of priming prevent activation of relevant phonological nodes. This effect is information specific, localized to phonological nodes because they are connected by single connections making them vulnerable to transmission deficits (see Figure 1). We tested this explanation using priming paradigms to progressively hone in on phonological processes over a series

13

of experiments. The goal was to test the prediction of the Transmission Deficit model that recent activation at a phonological level would improve word retrieval. Rastle & Burke (1996) demonstrated that prior processing of an answer to a general knowledge question increased production of the answer to the question and reduced TOTs. General knowledge questions were selected whose answers were relatively low frequency words that were likely to induce TOTs, e.g., What do you call a word or sentence that reads the same backwards or forwards, such as 'Madam I'm Adam (answer: palindrome). Before presentation of the questions, young and older adults performed the prior processing task, pronouncing aloud and rating the pronunciation difficulty of the words that were answers to half the questions. They then made one of three responses to each question: "Know" and produced the answer; “Don't know” or “TOT”. Performance was strongly influenced by the prior processing. Figure 5 shows that prior processing increased correct answers to the questions, and decreased TOTs by nearly 50% for both young and older adults, although older adults produced more TOTs. These findings are consistent with the hypothesis that TOT states are less likely for words that have been produced recently, and they support the Transmission Deficit model in which recent production of a word strengthens connections among phonological nodes, thus reducing the probability of a TOT. Because, however, this paradigm involved repetition of the same word, connections at a lexical as well as a phonological level may have been involved. In an effort to isolate the effects of priming at a phonological level, Rastle and Burke (1996) manipulated the type of processing of the answer in the prior processing task. Participants rated the pleasantness of the word in a semantic

Figure 5. Percentage of correct responses and TOTs as a function of age and prior processing. Adapted from Rastle and Burke (1996).

14

condition and counted the number of syllables in a phonological condition. They found that phonological processing of the target reduced TOTs, and adding semantic processing did not increase this priming effect. This supports the hypothesis that recency of target processing influences the likelihood of TOTs, and that the retrieval failure occurs at the phonological level, although lexical level effects are also possible here, despite the manipulation of type of prior processing, because the identical word was involved in the prior processing and the main production task. James and Burke (1998) removed lexical level effects by using words in the prior processing task that were phonologically similar (or dissimilar) to the target, but not identical to the target. All the words were semantically unrelated to the target word so there was no overlap of nodes at the semantic or lexical level between

Figure 6. Example of the prior phonological processing task and general knowledge questions in Experiment 1 of James and Burke (1998). The phonological components of related words that overlapped the answer are underlined. They were not underlined in the experiment. For the Unprimed condition, related words were replaced by words phonologically unrelated to the target.

15

prime and target words. The prior processing task occurred before presentation of each general knowledge question and involved 10 words phonologically unrelated to the answer to the question (Unprimed Condition) or 5 phonologically related and 5 unrelated words (Primed Condition). Figure 6 shows an example of this procedure in the Primed Condition. Each of the 10 words was presented one at a time and participants pronounced each word aloud and rated it on pronunciation difficulty. The general knowledge questions followed immediately. The Transmission Deficit model postulates that production of phonologically related words strengthens some connections in the phonological system required for production of the target. Thus, prior processing in the Primed condition should increase correct responses and decrease TOTs. Consistent with this, young and older adults increased correct responses by about 10% in the Primed condition and decreased TOTs about 10%. Both effects were statistically significant and there was no interaction with age. These results confirm the involvement of phonological connections in TOTs, and demonstrate that recent activation of phonological connections can preclude word retrieval failures. In a second experiment, James and Burke (1998) investigated the effect of phonological priming on target retrieval after a TOT had occurred. This experiment is relevant to a common TOT phenomenon: Naturally occurring TOTs are resolved by the target word popping into mind at a time when the person is no longer trying to retrieve the target and has directed their attention elsewhere. What causes these spontaneous word retrievals? This experiment tested the possibility that these "popups" arise when critical phonological components occur during everyday speech, inadvertently boosting phonological priming and enabling the word to pop into mind. For older adults the interval between the onset of a spontaneous TOT and a "pop up" is longer than for young adults (Burke et al., 1991). One interpretation of this is that older adults require more phonological priming and thus longer intervals for more stimulation to occur before a pop up is triggered. In this case, older adults may show smaller effects of phonological priming on retrieval than young adults in this experiment James and Burke (1998) induced TOT states in 18 young and 18 older adults using general knowledge questions as in the first experiment. When the response to a question was TOT or Don't Know, 10 words were presented as in Figure 6: Participants performed the same pronunciation and rating task as in Experiment 1 on 10 words phonologically unrelated to the TOT target or 5 phonologically related and 5 unrelated words. The same question was repeated immediately after presentation of the 10 words. Figure 7 shows the percent of correct responses to repeated questions that on their first presentation elicited a TOT responses. The Primed condition increased correct answers to the repeated question for both young and older adults and there was no age interaction, as can be seen in Figure 7. These results support the hypothesis that TOTs are caused by weak phonological connections that are strengthened by production of the relevant phonology. The only overlap between target and prime words was at the phonological level so lexical level effects can be ruled out. There is no evidence that older adults require more phonological production for resolution than young adults.

16

Figure 7. Percent correct responses to general knowledge questions repeated after an initial TOT response and a prior processing task with phonologically related (Primed condition) or unrelated words (Not Primed condition). What is the solution to the puzzle of why TOT targets come “spontaneously” to mind in everyday life when a person is no longer actively trying to retrieve the target? The results suggest the possibility that phonologically similar words occurring inadvertently in the environment activate phonological components of the target that had been unavailable because of transmission deficits. Activation of these components erases transmission deficits allowing the phonology for the TOT word to be activated, although somewhat belatedly. Why do such “pop ups” take longer in older than young adults (Burke et al., 1991)? In this laboratory study, language input and output during the TOT was held constant, and recovery of the target word occurred as rapidly for old as for young adults. Thus one possibility is that in everyday life there is less language input and output for older than young adults, providing more limited phonological stimulation. Moreover, there is some evidence that production, not just perception, of phonology is necessary for priming effects on older adults’ production (Small et al., 1995). Although this was not investigated in the present experiment because all prime words were spoken aloud, it is possible that older adults require speech output, not just input, to strengthen phonological connections involved in transmission deficits. SUMMARY: GENERAL OR SPECIFIC EFFECTS OF AGING ON WORD PRODUCTION

Impaired word production in old age seems to involve deficits in accessing specific types of information, namely, phonology. Our investigation of semantic competitor effects provided no evidence that older adults’ word finding deficits are caused by generalized inhibition deficits that increase interference with retrieval at a lexical level. Our investigation of priming at a phonological level provided evidence that

17

weak phonological connections caused word finding deficits and that activation of relevant phonology increased correct production of the target word. The pattern of findings in word production is most consistent with an information-specific theory because the age-related decline seems to be confined to one level of the language system, namely, production of phonology. Interestingly, age differences in picture naming increased for names with lower frequency or more syllables (Goulet et al., 1994), variables that affect the difficulty of accessing the phonological representation of the word (Griffin & Bock, 1998; Jescheniak & Levelt, 1994). This age effect, however, has been tested only with French speakers and additional research in English is needed. The Transmission Deficit model predicts age deficits in phonological retrieval, but not in semantic retrieval, because top-down connections for producing phonology are always one-to-one and this diverging characteristic of top-down connections increases their vulnerability to transmission deficits. Is the age-related word production deficit more general than naming and wordfinding? Recently, MacKay and Abrams (1998; MacKay, Abrams & Pedroza, in press) reported an important new age-related word production deficit that is predicted by Transmission Deficit model, but is so unexpected that it had been untested in experimental studies and self-report questionnaires alike: Older adults made more spelling errors than young adults in written production, an orthographic retrieval deficit. This age decline occurred despite age equivalence in the ability to detect spelling errors and despite the higher vocabulary and education levels of older compared to young adults. Older adults were more likely than young adults to misspell irregularly spelled letter combinations by regularizing them, e.g., calendar = > calender, and only the oldest group ( M = 77 years) misspelled regularly spelled combinations more than the young, e.g., calendar = > kalendar. Under the Transmission Deficit hypothesis, declines in producing phonology and orthography in old age are caused by the same mechanism, namely weak connections in the representational systems for phonology and orthography. Because both systems consist of many one-to-one connections, especially for irregularly spelled words, they are more vulnerable to age-related transmission deficits which disrupt retrieval (see MacKay & Abrams, 1998). Under the Transmission Deficit theory, word production deficits are information-specific and we would not expect older adults’ transmission deficits to affect language production at a higher level such as the production of semantically coherent discourse. In contrast, information-general theories such as the Inhibition Deficit theory predict impairments in older adults speech at the discourse level, not just the word level, because impaired inhibition affects information at all levels. Next we examine studies of aging and discourse to evaluate the adequacy of information-specific and information-general accounts. DISCOURSE PRODUCTION

Arbuckle, Gold and colleagues have demonstrated that older adults’ speech during interviews is more likely to lack focus and to stray off-topic (e.g., Arbuckle & Gold, 1993; Gold, Andres, Arbuckle, & Schwartzman, 1988). The explanation offered by

18

the Inhibition Deficit model is that older adults' reduced ability to inhibit irrelevant information makes it difficult or impossible for them to suppress thoughts that digress from the current speech topic, resulting in production of extraneous personal observations and unrelated information in their speech (Arbuckle & Gold, 1993; Zacks & Hasher, 1994). Indeed, off-topic speech in older adults has been attributed to inhibitory deficits caused by impaired frontal lobe function (Arbuckle & Gold, 1993; West, 1996; Zacks & Hasher, 1994). The view that off-topic speech is caused by a general deficit, namely, in inhibition, is inconsistent with findings that age-related increases in off-topic speech are not universal: Age differences are absent for some topics such as descriptions of a picture or a vacation (Cooper, 1990; Gould & Dixon, 1993). Moreover, if off-

Figure 8. Mean ratings on interest, informativeness, and story quality of descriptions about autobiographical topics of young and older speakers (a) and of older speakers in the high off-topic speech and low off-topic speech groups (b).

19

topic speech is the product of an impairment, it is surprising that people rate older adults’ narratives more highly than young adults’ (e.g., Kemper, Rash, Kynette, & Norman, 1990). James, Burke, Austin, & Hulme (1997) proposed that older adults’ off-topic speech results from age-related changes in pragmatic aspects of language, rather than from cognitive deficits. Older adults set different communicative goals than young adults under some conditions because they place greater value on personal narrative, reminiscence and establishing their identity in discourse (e.g., Coupland & Coupland, 1995). James et al. tested this account and the inhibition deficit explanation by examining age differences in off-topic speech for different discourse topics, and by examining ratings of the communicative quality of the discourse. In the first study, 20 young and 20 older adults described their education, their family, a vacation and three pictures. Analysis of verbatim transcriptions of their responses showed that older adults produced significantly more words and more off-topic speech than young adults, but only when describing the autobiographical topics, not the pictures. For the autobiographical topics, the percentage of words that were offtopic was 2.6% and 12.9% for young and older adults, respectively, almost a five fold difference. In a second study, 10 young and 10 older adults read the transcripts of the young and older adults’ autobiographical descriptions and rated them on several qualitative dimensions. As can be seen in Figure Sa, they rated older adults’ descriptions as more interesting and informative, and better stories than those of young adults. Both young and old raters showed this preference for older adults’ descriptions. Older adults were divided into a low off-topic speech group and a high off-topic speech group on the basis of their percentage of off-topic words for personal topics. As can be seen in Figure 8b, descriptions from older adults with high off-topic speech were rated higher on interest and story quality compared to those of older adults with low off-topic speech. These findings point to the limitations of decremental approaches to cognitive aging. The view that off-topic speech is a consequence of a general impairment, e.g., inhibition deficits, precludes the possibility of enhanced communicative value of off-topic speech. Qualitative evaluation of the speech, however, showed just that: more positive ratings for older than young adults’ descriptions and for descriptions of more verbose than less verbose older adults. Age-related increases in off-topic speech were found only for autobiographical topics suggesting that off-topic speech is a feature of a speech style selected under certain conditions to accomplish specific communicative goals. James et al. (1997) suggest a change in pragmatic aspects of language in old age whereby older adults intend to communicate a meaningful description of past life events, rather than a concise description of facts. This goal increases off-topic speech, but also yields a good story and enhances communicative quality. If off-topic speech were a consequence of an impaired ability to inhibit irrelevant information rather than a change in pragmatic goals, then older adult’s communication on other types of discourse should be disrupted by irrelevant information and inappropriate references. Several studies have investigated communication efficiency by comparing young and older adults on referential

20

communication tasks. These tasks require two people to place objects or drawing in the same locations or order, communicating only via verbal descriptions without being able to see each others array. In same or mixed age dyads, there was no age effect on the total time required or the number of questions required to achieve the same locations of objects on a checkerboard (Siegel & Gregora, 1985). Using same age dyads, Hupet, Chantraine and Nef (1993) reported that older adults used more words and more turns to achieve identical sequential orders for ambiguous figures. Older adults also made relatively more requests for repetition (e.g., “What?” “Huh?”) suggesting that their communication may have been impeded by hearing impairment. Kemper and her colleagues asked same and mixed age dyads to reproduce a route, visible only to the speaker, on a map or dot pattern. Both young and old listeners produced more errors in the route when older adults were speakers, but older speakers did not use more words than the young. The communication difficulty with older speakers may reflect inadequate conceptualization of the routes, rather than problems in producing the language, because older listeners expressed confusion more frequently than young listeners, regardless of speaker age (Kemper, Vandeputte, Rice, Cheung, & Gubarchuk, 1995; see also Kemper et al., 1996). Only one study has attempted to link accuracy on a referential communication task with off-topic speech. Older adults’ off-topic speech in conversation was correlated with time to complete a task similar to that of Hupet et al. (1993), but not with accuracy of performance on the task (Arbuckle, Pushkar, Nohara-LeClair, Basevitz, & Peled, 1998). Thus there is no evidence linking off-topic speech to impaired communication. Some studies do show poorer performance on a referential communication task with older rather than young speakers, but the evidence suggests that older adults suffer perceptual and conceptual deficits, rather than deficits in excluding irrelevant information. In more unstructured conversations, for example, a “get acquainted conversation,” older adults display as much social skill as young adults. There were no age differences in indices of the speaker’s responsiveness to a conversational partner, such as use of “you”, continuation of a topic raised by the partner, or asking the partner a question (Vandeputte, Kemper, Hummert, Kemtes, Shaner, & Segrin, in press). Interestingly, age of partner had a strong effect on these indices with both young and older adults producing less responsive speech with older partners. CONCLUSIONS

We have reviewed evidence that deficits in language production in old age are caused by changes in retrieval of certain types of information. The decline in word production occurs in situations where age-related deficits in working memory (Kemper, 1992) or new learning (MacKay & Burke, 1990) seem to have little influence, for example, naming a picture or producing a familiar name or spelling a well known word. Older adults’ deficits in word production have been localized to impairments in retrieval of phonology and orthography, and not to impairments in semantic retrieval. The pattern of results is compatible with an information-specific theory that postulates age-linked deficits in the transmission of priming. This impairs some aspects of language and not others, depending on the architecture and

21

processing components of the system. Language production at the level of discourse also shows changes in old age, namely, increased off-topic speech. These changes appear to be topic-dependent and are associated with increased communicative value. They can be explained by age-related shifts in pragmatic aspects of language, e.g., communicative goals, rather than a cognitive deficit. This asymmetric language change in old age presents a fundamental challenge for cognitive psychology. We must explain why some aspects of language are more vulnerabIe to aging than others. Information-universal theories predict general decrements which affect language across the board, contrary to observed performance (see Burke, 1997). Information-specific theories, however, are more compatible with the highly specific nature of language change in old age, and with positive change in old age. Accounting for positive change in language is as essential for the development of cognitive aging theory as accounting for decrements.

22

REFERENCES

Arbuckle, T.Y., & Gold, D.P. (1993). Aging, inhibition, and verbosity. Journal of Gerontology: Psychological Sciences, 48, P225-P232. Arbuckle, T.Y., Pushkar, D., Nohara-LeClair, M., Basevitz, P., &Peled, M. (1998, April). Variation in off-topic verbosity in relation to conversational context. Paper presented at the Cognitive Aging Conference. Bock, K. (1996). Language production: Methods and methodologies. Psychological Bulletin & Review, 3, 395-421. Brown, A.S., & Nix, L.A. (1996). Age-related changes in the tip-of-the-tongue experience. American Journal of Psychology, 109,79-91. Burke, D.M. (1997). Language, aging and inhibitory deficits: Evaluation of a theory. Journal of Gerontology: Psychological Sciences, 52B, P254-P264. Burke, D.M., & Austin, A. (1999). When are there age differences in producing proper names? Family names versus famous names. Manuscript in preparation. Burke, D.M., & Harrold, R. M. (1988). Automatic and effortful semantic processes in old age: Experimental and naturalistic approaches. In L. L. Light, & D. M. Burke, (Eds.), Language, memory and aging. (pp.100-116). New York: Cambridge University Press. Burke, D.M., & MacKay, D.G. (1997). Memory, language and ageing. Philosophical Transactions of the Royal Society: Biological Sciences, 352, 1845-1856. Burke, D.M., & Peters, L. (1986). Word associations in old age: Evidence for consistency in semantic encoding during adulthood. Psychology and Aging, 4, 283-292. Burke, D.M., MacKay, D.G., Worthley, J.S., & Wade, E. (1991). On the tip of the tongue: What causes word finding failures in young and older adults. Journal of Memory and Language, 30, 542-579. Cohen, G. (1994). Age-related problems in the use of proper names in communication. In M. L. Hummert, J. M. Wiemann, & J. N. Nussbaum (Eds.), Interpersonal communication in older adulthood, (pp. 40-57). Thousand Oaks, CA: Sage Publications. Cohen, G., & Faulkner, D. (1986). Memory for proper names: Age differences in retrieval. British Journal of Developmental Psychology, 4, 187-197. Cooper, P.V. (1990). Discourse production and normal aging: Performance on oral picture description tasks. Journal of Gerontology: Psychological Sciences, 45, P210-214. Coupland, N., & Coupland, J. (1995). Discourse, identity and aging. In J.F. Nussbaum & J. Coupland (Eds.), Handbook of communication and aging research (pp. 79-103). Mahway, NJ: Lawrence Erlbaum Associates. Dell, G.S. (1986). A spreading-activation theory of retrieval in sentence production. Psychological Review, 93, 283-321.

23

Dell, G.S., Burger, L.K., & Svec, W.R. (1997). Language production and serial order: A functional analysis and a model. Psychological Review, 104, 123-147. Fleischman, D.A., & Gabrieli, J.D.E. (1998). Repetition priming in normal aging and Alzheimer's disease: A review of findings and theories. Psychology and Aging, 13, 88-1 19. Giles, H., Coupland, N., & Wiemann, J. (1992). "Talk is cheap..." but "My word is my bond": beliefs about talk. In K. Bolton & H. Kwok (Eds.), Sociolinguistics today: International perspectives (pp. 2 18-243). London: Routledge. Glosser, G., & Deser, T. (1992). A comparison of changes in macrolinguistic and microlinguistic aspects of discourse production in normal aging. Journal of Gerontology: Psychological Sciences, 47, P266-P272. Gold, D., Andres, D., Arbuckle, T., & Schwartzman, A. (1988). Measurements and correlates of verbosity in elderly people. Journal of Gerontology: Psychological Sciences, 43, P27-P33. Gould, O.N., & Dixon, R.A. (1993). How we spent our vacation: Collaborative storytelling by young and older adults. Psychology and Aging, 8, 10-17. Goulet, P., Ska, B., & Kahn, H. J. (1994). Is there a decline in picture naming with advancing age? Journal of Speech and Hearing Research, 37,629-644. Griffin, Z. M., & Bock, K. (1998). Constraint, word frequency, and the relationship between lexical processing levels in spoken word production. Journal of Memory and Learning, 38, 313-338. Harley, T.A. (1993). Phonological activation of semantic competitors during lexical access in speech production. Language and Cognitive Processes, 8,291-309. Harley, T.A., & Brown, H.E. (1998). What causes a tip-of-the-tongue state? Evidence for lexical neighbourhood effects in speech production. British Journal of Psychology, 89, 151-174. Hasher, L., & Zacks, R.T. (1988). Working memory, comprehension, and aging: A review and a new view. In G.H. Bower (Ed.), The psychology of learning and motivation Vol. 22 (pp. 193-225). San Diego, CA: Academic Press. Heller, R.B., & Dobbs, A.R. (1993). Age differences in word finding in discourse and nondiscourse situations. Psychology and Aging, 8, 443-450. Howard, D.V. (1979). Restricted word association norms for adults between the ages of 20 and 80. JSAS Catalog of Selected Documents in Psychology, 10, (Ms. No.1991). Hummert, M.L. (1994). Stereotypes of the elderly and patronizing speech. In M.L. Hummert, J.M. Wiemann, & J.F. Nussbaum (Eds.), Interpersonal communication in older adulthood. (pp. 162-184). London: Sage Publications. Hupet, M., Chantraine, Y., Nef, F. (1993). References in conversation between young and old normal adults. Psychology and Aging, 8, 339-346. James, W. (1890). Principles of Psychology (Vol. 1). New York: Henry Holt and Company. James, L.E., & Burke, D.M. (1998). Phonological priming effects on word retrieval and tip of the tongue experiences in young and older adults. Manuscript submitted for publication.

24

James, L.E., Burke, D.M., Austin, A., & Hulme, E, (1998). Production and perception of verbosity in young and older adults. Psychology and Aging, 13, 355-367. Jescheniak, J.D., & Levelt, W.J.M. (1994). Word frequency effects in speech production: Retrieval of syntactic information and of phonological form. Journal of Experimental Psychology: Learning, Memory, and Cognition, 20, 824-843. Jones, G.V. (1989). Back to Woodworth: Role of interlopers in the tip of the tongue phenomenon. Memory & Cognition, 17,69-76. Kemper, S. (1992a). Adults' sentence fragments: Who, what, when, where, and why. Communication Research, 19,444-458. Kemper, S. (1992b). Language and aging. In F.I.M. Craik & T.A. Salthouse (Eds.), The handbook of aging and cognition (pp. 213-270). Hillsdale, NJ: Lawrence Erlbaum Associates. Kemper, S., Rash, S., Kynette, D., & Norman, S. (1990). Telling stories: The structure of adults' narratives. European Journal of Cognitive Psychology, 2, 205-228. Kemper, S., Othick, M., Warren, J., Gubarchuk, J., & Gerhing, H. (1996). Facilitating older adults' performance on a referential communication task through speech accommodations. Aging, Neuropsychology and Cognition, 3, 37-55. Kemper, S., Vandeputte, D., Rice, K., Cheung, H., & Gubarchuk, J. (1995). Speech adjustments to aging during a referential communication task. Journal of Language and Social Psychology, 14,40-59. Kroll, J.F.,& Curley, J. (1988). Lexical memory in novice bilinguals: The role of concepts in retrieving second language words. In M.M. Gruneberg, P.E. Morris, & R.N. Sykes (Eds.), Practical aspects of memory: Current research and issues, Vol. 2 (pp. 389-395). New York: John Wiley & Sons. Laver, G.D., & Burke, D.M. (1993). Why do semantic priming effects increase in old age? A meta-analysis. Psychology and Aging, 8,34-43. Levelt, W.J.M. (1989). Speaking: From intention to articulation. Cambridge, MA: The MIT Press. Levelt, W.J.M., Schriefers, H., Vorberg, D., Meyer, AS., Pechmann, T., & Havinga, J. (1991). The time course of lexical access in speech production: A study of picture naming. Psychological Review, 98, 122-142. Light, L.L., & Albertson, S.A. (1989). Direct and indirect tests of memory for category exemplars in young and older adults. Psychology and Aging, 4, 487492. Light, L.L. (1991). Memory and aging: Four hypotheses in search of data. In M.R. Rosenzweig & L.W. Porter (Eds.), Annual Review of Psychology. (pp. 333376). Palo Alto: Annual Reviews. Light, L.L., & Anderson, P.A. (1983). Memory for scripts in young and older adults. Memory and Cognition, 11,435-444. Light, L.L., Valencia-Laver, D., & Zavis, D. (1991). Instantiation of general terms in young and older adults. Psychology and Aging, 6, 337-351.

25

Lovelace, E.A., & Cooley, S. (1982). Free associations of older adults to single words and conceptually related word triads. Journal of Gerontology, 37, 432437. Lovelace, E.A., & Cooley, S. 1982 Free associations of older adults to single words and conceptually related word triads. Journal of Gerontology, 37, 432-437. Loveless, M., & Burke, D.M. (1999). Aging and the effects of primed semantic competitors on picture naming. Manuscript in preparation. Lupker, S.J. (1988). Picture naming: An investigation of the nature of categorical priming. Journal of Experimental Psychology: Learning, Memory, and Cognition, 14, 444-455. MacKay, D.G. (1982). The problems of flexibility, fluency, and speed-accuracy trade-off in skilled behavior. Psychological Review, 89, 483-506. MacKay, D.G. (1987). The organization of perception and action: A theory for language and other cognitive skills. New York: Springer-Verlag. MacKay, D.G., & Abrams, L. (1996). Language, memory and aging: Distributed deficits and the structure of new versus old connections. In J.E. Birren & W.K. Schaie (Eds.), Handbook of the psychology of aging, 4th ed. (pp. 251-265). San Diego: Academic Press. MacKay, D.G., & Abrams, L. (1998). Age-linked declines in retrieving orthographic knowledge: Empirical, practical and theoretical implications. Psychology and Aging, 13, 647-662. MacKay, D.G., Abrams, L., & Pedroza, M.J. (in press). Aging on the input versus output side: Theoretical implications of age-linked asymmetries between detecting versus retrieving orthographic knowledge. Psychology and Aging. MacKay, D.G., & Burke, D.M. (1990). Cognition and aging: New learning and the use of old connections. In T.M. Hess (Ed.), Aging and cognition: Knowledge organization and utilization (pp. 21 3-263). Amsterdam: North Holland. Maki, P.M., & Knopman, D.S. (1996). Limitations of the distinction between conceptual and perceptual implicit memory: A study of Alzheimer's disease. Neuropsychology, 10, 464-474. Maylor, E.A. (1990a). Age, blocking and the tip of the tongue state. British Journal of Psychology, 81, 123-134 Maylor, E.A. (1990b). Recognizing and naming faces: Aging, memory retrieval and the tip of the tongue state. Journal of Gerontology: Psychological Sciences, 45, P215-P225. McClelland, J.L., & Rumelhart, D.E. (1981). An interactive model of context effects in letter perception: Part 1. An account of basic findings. Psychological Review, 88,375-407. Pratt, M.W., Boyes, C., Robins, S., & Manchester, J. (1989). Telling tales: Aging, working memory, and the narrative cohesion of story retellings. Developmental Psychology, 25,628-635. Rabbitt, P., Maylor, E., McInnes, L., Bent, N., & Moore, B. (1995). What goods can self-assessment questionnaires deliver for cognitive gerontology? Applied Cognitive Psychology, 9, S127-S152.

26

Rastle, K.G., & Burke, D.M. (1996). Priming the tip of the tongue: Effects of prior processing on word retrieval in young and older adults. Journal of Memory and Language, 35, 586-605. Reason, J.T., & Lucas, D. (1984). Using cognitive diaries to investigate naturally occurring memory blocks. In J. E. Harris & P. E. Morris (Eds.), Everyday memory actions and absent-mindedness (pp. 53-70). London: Academic Press. Ryan, E.B. & Laurie, S. (1990). Evaluations of older and younger adult speakers: Influence of communication effectiveness and noise. Psychology and Aging, 5, 514-519. Ryan, E.B., See, S.K., Meneer, W.B., & Trovato, D. (1994). Age-based perceptions of conversational skills among younger and older adults. In M.L. Hummert, J.M. Wiemann, & J.N. Nussbaum (Eds.), Interpersonal communication in older adulthood (pp. 15-39). Thousand Oaks, CA: Sage Publications. Salthouse, T.A. (1982). Adult cognition: An experimental psychology of human aging. New York: Springer-Verlag. Salthouse, T.A. (1988). Effects of aging on verbal abilities: Examination of the psychometric literature. In L.L. Light & D.M. Burke (Eds.), Language, memory and aging (pp. 17-35). New York: Cambridge University Press. Siegel, G.M. & Gregora, A.W. (1985). Communication skills of elderly adults. Journal of Communication Disorders, 18,485-494. Small, B.J., Hultsch, D.F., & Masson, M.E.J. (1995). Adult age differences in perceptually based, but not conceptually based implicit tests of memory. Journal of Gerontology: Psychological Sciences, 50B, P162-P170. Stemberger, J.P. (1985). An interactive model of language production. In A. W. Ellis (Ed.), Progress in the psychology of language: Vol.1 (pp. 143-186). London: Lawrence Erlbaum Associates. Stine, E.A.L., & Wingfield, A. (1994). Older adults can inhibit high-probability competitors in speech recognition. Aging and Cognition, 1, 152-157. Sunderland, A., Watts, K., Baddeley, A.D., & Harris, J.E. (1986). Subjective memory assessment and test performance in the elderly. Journal of Gerontology, 41, 376-384. Tun, P.A., & Wingfield, A. (1993). Is speech special? Perception and recall of spoken language in complex environments. In J. Cerella, W. Hoyer, J. Rybash, & M.L. Commons (Eds.) Adult information processing: Limits on loss (pp.425-457). San Diego: Academic Press. Ulatowska, H.K., Hayashi, M.M., Cannito, M.P., & Fleming, S.G. (1986). Disruption of reference in aging. Brain and Language, 28, 24-41. Vandeputte, D.D., Kemper, S., Hummert, M.L., Kemtes, K.A., Shanner, J. & Segrin, C. (in press). Social skills of older people: Conversations in same and mixed age dyads. Discourse Processes. Vitkovitch, M. & Humphreys, G. W. (1991). Perseverant responding in speeded naming of pictures: It's in the links. Journal of Experimental Psychology: Learning, Memory, and Cognition, 17, 664-680. Vitkovitch, M., Humphreys, G. W., & Lloyd-Jones, T. J. (1993). On naming a giraffe a zebra: Picture naming errors across different object categories.

27

Journal of Experimental Psychology: Learning, Memory, and Cognition, 19, 243-259. West, R.L. (1996). An application of prefrontal cortex function theory to cognitive aging. Psychological Bulletin, 120, 272-292. Wheeldon, L. R., & Monsell, S. (1994). Inhibition of spoken word production by priming a semantic competitor. Journal of Memory and Language, 33, 332356. Woodworth, R.S. (1938). Experimental Psychology. New York: Henry Holt & Company. Zacks, R.T., & Hasher, L. (1994). Directed ignoring: Inhibitory regulation of working memory. In D. Dagenbach & T.H. Carr (Eds.), Inhibitory processes in attention, memory, and language (pp. 241-264). San Diego, CA: Academic Press.

28

ACKNOWLEDGMENTS

This research was supported in part by grant AG08835 from the National Institute on Aging. The author gratefully acknowledges the assistance of Jennifer Taylor, Ayda Austin and Peggy Christidis in the preparation of this article.

2

WORKING MEMORY AND SPOKEN LANGUAGE COMPREHENSION: THE CASE FOR AGE STABILITY IN CONCEPTUAL SHORT-TERM MEMORY Arthur Wingfield and Patricia A. Tun

Although the languages of the earth show an explosive variety in form and rules, the presence of a structured language system appears in all societies of the world. Indeed, where oral communication is not possible, sign languages have developed, also with a rich structure of lexicon and syntax, but with space and order of manual movements used to express objects, actions and their syntactic relations (Meier, 1991). As our understanding of the brain structures that carry language function has developed over the years, so too has our appreciation of the unique place language holds in human cognition (Goodglass & Wingfield, 1998). Language function may be among the most highly developed of human skills, but there are constraints on language performance dictated by factors such as the speed with which perceptual and cognitive operations can proceed, and the limitations of a finite memory system on how much we can take in and hold at any one time in the course of language comprehension. The ways in which these memory limits have been characterized have changed over the years. The assumption that memory limits constrain language processing, however, has not. EVOLUTION OF VERBAL SHORT-TERM MEMORY AND LIMITED RESOURCE MODELS

The concept of a limited-capacity input memory buffer was discussed in the literature in the 1800s, but we owe our modern understanding of short-term memory (STM) to a number of milestone studies. These include Peterson and Peterson (1959) who defined the duration of STM as 18 seconds without rehearsal, Waugh and Norman (1965) who emphasized the need for a rehearsal loop to keep a trace alive in STM and to transfer it into long-term memory (LTM), and Conrad (1963), who characterized the STM rehearsal loop as articulatory in nature. This was based on his observation that short-term recall errors for visually presented letters show acoustic/articulatory confusions (Q being recalled as U), rather than visual confusions (Q being recalled as O). Miller (1956) declared the capacity of STM as 29

30

7 +/-2 "chunks" of information. This picture of a sequential information flow from STM to LTM, along with several control processes, has sometimes been called the "modal model" of short-term memory (Atkinson & Shiffrin, 1968). If by the 1960s the presumption of a limited capacity short-term buffer memory for holding verbal materials was experimentally established, by the 1970s the literature suggested a role for STM in language comprehension. Gernsbacher (1985) summarizes this early history as a belief that the surface form of an utterance is held in STM "until a meaningful unit has been comprehended; then it is lost" (pg. 342). This meaningful unit was generally presumed to be the linguistic clause (Fodor, Bever, & Garrett, 1974). While some theorists focused on the limited-capacity limited-duration STM store, others stressed that there are also limits on attentional resources. This limitation was exemplified by the difficulty one has in handling more than one task or mental activity at a time. The best known of these limited-resource models was that of Kahneman (1973), who described processing limitations in terms of a central pool of attentional resources that must be allocated among the multiple mental activities needed in the execution of complex cognitive operations. As more effort is expended on one task or processing operation, so fewer resources will be available for other tasks or operations. This general capacity model largely replaced Broadbent's (197 1) earlier notion of time-sharing for access to a single processing channel. Although in somewhat different ways, both models included an important caveat. Some operations might require access to this central processing capacity (Kahneman, 1973), or single channel (Broadbent, 1971), but the drain on resources needed might be so minimal as not to create interference with a concurrent task, which has been held as the traditional evidence that two operations are competing for the same resource pool. Kahneman also added the second caveat that increasing task demands may increase one's level of physiological arousal, with a resulting increase in total resources. That is, resources are limited, but not necessarily fixed (Kahneman, 1973). From almost the first appearance of limited resource models there was controversy over whether different cognitive operations or processing domains compete for a single undifferentiated pool of resources (Kahneman, 1973), or whether some draw on different resource systems (Allport, Antonis, & Reynolds, 1972; Wickens, 1984). Dual-task effects, it was argued, could arise from the effort involved in keeping response streams separate, from response interference, or from other forms of overhead costs. For this reason, evidence for shared resources must not simply rest on reduced performance on one task while concurrently performing a second task. Rather, one would also need to see an incremental drop in performance on one task as one incrementally increased the difficulty of the other task (Kerr, 1973). Interestingly, although reports of dual-task interference are common in the literature, appearance of this full interaction necessary to support a single resource argument is exceedingly rare (see the review by Tun & Wingfield, 1993). Once one admits that the simple presence of dual-task interference does not prove single-resource theory, any more than the absence of behavioral effects in dual task studies disproves it, we can see that a belief in single resource or multiple

31

resource models rested less on hard data than on a given theorist's idea of parsimony and intuition. WHATEVER HAPPENED TO SHORT-TERM MEMORY?

Shiffrin (1993), one of the champions of the early modal model, reported having being asked by a colleague what had happened to short-term memory. In his colleague's words: "Didn't people used to study that?" Shiffrin's answer was that STM became incorporated into broader models, "to become virtually synonymous with cognition in general" (pg. 93). The best known of these broader models is the notion of working memory; a cognitive system that contains a limited computational space in which materials can be temporarily stored, monitored and manipulated (Baddeley, 1986; Just & Carpenter, 1992). In Baddeley's (1986) formulation, working memory has two "slave" systems (a phonological store and a visual-spatial store) and a limited capacity "central executive" that allocates resources to the operations performed by or within the working memory system (Baddeley, 1986). Just and Carpenter (1992) refer to a verbal working memory, with the presumption that all comprehension operations compete for this single computational space, while leaving open the possibility that other processing domains may tap other resources. In one form or another, however, the concept of working memory has come to dominate most contemporary discussions of constraints on language processing and short-term recall. WORKING MEMORY, AGE, AND LANGUAGE PROCESSING

This dominant position holds that working memory is needed to carry, and hence constrains, language comprehension. The most common conception of working memory is seen in terms of a limited capacity central executive that "schedules" and controls processing operations, and temporary storage buffers that hold incoming information for processing and that store the products of this processing for use and/or integration with previous or yet to be received information (Baddeley, 1986). The verbal buffer store, consisting of a phonological store and a subvocal rehearsal process to preserve the representation in the phonological store, has been wellstudied, although its relevance to actual language comprehension has been called into question (Baddeley, Gathercole, & Papagno, 1998). The belief that working memory resources constrain language processing has been kept alive by numerous reports of significant correlations between individuals' working memory spans and their performance on a variety of language tasks (Carpenter, Miyaki, & Just, 1994; Daneman & Merikle, 1996). The relevance of this argument to adult aging relates to the observation of systematic declines in older adults on verbal working memory tests such as the Daneman and Carpenter (1980) span test and other tests that require concurrent maintenance and processing of verbal materials (Wingfield, Stine, Lahar & Aberdeen, 1988). In the Daneman and Carpenter span test, subjects are asked to read or listen to a set of sentences and then to report back to the examiner the last

32

word of each of the sentences. Span is taken as the largest set-size of sentences for which the final words can be correctly recalled. Figure 1 shows data taken from Wingfield et al. (1988) in which the same groups of subjects were tested for simple digit span, simple word span, and working memory span using an auditory version of the Daneman and Carpenter (1980) span test. In the latter case, a true-false judgment was required after each sentence to insure that subjects were attending to the meanings of the sentences as well as attempting to remember their final words. All of the stimuli were presented over earphones at intensity levels set at a comfortable listening level for each of the subjects. The original study by Wingfield et al. contrasted young versus elderly adults. Figure 1 shows results on the three span tests for young adults (mean age = 19 years), and for the older subjects separated into two groups: a young-old group (mean age = 65) and an older-old group (mean age = 75). We can see a significant age difference for word span, but not for digit span, and a differentially larger age susceptibility to the added load of the working memory span test. We can also see

Figure 1.

Number of items recalled from lists of spoken digits, lists of words, and the final words of sets of sentences presented for comprehension (loaded span). (Data from Wingfield, Stine, Lahar & Aberdeen, 1988.)

33

that these differences are exaggerated for the older-old group relative to the youngold group. By contrast to declines in working memory capacity, knowledge of language structure and its procedural use remain stable in normal aging (Kemper, 1992; Light, 1990). Because of this general pattern of loss and sparing, when age differences have appeared in the comprehension of sentences with complex syntactic structures (e.g., left-branching sentences, sentences with embedded clauses, or sentences with a temporary closure ambiguity) it has been presumed that the age differences are not due to the loss of linguistic knowledge, but to an age-related reduction in working memory capacity (Kemper, 1992; Kemtes & Kemper, 1997). However intuitively appealing the working memory and language comprehension relationship, correlations between working memory span scores and performance differences in language comprehension are not always found, and when they are, they are often modest in size (Waters & Caplan, 1996). The inconsistent correlations between working memory spans and performance on language comprehension tasks have led to arguments that echo the earlier debates about single versus multiple resources in general models of attention. Caplan and Waters (in press) argue against the view that sentence comprehension is carried by the same working memory system that is measured by conventional span tests, such as the Daneman and Carpenter (1980) test. When such correlations appear, or when sentence comprehension appears to be affected by concurrent tasks such as having to remember a digit pre-load, it is argued that these are effects on post-interpretive processes that follow initial sentence comprehension. Caplan and Waters argue that sentence comprehension is carried by a separate syntax or sentence-specific resource. This general position has been supported by evidence from neurological populations who show reduced capacities of short-term verbal memory or executive function as measured by conventional span tests, but who nevertheless show good sentence comprehension, even for sentences with quite complex syntactic constructions (Caplan & Waters, in press; Martin & Romani, 1994). Similarly, the literature holds numerous cases of failures to find reliable correlations between working memory span scores and tests of speech comprehension and recall in young and elderly adults (Wingfield, Waters, & Tun, 1998). WHY

THE PROBLEM IS A DIFFICULT ONE

There are at least three reasons why correlations between working momory measures and comprehesion performance might be expected to be weak. (a) One reason is the lack of specificity with which working memory and its proposed components have been defined. This is especially true of central resources, which have been described with a variety of fanciful metaphors. These have ranged from early references to "psychic energy" (Titchener, 1908), to the engineering metaphor of a limited channel capacity (Broadbent, 1971), the abstraction of a limited capacity "resource pool" (Kahneman, 1973), or the homunculus-driven concept of

34

a limited capacity "central executive" (Baddeley, 1986). That is, it is easier to say that humans have difficulty doing more than one thing at a time than to come up with a less than whimsical metaphor to explain why this is so. (b) To the extent that working memory may be a viable construct, the modest and sometimes absent correlations between working memory span scores and performance on language tasks could be due to poor measurement techniques for estimating working memory. The inconsistency with which these correlations appear could suggest, for example, that current span measures may be capturing some elements of a putative working memory function, but with a clearer picture being fogged by flexible performance strategies (Waters & Caplan, 1996). It has also been argued that the standard testing procedure of presenting progressively larger sentence set-sizes can cause a buildup of proactive interference (PI). Age differences on these span tests might thus be caused or inflated by older adults' greater susceptibility to PI than young adults (Zacks, Hasher, & Li, to appear). (c) Finally, correlations between span scores and language performance might be affected by factors such as linguistic knowledge and verbal fluency that could moderate what might otherwise be clearer effects of limitations in raw computing power. In the current literature, these problems are only exacerbated by investigators using such terms as "working memory," "attentional resources," and "memory stores" as if they had commonly accepted meanings. For some, the term working memory has been used simply as a placeholder term for the empirically observed processing bottlenecks encountered in many language tasks. Baddeley argues for the functional utility of the working memory notion although recognizing that the early formulations of memory stores and a central executive are bound to undergo further fractionation into subcomponents as theory develops (Baddeley, 1998). COMPREHENDING SPOKEN LANGUAGE: A COMPONENTIAL ANALYSIS

An essential part of the working memory debate relates to the temporary memory representations that must be involved in sentence comprehension as well as whether any or all of them may be constrained by a single set of resource limitations. We can see this by looking closely at the operations that must be involved in comprehending spoken language. We represent these operations in the form of a flow diagram in Figure 2 to help guide our discussion. Although there is wide moment-to-moment variability, speech rates in ordinary conversation typically average between 140 and 180 words per minute (wpm). This requires that perceptual encoding of the input, identification of its lexical elements and their syntactic relations, and comprehending the speech at the discourse level, must all be carried out with the speech arriving at an average rate of 2 to 3 new

35

words each second. In speech, the sounds travel past the ear at 1,100 feet per second, such that one cannot take a "second look" as one can in reading (Huggins, 1975). Those operations that cannot be conducted instantaneously, as the speech is being heard, must be conducted on some form of memory representation of that input. Speech is thus an intrinsically temporal event in which the auditory input is constantly changing over time, and where no single instant of the speech signal carries sufficient information to be fully discriminating. At the level of phoneme identification, we know that how a phoneme is perceived will be affected by its phonemic context. For this context to operate, both the phoneme in question and its syllable surround must be held together within a single perceptual "window" even though the acoustic information itself has long since moved past the ear. Perceptual analysis at this level has been identified with the existence of a "preperceptual" auditory memory image lasting perhaps 100 to 125 ms (Huggins, 1975; Massaro, 1974; see also Mattys, 1997). There must also be a memory-dependent operation at a somewhat higher level. Unlike written text, in which words are separated by spaces, words in spoken discourse run together, frequently leading to areas in the acoustic stream where word boundaries are ambiguous (e.g., "he saw the cargo " versus "he saw the car go ") (Gow & Gordon, 1995). The size of the perceptual "window" necessary for segregation of the speech stream at this lexical level would thus have to be far larger than the auditory image described by Huggins (1975) or Massaro (1974). In turn, neither the duration, capacity, nor nature of the representation of these brief acoustic stores could be identified with the memory store needed to temporarily hold the products of syntactic analyses as part of discourse comprehension (van Dijk & Figure 2. Operations and processes that must be performed for successful comprehension of spoken language. Presumed short-term memory representations are indicated by horizontal arrows.

36

Kintsch, 1983), to use several words of a following context to perceptually identify a previously heard indistinct word (Grosjean, 1985; Wingfield, Alexander, & Cavigelli, 1994), or to hold enough input to allow resolution of temporary syntactic ambiguities (Frazier, 1987; Kemtes & Kemper, 1997). Indeed, just as one might argue that spoken language comprehension involves a hierarchy of processing units (syllables, morphemes, clauses, etc.), one may also propose sets of memory traces with increasing sizes and durations to support the perceptual and linguistic analyses at each level of processing. Our goal in this presentation is less to offer definitive answers than it is to frame the questions that we believe need to be answered. Only in this way can one correct the premature reification of working memory that has typified much of the language and aging literature. Our first step must be to "unpack" working memory. Of special interest to us is the specification of the memory representations that underlie language comprehension. We will argue in support of a conceptual shortterm memory (CSTM) as proposed by Potter and Lombardi (Lombardi & Potter, 1992; Potter, 1993; Potter & Lombardi, 1990), and what we see as its implications for language comprehension in adult aging. Among the difficulties cited earlier in attempting to specify the sources of memory constraints that underlie language performance are the compensations and repairs made possible by other knowledge that will be bound to cloud any one-toone correlation between a "hardware" decline and observed performance. These interactions, however, are an inherent part of language processing. An additional part of our task will thus be to identify some of these sources of compensation and to show how they interact with age-related changes in rapid perceptual processing and recall for what has been heard. CONCEPTUAL SHORT-TERM TEMPORARY STORES

MEMORY

(CSTM)

AND

ITS RELATION

TO

OTHER

If only the surface form of a sentence existed in short-term memory until the syntactic content of the sentence was recognized and encoded, then the immediate recall of a phrase or sentence would not be expected to show semantically based errors. Rather, acoustic confusions or word omissions would be expected to typify these errors. By contrast, since the time of Bartlett (1932) long-term recall has been thought to rest less on reproduction from a veridical memory trace of a stimulus event than on reconstructions from abstract semantic representations, or "schemata". Reconstructive contributions to immediate sentence recall have historically received less attention. Potter and Lombardi have argued that the appearance of accurate verbatim recall of a sentence need not be the consequence of a word-for-word readout from a buffer store containing the verbal sequence representing that sentence. Rather, recall could just as easily result from an immediately-formed conceptual representation of the sentence, with accurate recall resulting from a reconstruction of the original wording (Lombardi & Potter, 1992; Potter, 1993; Potter & Lombardi, 1990). Potter and Lombardi refer to this immediate conceptual trace as a conceptual short-term memory (CSTM).

37

According to Potter and Lombardi, in language comprehension the surface form of a sentence, although used for comprehension, is itself not represented in memory; only a conceptual representation of the sentence is formed and retained. In recall, the response system reconstructs the sentence from the CSTM representation of the core meaning of the sentence augmented by activation of critical entries in the lexical semantic system such as a head noun or main verb. (Activation of just-heard lexical entries can be contrasted with a verbatim phonological store that would have both the lexical items and their order represented.) Guided by the production rules of the language, the likelihood of the listener reinstantiating the original surface form of the sentence would be quite high (Lombardi & Potter, 1992). It can be argued that a verbatim short-term store of ordered sequences, kept alive by articulatory rehearsal can also exist, and surely does given that people can repeat nonsense sounds or words of a novel foreign language. This short-term phonological store could be formed even when a meaningful sentence of one's language is heard. The argument, however, is that this store is not used to carry sentence comprehension. This would explain the previously cited findings that some brain-injured adults who score poorly on tests of phonological memory, such as recall of word and digit lists, can nevertheless show unexpectedly good levels of sentence comprehension. These arguments are consistent with the postulate that as a sentence is being heard multiple memory traces are laid down. These include both an immediate semantic representation of the sentence and a verbatim phonological trace, with both traces being held concurrently. Evidence for a semantic trace appearing some period after one no longer sees evidence of a verbatim trace of the surface form of a sentence is evidence that these two kinds of traces have different decay rates. This should not, however, be taken as evidence that one form of trace has necessarily replaced the other. In short, the position we wish to advance is that the neural consequences of a single sensory event can result in concurrent memory traces in multiple formats overlapping in time. These multiple representations may differ in their ecological utility and ease of access, as well as in their susceptibility to interference from other activities. How MANY MEMORY TRACES?

The view that a single experience may lay down a number of concurrent traces representing different features of the stimulus has already appeared in the literature from a variety of perspectives. We have questioned the modal model's presumption that sentence comprehension follows a sequence in which the surface form of a sentence forms the initial trace, with this surface form discarded once the meaning has been extracted. At the level of word recognition there is also reason to question the presumption that variations in speakers' voices, speech rate, and other surface features are discarded as part of the normalization process that leads to the abstract phonological code used for determining word identity (Luce & Lyons, 1998). One might ask whether it would not be very inefficient to maintain lower-level stimulus-based representations when they are not needed for identification of the

38

word itself. If one conceptualized a model programmed solely to identify words, a use-and-discard system would certainly be a more efficient one. There is, however, some evidence in the speech perception literature that acoustic features of a word such as the vocal characteristics of the speaker, even though irrelevant to the word's identification, are maintained in memory not only before the abstract phonological features necessary for lexical identification are abstracted but also for some period beyond that (Goldinger, 1996). Our point here is that surface features of the stimulus at a number of levels may co-exist in memory along with higher-level abstract phonological and semantic representations of the lexical input. On the left side of Figure 2 our diagram of the operations and processes that must be performed for successful language comprehension begins with an analysis of the acoustic waveform. As indicated in our discussion, this includes phoneme identification, lexical access, and determination of the syntactic and semantic relations represented by the lexical elements. We have not, in this diagram, indicated whether there is an interaction between the phonological and conceptual traces. Nor does our diagram show the full array of factors operating on language comprehension. For example, it is undoubtedly the case that thematic role assignment may be determined not only by the syntax of the input but also by access to real-world knowledge. These factors would have to be included in any complete processing account. For the purpose of this illustration we have simplified the model presented here. It will be seen in the diagram that we have identified three memory traces, formed at different times, and decaying at different rates, but all being held concurrently for some period. These are a trace of the acoustic input (which would include factors such as voice quality), a phonological trace representing a verbatim surface form of the utterance, and a conceptual (CSTM) trace. Note that, in our diagram, one form of representation is not replaced by the other forms, but that they are held in parallel, albeit with different decay rates symbolized by the different lengths of the horizontal arrows. SPONTANEOUS SEGMENTATION

AND

SPEECH CONTENT

The essence of Potter and Lombardi's CSTM is that speech must be analyzed for structure and semantic content very rapidly as it is being heard. An argument for a sparing of CSTM in adult aging would require a demonstration of a conceptual trace that can still be developed rapidly in older adults in spite of the general slowing that is a virtual hallmark of normal aging (Salthouse, 1996). One of the lines of evidence we can draw on uses a technique we have referred to as "spontaneous segmentation." In this task subjects hear over headphones a prerecorded paragraph-length passage of prose and are told that their task is to recall what they have heard with as close to 100 percent accuracy as possible. Because of the length of the passage, subjects are told that they may press a pause button on the tape recorder and stop the tape at any time for immediate recall. In this way subjects work their way through the passage on a segment-by-segment basis, selecting a segment and recalling it, then selecting another segment and recalling it, and so on.

39

(In this paradigm subjects are instructed not to try to shadow the speech. Rather, they are told to begin their recall only after the tape has been stopped.) When given this task subjects spontaneously interrupt the speech primarily at major linguistic boundaries: The highest frequency of interruptions occurs at sentence and major clause boundaries, with fewer interruptions after noun and prepositional phrases, and still fewer interruptions after non-clausal points such as after nouns, verbs, prepositions, or other elements that could signal the nature of upcoming constituents. A very few interruptions (typically 11% or less) occur at points that do not coincide with recognized constituent boundaries, and still fewer interruptions occur that split a word. This latter point is an important one. Because there is an inherent time element involved in making the decision as to when to press the button to interrupt the speech, and in making the physical motor movement to do so, the decision as to where to interrupt the speech must be made some time before that point where the subject actually stops the tape. We have taken the finding of linguistically guided interruptions that rarely split a word as strong evidence that subjects are processing the input to determine its structure as it is being heard (Wingfield & Butterworth, 1984). We can see that spontaneous segmentation has much in common with the recently developed auditory moving window (AMW) technique, except that in the AMW method the speech is segmented by the experimenter, either word-by-word or sector-by-sector, and one measures the subject's latencies for pressing a key to hear the next segment (e.g., Ferreira, Henderson, Anes, Weeks, & McFarlane, 1996). Previous work using the spontaneous segmentation paradigm has shown that older adults generally select the same points for interruption of speech as do young adults, and that their recall of the selected segments is quite good, although somewhat poorer than the young adults' for longer segment sizes (Wingfield, Lahar, & Stine, 1989). Artificially accelerating the speech rate has little effect on where older adults interrupt speech for recall, demonstrating that older adults can perform these linguistic operations at rates even faster than normally encountered in everyday discourse (Wingfield & Stine, 1986). Subjects' selections of points of interruption reflect syntactic constituent detection at least at the surface level. Of interest in the present context is (a) whether complexity of the speech content affects where subjects choose to segment the input, (b) whether older adults use speech content in a manner similar to young adults, and (c) whether both groups will be sensitive to content even when the speech is accelerated to exceed rates ordinarily encountered in nature. This, we argue, would be a powerful demonstration that older adults have the processing power needed for rapid on-line encoding of speech necessary to form a CSTM. An experiment conducted by Wingfield and Lindfield (1995) has these requisites. This study tested whether subjects' points of spontaneous segmentation would be affected by the content difficulty of the speech passages. The presumption was that an early-stage semantic representation of the input would respect this content complexity, as distinct from a strictly verbatim store that would be immune to variation in content complexity of the speech input. This should be reflected in a decrease in the size of the segments selected by the subjects when the difficulty of the speech materials is increased. One would still expect to see subjects'

40

interruptions occurring at linguistic constituent boundaries. The smaller segment sizes predicted would be expected to be produced by subjects interrupting the input at more frequently occurring constituent boundaries than sentence and major clause boundaries. Speech difficulty was varied by using an empirically derived measure based on the average word predictability of the speech using a "cloze" procedure. The cloze value of a passage is derived from the percentage of subjects who can correctly guess the identity of words periodically deleted from the passage. The justification for using cloze values is based on the presumption that the probability that a subject will think of a particular word deleted from a text serves as a summary statistic that reflects the combined effects of the syntactic, semantic, and pragmatic constraints that operate on word choice. Consistent with this presumption, prior work has shown that average cloze predictability of a passage correlates highly with Figure 3. Percentage of interruptions following sentence and clause boundaries for high, medium and low predictability passages for young and older adults. (Data from Wingfield & Lindfield, 1995).

41

individuals' subjective estimates of passage difficulty and with actual recall scores (Aquino, 1969). In this study, well-educated young (mean age = 19 years) and older (mean age = 70 years) adults with good levels of education and verbal ability heard 150-word prose passages rated for cloze value by Miller and Coleman (1967). The passages were recorded at a comfortable speaking rate of approximately 150 wpm in natural intonation, and then time-compressed to produce mean speaking rates of 180, 230, and 300 wpm. The subjects' task was to listen to a speech passage as it was presented, interrupting the recording at points of their choosing in order to give immediate recall of the words in that segment. Subjects were told to strive for accuracy of recall. No mention was made of the fact that our main interest was in where they chose to interrupt the speech for recall. Although the sizes of the segments selected for recall showed wide variability, an analysis of variance verified an overall decline in average segment sizes selected as mean inter-word predictability of the passages decreased ( p < .001). There was no main effect of age, nor was there a significant age by passage predictability interaction. There was also no effect of speech rate on segment sizes selected, nor did speech rate interact with either age or passage predictability. The wide variability in sizes of segments selected reflected subjects' tendency to interrupt the input for recall not at regular-size segments, but at major linguistic boundaries that naturally vary in size. Figure 3 shows the mean percentage of interruptions that occurred at sentence and clause boundaries for the young and older adults as passage predictability decreased. Because approximately 90% or more of segmentations occurred at commonly defined syntactic boundaries, the decrease in the percentage of interruptions at sentence and major clause boundaries shown in Figure 3 represents a reciprocal increase in the percentage of interruptions that occurred at the previously defined minor constituent boundaries. This resulted in the progressive reduction in segment sizes just described. (The values shown in Figure 3 have been collapsed across the three speech rates.) An analysis of variance conducted on the data shown in Figure 3 confirmed the significant decline in the percentage of interruptions that occurred at sentence and clause boundaries with decreasing passage predictability ( p < .001). Nor did this effect differ for the older and younger adults either in terms of a main effect of age or a significant passage predictability by age interaction. (In this analysis there was a small effect of speech rate, reflecting subjects' tendency to interrupt the speech more frequently at minor constituent boundaries when the speech input became more rapid, but this did not interact with age or predictability. Indeed, as we saw, this speech rate effect was so small as not to appear in the previously cited analysis of variance conducted on mean segment sizes in terms of numbers of words.) The value of this study is two-fold. First, the study confirms previous findings that have demonstrated the similarity in where young and older adults choose to segment speech input for recall in terms of its surface syntactic constituents. Second, this study shows that both young and older subjects' segmentation patterns were sensitive to speech content as measured by average word predictability. Finally, these were segment selection choices that must have been made on-line, as the speech was being heard, an operation that did not show large age differences.

42

meanings of sentences even though those specific words had not actually occurred in the sentences (e.g., Potter & Lombardi, 1990). It could be argued that such findings could result from recall from a decaying verbatim surface trace constrained by linguistic production rules (Lee & Williams, 1997). Our spontaneous segmentation findings, however, clearly favor the Potter and Lombardi position. These findings would suggest that, although age differences do occur in text recall (they also did so in this experiment), the input to the memory system consisted of speech that had already been analyzed at the content level. This is consistent with recall being based on a CSTM. It is inconsistent with immediate recall being limited to reproduction of a verbatim (ordered) phonological store serving as a precursor to the determination of the syntactic structure and the semantic relations represented in the speech. As we saw, such an analysis must already have been conducted as the basis for subjects' points of segmentations. RECONSTRUCTIONS

AS

EVIDENCE

FOR

GENERATION

FROM

CSTM

Is short-term recall as reconstructive as Potter and Lombardi claim? These authors have certainly shown subjects to misidentify "lure" words related to the meanings of sentences even though those specific words had not actually occurred in the sentences (e.g., Potter & Lombardi, 1990). It could be argued that such findings could result from recall from a decaying verbatim surface trace constrained by linguistic production rules (Lee & Williams, 1997). Our spontaneous segmentation findings, however, clearly favor the Potter and Lombardi position. It is well-known that age differences in recall are smaller for sentences than for recall of random word lists of equivalent length (e.g., Wingfield, Poon, Lombardi, & Lowe, 1985). This would be an expected finding if, as we have argued, sentence recall is based on reconstruction from a spared CSTM, while random word list recall must rely on an age-compromised veridical store. We examined this question by looking at immediate recall of speech by younger and older adults when recall processes were challenged both by varying speech rates and by varying the way in which the information was grouped at presentation (Wingfield, Tun, & Rosen, 1995). For this purpose, we employed a variant of the spontaneous segmentation method described previously. In this case, passages were divided into segments by the experimenter, rather than the listener. Like the spontaneous segmentation paradigm, subjects were asked to give verbatim recall after each segment had ended. Half of the passages were segmented at normal syntactic boundaries, such as at the ends of clauses and sentences, while the remaining half of the passages were segmented at random non-syntactic points. The distribution of segment sizes were matched across the two presentation conditions. Thus, in each condition listeners would be required to recall segments of similar length (e.g., eight words), but in the syntactic condition those eight words would comprise a syntactically coherent clause, while in the non-syntactic condition the eight words might begin with the end of one clause and include only part of a subsequent one. In this study, we predicted that because the non-syntactic condition would present segments that did not represent a coherent syntactic or semantic unit, it

43

should produce poorer recall than would be found for the syntactically segmented passages that respected these coherent groupings. We further hypothesized that, if older adults are especially reliant on the naturally occurring structure of language, they should be especially disadvantaged by disruptions of this structure relative to young adults. In fact, this is what we found: Our older participants (mean age = 73 years) showed differentially greater recall declines than the young adults (mean age = 19 years) for the random segmentation condition relative to the syntactic segmentation condition (Wingfield et al., 1995). In addition to manipulating segmentation scheme, we also stressed processing load by artificially accelerating speech rates from an original rate of 155 wpm to 220 and 285 wpm. Consistent with earlier studies (e.g., Wingfield et al., 1985; Tun, Wingfield, Stine, & Mecsas, 1992), we found that faster speech rates were especially damaging to recall performance in older adults. Furthermore, the older adults' recall performance was particularly vulnerable, relative to the young adults, when rapid speech rates were combined with the non-syntactic segmentation scheme, especially for the longer segments. When the speech was presented in syntactically coherent units with a normal speech rate, however, the age difference in recall accuracy was minimal (see Wingfield et al., 1995, for details). Although the subjects were specifically told that their task was to recall each Figure 4. Number of reconstructions per sentence in young and older adults' recall of passages interrupted at random or at syntactically related intervals for recall when passages were presented at 155, 220, and 285 words per minute (Data from Wingfield, Tun & Rosen, 1995).

44

segment as accurately as possible, reconstructions in recall occurred for both the young and the older adults. In some cases the subjects' responses omitted a modifier such as an adjective or adverb that reduced the length of the response but that still left a meaningful utterance. In other cases lost words were replaced by others, or words were moved or added to preserve coherence. In fact, when a segment was not recalled correctly, an average of 97% of all recall responses were grammatically correct and semantically coherent. (The percentages ranged from 94% to 99% across age groups and conditions.) For the purposes of our analysis of subjects' errors we defined a reconstruction as the addition or substitution of a word or phrase that was not contained in the original utterance, but that nevertheless left the reported segment syntactically acceptable and semantically coherent. Figure 4 shows the mean number of reconstructions per segment for segments that were not reported exactly as heard. These data are shown for the young and older adults for syntactic and random segmentations at each of the three speech rates tested. Overall, both groups showed an increase in reconstructions as speech rates increased and with random versus syntactic segmentations. We wish to emphasize two points. The first is that the older adults showed a greater number of reconstructions than the younger adults, particularly at the faster speech rates. Indeed, this finding held even when we statistically controlled for the older adults' lower recall rates by expressing reconstructions as a proportion of correct recall (Wingfield et al., 1995). Second, older adults showed a relatively smaller increase than the young adults in the proportion of reconstructions produced at the fastest speech rate (285 wpm) when the segments were presented in the random segmentation condition. This is a condition where the older adults' recall accuracy was poorest, but that would also offer them the least basis for reasonable reconstructions. We see this as evidence that reconstructions in the older adults' recall were neither haphazard nor maladaptive. Under ordinary listening conditions where the emphasis is on gist, reconstruction from a semantic base is a perfectly adaptive way of functioning. In everyday life, for example, it is more adaptive to remember from a weather report that the day will be warm and sunny for a picnic, than to recall the exact details of temperature and humidity. Potter and Lombardi (1990) demonstrated reconstructions in immediate recall with young adults by testing sentence recall after subjects heard synonyms in an earlier distractor task. We found such semantically constrained intrusions occurring for both young and elderly subjects even without the presence of interpolated distractors. The Potter and Lombardi position echoes Bartlett's (1932) classic pronouncement that (long-term) memory is more reconstructive than reproductive. It would appear that this principle holds for short-term recall for meaningful speech as well as it does for long-term recall. Other evidence that CSTM is relatively well preserved in normal aging can be seen in the demonstration that recall of time-compressed speech is significantly improved when silent periods are inserted into speech passages following salient linguistic points such as sentence and clause boundaries. Adding additional processing time at these points would best serve the organization of the rapid input into the semantically based CSTM. When this is done one can restore both young

45

and older adults' recall close to their levels for normal speech rates (Wingfield, Tun, Koh, & Rosen, in press). Assuming that a system such as the CSTM described by Potter and Lombardi is the memory system that carries ordinary comprehension and recall of speech, then one would predict results reported in the literature that slowing speech by adding processing time at clauses is more beneficial than, for example, adding additional time at intervals that do not respect the natural processing units in spoken language, or uniform time expansion of all speech elements (see Wingfield et al., in press, for a review). The similar benefits shown by both young and older adults further support the contention that CSTM is well preserved in normal aging. VERBATIM

AND

CONCEPTUAL TRACES

IN

LONG-TERM MEMORY

As we have seen, traditional models of STM presumed that while storage in verbal short-term memory was in a verbatim or phonological form, storage in long-term memory was conceptual or semantic in nature. That is, the transfer from short- to long-term memory involved not simply a strengthening of the initial trace, but a transformation of the coding format. This view found support in many early studies that showed confusions in short-term memory for words with similar sounds but confusion in long-term memory for words with similar meanings (e.g., Baddeley, 1966). The fact is, however, that we can often remember a speaker's voice or the presentation modality of visually or auditorily presented items (Hintzman, Block, & Inskeep, 1972). These examples illustrate retention of sensory characteristics that do not fit the traditional STM-LTM transfer models. Other studies have shown listeners can remember the surface forms of sentences for long periods of time, as in the case of jokes, insults, and other cases in which the listener chooses to focus on the surface features of an utterance (Murphy & Shapiro, 1994). The ability to demonstrate knowledge of the sensory or surface features of verbal stimuli need not imply that the initial acoustic and phonological traces are being sustained in that form hours or days after the stimuli are heard. The occurrence of long-term retention of surface information, however, has led some to argue for the existence of multiple traces in long-term memory as well as in shortterm memory. As part of a larger model of cognitive processing, fuzzy trace theory, Brainerd and Reyna (1990) have argued for storage in long-term memory in the form of both verbatim and gist-based modes that function in parallel. Brainerd and Reyna (1993) propose several principles that interestingly parallel our view of storage and access in short-term memory. Most relevant to our present discussion are the presumptions (1) that gist extraction is the driving force behind encoding as the individual seeks the underlying sense of gist from incoming stimuli, (2) that information is stored on a fuzzy-to-verbatim continuum that ranges from the general gist of a message to an exact representations of the data, providing an array of options for retrieval, (3) that across the lifespan there is a fuzzyprocessing preference for reasoning from gist traces near the fuzzy end of the continuum, (4) that short-term memory is also reconstructive, and the degree to which gist traces or verbatim traces are called into play depends on the task

46

demands, and (5) that these various operations are not dependent on a common processing resource. Support for the presence of both fuzzy and verbatim traces comes from studies showing the stochastic independence of reasoning and memory performance, as well as differential decay rates, with verbatim traces typically forgotten more rapidly than fuzzy traces (Brainerd & Reyna, 1990). A number of findings in the current literature fit well with these general principles. These include developmental trends in memory distortions in adult aging (Tun, Wingfield, Rosen, & Blanchard, 1998) and differences in the time courses for true and false memories (Brainerd & Mojardin, in press). We can see a number of similarities between fuzzy trace theory and CSTM. The first of these is the presumption of parallel stores. That is, fuzzy trace theory posits a "network of multiple representations that vary in degree of approximation to background input," and that cognitive tasks can switch among these representations (Brainerd & Reyna, 1993, p. 47). Second, fuzzy trace theory also assumes that gist need not come second to verbatim information in the time course of encoding. This is suggested by studies in which children and adults can be shown to detect narrative gist even before all of the details of background information are presented (Brainerd & Reyna, 1993). Finally, Brainerd and Reyna also conclude that gist-based reconstructions increase with age, although in the case of long-term recall this effect may be the product of both relative availability of traces and age-related preferences for processing modes (Brainerd & Reyna, 1993). In sum, the past several years have seen a questioning of many of the early assumptions underlying the structure of the verbal memory system and its role in supporting and constraining language comprehension. In this presentation we have offered several of our own conclusions in this regard as well as pointing to developing trends we see in theoretical accounts of memory and resource models and language comprehension. QUESTIONS TO BE ANSWERED

We had observed earlier that our goal would be less to supply definitive conclusions than it would be to isolate what we believe to be important questions that need to be answered in regard to language, memory constraints, and adult aging. We have isolated three such question areas: (1) What are the multiple representations laid down when a sentence is heard? What is their nature and what are their relative durations? Of these representations, which actually contribute to language comprehension and which subserve other functions? (2)

Assuming that these multiple representations run in parallel, to what extent do they interact during sentence comprehension and immediate recall by young adults? Is it possible that an older, slower, system would show a greater degree of interaction between traces in recall than a younger, faster, system, or a shift in dependence on one type of trace

47

relative to another, and could this affect the way in which language is processed and recalled? (3)

Do the various levels of language processing draw to greater or lesser extents on a single pool of processing resources, or do different processing operations draw on different cognitive architectures and resource systems?

We suggest that the answers to these questions represent a necessary step to understanding cognitive constraints on language comprehension in young adults, and the increased processing challenges in older adulthood.

48

REFERENCES

Allport, D.A., Antonis, B., & Reynolds, P. (1972). On the division of attention: A disproof of the single channel hypothesis. Quarterly Journal of Experimental Psychology, 24, 225-235. Aquino, M.R. (1969). The validity of the Miller-Coleman readability scale. Reading Research Quarterly, 4, 332-357. Atkinson, R.C., & Shiffrin, R.M. (1968). Human memory: A proposed system and its control processes. In K.W. Spence & J.T. Spence (Eds.), The psychology of learning and motivation: Advances in research and theory (Vol. 2, pp. 89195). New York: Academic Press. Baddeley, A.D. (1966). The influence of acoustic and semantic similarity on longterm memory for word sequences. Quarterly Journal of Experimental Psychology, 18, 302-309. Baddeley, A.D. (1986). Working memory. Oxford: Oxford University Press. Baddeley, A.D. (1998). The central executive: A concept and some misconceptions. Journal of the International Neuropsychological Society, 4, 523-526. Baddeley, A.D., Gathercole, S., & Papagno, C. (1998). The phonological loop as a language learning device. Psychological Review, 105, 158-173. Bartlett, F.C. (1932). Remembering: A study in experimental and social psychology. Cambridge: Cambridge University Press. Brainerd, C. J., & Mojardin, A. H. (in press). Children's and adults' spontaneous false memories for sentences: Long-term persistence and mere-testing effects. Child Development. Brainerd, C. J., & Reyna, V. F. (1990). Gist is the grist: Fuzzy-trace theory and the new intuitionism. Developmental Review, 10, 3-47. Brainerd, C. J., & Reyna, V. F., (1993). Memory independence and memory interference in cognitive development. Psychological Review, 100,42-67. Brainerd, C. J., & Reyna, V. F. (in press). When things that were not experienced are easier to "remember" than things that were. Psychological Science. Broadbent, D.E. (1971) Decision and stress. New York: Academic Press. Caplan, D., & Waters, G.S. (1990). Short-term memory and language comprehension: A critical review of the neuropsychological literature. In G. Vallar & T. Shallice (Eds.), Neuropsychological impairments of short-term memory (pp. 337-389). Cambridge: Cambridge University Press. Caplan, D., & Waters, G.S. (in press) Verbal working memory and sentence comprehension. Behavioral and Brain Sciences. Carpenter, P.A., Miyaki, A., & Just, M.A. (1994). Working memory constraints in comprehension: Evidence from individual differences, aphasia, and aging. In M. Gernsbacher (Ed.), Handbook of psycholinguistics (pp. 1075-1 122). San Diego, CA: Academic Press. Conrad, R. (1963). Acoustic confusions and memory span for words. Nature, 197, 1029-1030. Daneman, M., & Carpenter, P.A. (1980). Individual differences in working memory and reading. Journal of Verbal Learning and Verbal Behavior, 19, 450-466.

49

Daneman, M., & Merikle, P.M. (1996). Working memory and language comprehension: A meta-analysis. Psychonomic Bulletin and Review, 3, 422433. Ferreira, F., Henderson, J.M., Anes, M.D., Weeks, Jr., P.A., & McFarlane, M.D. (1996). Effects of lexical frequency and syntactic complexity in spokenlanguage comprehension: Evidence from the auditory moving-window technique. Journal of Experimental Psychology: Learning, Memory, and Cognition, 22, 324-335. Fodor, J.A., Bever, T.G., & Garrett, M.F. (1974). The psychology of language. New York: McGraw-Hill. Frazier, L. (1987). Sentence processing: A tutorial review. In M. Coltheart (Ed.), Attention and performance XII (pp. 559-586). Hillsdale, NJ: Erlbaum. Gernsbacher, M.A. (1985). Surface information loss in comprehension. Cognitive Psychology, 17, 324-363. Goldinger, S.D. (1996). Words and voices: Episodic traces in spoken word identification and recognition memory. Journal of Experimental Psychology: Learning, Memory and Cognition, 22, 1166-1183. Goodglass, H., & Wingfield, A. (1998). The changing relationship between anatomic and cognitive explanation in the neuropsychology of language. Journal ofPsycholinguistic Research, 27, 147-165. Gow, D.W., & Gordon, P.C. (1995). Lexical and prelexical influences on word segmentation: Evidence from priming. Journal of Experimental Psychology: Human Perception and Performance, 21, 344-359. Grosjean, F. (1985). The recognition of words after their acoustic offset: evidence and implications. Perception and Psychophysics, 38, 299-3 10. Hintzman, D.L., Block, R.A., & Inskeep, N.R. (1972). Memory for mode of input. Journal of Verbal Learning and Verbal Behavior, 11, 741-740. Huggins, A.W.F. (1975). Temporally segmented speech and "echoic" storage. In A. Cohen & S.G. Nooteboom (Eds.), Structure and process in speech perception (pp. 209-225). New York: Springer-Verlag. Just, M.A., & Carpenter, P.A. (1992). A capacity theory of comprehension: Individual differences in working memory. Psychological Review, 99, 122149. Kahneman, D. (1973). Attention and effort. Englewood Cliffs, NJ: Prentice-Hall. Kemper, S. (1992). Language and aging. In F.I.M. Craik & T.A. Salthouse (Eds.), Handbook of aging and cognition (pp. 213-270). Hillsdale, NJ: Erlbaum. Kemtes, K. A., & Kemper, S. (1997). Younger and older adults' on-line processing of syntactically ambiguous sentences. Psychology and Aging, 12, 362-371. Kerr, B. (1973). Processing demands during mental operations. Memory and Cognition, 1, 401-412. Lee, M-G., & Williams, J.N. (1997). Why is short-term sentence recall verbatim? An evaluation of the role of lexical priming. Memory and Cognition, 25, 156172. Light, L.L. (1990). Interactions between memory and language in old age. In J.E. Birren and K.W. Schaie (Eds.), Handbook of the psychology of aging (3rd Ed., pp. 275-290). San Diego, CA: Academic Press.

50

Lombardi, L., & Potter, M. C. (1992). The regeneration of syntax in short-term memory. Journal of Memory and Language, 31,713-733. Luce, P.A., & Lyons, E.A. (1998). Specificity of memory representations for spoken words. Memory and Cognition, 26,708-715. Martin, R.C., & Romani, C. (1994). Verbal working memory and sentence comprehension: A multiple-components view. Neuropsychology, 8, 506-523. Massaro, D.W. (1974). Perceptual units in speech recognition. Journal of Experimental Psychology, 102, 199-208. Mattys, S.L. (1997). The use of time during lexical processing and segmentation: A review. Psychonomic Bulletin and Review, 4, 310-329. Meier, R.P. (1991). Language acquisition by deaf children. American Scientist, 79, 60-70. Miller, G.A. (1956). The magical number seven, plus or minus two: Some limits on our capacity for processing information. Psychological Review, 63, 8 1-96. Miller, G.R., & Coleman, E.B. (1967). A set of thirty-six prose passages calibrated for complexity. Journal of Verbal Learning and Verbal Behavior, 6, 851-854. Murphy, G.L., & Shapiro, A.M. (1994). Forgetting of verbatim information in discourse. Memory and Cognition, 22, 85-94. Peterson, L.R., & Peterson, M.J. (1959). Short-term retention of individual verbal items. Journal of Experimental Psychology, 58, 193-198. Potter, M.C. (1993). Very short-term conceptual memory. Memory and Cognition, 21, 156-161. Potter, M. C., & Lombardi, L. (1990). Regeneration in the short-term recall of sentences. Journal of Memory and Language, 29, 633-654. Salthouse, T. A. (1996). The processing-speed theory of adult age differences in cognition. Psychological Review, 103, 403-428. Shiffrin, R.M. (1993). Short-term memory: A brief commentary. Memory and Cognition, 21, 193-197. Titchener, E.B. (1908). Lectures on the elementary psychology of feeling and attention. New York: Macmillan. Tun, P.A., & Wingfield, A. (1993). Is speech special? Perception and recall of spoken language in complex environments. In J. Cerella, J. Rybash, W. Hoyer, & M.L. Commons (Eds.), Adult information processing: Limits on loss (pp. 425-457). San Diego: Academic Press. Tun, P. A. Wingfield, A. Rosen, M. J., & Blanchard, L. (1998). Response latencies for false memories: Gist-based processes in normal aging. Psychology and Aging, 13, 230-241. Tun, P.A., Wingfield, A., Stine, E.A.L., & Mecsas, C. (1992). Rapid speech processing and divided attention: Processing rate versus processing resources as an explanation of age effects. Psychology and Aging, 7, 546-550. van Dijk, T.A., & Kintsch, W. (1983). Strategies of discourse comprehension. New York: Academic Press. Waters, G., & Caplan, D. (1996). The capacity theory of sentence comprehension: Critique of Just and Carpenter (1992). Psychological Review, 103, 761-772. Waugh, N.C., & Norman, D.A. (1965). Primary memory. Psychological Review, 72, 89-104.

51

Wickens, C.D. (1984). Processing resources in attention. In R. Parasuraman & D.R. Davies (Eds.), Varieties of attention (pp. 63-102). New York: Academic Press. Wingfield, A., Alexander, A.H., & Cavigelli, S. (1994). Does memory constrain utilization of top-down information in spoken word recognition? Evidence from normal aging. Language and Speech, 37, 221-235. Wingfield, A., & Butterworth, B. (1984). Running memory for sentences and parts of sentences: Syntactic parsing as a control function in working memory. In H. Bouma & D.G. Bouwhuis (Eds.) Attention and performance X: Control of language processes (pp. 35 1-363). New York: Academic Press. Wingfield, A., Lahar, C.J., & Stine, E.A.L. (1989). Age and decision strategies in running memory for speech: Effects of prosody and linguistic structure. Journal of Gerontology: Psychological Sciences, 44, P106-P113. Wingfield, A. & Lindfield, K.C. (1995). Multiple memory systems in the processing of speech: Evidence from aging. Experimental Aging Research, 21, 101-121. Wingfield, A., Poon, L.W., Lombardi, L., & Lowe, D. (1985). Speed of processing in normal aging: Effects of speech rate, linguistic structure, and processing time. Journal of Gerontology, 40, 579-585. Wingfield, A., & Stine, E.A.L. (1986). Organizational strategies in immediate recall of rapid speech by young and elderly adults. Experimental Aging Research, 12, 79-83. Wingfield, A., Stine, E.A.L., Lahar, C.J., & Aberdeen, J.S. (1988). Does the capacity of working memory change with age? Experimental Aging Research, 14, 103-107. Wingfield, A., Tun, P.A., Koh, C.K., & Rosen, M.J. (in press). Regaining lost time: Adult aging and the effect of time restoration on recall of time-compressed speech. Psychology and Aging. Wingfield, A., Tun, P. A., & Rosen, M. J. (1995). Age differences in veridical and reconstructive recall of syntactically and randomly segmented speech. Journal ofGerontology: Psychological Sciences, SOB, P257-P266. Wingfield, A., Waters, G.S., & Tun, P.A. (1998). Does working memory work in language comprehension?: Evidence from behavioral neuroscsience. In. N. Raz (Ed.), The other side of the error term: Aging and development as model systems in cognitive neuroscience (pp. 3 19-393). Amsterdam: Elsevier. Zacks, R.T., Hasher, L., & Li, K.Z.H. (to appear). Human memory. In F.I.M. Craik & T.A. Salthouse (Eds.), Handbook of aging and cognition (2nd Edition).

52

ACKNOWLEDGMENTS

The authors' research is supported by NIH grants AG04517, AG15852 and AG13614 from the National Institute on Aging. We gratefully acknowledge support from the W.M. Keck Foundation. We also thank Jill Garland for her help preparing this manuscript.

3

DISCOURSE PROCESSING AND AGING: RESOURCE ALLOCATION AS A LIMITING FACTOR

Elizabeth A. L. Stine-Morrow and Lisa M. Soederberg Miller

Time is a central construct in current cognitive aging research. A perusal of recent issues of Psychology and Aging, Journals of Gerontology, and Aging, Neuropsychology, and Cognition, and other major journals (Bashore, Ridderinkhof & van der Molen, 1997; Bryan & Luszcz, 1996; Jagacinski, Liao, & Fayyad, 1995; Myerson, Hale, Wagstaff, Poon, & Smith, 1990; Salthouse, 1996; Sommers, 1996) suggests that cognitive slowing is viewed by many researchers as an important contributor to age deficits in a variety of domains of functioning. We measure the processing time of younger and older adults on a wide array of tasks, find that older adults are slower -- particularly as the task becomes more complex -- and take this as evidence of mental decline. To oversimplify a bit, the implication is that to do things fast is efficient and good and to do things slowly is inefficient and bad. This certainly fits with a large number of everyday instances in which we encounter our own processing limits. For example, our lives would be easier if we could clean up the kitchen faster after dinner or respond to the ATM’s queries with faster button presses, or more quickly digest the obtuse instructions of the IRS. On the other hand, there are a number of other activities for which there hardly seems to be any advantage at all to completing things quickly ... reading a child a bedtime story, drinking a glass of Murphy Goode Reserve Chardonnay, or engaging in a kiss. In fact, for these instances, not only does there seem to be no advantage at all to speed, but speed would rather seem to diminish the experience. In a nutshell, the argument we wish to make is that for many goals, reading falls into this latter class of experiences and that there is something to be gained by considering the advantages conferred by the productive allocation of time to text. First we should make some disclaimers: We are not taking the ridiculous position that speed of processing is never advantageous or important in reading. There is certainly evidence that the experience of reading is diminished for readers who are slower in decoding the orthography of written prose into meaningful concepts. (See West, Stanovich, & Cunningham (1995) for a review.) We are also not discounting the utility of the slowing hypothesis in general. The data supporting 53

54

the position that cognitive processes slow with age and that this slowing can account for a wide variety of performance limitations is voluminous, and there is much value in being able to so parsimoniously account for such a pervasive phenomenon (Salthouse, 1988b). Nevertheless, this focus on processing speed in the current zeitgeist of cognitive aging research may be causing us to neglect the role of time well-spent as we meticulously chart the role of time efficiently spent. In other words, time is a resource that we allocate, and the way in which we allocate resources during reading directly influences the nature of the representation of the text, and consequently, our ability to remember and problem-solve using the text. There appear to be independent domain-specific pools of resources, e.g., Shah & Miyake (1996), but Kahneman’s (1973) basic argument that “there is a ... limit on [the] capacity to perform mental work, [and] this limited capacity can be allocated with considerable freedom among concurrent activities” (p. 8) still applies with domain. The activity of language understanding is one that requires cognitive resources to be allocated for the construction of a complex multi-layered representation, which encompasses word-level meaning, text-level meaning, and discourse-level meaning (see Stine, Soederberg, & Morrow, 1996; Wingfield & Stine-Morrow (in press) for reviews). While these layers of representation may complement and reinforce one another once constructed, there is probably competition for resources in the construction process itself, and resource demands among the three components may be differentially met depending upon reader goals (Kintsch, 1994; Kintsch, 1998; Zwann, Magliano, & Graesser, 1995b). Given age-related declines in cognitive mechanics, the strategic management of resource allocation may well be especially important for older readers in maintaining language processing abilities. In the parlance of the framework suggested by Baltes and Baltes (1990), successful older readers might be expected to be selective about their allocation of resources so as to optimize the construction of the text representation within their constraints. THE METHODOLOGICAL APPROACH

The techniques we have been using to measure resource allocation are the gardenvariety computer methods of measuring self-paced reading time, either sentence-bysentence, constituent-by-constituent, or word-by word, using the moving window method (Just, Carpenter, & Wooley, 1982). In most of the research we will discuss, regression is used to decompose the individual reading times into time allocated as a function of different features of the text. This technique, pioneered by Doris Aaronson (1976; 1977) and Just and Carpenter (1980) two decades ago, essentially assumes that reading is a divided attention task. At every point, cognitive resources must be allocated to word-, text-, and discourse-level processes; allocation to these processes can be estimated by the regression coefficients of their associated text features. Table 1 summarizes the cognitive processes modeled with this technique and their associated operationalization, along with an empirical example (this list of references is far from exhaustive).

55

For example, at the word level, the time for orthographic decoding is estimated by regressing word or sentence reading times onto the number of letters (or syllables); the resulting coefficient is a measure of the time allocated per letter (or syllable) in on-line reading. Lexical access is modeled in terms of log word frequency; because less frequently encountered words take longer to read than more frequently encountered words, the facilitation coefficient (longer reading times for low-frequency words) reflects more extensive elaborative encoding of the features of word meaning. The argument is analogous for variables reflecting text-level processes which result in a proposition-based representation of the text content and for those reflecting a discourse-level representation. Text-level processes are fairly uncontroversial, with numerous empirical examples available for each (e.g., Aaronson & Ferres, 1984b; Haberlandt, Graesser, Schneider, & Kiely, 1986; Kintsch & Keenan, 1973). The product of such processes is an integrated conceptual representation of text content (i.e., the “text-base”). The time allotted to process text-based idea units (i.e., propositions representing the minimal conceptual relation) is most easily measured sentence-by-sentence (or constituent-byconstituent) reading time; at this level propositions are fairly reliable predictors of reading time. Word-by-word reading times are most sensitive to variables marking the conceptual organization. Reading times are reliably longer at the ends of sentences and major intra-sentence syntactic constituents. Because this is the point at which readers integrate information, resolve ambiguities, and so forth, this phenomenon has been called “wrap-up” (Just & Carpenter, 1980) and could be thought of as an empirical indicator of the segment-by-segment processing of discourse that Kintsch and van Dijk (1978) has described in terms of “input cycles.” Resources allocated to wrap-up can be estimated simply in terms of a dummy-coded variable for the presence or absence of such boundaries. Interestingly, the time that readers allocate to wrap-up has been found to be linearly related to the number of new concepts introduced up to that point in the sentence (e.g., Haberlandt et al., 1986). So a more finely tuned estimate of conceptual organization can be attained by including the appropriate multiplicative term (i.e., the dummy code for the presence of the relevant boundary times the number of new concepts). The resulting coefficient provides an estimate of the time per new concept allocated at the boundary. The set of discourse-level processes is not as thoroughly established as those used to construct the text-base, though important strides in this domain have been made in the last few years. Some researchers refer to a “schema” that readers build early in the text which then facilitates processing of subsequent text (Haberlandt, 1984); this is operationalized in terms of serial position (which at the discourse level, yields a negative parameter reflecting facilitation). “Story grammars” (Mandler & Johnson, 1977) were early attempts to model the narrative structure that affords readers a strong level of predictability when processing narrative texts. This can be operationalized by first analyzing the node structure of a narrative. Once constructed, a couple of measures can be calculated for each text segment. The depth in the story grammar tree can be calculated in a fashion analogous to Kemper’s technique with Yngve depth (Kemper, 1992). Readers tend to speed up when they are deep into the plot, as indexed by a negative regression coefficient for

56

depth, suggesting that attention to the narrative structure can facilitate processing. Another measure that is predictive of reading time is a dummy-coded variable for whether or not the current text segment is an episode or story ending; consistent with the depth effects, readers are relatively faster when reading endings. Most recently, research characterizing discourse-level processing has hinged on the concept of the “situation model” (van Dijk & Kintsch, 1983), a representation of “what the text is about” (in contrast to information simply given by the text) that integrates elaborations from world knowledge into the representation of text content; such a representation is argued to enable inferential reasoning and problem solving from the text (Kintsch, 1994). Zwann, Langston, and Graesser (1995a) have proposed an “event-indexing model” of text understanding in which events and intentional actions of the characters are the focal points of the situation model. Resources must be expended to monitor and update the situation model when there is a break in temporal, spatial, causal, or goal coherence in the description of events involving the characters. Consistent with this proposal, readers slow down on text segments representing such breaks (Zwann et al., 1995b). The situation model, then, is conceptualized as a multidimensional representation (Zwann & Radvansky, 1998), though perhaps the most well-studied dimension of the situation model is space. One phenomenon that has been used to provide empirical support for the construction of a spatial situation model is the “distance effect,” the fact that during narrative comprehension readers are facilitated in processing information about objects in close proximity to the protagonist’s current location (Morrow, Greenspan,, & Bower, 1987). In the methodological paradigm typically used to demonstrate the distance effect, readers first memorize a map of the setting in which the narratives they will subsequently read take place. The distance effect can then be demonstrated in either on-line reading time (Rinck & Bower, 1995) or verification times to probes which query relative locations of objects (Morrow et al., 1987). In either case, situation model updating is measured in terms of the protagonist’s movement in the narrative relative to the original layout as learned from the map. As the protagonist moves through the spatial array, some features of the layout are foregrounded and relatively accessible while others recede into the background; once backgrounded, resources are required to activate this information. The variables summarized in Table 1 represent a larger set than would be feasible to examine within a single study. The general approach is to select a set of predictors that cover the processes of interest but avoid multicollinearity (Knight, 1984). Individual regression models are constructed for each subject by regressing the text variables of interest onto reading time (Lorch & Myers, 1990) so that resource allocation patterns for each individual are estimated in terms of the set of beta weights from the regression. Hypotheses about group or task differences can be tested by analyzing the beta weights in a repeated measures ANOVA or a MANOVA. Most of the research described in this chapter will rely on this regression technique in which the multiple demands on resources during text processing are modeled simultaneously.

Table 1.

Modeled language processes and associated text variable used in regression analysis.

THEORETICAL PROCESS

TEXT VARIABLE

REFERENCES

# letters (Ltr) # syllables (Syll) log word f

Aaronson & Just & Carpenter,

Decoding idea units for representation of meaning

# propositions (Prop)

Kintsch & Keenan,

Immediate processing of idea units

New concepts (0/1) (NC)

Immediate organization of idea units

Cumulative new concepts (CumNC)

Parsing / Input cycles

Intrasentence boundary (0/1) (IntsB) Sentence boundary (0/1) (SntB)

Aaronson &

Parsing

Yngve depth (YngD)

Stine-Morrow, Soederberg, Haberlandt & Haberlandt, Graesser, & Kiely, 1986)

WORD Orthographic decoding Lexical access

Aaronson & Carpenter & Just & Carpenter,

TEXT-BASE

57

Buffering (orgn/int)

57

CumNC X IntsB (0/n) (ConcIntsB) CumNC X SntB (O/n) (ConcSntB)

58

DISCOURSE / SITUATION MODEL Schema-based processing

Serial position (SP)

Haberlandt, 1984

Temporal coherence breaks

Zwann, Magliano, & Graesser, 1995

Spatial organization

Spatial coherence breaks Target distance from protagonist

Emotional tone

Emotional coherence breaks

Zwann et al., 1995 Morrow, Greenspan, & Bower, 1987 Gernsbacher, Goldsmith, & Robertson, 1992 Stine-Morrow, Miller, & Leno, in preparation

Story grammar processing

Depth (SG Depth) Ending (SG Ending)

58

Temporal organization

59

AGE DIFFERENCES

IN

PATTERNS

OF

RESOURCE ALLOCATION

Over the last several years, the research in our lab has been focused on looking at individual differences in these patterns of resource allocation, particularly at age differences. To this point, this research could be summarized as showing the following: (1) Older readers are often somewhat slower (show a higher intercept), but their reading times are generally sensitive to the same class of text variables as those of younger adults (Miller & Stine-Morrow, 1998; Stine, 1990; Stine, Cheung, & Henderson, 1995; Stine & Hindman, 1994; Stine-Morrow, Loveless, & Soederberg, 1996). (2) One frequent and important exception to this rule is that older adults allocate less time for conceptual processing, especially at sentence boundaries (Stine, 1990; Stine et al., 1995); when they do wrap-up, they appear to allocate relatively more resources for wrap-up after smaller intrasentence constituents rather than after sentences (Miller & Stine-Morrow, 1998). (3) Readers who are above average in subsequent memory performance allocate time differently from the average reader or from below-average readers. For both younger and older readers, successful outcome is related to longer reading time overall, i.e., a higher intercept (e.g., Stine, 1990; Stine et al., 1995) and more thorough processing of complex syntax (Stine et al., 1996). (4) There also appear to be age differences in the reading strategies that engender good memory performance. For younger readers, successful outcome is related to conceptual processing, especially wrap-up at larger constituents like sentences (Stine, 1990; Miller & Stine-Morrow, 1998). For older readers, successful outcome may be less likely to be related to conceptual processing, but relatively more likely to be related to discourse-level processing. For example, successful older readers show a steeper serial position effect (StineMorrow et al., 1996), presumably reflecting more schema based processing (Haberlandt, 1984) and allocate relatively more time to repair spatial coherence breaks (Morrow et al., 1997). Thus, what the reader “does” when reading appears to be related to the nature of the representation when finished. And there are several tantalizing suggestions of ways in which older readers have to do different things from younger adults in order to have a comparable product from reading so as to demonstrate good memory performance. Generally speaking, older adults are more effective when they implement strategies that enable them to circumvent working memory limits, e.g., by wrapping-up more frequently and by taking advantage of discourse-level organization. In particular, these data are consistent with Adams’ (Adams, 1991; Adams, Labouvie-Vief, Hobart, & Dorosz, 1990; Adams, Smith, Nyquist, & Perlmutter, 1997) notion that younger readers are more literal and text-bound in the way in which they approach the text while older adults are more holistic, especially in terms of the strategies that engender good memory performance. This research, however, is limited in several ways -- ways that may well give the appearance of elders being at a disadvantage in conceptual processing. Thus, the thrust of this chapter will be to address these limits, considering some of the recent research from our lab that in some ways challenges our view of the older reader. To summarize (and elaborate on) the argument to this point, our basic premise is that the productive allocation of resources is a necessary condition for the construction

60

of an organized, elaborated and distinctive, meaning-based representation of text. Research from our lab and elsewhere (Hartley, Stojack, Mushaney, Annon, & Lee, 1994; Ratner, Schell, Crimmins, Mittelman, & Baldinelli, 1987; Zabrucky & Moore, 1994) suggests that on average older adults may not allocate resources during online processing so as to create such a representation, particular for the text-base; this may contribute in part to oft-noted age-related declines in discourse memory. The remainder of the chapter is organized around four factors which may encourage the productive allocation of resources among older readers, thus maximizing the utility of the constructed representation. OLDER ADULTS ALLOCATE RESOURCES

TO

NARRATIVE TEXT

Narrative texts are those that tell a story, most typically by focusing on a protagonist that encounters and resolves one or more conflicts through a telling that unfolds in time. Readers generally read narratives more quickly and remember more from them than expository texts. One account of this phenomenon is that narratives consume cognitive capacity. For example, Britton et al. (1983) demonstrated that simple reaction time in a secondary task was longer when the primary task was to read narrative passages than when it was to read expository passages. Much in the way that it is easier to redirect attention (to answer a telephone, for instance) from reading a newspaper account of the latest university funding crisis than it is when reading a Richard Russo narrative on university life, Britton’s subjects were relatively more absorbed in the narratives, taking longer to respond to the secondary task. Such data prompted them to argue that narratives draw cognitive resources because of the "meaning that is produced by the text in the reader's cognitive system" (p. 41). In other words, the narrative structure of a good story creates an obligatory demand for resources that is difficult to ignore. It may not be only the structure that generates differences in resource allocation, however. Zwann (1994) showed that younger adults read identical passages differently depending on whether they were told that the passages were excerpts from news stories or novels. Thus, genre effects on resource allocation may ultimately be due to a combination of text features and expectations about what is typically required in reading in that genre. There is a small literature in cognitive aging that has explored the narrative advantage among elderly readers. Elderly readers appear to be especially efficient at encoding narratives (relative to expository texts) as measured by reading time per proposition recalled (Tun, 1989). With respect to memory organization, older readers do as well as (Tun, 1989) or better than (Stine & Wingfield, 1987; Stine & Wingfield, 1990) young adult readers in using narrative structure in selective memory for gist over detail. Such findings may appear to be paradoxical if we assume that narratives demand processing resources (Britton et al., 1983), but that aging brings a depletion of resources (Salthouse, 1988a). In fact, using Britton’s secondary task approach, Tun (1989) showed that while younger readers demonstrated a genre effect on secondary task performance (replicating the Britton work), older readers did not, even though older adults showed a differential benefit from genre in processing efficiency. Nevertheless, Tun concedes that the secondary task, which generates very small genre effects among the young (30 msec), may

61

Figure 1. Reading time allocation to different text features of narratives by younger and older adults.

have not been sensitive in an older sample. The analysis of resource allocation from reading times allowed us a more direct text of Tun’s hypothesis that older adults rely on the narrative structure to support self-initiated processing (e.g., Craik & Jennings, 1992). Thus, even though narratives are resource-consuming, their well-defined organization (as well as readers’ well-learned skills in how to approach this genre) may provide support that elders use to meet resource demands. In our study (Stine-Morrow, Miller, & Leno, in preparation), 104 younger adults and 100 older adults read two extended and highly engaging “elder tales,” “The Woodcutter” and “The Alchemist” (Chinen, 1989) for subsequent recall. We should point out that our participants read only narrative passages, and our focus was on examining on-line resource allocation to this genre alone. While we cannot draw conclusions about comparisons between genres, we can examine (in a more fine-grained way than has been done before) age differences in processing narratives. In particular, we were interested in finding out whether, under these optimum conditions (i.e., highly schematic narratives expressing themes presumably of especial relevance in late life), older adults would be compelled to engage in conceptual processing. In terms of overall recall, the two groups were quite similar, with older adults recalling 29.7% of the propositions and younger adults recalling

62

31.2%. Figure 1 shows the reading time allocation patterns for these two age groups. What is striking about these data is that that there are negligible age differences in the patterns of resource allocation, multivariate F(10, 188) = 1.59, p > .1. Most importantly, younger and older readers appeared to respond to the demands for conceptual processing and integration in exactly the same way and to the same extent. In particular, older adults appeared to engage in sentence wrap-up in the same way that younger adults did. Neither was there a substantial difference in subsequent recall. Comparing this to the earlier studies, the data suggest that older adults are using the narrative schema of the text to support resource allocation to the text base. This conclusion is bolstered by the fact that those subjects who were most facilitated in their reading by story grammar depth and ending showed larger sentence wrap-up effects ( r = -.19, p < .01 for depth, and r = -.24, p < .001 for ending). Also, an analysis based on a median split of subsequent recall showed that while elders above-average in recall were more facilitated by story grammar ending and serial position than those below-average in recall, p < .05 for both, younger groups did not show this difference. So it appears that in the case of highly engaging narrative texts, older readers can allocate resources to text-base level conceptual integration. This stands in contrast to our results with expository texts and short narratives in which older adults demonstrated reduced wrap-up effects. In addition, such processing contributed to good recall performance. In a hierarchical regression analysis, ability measures and strategy measures independently predicted recall performance, with ability measures carrying about 17% of the variance, and strategy variables (primarily sentence wrap-up) carrying about 9% (this is the case regardless of the order of entry). AGEDIFFERENCESINRESOURCEALLOCATIONCANDEPENDUPONREADER GOALS

The way in which readers allocate resources to the text has been shown to depend on the goal with which they approach the text. For example, Aaronson and Ferres (1984a) showed that readers allocate relatively more time to lexical items conveying structural features of language (e.g., conjunctions and prepositions) when they read for recall, but relatively more time to lexical items conveying content (e.g., adjectives) when reading for comprehension. Similarly, Kintsch (1994) has argued that comprehension and problem-solving goals promote greater processing of the situation model, while recall goals promote relatively greater attention to the text base. Consistent with this position, Zwann, Magliano, and Graesser (1995b) have shown that among college readers, resources are disproportionately allocated to processing the situation model when narratives are read for comprehension, but to the text base for recall. Reader goals are perhaps particularly important in comparing resource allocation strategies of young and old. Younger adults engaged in (or not far from) formal educational experience often find themselves reading in order to be able to recall the information later. In spite of the professor’s overtures to the contrary,

63

students often prepare for retrieval by focusing on constructing the text base representation, giving short shrift to the situation model. Older adults, on the other hand, are not typically in an ecological niche which requires recall. Rather, they are likely to read for comprehension, for example, for entertainment or for learning how to do something. Thus, it might be expected that even though older adults may be less sensitive to text demands when asked to produce subsequent recall, this may not be the case when they are asked to read for comprehension. In our lab, we tested this hypothesis in an experiment in which younger and older adults read single sentences word-by-word either for recall or comprehension. We should begin with the caveat that this is a preliminary study purely examining sensitivity to text features for sentence processing, so we are limited in being able to address only text-based features (and not situation model features, which are certainly of interest in the long run). Figure 2. Reading time allocation to text features as a function of reader goals for younger and older adults.

64

In this study, 52 university undergraduates and 50 community-dwelling elders read a series of sentences (16-18 words in length) dealing with nature, geography, and history (similar to materials used by Stine and Hindman (1994)). Subjects within each age group were randomly assigned to either a read-for-recall or read-forcomprehension group; those in the former condition simply produced immediate recall for each sentence and those in the latter answered a single question after reading each sentence. Questions were designed to test the gist of the sentence and important details. For example, the sentence “The snowshoe rabbit has white fur in the winter which turns brown in the warmer seasons” was followed with the T/F item, “The snowshoe rabbit is brown in the summer”; the sentence “Fossil reefs formed from limestone bedrock give the ground under Chicago the strength to support tall skyscrapers” was tested with the T/F item, “A layer of granite under Chicago supports its buildings.” The patterns of reading time allocation as a function of reader goal and age are presented in Figure 2. When reading for recall (lower panel of Figure 2), older adults allocated less time to conceptual integration than did the young, as has been previously demonstrated in the word-by-word paradigm (Stine, 1990; Stine et al., 1995). Allocation patterns to achieve comprehension were different from those used to achieve recall for both age groups. First, and most obviously, reading times in the comprehension condition were less sensitive to our target text variables (note that in the upper panel of Figure 2, the scale of time allocation is expanded so as to highlight the relative importance of different text features). Second, there were relatively fewer resources allocated to conceptual integration and relatively more on elaborative encoding of new concepts (NewConc) the first time they were introduced and on lexical access (word f). Third, there was no intrasentence wrapup, and in fact, this variable (ContIntS) produced a suppression effect because of its correlation with NewConc ( r = .72) in this stimulus set. Most importantly, in contrast to the recall condition, there were no age differences at all in reading time allocation, F (4,396)=6.69, p <.001, for the Age by Retrieval Condition by Text Variable interaction. Thus, with the more typical and less resource-consuming reading goal, older readers appeared to meet the resource demands of comprehension. In terms of ultimate performance, the age difference in proportion of propositions recalled (MY = .68, se = .03; MO= .72, se = .02) was not significant, t (49) = 1.37, and older readers even outperformed the young on the comprehension task (MY= .80, se = .02; MO= .89, se = .01), t (50) = 3.85, p < .05. The asymmetry in these results (i.e., age differences in resource allocation leading to age similarity in recall, but age similarity in resource allocation leading to an elder-superiority in comprehension) is not easy to explain. It is not uncommon to find older readers – even high-performing ones – allocating relative few resources to conceptual processing under recall instructions, and it may certainly be that elders can achieve high levels of memory performance by allocating resources to text features not measured in the present study. So one explanation is that elderly readers were engaging in some unmeasured discourse-level processes (e.g., Adams; StineMorrow et al., 1996); though it is difficult to postulate what these processes might be for single sentences) that enabled them to equal (in recall) or outperform (in

65

comprehension) the younger readers. Nevertheless, even though earlier research has demonstrated a relationship between wrap-up and subsequent memory for text (e.g., Haberlandt et al., 1986; Stine, 1990; Miller & Stine-Morrow, 1998), this was not the case in the present data set. In fact, none of our allocation variables predicted performance in either goal condition (recall performance was positively related to both WAIS vocabulary, r = .34, p < .02, and to working memory span, r = .33, p < .02, and comprehension performance was positively related to vocabulary alone, r = .43, p < .001). Thus, even though this particular data set does not speak to the issue of the patterns of allocation that engender good memory performance, they are informative with respect to spontaneous change in allocation strategy in response to task demands: while older readers may differ from the young in how they allocate resources to text for a recall task, they may use strategies quite similar to the young when they read for comprehension. OLDER READERS ALLOCATE RESOURCES

TO THE

SITUATION MODEL

Although the text-base representation is often inefficiently (Hartley et al., 1994) and fragilely (Cohen & Faulkner, 1981; Light & Capps, 1986) constructed among older adults, the mental model has been found to be fairly resilient to the effects of aging (Morrow, Stine-Morrow, Leirer, Andrassy, & Kahn, 1997; Radvansky, Gerard, Zacks, & Hasher, 1990; Radvansky & Curiel, 1998; Soederberg & Stine, 1995). The next experiment we present reinforces the point that older readers show preserved situation model processing and demonstrates that they may be particularly dependent on this mode of processing to achieve good memory performance. We focus on spatial aspects of the situation model, and the logic of our argument hinges on the “distance effect” discussed earlier. Even though resources to the spatial situation model can be modeled using the global regression techniques illustrated in the two studies presented so far (Zwann et al., 1995b), in this case, we used an experimental approach in which word- and text-level variables are held constant to isolate the effects of spatial distance. Earlier research has shown that older readers show a distance effect as they read (Morrow et al., 1997), suggesting that they build and update the spatial situation as the character moves through the setting as younger adults do. In our most recent experiment on this topic (Stine-Morrow, Morrow, & O’Brien, 1998), we were interested in comparing how younger and older adults would deal with new information from the text in constructing a situation model. The participants were 49 university students and 53 community dwelling elderly adults. The setting for all of the narratives was a ten-room research center. In each of the six narratives, a plot was developed for a different protagonist which provided some motivation for him/her to move about the center, interacting with other characters and objects. Before reading the narratives, participants memorized a pictorial layout of the setting which included three objects in each room. In the first few paragraphs of the narrative, three new objects were introduced with a modifier and location, mentioned again explicitly, and mentioned implicitly a third time pronominally. Over the course of the rest of the narrative, there were six critical motion sentences which described a protagonist moving from one room (the

66

Figure 3. Sentence reading time as a function of distance and object type for younger and older adults.

“source” room) to another (the “goal” room) through an unmentioned (“path”) room. Following the motion sentence was a target sentence in which the protagonist was described as mentally interacting (e.g., remembering, thinking about, wondering about) with an object in the layout. Half of the objects in the target sentences were from the layout as originally memorized (“original objects”) and half were those introduced in the text (“new objects”). Thus, there were six cells in the withinsubject design created by factorially combining two levels of Object Type (original, new) and three levels of distance from the protagonist (goal, path, source). After reading each narrative, participants answered a series of Y/N comprehension questions which probed understanding of the protagonist’s goals, subgoals organized to achieve goals, emotional tone, location of the protagonist at critical points in the narrative, as well as the location of learned and new objects. Older adults took longer than the young to learn the narrative layout, as measured by both trials-to-criterion (TTC), t (100) = 7.26, p < .001, and total study time, t (100) = 2.05, p < .05, but were similar to the young in terms of overall comprehension accuracy, t (94) = 1.23, ns. Reading time data were analyzed by first calculating distance effects for learned and new objects for each subject as slope values derived from regressing average sentence reading time onto distance (dummy coded as 0, 1, 2), These slope values were analyzed in a 2 (Age) X 2 (Object Type: original, new) repeated measures analysis of variance. There was a marginal trend for the distance effect to be greater for original objects than for new objects, F (1, 100) = 3.31, p < .075, as would be expected if the a priori learning of the spatial layout enhanced organization of the situation model. In other words, subjects read sentences more quickly when they referred to objects close to the protagonist than when they referred to objects farther away, but this effect was more pronounced

67

when the objects were those learned in the original layout. There was no age difference in the distance effect, nor was the Age by Object Type interaction significant, F < 1 for both. In fact, both younger and older readers demonstrated a significant distance effect for both learned and new objects, with the regression slope significantly greater than zero in all four cases, p < .05. These data suggest that, on average, both younger and older adults can integrate new information from the text into the situation model. Furthermore, an examination of correlations between the distance effect and comprehension performance suggested that mental model updating was predictive of comprehension accuracy, with the distance slope showing significant relationship to overall comprehension accuracy, r (96) = .21, p < .03, as well as to memory for the location of the new objects, r (96) = .28, p < .01, and the protagonist, r (96) = .30, p < .01. To further explore the resource allocation patterns that engendered successful comprehension, distance slopes were analyzed for subjects who achieved comprehension accuracy greater than or equal to 80%. As shown in Figure 4, when conditionalized on high levels of subsequent comprehension performance, younger adults showed a reduced distance effect for new objects relative to original objects (this was the Object Type by Distance interaction evident in the first analysis), suggesting that they were less likely to integrate the new information from the text into the situation model. Older adults, on the other hand, showed similarly large distance effects for both types of objects. This Age X Object Type interaction for the distance effect was significant, F (1,76) = 4.21, p < .05. These data suggest that older adults were able to integrate new information into the situation model from text at least as well as younger adults, and that this mode of processing was particularly apparent among those who were successful in answering the comprehension questions. Thus, older adults who are successful comprehenders appear to allocate relatively more resources than do the young to mental model updating for newly learned information. OLDER READERS ALLOCATE RESOURCES WHEN SUPPORTED ALREADY KNOW

BY

WHAT THEY

The final piece of research we describe addresses the extent to which knowledge can guide the allocation of processing resources (Miller, in preparation). The benefits of knowledge on the products of discourse processing, such as recall and comprehension, are well-established. For example, knowledge has been shown to facilitate language processing among younger adults in terms of recall (Spilich, Vesonder, Chiesi, & Voss, 1979), recognition (Chiesi, Spilich, & Voss, 1979), and coherent production (Voss, Vesonder, & Spilich, 1980) of domain-related texts. Recent work on expertise also attests to the merits of an extensive and wellorganized knowledge base (cf. Ericsson & Charness, 1994) that can help the reader form a situation model (Kintsch, 1998). However, we know little about how knowledge influences on-line reading. The work of Sharkey and Sharkey (1987), and more recently Miller and Stine-Morrow (1998), has shown that knowledge can speed processing by making unfamiliar concepts more accessible and by facilitating

68

conceptual integration. But there is something else that knowledge does for us: it structures the text for us so that we can productively allocate resources to it, as is required whenever we encounter conceptually difficult material in our domain. To explain how knowledge promotes processing, Ericsson and Kintsch (1995) proposed the notion of retrieval structures. Retrieval structures are an elaborate system of retrieval cues in short-term memory that provide rapid access to knowledge structures in long-term memory. Because of this, they refer to this system as long-term working memory (LTWM). High-knowledge readers construct retrieval structures in LTWM as they progress through a text which can enable them to more efficiently encode and retrieve material that directly maps onto relationships stored in long-term memory. Empirically, this may correspond to more efficient (i.e., faster) conceptual integration (cf. Sharkey & Sharkey, 1987; Miller & StineMorrow, 1998). When knowledgeable readers read texts in their domain, the retrieval structures that they construct allow a more complex representation to be stored in LTWM relative to that of the novice (who does not have complicated chunks to retrieve). Our argument is that to the extent that information from the text allows the expert to augment the current knowledge base (e.g., by adding new conceptual relations), processing novel information in the domain may actually be resourceconsuming. Thus, when an expert reads highly familiar material, s/he may be facilitated in conceptual integration, but when the expert is building on the extant knowledge base, s/he can use well-developed retrieval structures to productively expend resources toward the expansion of that knowledge base. Under this latter condition, knowledgeable individuals will actually show more extensive resource allocation (cf. Britton & Tesser, 1982; Britton, Holdredge, Curry, & Westbrook, 1979). Figure 4. Reading time allocation to conceptual processing at the immediate boundaries (INTRASNT), and intersentence boundaries (INTERSNT) as a function of passage type among older readers.

69

From an intuitive standpoint, one could image that reading a journal article within one’s domain of expertise might entail a different allotment of cognitive resources, than, say, reading a newspaper article about research aimed at the general public. The newspaper article can be read quickly by the expert because the concepts are already familiar and highly integrated. The journal article, on the other hand, probably contains new concepts that require cognitive resources by the expert to integrate. The novice, however, would be less likely to expend resources since there are no retrieval structures to promote their productive allocation. In everyday reading, we often read to learn more about something we already know about; given the age-related growth in crystallized abilities (e.g., Schaie, 1996), this is probably even more true of older readers, and it may give them an advantage that is not captured by laboratory passages carefully screened so as to be unfamiliar. Thus, we wish to entertain the possibility that, under some circumstances, knowledge may encourage the older reader to allocate processing resources. Assuming that knowledge facilitates processing of the situation model (Kintsch, 1998), that the situation model promotes comprehension/learning rather than simple recall (Kintsch, 1998), that older adults may be more likely to wrap-up when the goal is comprehension (cf. Figure 2), and that older adults may rely more on the situation model in text processing (cf. Figure 3), it may be that highknowledge elders will expend resources for conceptual wrap-up to learn more about something within a domain in which they are already well-versed. In a demonstration of this principle, Miller (in preparation) asked 50 community-dwelling elders varying in background knowledge of cooking to read fairly technical cooking passages as well as control passages unrelated to cooking. Based on scores on a paper-and-pencil measure of cooking knowledge (an instrument developed and validated using professional chefs and chef trainees), a median split was used to divide this group into those above- and below-average in cooking knowledge. The domain-related passages, taken from cooking textbooks, contained concepts and terminology specific to the area of cooking with terms such as glutin, persillade, and rosemary. The control passages were about jumping beans, swordmaking, and whales and contained concepts like baleen, gulpers, and skimmers. The recall data were consistent with past research showing that knowledge facilitated performance (e.g., Spilich et al., 1979). While there was no group difference in recall of the control passages (32.3 vs. 33.6 propositions for low- and high-knowledge groups, respectively), for the cooking passages, high-knowledge readers demonstrated better recall than low-knowledge ones (24.3 vs. 19.4), t (49) = 1.79, p < .05. Figure 4 shows the patterns of resources allocated to conceptual processing (either immediately or for wrap-up) to cooking and control passages (in this case, the dummy-codes for boundaries were entered without being weighted by conceptual load). For sentence wrap-up, the Group by Passage Type interaction was significant, F (1,46) = 5.32, p < .05, showing that high-knowledge readers were differentially more likely to allocate time to wrap-up for passages in their domain of expertise. While there were no group effects on intrasentence wrap-up at minor boundaries, high-knowledge subjects allocated marginally more resources to the

70

immediate processing of new concepts, F (1,46) = 3.55, p < .07. Thus, it seems that because the older high-knowledge readers had the background knowledge needed to form retrieval structures, they were able to allocate the resources needed to comprehend and remember these challenging texts. CONCLUSION

To wrap up, the literature in discourse processing and aging has been somewhat equivocal with respect to the existence of age deficits. Age deficits have been most apparent when texts are expository and demanding in their requirements of text-base integration. The measurement of on-line processing has related memory deficits among the old to their failure to allocate processing resources to the construction of the text-base. Thus, in processing the text-base, older adults are often fast and “efficient.” The consequent representation does not always serve them well in memory performance. The work we have reviewed, while in many ways still only suggestive, shows that there are certain conditions, namely narrative structure, comprehension goals, situation model availability, and knowledge, which can promote the productive allocation of resources to text among older adults. Perhaps the most provocative aspect of this research is that it suggests that it may wind up being an oversimplification to say that elders can maintain their discourse processing ability by focusing on discourse-level features (e.g., Adams et al., 1990; Stine-Morrow et al., 1996). Rather, it may be that their use of discourselevel features, such as the situation model and narrative structure, provides support to enable them to create a distinct and elaborated text-base on par with that of the young.

71

REFERENCES

Aaronson, D., & Ferres, S. (1984a). A structure and meaning based classification of lexical categories. Annals of the NY Academy of Sciences, 43,21-57. Aaronson, D., & Ferres, S. (1984b). The word-by-word reading paradigm: An experimental and theoretical approach. In D. E. Kieras & M. A. Just (Eds.), New methods in reading comprehension research (pp. 31-68). Hillsdale, N. J.: Erlbaum. Aaronson, D., & Scarborough, H. S. (1976). Performance theories for sentence coding: Some qualitative evidence. Journal of Experimental Psychology: Human Perception and Performance, 2, 56-70. Aaronson, D., & Scarborough, H. S. (1977). Performance theories for sentence coding: Some quantitative models. Journal of Verbal Learning and Verbal Behavior, 16, 277-303. Adams, C. (1991). Qualitative age differences in memory for text: A life-span developmental perspective. Psychology and Aging, 6, 323-336. Adams, C., Labouvie-Vief, G., Hobart, C. J., & Dorosz, M. (1990). Adult age group differences in story recall style. Journal of Gerontology: Psychological Sciences, 45, P17-27. Adams, C., Smith, M. C., Nyquist, L., & Perlmutter, M. (1997). Adult age-group differences in recall for the literal and interpretive meanings of narrative text. Journal of Gerontology: Psychological Sciences, 52B, P187-P195. Baltes, P. B., & Baltes, M. M. (1990). Psychological perspectives on successful aging: The model of selective optimization with compensation. In P. B. Baltes & M. M. Baltes (Eds.), Successful aging (pp. 1-34). New York: Cambridge University Press. Bashore, T. R., Ridderinkhof, K. R., & van der Molen, M. W. (1997). The decline of cognitive processing speed in old age. Current Directions in Psychological Science, 6, 163-169. Britton, B. K., Graesser, A. C., Glynn, S. M., Hamilton, T., & Penland, M. (1983). Use of cognitive capacity in reading: Effects of some content features of text. Discourse Processes, 6, 39-57. Britton, B. K., Holdredge, T. S., Curry, C., & Westbrook, R. D. (1979). Use of cognitive capacity in reading identical texts with different amounts of discourse level meaning. Journal of Experimental Psychology: Human Learning and Memory, 5, 262-270. Britton, B., & Tesser, A. (1982). Effects of prior knowledge on use of cognitive capacity in three complex cognitive tasks. Journal of Verbal Learning and Verbal Behavior, 21, 421-436. Bryan, J., & Luszcz, M. A. (1996). Speed of information processing as a mediator between age and free-recall performance. Psychology and Aging, 11, 3-9. Carpenter, P. A., & Just, M. A. (1989). The role of working memory in language comprehension. In D. Klahr & K. Kotovsky (Eds.), Complex information processing: The impact of Herbert A. Simon (pp. 3 1-68). Hillsdale: Erlbaum.

72

Chiesi, H., Spilich, G., & Voss, J. (1979). Acquisition of domain-related information in relation to high and low domain knowledge. Journal of Verbal Learning and Verbal Behavior, 18, 257-273 Chinen, A. (1989). In the ever after. Wilmette, IL: Chiron. Cohen, G., & Faulkner, D. (1981). Memory for discourse in old age. Discourse Processes, 4,253-265. Craik, F. I. M., & Jennings, J. M. (1992). Human memory. In F. I. M. Craik & T. A. Salthouse (Eds.), The handbook of aging and cognition (pp. 51-110). Hillsdale, NJ: Erlbaum. Ericsson, K. A., & Charness, N. (1994). Expert performance: Its structure and acquisition. American Psychologist, 49, 725-747. Ericsson, K. A., & Kintsch, W. (1995). Long-term working memory. Psychological Review, 102, 211-245. Gernsbacher, M. A., Goldsmith, H. H., & Robertson, R. R. W. (1992). Do readers mentally represent characters' emotional states? Cognition and Emotion, 6, 89111. Haberlandt, K. (1984). Components of sentence and word reading times. In D. E. Kieras & M. A. Just (Eds.), New methods in reading comprehension research (pp. 219-251). Hillsdale, NJ: Erlbaum. Haberlandt, K., & Graesser, A. C. (1989). Buffering new information during reading. Discourse Processes, 12, 479-494. Haberlandt, K. F., Graesser, A. C., Schneider, N. J., & Kiely, J. (1986). Effects of task and new arguments on word reading times. Journal of Memory and Language, 25, 3 14-322. Hartley, J. T., Stojack, C. C., Mushaney, T. J., Annon, T. A. K., & Lee, D. W. (1994). Reading speed and prose memory in older and younger adults. Psychology and Aging, 9, 216-223. Jagacinski, R. J., Liao, M., & Fayyad, E. A. (1995). Generalized slowing in sidusoidal tracking in older adults. Psychology and Aging, 10, 8-19. Just, M. A., & Carpenter, P. A. (1980). A theory of reading: From eye fixations to comprehension. Psychological Review, 87, 329-354. Just, M. A., Carpenter, P. A., & Wooley, J. D. (1982). Paradigms and processes in reading comprehension. Journal of Experimental Psychology: General, 111, 228-238. Kahneman, D. (1973). Attention and effort. Englewood Cliffs, NJ: Prentice-Hall, Inc. Kemper, S. (1992). Language and aging. In F. I. M. Craik & T. A. Salthouse (Eds.), The handbook of aging and cognition (pp. 213-270). Hillsdale, NJ: Erlbaum. Kintsch, W. (1994). Text comprehension, memory, and learning. American Psychologist, 49, 294-303. Kintsch, W. (1998). Comprehension: A paradigm for cognition. New York: Cambridge University Press. Kintsch, W., & Keenan, J. M. (1973). Reading rate and retention as a function of the number of propositions in the base structure of sentences. Cognitive Psychology, 5, 257-274.

73

Kintsch, W., & van Dijk, T. A. (1978). Toward a model of text comprehension and production. Psychological Review, 85, 363-394. Knight, G. P. (1984). A survey of some important techniques and issues in multiple regression. In D. E. Kieras & M. A. Just (Eds.), New methods in reading comprehension research. (pp. 13-30). Hillsdale, N. J.: Erlbaum. Light, L. L., & Capps, J. L. (1986). Comprehension of pronouns in younger and older adults. Developmental Psychology, 22, 580-585. Lorch, R. F., & Myers, J. L. (1990). Regression analyses of repeated measures data in cognitive research. Journal of Experimental Psychology: Learning, Memory, and Cognition, 16, 149-157. Mandler, J. M., & Johnson, N. S. (1977). Remembrance of things parsed: Story structure and recall. Cognitive Psychology, 9, 111-151. Miller, L. M. S. (in preparation). The effects of real-world knowledge on text processing among older adults. Miller, L. M. S., & Stine-Morrow, E. A. L. (1998). Aging and the effects of knowledge on on-line reading strategies. Journal of Gerontology: Psychological Sciences, 53B, P223-P233. Morrow, D. G., Stine-Morrow, E. A. L., Leirer, V. O., Andrassy, J. M., & Kahn, J. (1997). The role of reader age and focus of attention in creating situation models from narratives. Journal of Gerontology: Psychological Sciences, 52B, P73-P80. Morrow, D. G., Greenspan, S. L., & Bower, G. H. (1987). Accessibility and situation models in narrative comprehension. Journal of Memory and Language, 26, 165-187 Myerson, J., Hale, S., Wagstaff, D., Poon, L. W., & Smith, G. A. (1990). The information loss model: A mathematical theory of age-related cognitive slowing. Psychological Review, 97, 475-487. Radvansky, G., Gerard, L., Zacks, R., & Hasher, L. (1990). Younger and older adults' use of mental models as representations for text materials. Psychology and Aging, 5, 209-214. Radvansky, G. A., & Curiel, J. M. (1998). Narrative comprehension and aging: The fact of completed goal information. Psychology and Aging, 13, 69-79. Ratner, H. H., Schell, D., Crimmins, A., Mittelman, D., & Baldinelli, L. (1987). Changes in adults' prose recall: Aging or cognitive demand? Developmental Psychology, 23, 521-525. Rinck, M., & Bower, G. H. (1995). Anaphora resolution and the focus of attention in situation models. Journal of Memory and Language, 34, 110- 131. Salthouse, T. A. (1988a). Resource-reduction interpretations of cognitive aging. Developmental Review, 8, 1-35. Salthouse, T. A. (1988b). The role of processing resources in cognitive aging. In M. L. Howe & C. Brainerd (Eds.), Cognitive development in adulthood (Vol. Springer-Verlag, pp. 185-239): New York. Salthouse, T. A. (1996). The processing-speed theory of adult age differences in cognition. Psychological Review, 103, 403-428.

74

Schaie, K. W. (1996). Intellectual development in adulthood. In J. E. Birren & K. W. Schaie (Eds.), Handbook of the psychology of aging (Fourth edition) (pp. 266-286). Boston: Academic Press. Shah, R., & Miyake, A. (1996). The separability of working memory resources for spatial thinking and language processing: An individual differences approach. Journal of Experimental Psychology: General, 125,4-27. Sharkey, N., & Sharkey, A. (1987). What is the point of facilitation? The loci of knowledge-based facilitation in sentence processing. Journal of Memory and Language, 26,255-276. Soederberg, L. M., & Stine, E. A. L. (1995). Activation of emotion information in text among younger and older adults. Journal of Adult Development, 2, 253270. Sommers, M. S. (1996). The structural organization of the mental lexicon and its contribution to age-related declines in spoken-word recognition. Psychology and Aging, 11, 333-341. Spilich, G., Vesonder, G., Chiesi, H., & Voss, J. (1979). Text processing of domainrelated information for individuals with high and low domain knowledge. Journal of Verbal Learning and Verbal Behavior, 18, 275-290. Stine, E. A. L. (1990). On-line processing of written text by younger and older adults. Psychology and Aging, 5,68-78. Stine, E. A. L., Cheung, H., & Henderson, D. T. (1995). Adult age differences in the on-line processing of new concepts in discourse. Aging and Cognition, 2, 1-18. Stine, E. A. L., & Hindman, J. (1994). Age differences in reading time allocation for propositionally dense sentences. Aging and Cognition, 1, 2-16. Stine, E. A. L., Soederberg, L. M., & Morrow, D. G. (1996). Language and discourse processing through adulthood. In F. Blanchard-Fields & T. M. Hess (Eds.), Perspectives on cognition in adulthood and aging (pp. 255-290). New York: McGraw-Hill. Stine, E. A. L., & Wingfield, A. (1987). Levels upon levels: Predicting age differences in text recall. Experimental Aging Research, 13, 179-183. Stine, E. A. L., & Wingfield, A. (1990). The assessment of qualitative age differences in discourse processing. In T. M. Hess (Ed.), Aging and cognition: Knowledge organization and utilization (pp. 33-92). New York: Elsevier. Stine-Morrow, E. A. L., Loveless, M. K., & Soederberg, L. M. (1996). Resource allocation in on-line reading by younger and older adults. Psychology and Aging, 11,475-486. Tun, P. A. (1989). Age differences in processing expository and narrative texts. Journal of Gerontology: Psychological Sciences, 44, P9-P15. van Dijk, T. A., & Kintsch, W. (1983). Strategies of discourse comprehension. New York: Academic Press. Voss, J., Vesonder, G., & Spilich, G. (1980). Text generation and recall by highknowledge and low-knowledge individuals. Journal of Verbal Learning and Verbal Behavior, 19, 651-667 West, R. F., Stanovich, K. E., & Cunningham, A. E. (1995). Compensatory processes in reading. In R. A. Dixon & L. Bäckman (Eds.), Compensating for

75

psychological deficits and declines: Managing losses and promoting gains (pp. 275-296). Mahwah, NJ: Erlbaum. Wingfield, A., & Stine-Morrow, E. A. L. (in press). Language and speech. In F. I. M. Craik & T. A. Salthouse (Eds.), Handbook of aging and cognition (Second edition). Mahwah, NJ: Erlbaum. Zabrucky, K., & Moore, D. (1994). Contributions of working memory and evaluation and regulation of understanding to adults' recall of texts. Journal of Gerontology: Psychological Sciences, 49, P201-P212. Zwann, R. A. (1994). Effect of genre expectations on text comprehension. Journal of Experimental Psychology: Learning, Memory, and Cognition, 20, 920-933. Zwann, R. A., Langston, M. C., & Graesser, A. C. (1995a). The construction of situation models in narrative comprehension: An event-indexing model. Psychological Science, 6, 292-297. Zwann, R. A., Magliano, J. P., & Graesser, A. C. (1995b). Dimensions of situation model construction in narrative comprehension. Journal of Experimental Psychology: Learning, Memory, and Cognition, 21, 386-397. Zwann, R. A., & Radvansky, G. A. (1998). Situation models in language comprehension and memory. Psychological Bulletin, 123, 162-185.

76

ACKNOWLEDGMENTS

The authors’ research described in this chapter was conducted with the support of grants R01 AG13935 and F31 MH10937. We thank Steve Moynihan and Ken Bell for help with data collection. The first author is indebted to the Merrill Advanced Studies Institute and the participants in the Sedona workshop for a unique and stimulating intellectual experience.

Part 2

CONSTRAINTS ON LANGUAGE: MEMORY

This page intentionally left blank.

4L

IMITATIONS ON SYNTACTIC PROCESSING Susan Kemper and Karen A. Kemtes

GENERAL MODELS

OF

PRODUCTION

AND

COMPREHENSION

There has been far too little research on how aging affects many aspects of language production or processing. For instance, little is known about how aging affects speech errors at syntactic, semantic, and phonological levels; how word order variation, quantifier scope, and attachment ambiguities are affected by normal and pathological aging; and how discourse planning may show positive (Burke, 1997; James, Burke, Austin, & Hulme, 1998) as well as negative effects (Arbuckle & Gold, 1993) of normal aging. One of the most well-established age-related changes to cognition is the loss of working memory capacity (Salthouse, 1991). Although exceptions have often been reported, older adults commonly perform less well on tests of digit or word span as well as on more demanding tests of reading or listening span and computational span. It is not surprising, therefore, that age-related changes to working memory have been linked to age-related differences in language processing. A central hypothesis has been that working memory limitations affect older adults' ability to process hierarchically structure, particularly syntactic constructions involving embedded and subordinate clauses (Kemper, 1992). This hypothesis, thus, challenges two issues of central importance to psycholinguistics, the modularity hypothesis and claims about the serial nature of language processing. Psycholinguistic models of language production and comprehension have tended to focus on two issues: (1) the modularity of syntactic, semantic, and/or pragmatic processes and (2) serial versus hierarchical accounts of language production and comprehension (Balota, d’Arcais, & Rayner, 1990; Bock, 1987; Dell, 1986; Frazier & Fodor, 1978; Garrett, 1988; Kintsch, & van Dijk, 1978; MacKay, 1987; McClelland & Rumelhart, 1981; Rayner & Pollatsek, 1989; Seidenberg, 1989; Seidenberg & McClelland, 1989; Trabasso & van den Broek, 1985). Modularity (Fodor, 1982) or autonomy theory holds that message production involves a sequence of comprehension stages or levels. Typically four properties 79

80

are ascribed to this sequence of processing stages: (1) each stage corresponds to a distinct linguistic rule system, (2) each stage involves a discrete representational system; (3) processing flows unidirectionally through the sequence of stages, and (4) each stage may be characterized by independent constraints on the rules, representations, or processing operations at that stage. Although messages are produced “one word at a time” (Bloom, 1975), message structure is inherently hierarchical. A number of phenomena are typically discussed to illustrate this tension between serial and hierarchical aspects of language: (i) in English, datives and objects can alternate in the linear sequence for some verbs such as give (compare Mary gave a cookie to me to Mary gave me a cookie) but not for others such as donate (Mary donated a million dollars to me versus Mary donated me a million dollars); (ii) verbs must agree with their subjects in person and number; this constraint is violated in Efforts to make English the official language is gaining strength throughout the U. S. (The New Yorker, November 17, 1986, p. 94); although the verb "is gaining" agrees with the immediately preceding noun language, the grammatical subject of the sentence is the plural noun "efforts"; (iii) the interpretation of the scope of quantifiers also is influenced by word-order variation and clause embedding. Compare Everyone in this room speaks two languages to Two languages are spoken by everyone in this room. Whereas the first sentence implies only that each individual is fluent in two languages, the second implies that they are fluent in the same two languages; (iv) ambiguities can arise whenever the linear sequence can be assigned to multiple hierarchical structures. The sequence The boy chased the dog with two bones could be interpreted as indicating that the boy had two bones by attaching the prepositional phrase to the verb phrase ([[chased V] [the dog NP] [with two bones PP] VP]) or that the dog had two bones by attaching the prepositional phrase to the object noun phrase ([[chased V] [the dog [with two bones PP] NP] VP]); (v) complexity increases as clauses and phrases are hierarchically embedded in left-branching or center-embedded structures as in The man the woman the boy saw knew died compared to right-branching (The boy saw the woman who knew the man who died) or serially connected (The boy saw the woman, she knew the man, and he died) structures. Processing models have in common the idea that messages are represented at a number of levels. Processing models vary with respect to how these comprehension processes are implemented (cf. Balota, D'Arcais, & Rayner, 1980, or Gernsbacher, 1990, for detailed discussions of processing models). Most models assume that there are a number of autonomous levels of processing including: orthographic or acoustic levels since the individual words must be recognized from the incoming visual or auditory signal; a level at which lexical information (e.g., category, meaning) for each word is accessed; a syntactic level in which individual words are formed into a hierarchy of syntactic constituents; a semantic level at which meaning relations within and between words are determined; and a propositional level of message meaning. Specific models do differ with regards to how these levels are arranged and how information flows between levels. For example, modular models of language comprehension (e.g., Frazier & Fodor, 1978) propose that

81

comprehension involves a series of discrete and sequential stages of processing: signal decoding (auditory or visual), lexical access, syntactic analysis, semantic analysis, and discourse analysis. In contrast, interactive models of language comprehension (e.g., McClelland & Rumelhart, 198 1) posit that the various stages of analysis occur in parallel and are interactive. Processing models of text structure tend to differ from processing models for individual sentences by focusing on the underlying message representation of a discourse or text (cf. Kintsch and van Dijk, 1978; Mandler & Johnson, 1977; Meyer, 1975; Trabasso, & van den Broek, 1985). Central to text structure models is the idea that messages are decomposed into hierarchically ordered propositionbased idea units during processing. These models generally outline methods for determining the microlevel relations between word units within a text and relating the temporal and causal connections between these idea units. For example, Mandler and Johnson's story grammar approach (1977) views message analysis in terms of an underlying story schema which is used to focus information for comprehension or recall. The structure of the story grammar is tree-based with nodes referring to various constituents (states and events) and branches referring to the causal or temporal connections between constituent nodes. The structure also interacts with general world knowledge as to how stories are constructed (the notions of schema or scripts). These transformational rules are generative in nature and are not specific to the semantic content of the text. In Kintsch and van Dijk's model (1978), text comprehension involves several stages: a text is first decomposed into propositions, propositions are arranged into a hierarchy ranging from the most general propositions to the most detailed, and the propositional hierarchy is stored in memory. Meyer's (1985) model of prose analysis focuses on the logical relationships between the 'micropropositional" level of text, which relates information within and between sentences; the "macropropositional" level of text, which focuses on how text is organized (i. e., gist) and relates logical and causal connections within text; and the top-level structure of text which focuses on the global representation of the text. AGING, WORKING MEMORY,

AND

SYNTACTIC PROCESSING

Within cognitive psychology, working memory is viewed as a limited-capacity storage and processing mechanism. Baddeley (1986) conceived of working memory as involving a central executive, which schedules and assigns processing tasks, and two temporary storage buffers -- an articulatory loop which retains phonological information for subsequent processing and a visual scratch pad which preserves visual information. Similar limited capacity components are commonly included in formal models of syntactic parsing mechanisms (Gibson, Pearlmutter, CansecoGonzales, 1996; Gibson, Schultze, & Salomon, 1996; Lewis, 1996); linguistic analyses place great demands on working memory whenever the amount of information to be processed exceeds working memory's capacity, perhaps by overloading the articulatory loop, or whenever the processing operations themselves, such as those required to parse complex syntactic structures, are excessive and thus over-load the central executive.

82

Working memory limitations have been commonly assumed to account for a wide range of age-related linguistic phenomena including age-related changes to spontaneous production. Although sentence length in words remains constant, older adults show a reduction in their use of complex syntactic constructions such as those involving subordinate and embedded clauses. (Benjamin, 1988; Cooper, 1990; Davis, 1984; Kemper, 1992; Kemper, Kynette, Rash, Sprott, & O’Brien, 1989; Kemper, Rash, Kynette, & Norman, 1990; Kynette & Kemper, 1986; Shewan & Henderson, 1988; Ulatowska, Freedman-Stern, Weiss-Doyle, Macaluso-Haynes, & North, 1983; Walker, Roberts, & Hedrick, 1988.) Kemper (1987a) analyzed the incidence of different types of embedded clauses in both a longitudinal sample and a cohort-sequential sample of adults’ writings taken from diary entries. The longitudinal record spanned seven decades; the cohort-sequential sample contrasted adults born in the 1820s with those born in the 1860s for diary entries made when the adults were in their 40s versus in their 80s. The primary finding was the overall complexity of the adults’ writing declined across the life-span; 70 and 80-year olds produce few sentences with embedded clauses, especially left-branching embeddings. In spontaneous speech, older adults favor coordinate or rightbranching constructions, e.g., She’s awfully young to be running a nursery school for our church, over left-branching constructions, e.g., The gal who runs a nursery school for our church is awfully young. During the production of the left-branching constructions (in which the embedded clause occurs to the left of the main clause), the form of the subject “the gal” must be retained and the grammatical form of the main clause verb “is” (which must agree with its subject in person and number) must be anticipated while the embedded clause “who runs a nursery school for our church” is being produced. Each clause is produced sequentially in the rightbranching construction (in which the embedded clause occurs to the right of the main clause). This asymmetry between left- and right-branching constructions has been assumed to reflect working memory limitations on the production of leftbranching constructions. Kemper et al. (1989) reported that the mean number of clauses per utterance (MCU), a general measure of the complexity of adults language, is positively correlated with the adults backward digit span using the WAIS subtest (Wechsler, 1958). Further, Kemper and Rash (1988) calculated Yngve depth (Yngve, 1960), a measure of the working memory demands of sentence production, and found that it was positively correlated with WAIS digit span as well as with MCU. This line of research, therefore, supports the hypothesis that working memory limitations may affect older adults’ production of complex syntactic constructions. Kemper and her colleagues have also investigated the role of working memory in limiting adults’ processing of complex syntactic constructions. Kemper (1987b) tested adults’ ability to imitate sentences containing different kinds of embedded sentences. The embedded clauses varied in length and locus. The sentences also varied in grammaticality. Whereas the elderly adults, 70 to 89 years of age, were able to imitate the short sentences correctly, they were unable to imitate the long sentences or sentences with a left-branching embedding as in Baking ginger cookies tires me out. The older adults tended to recall either the first clause, as in “I was baking ginger cookes” or the second clause “The cookies tired me“ but not both.

83

The young, college-aged adults were able to imitate the sentences correctly regardless of length, embedding, or grammaticality. Kemper suggested that aging impairs adults' syntactic processing by limiting how many different grammatical operations can be simultaneously performed. Kemper and Rash (1988) and Norman, Kemper, and Kynette (1992) have suggested that working memory limitations on syntactic processing also contribute to older adults' text processing problems by increasing processing demands whenever multiple syntactic constituents must be simultaneously analyzed and interrelated. Norman et al. (1992) compared older adults' text processing comprehension and rates for texts which varied in syntactic complexity but not in content. The most complex version of each text was characterized by many embedded clauses that preceded or modified the sentence subject: "By 1888 with the spreading of civilization, coast-to-coast railroad tracks, which had been laid across the country, replaced the wagon trains. The surveyors marked off farmland to discourage freegrazing. Land which had belonged to the frontier was now owned by settlers with families. The Old West was a thing of the past." In contrast, the simplest version was made of one-clause sentences: "By 1888 civilization had spread from coast to coast. Railroad tracks were laid across the country. They replaced the wagon trains. The surveys marked off farmland. This discouraged freegrazing. Land no longer belonged to the frontier. Settlers with families now owned the land. The Old West was a thing of the past." Norman et al.(1992) demonstrated that older adults' text comprehension and reading speed declined as syntactic complexity increased and concluded that the use of embedded clauses, particularly those modifying the sentence subject, impairs older adults' reading comprehension. Other evidence also supported the hypothesis that working memory limitations affect older adults' processing of linguistic information. For example, Light, Capps, Singh, & Albertson Owens (1985), following Light and Capps (1986) and Light and Singh (1987), found that older adults are less likely to establish the referent of a pronoun when linguistic information intervenes between the pronoun and its antecedent as in "John stood watching while Henry jumped across a ravine. The ground was rocky and uneven that only goats used this path. There were no flowers but a few weeds grew here and there. He fell in the river." although they can do so in when little information intervenes, as in "Henry spoke at a meeting while John drove to the beach. He brought along a surfboard." A similar conclusion was drawn by Zurif, Swinney, Prather, Wingfield, and Brownell (1995) from a study of older adults' on-line processing of object-and subject-relative sentences using a cross-modal priming task. In object-relative sentences, the object 'moves' from the object position of the subordinate clause and leaves a 'gap' or trace (e.g., The tailor hemmed the cloaki that the actor from the studio needed (ti) for the performance). In subject-relative sentences, the gap is indexed by the object of the matrix clause (e.g., The gymnast loved the professori from the Northwestern city who (ti) complained about the bad coffee). The focus of their analysis was to determine whether reactivation of the antecedent occurs at the gap during sentence processing. Zurif et al. found that older adults evidenced priming for the subject- but not object-relative sentences (experiment 1). In a

84

second experiment, Zurif et al. reduced the distance between gap and antecedent in object-relativesentences from seven or eight intervening words to five and found a significant priming effect at the gap position. The authors conclude that older adults reactivate the antecedent when the distance between antecedent and gap is short. Zurif et al. do not report a direct comparison of young and old but interpret their results as showing that older adults’ immediate syntactic analysis of a sentence is affected by working memory limitations that affect the retention of antecedents. Working memory limitations also affect adults’ metalinguistic judgments about the grammaticality of sentences. Pye, Cheung, and Kemper (1992) found that adults of all ages are able to detect violations of grammatical rules as in *Whom did you see the woman from the apartment house next door and? or *John is expected the woman from the city treasurer’s office to help. However, older adults, particularly those in their 80s, also rated some grammatical sentences as ungrammatical. For example, You saw the woman from the apartment house next door and whom? and The woman from the city treasurer's office is expected to help John are grammatical although the older adults typically rated these sentences as ungrammatical. Kemper (1997) also examined metalinguistic judgments of older adults as well as adults with Alzheimer’s disease. Two types of sentences were tested: the first type of sentences tested linguistic constraints on phrase structure, such as the contrast in acceptability for Jane gave the library a book versus Jane donated the library a book or The bed was slept on by Washington versus Tuesday was slept on by Washington. Young adults and healthy older adults tended to reject as acceptable the sentences which violated linguistic constraints on phrase structure whereas adults with Alzheimer’s disease tended to find Jane donated the library a book and Tuesday was slept on by Washington to be acceptable. This finding suggests that adults with Alzheimer’s disease are not sensitive to subtle aspects of verb meaning which regulate their use in various phrase structures. The second type of sentence Kemper tested involved linguistic constraints on transformations of linguistic structure. Some alternative forms of sentences can be legitimately derived whereas others are blocked by linguistic constraints. Both The fact is irrelevant that John gave Bill all his old books and The fact that John gave Bill all his old books is irrelevant are permitted whereas The fact that John gave Bill is irrelevant all his old books is blocked by a linguistic constraint. Kemper found that young adults’ metalinguistic judgments match the predictions of linguistic theory whereas older adults and adults with Alzheimer’s disease tend to find all three variants to be acceptable. This pattern was correlated with working memory capacity, suggesting that the older adults and adults with Alzheimer’s disease were unable to fully process the long, multi-clause sentences due to working memory limitations; hence, they were unable to detect the violation of the linguistic constraint. At least part of the observed age-related decrements in language processing and working memory may be due to age-related slowing of phonological or articulatory processes. Kynette, Kemper, Norman, Cheung, and Anagnopoulos (1990) have confirmed a link between adults’ word span and word repetition rates (Hulme, Thomson, Muir, & Lawrence, 1984; Schweickert & Boruff, 1986). Elderly adults are able to recall as much as they can say in approximately 1.2 seconds; thus word span, as well as word repetition rates, for short one-syllable words exceed

85

those for longer two- or three-syllable words. This relationship between word span and word repetition is stable across the life-span and appears to be an accurate index of the capacity/duration of the articulatory loop component of working memory. A similar account of some forms of childhood reading impairments has been recently put forth by Crain and Shankweiler (1988, 1990) and Gathercole and Baddeley (1989, 1990). Crain and Shankweiler (1988, 1990) note that poor readers lag behind good readers in their comprehension of complex syntactic structures such as relative clauses and that poor readers also evidence a variety of working memory limitations, especially those involving phonological analysis. Language processing deficits, including reading disorders in childhood and syntactic processing limitations in late adulthood, may arise whenever sentences impose severe processing demands on working memory. IN SUPPORT

OF

WORKING MEMORY LIMITATIONS

ON

SYNTACTIC PROCESSING

Much of the evidence for attributing age-related differences in language production and comprehension to working memory limitations hinges on a contrast between left-branching and right-branching syntactic constructions. Left-branching constructions are generally assumed to be more difficult to process than rightbranching ones. One classic parsing model, the so-called Sausage Machine, of Frazier and Fodor (1978) involves two parsing stages: a limited-capacity first stage parser and an unlimited second stage parser. The model explains the asymmetry in the processing left- and right-branching clauses as arising from the restriction of the first-stage parser to the analysis of six or so words at a time. The first-stage parser attempts to form meaningful grammatical constituents from each group of six words. These constituents are then assembled into clauses by the second stage parser. Sometimes the first-stage parser is not successful or the constituents it forms are not correct; the second-stage parser must then re-analyze the words into the correct constituents. Left-branching clauses which exceed the capacity of the first-stage parser will trigger such re-analysis. For example, the first-stage parser will initially (incorrectly) analyze the center-embedded left-branching sentence The man the woman the girl knew cursed died as a six-word coordinate noun phrase followed by a six-word coordinate verb phrase. The second stage parser must break up these constituents and re-analyze the input in order to correctly pair each noun phrase with the appropriate verb. No such re-analysis is required for the right-branching sentence The girl knew the woman who cursed the man who died. The first stage parser will supply the correct constituents, segmenting the first group of words into two noun phrases and a verb and the second group of six words into three noun phrases and two verbs. These constituents can then be readily assembled into clauses by the second stage parser. This parsing model can be naturally extended to account for the effects of aging on syntactic processing. Yngve (1960) suggested Miller's (1962) "7+2" as a candidate for the maximum depth of spoken sentences and that "a depth factor in language change should be easily observable..." (p. 452). Aging may provide just such a "depth factor" by imposing a lower limit on the depth of constituent structures which can be produced. Reducing maximum depth to "5+2" would

86

effectively restrict the production of most left-branching constructions as well as limit the production of other constructions involving, e.g., elaborated noun phrases, prepositional phrases, and auxiliary verb sequences. Reducing the capacity of the first stage parser in the Frazier and Fodor model would produce a similar effect on sentence comprehension. If the first stage parser was restricted to operating, not on six words at a time, but on four words at a time, comprehension of most leftbranching constructions would be disrupted. Although more contemporary parsing models are available, constraints and limitations are incorporated in most in an explicit attempt to account for the difficulty of parsing complexity structures such as center-embedded sentences (see Lewis, 1996, for a review) as constituent "look-ahead" buffers holding to-beanalyzed information may be constrained or temporary memory stores or stacks holding partially analyzed constituents. Formal models of the architecture of human cognition such as SOAR (Laird, Newell, & Rosenbloom, 1987; Newell, 1990) and EPIC (Meyer & Kieras, 1997 a, b) are explicitly designed to incorporate working memory limitations on syntactic processing. According to such parsing models, working memory limitations on syntactic processing should affect a variety of different types of constructions. EXTENDING

THE

HYPOTHESIS

Kemtes and Kemper (1997) sought further support for the hypothesis that agerelated working memory limitations affect syntactic processing by examining on-line reading times for wh-questions. Two wh-question types were chosen for testing: argument questions, e.g., Who did John ask how to paint?, and adjunct questions, e.g., When did John ask how to paint? These types of wh-questions raise significant issues for models of syntactic processing that assume working memory limitations constrain the analysis of complex constructions (Gibson et al., 1996 a & b; Lewis, 1996). Like the filler-gap constructions examined by Zurif et al. (1995), processing wh-questions requires the reader to detect and fill-in a gap; the presence of the gap is signaled by the wh-word, e.g., "who" or "when," which also provides semantic information about the missing element. The gaps can occur at multiple sites associated with either the main verb of the sentence, "ask," or the embedded verb, "to paint." The distinction between argument questions and adjunct questions arises from current linguistic theories of verb structure (Grimshaw, 1991): verbs are classified according to how many arguments, or obligatory constituents, they require. Verb arguments include subjects, direct objects, and, for some verbs, indirect objects or other verbal complements. A verb such as ask requires three arguments: the subject who does the asking, the direct object who is asked, and a verbal complement, the question itself. A verb such as see only requires two arguments, a subject and a direct object (DO). Adjuncts are optional constituents usually conveyed by prepositional phrases, that indicate time or manner. Who and what typically query verb arguments, how, when, and where typically query verb adjuncts. Of particular interest is whether there are age differences in the interpretation of argument and adjunct questions. Older adults were predicted to have more difficulty comprehending adjunct questions because older adults'

87

working memory limitations should make processing optional elements such as adjuncts more difficult. A particular type of wh-question is ambiguous. Who did John ask to paint? has two interpretations. In the first, sometimes called the "'upstairs" interpretation, who is interpreted as referring to the DO of the verb ask In the second interpretation, sometimes called the "downstairs" interpretation, who refers to the DO of the verb paint. Although some details remain under dispute, the relevant linguistic theory (Chomsky, 1986) holds that the wh-word originates as the argument to a verb, in this case as the direct object (DO) of either the verb ask or the verb paint. The wh-word is then raised up from the verb to the front of the sentence in a series of steps or cycles. An intervening wh-word will block this process and permit only an "upstairs" interpretation: How did John ask who to paint? is not ambiguous. This question can only be interpreted as a "how" question about John's asking (e.g., the answer might be "by telephone" not "by using a spray gun"). However, the linguistic constraint is more complicated since Who did John ask how to paint? is ambiguous. It can be interpreted as a "who" question referring to the DO of "ask" (the upstairs interpretation) or as a "who" question referring to the DO of "paint" (the downstairs interpretation). The difference lies in the nature of the intervening wh-word: who is an argument, an obligatory complement of the verb, whereas how is an adjunct, an optional complement to the verb. Arguments can be raised up, jumping past adjuncts, as in Who did John ask how to paint? but adjuncts cannot be raised up past arguments, blocking the downstairs interpretation of How did John ask who to paint? Research by de Villiers and her colleagues (de Villiers, 1996) has shown that very young children recognize the ambiguity of Who did John ask to paint? and produce answers consistent with either the upstairs interpretation or the downstairs interpretation and find How did John ask who to paint? to be unambiguous, producing only upstairs answers. Children do, on occasion, produce an interesting error, interpreting a wh-question with an intervening wh-word, as in Who did John ask how to paint? as a "how" question. Thus, for children, Who did John ask how to paint? is three-ways ambiguous, permitting an upstairs interpretation, e.g., who did John ask?, a downstairs interpretation, e.g., who did John paint?, and a second downstairs interpretation, how did John paint? The metalinguistic study of Pye, Cheung, and Kemper (1992) suggested that such knowledge of linguistic constraints may be offset in late adulthood by working memory limitations on the processing of complex sentences. Consequently, older adults were predicted to be unable to derive both interpretations of Who did John ask to paint? or Who did John ask how to paint? and to prefer either an upstairs interpretation or the downstairs interpretation. To validate the questions and answers, a preliminary study was conducted using an answer acceptability ratings task. Young and older adults read the stories and a question about each story. Each question was paired with two answers. Each answer corresponded to a different interpretation of the question. Participants were asked to rate the plausibility of the answer on a Likert-based scale where 1 = Not very plausible and 5 = Very plausible. In agreement with linguistic theory, the argument questions were ambiguous with two plausible answers and an intervening

88

adjunct rendered the argument adjunct questions unambiguous. Adjunct questions were also unambiguously interpreted by both young and older adults. All participants completed four working memory-based measures in the experiment. The first two tasks, the WAIS-R (Wechsler, 1981) forward and backward digit spans, were included as measures of short-term memory processing. Participants also completed a reading span task which was based on the original Daneman and Carpenter (1980) reading span task and is reported in Kemtes and Kemper (1997). In the reading span task, participants are required to read aloud progressively longer sets of sentences without pausing and then recall the sentencefinal word from each sentence in the set. The reading span score was defined as the highest level at which participants correctly recalled all of the words from two of the three sets. Participants received an additional half point if they correctly recalled one of the three sets from the next highest level. Finally, participants completed a listening span task (Salthouse, Babcock, & Shaw, 1991). In the listening span task, individuals were required to listen to progressively longer sets of short sentences and answer a short question after each sentence. At the end of each level, individuals recalled the sentence-final words in their presented order. The listening span score was defined as the highest level (of six) at which participants correctly recalled all of the words from three of the five sets. Participants received an additional half point if they correctly recalled one of the three sets from the next highest level. Composite working memory scores were formed using the four measures described above. In order to form a composite score that accurately reflected the relative contribution of the four measures used, we conducted a confirmatory factor analysis with a single working memory latent variable. The working memory composite weighted each score on the individual measure according to its association with the working memory factor. Based on a medium split of these composite working memory scores, performed separately for each age group, participants were assigned to either a high-span or a low-span group. High span young adults had an average composite score of 28.5 ( SD = 2.9) whereas low span young adults had an average composite score of 23.8 ( SD = 2.7). Composite scores for the older adults were lower: high span older adults had an average composite score of 22.0 ( SD= 4.7) and low span older adults had an average composite score of 15.5 ( SD = 2.5). The high and low span young and older adults were tested on their comprehension of wh-questions using a word-by-word reading time procedure. The wh-questions tested their comprehension of short stories. Each story followed the same sequence: sentence one introduced the main character and a "how to..." verb; the second sentence introduced the day of the event and two additional characters: the individual to whom the question was addressed and the subject of the query; sentence three repeated the "how to..." action; and the final sentence restated the main character's name and the main action. Four wh-questions were prepared for each story. See (1). Two argument questions beginning with who or what and two adjunct questions beginning with when or how were prepared for each story. Argument questions were of the form "Who did PERSON ask to VERB2?," e.g., Who did John ask to paint? There are two possible answers: who can be interpreted as the DO of

89

ask or the DO of VERB2. An adjunct was inserted into the question to create an argument-adjunct question of the form "Who did PERSON ask how to VERB2?," e.g., Who did John ask how to paint? The question is also ambiguous: it can be interpreted as a who question about the DO of ask or as a who question about the DO of VERB2 since the intervening adjunct how does not block the second interpretation. There is also a third possibility, as some children in the deVillers et al. (1990) study interpreted Who did PERSON ask how to VERB2? as a how question. The adjunct questions were of the form "When did PERSON ask ______ to VERB2?" and the blank could be filled by either an argument, e.g., When did John ask who to paint? or by an adjunct, e.g., When did John ask how to paint? In contrast to the argument question, the adjunct questions should be unambiguously interpreted as when questions about ask Linguistic constraints should block the second interpretation of the adjunct-argument questions as a who question about the DO of VERB2. The downstairs reading of the adjunct adjunct questions should also be blocked so that When did John ask how to paint? should be unambiguously interpreted as a when question about ask (1) Example Story and Questions. A Trace, t, is inserted to Indicate where Answers Originate in the Underlying Structure of the Questions. John is a student in a community art program and is learning how to paint by rotating a brush. On Monday, John was eager to start and asked the instructor if he could paint the class model. John then asked the instructor how to rotate the brush. Finally, John was ready to paint. Argument Questions: Who did John ask t1 to paint t2? Upstairs Interpretation: Who refers to t1 such that John asked the person (i.e., the instructor) a question Downstairs Interpretation: Who refers to t2 such that John asked to paint this person (i.e., the model) Argument Adjunct Questions: Who did John ask t1 how to paint t2 t3? Upstairs Interpretation: Who refers to t1 such that John asked the person (i.e., the instructor) a question Downstairs Interpretation: Who refers to t3 such that John asked to paint this person (i.e., the model) *Optional Downstairs Interpretation: How refers to t2 the method (i.e., by rotating brush) by which John executed the painting. Adjunct Argument Questions: When did John ask t1 who to paint t2? Upstairs Interpretation: When refers to t1 the time (i.e., on Monday) at which John asked the question *Blocked Downstairs Interpretation: Who refers to t2 such that John asked to paint this person (i.e., the model)

90

Adjunct Adjunct Questions: When did John ask t1 how to paint t2? Upstairs Interpretation: When refers to t1 the time (i.e., on Monday) at which John asked the question *Blocked Downstairs Interpretation: How refers to t2 the method (i.e., by rotating brush) by which John executed the action. Reading times for the questions were collected on a word-by-word basis but analyzed separately for four critical segments. The critical segments corresponding to the initial wh-word, the main clause subject and verb, the intervening wh-word (except for argument questions lacking a intervening wh-word), and the final infinitive phrase, as indicated in (2). (2) Question Type Argument Argument Adjunct Adjunct Argument Adjunct Adjunct

Segment 1

2

3

4

Who Who When When

did John ask did John ask did John ask did John ask

--how who how

to paint? to paint? to paint? to paint?

Separate analyses were performed on the question reading times for each segment. Young adults read segment 1, the initial wh-word, more rapidly than older adults ( M Y = 374, SD Y = 179; M O = 583, SD O = 385) and high span adults read segment 1 more rapidly than low span adults ( M H = 425, SD H = 252; M L = 533, SD L = 313). Young adults also read segment 2 more rapidly than older adults ( M Y = 309, SD Y = 94; M O = 475, SD O = 163) and high span adults read segment 2 more rapidly than low span adults ( M H = 346, SD H = 141; M L = 454, SD L= 123). More critcially, young adults read segment 3, corresponding to the embedded wh-word, more rapidly than older adults and high span adults read the segment more rapidly than low span adults; however, low span young adults read segment 3 as rapidly has high span young adults ( M H = 318, SD H = 244; M L = 334, SD L = 113) whereas low span older adults read more slowly than high span older adults ( M H = 416, SD H = 244; M L = 606, SD L = 275). See Figure 1. Reading times for segment 3 did not differ for the three types of questions containing intervening wh-words. Low span young adults read segment 4 as rapidly has high span young adults ( M H = 404, SD H = 390; M L = 461, SD L = 304) whereas low span older adults read more slowly than high span older adults ( M H = 577, SD H = 386; M L = 919, SD L = 482). See Figure 2. Reading times for segment 4 differed for the four types of questions. The final infinitive phrase of adjunct argument questions ( M = 735, SD = 601) was read more slowly than the final infinitive phrase of the other three types of questions ( M = 574, SD = 387). Figure 3 presents the difference scores for the acceptance of the alternative answers to each type of wh-question. The difference scores were calculated for each participant such that positive scores represent a bias for the upstairs interpretation and negative scores represent a bias for the downstairs interpretation. For argument questions, young adults preferred the downstairs answer corresponding to the DO of

91

VERB2 whereas older adults had a slight preference for the upstairs answer corresponding to the DO of ask. For argument adjunct questions, young adults preferred either downstairs interpretation over the upstairs interpretation, whereas older adults preferred the upstairs answer corresponding to the DO of ask over either downstairs interpretation. For adjunct argument questions, young adults again preferred the downstairs answer corresponding to the DO of VERB2 and older adults had a slight preference for the upstairs answer corresponding to the DO of ask. Young adults found both answers to adjunct adjunct questions to be equally acceptable; however, older adults had a preference for the upstairs answer corresponding to the DO of ask. These results suggest that answering complex wh-questions is affected by nonlinguistic biases. Neither pattern of answers is consistent with the predictions based on linguistic theory. Young adults appear to have a bias favoring downstairs interpretations. This downstairs bias renders argument questions unambiguous, over-rides the constraint blocking downstairs interpretations of argument adjunct and adjunct adjunct questions, and prevails over the upstairs interpretation of adjunct argument questions. Older adults appear to have a different bias, one favoring upstairs interpretations: this bias renders argument questions nambiguous and coincides with the "correct" upstairs interpretation of adjunct argument, argument adjunct, and adjunct adjunct questions. One reason young and older adults might have preferred different answers to the complex wh-questions was that the requisite information to answer the questions was not as salient to older adults as it was to the other participants. If older adults remembered the contexts differently, then they might be expected to prefer different answers to the questions. Such an explanation might also account for why the preferred answers differ from those predicted by linguistic theory. For example, if older adults, for example, were unable to recall that a model had been mentioned in the story (see Table 1), they might be unable to answer Who did John paint? producing a bias against the downstairs interpretation of Who did John ask to paint? If so, older adults should prefer different answers to simple wh-questions such as Who did John ask? or Who did John paint? after reading these same stories. To investigate this possibility, a second experiment was conducted using only simple wh-questions. Figure 1. Reading times for segment 3.

92

The results of this second experiment were clear-cut: older and young adults agreed on the preferred answers to the simple wh-questions even during on-line processing. The stories provided the appropriate answers and both young and older adults were able to recall this information when asked to verify answers to the simple wh-questions. These results suggest that the different answer preferences of young and older adults to complex wh-questions reflect qualitatively different interpretations of the questions, not age-differences in understanding or remembering the story information. Although young and older adults were able to answer all four types of questions equally accurately in the second experiment, the reading times for the four types of questions did differ. Simple adjunct questions were more difficult to process than simple argument questions, perhaps because adjuncts are optional verb complements whereas arguments are obligatory elements of the verb phrase. In addition, working memory span affected older adults' processing of simple whquestions as it did their processing of complex wh-questions. The increased reading time required by the older adults, particularly the low span older adults, appears to reflect the demands placed on working memory by the immediate syntactic analysis of the questions. Summary. Answering wh-questions, either simple, one-clause questions such as Who did John ask?, or complex questions such as Who did John ask to paint?, imposes demands on working memory for the processing of semantic and pragmatic information as well as the analysis of the syntax of the question itself. Analyzing some types of wh-questions is more demanding than analyzing other types. Experiment 2 showed that simple adjunct questions asking "how" or "when" something occurred are more difficult to process than simple argument questions about "who" or "what" Figure 2. Reading times for segment 4. was involved and Experiment 1 showed that complex adjunct argument questions of the form When did John ask who to paint? are more difficult to process than other types of complex whquestions. Adjunct questions query optional verb phrase complements, whereas argument questions query obligatory verb complements such as subjects and direct objects and this contrast between

93

optional and obligatory complements apparently affects the speed with which the underlying syntax of a question can determined. Older adults with limited working memory spans, as indexed by a composite factor score obtained from multiple tasks, required more time to analyze both simple and complex wh-questions than younger adults with larger working memory spans. Further, low span older adults with severely limited working memories, processed simple and complex wh-questions even more slowly than high span older adults. Working memory span did not appear to affect young adults' processing of either simple or complex wh-questions. Even the low span young adults had sufficient working memory capacity to process the wh-questions, whereas older adults, even those with relatively high working memory spans, did not. This pattern of results suggests that the effects of working memory capacity on language processing may not be evident unless a threshold is crossed; a threshold of working memory capacity may be imposed by processing tasks such that individuals whose working memory exceeds the thresold are able to perform the task whereas those whose working memory capacity falls below the threshold are not. Further processing decrements may also occur, as in the case of low span older adults, if working memory capacity falls very much below this threshold. In the present case, low span young adults ( M = 23.8) had sufficient working memory capacity to analyze complex wh-questions, whereas high span older adults ( M = 22.0) and low span older adults (M = 15.5) did not. During the validation study, both older and young adults were asked to select Figure 3. Answer Biases of Young and Older Adults

94

among two answer alternatives which were presented along with each question. When asked to choose among possible answers, older adults were able to make both interpretations of the argument questions and found both answer alternatives to be acceptable. This forced-choice procedure also caused young adults to ignore or overlook contextually-plausible "downstairs" interpretations of the wh-questions in favor of the "best" answer, namely the one consistent with linguistic theory. Thus, using this forced-choice procedure, young and older adults had the same preference for answers to the four types of wh-questions and their answers were in accord with the predictions based on linguistic theory. The experimental procedure required the participants to accept or reject a single possible answer to the wh-question. In this situation, older adults appear to interpret complex wh-questions qualitatively differently than do young adults, preferring to answer the first or upstairs interpretation. One possibility is that this primacy bias may result from a working memory limitation on their ability to process both clauses, generate multiple interpretations, apply linguistic constraints on wh-raising to block some interpretations, and select an answer from alternatives held in memory. When a representation of the discourse must be held in working memory, the burden on working memory may be such that older adults do not attempt to syntactically process the entire wh-sentences but attend to only the first clause and retrieve an answer alternative based on that partial interpretation. This account is not supported by the pattern of reading times for the critical regions of the wh-questions. These reading times indicate that the older adults, particularly the low span older adults, take more time, not less time, to process critical regions 3 and 4. Hence, it appears that the older adults did attempt to process the entire whquestion. Despite allocating additional processing time to the critical regions of the whquestions, older adults may have attempted to simplify the task by retaining only the first, or upstairs, intepretation of the wh-question. Hence, when presented with a candidate answer, they may only accept it if it is consistent with what they remember from the discourse context and if it is a plausible answer to what they remember from the question - the upstairs interpretation. This bias renders the argument and argument adjunct questions unambiguous in favor of the upstairs interpretation and produces an answer preference in accord with the predictions of linguistic theory for adjunct argument and adjunct adjunct questions. Young adults apparently also relied on a nonlinguistic bias. Young adults appeared to use a recency strategy, answering the most recent, or downstairs, interpretation. Young adults override the linguistic constraints on wh-questions when they are presented with a candidate answer and the the discourse context establishes a plausible "downstairs" intepretation of the argument adjunct and adjunct argument questions. This bias, then, also rendered the argument and argument adjunct questions unambiguous but favored the downstairs interpretation and resulted in a preference for the downstairs intepretations of the adjunct argument and adjunct adjunct questions. Working memory limitations thus affect older adults' processing of complex wh-questions in two ways. First, older adults, particularly those with limited working memories, allocate additional processing time to the analysis of the critical

95

regions of wh-questions. These critical regions include the medial wh-word as well as the final infinitive. Older adults' answers to wh-questions are also apparently affected by working memory limitations. Their preference for the upstairs interpretation of all four types of complex wh-questions implies an additional working memory limitation on question answering. RECONCEPTUALIZING THE RELATIONSHIP LANGUAGE PROCESSING

BETWEEN

AGING, WORKING MEMORY,

AND

The hypothesis that working memory limtations affect syntactic processing has recently come under careful scruitiny by a number of different theorists. Three reconceptualizations of the relationship between aging, working memory, and langauge processing are considered below: threshold models, inhibitory breakdown, and immediate versus post-comprehension processing. Threshold models. One challenge to the hypothesis that working memory limitations cause older adults' language processing problems comes from a series of studies which have failed to find effects of working memory limitations on sentence processing. These studies use on-line sentence processing tasks rather than the production, imitation, and recall tasks reviewed in the second section of this chapter. For example, Kemtes and Kemper (1997) examined the relationship between younger and older adults' working memory and on-line syntactic processing. They used a word-by-word reading paradigm to assess younger and older adults' on-line comprehension of temporarily ambiguous sentences (e.g. Several angry workers warned about low wages...) that were resolved with either a main verb (MV) interpretation (Several angry workers warned about low wages during the holiday season), or a reduced relative (RRC) clause interpretation (Several angry workers warned about low wages decided to file complaints). Reading times for sentences resolved with the MV interpretation were compared to those for sentences that were not temporarily ambiguous such as Several angry workers spoke about low wages which can only be assigned a MV interpretation. MacDonald, Just, and Carpenter (1992) has previously reported differential patterns of word-by-word reading times for young adults as a function of working memory span. Low span young adults showed little effect of ambiguity whereas high span young adults were affected by the temporary ambiguity. High span young adults required more time to process the final region of the sentence, following the temporary ambiguity. MacDonald et al. interpreted this finding as indicating that the high span young adults initially made both interpretations of the initial ambiguous portion of the sentence and retained both interpretations until the disambiguating information was encountered at the end of the sentence. They then required additional processing time to integrate the sentence-final information with the correct interpretation of the initial ambiguous portion of the sentence. Low span readers, they suggested, made only the most plausible interpretation, interpreting the ambiguous portion of the sentence as a RRC. When inconsistent information was later encountered, they were unable to integrate the information with their RRC interpretation and, hence, performed poorly on a comprehension test.

96

The primary finding from Kemtes and Kemper's (1997) replication was that while older adults' on-line reading times were slower than those of younger adults, syntactic ambiguity did not differentially impair older adults' on-line comprehension of the sentences. High span and low span young adults exhibited the same pattern of reading time latencies as did high and low span older adults. In contrast, older adults' off-line question comprehension was influenced by the syntactic ambiguity manipulation in that question comprehension was reliably poorer, relative to young, for the syntactically ambiguous sentences. These findings pose a challenge to the hypothesis that working memory limitations affect syntactic processing; not only did Kemtes and Kemper fail to replicate MacDonald et al. (1992) finding that high and low span young adults allocate reading times differentially but they also failed to link age differences on the comprehension test to on-line processing differences. The on-line processing differences between young adults and high and low span older adults for critical regions of the complex wh-questions (reported in the previous section of this chapter) suggested that a threshold of working memory capacity must be crossed before processing differences will be observed. If a threshold of working memory capacity must be crossed before processing differences can be observed, it may be that the threshold for the effect of temporary syntactic ambiguities on processing falls above the processing threshold for Kemtes and Kemper's (1997) participants. MacDonald et al. (1992) classified their participants based on the Daneman and Carpenter (1980) reading span task; high span participants had reading spans of 3.5 words or higher whereas low span participants had reading spans of 2.5 or lower (no further distributional information is provided). Kemtes and Kemper adopted a different approach; classifying their participants based on a composite measure derived from forward and backward digit spans and reading spans. They report that high span young adults had reading span scores averaging 3.7 words ( SD = 1.4) whereas low span young adults had reading span scores averaging 3.10 words ( SD = 10.) and that high span older adults had reading span scores averaging 3.6 words ( SD = 0.8) and low span older adults had reading span scores averaging 2.5 words ( SD = 0.5). Note that if there is a threshold, in the MacDonald et al. (1992) paradigm, it must be for the end of sentence INCREASE in reading time for high span participants, reflecting extra processing time required to resolve the ambiguity by selecting among alternative interpretations. Thus, Kemtes and Kemper may have failed to find such a sentence-final effect because many of their "high span" participants were misclassifed and failed to meet the processing threshold. Hence, many of these "high span" participants may not have had sufficient working memory capacity to make both interpretations of the temporary ambiguities. Hence, they were not able to maintain both interpretations through to the end of the sentence and so did not to show a sentence-final increase in reading time as they resolved the ambiguity by selecting among the alternative interpretations. Measurement problems, including the selection of critical measures of working memory capacity, as well as methodological considerations in classifying participants as high versus low span, may contribute to the lack of uniformity in research findings regarding the effects of working memory limitations on syntactic processing. Since most researchers have assumed that the effects should be linear,

97

alternative patterns of the effects, such as discontinuous threshold models, have not been considered. Inhibitory breakdown. Another reconceptualization of the relationship between aging, working memory, and language processing has been advanced by Hasher and Zacks (1988). They suggest that the capacity of working memory is not affected by aging; rather, aging weakens inhibitory mechanisms and permits irrelevant thoughts, personal preoccupations, and idiosyncratic associations to intrude during language encoding and retrieval. These irrelevant thoughts compete for processing resources, such as working memory capacity, and so impair older adults' comprehension and recall. Hence, older adults' comprehension may be affected by distractions or intrusive thoughts. For example, when a text contains distracting words printed in a different font, young adults are able to ignore the distracting material, even when it is related to the text, whereas older adults are not able to ignore the distracting material, which slows their reading, impairs their comprehension, and renders them subject to memory distortions (Carlson, Hasher, Connelly, & Zacks, 1995; Connelly, Hasher, & Zacks, 1991; Zacks & Hasher, 1997). Hasher, Zacks, and May (in press) postulate three functions of inhibition: preventing irrelevant information from entering working memory, deleting irrelevant information from working memory, and restraining probable responses until their appropriateness can be assessed. They argue that older adults suffer from a variety of processing impairments that can be attributed to decreased inhibitory mechanisms (but see Burke, 1997 and McDowd, 1977 for alternative views). Hence, older adults' language processing may mirror that of young adults whenever the task requires the active application of processing strategies since excitatory mechanisms are spared, whereas older adults' language processing may be impaired, relative to young adults', whenever inhibitory mechanisms are required to block out distractions, clear way irrelevancies, or switch between activities. Individuals with poor inhibitory mechanisms may not only be more susceptible to distraction, but they may also be less able to switch rapidly from one task to another and they may rely on well-learned "stereotypes, heuristics, and schemas" (p. 123) (Yoon, May, & Hasher, 1998). This reconceptualization of the nature of working memory and how it is affected by aging receives support from a study by Kwong See and Ryan (1995). Kwong See and Ryan examined individual differences in text processing attributable to working memory capacity (Stine, 1990), efficiency of inhibitory processes (Gernsbacher, 1990), and processing speed (Cohen, 1979), estimated by backward digit span, color naming speed, and Stroop interference, respectively. Their analysis suggested that working memory capacity is correlated with processing speed and inhibitory efficiency and that older adults' language processing difficulties can be attributed to slower processing and less efficient inhibition, rather than to working memory limitations. The inhibitory breakdown account of the relationship between aging, language processing, and working memory suggests that many of the age deficits reviewed in the second section of this chapter may be attributable to inhibitory breakdowns that affect older adults' ability to process complex materials. For example, inhibitory

98

mechanisms may be required in order to sustain a high level of performance on the grammaticality judgment tasks of Pye et al. (1992) and Kemper (1997). Distracting thoughts may intrude and affect older adults' ability to fully process a complex sentence such as The woman from the city treasurer's office is expected to help John, particularly as older adults may fail to understand the reasons for evaluating the grammaticality of a long list of sentences whereas college students may be more accustomed to such tasks. Immediate versus Post-comprehension Processing. Other researchers using other paradigms have also failed to find support for the hypothesis that working memory limitations affect syntactic processing. For example, Stine (1990) found that younger and older adults allocated word-by-word reading times similarly for word-level and more global phrase-level features of the text. Younger adults allocated additional reading time to the ends of phrases, clauses, and sentences whereas older adults paused at clause boundaries only. A related study by Stine, Cheung, and Henderson (1995) extended this earlier research by showing that specific word-, phrase-, sentence-, and discourse-level features of text influenced older adults' word-by-word reading times and explicit recall of narrative texts such that overall, older adults tended to allocate less reading time to processing new concepts. Stine, Loveless, and Soderberg (1996) demonstrated that younger and older adults' on-line reading times were qualitatively similar in that both age groups allocated more reading time to text segments with complex syntactic, new concepts, and longer words. However, older adults did allocate less reading time, relative to young, for new concepts. The effects of working memory limitations on syntactic processing were studied by Wingfield and Lindfield (1995) using the spontaneous speech segmentation technique. This technique allows listeners to interrupt the flow of speech at any point in order to recall the preceding portion. Wingfield and Lindfield varied the predictability of the speech by using passages that differed in cloze predictability. They also varied speech rate using passages presented at 180 wpm and ones time-compressed to approximately 230 and 300 wpm. Both young and older adults tended to select smaller segments as passage predictability declines. Most interruptions occurred at sentence boundaries or major clause boundaries and more occurred at minor phrase boundaries as predictability decreased and as speech rate increased. More critically, despite lower working memory scores for the older adults and despite their poor recall of the speech segments, the older adults tended to segment the speech in the same way as the young adults. Hence, the older adults' immediate processing of the speech appeared to be unaffected by working memory limitations although such limitations did affect their recall. Further challenges to the hypothesis linking working memory limitations to language processing problems come from careful studies of the effects of neurological impairments on language processing. Caplan and Waters (1996a; in press) have considered a number of lines of evidence from studies young and older adults as well as individuals with aphasia and dementia. They distinguish between immediate, interpretive syntactic processing and post-interpretative semantic and pragmatic analyses. Caplan and Waters argue that there is little evidence to support the hypothesis that working memory limitations affect immediate syntactic

99

processes; rather, working memory limitations affect post-interpretative processes involved in retaining information in memory in order to recall it or use it, e.g., to answer questions or match sentences against pictures. In a variety of studies comparing adults stratified into groups based on measures of working memory, Caplan and Waters (1996b) note that effects of syntactic complexity do not differentially affect high versus low span readers or listeners. And they report that secondary tasks that impose additional processing demands on working memory do not differentially affect the processing of complex sentences (Waters, Caplan, & Rochon, 1995). Caplan and Waters (in press) consider aphasic patients such as B. 0. (Waters, Caplan, & Hildebrandt, 1991) who had a digit span of only 2 or 3 digits but who was able to perform as well as normal healthy older adults on a wide range of tasks with complex sentences. They also note that patients with Alzheimer's dementia, who also show severely limited working memory capacity, are able to make speeded acceptability judgments of complex sentences as accurately as nondemented controls (Waters & Caplan, 1997). Caplan and Waters (in press) conclude "the working memory system involved in sentence interpretation is separate from that measured by standard tests of working memory" (p. 23) and that the " 'obligatory, on-line psycholinguistic operations'...that transform the acoustic signal into a preferred, discourse-coherent, semantic representation" draw on processing resources that are separate from those used in other 'controlled, verbally mediated tasks' " (1995, p. 770). Kintsch (1998) has offered a similar reconceptualization. Building on the "long-term working memory" model of Ericsson and Kintsch (1995), he suggests that reading span measures the efficiency with which readers can process and store verbal information in working memory. Reading span thus measures language processing skill, not the capacity of working memory. Kintsch also states that "More skilled readers construct better [memory] representations and hence have available more effective retrieval structures" (p. 239). From this point of view, it is a misnomer to label those who do well on reading span tests as "high span" individuals as this implies greater capacity, not greater processing skill. High skill readers may include those who are able to do well on reading span tests and who are able to spot the temporary ambiguity in sentences such as The defendant examined by the lawyer shocked the jury. High and low skill readers may allocate processing times to words and phrases in a similar fashion and adopt speech segmentation strategies that are similar yet form different types of long-term retrieval structures and thus differ in the long term retention, retrieval, and application of linguistic information. Conclusion. The hypothesis that working memory constraints syntactic processing, as it was originally formatted, lies at the heart of contemporary psycholinguistics. Modularity theory makes a strong prediction regarding the relationship between general cognitive limitations and syntactic processing: syntactic processing, particularly that concerned with the analysis of hierarchical or embedded structures, should be autonomous. Hence, working memory limitations, such as those long associated with aging, should not affect individuals' ability to analyze complex sentences. Whether working memory limitations are considered to be linear or to conform to a threshold model, or whether they are viewed as arising

100

from capacity limitations or a breakdown of inhibitory processes, syntactic processing should be, according to modularity theory, buffered from the effects of aging. Reconceptualizing working memory limitations as affecting postcomprehension processes, not immediate syntactic processing, preserves modularity theory yet recognizes that aging imposes severe constraints on language production andcomprehension.

101

REFERENCES

Arbuckle, T., & Gold, D. P. (1993). Aging, inhibition, and verbosity. Journal of Gerontology: Psychological Sciences, 48, P225-P232. Baddeley, A. (1986). Working memory. Oxford: Clarendon Press. Balota, D. A., Flores D'Arcais, G. B., & Rayner, K. (1990). Comprehension processes in reading. Hillsdale, NJ: Erlbaum. Benjamin, B. J. (1988). Changes in speech production and linguistic behavior with aging. In B. Shadden (Ed.), Communication behavior and aging (pp. 163181). Boston: Williams & Wilkins. Bloom, L. (1975). One word at a time. The Hague: Mouton. Bock, J. K. (1987). Coordinating words and syntax in speech plans. In A. Ellis (Ed.), Progress in the psychology of language (pp. 337-390). London: Erlbaum Associates. Burke, D. (1997). Language, aging, and inhibitory deficits: Evaluation of a theory. Journal of Gerontology: Psychological Sciences, 52B, P254-P264. Caplan, D., & Waters, G. (in press). Verbal working memory and sentence comprehension. Behavioral and Brain Sciences. Carlson, M. C., Hasher, L., Connelly, S. L., & Zacks, R. T. (1995). Aging, distraction, and the benefits of predictable location. Psychology and Aging, 10, 427-436. Chomsky, N. (1986). Barriers. Cambridge, MA: MIT Press. Cohen, G. (1979). Language comprehension in old age. Cognitive Psychology, 11, 412-429. Connelly, S. L., Hasher, L., & Zacks, R. T. (1991). Age and reading: The impact of distraction. Psychology and Aging, 6, 533-541. Cooper, P. V. (1990). Discourse production and normal aging: Performance on oral picture description tasks. Journal of Gerontology: Psychological Sciences, 45, P210-214. Crain, S., & Shankweiler, D. (1988). Syntactic complexity and reading acquisition. In A. Davison & G. Green (Eds.), Critical approaches to readability (pp. 167192). Hillsdale, NJ: Erlbaum. Crain, S., & Shankweiler, D. (1990). Explaining failures in spoken language comprehension by children with reading disability. In D. A. Balota, G. B. Flores d'Arcais, & K. Rayner (Eds.), Comprehension processes in reading (pp. 529-556). Hillsdale, NJ: Erlbaum. Daneman, M., & Carpenter, P. A. (1980). Individual differences in working memory and reading. Journal of Verbal Learning and Verbal Ability, 19, 450-466. Davis, G. A. (1984). Effects of aging on normal language. In A. Holland (Ed.), Language Disorders in adults. San Diego: College-Hill Press. de Villiers, J. (1996). Defining the open and closed program for acquisition: The case for Wh questions. In M. L. Rice (Ed.), Toward a genetics of language. Hillsdale, NJ: Erlbaum. Dell, G. S. (1986). A spreading-activation theory of retrieval in sentence production. Psychological Review, 93, 283-321.

102

Ericsson, K. A., & Kintsch, W. (1995). Long-term working memory. Psychological Review, 102, 211-245. Fodor, J. A. (1982). Modularity of mind. Cambridge, MA: MIT Press. Frazier, L., & Fodor, J. D. (1978). The sausage machine: A new two-stage parsing model. Cognition, 6, 291-325. Garrett, M. F. (1988). Processes in language production. In F. J. Newmeyer (Ed.), Linguistics: The Cambridge survey, Ill: Language: Psychological and biological aspects (pp. 69-96). Cambridge: Cambridge University Press. Gathercole, S. E., & Baddeley, A. D. (1989). Evaluation of the role of phonological STM in the development of vocabulary in children: A longitudinal study. Journal of Memory and Language, 28, 200-213. Gathercole, S. E., & Baddeley, A. D. (1990). Phonological memory deficits in language disordered children: Is there a causal connection? Journal of Memory and Language, 29, 336-360. Gernsbacher, M. A. (1990). Language comprehension as structure building. Hillsdale, NJ: Erlbaum. Gibson, E., Pearlmutter, N., Canseco-Gonzalez, E., & Hickok, G. (1996a). Recency preference in the human sentence processing mechanism. Cognition, 59, 23-59. Gibson, E., Schutze, C., & Salomon, C. (1996b). The relationship between the frequency and the processing of complex linguistic structures. Journal of Psycholinguistic Research, 25,59-92. Hasher, L., & Zacks, R. T. (1988). Working memory, comprehension, and aging: A review and a new view. In G. H. Bower (Ed.), The Psychology of Learning and Motivation (Vol. 22, pp. 193-226). New York: Academic. Hasher, L., Zacks, R. T., & May, C. P. (in press). Inhibitory control, circadian arousal, and age. In D. Gopher & A. Koriat (Eds.), Attention and performance XVII: Cognitive regulation of performance: Interaction of theory and application. Cambridge, MA: MIT Press. Hulme, C., Thomson, N., Muir, C., & Lawrence, A. (1984). Speech rate and the development of short-term memory span. Journal of Experimental Child Psychology, 38,241-253. Grimshaw, J. (199 1). Argument structure. Cambridge, MA: MIT Press. James, L. E., Burke, D. M., Austin, A.., & Hulme, E. (1998). Production and perception of "verbosity" in younger and older adults. Psychology and Aging, 13, 355-368. Kemper, S. (1987a). Life-span changes in syntactic complexity. Journal of Gerontology, 42, 323-328. Kemper, S. (1987b). Syntactic complexity and the recall of prose by middle-aged and elderly adults. Experimental Aging Research, 13,47-52. Kemper, S. (1992). Language and aging. In F. I. M. Craik & T. A. Salthouse (Eds.), Handbook of aging and cognition (pp. 2 13-270). Hillsdale, NJ: Erlbaum. Kemper, S. (1997). Metalinguistic judgments in normal aging and Alzheimer's disease. Journal of Gerontology: Psychological Sciences, 52, P147-PI55. Kemper, S., Kynette, D., Rash, S., Sprott, R., & O'Brien, K. (1989). Life-span changes to adults' language: Effects of memory and genre. Applied Psycholinguistics, 10, 49-66.

103

Kemper, S., & Rash, S. (1988). Speech and writing across the life-span. In M. M. Gruneberg, P. E. Morris, & R. N. Sykes (Eds.), Practical aspects of memory: Current research and issues (pp. 107-1 12). Chichester: John Wiley & Sons. Kemper, S., Rash, S. R., Kynette, D., & Norman, S. (1990). Telling stories: The structure of adults' narratives. European Journal of Cognitive Psychology, 2, 205-228. Kemtes, K. A., & Kemper, S. (1997). Younger and older adults' on-line processing of syntactic ambiguities. Psychology and Aging, 12, 362-371. Kintsch, W. (1 988). Comprehension: A paradigm for cognition. Cambridge: Cambridge University Press. Kintsch, W., & van Dijk, T. A. (1978). Toward a model of text comprehension and production. Psychological Review, 85, 363-393. Kwong See, S. T., & Ryan, E. B. (1995). Cognitive mediation of adult age differences in language performance. Psychology and Aging, 10, 458-468. Kynette, D., & Kemper, S. (1986). Aging and the loss of grammatical forms: A cross-sectional study of language performance. Language and Communication, 6, 65-72. Kynette, D., Kemper, S., Norman, S., Cheung, H., & Anagnopoulos, C. (1990). Adults' word recall and word repetition. Experimental Aging Research, 15, 117-121. Laird, J. E., Newell, A., & Rosenbloom, P. S. (1987). SOAR: An architecture for general intelligence. Artificial Intelligence, 33, 1-64. Lewis, R. I. (1996). Interference in short-term memory: The magical number two (or three) in sentence processing. Journal of Psycholinguistic Research, 25, 93-115. Light, L., & Capps, J. L. (1986). Comprehension of pronouns in younger and older adults. Developmental Psychology, 22, 580-585. Light, L. L., & Singh, A. (1987). Implicit and explicit memory in young and older adults. Journal of Experimental Psychology: Learning, Memory and Cognition, 13, 531-541. Light, L. L., Capps, J. L., Singh, A., & Albertson Owens, S. A. (1994). Comprehension and use of anaphoric devices in younger and older adults. Discourse Processes, 18, 77-103. MacDonald, M., Just, M. A., & Carpenter, P. A. (1992). Working memory constraints on the processing of syntactic ambiguity. Cognitive Psychology, 24, 56-98. MacKay, D. G. (1987). The organization of perception and action. New York: Springer-Verlag. Mandler, J. M., & Johnson, N. S. (1977). Remembrance of things parsed: Story structures and recall. Cognitive Psychology, 9, 111-151. McClelIand, J. L., & Rumelhart, D. E. (1981). An interactive activation model of context effects in letter perception: Part 1: An account of basic findings. Psychological Review, 88, 375-407. McDowd, D. (1987). Inhibition in attention and aging. Journal of Gerontology: Psychological Sciences, 52B, P265-P274.

104

Meyer, B. J. F. (1975). The organization of text and its effect on memory. Amsterdam: North-Holland. Meyer, D. E., & Kieras, D. E. (1997). A computational theory of executive cognitive processes in multiple task performance: Part 1 Basic Mechanisms. Psychological Review, 104,3-65. Meyer, D. E., & Kieras, D. E. (1997). A computational theory of executive cognitive processes in multiple task performance: Part 2 Accounts of psychological refractory period phenomena. Psychological Review, 104, 749800. Miller, G. (1962). Some psychological studies of grammar. American Psychologist, 17, 748-762. Newell, A. (1990). Unified theories of cognition. Cambridge, MA: Harvard University. Norman, S., Kemper, S., & Kynette, D. (1992). Adults' reading comprehension: Effects of syntactic complexity and working memory. Journal of Gerontology: Psychological Sciences, 47, P258-265. Pye, C., Cheung, H., & Kemper, S. (1992). Islands at eighty. In H. Goodluck & M. Rochemont (Eds.), Island constraints: Theory, acquisition, and processing (pp. 351-372). Dordrecht: D. Reidel. Rayner, K., & Pollatsek, A. (1989). The psychology of reading. Englewood Cliffs, NJ: Prentice-Hall. Salthouse, T. A. (1991). Mediation of adult age differences in cognition by reductions in working memory and speed of processing. Psychological Science, 2, 179-183. Salthouse, T. A., Babcock, R. L., & Shaw, R. J. (1991). Effects of adult age on structural and operational capacities in working memory. Psychology and Aging, 6, 118-127. Schweickert, R., & Boruff, B. (1986). Short-term memory capacity: Magic number or magic stuff? Journal of Experimental Psychology: Learning, Memory, & Cognition, 12, 419-425. Seidenberg, M. S. (1989). Visual word recognition and naming: A computational model and its implications. In W. D. Marslen-Wilson (Ed.), Lexical representation and process (pp. 25-74). Cambridge, MA: MIT Press. Seidenberg, M. S., & McClelland, J. L. (1989). A distributed, developmental model of word recognition and naming. Psychological Review, 96, 523-568. Shewan, C. M., & Henderson, V. L. (1988). Analysis of spontaneous language in the older normal population. Journal of Communication Disorders, 21, 139-154. Stine, E. A. L. (1990). On-Line processing of written text by younger and older adults. Psychology and Aging, 5, 68-78. Stine, E. A. L., Chueng, H., & Henderson, D. (1995). Adult age differences in the on-line processing of new concepts in discourse. Aging and Cogntion, 2, 1-18. Stine-Morrow, E. A. L., Loveless, M. K., & Soederberg, L. M. (1996). Resourse allocation in on-line reading by younger and older adults. Psychology and Aging, 11,475-486. Trabasso, T., & van den Broek, P. (1985). Causal thinking and the representation of narrative events. Journal of Memory and Language, 24, 612-630.

105

Ulatowska, H. K., Freedman-Stern, R., Weiss-Doyle, A., Macaluso-Haynes, S., & North, A. J. (1983). Production of narrative discourse in aphasia. Brain and Language, 19, 317-334. Walker, V. G., Roberts, P. M., & Hedrick, D. L. (1988). Linguistic analyses of the discourse narratives of young and aged women. Folia Phoniatica, 40, 58-64. Waters, G. S., & Caplan, D. (1996a). The capacity theory of sentence comprehension: Critique of Just and Carpenter (1992). Psychological Review, 103, 761-772. Waters, G. S., & Caplan, D. (1996b). Processing resource capacity and the comprehension of garden path sentences. Memory and Cognition, 24, 342-355. Waters, G. S., & Caplan, D. (1997). Working memory and on-line sentence comprehension in patients with Alzheimer's disease. Journal of Psycholinguistic Research, 26, 337-400. Waters, G. S., Caplan, D., & Rochon, E. (1995). Processing capacity and sentence comprehension in patients with Alzheimer's disease. Cognitive Neuropsychology, 12, 1-30. Wechsler, D. (198 1). WAIS-R Manual. New York: Psychological Corporation. Wingfield, A., & Lindfield, K. C. (1995). Multiple memory systems in the processing of speech: Evidence from aging. Experimental Aging Research, 21, 101-121. Wingfield, A., Tun, P. A., & Rosen, M. J. (1995). Age differences in veridical and reconstructive recall of syntactically and randomly segmented speech. Journal of Gerontology: Psychological Sciences, 50B, P257-266. Yngve, V. (1960). A model and a hypothesis for language structure. Proceedings of the American Philosophical Society, 104, 444-466. Yoon, C., May, C. P., & Hasher, L. (1988). Aging, circadian arousal patterns, and cognition. Philadelphia, PA: Psychology Press. Zacks, R., & Hasher, L. (1997). Cognitive gerontology and attentional inhibition: A reply to Burke and McDowd. Journal of Gerontology: Psychological Sciences, 52B, P274-P283. Zurif, E., Swinney, D., Prather, P., Wingfield, A., & Brownell, H. (1995). The allocation of memory resources during sentence comprehension: Evidence from the elderly. Journal of Psycholinguistic Research, 24, 165-182.

106

ACKNOWLEDGEMENTS

Preparation of this chapter was supported by grant RO1 AG0092 from the National Institute on Aging as well as by the Research Training Program in Communication and Aging, supported by NIA grant T32 AG00226. We thank Tamara Harden for her assistance with this research. Kemtes is now a Postdoctoral Fellow at the Volen National Center for Complex Systems, Brandeis University.

5V

WORKING MEMORY CAPACITY ON-LINE SENTENCE PROCESSING EFFICIENCY IN THE ELDERLY

ERBAL

AND

Gloria Waters and David Caplan

In the past decade there has been a proliferation of research addressing the question of the effects of aging on language processing efficiency. Much of this research has focused on the ability of elderly individuals to process and remember information presented in texts (e.g., Tun et al., 1991). Several researchers have investigated sentence processing abilities in aging (Kemper, 1986; 1987a, b; 1992; Kemper & Rash, 1988; Kemper et al., 1989, Kemper et al., 1990). However, much of this work has centered on sentence production. The focus of this chapter is on the effects of aging on sentence comprehension in the elderly. The effects of aging on sentence comprehension abilities have been examined using a variety of tasks, such as object manipulation (Feier & Gertsman, 1980), question answering (Emery, 1985; Davis & Ball, 1989), acceptability judgment (Kemper, 1988; Obler et al., 1991), and sentence recall (Norman et al., 1991). Some studies have found that elderly subjects perform more poorly overall, but that they are not differentially impaired on syntactically more complex sentences (e.g., Feier & Gerstman, 1980). Other studies claim to have found decreased comprehension of more complex syntactic structures in the elderly (e.g., Obler et al., 1991; Davis & Ball, 1989). However, a review of these studies suggests that the effect of age on syntactic comprehension seen in many studies may not be directly attributable to difficulties subjects have in constructing syntactic structures but rather to difficulties in performing operations on the meaning that has been extracted. The tasks on which elderly subjects have shown effects of syntactic complexity have tended to be ones that require them to perform some sort of operation on the material that they have interpreted. This includes tasks which require the subject to retain and re-order large amounts of material in memory (Kemper, 1986; Light, 1990) or to interpret implausible sentences (Davis & Ball, 1989; Obler et al., 1991). This observation has led us to argue that a distinction should be made between the processes that are used to extract the meaning of a sentence from the signal, which we refer to as interpretive processing, and the process of using the meaning that has been extracted to perform other tasks, which we refer to as post-interpretive processing 107

108

(Waters & Caplan, 1996c; Caplan & Waters, 1998). We have argued that elderly individuals are more likely to have impairments in post-interpretive than in interpretive processing. One limitation of many of the studies examining sentence interpretation in the elderly is that they use what has been referred to as “off-line” measures of sentence processing. The term off-line is used to refer to experiments in which subjects must perform a task after the sentence has been understood (e.g., match a spoken sentence to one of several pictures). In contrast, on-line tasks are sensitive to the time-course of the largely unconscious, obligatory, processing that occurs as the words in a sentence are attended to (Marslen-Wilson, 1987). Self-paced word-by-word reading, word or phoneme monitoring, and cross-modal naming or lexical decision are examples of on-line tasks (see Ferreira & Anes, 1994, for a review). The basic rationale of these tasks is that, when other factors are held constant or partialed out, the measurement of reaction times can be interpreted as reflecting the demands of processing of words and phrases as they are perceived and integrated into the developing representation of the sentence. It is possible that if sentence interpretation were measured on-line, differences between younger and older subjects would emerge. Baum (1991) and Waldstein and Baum (1992) used the word monitoring paradigm to investigate the on-line sensitivity of younger and older adults to local and long distance ungrammaticalities. Although processing times and error rates of the elderly were higher overall than those of the younger subjects, there was no evidence that elderly subjects were more reliant on sentential context or that they were less sensitive to ungrammaticalities. Kemtes and Kemper (1996) also found that older and younger subjects did not differ in the effect of syntactic ambiguity on word-by-word reading times, although the older subjects were more affected on an off-line measure of accuracy in responding to questions. Zurif et al. (1995) did find that older subjects were delayed at establishing the connection between a gap in a relative clause and the head of the clause (e.g., determining that it is the man who is kissed in a sentence such as The man who the woman kissed was embarrassed ) using a cross-modal naming paradigm. However, Zurif et al.’s data are difficult to interpret, since a comparison group of younger subjects was not tested on the same materials. Thus, the existing data are at best equivocal as to whether there is a decrease with age in the ability to structure sentences syntactically. It is generally believed that if sentence comprehension abilities do decline with age, that this decline is related to a reduction in working memory capacity or processing resources (Just & Carpenter, 1952; Carpenter et al., 1994). This suggestion stems from work with younger subjects that claims that individual differences in the ability to structure sentences syntactically are related to individual differences in performance on a task that was designed to measure verbal working memory capacity -- the Daneman and Carpenter (1980) reading span task. On this task, subjects are required to read aloud increasingly longer sequences of sentences and to recall the final word of all of the sentences in each sequence. A subject’s working memory span is defined as the longest list length at which they are able to recall the sentence-final words on the majority of trials. Daneman and Carpenter showed that this reading span measure is a better predictor of language

109

comprehension abilities than measures such as digit span. A widespread view is that this is because complex or operation span tasks, such as reading span, involve both a processing and a storage component, and therefore are a better approximation of the working memory requirements of language processing tasks than simple span, which has only a storage component. The results of a variety of experiments have been interpreted as showing that individuals with lower reading spans are less efficient at structuring sentences syntactically than are subjects with higher spans. This in turn, has led to the claim that the working memory system that is measured by the reading span task is involved in syntactic processing during sentence comprehension. However, there is considerable debate about whether subjects with lower reading spans are less efficient at structuring sentences syntactically. We have argued that there are numerous methodological and interpretive problems with many of the studies claiming that there is a significant relationship between reading span and the ability to structure sentences syntactically (Waters & Caplan, 1996c; Caplan & Waters, a & b, in press). In addition, there is considerable controversy about the use of the Daneman and Carpenter task as a measure of verbal working memory capacity. One problem with the Daneman and Carpenter task is that the measure of a subject’s working memory span does not take into account the efficiency with which psycholinguistic computations are carried out, as it is based solely on the storage component of the task. Good performance may reflect a shift of attention away from the sentence aspect of the task, rather than a high level of a central processing resource (Turner & Engle, 1989). As has been recognized by many researchers, subjects may be trading off between components in many ways, making a measure based only on the storage component difficult to interpret (Baddeley, Logie, & Nimmo-Smith, 1985; Daneman & Tardiff, 1987; Turner & Engle, 1986; Tirre & Pena, 1992; Turner & Engle, 1989). In summary, it is commonly believed that working memory capacity declines with age and that this decline is captured by performance on the Daneman and Carpenter task. This reduction in working memory capacity is thought to be associated with reduced syntactic comprehension abilities. However, there is considerable debate about the adequacy of the Daneman and Carpenter task as a measure of verbal working memory capacity. In addition, relatively few studies have examined on-line sentence comprehension abilities in the elderly and the results of those that have are equivocal. In the experiment reported here we studied sentence comprehension in elderly subjects who differ in working memory capacity using a recently developed on-line method -- the auditory moving windows paradigm. The auditory moving windows paradigm provides a measure of processing at each word in a sentence and has been shown to be sensitive to local increases in processing load (Fereirra et al., 1996). Subjects were tested on two different comparisons of sentence types that differ in terms of syntactic structure, cleft-subject versus cleft-object sentences and objectsubject versus subject-object sentences, as seen in Table 1. Numerous linguistic theories and computer-based parsing models maintain that cleft-subject and object-subject sentences are syntactically simpler than cleft-object and subject-object sentences. According to Chomsky’s theory (1981, 1986, 1993), the second of each of these pairs of sentences contain a noun phrase that has been

110

moved to the left of another noun phrase, leaving a Wh-trace. This trace must be related (co-indexed) to its antecedent in order for the thematic roles assigned to the grammatical position that it occupies to be assigned. The memory storage and computational requirements of this operation make the processing load greater in these sentences than in the first members of the pairs (Berwick & Weinberg, 1984; Haarmann et al., 1997). Consistent with this hypothesis, our work with college students has shown that there is an increase in listening time at the embedded verb (V) in cleft-object sentences and at V1 and V2 in subject-object sentences (Waters & Caplan, submitted).

Table 1. Sample stimuli used in the auditory moving windows study.

In the present study, verbal working memory capacity was measured in several ways. Subjects were tested on a variant of the Daneman and Carpenter reading span task in which they were asked to make acceptability judgments about increasingly longer sequences of sentences and to recall the final word of all of the sentences in each sequence (Waters & Caplan, 1996b). Reaction times and errors in making the acceptability judgment were measured. Working memory capacity was tested using five additional operation span tasks -- alphabet span (Craik, 1986), backward digit span (Botwinick & Storandt, 1974), missing digit span (Talland, 1965), subtract 2 span (Salthouse, 1988), and running item span (Talland, 1965).

111

The data from the reading span task were examined to determine whether the traditional reading span measure (performance on the sentence-final word recall component of the task) provides an adequate measure of a subjects’ working memory capacity. If it is a reliable and valid measure of verbal working memory capacity, subjects should not trade-off on the various components of the task and the various components of the task should result in subjects being assigned to the same working memory span group. Moreover, performance on the reading span task should be related to that on other operation span tasks which are claimed to measure verbal working memory capacity. In addition, if on-line sentence processing efficiency is related to verbal working memory capacity as measured by the reading span task, elderly subjects with reduced working memory capacity would be expected to have longer listening times compared to subjects with less reduced capacity, particularly at the verb in acceptable cleft-object compared to cleft-subject sentences and at V1 and V2 in acceptable subject-object compared to object-subject sentences. METHODS

Subjects. Seventy individuals who ranged from 60 to 88 years of age participated in the study. They were recruited through ads posted in churches, synagogues, and newsletters to seniors, and were paid for their participation. In order to participate, subjects were required to have English as their mother tongue, normal pure tone audiometry, at least a high school education, and to report that they were aging normally and living independently. Background characteristics. All subjects were pre-tested on a battery of Neuropsychological tests to rule out any evidence of cognitive decline or dementia. These background measures included the Mini-Mental State exam (MMSE), the Logical Memory I (LMI) subtest of the Wechsler Memory Scale, the vocabulary subtest of the Wechsler Adult Intelligence Scale (WAIS), the reading vocabulary subtest of the Nelson-Denny Reading Test Form A (1960) and the Boston Naming Test (BNT). In addition, the reading comprehension subtest of Form A of the Nelson-Denny reading test was used as global measures of language comprehension and the reading rate measure was used as a global measure of language processing efficiency. Subjects were tested individually over several sessions. Measurement of working memory capacity. As noted above, working memory capacity was measured in several ways. Reading span (Daneman & Carpenter, 1980) was tested using the methods and a subset of the materials from Waters, Caplan, and Hildebrandt (1987, Experiment 2 A). Subjects were presented with a series of sentences on the video screen of a computer and were required to read each sentence silently and make a judgment about the acceptability of each sentence. Half of the sentences were of the syntactically simple cleft subject (CS) form (e.g., It was the jeweler who adjusted the clock ) and half were of the syntactically more complex subject-object (SO) form (e.g., The meat that the butcher cut delighted the customer ). The sentences of each type were presented in blocked form. Half of the sentences of each type were acceptable and half were unacceptable. As soon as a decision about one sentence had been made, the next sentence in the series

112

appeared. When the subject had made a decision about the last sentence in the series, an asterisk appeared to indicate recall of the last word of each of the sentences in the series in the correct serial order. Subjects were instructed not to recall the last word presented first. They were instructed to perform the sentence task very accurately and then to perform as well as they could on the recall task. For each sentence type, testing began with span size 2 and was discontinued at the span size at which the subject could no longer recall the sentence final words in the correct serial order on 2 out of 5 trials. Reading span was defined as the largest set size at which all of the words had been recalled in the correct serial order on at least 3 out of the 5 trials. An additional 0.5 was added to the subjects’ score if they correctly recalled the words on at least 2 of the 5 trials at the next span size. Reading span was calculated separately for each of the two sentence types and then an average reading span was calculated. Mean reaction time for correct acceptability judgments, as well as accuracy on the acceptability judgment portion of the task, was also calculated at span for each subject for each of the two sentence types. The alphabet span task required that subjects repeat a series of words after rearranging them in alphabetical order. The stimuli consisted of monosyllabic words of moderate frequency. The words presented on each trial were semantically and phonologically dissimilar and no words were repeated within a trial. For this task, as well as for the backward digit span, missing digit span and subtract 2 span tasks, testing began at span size 2 and continued through span size 8. There were 5 trials at each span size. Span was defined as the longest list length at which subjects were correct on 3/5 trials. An additional 0.5 was added if subjects were correct on 2/5 trials at the next span size. In the backward digit span task on each trial subjects were required to repeat a series of digits in reverse order of presentation. The stimuli for this task, as well as for the missing digit and subtract 2 tasks outlined below, were digits drawn from the digits one to nine and presented randomly. Missing digit span required subjects to read a string of digits. The experimenter then re-read the string in a different random order with one item omitted. The subject was required to report the missing item. The subtract 2 span task required subjects to repeat a random sequence of digits after subtracting 2 from each. In the running item span task, subjects were required to recall the final items in a list of an unknown length. On each trial, subjects were presented with a list that was 9, 11, 14, 15 or 17 digits long. They were asked to recall the last 2, 3, 4, 5, 6, 7 or 8 digits presented on each of 5 trials. The list lengths presented and the number of digits subjects were asked to recall were randomized across trials. Span was considered to be the list length of the number of digits they were able to correctly recall on 3/5 trials, with an additional 0.5 if the subject correctly recalled the digits on 2/5 trials at the next span size. Measurement of on-line sentence processing efficiency. On-line sentence processing efficiency was assessed using the auditory moving windows paradigm (Ferreira, Henderson, Anes, Weeks, & McFarlane, 1996). The methods and materials were taken from a previous study with college students (Waters & Caplan, submitted). In this task, on each trial subjects heard a sentence that had been

113

digitized and broken up into a series of phrases. The target stimuli consisted of 104 semantically acceptable and 104 semantically unacceptable sentences divided equally among the 4 sentence types shown in Table 1. Subjects were required to pace their way through the sentence as quickly as possible, by pressing a button on a box interfaced with the computer for the successive presentation of each phrase, and then to make an acceptability judgment about the sentence they had just heard. Reaction times for each button press, as well as response time and accuracy on the acceptability judgment, were recorded. Since the response time for each segment included the duration of the segment, as well as the time required by the subject to comprehend it, difference times were calculated by subtracting the segment’s duration from the response time. RT’s and As for the sentence acceptability judgments also served as a measure of the effect of syntactic complexity on sentence processing. RESULTS

Analysis Based on Traditional Reading Span Measure As noted above, subject’s reading spans were calculated in the traditional way using a procedure similar to that outlined by Daneman and Carpenter (1980). This procedure is based solely on performance on the storage component of the reading span task. Reading span was calculated separately for syntactically simple (CS) and complex (SO) sentences. Each subjects’ mean span across the two sentence types was then averaged and converted to a Z score. The bottom 1/3 of subjects in terms of Z scores were classified as low span subjects, the middle third as medium span subjects, and the top third as high span subjects. Table 2 shows the characteristics of the subjects in the three reading span groups. One-way ANOVAs followed by Tukey post-hoc tests were carried out on these scores to determine if there were any significant differences across the groups. The three groups did not differ in terms of age or education. The only significant differences on the background Neuropsychological tests were on the MMSE and on the WAIS vocabulary test. On the MMSE, the scores of medium span subjects were significantly lower than those of high span subjects and on the WAIS vocabulary test the scores of low and medium span subjects were lower than those of high span subjects. The latter finding is consistent with previous studies that have found that high span subjects tend to have higher verbal skills than low span subjects. Working memory assessment. Table 3 shows the performance of the span groups on the three measures obtained from the reading span task -- final word recall (span), sentence processing RT, and accuracy in making a judgment about the sentence, collapsed across the two sentence types. Not surprisingly, all three subject groups differed in terms of span. The three subject groups performed similarly in terms of the accuracy component of the acceptability judgment task (A' scores). However, there were large differences across the groups in terms of sentence processing times and the rank ordering of the groups in terms of sentence processing times was not the same as that obtained on the sentence final word recall measure. On this component of the task, the high and low span subjects had very similar

114

scores, while the performance of the medium span subjects was much poorer. Moreover, inspection of the range of sentence processing times across the three span groups showed that there was a very large range of RTs in each group. Mean RTs ranged from 2,611 msec to 11,508 msec in the low span group, 2,669 msec to 15,041 msec in the medium span group, and from 2,906 msec to 10,768 msec in the high span group. This finding is similar to that of Waters and Caplan (1996b) with college students and suggests that different subjects were trading-off on the storage and processing components of the task in different ways.

Table 2. Characteristics of subjects split by span group.

115

Table 3. Performance on components of the reading span task

In order to investigate this further, correlation coefficients were calculated between the three components of the task for each of the sentence types. The correlations between span and RT, span and accuracy, and RT and accuracy were .12, -.03, and .01 respectively for CS sentences and -.03, .13, and -.02, respectively for SO sentences. These correlations were all non-significant, and further support the argument that different subjects were trading-off in different ways on the three components of the task. Table 4 shows the performance of these three subject groups on the five additional operation span tasks. Mean span scores for each group show that the operation span tasks differ widely in overall level of difficulty. Although low span subject had a mean reading span of only 1.5, they had a span of 6.5 on the missing digit span task and 5.0 on the backward digit span task. More importantly, groups that are chosen on the basis of performance on one measure of verbal working memory capacity (reading span), do not necessarily differ on other measures which are also thought to measure verbal working memory capacity. The groups did not differ on the alphabet or missing digit span tasks. On the backward digit span task, low and medium span subjects had lower scores than high span subjects, but medium and high span subjects did not differ. On the subtract 2 span task, medium span subjects had lower scores than high span subjects but low and medium span subjects and low and high span subjects did not differ. Finally, on the running item task, the scores of low span subjects were lower than those of both medium and high span subjects who did not differ from one another. Correlation coefficients were calculated in order to further investigate the relationship between these different measures of verbal working memory capacity and between these measures and the reading span measures. Table 5 shows the data. There were low to moderate correlations between all of the measures other than the

116

missing item span measure. As expected, the highest correlations were between the two reading span measures. An exploratory factor analysis was carried out on the operation span measures and the RT and span measures from the reading span tasks. This analysis showed that the operation span measures, other than missing item, and the reading span measures loaded on one factor. However, the sentence processing measure from the CS and SO sentences loaded on an independent factor. This confirms the conclusion from the correlational analysis presented above that performance on the sentence processing component of the reading span task is not captured by the span measure for this task.

Table 4. Operation span scores of subjects split by span group.

On-line Measure of Sentence Processing Efficiency. The dependent measure for this task consisted of the response time for each phrase. As noted above, since the response times for each of the segments in this task included the duration of the segment, as well as the time required by the subject to comprehend it, difference times were first calculated by subtracting the segment’s tag-to-tag duration from the response time. Listening times for the cleft subject versus cleft object sentences were analyzed in 3 (Age Group) x 2 (Sentence type) x 4 (Position) ANOVAs using both subject and item means as units. Scores for the object-subject versus subject-object sentences were analyzed in 3 (Group) x 2 (Sentence type) x 5 (Position) ANOVAs.

117

Mean listening times for the three subject groups on CS and CO sentences are shown in Figure 1. The analysis showed that listening times were longer at V in CO sentences than in CS sentences and at NP2 in CS than in CO sentences. Most importantly, there was no effect of Group and no interaction with the Group factor. Table 5. Correlations between different measures of verbal working memory capacity.

The effect at V in CO sentences is predicted by linguistic theory which claims that this is the locus of increased processing load in these sentences. However, V is also the sentence final-word in CO sentences and previous research has shown that reading and listening times tend to increase on the sentence-final word. The finding of increased listening times at NP2 in CS sentences is consistent with this, since this is the last word in these sentences. The critical finding is that the increase at V in CO sentences was significantly larger than that at NP2 in CS sentences, suggesting that the effect in CO sentences is at least in part due to the increase in processing load and not simply due to its position in the sentence. However, contrary to the theory that maintains that the working memory measured by the reading span task is the same as that used in structuring sentences syntactically, subjects who had lower

118

working memory spans did not differ from those with higher spans in terms of the magnitude of the increase in listening time at V. Analysis of the data from OS and SO sentences shown in Figure 2 revealed that listening times at V1 and NP3 were longer for SO than for OS sentences. However, this effect was only seen for high and low span subjects. The effect at V1 was marginally significant for medium span subjects. Thus, the results of this analysis are consistent with the analysis of CS and CO sentences in suggesting that the increase in processing time at the most capacity demanding portion of complex sentences is not greater for low than for high span subjects. Moreover, since the capacity demanding portion of the more complex sentence in this case is not the sentence final word, this finding also supports the conclusion that the increased

119

processing time at V in CO sentences does not simply reflect an end-of -sentence effect. Figure 3 shows the mean reaction times for correct responses on the acceptability judgment portion of the auditory moving windows task. Judgment times for CO sentences were longer than those for CS sentences, and for SO sentences were longer than for OS sentences. In addition, reaction times of medium span subjects were longer than those of high span subjects. A's for this portion of the task are shown in Table 6. A's were lower for CO than for CS sentences for medium span subjects and for SO than for OS sentences for low and medium span subjects.

Table 6. Performance on the acceptability judgment task (A) split by span group.

120

Summary of Analysis Based on Traditional Reading Span Measures. The analyses presented so far show that subjects who are categorized as high, medium, or low span on the basis of one measure of verbal working memory capacity (reading span), would not necessarily be categorized as such on the basis of other measures. There is only a moderate correlation between different measures of verbal working memory capacity, although all of the different operation span measures did load on one factor using factor analysis. In addition, these data provide considerable evidence that different subjects trade-off in different ways on the storage and processing components of the reading span task. Overall, the data from the auditory moving windows task show that this paradigm is sensitive to local increases in processing load as reflected by increased processing times at the verb in CO and SO sentences and at the final word in both sentence types. However, the data do not support the hypothesis that individuals with reduced working memory capacity as measured by the Daneman and Carpenter task are more affected by these local increases in processing load. One problem with the Daneman and Carpenter task which may be related to its insensitivity to on-line sentence processing efficiency is the fact that the span measure does not adequately reflect performance on the entire task. As seen above the correlations between RT, accuracy scores and span on this task were nonsignificant. We therefore re-analyzed the data presented above in two additional ways. In one, we divided subjects into groups on the basis of their performance on the sentence processing component rather than the storage component of the Daneman and Carpenter task. It might be expected that performance on this portion of the task would be more related to on-line sentence processing efficiency. In addition, we divided the subjects into groups on the basis of a measure that we had previously devised (Comp Z) (Waters & Caplan, 1996b) that takes performance on both the sentence processing and storage components of the task into account. Inspection of the subjects designated as high, medium, or low span using these three different methods of classification showed that there was very little overlap so that subjects designated as low span on the basis of one method were unlikely to be classified as such by another. Analysis Based on Sentence Processing Efficiency The second method of dividing subjects into groups was based on their performance on the sentence processing component of the reading span task. Mean reaction times for correct responses were calculated for each subject at their span and converted to Z scores as outlined above. Once again, subjects were divided into three groups with subjects with the longest reaction times being classified as slow, those in the middle as medium, and those with the fastest reaction times being classified as fast. Background characteristics. Table 7 shows the characteristics of subjects in the three groups based on sentence processing efficiency. ANOVAs showed that the groups differed in terms of age, with the fast subjects being younger than the slow subjects. The only other significant between-group difference was on the NelsonDenny reading rate measure. On this measure, the slow subjects performed

121

significantly more poorly than the fast subjects. Thus, groups that are chosen on the basis of sentence judgment processing time also tend to differ in terms of passage reading time on a standardized test. In addition, subjects with faster judgment times tend to be younger than those with slower times. Table 7. Characteristics of subjects split by reaction time.

Working memory assessment. Table 8 shows the performance of the three subject groups on the components of the reading span task. As expected, all three subject groups differed in terms of RTs on the acceptability judgment portion of the

122

reading span task. The groups did not differ statistically on the span or the accuracy measures for this task. Table 9 shows the operation span measures for the subject groups based on sentence processing efficiency. On the alphabet and missing digit tasks, slow subjects had lower spans than fast subjects. The groups did not differ on the other three measures. Thus, groups that are chosen on the basis of the sentence processing efficiency component of the reading span task also differ on some measures of verbal working memory capacity but not others. Table 8. Performance on components of the reading span task for subjects split by RT group.

123

Table 9. Operation span scores subjects split by RT group.

On-line Measure of sentence processing efficiency. Mean listening times for the three subject groups on CS and CO sentences are shown in Figure 4. These data were analyzed in the same manner as for the subject groups based on span. Contrary to the analysis based on span, in this analysis there was a 3-way interaction between group, sentence type, and phrase. Post-hoc tests showed that listening times were longer at V in CO sentences than in CS sentences for all three subject groups and longer at NP2 in CS than in CO sentences, but only for slow subjects. In order to determine whether the magnitude of the effect at V was larger for slow than for medium and fast subjects, difference scores were calculated (CO-CS) for each phrase and analyzed in a 3 (Group) x 4 (Phrase) ANOVA. This analysis showed that the increase in processing time at V on CO sentences was significantly larger for slow than for medium or fast subjects. However, as noted above, V is the last word in CO sentences. Thus, the increase in processing time for slow subjects could at least in part reflect an end-of-sentence effect. Figure 5 shows subjects' performance on OS and SO sentences. On these sentence types, the listening times of slow subjects were significantly longer than those of fast subjects overall. Listening times were longer in SO than OS sentences at V1, V2 and NP3. However, the only difference seen across the three groups was at NP3, where the increase for slow subjects was found to be larger than for medium or fast subjects. The finding that slow subjects did not show larger effects than medium or fast subjects at V1 and V2 but did show a larger end-of-sentence effect

124

suggests that the increased effect found at V in CO sentences for this group likely reflects an end-of-sentence effect. There is not consistent evidence that subjects defined as slow on the basis of sentence processing efficiency have increased processing times at the most capacity demanding portions of sentences.

125

Figure 6 shows the mean reaction times for correct responses on the acceptability judgment portion of the auditory moving windows task. This measure is very similar to the RT measure obtained from the acceptability judgment component of the reading span task which was used to divide the subjects into the three subject groups. Thus, it is not surprising that overall, slow subjects had longer RTs than fast subjects on this task. Judgment times for CO sentences were longer than those for CS sentences, and for SO sentences were longer than for OS sentences. However, slow subjects were not differentially impaired on the harder sentence types. A’s for this portion of the task are shown in Table 10. A’s were lower for CO than for CS sentences for medium subjects and for SO than for OS sentences for all subject groups. Table 10. Performance on the acceptability judgment task (A’) split by reaction time group.

Summary of Analysis Based on Groups Divided by Sentence Processing Efficiency. The results of this analysis were very similar to those found when subjects were divided on the basis of the traditional reading span measure. Not surprisingly, slow subjects did show evidence of longer listening times overall for OS and SO sentences and did show larger end-of-sentence effects for these sentences. Slow subjects also showed longer effects at V in CO sentences. However, given that this word is also the end of the sentence, and that slow subjects did not show increased processing times at V in the comparison of OS and SO sentences, this effect is likely also an end-of-sentence effect for these subjects. Thus, these data do not support the notion that subjects who perform most poorly on the sentence processing component of a Daneman and Carpenter type-task are the most affected by local increases in processing load on complex sentences. Analysis Based on Combined Span and Sentence Processing Efficiency Measures The final method of dividing subjects into groups was based on previous work by Waters & Caplan (1996b). Their Composite Z metric takes performance on both the

126

processing and the storage component of the reading span task into account when assigning subjects to working memory span groups. Mean reaction times (RT) for correct responses and percent of errors on the sentence acceptability component Table 11. Characteristics of subjects split by Comp Z group.

of the reading span task were calculated for each subject at their span. The RT and error scores, as well as the traditional reading span score based on sentence-final word recall, were each converted to Z scores. Comp Z is the average of the reaction

127

time, error, and recall Z scores. Subjects were then divided into three equal groups - high, medium, and low span, based on their Comp Z scores. Background characteristics. The characteristics of subjects classified by Comp Z scores are shown in Table 11. The three subject groups did not differ in terms of either age or education. There were, however, significant differences between the groups on all of the other background measures. The scores of low span subjects were significantly lower than those of high span subjects on all measures, except for the Logical Memory subtests of the Wechsler Memory Scale, where the low subjects differed from the medium but not the high span subjects. Low span subjects also differed from medium span subjects on the MMSE and the Nelson Denny vocabulary subtest. These data are quite different from those obtained when the subjects were divided into groups simply on the basis of either the storage or the processing component of the reading span task. They indicate that subject groups chosen in this manner differ on a range of cognitive variables. Table 12 shows subjects’ performance on the three components of the reading span task. As expected, subjects in the three groups differed on all three components of the reading span task. Subjects’ performance on the five additional operation span tasks is shown in Table 13. There were significant differences between the groups on all five operation span measures. Low span subjects differed from high span subjects on all tasks. In addition, medium and high span subjects differed on the backward digit span task and on the subtract 2 span task. Once again, these data are in contrast to those obtained when the subjects are divided into groups on the basis of one component of the reading span task. Table 12. Performance on components of the reading span task for subjects split by Comp Z group.

128

Table 13. Operation span scores of subjects split by Comp Z group.

129

Mean acceptability judgment times are seen in Figure 9. On this measure, all three subject groups had longer RTs for CO than for CS sentences. Only the low span subjects had longer RTs for SO than for OS sentences. A' scores are in Table 14. Overall, low span subjects had lower scores than high span subjects. In addition, judgments about CO sentences were less accurate than those about CS sentences, and those about SO were less accurate than for OS sentences. Figure 7 shows the performance of the Comp Z groups on CS and CO sentences. As can be seen in the graph, listening times were longer at V in CO sentences and at NP2 in CS sentences. The sentence type and phrase factors did not

130

interact with group, however, indicating that the magnitude of these effects did not differ across the three groups. Listening times for OS and SO sentences are seen in Figure 8. Listening times were longer at V1, V2, and NP3 in SO sentences than in OS sentence, however, the magnitude of these differences did not vary across the three subject groups. Summary ofAnalysis Based on Groups Divided by Comp Z Scores. The results of the analysis based on Comp Z scores showed that subjects who are divided in this manner differ on a wide range of background measures and additional measures of working memory capacity. Nonetheless, groups divided in this manner do not show the predicted differences in terms of on-line sentence processing efficiency. Once again, none of the analyses provided support for the notion that low span subjects have increased processing difficulty at the most capacity demanding portions of sentences.

Table 14. Performance on the acceptability judgment task (A') split by Comp Z group.

CONCLUSIONS

The research presented here addresses three questions: (1) the relationship between the reading span task and other measures of verbal working memory capacity, (2) the relationship between the storage and processing components of a working memory task similar to the Daneman and Carpenter task and (3) the relationship between reading span and on-line sentence processing efficiency. We will discuss each of these issues in turn. In this study performance on the reading span task was compared to that on five operation span measures that are widely used in the aging literature -- alphabet span, backward digit span, missing digit span, subtract 2 span and running item span. In addition, subjects were tested on the reading span task twice -- once with syntactically simple CS sentences and once with syntactically more complex SO sentences. For the most part, correlations between the different operation span

131

measures were in the moderate range with the entire range being from .16 to .80. The one task that was virtually unrelated to the others was the missing digit span task. In this task, subjects read a string of digits ranging from 2 to 8 items and then the experimenter re-read the string in a different random order with one item omitted. The subject was required to report the missing item. Subjects performed extremely well on this task with mean spans being 6.5, 6.5, and 6.8 for the low, medium, and high span subjects, respectively. Some subjects indicated that this task was easier at the larger set sizes, since at high span sizes they used a strategy of remembering the items that were not mentioned and so had less to remember. This may be one possible reason for the high level of performance on this task and its failure to correlate with other measures. The highest correlation (.80) was found between the two versions of the reading span task. This correlation is slightly higher than that found by Waters and Caplan (1996b) who used the same materials with college students. The inter-correlations among the five operations span measures and the correlations between the operation span measures and reading span found in this study were higher than those found by Waters and Caplan who examined the relationship between reading span and working memory measures in college students. However, different working memory measures were examined in the two studies. In the Waters and Caplan study, the working memory measures consisted of digit span, reading span for CS and SO sentences and missing digit span (which was referred to as externally ordered number generation in that study) as in this study, as well as a self-ordered number generation task in which on each trial subjects were required to generate a new random sequence of the digits 1 to 10 without missing or repeating any digits. In addition, subjects performed an externally ordered and selfordered design generation task. These tasks were the same as the number generation tasks but used abstract designs that did not have any verbal labels. Waters and Caplan found correlations of between .29 and .42 between the self-ordered and externally-ordered random number generation tasks and their reading span measures. Factor analysis in the Waters and Caplan (1996b) study showed no factor that could be related to a central verbal working memory factor; rotated factors suggested grouping of tests into factors that corresponded to digit-related tasks, spatial tasks, sentence processing in the reading span task, and recall in the reading span task. These results are similar to the present study in that the sentence processing measures loaded on a different factor than the final-word recall span measures. They are also similar in that the random number generation task loaded on a different factor than the reading span tasks, just as the missing item span task did in this study. However, the results differ in that the present study does suggest that the reading span, alphabet span, backward digit span, subtract 2 span and running item span tasks do load on one factor, suggesting that a central verbal working memory factor is measured by these tasks. The results of this study were consistent with the Waters and Caplan (1996b) study in showing that the subjects’ performances on the storage and processing components of the reading span task are, to all intents and purposes, uncorrelated. Daneman and Carpenter’s original insight was that a task that required both

132

processing and storage might be a better measure of working memory than one that required only storage. However, though their task requires both processing and storage, it only measures storage. RTs within a single reading span group ranged from 2.5 seconds to over 15 seconds. As in the Waters and Caplan study, this scatter does not represent the performance of only a few subjects: standard deviations were approximately one third of the RT means. The correlations between performance on the recall measure and the speed of sentence processing measures, as well as on the recall and the sentence accuracy measures were very low and non-significant. These results are also similar to those reported by Turner and Engle (1989) who reported that only 7 of 72 correlations between their sentence task and recall were significant. Once again, they indicate that the measure of recall is insufficient as a measure of overall task performance. The principal use of working memory measures has been to predict performance on other cognitive tasks. As noted in the introduction, the results of several studies have been taken to suggest that performance on reading span tasks is predictive of on-line sentence processing efficiency. The present study failed to find evidence of any relationship between performance on the reading span task and measures of on-line sentence processing efficiency. This was true regardless of whether subjects were divided into reading span groups on the basis of the traditional reading span measure which only takes performance on the storage or recall portion of the task into account, on the basis of the sentence processing component of the reading span task, or a measure which takes performance on both components into account. On the surface, these results appear to be inconsistent with those of King and Just (1991) and MacDonald, Just and Carpenter (1992) with college students. However, there are numerous methodological and interpretive problems with these studies (Waters & Caplan, 1996 a, c; Caplan & Waters, a, b, in press). In other work we have also failed to find that college students differing in working memory capacity differ in the efficiency with which they structure sentences syntactically. This includes studies using the same methods and materials as were used here (Waters & Caplan, submitted), as well as studies of a variety of other syntactic structures (Waters & Caplan, 1996a). Together, these results suggest that intrinsic limitations in working memory capacity are not associated with impaired syntactic comprehension. This provides support for the view that the processing resource system used in syntactic processing is at least partially separate from that measured by working memory tests such as the reading span task.

133

REFERENCES

Baddeley, A., Logie, R. & Nimmo-Smith, I. (1985). Components of fluent reading. Journal of Memory and Language, 24, 119-131. Baum, S. (1991). Sensitivity to syntactic violations across the age span: Evidence from a word monitoring task. Journal of Clinical Linguistics and Phonetics, 5, 317-328. Berwick, R. C., & Weinberg, A. (1984). The grammatical basis of linguistic performance: language use and acquisition. Cambridge, Mass.: MIT Press. Botwinick, J., & Storandt, M. (1974). Memory, related functions and age. Springfield, IL: Charles C. Thomas. Caplan, D. & Waters, G. S. (in press a). Verbal working memory capacity and language comprehension. Behavioral and Brain Sciences. Caplan, D. & Waters, G.S. (in press b). Issues regarding general and domainspecific resources. Behavioral and Brain Sciences. Carpenter, P. A., Miyake, A., & Just, M. A. (1994). Working memory constraints in comprehension. In M. A. Gernsbacher (Ed.), Handbook of psycholinguistics (pp. 1075-1 122). San Diego: Academic Press. Chomsky, N. (1981). Lectures on government and binding. Dordrecht: Foris. Chomsky, N. (1986). Knowledge of language. New York: Praeger. Chomsky, N. (1993). The minimalist program, Cambridge, MA: MIT Press. Craik, F. I. M. (1986). A functional account of age differences in memory. In F. Klix, & H. Hagendorf (Ed.), Human memory and cognitive capabilities (pp. 409-422). Amsterdam: Elsevier. Daneman, M., & Carpenter, P. (1980). Individual differences in working memory and reading. Journal of Verbal Learning and Verbal Behavior, 19, 450-466. Daneman, M. & Tardiff, T. (1987). Working memory and reading skill re-examined. In M. Coltheart (Ed.), Attention and performance XII: The psychology of reading (pp. 491-508). London: Lawrence Erlbaum. Davis, C. A., & Ball, H. E. (1989). Effects of age on comprehension of complex sentences in adulthood. Journal of Speech and Hearing Research, 32, 143150. Emery, 0. B. (1985). Language and aging. Experimental Aging Research (Monograph), 11, 3-60. Feier, C.D., & Gerstman, L.J. (1980). Sentence comprehension abilities throughout the adult life span. Journal of Gerontology, 35, 722-728. Ferreira, F., & Anes, M. (1994). Why study spoken language? In M. A. Gernsbacher (Ed.), Handbook of psycholinguistics (pp. 33-56). San Diego: Academic Press. Ferreira, F., Henderson, J. M., Anes, M. D., Weeks Jr., P. A., & McFarlane, D. K. (1996). Effects of lexical frequency and syntactic complexity in spoken language comprehension: Evidence from the auditory moving window technique. Journal of Experimental Psychology: Learning, Memory & Cognition, 22, 324-335. Haarmann, H.J., Just, M.A., & Carpenter, P. A. (1997). Aphasic sentence comprehension as a resource deficit: A Computational approach. Brain and Language, 59,76-120.

134

Just, M. A., & Carpenter, P. A. (1992). A capacity theory of comprehension: Individual differences in working memory. Psychological Review, 99(1), 122149. Kemper, S. (1986). Imitation of complex syntactic constructions by elderly adults. Applied Psycholinguistics, 7, 277-287. Kemper, S. (1987a). Life-span changes in syntactic complexity. Journal of gerontology, 42, 323-328. Kemper, S. (1987b). Syntactic complexity and elderly adults' prose recall. Experimental Aging Research, 13,47-52. Kemper, S. (1988). Geriatric psycholinguistics: Syntactic limitations of oral and written language. In L. L. Light, & D. M. Burke (Ed.), Language, memory, and aging (pp. 58-76). New York: Cambridge University Press. Kemper, S. (1992). Language and aging. In F. I. M. Craik, & T. A. Salthouse (Ed.), Handbook of aging and cognition (pp. 21 3-270). Hillsdale, NJ: Erlbaum. Kemper, S., & Rash, S. (1988). Practical aspects of memory: Current research and issues. London: Cambridge University Press. Kemper, S., Kynette, D., Rash, S., O'Brien, K., & Sprott, R. (1989). Life-span changes to adults' language: Effects of memory and genre. Applied Psycholinguistics, 10, 49-66. Kempler, S., Rash, S., Kynette, D., & Norman, S. (1990). Telling stories: The structure of adults' narratives. Journal of Cognitive Psychology, 2, 205-228. Kemtes, K. A., & Kemper, S. (1996). Younger and older adults' working memory and on-line processing of syntactically ambiguous sentences. Poster presented at the Cognitive Aging Conference, Atlanta, King, J., & Just, M. A. (1991). Individual differences in syntactic processing: The role of working memory. Journal of Memory and Language, 30, 580-602. Light, L. L. (1990). Interactions between memory and language in old age. In J. E. Birren, & K. W. Schaie (Ed.), Handbook of the psychology of aging (3rd edition) (pp. 275-290). San Diego: Academic. MacDonald, M. C., Just, M. A., & Carpenter, P. A. (1992). Working memory constraints on the processing of syntactic ambiguity. Cognitive Psychology, 24, 56-98. Marslen-Wilson, W. D. (1987). Functional parallelism in spoken word-recognition. Cognition, 25,71-102. Norman, S., Kemper, S., Kynette, D., Cheung, H., & Anagnopoulos, C. (1991). Syntactic complexity and adults' running memory span. Journal of Gerontology: Psychological Sciences, 46, 346-351. Obler, L. K., Fein, D., Nicholas, M., & Albert, M. L. (1991). Auditory comprehension and aging: Decline in syntactic processing. Applied Psycholinguistics, 12,433-452. Salthouse, T. A. (1988). The role of processing resources in cognitive aging. In M. L. Howe, & C. J. Brainerd (Ed.), Cognitive development in adulthood (pp. 185-239). New York: Springer-Verlag. Talland, G. A. (1965). Three estimates of the word span and their stability over the adult years. Quarterly Journal of Experimental Psychology, 17, 301-307.

135

Tirre, W., & Pena, C. (1992). Investigation of functional working memory in the reading span test. Journal of Educational Psychology, 84, 462-472. Tun, P. A., Wingfield, A., & Stine, E. A. L. (1991). Speech-processing capacity in young and older adults: A dual-task study. Psychology and Aging, 6, 3-9. Turner, M. & Engle, R.W. (1986). Working memory. Proceedings of the Human Factors Society, 30, 1273-1277. Turner, M. & Engle, R.W. (1989). Is working memory capacity task dependent? Journal of Memory and Language, 28, 127-154. Waldstein, R., & Baum, S. (1992). The influence of syntactic and semantic context on word monitoring latencies in normal aging. Journal of Speech Language Pathology and Audiology, 6,217-222. Waters, G.S., & Caplan, D. (submitted). Verbal working memory capacity and online sentence processing efficiency in college students. Waters, G., & Caplan, D. (1996a). Processing resource capacity and the comprehension of garden path sentences. Memory and Cognition, 24, 342-355. Waters, G., & Caplan, D. (1996b). The measurement of verbal working memory capacity and its relation to reading comprehension. The Quarterly Journal of Experimental Psychology, 49A, 5 1-79. Waters, G., & Caplan, D. (1996c). The capacity theory of sentence comprehension: A reply to Just and Carpenter (1992). Psychological Review, 103,761-772. Waters, G., Caplan, D., & Hildebrandt, N. (1987). Working memory and written sentence comprehension. In M. Coltheart (Ed.), Attention and performance XII: The psychology of reading (pp. 531-555). London: Lawrence Erlbaum. Zurif, E., Swinney, D., Prather, P., Wingfield, A., & Brownell, H. (1995). The allocation of memory resources during sentence comprehension: Evidence from the elderly. Journal of Psycholinguistic Research, 24, 165-1 82.

ACKNOWLEDGEMENT

This work was supported by a grant from the National Institute on Aging (AG009661-07).

This page intentionally left blank.

6 TESTING AGE INVARIANCE IN

LANGUAGEPROCESSES

Reinhold Kliegl, Ulrich Mayr, Martina Junker and Gisbert Fanselow

INTRODUCTION

Has there been too much ado about the age sensitivity of working memory or processing-rate as far as language-related performance is concerned? If these generic processing resources are subserving language comprehension, we should expect a systematic relation between task difficulty/complexity and the associated age difference, as it has been reported for numerous non-lexical tasks such as visual search and reasoning (Brinley, 1965; Cerella, 1990; Salthouse, 1985). In this chapter we will review two examples from our previous research on cognitive aging and present a new set of data that are suggestive that this is not the case in lexical access and may be so only under specific types of syntactic complexity. The conclusion we draw is that while language-related processing demands can be conceptualized in analogy to those in other cognitive tasks the allocation of cognitive processing resources arising in the former appears to be handled differently and buffered against age-related decline, in line with accounts inspired by modularity notions (Caplan & Waters, 1998), but even subtle changes of task demands may reveal effects of age that are similar to what has been found under coordinatively complex demands on working memory (e. g., Mayr & Kliegl, 1993). We describe three experimental paradigms that go somewhat beyond current research paradigms in cognitive aging. They explicitly address the complexity hypothesis, that is the notion that age differences in a specific experimental condition are systematically related to the processing difficulty young adults experience in the same condition irrespective of the type of task (Cerella, 1990). We present these three paradigms as alternative proposals about how to delineate process-specific or domain-specific effects from a general decline in processing efficiency. They are (1) the determination of time-accuracy functions (Kliegl, Mayr, 137

138

& Krampe, 1994) (2) the determination of search-depth functions (Mayr & Kliegl, 1998), and (3) the determination of systematic relations for syntactic complexity effects. We test age invariance in the following language-related tasks: (1) in semantic retrieval of arithmetic facts (Verhaeghen, Kliegl, & Mayr, 1997), (2) in the production of exemplars from semantic categories (Mayr & Kliegl, 1998), and (3) in off-line comprehension accuracy of German sentences with a center-embedded relative clause (Kliegl, Fanselow, Schlesewsky, & Oberauer, 1999). We present some background information on the issue of dissociating process-specific or domain-specific decline from general age-related decline before we turn to the research examples. GENERAL AND SPECIFIC AGE DIFFERENCES

In traditional experimental cognitive aging research a typical experiment involves groups of young and old adults and an experimental design with one or several independent variables each implementing a manipulation of some hypothetical cognitive process. For example, in the case of language, a manipulation of category difficulty may be examined with respect to lexical access times in a verbal-fluency task. Or comprehension accuracy may be assessed for sentences varying in degree of syntactic complexity. Response times or accuracy serve as primary dependent variables of processing efficiency. In either case the expected outcome is that the age difference is larger in the more difficult condition. If the pattern is not obtained the researcher is faced with arguing the null hypothesis (i. e., there is a main effect of age but no interaction). In this case one would check whether the means exhibit a pattern in the expected direction, in which case recruiting more participants might be advised. When accuracy Figure 1. Old adults' latencies or criterion-referenced (or errors) are used as time demands are frequently well dependent variable, described as a linear function of young interpretation of results adults' values in corresponding conditions. may be further The slope of the function (proportionate complicated by the factor) depends on task domain and task potential presence of floor complexity. or ceiling effects.

139

Even with significant interactions the usual inference of a process-specific age deficit for the complex condition has been questioned. Metaanalyses of published cognitive aging research suggest that age differences in a specific condition can be predicted from the processing difficulty young adults exhibit in the same condition (e. g., Cerella, 1990). Consequently, when old adults' latencies or criterionreferenced time demands (i. e., time demands for different criteria of accuracy) in experimental conditions are plotted over corresponding young adults' latencies or time demands, points cluster along monotonous functions. Cognitive aging research revealed at least three types of such systematic relations. For lexical tasks such as lexical decision the means appear to fall along the main diagonal with a slope slightly larger than 1, that is about 1.2 to 1.5 (Lima, Hale, & Myerson, 1991; see Figure 1). For non-lexical tasks Mayr and Kliegl (1993) introduced the distinction between sequential and coordinative complexity. Sequential complexity refers to the number of successive processing steps that must be performed to reach a solution. A purely sequentially complex task requires a sequence of cognitive operations, each one applied to the outcome of its immediate predecessor, so that only one information element has to be held in working memory at a time. Obviously a task will generate longer response times as the number of operations increases. In terms of age differences, old adults' means were well characterized by a function with a slope between 1.5 and 2.0 for tasks requiring visual checking of object features (Figure 1). Coordinative complexity designates the executive demands required to organize a chain of interdependent processing operations. For example, when the computation in an arithmetic chain is complicated by parentheses the task becomes coordinatively complex because the outcome of operations within brackets have to be held available while further operations are performed. In the Mayr and Kliegl (1993) study, processes required to identify figural transformations had to be changed depending on the results of earlier checking processes. Again, condition means in old-over-young plots were well fit by a linear function. This time, however, a slope of 3.0 characterized the proportional age differences (Figure 1). Mayr and Kliegl proposed a model according to which processing steps related to the coordinative load had to be repeated with a higher probability by old than young adults. Such analyses of systematic relations between the performance of old and young adults go beyond the traditional experimental design of cognitive aging research because in traditional designs any two non-lexical task conditions which differ significantly for young adults will generate a task x age interaction. All of these potential traditional interactions, however, are generated by approximately the same proportionate factor reflected in the slope. Importantly, if slopes differ by processing domain, they can not be reduced to something like a "super"-slowing factor without additional assumptions. Thus, processing domains are said to be affected differently by age if tasks from the two domains belong to different functions (Kliegl, Mayr, & Krampe, 1994). One generalization of this research is that in proportionate measurement space apparently at least three domains can be distinguished: a lexical domain which appears to be (almost) invariant and a nonlexical domain which generates two slowing functions for sequentially and

140

coordinatively complex tasks. Note, that at least a priori, the sequentialcoordinative complexity distinction is independent of processing domain so that it is possible that more functions could be obtained by crossing types of domains with types of complexity. However, it is also possible that domains of relatively preserved functioning (e. g., verbal processing) are protected against the coordinative-complexity age effects found in non-verbal domains. We will discuss some evidence on this question in the course of this chapter. In this chapter we start from the observation that the language domain is almost age invariant. For example, the old-young function for lexical tasks exhibits a slope somewhat larger than one. The small age difference could be primarily due to the fact that lexical tasks are very easy relative to non-lexical tasks; past research may have underestimated the effect of age on language-related processes by looking only at a very restricted range of task difficulty. Lexical tasks might cluster with nonlexical tasks when their difficulty is increased. Alternatively, the slight deviation from complete invariance could be related to a perceptual-motor component associated with all visual tasks (Cerella, 1985). Cerella (1990) computes the corresponding old-to-young ratio as 1.22. Therefore, in a paradigm assessing processing efficiency without involvement of a motor component, lexical access may turn out as age invariant, that is with a slope of one in old-over-young plots. Finally, the slight deviation from age invariance could be due to minor contaminations from generic cognitive processes which are known to be affected by age (e. g., Laver & Burke, 1993). In general, it is difficult to conceive of experimental tasks that do not involve some aspects of visual search and working memory; and this is also true of language tasks. What is needed, then, are functions in which generic cognitive processes, such as those related to working memory, and language-specific processes are reflected in different parameters of the function. In this case, age invariance would not be observed for the entire function but restricted to parameters which are expected to reflect language-related processes. SEMANTIC MEMORY ACCESS

Time-Accuracy Functions: Retrieval Of Arithmetic Facts Numerous metaanalyses of cognitive aging research suggest that a conceptualization of age differences in a proportionate manner leads to a more parsimonious picture than traditional experimental research which focused on absolute differences (Cerella, 1990). In a single experiment a related but extensive (and expensive) approach to separate task difficulty and effects of task complexity involves the determination of complete time-accuracy functions for each individual in each experimental condition (Kliegl, Mayr, & Krampe, 1994; Mayr, Kliegl, & Krampe, 1996). In this approach one determines for each individual the (presentation) time required to reach different levels of accuracy in a specific experimental condition by means of criterion-referenced adjustments of presentation times. The procedure is analogous to the method of limits in psychophysics with the difference that presentation time, rather than stimulus energy, is adjusted upward or downward depending on whether or not a specific accuracy was met on the previous trial.

141

Moreover, in contrast to traditional response-time tasks, criterion-referenced presentation times do not contain times related to motor components of response execution; they reflect only mental processing time. Thus, age differences in such peripheral components will not contribute to demands on processing time. Finally, as participants are typically instructed to be as accurate as possible (even at the cost of responding slower), the response format is equivalent to so-called power tests. These procedural features are relevant for aging research because in traditional response-time tasks the weight of age-differential contributions by motor components and of age-differential criteria on the speed-accuracy tradeoff continuum are simply not known. After collapsing data collected for different accuracy criteria, accuracy can be described as a function of presentation time for the entire range from chance to the asymptotic maximum score. Specifically, across a diverse set of tasks a negatively accelerated exponential function has performed very well in this respect (Kliegl et al. 1994; Mayr et al, 1996; Verhaeghen et al., 1997). By adopting this function one assumes that manifest performance is monotonically related to the amount of available presentation time. Moreover, the mechanism translating presentation time into accuracy gains is assumed to be the same at all levels of accuracy. Consequently, manipulations of criterion accuracy are manipulations of general task difficulty: The higher the accuracy to be achieved, the more difficult is the task, and the more presentation time will be needed. Within the same task, longer presentation times are indicative of a larger number of processing cycles through the same algorithm. In this sense task complexity is invariant across levels of task difficulty. We now have an operational definition of task difficulty that does not require the specification of a process model. Within a given task its difficulty is tied to the accuracy we want a person to achieve. This allows us to introduce task complexity as a contrast between two task conditions. Specifically, if two conditions differ in the amount of time they need to achieve the same relative gain in accuracy (e. g., from 65% to 85%), we call the more time-consuming condition the more complex condition. If we design our conditions such that they differ in some aspect of theoretical complexity, we can assess whether this complexity effect is maintained across changes of task difficulty. In other words, task difficulty is nested intraindividually within levels of task complexity and therefore not confounded with it. Indeed we use differences in time demand for corresponding accuracy gains (to be precise: for corresponding reductions in proportionate error) as evidence for differences in task complexity. An example of this approach is the mental-arithmetic study by Verhaeghen et al. (1997) which was conceptualized as another test of the distinction between sequential and coordinative complexity in a domain in which sequential-complexity age differences could be expected to be relatively small. Verhaeghen et al. report an average old-to-young ratio of 1.3 for response times in access time to arithmetic facts for 10 earlier studies (e. g., Charness & Campbell, 1988; Geary, Frensch & Wiley, 1993; Salthouse & Coon, 1994). That even these small age differences could have been due to peripheral factors influencing response times led us to expect even true age invariance when examining arithmetic-fact access via time-accuracy

142

functions. Examples of the four task conditions are given in the panels of Figure 2. Participants had to compute the solution within the allotted presentation times. Intermediate and final results were never smaller than one or larger than nine. The degree of sequential complexity was manipulated by changing the number of operations that needed to be carried out. This manipulation should not affect the cognitive mechanism translating time into accuracy; it only needs to run longer when 10 instead of 5 operations are to be computed. Coordinative complexity was introduced by placing brackets in a line of addition and subtraction problems. Given the need to store and access intermediate results in this condition, this clearly is a coordinatively complex condition. Consequently, sequential and coordinative conditions should differ in the rate with which presentation time can be converted into gains in accuracy. Of central concern, finally, was how young and old adults would respond to these manipulations of task difficulty and task complexity. Four negative exponential functions, one for each experimental condition, were estimated for 18 students with a mean age of 25 years and 16 healthy old adults with a mean age of 72 years. Data collection extended across 8 experimental sessions lasting 45 to 90 minutes each. Three parameters determine each function: the minimum time needed to move performance away from chance, the steepness of the function, and the asymptote. These parameters were averaged for each condition and separately for young and old adults. Curves in Figure 2 represent the conditionspecific curves for the two age groups. Individual curves fit the data quite well; pseudo-R2 ranged from .68 to .89, with a mean of .78. There was no age difference in the two sequential conditions. Young and old adults needed the same amount of presentation time for all levels of accuracy. These results are very noteworthy because age invariance was obtained for two very different manipulations of task difficulty. First, as described above, task difficulty is linked to accuracy: the higher the accuracy, the more presentation time is required. Nevertheless, there was no age difference for the entire accuracy range between chance and asymptotic levels. Thus, young and old adults responded to this increase in task difficulty in exactly the same way. Second, there were two sequential conditions, one involving five, the other ten operations. Obviously, carrying out ten operations is the more difficult condition. As the rightward shift of the functions in Figure 2 indicates, for any given level of accuracy much more time is needed. Nevertheless, again, young and old adults needed the same amount of presentation time under both conditions. Contrary to what one might have expected from the argument that age differences increase with task difficulty, nothing of this kind was detected for the retrieval of simple and highly overlearned mental arithmetic addition and subtraction facts. A rather different picture emerges when we look at the time-accuracy functions for coordinatively complex tasks, that is at those tasks in which intermediate results had to be memorized while a bracket term was solved. Main effects of age, number, and complexity and, most importantly, the age x complexity interaction were significant for the intercept and the asymptote of the function. Older adults had significantly lower asymptotes in the coordination conditions. Asymptote differences reflect differences in the quality of the computed representation. The demand of keeping intermediate results alive in working memory led to a higher

143

error rate in old than young adults. There were no age differences in the processing rate parameters (i. e., the slopes of the functions). Our interpretation of this result is that in this experiment processing rate reflected primarily the time needed to retrieve simple arithmetic facts in permanent knowledge; irrespective of whether or not there was a need to hold results in memory. Thus, it may be possible to isolate language-related and working-memory related effects in the context of a Figure 2. Time-accuracy functions for sequentially coordinatively complex and coordinatively complex mental task. arithmetic tasks for young and old adults In summary, the (after Verhaeghen et al., 1997). Verhaeghen et al. (1997) study provided evidence for age invariance in sequentially retrieving arithmetic facts (residing, we assume, in semantic memory) and potentially in the TAF slopes of coordinative tasks. Most importantly, the two dimensions of task difficulty encompassed the entire range from chance to asymptotic maximum performance for a small and a large number of consecutive retrieval operations. Contrary to what would be predicted from general slowing models age differences did not respond at all to these very far ranging manipulations of task difficulty. Obviously, if we plot old adults' presentation times for various accuracy criteria in sequential task conditions over those of young adults' for corresponding accuracies, we obtain the main diagonal of Figure 1. On the contrary, a manipulation of coordinative complexity, induced by inserting parentheses that force storage and access of intermediate processing results, showed that young adults need less time to move from chance performance and that they reach a higher performance asymptote for long presentation times. Thus, difficulty and complexity can be dissociated. The fact that we did find reliable age differences as soon as coordinative complexity was introduced suggests some degree of independence between domain of processing and type of complexity as two important factors that modulate the size of age differences. Obviously, the age resilience of arithmetic-fact retrieval did not protect

144

against the age-detrimental effects of coordinative complexity manipulations operating on top of domain-specific processes. Search-Depth-Functions: Retrieval From Semantic Categories Another test of age differences in semantic-memory retrieval can be devised in the context of a verbal-fluency task in which participants are asked to name as many exemplars of a particular category (e. g., birds, vegetables) as quickly as possible. This is a task which produced mixed results in the past, most studies showing moderate age differences, some showing age invariance. And again, a pattern of true age invariance in semantic access per se may have been obscured by additional non-semantic processes involved in fluency tasks. One such process, wordpronunciation time, can be readily excluded because age differences therein are negligible (e. g., Balota and Duchek, 1988). A more likely candidate are executive processes required to organize the sequence of retrieval attempts (e. g., Troyer, Moscovitch, & Winocur, 1997). The problem, thus, is to find a way to dissociate potentially age-invariant, semantic and potentially age-sensitive, executive components to verbal-fluency retrieval times. Mayr and Kliegl (1998) proposed a novel analytic method for such a dissociation. Specifically, they made the assumption that retrieval times reflect semantic memory access time and executive processing time as two additive components. Further, they assumed that the farther one proceeds within the fluency recall sequence (i. e., search depth), the more semantically difficult the task becomes whereas the executive Figure 3. Inter-Word-Times in verbal fluency conditions as a function of ordinal component should remain constant. To number of to-be-retrieved category test these assumptions exemplar. Mayr and Kliegl (1998) asked 24 old and 24 young subjects to produce 10 words from a given category for a total of 24 categories grouped into three levels of difficulty (e. g.,

145

colors vs. spices vs. insects). The top panels of Figure 3 show the inter-word times (IWTs) as a function of position in the recall sequence (i. e., search depth) and category difficulty. Consistent with the additive model, we found that IWTs could be represented adequately through a simple linear function (i. e., the search-depth function) relating IWTs to words in the recall position. On the basis of our simple model we assume that the slope parameter reflects the semantic memory component, whereas the intercept reflects the executive component. Consistent with this assumption we found in young adults that the slope parameter increased with difficulty of the semantic category, whereas the intercept (reflecting the executive component) remained constant. Of most interest in the present context is that we found no difference in the slope parameter between young and old adults. Thus, similar as in the Verhaeghen et al. (1997) study, we found a measure thought to reflect access to semantic memory to be age invariant. This finding is particularly noteworthy given that judged in terms of length of retrieval times (i. e., in part several seconds) this is a fairly complex task. Finally, and also consistent with general expectations, we did find reliable age differences in the intercept parameter of the search function, which we interpret in terms of age differences in executive control. Thus, the analysis of fluency protocols via the search-depth function suggests that the pattern of moderate age differences typically found in semantic fluency tasks is the result of a mixture between two different processes. One of them, the semantic component is age invariant, the other, the executive component, is age sensitive. Within the same study, we also, again, attempted to examine the role of what we initially considered to be an additional, powerful manipulation of coordinative and executive control demands. Specifically, for half of the categories we used a condition in which subjects had to alternate their recall between two different categories. According to some accounts the switching in the course of semantic fluency should be particularly age sensitive (e. g., Troyer et al., 1997). As can be seen in the lower panels of Figure 3, the switch manipulation had a substantial effect, in particular on the intercept parameter. To our great surprise, however, this effect did not interact with age and there was only a very subtle age-specific increase of the search-function slope. Thus, contrary to our general idea about the role of coordinative demands, the manipulation of executive and coordinative demands we used here did not reveal a marked increase of age differences. This finding may suggest that in this particular domain, and different from what we found in Verhaeghen et al. (1997), age-invariance in primary processes "protects" against age-related loss in superimposed coordinative processing. However, we believe that a different view is also possible here. This requires a reinterpretation of the nature of the "switch operation" that is necessary when moving from one category to the other. Instead of some kind of domain-unspecific executive process the switch time may reflect primarily semantic-memory retrieval time, however, not for specific instances of a category, but for the category itself. Consistent with this idea is the finding that switch times showed a clear dependency on the difficulty of semantic categories (which should not have happened if switch costs reflected some kind of domain-independent processing component). Together with the result that retrieval of category exemplars is age-invariant, this interpretation is also consistent with the

146

fact that no age differences were found in the "switch component". This interpretation of the switching condition, however, needs independent corroboration which we are currently seeking. The approach advocated here holds promise for a better delineation of agesensitive and age-invariant components in fluency tasks. Reliable age differences in verbal fluency have been reported in a number of studies - two recent ones are Bäckman and Nilsson (1996) and Troyer, Moscovitch, and Winocur (1997) - but there is also some evidence to the contrary (Fitzgerald, 1983). Our analyses suggest that the main reason for the conflicting evidence is related to the separability of semantic and non-semantic components. For verbal fluency tasks it makes sense to distinguish between the semantic memory access/retrieval and the executive control processes. Effects of age may be restricted to the latter. Mayr and Kliegl (1998) also proposed a validity check of the hypothesis that intercept and slope of the SDF are linked to two different anatomical structures of the brain: Frontal-lobe patients should exhibit a selective increase in the intercept; temporal lobe patients should exhibit a selective increase in the slope. The rationale is that executive control appears to be handled by frontal lobes where age effects are pronounced (e. g., West, 1996) and that semantic memory is associated with temporal regions (e. g., Moscovitch, 1994). SYNTACTIC COMPLEXITIES

An understanding of age differences in cognitive functions is facilitated by mapping performance within specific levels of task complexity across as wide a range of task difficulty as possible. Indeed we claim that this is necessary if one wants to escape the interpretational ambiguity of ordinal interactions (Kliegl et al., 1994, Verhaeghen, in press). In the mental-arithmetic study the range between chance and asymptotic performance was mapped within levels of sequential complexity and within levels of coordinative complexity by manipulations of presentation time; age effects were restricted to conditions of coordinative complexity. In the verbalfluency task interword times were shown to increase linearly with the ordinal position of examples to be retrieved from a semantic category; it is more difficult to produce the sixth than the fifth word. Again, this manipulation of task difficulty was carried out within several levels of task complexity. In this case age differences were associated mostly with the intercept rather than the slope of search-depth functions. In this section, for the case of syntax, the goal is again to distinguish between manipulations that could potentially produce age-specific effects and manipulations that do not. Moreover, we want to trace these effects in absolute and proportionate space. To this end we will contrast different old-over-young plots based on a large number of experimental conditions. For a matter of convenience we call comparisons that are based solely on young adults' performance as reflecting effects of syntactic difficulty (i. e., the technique used most frequently in metaanalyses). Old-over-young plots that are based on theoretically specified contrasts derived from experimental conditions are said to reflect effects of syntactic complexity. (Age-)differences in task difficulty reflect an unknown mixture of syntactic

147

complexities whereas differences in task complexity are tied to specific experimental manipulations. From the perspective of cognitive aging the basic question remains the same: Can we predict comprehension accuracy of old adults from corresponding scores of young adults? In the end we want to determine whether one or two of the lines displayed in Figure 1 also capture the relation between old and young adults' performance across a large number of syntactic conditions. Moreover, a special feature of our design is that we imposed specific restrictions on syntactic complexity, In particular we wanted to avoid a confound of syntactic complexity and the amount of material that must be processed. This is in agreement with Rochon, Waters, and Caplan (1994; also Waters, Caplan, & Rochon, 1995) who stipulated that for the pure assessment of syntactic complexity one should compare sentences with canonical and non-canonical orders of thematic roles; in addition, sentences should be matched for length and number of propositions. Experimental Paradigm Kliegl et al. (1999) had participants read German sentences of the following type in an RSVP-format with a fixed amount of time per word: (1) (1’) (2) (2’)

Vielleicht hat der Mann, der den Arbeiter erblickt hat, den Clown verehrt. Perhaps has thenom man, whonom theacc worker seen has, theacc clown honored. (Perhaps the man who saw the worker honored the clown.) Vielleicht hat den Mann der Arbeiter, den der Clown erblickt hat, verehrt. Perhaps has theacc man thenom worker, whoacc thenom clown seen has, honored. (Perhaps [it is] the man [that] the worker who the clown saw honored.)

The paradigm was modeled after a self-paced reading study by Koepcke and MacWhinney (unpublished) with fewer and slightly different design factors. The dependent variable in the present research was the accuracy with which participants could answer four types of questions about the nouns of each sentence. Questions were based on the main clause (MC) or relative clause (RC) verb and asked for the subject (S) or the object (0) of the clause ( Who has honored?, Who was honored?, Who has seen?, Who was seen? in sentences 1 and 2). The factor "subject/object question" was recoded as a factor that coded whether the question focused the noun with 1 role or the noun with two roles (i. e., the noun carrying the RC). Sentences 1 and 2 represent two of eight different sentence types which result from a 2 x 2 x 2 design with the factors (1) subject versus object main clause (S/O MC), (2) subject versus object relative clause (S/O RC), and (3) position of the relative clause at MCnoun 1 or at MC-noun 2 as the three experimental factors. Thus, together with the 2 factors related to the type of question the design comprised 5 factors with 2 levels each or a total of 32 different experimental conditions. A computer program assembled sentences by randomly sampling without replacement from lists of adverbs, masculine nouns without overt accusative case marking (e. g., "der Mann - den Mann" [thenom man - theacc man"]), and verbs with identical forms for present and past tense both in active and passive voice (e. g., "x

148

erblickt" ["x sees"]," x wird erblickt" ["x is seen"]," x hat erblickt" ["x has seen"], " x wurde erblickt" ["x was seen"]). Note this procedure perfectly implemented the Rochon et al. (1994) criteria: All sentences were 12 words long and contained exactly two propositions. Syntactic complexity, then, was induced only by manipulations of word order and by the type of question that was asked about the sentence. Moreover, the random assignment of words to templates prevented semantic biases in the sentences. Thus, all sentences were grammatical expressed a possible scenario, and none of the sentences was semantically anomalous. There are two reasons why a design of this complexity is needed for the question at hand. First, sentences comprising one main and at least one subordinate clause are at the lower end of what might lead to theoretically interesting effects of syntactic complexity. Given this lower limit of complexity it is difficult to specify a design with fewer than three factors for sentence construction and two factors for assessing the quality of the representation. Second, for the assessment of syntactic complexity effects in proportionate space we need a sufficiently large number of conditions of simple and complex processing demands; 32 conditions meets the conventional criteria for sample sizes in metaanalyses, whereas 16, for example, would hardly be enough. Contrast Coding Of Syntactic Complexities For 32 experimental conditions one can specify at most 31 orthogonal contrasts. Typically, such an experiment is analyzed as a five-factorial within-subject design augmented with age as a between-group factor. There are, however, two problems associated with the routine application of ANOVA. First, it is not uncommon that designs of this kind generate a large number of higher-order interactions that are difficult to interpret. For example, aside from the 5 main effects, the standard ANOVA yields 10, 10, 5, and 1 interactions involving 2, 3, 4, and 5 factors, respectively. Although each of those factors contrasts only two levels, interpretation of such constellations are typically very challenging. Second, the experimental sentences exhibit additional linguistic regularities which emerge from the combination of the factors. For example, the noun carrying the relative clause (i. e., the head of the noun-phrase/relative-clause construction) can have the same or a different case as the relative pronoun (see Table 1). This produces a contrast of congruency and incongruency in grammatical or thematic roles. Or the main clause and the relative clause can be congruent or incongruent with respect to subject-initiality or object-initiality. This has been called parallel function or perspective shift (MacWhinney, 1999). Further, questions can focus the noun with one role or the noun carrying the relative clause. For all these examples it is theoretically conceivable that they contribute to comprehension accuracy. One routine solution is to contrast these conditions in a post-hoc fashion but their relation to the factors of the experimental design is anything but obvious.

149

Table 1 Illustration of Identity of Higher-Order Interaction and Implicit Congruency Main Effect

Both problems are substantially reduced in scope once one realises that theoretically relevant contrasts that were not explicitly specified as factors of the experimental design are often mathematically identical with higher-order interactions. Indeed, it is almost as if in the wisdom of language complicated interactions already crystallised into simple concepts. As an illustration consider three factors of the present paradigm: MC S/O-initiality, RC S/O-initiality, and RC position. All ANOVA main effects and interactions for such a design are computed from linear contrasts in which four conditions (i. e., sentence templates) carry a positive weight and the other four conditions carry a negative weight. Subject MC versus object MC (coded as "U" in Table 2). Grammatical processing difficulty is higher for object than subject main clauses as shown with reading times for German sentences by Krems (1984) and with comprehension times by Pechmann, Uszkoreit, Engelkamp, and Zerbst (1994) and Rösler, Pechmann, Streb, Röder, and Henninghausen (1998). Schlesewsky, Fanselow, Kliegl, & Krems (in press) review several explanations without a clear favourite at this time (see also Fanselow, Kliegl, & Schlesewsky, this volume). Similarly, previous research would also predict larger age differences for object MCs than subject MCs (e. g., Kemper, 1986, 1992). This contrast is tested with the difference between cells 1, 2, 5, 6 and cells 3, 4, 7, 8 of Table 1. Subject RC versus object RC (V). Reliable object-initiality disadvantages have been demonstrated for subject versus object relative clauses both in on-line and offline measures in a large number of studies in different languages (for a review see MacWhinney and Pléh, 1988). As an explanation, Ford (1983) argued that there is a greater number of unconnected fragments in object-relative than subject-relative sentences (see also Frazier, 1987). In addition, the arguments for object initiality effects presented above also apply to the processing of an embedded relative clause: The accusative pronoun may signal the need to reserve a slot for an incoming subject and there may be a need to update context and to inhibit the automatically provided default context. This contrast is tested with the difference between cells 1, 3, 5, 7 and cells 2, 4, 6, 8 in Table 1. RC at noun 1 versus RC at noun 2 (W). All sentences comprised a main clause (MC) and a relative clause (RC) which was embedded either after the first or the second MC noun. How does the position of the RC affect comprehension difficulty?

150

If the RC follows the second MC-noun, MC comprehension requires that both MC nouns are held in working memory during RC processing. If the RC follows the first MC noun only the first noun must be stored. Even more detrimental to performance with a late RC should be the high confusability of the two determiners associated with the two MC nouns (i. e., participants must remember whether der went with the first noun and den with the second noun or vice versa). In contrast, if the RC follows the first MC-noun, the second MC-noun (plus its determiner) enjoy a recency position just before the sentence-final verb. Thus, if the final three words could be held in a phonological buffer, the case of the first MC noun can be inferred. Therefore, MC comprehension should be much worse with RC after the second MCnoun compared to RC after the first MC-noun. We expected that these processing differences would also lead to an age-differential effect as it has been demonstrated for a variety of grammatically complex constructions (Norman, Kemper, Kynette, Cheung, & Anagnopoulos, 1991). Keeping two (rather than one) word in temporary storage plus the high confusability of determiners when RC follows the second MC noun should lead to a reliable contrast and also to a larger difference between young and old adults. This contrast is significant if the difference between cells 1, 2, 3, 4 and cells 5, 6, 7, 8 of Table 1 is larger than zero. Clause congruency (X). MC and RC are called clause congruent if they are both subject or object clauses. MacWhinney (1999) argued that processing difficulties arise whenever one has to change perspective upon entering a new clause. In the present design this negative effect of perspective shift occurs for subject MCs and object RCs or vice versa. Conversely, processing should be easy, that is no perspective shift is involved, if clauses are congruent. The position of the relative clause is immaterial to this account. Therefore, a contrast between cells 1, 4, 5, 8 and cells 2, 3, 6, 7 in Table 1 captures this manipulation. This contrast corresponds to the interaction between MC initiality and RC initiality. RC modifies MC subject or MC object (Y). We can also speculate that qualifying an MC subject with a relative clause might be less difficult than qualifying an MC object given the default assignments sometimes assumed for sentence subjects. Feier and Gerstman (1980) did not find any age-differential effects but ceiling effects complicated the interpretation. In terms of cells of Table 1 this effect is captured by a contrast of cells 1, 2, 7, 8 and cells 3, 4, 5, 6. This contrast corresponds to the interaction between MC initiality and RC position. Role congruency (Z). In each sentence there is a noun carrying an RC. This noun has two roles which are congruent if the grammatical function is identical in MC and RC, that is if the noun is the subject or object in both clauses (e. g., in Sentence 1: "... der Senator, der ..."). Role incongruency refers to the two remaining constellations when the noun is the subject of the MC and the object of the RC or vice versa (e. g., in Sentence 2: "... der Dekan, den ..."). Role incongruency forces a switch in assignment of roles when the relative pronoun is processed. This switch might be costly in terms of processing but there is no obvious reason to expect that this processing should lead to differences in storage demand in working memory. From a recall perspective, role incongruency might set up a problem of discriminability. It should be difficult to remember whether der was the determiner and den the pronoun or vice versa. In contrast, for role

congruency the repetition of der or den may lead to a more solid representation of noun role. This effect is significant if the difference between cells 1, 4, 6, 7 and cells 2, 3, 5, 8 in Table 1 is different from zero. The contrast corresponds to the interaction between the three primary design factors MC initiality, RC initiality, and RC position at MC noun 1 versus MC noun 2. RC initiality x RC position (VW). There is one interaction in this 3-factorial design involving RC S/O initiality and the position of RC for which we could not derive an implicit interpretation as a main effect. Nevertheless, we can formulate an expectation based on the contributing main effects. If object RCs are more difficult than subject RCs and a late RC position more difficult than an early RC position a

152

reliable interaction indicates overadditivity or underadditivity of these two factors. If syntactic complexity scales in the expected direction we would expect overadditivity. Preliminary summary. There were three factors that determined the structure of our experimental sentences: MC initiality (coded as "U" in Table 2), RC initiality (V), and RC position (W). Instead of 3 main effects, 3 two-way interactions, and 1 three-way interaction, the conceptual interpretation of interactions led to a factorial design with 3 main effects, 3 implicit main effects and 1 two-way interaction. Implicit main effects such as congruency (Z) are different in that they are not crossed with traditional main effects. Thus, there is no interaction between "congruency" (Z) and "RC position" (W). However, implicit main effects are statistically independent of original design factors (i. e., they are orthogonal to the main effects). The complete list of ANOVA sources of variance for the nested design (see next section) of this experiment is given in the second column of Table 2. In column 3, one sees which traditional interactions can be interpreted as implicit main effects and interactions. Nesting Factors Of Syntactic Complexity Main clause questions versus relative clause questions (A). Inspection of interactions based on orthogonal contrasts may conceptually simplify interactions in an experimental design. To further reduce the complexity of the experimental design one can also specify factors or combinations of factors as nested under one of the experimental manipulations. Nesting is justified (or even called for) if a factor is not meaningfully crossed with other factors. In the present experimental design this applies to the factor that codes whether the question about the sentence focused the main clause (MC) or the relative clause (RC) because MC and RC parts are obviously of a very different structure (i. e., RC is embedded in MC but not vice versa). Therefore, the set of orthogonal contrasts introduced above was tested separately for MC and RC questions. Main effects and their interactions are tested for each of the levels of the nesting factor. In addition, the main effect associated with the nesting factor itself can be assessed (i. e., Are MC questions easier than RC questions?). One consequences of nesting is that the nesting factor can not interact with the factors nested under it. More troublesome is the substantial reduction in statistical power for nested effects because with a two-level nesting factor these are based on only half the experimental conditions. In terms of contrasts the fourfactorial design now comprises 13 main effects and 2 simple interactions which should be quite manageable. We now continue with the description of syntactic complexity effects embodied in the experimental design. Number of roles (B). The final a priori complexity manipulation of the experimental design was whether the question focused the noun with 1 role or the noun with 2 roles in the clause. Our expectation was that accuracy should be lower for the latter because more processing should be required in this case. In addition, from a processing-efficiency perspective, discriminability might be reduced in the two-role case (i. e., similar to a fan-2 condition, Anderson, 1974) and lower recall might be expected for this reason. This effect might be more pronounced for the RC

153

than the MC question because in the former case the target noun is "physically" part of the main clause and must be linked into the RC via the pronoun. Noun position (C). Number of roles (B) can interact with the six main effects (U to Z) and the one interaction (VW) described above. Again, we can check whether any of these interactions lend themselves to a simple conceptual interpretation. One positive example is the interaction between number of roles (B) and RC position (W). For an MC question this interaction translates into a difference between questions focusing the first noun of the MC and those focusing the second noun of the MC. We expected that overall the first noun might be easier to recall because it always enjoys a primacy position in the series of three sentence nouns whereas the second MC noun occurs equally often before and after the RC noun. The corresponding effect for RC questions is identical with the number-ofroles factor because the first RC noun is always the head of the noun-phrase/relativeclause construction (i. e., the one with two roles). Thus, for the RC question this interaction must be interpreted the "traditional" way if it bears out as a reliable source of variance. Active versus passive questions (agent vs. patient questions; D). The difference between active and passive questions (or between questions focusing the agent and questions focusing the patient) of a clause can also be recovered from interactions involving number of roles (B). Nesting effects under MC and RC questions proved helpful because the interactions corresponding to this implicit main effect differed for MC and RC questions. For MC questions, the effect of agent versus patient question is captured by the triple interaction of number of roles (B), MC initiality (U), and RC position (W). For RC questions this effect is reflected in the interaction of number of roles (B) and MC initiality (U). The belief that passive questions (or questions for the object of a clause) are more difficult than active questions (or questions for the subject) is widely held. Interestingly, empirical evidence is tied to rather specific conditions or even points in the opposite direction (see Carrithers, 1989, for a review). Note that as a consequence of the coding scheme an advantage of passive over active voice is reflected in a positive difference for MC questions and in a negative difference for RC questions (see Table 2). Nesting congruency within number of roles. Another example where nesting rather than crossing of factors is indicated relates to number of roles (B) and congruency (Z). If the 2-role noun is in the focus of the question, the effect of role congruency is assessed directly. If the 1-role noun is in the focus of the question (i. e., the isolated noun in MC or RC), the effect of role congruency is indirect only. Therefore, these two conditions are not orthogonal in a strict sense. Consequently, congruency (Z) was specified as nested under number of roles (B). In terms of the traditional full factorial ANOVA the direct and indirect effects of congruency replace the implicit main effects of congruency (i. e., the U x V x W interaction) and the interaction of congruency and number of roles (see Table 2). Other interactions. So far the respecification of interactions led to 20 main effects. Thus, there are 11 interactions to be accounted for. As can be seen from Table 2, all of these involve only two of the contrasts described. Moreover, as there are specific expectations of syntactic difficulty (at least tentatively) for all (implicit)

154

main effects, the generalization to these interactions is straightforward. In general, if an interaction were reliable, we would expect that the combination of two syntactically complex conditions might produce a lower level of comprehension accuracy than predicted by the additive "costs" associated with the (implicit) main effects. Summary. We identified 10 syntactic manipulations in this design which could reduce recall accuracy. Specifically, we expected lower accuracy for (1) object MC, (2) object RC, (3) late RC position, (4) perspective shift, (5) RC modifies MC object, (6) questions focusing the second MC noun, (7) passive questions (questions focusing the object of the clause), (8) questions focusing 2-role nouns, (9) direct incongruency (i. e., incongruency for questions focusing 2-role nouns), and (10) indirect incongruency (i. e., incongruency for questions focusing 1-role nouns). Moreover, each of these effects, except (6), is available for MC and for RC questions. The remaining contrasts reflect simple interactions among two of these ten contrasts. Systematic Relations In Old-Over-Young Plots We report new data from participants of the Kliegl et al. (1999) study who were asked to return for two additional sessions. They carried out the experimental task once more but there were two changes in the procedure. Specifically, instead of identical presentation times of 750 ms per word for both groups, presentation time was restricted to 375 ms per word for young adults. This reduction of presentation time for young adults reduced their overall accuracy from .71 to .67; old adults scored a bit higher (i. e., .55 compared .54). Also, as a secondary task, all participants had to detect four additional ungrammatical sentences in each block of 32. In ungrammatical sentences both MC nouns were preceded by the subject or the object determiner. The detection was difficult because in ungrammatical sentences the relative clause was always attached to the first MC noun. Overall, young adults detected 56% and old adults 20% of ungrammatical sentences. Thus, young adults' higher comprehension accuracy can not be explained by an age-differential trade-off between primary and secondary task. Moreover, it appeared that - at least for old adults - practice-related gains compensated for the additional demand to detect ungrammatical sentences such that overall level of performance was very much the same in both experiments. The critical and puzzling results of the original study which we plan to follow up in this chapter relate (1) to the contrast between subject and object MCs and (2) to the contrast between early and late RC position for MC questions. We expected larger age differences for object MCs and late RC positions. Both in Kliegl et al. (1999) and for the present data this was true for the first but not the second contrast despite the fact that both main effects were very strong (i. e., differences of .27 and .23 in the present experiment) and of similar size. The fact that the experimental paradigm is sensitive to grammatical manipulations is reflected in 12 significant contrasts of syntactic complexity; these are marked with an asterisk in column 6 (C) of Table 2. It is perhaps noteworthy that none of the seven significant contrasts related to RC questions interacted with age in the present study.

155

There were four significant interactions with age group (column 7, I, in Table 2). Three contrasts were significant only for old adults (i. e., BU, UW, and VW). These interactions were not reliable across experiments and will not be pursued here. One contrast was significant only for young adults (i. e., A in Table 2): Young adults were more accurate in answering MC than RC questions. This contrast was not significant in the initial study of Kliegl et al. One interaction with age was not replicated: Kliegl et al. reported a larger age difference for RC questions given a subject MC. This interaction reflected a benefit for young adults from an easy MC condition. The reduction of presentation time eliminated this benefit which brought about a lower RC accuracy for young adults, and, consequently, introduced the age x type of question interaction not seen in Experiment 1. In the following sections we present three analyses of comprehension accuracy to illustrate the potential of our respecification of the design in terms of orthogonal contrasts. In these analyses we always plot old adults' accuracies over young adults' accuracies from corresponding conditions. Systematic Relations Based On Syntactic Difficulty There were 32 experimental conditions (i. e., cells of the experimental design) for which old adults' comprehension accuracy can be plotted over that of young adults as shown in Figure 4. Verhaeghen and Marcoen (1993) used such a format for a metaanalysis of age differences in episodic memory. Data points are mostly below the main diagonal of the figure reflecting older adults' lower accuracy overall. Linear regression of old adults' means on young adults' means accounted for 63% of the variance. There are two perspectives one can take on such plots - one focuses the general pattern and the other one checks for outliers. The general pattern suggests that, as in the previous research examples reviewed in this chapter, we covered a wide range of task difficulty across experimental conditions varying from about .30 (chance) to .93. The intercept of the Figure 4. Old-over-young plot of means of 32 experimental conditions (i. e., cells of the regression line is design; R2 = .63; slope = 1.03, intercept = estimated at -.14 and -.14). indicates the overall

156

difference between old and young adults. The slope of 1.03 suggests that young and old adults responded in the same way to syntactic difficulty, that is age differences did not depend on the difficulty of the manipulation as indexed by young-adults' scores. An even slightly better fit (R2 = .69) and a slope of 1.00 was obtained for probit scores which take into account the change in variance across the probability range (i. e., probabilities are considered as areas under the standard normal distribution and converted to corresponding z-scores). In summary, there obviously was no evidence of a proportionate change in the age difference in response to overall task difficulty. The second perspective for such a plot is to look for outliers. In the present case, relative to approximately 95%-confidence intervals around the slope, there was one condition in which old adults performed clearly worse than young adults (see Figure 4). This outlier represents sentences with an object MC, an object RC, and an early (i. e., easy) RC position with questions focusing the isolated noun of the MC. Obviously, given the mixture of conditions involved, this is theoretically quite uninformative. Both groups performed best for the condition which was easy according to our coding of effects on all five design factors (i. e., subject MC, subject RC and easy RC position with a question about the isolated MC noun). Sentences leading to the second best score contained object RCs but were identical in all other aspects. Old adults found it most difficult to comprehend sentences of the type "object MC + subject RC + late RC position" in MC questions focusing either the 2-role noun or the 1-role noun. Note that these sentence types were not easy for young adults either. In general, these results are compatible with expectations but the conclusions we can draw from isolated cells of the design are rather limited. Moreover, although we described the extreme conditions in terms of the factors of the experimental design, the contrast coding introduced earlier, showed that interactions among these factors imply other meaningful contrasts as well (see Table 2). For example, the two most difficult conditions we just described were also clause incongruent, that is they required a perspective shift (object MC + subject RC). Finally, it is unclear what happened to the S/O MC x age interaction that was significant in the ANOVA. In summary, this type of analysis clearly does not exploit the power of the orthogonal design. Systematic Relations Based On Syntactic Complexity: Simple Versus Complex Conditions Of Orthogonal Contrasts The cells of the experimental design reflect combinations of theoretically motivated manipulations of syntactic complexity. Both the specification of orthogonal contrasts and the nesting of factors imply an averaging of cells for the computation of main effects and of effects associated with interactions. Each orthogonal contrast is based on a difference between two levels of syntactic complexity. Thus, for each contrast listed in Table 2, we can distinguish a syntactically simple and a syntactically complex condition. By plotting these means in old-young accuracy space (see Figure 5), we can check whether young adults' accuracy across the 31 contrasts of the present experiment is predictive of old adults' means and whether

157

different proportional factors (i. e., slopes) are associated with simple and complex conditions. The general pattern reveals that, as expected, (a) old adults performed worse than young adults (i. e., data cluster towards the lower right part of the figure), (b) accuracy in complex conditions (filled symbols) is lower than accuracy in simple conditions (open Figure 5. Old-over-young plot of 31 orthogonal symbols), and, without syntactically simple (open symbols) the four marked and 31 complex (filled symbols) outliers, (c) the data fall conditions (R2 = .39; slope = .30, along a common linear intercept = .34; w/o 4 outliers). regression line (R2 = .39; slope = .30, intercept = .34). Adding the distinction between simple and complex conditions as a predictor accounted for a marginally significant additional 4% of the variance ( p < .06) but the associated intercept difference between simple and complex conditions was estimated at only .01. A multiplicative interaction term testing the difference between slopes of simple and complex conditions was far from reliable. In summary, old adults' accuracies associated with simple and complex levels of syntactic complexity were predicted moderately well by young adults' scores. The strongest discrepancy between Figures 4 and 5 concerns the slopes. For cells of the experimental design the slope was 1.0 indicating a constant age difference across a wide range of difficulty of conditions. For levels of syntactic complexity the slope was .30 reflecting a proportionate increase of the age difference with increasing accuracy of young adults. Thus, in terms of error probability the old-young ratio was about 3: 1 for both simple and complex levels of syntactic complexity. In other words, there was no evidence for an age dissociation as reported, for example, for the distinction between sequential and coordinative complexity (see Figure 1; Mayr & Kliegl, 1993). Interestingly, however, three-toone is a large age-ratio, comparable in size to that observed for time demands in coordinatively complex tasks. As in the case of latencies such a proportional factor could be reflective of a general age difference cutting across a wide variety of manipulations of syntactic complexity or being indicative of a pervasive role of working memory in the present task. With enough statistical power specific interactions between age and syntactic complexity might have been inferred from age differences in condition means when indeed these effects could in principle be traced to a common source.

158

There is one caveat on this interpretation. The .30-slope of the present analysis can be interpreted as a proportional factor only if the intercept of the regression line passes through the x and y coordinates for chance performance (i. e., the [.33, .33]coordinate in the present case). This requirement was not met here. Rather, for a .33-score of young adults we obtain an unreasonably high score of .45 for old adults. Verhaeghen and Marcoen (1993) discuss problems associated with interpreting such old-over-young accuracy plots and suggest to fit quadratic functions or force the function through the origin. Neither of these proposals helped the interpretation in the present case but an analysis of probits suggested a solution. For probittransformed scores the regression line went through the origin (intercept = -.01) with a slope of .28 and an R2 of .39. The origin of probit space corresponds to the [SO, SO]-coordinate in probability space. As can be seen in Figure 5, the regression line for probabilities indeed also passes through this point, precisely at [.50, .49]. There were four outliers in Figure 5. They are of special theoretical relevance because they specify the effects for which we had expected a very high involvement of general working memory and, consequently, particularly large age differences. For simple conditions (open symbols) they represent subject MC and early RC position. These are the word orders of the experimental sentences for which we had predicted no or small working-memory involvement. In the context of the other conditions they were obviously associated with the highest accuracies for young and even more so for old adults. For complex conditions (filled symbols) the "partner" levels, that is object MC and late RC position, occurred as outliers in the opposite direction. Interestingly, however, their outlier status was only due to old adults' performance. For young adults both complex conditions were clearly within the range of the other scores. (To visualize this age difference imagine the data points as projected onto the y-axis or the x-axis of Figure 5 for old and young adults, respectively). This pattern strongly suggests that old adults dealt with complex sentences of the object MC and late RC position type in a different way than young adults. As displayed in Figure 5, there can be little doubt that they are responded to in a similar way - in contrast to what the absence of the ANOVA interaction for age and RC position suggests. Systematic Relations Based On Syntactic Complexity: MC Versus RC Questions The general pattern of Figure 5 suggested the absence of a difference between syntactically simple and complex conditions of orthogonal contrasts in proportionate space (i. e., a single regression line accounts for both types of complexity). However, simple and complex conditions are defined relative to a specific contrast. Consequently the simple level of one contrast could be more difficult (in terms of young adults' means) than the complex level of another contrast, as is obvious from the overlap of filled and unfilled symbols in Figure 5. Ideally, classification of condition means as simple and complex should be based on a syntactic principle that applies generally. One such alternative classification pertains to the distinction between MC and RC questions. This contrast is motivated by a potentially greater involvement of working-memory related processes during MC than RC processing

159

(i. e., MC processing is disrupted by RC processing but not vice versa) and is displayed in Figure 6. Except for the means of MC and RC questions which, of course, were not included here, the data are identical to those in Figure 5. The figure nicely reveals the age x type of question interaction which was significant in the ANOVA: For young adults conditions with MC questions are clearly Figure 6. Old-over-young plot of 30 means from answered more accurately than those with RC RC questions (open symbols; R2 = .68; questions whereas no such slope = .82, intercept = .02 ) and 30 means from MC questions (filled separation is visible for old adults. (Again, for a symbols; R2 = .68; slope = 1.24, visualization, imagine data intercept = -.33; w/o 4 outliers: R2 = .08; slope = .29, intercept = .34). points as projected onto the x-axis or the y-axis.) In two hierarchical multiple regression analyses (i. e., one with and one without four outliers) with (1) accuracy of young adults, (2) a dummy variable coding the MC versus RC question, and (3) a multiplicative term between the first two predictors all led to significant increments in amount of variance explained. Therefore, for both analyses the data are best described by separate regression lines for MC and RC questions. Coefficients after the third step are given in the figure legend. The results can be summarized as follows. First, for RC questions the slope of the function was .82 (which is not significantly different from 1.0) and the intercept .02. Thus, we might want to conclude that processing of RC questions is almost age invariant. Processing of the embedded RC clause is continuous and does not draw upon general working-memory resources. Second, if we remove the four outliers from of the analysis, the slope for MCquestions drops to .29 which is close to the 3:1 age-ratio observed for means used in orthogonal contrasts (see Figure 5). This interpretation is particularly attractive because it suggests that MC clause processing invokes processes similar in demands to what we called coordinatively complex tasks (see Figure 1). This is not implausible given that MC clause processing is suspended during RC processing and this may require executive demands to organize a chain of interdependent processing operations which is how we defined coordinative complexity earlier in the chapter.

160

Third, there is the issue of how to interpret the outliers. And we see two possible perspectives which are clearly in need of experimental corroboration. The first one assumes that the gaps between the bulk of data and the outliers above and below it could be filled with additional condition means, the second one assumes the outliers to be just that - evidence for disproportionate effects of aging due to particular processes required in these conditions. The continuum perspective suggests to include outliers in the hierarchical regression analysis. In this case, MCquestions means fall along an even steeper linear slope than the one observed for RC questions. As indicated by the dashed line in Figure 6, the slope was 1.24 and significantly larger than the .82-slope for RC questions. Additional data might also reveal that RC and MC questions both follow a unit-slope regression line with MCquestion conditions displaced to the right of the main diagonal, a pattern analogous to the one in Figure 4. The perspective of treating outliers as outliers could start from the assumption that the two "simple" outliers (i. e., subject MC and early RC position) are actually part of the RC-question regression line. Thus, under these default MC conditions RC processing might not invoke executive demands. Consequently, according to this scenario and consistent with reasoning presented by Kliegl et al. (1999) and earlier in this chapter, only the "complex" outliers (i. e., object MC and late RC position) are disproportionately affected by age. We can not offer a theoretical mechanism that would account for the transitions from age invariance to proportionate age effects of the coordinatively complex kind to disproportionate age effects. More importantly, it would be highly desirable to replicate this taxonomy of dissociations which was not obtained in the first experiment with this participants reported by Kliegl et al. (1999). Discussion The main message of this section is that if comprehension accuracy is assessed across a large range of syntactic complexity effects, language-specific effects of cognitive aging almost appear to play a game of now you see us and now you don't. We examined three types of proportionate effects in old-young space in addition to absolute differences in ANOVA contrasts. First, for experimental conditions (i. e, the 32 design cells) the slope relating old adults' means to those of young adults was 1.03 but displaced to the right of the main diagonal suggesting a main and constant effect of age across a wide range of syntactic difficulty (Figure 4). Second, for means derived from the orthogonal contrasts of the experimental design the slope was .30 suggesting that age differences increase proportionally with syntactic complexity and are similar in size reported for tasks with coordinative processing demands (Figure 5). This trend was general in the sense that it was observed both for simple and complex syntactic conditions. In addition, specific age differences were associated with two contrasts, MC S/O initiality and RC position. Third, for the same data, RC questions appeared as almost age invariant whereas MC questions elicited a varied picture of age differences (Figure 6). The background for these observations, analyses and exploratory speculations was a respecification of a fivefactorial psycholinguistic design with 32 conditions in terms of 20 interpretable

161

simple contrasts of syntactic complexities and 11 simple interactions all of which were orthogonal to each other. In summary, a joint consideration of absolute and proportionate effects suggested some syntax-specific age invariance against a background of general effects of cognitive difficulty, most likely reflecting coordinative demands in executive control processes. Verhaeghen (in press) pointed out that the underlying nonlinearity of processing time-demand and accuracy may lead to false negative conclusions about theoretically valid interactions involving age. The difficulty of documenting the age sensitivity of late RC position in an ANOVA contrast may well be an example of this kind. There was no indication of an interaction in the ANOVA but a clear clustering of means associated with this contrast. Means associated with the contrast on subject/object initiality of main clauses (for which interactions with age were obtained in the ANOVA) and for early and late RC positions (for which the interaction with age was clearly not significant in the ANOVA) were similar to each other and clearly distinct from other conditions in old-over-young plot (see Figures 5 and 6). Most importantly, old-over-young probability plots can be interpreted as originating in time-accuracy functions such as the ones presented for mental arithmetic earlier (see Figure 2). It is conceivable that differences in comprehension accuracies are a reflection of differences in demand for internal processing time and that the different types of syntactic complexities are driven by a few dissociable mechanisms. Verhaeghen (in press) showed for the general case that an old-overyoung plot of accuracies such as the one reported in Figure 5 or the one obtained for MC questions without outliers in Figure 6 can be derived from time-accuracy functions for young and old adults with different slopes. The pattern for MC questions including outliers in Figure 6 is compatible with an age difference in the asymptote. Finally, a pattern such as the one displayed in Figure 4 can be derived from time-accuracy functions that differ both in onset and asymptote. Consequently, the determination of complete time-accuracy functions for critical syntactic complexity manipulations may allow us to rule out some of the alternative interpretations offered above. There are some qualifications of the present experiment and analyses. First, the dependent measure was comprehension accuracy which is a classical off-line measure of sentence processing. On-line measures such as self-paced reading times or eye-fixation durations might be more sensitive to some of the syntactic manipulations. Of course, the analysis framework transfers without problems to these dependent variables. Second, inference-statistical aspects analyses reported in this section assume independence of observations which was clearly not the case. Consequently, standard errors associated with intercepts and slopes are not exact. However, intercepts and slopes themselves are correct descriptive summary statements. Moreover, one should note that the strongest criticism addressed to such analyses of old-over-young plots refers to the fact that frequently data are aggregated across experiments without specifying experiment as a nesting factor (Sliwinski & Hall, 1998). Obviously, this was not a problem for the single experiment reported here. Finally, there are some discrepancies between Kliegl et al. (1999) and the present experiment (based on the same participants) which

162

probably can not be resolved without additional research. Most importantly, in oldover-young plots of the data from the first experiment MC S/O-initiality and RC position did not occupy the outlier position seen here. Perhaps the secondary task (i. e., checking for ungrammatical sentences) added a critical amount of demand for executive control for the effects to appear - even though the overall level of performance was not affected very much. In general, however, the ensemble of analyses presented here should prove useful for delineating language-specific and general cognitive effects in other settings as well. DELINEATING LANGUAGE AND COGNITIVE PROCESSES

In this final section we will briefly review some general issues that were touched upon in this chapter. They relate to the two main classes of language processes we examined, lexical access and syntactic complexity, to age simulation and to the need to unconfound task difficulty and task complexity. Lexical Access Two results stand out. First, unspecific task difficulty appears to be a poor guide to age effects in language-related tasks. Especially, in semantic access and retrieval times the difficulty of the task did not interact with age. Almost to the contrary, the age invariance observed across levels of task difficulty could serve as an ideal baseline in cognitive aging research against which age effects in other domains of cognition can be assessed. This proposal is similar to the current practice of reporting age invariance in measures of vocabulary or crystallized intelligence. It goes beyond this practice in requiring the invariance across a wide range of task difficulty. Second, manipulations of task complexity taxing the access capacity of working memory or executive control processes lead to reliable age differences but these effects appear to be weaker than the disproportionate dissociations between age and task complexity found for non-lexical tasks. The reason may be that working memory has a privileged access to practiced and overlearned lexical information in contrast to the mostly novel and non-familiar information that has to be handled in non-lexical tasks. Clearly, this speculation needs more work. Syntactic Complexity And Processing Efficiency Two results should be highlighted here as well. First, there is striking contrast between plotting experimental conditions in old-over-young fashion with a unit slope indicating no proportional age differences and the .30-slope for a similar plot based on contrasts of the experimental design. The former would be compatible with age invariance as found for lexical tasks; the latter is similar to the proportional factor reported for coodinatively complex tasks suggesting a heavy involvement of working memory or executive control. Second, object-initial main clauses and late relative clauses constituted particularly high processing problems for old adults. This was expected and relates well to the assumption that for very difficult syntactic constructions general resources of working memory must be allocated for successful

163

processing. In the analyses of orthogonal contrasts the interaction with age was significant only for the MC S/O initiality. In other words, the weak status of working memory in this line of research was initially corroborated by the fact that there was no hint of any interaction between age and the position of the relative clause in the main clause although both main effects were as strong as expected. Fortunately, the outlier analyses resolved this discrepancy and revealed the similarity between MC S/O initiality and RC position as well as their special status relative to the other grammatical manipulations. Obviously, more research is needed to corroborate this interpretation which emerged in the context of a set of exploratory analyses. Age Simulation The divergence of results was counter to our expectations and remains puzzling. In ongoing research we are testing whether these results can be reconciled in an age simulation (Baltes & Goulet, 1971; Baltes, Reese, & Nesselroade, 1977). Initial results suggest that across a wide range of reliable effects of syntactic complexity (such as those listed in Table 2), main effects of age and age x complexity interactions can be made to disappear by age simulation of young adults. With less time per word young adults' profile traces that of old adults with remarkable precision and only a few exceptions. Particular noteworthy is the fact that there is no monotonous rescaling of the dependent variable that could achieve the same result (Kliegl et al., 1999). Moreover, a 3-digits memory load for young adults also equated both age groups in overall performance. In this case, however, the age x complexity interactions were preserved (Junker, Oberauer, & Kliegl, 1999). On the assumption that these preliminary reports hold up under further tests, one might want to conclude that syntax-related age differences can be explained more easily with reference to proposals of age-related slowing than proposals of age-related decline in working memory resources. It is not clear how these results will be reconciled with the varied pattern of age dissociations reported in the last section. Unconfounding Task Complexity And Task Difficulty It has almost become customary in cognitive aging research to relate age differences in any domain to slowing, reduced working memory capacity or inhibitory deficits. One common problem has been the confound of task difficulty and task complexity. The present chapter has argued for approaches in which for a given level of theoretical complexity (e. g., sequential vs. coordinative conditions; no-switch versus switch conditions; subject-initial versus object-initial main and relative clauses) task difficulty is varied across a wide range. In other words, we propose to always have task difficulty nested as a factor within levels of task complexity in experimental settings. Mapping out time-accuracy functions or search-depth functions or unpacking interactions of multifactor experimental designs appear to lead to consistent and clearly delineated domains of cognitive functioning with quite distinct age-related characteristics. We consider these approaches as very attractive alternatives to the customary statistical-control techniques for which serious

164

interpretational problems have been raised in recent years (Kliegl & Mayr, 1992; Lindenberger & Potter, 1998). CONCLUSION

We believe the methodological proposals in this chapter can help focus theoretical controversies about the role of age in the processing of language. Of course (unfortunately), the experimental paradigms we propose do not substitute for good theory. Especially in the case of syntactic complexity, we apparently are only at the beginning of understanding the interplay of language-related and general cognitive mechanisms such as working memory or processing rate. Models tracing age differences to some form of general resource deficiency were based on data from experimental paradigms that frequently confounded task difficulty with task complexity. We are optimistic that experimental control of unspecific task difficulty is like removing a veil under which effects linked to theoretical notions of processing complexity will appear in a clear view.

165

REFERENCES

Anderson, J. R. (1974). Retrieval of propositional information from long-term memory. Cognitive Psychology, 6, 451-474. Bäckman, L., & Nilsson, L.-G. (1996). Semantic memory functioning across the adult life span. European Psychologist, 1, 27-33. Balota, D. A., & Duchek, J. M. (1988). Age-related differences in lexical access, spreading activation, and simple pronunciation. Psychology and Aging, 3, 8493. Baltes, P. B., & Goulet, L. R. (1971). Exploration of developmental variables by manipulation and simulation of age differences in behavior. Human Development, 14, 149-170. Baltes, P. B., Reese, H. W., & Nesselroade, J. R. (1977). Life-span developmental psychology: Introduction to research methods. Monterey, CA: Brooks Cole. Brinley, J. F. (1965). Cognitive sets, speed and accuracy of performance in the elderly. In A. T. Welford & J. E. Birren (Eds.), Behavior, aging, and the nervous system (pp. 114-149). Springfield, IL: Charles C. Thomas. Caplan, D., & Waters, G. S. (1998). Verbal working memory and sentence comprehension. Behavioral and Brain Sciences. Carrithers, J. (1989). Syntactic complexity does not necessarily make sentences harder to understand. Journal of Psycholinguistic Research, 18, 75-88. Cerrella, J. (1985). Information processing rates in the elderly. Psychological Bulletin, 98, 67-83. Cerella, J. (1990) Aging and information processing rate. In J. E. Birren & K. W. Schaie (Eds.), Handbook of the psychology of aging (pp. 201-221). San Diego: Academic Press. Charness, N., & Campbell, J. D. (1988). Acquiring skill at mental arithmetic in adulthood. Journal ofExperimental Psychology, General, 11 7, 115-129. Feier, C. D., & Gerstman, L. (1980). Sentence comprehension abilities throughout the adult life span. Journal of Gerontology, 35, 722-728. Fitzgerald, J. M. (1983). A developmental study of recall from natural categories. Developmental Psychology, 19, 9-14.Ford (1983) Frazier, L. (1987). Syntactic processing: Evidence from Dutch. Natural Language and Linguistic Theory, 5, 519-559. Geary, D. C., Frensch, P. A., & Wiley, J. G. (1993). Simple and complex subtraction: Strategy choice, and speed-of-processing differences in young and elderly adults. Psychology and Aging, 8, 242-256. Junker, M., Oberauer, K., & Kliegl, R. (1999). Age simulation of syntactic complexity effects with a working memory load. Manuscript in preparation. Kemper, S. (1986). Imitation of complex syntactic constructions by elderly adults. Applied Psycholinguistics, 7, 277-288. Kemper, S. (1992). Language and aging. In F. I. M. Craik & T. A. Salthouse (Eds.), Handbook of aging and cognition (pp. 213-270). Hillsdale, NJ: Erlbaum. Kliegl, R., Fanselow, G., Schlesewsky, M., & Oberauer, K. (1999). Age Simulation of Syntactic Complexity Effects with Manipulations of Presentation Rate. Manuscript submitted for publication.

166

Kliegl, R., & Mayr, U. (1992). Commentary. Human Development, 35, 343-349. Kliegl, R., Mayr, U., & Krampe, R. T. (1994). Time-accuracy functions for determining process and person differences: an application to cognitive aging. Cognitive Psychology, 26, 134-164. Krems, J. (1984). Erwartungsgeleitete Sprachverarbeitung [Language processing guided by expectations.] Frankfurt: Lang. Laver, G. D., & Burke, D. M. (1993). Why do semantic priming effects increase in old age? A meta-analysis. Psychology and Aging, 8, 34-43. Lima, S. & Hale, S., & Myerson, J. (1991). How general is general slowing? Evidence from the lexical domain. Psychology and Aging, 6, 416-425. Lindenberger, U., & Potter, U. (1998). The complex nature of unique and shared effects in hierarchical linear regression: Implications for developmental psychology. Psychological Methods, 3, 218-230. MacWhinney, B. (1987). The Competition Model. In B. MacWhinney (Ed.), Mechanisms of language acquisition, . Hillsdale: NJ: Erlbaum. MacWhinney, B. (1999) The emergence of language from embodiment. In B. MacWhinney (Ed.), The emergence of language. Mahwah, NJ: Lawrence Erlbaum. MacWhinney, B., & Pleh, C. (1988). The processing of restrictive relative clauses in Hungarian. Cognition, 29, 95-141. Mayr, U., & Kliegl, R. (1993). Sequential and coordinative complexity: Age-based processing limitations in figural transformations. Journal of Experimental Psychology: Learning, Memory, and Cognition, 19, 1297-1320. Mayr, U., & Kliegl, R. (1998). Complex semantic processing in old age: Does it stay or does it go? Manuscript submitted for publication. Mayr, U., & Kliegl, R. (1993). Sequential and coordinative complexity: Age-based processing limitations in figural transformations. Journal of Experimental Psychology: Learning, Memory, and Cognition, 19, 1297-1320. Mayr, U., Kliegl, R., & Krampe, R. T. (1996). Sequential and coordinative processing dynamics in figural transformations across the life span. Cognition, 59, 61-90. Moscovitch, M. (1994). Cognitive resources and dual-task interference effects at retrieval in normal people: The role of the frontal lobes and medial temporal cortex. Neuropsychology, 8, 524-534. Norman, S., Kemper, S., Kynette, D., Cheung, H., & Anagnopoulus, C. (1991). Syntactic complexity and adults' running memory span. Journal of Gerontology: Psychological Sciences, 46, 346-351. Pechmann, T., Uszkoreit, H., Engelkamp, J., & Zerbst, D. (1994). Word order in the German middle field (Report 43): Computational Linguistics at the University of the Saarland. Rochon, E., Waters, G. S., & Caplan, D. (1994). Sentence comprehension in patients with Alzheimer's Disease. Brain & Language, 46, 329-349. Rösler, F., Pechmann, T., Streb, J., Röder, B. & Henninghausen, E. (1998). Parsing of sentences in a language with varying word order: Word-by-word variations of processing demands are revealed by event-related brain potentials. Journal of Memory and Language, 38, 150-176.

167

Salthouse, T. A. (1985). A theory of cognitive aging. Amsterdam: North Holland Publ. Salthouse, T. A., & Coon, V. E. (1994). Interpretation of differential deficits: The case of aging and mental arithmetic. Journal of Experimental Psychology: Learning, Memory, and Cognition, 20, 1172-1182. Schlesewsky, Fanselow, Kliegl, & Krems (in press). Preferences for grammatical functions in the processing of locally ambiguous wh-questions in German. B. Hemforth & L. Konieczny (Eds.), Cognitive parsing of German. Dordrecht: Kluwer. Sliwinski, M. J., & Hall, C. B. (1998). Constraints on general slowing: A metaanalysis using hierarchical linear models. Psychology and Aging, 13, 164-175. Troyer, A., Moscovitch, M., & Winocur, G. (1997). Clustering and switching as two components of verbal fluency: Evidence from younger and older healthy adults. Neuropsychology, 11, 138-146. Verhaeghen, P. (in press). The parallels in beauty's brow: Time-accuracy functions and their implications for cognitive aging theories. In T. Perfect & E. Maylor (Eds.), Theoretical debate in cognitive aging. Oxford: Oxford University Press. Verhaeghen, P., Kliegl, R., & Mayr, U. (1997). Sequential and coordinative complexity in time-accuracy functions for mental arithmetic. Psychology and Aging, 12, 555-564. Verhaeghen, P., & Marcoen, A. (1993). Memory aging as a general phenomenon: Episodic recall of old adults is a function of episodic recall of young adults. Psychology and Aging, 8, 380-388. Waters, G. S., Caplan, D., & Rochon, E. (1995). Processing resources and sentence comprehension in patients with Alzheimer's Disease. Cognitive Neuropsychology, 12, 1-30. West, R. L. (1996). An application of prefrontal cortex functioning theory to cognitive aging. Psychological Bulletin, 120, 272-292.

168

ACKNOWLEDGMENTS

This research was supported by a grant of the German Research Foundation (DFG; INK 12/A1; Projects "Control and representation of sequential behavior" and "Syntax and Working Memory"). We thank Ina Hockl, Susan Kemper, Klaus Oberauer, Matthias Schlesewsky, and Peter Staudacher for many very helpful discussions. Address for correspondence: Reinhold Kliegl, Department of Psychology, University of Potsdam, PO Box 60 15 53, D-14415 Potsdam, Germany. E-mail: [email protected].

Part 3

CONSTRAINTS ON LANGUAGE: GRAMMAR

This page intentionally left blank.

7P

DIFFICULTY AND PRINCIPLES OF GRAMMAR

ROCESSING

Gisbert Fanselow, Reinhold Kliegl, and Matthias Schlesewsky

INTRODUCTION

Some words are more difficult to pronounce than others, and, similarly, some sentence types are harder to process thanothers. Such processing differences are due to properties of the human parser, and these may be responsible for certain laws of natural language syntax. This is not a new idea; it is a key concept in linguistic typology. This chapter investigates the merits of the proposal that two core principles of current generative syntax, namely the principle that syntactic movement is costly, and the principle that the costs ofmovement are proportional to the distance covered (Chomsky 1995), can be explained in terms of processing theory. The chapter is not the first attempt of relating abstract syntactic laws to processing facts (cf., e.g., Marcus, 1980, Staudacher, 1993), but for such an approachtobesuccessful, severalrequirements mustbemet: •

assumptions concerning processing difficulty must be justified independently

•

the full range of empirical facts of syntax must be captured, and,

•

the approach must be explicit about the link between processing difficulty and syntactic laws.

After introducing the facts to be explained, this chapter makes a few principled but obvious remarks on the last aspect, to which we return in the final section. The third section sketches the general line ofthe argument. The fourth section introduces evidence forthe claim that movement is cognitively costly, and discusses processing models that predict such costs. Particular attention is given to approaches involving memory load. The fifth section tries to assess to what extent the two key laws of syntax introduced above can be derived from such processing considerations. The 171

172

paper reports work in progress, so some of the points presently depend more on plausibility arguments than on "hard core data". The conclusion we will arrive at is somewhat different from the one we originally found plausible. We still believe that the processing facts are compatible with the view that processing shapes grammar, but there are too many gaps in the grammaticalization account for it to be likely to be true. PROCESSING

AND

SYNTAX: A SURPRISING SIMILARITY

Processes by which words or phrases are moved from their canonical position to another belong to the inventory of operations in many, if not all, natural languages. Thus, in English, direct objects of verbs typically appear in a postverbal position (la), but in a constituent question, a wh-object needs to be fronted, as in (1b/b'). (1) a. b. b.'

he saw it he saw what (guess) what he saw t

In on-line processing, local ambiguities involving the grammatical function of such fronted wh-phrases arise frequently. Thus, clause initial what may turn out to be the direct object of a matrix clause (as in (2a)), the complement of a prepositional phrase (as in (2b)), or the subject of a complement clause (as in (2c)). (2) a. b. C.

what did you sing t what did you sing a song about t what did you believe t convinced him

As was shown by Stowe (1986), among others, the human parser has clear preferences in this domain, which have been described successfully in terms of trace theory. At least according to certain parsing theories (see Pickering & Barry, 1991 for a different view), the processing of constituent questions involves the reconstruction of the relation between the actual position of the wh-phrase and its canonical (pre-movement) position, assumed to be filled by a "trace" (represented by "t" in (2)) in many grammatical models (Chomsky, 1981). Parsing preferences in the case of local ambiguities involving the grammatical function of wh-phrases are correctly predicted by the assumption that the parser follows an "Active Filler Strategy" (Clifton & Frazier, 1989), which implies that the parser tries to keep the distance between the moved phrase and the canonical position as short as possible. (3) Active Filler Strategy (AFS, non-canonical fomulation) Ceteris paribus, the parser prefers structure S over structure T if the distance between the wh-phrase and its trace is shorter in S than it is in T. The AFS predicts standard processing asymmetries for English questions (see Frazier & Clifton 1989), and seems to be responsible for the subject preference in

173

locally ambiguous wh-phrases established experimentally, e.g., for Dutch (Frazier & Flores d'Arcais, 1989), Italian (de Vincenzi, 1991), and German (Meng, 1997, Schlesewsky, Fanselow, Kliegl, & Krems, in press). Consider (4). (4) a. welche Frau hat t den Mann eingeladen woman has theacc man invited whichambiguous (wh=subject = preferred) "which woman has invited the man?" b. welche Frau hat der Mann t eingeladen woman has thenom man invited whichambiguous (wh=object = dispreferred) "which woman has the man invited?" The grammatical function of the wh-phrase in (4) is not determined by its morphology. The studies mentioned above report evidence that the subject interpretation is preferred by the human parser. This is in line with the AFS: German is a subjectobject-verb-language underlyingly, so the distance between the wh-phrase and its trace t is shorter in (4a) than it is in (4b), as one can read off the representations easily. The AFS is thus a well-supported parsing strategy. Quite surprisingly, grammar obeys a principle similar to AFS in similar contexts: it involves a "superiority" condition (Chomsky, 1973) or a Minimal Link Condition (MLC) (Chomsky ,1995). The AFS expresses a preference for shorter links when there is no clear evidence about the pre-movement position of a phrase. The MLC requires that only the shorter link be formed when two phrases might undergo movement, that is, when there also is a "local ambiguity" of rule application. Thus, the grammar of English requires that exactly one wh-phrase is fronted in a constituent question. If the sentence hosts two wh-phrases, only the one that is closer to the landing site may move, as (5) - (6) illustrate. (6) is particularly telling since it also illustrates a subject-object asymmetry. The observations in (5) and (6) can be reduced to a principle such as (7). (5) a. b. C.

you persuade who to say what who did you persuade t to say what *what did you persuade who to say t

(6) a. b. C.

you expect who to do what who do you expect t to do what *what do you expect who to do t

(7) Minimal Link Condition (MLC, non-canonical fomulation) Ceteris paribus, the grammar accepts structure S and rejects structure T if the distance between a moved phrase and its trace is shorter in S than in T.

174

From the perspective of grammar, the most interesting question about (7) is what is meant by ceteris paribus, but for this chapter, the parallel between the grammar and the parser implicit in (3)/(7) is the most important aspect: whenever the constitution of a chain between a moved element and a trace is not uniquely determined, the parser and the grammar prefer to (re-)construct the shortest chain. Such similarities call for an explanation, and logically, there are three possibilities: principles of grammar might shape the way the parser operates, it may be the other way round, and, finally, the shape of the grammar and of the parser might be influenced indirectly in the same way by a third causal factor. The first alternative is discussed in detail in Fanselow, Schlesewsky, & Kliegl (1998), while the second is in focus in this chapter. A few remarks on potential third factors can be found below and in the other work just mentioned. PROCESSING

AND

SYNTAX: HOW LINKS

CAN BE

CREATED

That the form of a grammar is partially determined by processing difficulty is an old idea, but the two domains need a mediator: some sentences are difficult to process but grammatical - multiply center-embedded relative clauses such as (8) are cases in point. Some sentences are easy to process yet ungrammatical - as so-called thattrace-violations (9). Such observations suggest that there is a difference between the grammar and the parser, and that the causal connection between grammaticality and processing difficulty has to be an indirect one. (8) the man the dog the cat the mouse feared chased bit consulted a doctor (9) *who do you think that t loves Mary This indirect link is "grammaticalization" (cf., e.g., Hawkins, 1994 for suggestions): By a syntactic change, a process that is unlikely (or difficult) at a given stage in the history of a language is ruled out (ungrammatical) at later stages. Furthermore, there is a consensus that grammars change mainly because they have to be acquired by children. Children do not have direct access to the grammar used by the adult world, rather, they reconstruct a grammar appropriate for their linguistic input. The result need not be identical with the adult model. If there is a likelihood above 0.5 that changes they introduce go in one direction rather than the other, and if languages have gone through a sufficient number of acquisitional cycles (as they have), it is likely that most (or all) languages end up possessing a certain property P. Thus, any factor making certain changes even slightly more likely than others can shape grammars quite substantially. Suppose now that processing difficulty plays a significant role in language acquisition. That children replace a difficult option by a simpler one rather than the other way round may be taken to be a default assumption. Thus, processing difficulty may determine the direction syntactic changes take. After a sufficient number of acquisitional cycles, processing difficulty can thus have had a substantial impact on the form of grammar in natural languages.

175

However, this reasoning involves two assumptions that need not be correct. First, it has to be shown that constructions that are hard to process for adults are difficult for children, too (and vice versa) - grammaticalization implies that children's (and not adult's) difficulties are frozen into grammar. Probably, the overlap in processing difficulty between adults and children is substantial, so that this potential problem does not endanger the enterprise. This may be different for the other presupposition: it is not an established fact that the syntactic changes introduced by children simplify the grammatical system in a processing -cognitive grammatical sense. As Hale (1998) has pointed out recently, syntactic change may be sporadic, and the direction it takes may be accidental. If this is correct, grammaticalization explanations are in trouble. See below for some remarks. THE COSTS

OF

MOVEMENT

The parallel between the parser and the grammar considered above can be due to a causal link between the two domains. An argument in favor of this view involves at least the following steps: (a) we must establish that movement has a cognitive cost proportional to the length of the path independently of syntax specific heuristic parsing strategies (this section) (b) we must show that what characterizes the parser is sufficiently close to what holds for grammar (We do not need to assume that their laws are identical, however, because the laws of grammaticalization may, e.g., force a form of grammar that does not mirror processing ease in certain subdomains). (c) one needs to be explicit about how grammaticalization works in the domain under consideration. We concentrate on the first issue in this section. Our argument begins with the observation that the human parser prefers syntactic analyses that involve shorter movement links whenever there is a local ambiguity for the grammatical function/ the pre-movement position of a moved wh-phrase. If this behavior of the parser is due to an irreducible heuristic strategy for ambiguity resolution, it is hard to see how it could influence the grammar of a language. What needs to be shown (or made plausible) is that longer movement paths are cognitively more costly in general (not just in the case of an ambiguity), and that this can be linked to the costly nature of movement in terms of grammar. Frazier (1987:548) speculates that subject-object asymmetries as in (4) may be due to the greater complexity of object-initial clauses. According to her, the moved item must be "held in a special memory buffer [...] for longer than is necessary" for the subject initial case. Under this perspective, the validity of her Active Filler Hypothesis (see above) derives from the assumption that the parser minimizes

176

cognitive costs in the case of an ambiguity, if the costs of a structure are related to the amount of time for which moved items are kept in memory. The assumption that the AFS reduces to a processing time difference between the two competing structural hypotheses is related to the idea of "race-based" parsing: the faster structural alternative inhibits the computation of the slower ones, a fact that is relevant for our discussion if cognitive load is inversely related to processing speed. The assumptions concerning items held in memory in different construction types follow if a moved item must be kept in memory up to the point at which the pre-movement position can be integrated into the parse tree - which can be done earlier for subjects than for objects. This approach predicts that the additional cognitive load of object initial structures is visible in unambiguous clauses, too. If it is costly to hold a moved item in memory, costs should show up irrespective of whether there is an additional local ambiguity. That this is true is suggested by findings of King & Just (1991), according to which English object-initial relative clauses are harder to process than subject-initial ones. Somewhat clearer evidence can be found in Krems (1984), a study establishing that total reading times are lower for subject initial declaratives (such as (10a)) than for their object initial counterparts (such as (10b)) even when overt case morphology leaves no room for (relevant) local ambiguities. (10)a. b.

der Mann sah den Fisch thenom man saw theacc fish den Fisch sah der Mann theacc fish saw thenom man "the man saw the fish"

As Schlesewsky, Fanselow, & Kliegl (submitted) point out, subject-objectasymmetries in declarative (and relative) clauses are difficult to interpret because factors independent of movement (pragmatic preferences, etc.) may favor subject initiality. Such extrasyntactic factors play no role in the processing of constituent questions. Therefore, we carried out a set of experiments reported in the article just cited which studied the processing of German constituent question and which are summarized below because they shed some light on the costs of movement. Consider the abstract clausal grids (11) for German embedded questions: (11) a. wh-phrasenominative adverb-1 adverb-2 object verb b. wh-phraseaccusative adverb- 1 adverb-2 subject verb c. "whether" adverb-1 adverb-2 subject object verb As in English, complement questions can begin with a wh-phrase (11a-b) or with a question complementizer meaning "whether". This initial element can be followed by adverbs, which in turn may be followed by the subject, the object, or both (depending on what appeared in clause initial position). A series of reading experiments comparing reading times for these (and similar) structures yielded the following results, which are also partially visible in Experiment 1 introduced below (see the appendix).

177

a.

Reading times for unambiguous clause initial wh-phrases are longer for object-initial questions. Since subject initial questions are not favored pragmatically, the object-initiality disadvantage in questions is a genuine formal effect.

b. A naming task (see Schlesewsky et al., submitted) showed that the access time of a wh-determiner is shorter if it allows a nominative (subject) interpretation (among others) than if it allows object interpretations only. Thus, it cannot be excluded that the reading time difference introduced in [a] is partially due to a difference in lexical access times. c. However, the reading time advantage for subject-initial questions continues to be visible on the two adverbs following the initial wh-phrase. The effect was always statistically significant for the first adverb, and was so for the second adverb in some experiments, too - high variances in reading times on the second adverb position may have blurred effects sometimes. It is not likely (Schlesewsky et al., submitted) that the object-initiality effect visible on the two adverbs is a spillover of a lexical access problem in the sense of [B]. Therefore, there are additional costs of object-initiality. One might suspect that this additional cost is due to a problem in the processing of sentences in which the subject comes late (as is the case for (11b), as compared to (11a)). That such an interpretation is not unlikely follows from the following observations: d. Comparing the reading times of subject-initial questions (1 la) with those of "whether-initial'' questions (such as (11c), in which the subject also comes late), one observes that reading times in the subject initial condition are shorter for the two adverbs. Since no movement is involved in (11c), we conclude that structures with late subjects are difficult per se - because of the position of the subject. e.

However, a comparison of reading times for the object-initial condition (11b) with the "whether"-condition (11c) reveals a further contrast: reading times for the adverb are longer in the object-initial case. Since (11b) and (11c) share the property of having a late subject, this processing difference must be due to yet another factor - that an object is preposed in (11b), but not in (11c) is the only obvious difference.

Taking a. - e. together, two conclusions may be drawn: the additional costs of object initial structures might be caused by a variety of factors, and lexical access and the difficulty of structures with late subjects come into play. But there is also an apparently irreducible cost unit incurred by object fronting itself. It is possible that

178

this pure object-fronting penalty can be explained along the lines suggested by Frazier (1987). Note that the effect disappears as soon as the subject is encountered. German is (underlyingly) a subject-object-verb language, and adverb positions are fairly free. The first position in a German wh-clause at which the trace of a subject wh-phrase can be postulated thus follows the wh-phrase itself (12) a. wh-subject [tsubject adverb adverb object verb] The object trace needs to follow the subject, though, because all objects do (unless they change position due to processes that need not concern us): (12) b. wh-object [adverb adverb subject tobject verb] Thus, the pure object-initiality-disadvantage disappears when the category immediately preceding the first legal slot for the trace of wh-movement (the category immediately preceding the object's canonical position, if you prefer) is encountered. If parsing is strictly incremental, this means that the object-initiality disadvantage disappears as soon as a position has been reached (viz. the subject) which allows the postulation of the object trace and its integration into the parse tree without violating strict left-to-right incrementality. Arguably, the wh-phrase cannot be removed from memory unless its trace/its canonical position has been reached in incremental left-to-right parsing. The results of our experiments suggest, then, that additional processing time is necessary as long as a wh-phrase is kept in memory. In this sense, movement, a process creating the need of storing phrases up to their canonical position, is costly as such. There is a cognitive cost of movement, and the time for which the additional cost arises is proportional to the distance between the moved phrase and the trace. This is a nice result for the general point pursued in this chapter: All current generative models, the Minimalist Program (Chomsky, 1995) and Optimality Theory (Grimshaw, 1997) take movement to be costly in grammatical terms, in the following sense: phrases must not be moved - unless there are more important factors forcing it. The relation between cognitive and grammatical costs of movement is indirect, however. This is related to, but not identical with, the observation discussed above that grammaticalization must mediate between processing difficulty and grammar. Our results suggest that wh-movement of question phrases is cognitively costly. There is little empirical reason to believe that, say, the movement of a verb from one position to another (as motivated for the grammars of French (Emonds, 1978) and German (Bach, 1962; Thiersch, 1978) creates a cognitive load. We are thus far from having established that movement is cognitively costly as such. The mediating role of grammaticalization may be helpful here, and in a further respect. The notions of "closeness" or "distance" in grammar are hierarchical: they involve relations such as c-command that make crucial reference to an elaborate structural representation. It remains to be shown (and may be false) that the notion

179

of distance relevant for the parser is purely structural as well, and that it is identical with the one used by grammar. This does not, however, necessarily endanger the enterprise of deriving properties of grammar from properties of the parser. Processing difficulty has to be grammaticalized. This grammaticalization is triggered by processing difficulty, but its results must fall within what is expressible in terms of grammar. Suppose, then, (as most linguists do) that there are substantial restrictions on the terms and relations that can appear in a grammar (or, rather, in its mental representation) - restrictions that are independent of processing difficulty. Thus, in most if not all approaches to grammar, linear distance does not play role at all. We may thus assume that "linear distance" is not a concept that could appear in a grammar. If the triggering factor involves linear distance, this must be translated into something that makes sense within a grammar: hierarchical relations such as c-command among elements in a structural representation. Anything related to linear distance that ends up being grammaticalized is necessarily translated into a concept involving hierarchical, structural notions of grammar. Even if the AFS crucially involves differences in linear distance (which we do not know), grammaticalization may translate this into the structural relations underlying the MLC. In this context, then, it need not concern us too much whether the details of the AFS and the MLC are identical. This may be different for the grammaticalization of the costs of movement in terms of a ban against unmotivated movement. After all, grammar seems to make a distinction between verb movement and wh-movement, so it is unclear why costs of wh-movement could not be grammaticalized in a form affecting wh-movement only, and nothing else. On the one hand, the grammaticalization process itself might be constrained in a way that prevents specific principles like "Don't move wh-phrases" from arising. On the other hand, it is not obvious at all that there are movement operations other than wh-movement. Verb movement is incompatible with a number of fundamental assumptions of Chomsky (1995), so severel stipulations were necessary to allow the operations. Verb movement is thus not well-founded. Similarly, changes in the theory of thematic roles as proposed in Fanselow (submitted) may make so-called NP-movement superfluous as well. DOES

IT HAVE TO BE

MEMORY COSTS? AND

IF SO, WHAT TYPE OF MEMORY?

Before we proceed, the role of the recourse to memory load should be clarified, and we should be more explicit about what is understood by "memory". One observation suggests that the "memory component" used above cannot be identified with working memory in a cognitive psychology sense. The work of Kemper and colleagues (Kernper, 1992; Norman et al., 1991) has demonstrated an age effect on linguistic performance that can be explained in terms of a reduced capacity of the working memory. If a working memory load is responsible for the additional costs of object-initial clauses, one expects a specific age effect for object initial structures. In Experiment 1 described in the appendix, we confronted young and old adults with sentence material with the structure of (11), that is, we tested for possible age effects on the parameters 'early versus late subject' and object-initiality. Although there was a significant main effect of age (old adults'

180

reading times are longer), no interaction between age and any of the syntactic factors emerged. The results of Experiment 1 suggest that there is no particular age effect on object-initiality. If the "memory component" causing the costs of movement would be working memory, such an effect should have been visible. Of course, the absence of an effect does not prove a lot, but the results of Experiment 1 are in line with studies described in detail in Kliegl, Fanselow, Schlesewsky & Oberauer (1998), see also Kliegl et al. (this volume). In these studies, accuracy of comprehension was tested for main clauses that contained a single relative clause embedding. There was a significant age by object-initiality interaction, but just for main clause scrambling (different in theoretical terms from wh-fronting), and not for relative clauses (close to wh-fronting in theoretical terms -- but there was an insignificant tendency for an age effect). In follow-up research, Junker, Oberauer & Kliegl (in prep.) show that the age by complexity interaction did not disappear when young adults had to carry out a secondary memory related task (as one would expect if working memory was crucial), but it did so when presentation time was reduced for young adults. Thus, one may at least conclude that the ageing studies have not produced evidence for the idea that working memory in a standard sense is involved in the processing of object-initial structure. If this is correct, the claim that recourse to a syntax-specific memory buffer is costly for the parser is not supported independently. THE FREQUENCY ALTERNATIVE

Since the cognitive costs of movement are not likely to be caused by a load on working memory, it is worth while to also consider a further alternative to the idea that there is a special syntactic working memory (not affected by ageing). This alternative to syntax-based accounts of object-initiality is a clause-type frequency explanation. In particular in the light of the many successes of the so-called tuning hypothesis (Cuetos & Mitchell, 1988), it seems reasonable that processing speed is related to type frequency in the case of syntactic configurations as well. Versions of such approaches which ignore factors different from individual type frequency face the problem of identifying an appropriate level of classification once and for all. Thus, object-initial which-questions seem to be more frequent than their subject initial counterparts (Schlesewsky et al., in press), while subject-initial wh-questions seem to be at least as frequent as object initial questions in general (Schlesewsky et al., in press; Meng , 1997). Furthermore, given the heavy bias in favor of subject initial declaratives (9:1), the total number of structures that are object initial (disregarding further differences) is much smaller than the totality of subject-initial clauses. Thus, it seems that any experimental result in this domain might find a frequency explanation. In more sophisticated approaches as used in connectionist models, processing ease is not only determined by the frequency of individual cases, since "neighboring" similar structures are also activated. Type frequencies in these neighbor domains therefore play a role as well, in particular if they show a clearer pattern. Thus, MacDonald (1998) argues that the object-initiality disadvantage for relative clauses may be due to the high frequency of neighboring 'regular" subject-initial

181

declaratives. In connectionist systems, the level of classification issue thus disappears. We expect even subject initial which-questions to be easier than object initial ones, due to the strong similarity of the former with the canonical and top frequent standard declarative clause. There is little psycholinguistic evidence that refutes a theory in which frequency and similarity to regular structures account for processing difficulty: the easier alternatives are (in most cases) the more frequent ones, or the ones most similar to top frequent standard types. This is not the fault of the approach: facts of language could have been different. Suppose, for example, that language L has a subject-verb object base order, but that a conspiracy of further constraints forces the preposing of objects in, say, 90 percent of the cases. Connectionist systems and symbol-manipulating grammatical approaches now make different predictions: ceteris paribus, there is no reason for why the subject-initial structure should be easy to parse in the former approaches, while the latter should predict an object-initiality penalty due to the need of keeping preposed objects in memory. The particular example is not likely to arise, but there is a less exotic case: German is a verb-final language underlyingly (this word order shows up in complement clauses), and the finite verb obligatorily moves to second position in main clauses. From a grammatical point of view, embedded clauses should thus be simpler than main clauses (because they involve one movement operation less) while a connectionist model would predict that it is just the other way around (because main clauses are more frequent). We have no evidence that decides the issue (and recall verb movement may turn out to be non-existent), but in principle, a comparison of the two constructions could settle the debate. While overall results are compatible with experience based accounts, one might claim they do not provide an explanation for the internal structure of processing difficulty effects. This may be false, too. It is by no means established that what matters for processing in experience based models is unanalyzable clause patterns. Note that a segment of a clause may itself bear resemblance to a (top frequent) clause pattern. Thus, the object initial sequence (13) resembles the top frequent subject initial pattern from the fourth word on - recall that the object initiality effect disappears when the subject was encountered. (13) wh-object adverb adverb subject .... verb The latter observation already leads to the central point: in a sense, experience based connectionist models may be able to predict "costs of movement", too. Suppose =... . .... ... is the canonical top frequent pattern. Suppose furthermore has been fronted so that = ... ... .... ... arises. The reasoning proposed above implies that should be more difficult than , up to the point when we reach . The two models differ, of course, substantially for certain configurations, but we doubt that data have been collected already that allow a decision between the two approaches. Thus, there is a connectionist alternative to our memory based model that could be correct, but if so, this does not affect the major point we wish to discuss, viz., the likelihood of the parser shaping the form of the grammar.

182

THE θ -PREDICTION ALTERNATIVE

The experimental findings discussed so far may be related to yet another parsing approach. Suppose a clause c is subject-initial, C need not contain an object - after all, the clause could be intransitive. If the human parser reacts in a conservative way, that is, if it tries to make as few commitments as possible in terms of the number of arguments in the clause, it will initially take subject-initial structures to be intransitive - up to the point when there is evidence to the contrary. If the structure is object-initial, however, it must immediately be processed as being transitive, in order to have a chance to be grammatical at all. Suppose that the human parser is conservative, and suppose that it is costly in cognitive terms to keep unlinked argumental expressions or unlinked argument slots of verbs in memory (or to pass pertinent information through the parse tree). Under such premises, longer reading times for object initial clauses are predicted again. Consider (14) in this respect. (14)

α....β.... V

If α=subject and β=object, the parser operates with one unlinked argument expression (viz.α) up to the point when it encounters β, and thus finds out that the structure is transitive, that is, that it involves two arguments rather than one. If α=object, two arguments must be assumed from the beginning of the clause on. We thus expect subject initial clauses to be faster to process up to the point when the second noun phrase is encountered - and this is what we found in our experiments. Models based on predictions concerning argument roles and expressions (and the costs of not having them linked) are thus in line with the experimental evidence discussed so far. See Gibson, Hickok & Schutze (1994) for this approach. As in the case of the connectionist alternative, it may be pointed out that a grammaticalization pattern might arise in response to parsing difficulty as defined by number of unlinked thematic roles that is not much different from what it would be in the memory theory of the costs of movement. The preposing of creates a difficulty because it will bring costs of (unlinked) argumental expression earlier to bear - as long as movement goes to the left. Consider, however, a sentence type of German exemplified in (15). The examples in (15) involve "long" movement of a wh-phrase out of a complement clause. This complement clause lacks a complementizer, so according to the laws of German syntax, the verb must be preposed to the position that would otherwise be filled by the complementizer (see e.g., Grewendorf, 1988; Staudacher, 1990). (15) a. welcher Mann denkst Du kennt den Professor whichnom man think you knows theacc professor "which man do you think knows the professor?" b. welchen Mann denkst Du kennt der Professor whichacc man think you knows thenom professor "which man do you think the professor knows?"

183

The particular composition of the examples in (15) involves a further aspect. The wh-phrase is immediately followed by the main clause verb in (15). This verb makes it clear that the wh-phrase has undergone long movement: In (15a), the nominative wh-phrase is third person singular, while the verb bears explicit secondperson morphology - but subjects and verbs have to agree in German. Verbs do not agree with objects in German, but they govern case. The verb denken "think" used in (15) is incompatible with an (animate) accusative noun phrase object, so the case clash rules out a matrix object interpretation in (15b). The memory and the O-role account of object initiality effects make different predictions concerning readings times for these structures. In the memory theory, one expects longer reading times for the initial whphrase in the case of (15b): after all, the structure is object initial. The verb following this noun phrase rules out the prediction that the wh-phrase is a matrix constituent in both cases. Given that the parser processes the matrix clause when it copes with the verb, it needs to keep both the wh-subject and the wh-object in memory. Thus, reading times should not differ between (15a) and (15b) for the second element (the matrix verb) and the third element (the matrix subject). The two conditions have a chance of differing in terms of reading times only from the fourth segment (=the complement verb) on - when the complement clause is encountered, the subject may be dropped from memory earlier than the object (see above). Predictions are different in accounts taking recourse to -theory. The number of unlinked arguments/thematic roles that a conservative parser assumes in the presence of a clause initial nominative and accusative noun phrase, respectively, is independent of whether this prediction is formulated for the matrix clause or for a complement clause. Thus, the reinterpreation of the wh-phrase as a complement clause constituent that the parser carries out when it is forced by the verb to do so does not affect these predictions. To be more precise, the case difference of the initial wh-phrase in (15) implies that one -role/argument is expected when the first element is parsed in (15a), but that two such -roles/arguments are expected in (15b). When a matrix verb like denkst is encountered, the parser realizes that the matrix clause has two thematic roles (a subject and a clausal complement), and it now expects one additional -role/argument for the complement clause for (15a), but two such roles for (15b). Thus, the difference in the number or predicted arguments/ -roles is stable (in contrast to the memory account) between the two conditions, it is just shifted to the complement clause. Only when the complement clause verb kennt is encountered is there a chance for the difference to disappear. The difference in load predictions between the two main approaches can thus be summarized as in Table 1:

184

Table 1. Different predictions of the two theories.

The shaded areas in Table 1 mark the segments of the sentences in (15) for which one expects to see a reading time difference between the subject initial and the object initial condition in the two theories. The experiments 2 - 4 described in the appendix show a clear result: there are reading time differences between the two crucial conditions for segments (a) and (d), but not for the other segments. In this respect, the predictions of the cost of memory theory seem to be borne out, in contrast to what holds for the unsaturated -role approach. DOES

THE GRAMMAR CARE?

The preceding sections have summarized some evidence supporting the view that movement is costly in cognitive terms. It is therefore conceivable that a process of grammaticalization has shaped the form of grammars so that they respond to such costs. In this context, the surprising parallel between the grammar and the parser discussed in the initial part of the chapter could find an explanation. Do grammars really care for costs of movement? They specify a (violable) ban against movement, and a Minimal Link Condition. Let us, however, be more explicit about the former aspect. Both minimalist approaches (Chomsky 1995) and Optimality Theory (Grimshaw, 1997) assume that movement should be avoided. In the relevant domain of wh-questions, languages should be like Japanese: there is no movement to clause-initial position in complement questions: (16) John-ga dare-o butta ka sirinai Johnnom whoacc hit Q know not "I don't know who John hit"

185

Obviously, Japanese does not represent a universal pattern. After all, whphrases are fronted to clause initial position in English (17). Languages such as English might simply have been too lax in responding to processing demands, or there might be other demands that English meets. A consideration of Chinese (18) suggests a candidate for such further demands. (17) what did you say t? (18) Zhangsan zhidao she mai-le shu Z know who buy-Asp book "Zhangsan knows who bought books" "who does Zhangsan know bought books" Chinese lacks wh-movement and obligatory scope marking for question phrases. Therefore, (18) is ambiguous: the sentences can be understood as a declarative with an embedded indirect question, or as a question with an embedded declarative complement clause. In contrast, wh-movement in (19) serves the purpose of what Cheng (1997) calls "clausal typing": movement (a) identifies the type of the clause (declarative vs. question) and (b) indicates the scope of the wh-phrase. (19) a. who do you know that she likes b. you know who she likes We have to assume, then, that grammars of natural language do not only respond to cognitive costs of movement (if they do at all) - there are other requirements that have to be met if possible and that may override costs of movement. This in itself does not endanger the project of deriving grammar from processing costs, but the factor counteracting cognitive simplicity must be identified. Note that neither (a) nor (b) can force movement as such, because clausal type can be indicated without movement (as in Japanese (16)), and the same is possible for scope, as constructions with scope markers such as Hindi kyaa may show. (20) a. Raam-ne kyaa socaa ki ravi-ne kyaa kahaa ki kon sa aadmii aayaa thaa Raam-erg what thinks that Ravi-erg what said that which man came? "which man does Rama think that Ravi said came?" b. Raam-ne kyaa socaa ki ravi-ne kon sa aadmii kahaa ki aayaa thaa c. Raam-ne kon sa aadmii socaa ki ravi-ne kahaa ki aayaa thaa If (a) and (b) can be met without movement, and if movement is cognitively costly, it is unclear why movement is tolerated when processing difficulty is grammaticalized. This problem disappears, however, if (only if?) e.g., both [I] and [II] hold; that is, if the scope marking strategy employed in Hindi (20a,b) itself involves cognitive costs, perhaps comparable to the costs of movement.

186

[I] Movement is cognitively costly [II] A construction is cognitively costly if the syntactic scope of does not correspond to its semantic scope.

in

Obviously, the only way to respond to both processing demands (if II is correct at all) at the same time (that is, the only way to eat the cake and keep it) is to restrict question formation to subject questions - in which the wh-phrase does not move to the clause initial position indicating its scope, because it already occupies this slot in the base structure. This option seems to characterize Kwakwala (Anderson, 1984). Here, the scope of the wh-phrase is identical with its semantic scope without creating movement costs - but the price Kwakwala pays is considerable - the language has to provide many grammatical function changing operations such as passive and apply them a considerable number of times, because one still must be able to ask: what do you want? (by saying: what is wanted by you?). Typically, languages rather decide which of [I] and [II] they attribute more weight to - [I] and [II] are two processing demands that cannot be met simultaneously. Reference to two different factors that try to pull grammar in two different directions reduces the attractivity of the processing explanation for grammatical principles substantially, however: recourse to processing difficulty can now simply be dropped. A language has to "decide" whether it indicates the scope of wh-phrases explicitly or not, and if so, which means it uses for this. If it opts for the latter, it uses what languages always use when something (grammatical function, focussing, topicality) must be marked: morphological means or positional ones. The domain of options seems restricted by the laws of grammar, and it seems that all options do the job equally well. If this picture is correct, processing considerations might come into play in a very indirect way only: if all possibilities are costly in cognitive terms, processing does not restrict the grammars' choice. We will leave it open here whether this is substantially different with the Minimal Link Condition. Chomsky (1995) takes it to be an inviolable constraint of grammar, but there is some evidence (see, e.g., Müller, 1998) that it can be overriden by quite diverse other types of considerations. IS

THE

GRAMMAR

ABLE TO

CARE?

One additional problem, at least in terms of the empirical foundation of an attempt to derive grammatical costs of movement from processing costs, lies in our complete ignorance of the mechanisms by which languages acquire or lose movement for constituent questions in their history. Ian Roberts (p.c.) suggests that languages acquire the obligatory fronting of wh-words in questions as a re-interpretation of the (less obligatory) preposing of focussed material, in the sense that wh-phrases represent the focus of a question. Historical linguists are less willing to speculate on how language lose whmovement (the crucial part of the grammaticalization explanation), so we have to offer a speculation of our own. If Anoop Mahajan (p.c.) is correct, certain languages

187

like Hindi allow the preposing of topicalized material in front of a preposed whphrase in questions. Suppose a language L both has obligatory wh-fronting and optional fronting of topicalized material to the left of wh-phrases. Then structures such as (21) can arise. (21) [topic: subject, [wh-object2 [t-1 t-2 verb]]] But the phonetic sequence of (21) allows an analysis without movement as well. This analysis is false for language L (recall that wh-phrases have to be moved), but if the topicalization option is chosen frequently enough, and in conversation with children, the children might not have enough evidence for constructing the more complex structure (21) instead of the simpler alternative (22). By this, the language loseswh-movement. (22) subject-object verb If this account of the loss of wh-movement is correct, the processing explanation of the grammatical costs of movement faces two problems: the grammaticalization of the ban against wh-movement in the history of a language presupposes that a language allows massive movement options in the stage immediately preceding the breakdown of the movement analysis. In other words, prior to the loss of wh-movement, children would have to go in exactly the opposite direction of what processing difficulty would predict. And note that the final step in the process does not make any reference to processing difficulty at all: the crucial point rather is that the language ceases to offer clear evidence for the application of movement. Things might even be worse. Studies on the acquisition of wh-movement by children learning English or German reveal that children may omit auxiliary inversion or delete the wh-phrase in early acquisitional stages - they do not try to leave a wh-phrase in situ instead of moving it. In languages like French which appear to allow a choice between a movement and an in situ strategy for question formation, the preferences of the children are clear: they begin forming wh-question by moving the wh-element (Weissenborn, 1993). CONCLUSIONS

The grammar and the parser (understood as a system of strategies and rules for on line syntax processing) resemble each other in many domains. In this paper, we have considered one particular kind of similarity, the costs of movement. Movement can be shown to be costly in cognitive terms, and it is tempting to make such cognitive costs responsible for corresponding aspects of the grammatical system. Such grammaticalization accounts may seem plausible at first glance, but they presuppose the validity of a number of assumptions that may very well be false:

188

(a) In general, it has not been shown so far that processing difficulty plays a decisive role in determining the direction of syntactic changes that shape the overall properties of natural language grammars in the long run. (b) It is not clear whether the cognitive costs of movement are not compensated for by other cognitive costs that arise in structures in which semantic and syntactic scope do not go hand in hand. If so, the "balance of powers" may simply ensure that syntactic change in the domain of question formation can go in any direction. (c) It is not clear whether the actual path of syntactic change in the domain of constituent question formation follows the lines predicted by a processing optimization account. It thus seems mandatory to look for other ways of explaining parallels between the grammar and the parser.

189

APPENDIX: FOUR EXPERIMENTAL STUDIES

This appendix presents the results of four experimental studies which complement experiments we have reported elsewhere but which are crucial for certain of the points we wish to make. EXPERIMENT 1: THE

PROCESSING OF WH-QUESTIONS IN OLD AND YOUNG ADULTS

With one exception, the constructional aspects of Experiment 1 are identical with those in one study reported in Schlesewsky et al. (submitted). While the experiments reported there focus on establishing a syntactic object initiality effect, the purpose of Experiment 1 was to control for a possible interaction of age and object-initiality. Method Subjects. Thirty two subjects participated in the experiment: sixteen young adults (mean age: 20) and sixteen old adults (mean age: 69). They were native speakers of German. They had not participated in any previous psycholinguistic experiment, and were not familiar with the purpose of the study. They were paid for participation. Procedure. Subjects read the experimental material in a self-paced reading study with non-stationary presentation and phrase by phrase retrieval. The segments for phrasewise retrieval are indicated in Table 2. Sentences ended with a punctuation mark. After the presentation of the punctuation mark, the participants had to carry out a sentence matching task. By pressing a "yes"- or a "no"-button, subjects had to decide whether a control sentence was a verbatim repetition of the preceding sentence. The control manipulation did not involve the proper analysis of the grammatical function of the initial wh-phrase: a negation or an adverb could be missing or be added, or a noun could have been changed. Material. The experimental items were sentences of the type represented abstractly in (11). They consisted of a main clause followed by an indirect "who"question (nominative or accusative initial) or an indirect whether question, see also (23). (23) es ist egal "it does not matter" a. wer vermutlich glücklicherweise den Mann erkannte theacc man recognized whonom presumably fortunately b. wen vermutlich glücklicherweise der Mann erkannte thenom man recognized whoacc presumably fortunately c. ob vermutlich glücklicherweise der Mann den Dekan erkannte whether presumably fortunately thenom man theacc dean recognized The wh-phrase was followed by two sentential adverbs, which may precede or follow subjects in German. These were in turn followed by a noun phrase explicitly marked for the complementary grammatical function. In the experimental items for

190

the "whether/if" condition, the wh-complementizer was followed by the adverbs, the subject and the object, in that order. There were thus three experimental conditions in the experimental material: subject-initial, object-initial, “whether”-initial. The participants read five experimental items per condition, and were never confronted with two members belonging to a single pair. There were 140 distractor items not involving material analyzable as crucial for the contrast between the two conditions. The segmentation for self-paced reading is given in Table 2. Results The data of one participant had to be excluded from the analysis because of the high error rates in the control task. Table 2 summarizes mean reading times in msec. and accuracy in the sentence matching task in percent. Table 2. Results of Experiment 1: All participants

191

Table 3 summarizes mean reading times for young adults, while Table 4 does so for old adults. There was a main effect of age on reading times ( F(1,30)= 12.25, p <.01), but no interaction of age by position.

Table 3. Results of Experiment 1: young adults (n=16)

Table 4. Results of Experiment 1: old adults (n=15)

Discussion The overall reading time pattern found in Experiment 1 is roughly identical with the findings reported in Schlesewsky et al. (submitted): there is a significant reading time difference between the object and the subject initial condition, that may be blurred on the initial segment (=1) of the embedded clause and the second adverb (=segment 3), for the reasons discussed in the work just mentioned. The experiment fails to show an interaction of age and object-initiality, and would therefore not support the view that the memory necessary for the storage of wh-phrases should be identified with standard working memory.

192

EXPERIMENT 2: LONG

MOVEMENT FROM VERB-SECOND COMPLEMENTS

Experiment 2 is the first of a series of studies that tries to decide between the two major (non-frequency) accounts of the subject initiality advantage discussed above: the idea that wh-phrases have to be memorized in a costly way versus the idea that the number of unlinked but predicted (bearers of) thematic roles is the primary cost factor. Table 1 above summarizes the respective predictions of the two theories for an experiment measuring reading times for verb second complement clauses like (15). Method Subjects. Thirty students of the University of Potsdam participated in the experiment. They were native speakers of German. They were neither familiar with the purpose of the study, nor had they participated in any previous reading time experiment. They were paid for participation or received credits. Procedure. We employed the self-paced reading technique introduced above. Material. The experimental items had the overall structure given in (24), and could appear in one of the four conditions described below. (24) a. welcher Mann denkst Du kennt den Professor whichnom man think you knows theacc professor "which man do you think knows the professor?" b. welchen Mann denkst Du kennt der Professor whichacc man think you knows thenom professor "which man do you think the professor knows?" c. welcher Mann hast Du gedacht kennt den Professor whichnom man have you thought knows theacc professor "which man have you thought knows the professor?" d. welchen Mann hast Du gedacht kennt der Professor whichacc man have you thought knows thenom professor "which man do you think the professor knows?" All clauses began with a singular masculine "which"-wh-phrase, the morphology of which unambiguously indicated nominative or accusative case (subject- vs. object-initial condition). The second noun phrase in the complement clause was also morphologically unambiguous. The material was constructed in such a way that the agreement morphology of the matrix verb excluded an analysis in which an initial nominative noun phrase could be the subject of the main clause. That the wh-phrase has undergone long movement out of a complement clause was therefore always indicated unambiguously by the verb in the case of nominative initial noun phrases. The situation is different for object initial questions. The main clauses could either have a simple (24a,b) or a complex tense (24c,d) (simple vs. complex condition). We selected such matrix main verbs for the experimental material that do not accept an accusative object, so that a lexical verb following the wh-phrase immediately forces a long movement analysis of the wh-phrases in the case of

193

simple matrix clauses. In complex matrix clauses, the auxiliary haben "have" is locally compatible with a transitive matrix verb, so that the need for a long movement analysis becomes clear only at the point when the verbal participle is encountered. The experimental material ended with a prepositional phrase. There were seven items per experimental condition, and 118 distractor clauses. The segmentation for phrase-wise presentation is indicated in Table 5. Results Table 5 summarizes mean reading times in msec. and accuracy of comprehension in percent. A repeated measures ANOVA showed that there was a significant reading time difference on the first segment (=the wh-phrase) between subject and object initial questions, the former being read faster ( F1(1,29)=9.73, p<.01, F2(1,7)=8.90, p<.05). The fifth segment (=the complement verb) was read faster in subject initial sentences than in object initial ones ( F1(1,29)=5.41, p<.05, F2(1,7)=9.87, p<.01) and faster in simple matrix clauses than in complex ones, but the latter effect was significant in the subject analysis only ( F1(1,29)=11.85, p<.01). A comparable effect concerning the simple versus complex condition was found on the sixth segment (F1(1,29)=36.37, p<.01). There were no significant effects for the second and the fourth segment. Reading times were faster on the third segment in the simple matrix condition, but the effect reached significance in the subject analysis only ( F 1(1,29)=20.81, p<.01). An analysis confined to reading times for the complex matrix condition showed a marginally significant reading time advantage for object-initial questions on segment 2 (=auxiliary), but in the subject analysis only (F1(1,29)=3.01), p<.1). No effects on segment 4 (=participle) approached significance. The interaction between the two position was, however, significant in the subject analysis (F1(1,29)=5.49, p<.03). A simple ANOVA revealed a significant main effect for accuracy ( F(3,587)=3.76, p<.01), a post hoc Scheffe test showed this to be due to a difference in the condition simple matrix clause. Discussion The major result of Experiment 2 consists of an object initiality effect that appears on exactly two segments: the wh-phrase and the verb of the embedded clause. The higher reading times on the initial wh-phrase in the object initial condition come as no surprise. Furthermore, there is no object initiality effect on segments 2, 3, and 4, that is, on segments belonging to the matrix clause and to which the wh-phrase is not related thematically. This is not in line with a model which takes the number of predicted but unlinked (bearers of) thematic roles to be predictors of processing difficulty, because the initial difference between two versus one predicted thematic roles is not eliminated but just shifted to the complement clause on segments 2 to 4. On the other hand, the results correspond to what the memory theory would lead one to expect. The interaction between the reading times of segment 2 (auxiliary) and segment 4 (verbal participle) in the complex matrix clause condition reflects the pattern we expected from the relevant aspects in the construction of the experimental material. Recall that in complex matrix clauses the finite auxiliary forces the correct

194

long movement analysis for nominative wh-phrases only (due to a person/number mismatch), while the auxiliary is compatible with an interpretation of the initial accusative wh-phrase as the direct object of the main clause. Both the interaction between the two positions and the marginally significant reading time advantage of object initial questions on segment 2 suggest that there is an early reanalysis effect

Table 5. Results of Experiment 2

for nominative initial questions (the assignment of the role of subject of the matrix clause must be retracted), but not for object initial questions in the complex matrix condition. This pattern is expected if the participants start out with an analysis in which the wh-phrases have not been moved out of a complement clauses, an assumption that is in line with the Active Filler Strategy. The reading time difference between the subject and the object initial condition reappears on segment 5, that is, as soon as the participants begin with the processing of the complement clause. As we have argued above, this is again not in line with the predictions of the unlinked theta-role model, but compatible with expectations that can be linked to the memory theory. This reading pattern was replicated in two further studies.

195

EXPERIMENT 3: POSSIBLE

ANIMACY

EFFECTS

IN

THE

PROCESSING

OF

WH-

QUESTIONS

Method Subjects. Forty-two students of the University of Potsdam participated in the experiment. They were native speakers of German. They were neither familiar with the purpose of the study, nor had they participated in the previous experiment, or any other reading time experiment related to our purposes. They were paid for participation or received credits. Material. The method was identical with the one applied in the previous experiment. The experimental items had the overall structure given in (24a-b), that is, the initial wh-phrase could either bear nominative or accusative morphology, and all matrix clauses appeared with a simple tense form. In addition to the subject versus object condition, the animacy of the initial wh-phrase was systematically varied. We confined ourselves to three experimental items for all of the four experimental conditions (subject vs. object x [±animate]). All other aspects were kept as in the preceding experiment. There were 138 distractor items. Results Table 6 summarizes mean reading times for the segments in Table 1 in msec. and accuracy of comprehension. A repeated measures ANOVA of reading times showed an effect in the interaction of position and the subject-object condition that was significant in the subject and marginally significant in the item analysis (F1(5,205) = 8.94, MSe = 27802, p <.01; F2(5,85) = 2.14, MSe = 46568, p<.07). Sentences beginning with a subject wh-phrase were read faster than object initial questions independent of animacy. Reading time differences between subject and object-initial questions were significant on segment 1 (F1(1,41) = 25.59, MSe = 26881, p <.01, F2(1,17) = 11,68, MSe = 28620, p <.01) and on segment 4 (F1 (1,41) = 13.65, MSe = 38272, p<.01, F2 (1,17) = 6.93, MSe = 42846, p<.05). No other effects reached the level of significance, in particular, no animacy effect could be detected. Discussion Experiment 3 replicated the results of Experiment 2: subject initial questions are processed faster than object initial questions, an effect that shows up both on the morphologically unambiguous wh-phrase and on the verb in the Comp position of the complement clause. In this respect, Experiment 3 is in line with the memory theory of the object initiality effect, but fails to bear out the prediction of a model working with unlinked thematic roles. Experiment 3 also shows that the animacy cue does not contribute to this finding. Animacy has no effect on the processing of the wh-structures under consideration.

196

Table 6. Results of Experiment 3

Experiment 4: Possible frequency effects in the processing of whquestions

Method Subjects. Thirty-eight high school students of a grammar school in Potsdam participated in the experiment, all aged 18 and above. They were native speakers of German. They were neither familiar with the purpose of the study, nor had they participated in any previous psycholinguistic experiment. They were paid for participation. Material. We used the self-paced reading time technique described above. The experimental items had the overall structure given in (24a-b). In addition to the subject versus object condition of the preceding experiments, the following condition was added: the noun of the initial wh-phrase could either be a high frequency lexical item (such as Lehrer "teacher") or a low frequency lexical item (such as Oologe "egg researcher"). The experimental material was constructed in the following way: a pair of a high frequency and a low frequency noun was assigned to each complement clause verb, such that the high frequency item could appear either in the wh-phrase and the low-frequency item in the NE' remaining in the complement clause, or vice versa, and the grammatical function as expressed by case morphology was also systematically varied. There were seven items per condition and 102 distractor items.

197

Results The data of one subject had to be excluded from the analysis, because he/she failed to obey the instructions. Table 7 summarizes mean reading times for the segments in (3) in msec. A repeated measures ANOVA showed there was a significant reading time difference between the subject and the object condition on segment 1 (F1(1,36) = 29.44, MSe = 103,828.012, p <.001, F2 (1,25) = 18,42, MSe = 114,045.31, p <. 001) and on segment 4 (F1(1,36) = 15.62, MSe= 15,344.32, p <.001, F2(1,25) = 5.15, MSe = 39.464.87, p<.05), which were read faster in the subject-initial condition. Reading time difference reached significance in the high versus lowfrequency condition on segment 1 (F1(1,36)=158.22, MSe=142,339.36, p<.001, F2(1,25)=83.11, MSe=194,017.13, p<.001) and segment 5 (F1(1,36)=79.65, MSe=202,054.07, p<.001, F2(1,25)=45.58, MSe=238,963.07, p<.001). No other effects reached the level of significance.

Table 7. Results of Experiment 4

Discussion With respect to the subject-object condition, Experiment 4 replicated the results of the preceding two experiments: there is a stable advantage in reading times for subject-initial structures showing up on the wh-phrase and on the complement verb. The pattern strongly supports the memory explanation of the object initiality disadvantage, and is not compatible with the predictions of an approach that takes the number of unlinked (bearers of) thematic roles to be crucial.

198

With respect to the high versus low-frequency condition, Experiment 4 yielded results that would be expected under nearly any theory of lexical access: reading times were higher for NPs containing a low-frequency noun, irrespective of the structural position in which this NP shows up. This frequency effect cannot, however, be detected on the verb of the complement clause.

199

REFERENCES

Anderson, S. (1984). Kwakwala Syntax and the Government-Binding-Theory. In: Cook, E. (Ed.), Syntax and Semantics, 16, 21-75. Bach, E. (1962). The order of elements in a transformational grammar of German. Language, 38, 263-269. Cheng, L. (1997). On the typology of wh-questions. New York: Garland. Chomsky, N. (1973). Conditions on Transformations. In: Anderson, P. & P. Kiparsky (Eds.), A festschrift for Morris Halle (pp. 232-286). . New York: Holt, Rinehart & Winston. Chomsky, N. (1981). Lectures on government and binding. Dordrecht: Foris. Chomsky, N. (1995). The minimalist program. Cambridge, Mass.: MIT Press. Clifton, C,. & Frazier, L. (1989). Comprehending sentences with long distance dependencies. In: G. Carlson, & M. Tanenhaus (Eds.), Linguistic structure in language processing (pp. 273-3 17). Dordrecht: Kluwer. Cuetos, F,. & Mitchell, D.C. (1988). Cross-linguistic diffrences in parsing: Restrictions on the use of the Late Closure strategy in Spanish. Cognition, 30, 73-105. de Vincenzi, M. (1991). Syntactic parsing strategies in Italian. Dordrecht: Kluwer. Emonds, J. (1978). The verbal complex V-V in French. Linguistic Inquiry 9: 151175. Fanselow. G., (1996). Features, -roles, and free constituent order. Paper, presented at the 1996 GLOW colloquium, Athens). Fanselow, G., Schlesewsky, M., & Kliegl, R. (1998). Optimal Parsing. Paper presented at the 1998 AMLaP conference, Freiburg and at the 2nd Workshop on Optimality Theory, Stuttgart. Frazier, L. (1987). Syntactic Processing: Evidence from Dutch. Natural Language and Linguistic Theory, 5, 519-559. Frazier, L., & Flores d’Arcais, G., (1989). Filler-driven parsing: A study of gap filling in Dutch. Journal of Memory and Language, 28, 331-344 Gibson, E., Hickok, & Schutze, C. (1994). Processing empty categories: a parallel approach. Journal of Psycholinguistic Research, 23, 381-406. Grewendorf, G. (1988). Aspekte der deutschen Syntax. Tübingen: Narr. Grimshaw, J. (1997). Projections, Heads, and Optimality. Linguistic Inquiry, 28, 373-422. Hale, M. (1998). Diachronic Syntax. Syntax, 1, 1-18. Hawkins, J. (1994). A performance theory of order and constituency. Cambridge: Cambridge UP. Junker, M., Oberauer, K., & Kliegl, R. (in preparation). Age simulation of syntactic complexity effects with a working memory load. Manuscript, University of Potsdam. Kemper, S., 1992. Language and aging. In: Craik, F.I. M., & Salthouse, T.A. (Eds.). The handbook of cognitive aging (pp. 213-270). Hillsdale, NJ.: LEA. King, J., & Just, M. (1991). Individual differences in syntactic processing: The role of working memory. Journal of Memory and Language, 30, 580-602.

200

Kliegl, R., Fanselow, G., Schlesewsky, M., & Oberauer, K. (1998). Syntactic complexity and processing efficiency: An age comparative study. Paper and poster presented at the 1998 AMLaP conference, Freiburg. Krems, J., (1974). Erwartungsgeleitete Sprachverarbeitung. Frankfurt: Lang. Marcus, M. (1980). A Theory of syntactic recognition. Cambridge, Mass.: MITPress. MacDonald, M., (1998). Theories of Working Memory and Sentence Processing. Paper presented at the 1998 AMLaP conference, Freiburg. Meng, M., (1997). Preferences and reanalysis in processing wh-questions. PhD thesis, Jena. Muller, G. (1998). Parallel movement. Manuscript, University of Tubingen. Norman, S., Kemper, S., Kynette, D., Cheung, H., & Anagnopulos, C. (1991). Syntactic complexity and adults' running memory span. Journal of Gereontology: Psychological Sciences, 46, 346-351. Pickering, M., & Barry, G. (1991). Sentence processing without empty categories. Language and Cognitive Processes, 6, 229-259. Schlesewsky, M., Fanselow, G., Kliegl, R., & Krems, J. (in press). Preferences for grammatical functions in the processing of locally ambiguous wh-questions in German. To appear in: B. Hemforth & L. Konieczny (Eds.), Cognitive parsing of German. Dordrecht, Kluwer Schlesewsky, M., Fanselow, G., & Kliegl, R., (submitted). The Processing of Unambiguous Wh-Questions in German. Staudacher, P. (1990). Long movement from Verb Second complements in German. In: Grewendorf, G. & Sternefeld, W., (Eds.). Scrambling and barriers (pp. 319-339). Amsterdam: Benjamins. Staudacher, P. (1993). Prinzipienorientierte syntaxanalyse. Habilitation thesis, Regensburg. Stowe, L., 1986. Parsing wh-constructions: Evidence for on-line gap location. Language and Cognitive Processes, 2, 227-246. Thiersch, C., 1978. Topics in German syntax. PhD thesis, MIT. Weissenborn, J. (1993). Matrix infinitives and economy in language development. Paper presented at the 5th OTS Anniversary Conference, Utrecht.

201

ACKNOWLEDGMENTS

Parts of this paper have been presented at the Sedona workshop, and on various other occasions at the Universities in Delhi, Groningen, and Stuttgart. We would like to thank the participants of the Sedona workshop, and the audiences in Delhi, Groningen, and Stuttgart for their comments and suggestions. Thanks also go to Ina Hockl, Martina Junker, Klaus Oberauer, Douglas Saddy, and Peter Staudacher for hints and discussion, and to Petra Grüttner and Hannelore Gensel for technical support. We are particularly indebted to Susan Kemper, Anoop Mahajan, and Gereon Muller for helpful discussions that had a substantial impact on the present paper. The research reported in this paper was supported by the grant INK 12/A1, the Innovationskolleg "Formal Models of Cognitive Complexity", financed by the German Federal Ministry of Science and administered by the German Research Foundation.

This page intentionally left blank.

8P

ARSING AND

MEMORY Lyn Frazier

INTRODUCTION

From a neuropsychological point of view, the questions about memory in sentence processing revolve around the issue of whether special memory stores are implicated in sentence processing and what neural subsystems support these stores. The current answers, as I understand them, are that active verbal working memory is a specialized store implicated in processing overt verbal material such as sentences and covert verbal material (e.g., subject-generated linguistic labels) in object recognition. The active or rehearsal component of verbal working memory is subserved by and therefore shows activation in Broca's area, premotor areas, and the supplementary motor area in the left-hemisphere whereas passive storage is subserved by posterior parietal areas in the left hemisphere (in particular see Smith & Jonides, 1997). The above view of memory is based primarily on PET studies exploiting letter recognition tasks. For example, a display of four upper case letters is presented. Following an interval of several seconds, a target lower case letter is presented. The subject must decide whether the target letter occurred in the initial display. Only the name of the letter allows the subject to perform the task because upper case and lower case letters are visually dissimilar. Although the letter recognition task implicates verbal working memory, it obviously is not a typical language comprehension task. It is therefore informative that data from brain-damaged patients converges on the Smith & Jonides view of verbal working memory. To some extent, data from plausibility judgment tasks also converges on the Smith & Jonides view. In a PET study, Stromswold, Caplan, Alpert & Rauch (1996) presented normal adults with a plausibility judgment task and found evidence that judging the plausibility of difficult (center-embedded) sentences resulted in greater activation of Broca's area, in particular the pars opercularis, than judging the plausibility of less difficult (right-branching) sentences. 203

204

Reading studies like those above, I'm frankly impressed. It is extremely exciting that credible answers to basic neuropsychological questions are beginning to emerge. But I'm also concerned, because the notion of active verbal working memory is far too undifferentiated to map onto theories of normal sentence processing (as I'm sure authors of the studies cited above would agree). Implicit in many discussions of verbal working memory are the following assumptions: For processing the structure of a sentence presented in isoloation, there's a single postlexical representation of the sentence. Memory burden is a function of how much material, or how much unstructured (or uninterpreted) material must be held for how long. This assumption is made explicit in one form in Gibson (1998). The assumption of one (active) verbal memory system gives rise to the expectation that it will reveal an advantage for recently presented material, or it won't. Similarity among items will facilitate (or inhibit) performance, or it won't. In what follows, I will address the problem of verbal working memory from a psycholinguistic perspective derived from research on normal adult sentence comprehension. I will raise questions about the implicit assumptions identified above. Let me emphasize at the outset my own assumptions about memory. I assume that properties of the storage system are related to properties of the computational system responsible for processing material. This is an assumption shared by everyone, as far as I can determine. The very notion of verbal working memory implies a form of modularity which requires distinct memory systems for linguistic versus spatial tasks, for example. At the level of representation that will be addressed below, the central distinction is not whether an input is, say, auditory or visual but whether it is processed linguistically. I will also assume that the characteristics of the memory system or systems under investigation will emerge differently depending on the tasks used to investigate them. The apparent properties of the storage system for material may depend on what the processor must do with the material being stored. In the case of experimental task demands, this is a standard assumption. What is not universally recognized, however, is that natural or "stable" task demands of ordinary comprehension may influence how material is stored in memory. In the case of sentences, I assume the natural or stable task demands are those implied by the need to structure and interpret the sentence. Experimental task demands, such as the demands of a verbatim memory or probe recognition task, may be viewed as superimposed on the demands of normal comprehension, perhaps influencing how the stable tasks are executed but rarely if ever allowing the perceiver to elude or sidestep the stable demands of ordinary comprehension. Presumably it is the nature of the stable task demands of ordinary sentence comprehension that accounts for the automaticity of early stages of sentence processing. Trying to account for the memory properties of, say, words without recognizing the effects of later stages of automatic processing strikes me as folly, doomed to failure.

205

ONE POSTLEXICAL REPRESENTATION?

Is just a single postlexical representation of a sentence computed when the sentence appears in isolation? If so, then we might conclude that the memory demands associated with constructing and maintaining this representation will directly index the memory burden imposed on (active) verbal working memory during processing of the sentence. But wait! Sentences often appear in discourses, not in isolation. Should one necessarily assume that no discourse representation is computed for a single sentence just because it lacks an overt discourse context? Consider the examples in (1), due to Pesetsky (1987). Pesetsky argues that the interrogative which in (1b) is discourse-linked ("d-linked").

(1) a. Some men entered the room. Mary talked to them. b. Some men entered the room. Which (ones) did Mary talk to? c. Some men entered the room. Who did Mary talk to? It is essentially obligatory to interpret which as referring to a subset of the men that entered the room. In other words, which N' implies the existence of a context set from which the perceiver is asked to identify a subset. Who is not d-linked and thus it does not imply that the interrogative ranges over members of an already established context set. Clifton & Frazier (in progress) hypothesize that perceivers establish a discourse representation for d-linked phrases even when they occur in isolation. When the perceiver encounters a phrase like which boy in (2), it sets up a singular masculine discourse referent. (2) a. b. c. d.

Which boy did Tom say that every girl saw? Who did Tom say that every girl saw? Which boy did Tom say that every girl married? Who did Tom say that every girl married?

In (2a), this discourse assumption is consistent with the remainder of the sentence. The perceiver may assume that every girl saw some particular boy. However, in (2c) the embedded verb is biased to a one-one relation; typically, every girl marries a different boy, not the same boy. Hence in (2c) the perceiver may have to retract the discourse assumption that there is just a single boy. Assuming that retracting this discourse assumption takes time, reading (2c) should take longer than reading (2a). By contrast, who is not d-linked. By hypothesis, no discourse entity is postulated when who is first encountered and consequently there's no need to alter a discourse representation in (2d) when the biased verb (marry) is encountered. Therefore we predicted that (2c) would take longer to read than (2a) but that (2d) would not differ from (2b). These predictions were confirmed in a self-paced reading study.

206

If a discourse entity is set up when a d-linked phrase is processed, then one might expect this entity to be readily available as the antecedent of a pronoun. In a questionnaire study, we tested this prediction using embedded (concealed) questions like (3) and matrix questions like (4). The results are given in Table 1. (3) a. Rick knew who Janice sang a song to before he went to sleep. b. Rick knew which brother Janice sang a song to before he went to sleep. (4) a. Who did Bradley send a rifle to when he was threatened? b. Which guy did Bradley send a rifle to when he was threatened?

Table 1 Wh-item

Embedded Questions

Matrix Questions

All Questions

Who

.39

.42

.41

Which-N

.56

.55

.56

As expected, subjects chose the d-linked interrogative phrase which N' as the antecedent of the pronoun more often than they chose the non-d-linked interrogative who as antecedent. In a self-paced reading study, we investigated reading times for disambiguated questions like those in (5) and (6) where only the interrogative could serve as the antecedent of the pronoun because all other NPs in the sentence were gender incompatible with the pronoun. As expected, the questions with d-linked interrogatives were read faster than those with non-d-linked phrases. (5) a. Rick knew who John sang a song to ˆ before she went to sleep. b. Rick knew which sister John sang a song to ˆ before she went to sleep. (6) a. Who did Barbara send a rifle to ˆ when he was threatened? b. Which guy did Barbara send a rifle to ˆ when he was threatened? In short, each of the above studies confirms the idea that perceivers postulate a discourse entity when they first process a d-linked phrase but not when they first process a non-d-linked phrase. In each of these studies, the question or sentence was presented in isolation. Hence, the results suggest that perceivers may construct discourse representations even for sentences presented without overt context. On the one hand, this shouldn't surprise us. In a sense, a d-linked phrase carries its own context. And the stable task demands of sentence comprehension involves relating a d-linked phrase to its overt (or implied) context. On the other hand, it's clear that processing a sentence presented in isolation does not necessarily implicate just a single post-lexical representation. Logically, of course, the memory system

207

supporting the syntactic representation and the memory system supporting the discourse representation might be the same. We will return to this issue below. DISTINCT REPRESENTATIONS

AND

DISTINCT DEFAULTS?

The concept of 'memory' is generally invoked to explain two types of phenomena: limitations on the amount of decay-prone material that may be held temporarily in store and the accessibility relations among the items stored. Investigating memory limitations involves stressing the system to see at what point it is overloaded. If multiple verbal memory systems exist and if they can compensate for each other to some extent, then experimental manipulations of memory load may obscure the properties of any given system until we have learned how to isolate the different systems. Rather than pursuing the capacity limitations of verbal memory systems, I will proceed by investigating the accessibility relations implied by general "defaults". If distinct verbal memory systems exist, it seems likely that they subserve distinct functions and thus exhibit accessibility relations related to those functions. The most accessible material should serve as a default in the sense that it is the material most quickly and most reliably available in the system (presumably because of the particular function the system generally subserves). The assumption that distinct memory systems exhibit distinct defaults need not be correct, but I will adopt it here as a working assumption. Consider the processing of pronouns. Is there a general or default preference for a particular antecedent for a pronoun? Arguably there are two general preferences: a preference for a topical antecedent and a preference for a recent antecedent. Turning first to the topic preference, consider the results of Ferreira & Clifton (1987). They conducted a self-paced reading study using discourses like those in (7) where the pronoun she in the final sentence could refer to a topical or nontopical antecedent. The antecedent could be near the pronoun (7a,c) or far (7b,d).

Table 2 Sample Items, Experiment 2 Near Topic Antecedent (Topic Change Before Anaphor) Weddings can be / very emotional experiences for everyone involved. / The cigar smoking caterer / was obviously / on the verge / of tears, / and the others / were pretty upset too. / In fact, / THE ORGANIST, / who was an old maid, / looked across the room / and sighed. / (She, The organist) was / still looking for / a husband.

208

Far Topic Antecedent (No Topic Change Before Anaphor) Weddings can be / very emotional experiences for everyone involved. / THE ORGANIST, / who was an old maid, / was obviously / on the verge / of tears, / having just noticed that / the cigar smoking caterer / was holding hands / with someone else. / (She, The organist was / still looking for / a husband.

Near Nontopic Antecedent (No Topic Change Before Anaphor) Weddings can be / very emotional experiences for everyone involved. / The cigar smoking caterer / was obviously / on the verge / of tears, / having just noticed that / THE ORGANIST, / who was an old maid, / was holding hands / with someone else. / (She, The organist) was / still looking for / a husband.

Far Nontopic Antecedent (Topic Change Before Anaphor) Weddings can be / very emotional experiences for everyone involved, / THE ORGANIST, / who was an old maid, / was obviously / on the verge / of tears, / and the others / were pretty upset too. / In fact, / the cigar smoking caterer / looked across the room / and sighed. / (She, The organist) was / still looking for / a husband.

Ferreira & Clifton found that subjects read the final sentences of the discourses with topical antecedents faster than those with nontopical antecedents. Sentences with distant antecedents did not differ from those with near antecedents. These results suggest the existence of a topic antecedent preference for pronouns with a discourse antecedent. The Ferreira & Clifton discourses required an antecedent outside the sentence because the critical pronoun occurred as the subject of the final sentence. Further, with no potential sentence-internal antecedent, the distance between the pronoun and antecedent did not matter, as expected if discourse representations are structured according to discourse-principles and content-based inferences rather than simply consisting of annotated syntactic representations with linear order preserved. As we will see immediately below it may also be important that the pronouns in this study were phrasal (NPs or DPs). Is a topical entity always the preferred antecedent for a pronoun? In a reading study by Clifton, Frazier & Deevy (in progress) we examine the processing of sentences like those in (8).

209

(8) a. b. c. d. e. f. g.

John thinks that Bill owes his sister another chance to solve the problem. John thinks that Betsy owes his sister another chance to solve the problem. Joan thinks that Bill owes his sister another chance to solve the problem. John thinks that Bill owes him another chance to solve the problem. John thinks that Betsy owes him another chance to solve the problem. John thinks that Bill owes himself another chance to solve the problem. Joan thinks that Bill owes himself another chance to solve the problem.

Sentences with phrasal pronouns (8d,e) were read equally quickly as long as the sentence subject (default topic) could be taken as antecedent. It didn't matter if a closer NP matched the pronoun's gender (8d) or not (8c). Likewise for reflexives (8f,g) it didn't matter if a nonantecedent NP matched the gender of the reflexive (8f) or not (8g). So far these results support the claim that a phrasal pronoun preferentially takes the topic as antecedent; reflexives in the sentences must take local antecedents. Turning to the sentences with possessive pronouns (his in 8a,b,c), a different pattern emerged. If the possessive pronoun could take the local subject as antecedent, as in (8a,c), the sentence was read quickly compared to sentence (8b) where the local subject was gender inappropriate to be antecedent. When the local subject could be antecedent (8a,c), it made no difference if the distant subject matched the pronoun in gender (Sa) or not (8c). Why doesn't the possessive pronoun prefer a topic antecedent? And why doesn't a gender appropriate non-antecedent interfere with the processing of (8a) relative to (8c)? Assuming that English possessive pronouns (his) are determiners not NPs or DPs, we might hypothesize that perceivers favor discourse antecedents, or initially check discourse representations only when processing phrases, not individual words. Given this assumption perceivers initially check the syntactic representation (not the discourse representation) for an antecedent for the possessive pronoun in (8a,c). The preference for the closer antecedent is then naturally attributed to the greater accessibility of recent phrases than distant phrases in the syntactic representation. The examples in (9), due to Dahl (1973), further support the idea that possessives prefer local antecedents. (9) a. b. c. d.

Maxi said he saw hisi mother and Oscark did (hei saw hisi mother) too. Maxi said he saw hisi mother and Oscark did (hek saw hisi mother) too. *Maxi said he saw hisi mother and Oscark did (hei saw hisk mother) too. Maxi said he saw hisi mother and Oscark did (hek saw hisk mother) too.

In addition to the strict reading in (9a), where Oscar said Max saw Max's mother, and the sloppy reading in (9d), where Oscar said Oscar saw Oscar's mother, one crossed reading, (9b), is alright, where Oscar said Oscar saw Max's mother. The reading that is not present is the one in (9c). To compute this reading, the possessive his must take an unpreferred option for which the processor has no evidence. [Note: In (9b), it only appears that the possessive takes a nonlocal antecedent. It really takes the same referential value that it was assigned in the first

210

conjunct.] In general, faced with one or more well-formed sensible analyses of a sentence, perceivers do not abandon an already computed analysis without some motivation. (See for example the discussion of (13b) below). Hence, the unavailability of (9c) is expected.1 Thus (9), like (8), suggests a preference for recent antecedents. I have suggested that phrasal pronouns prefer topical antecedents found in the discourse representation whereas nonphrasal pronouns prefer recent antecedents found in the syntactic representation. This hypothesis suggests that distinct memory systems support the syntactic representation and the discourse representation; otherwise we would have expected a distance effect in the Ferreira & Clifton study and we would possibly also expect a topic interference effect in processing (8a) The assumption of distinct representations with distinct defaults or accessibility relations (e.g., topic/focus vs. recency) allows a natural explanation for why a topicality effect can occur in the absence of a recency effect and vice versa. Further, I think it is natural that it is the interpretation of phrases that implicates the discourse representation and information-structure notions like topic (and focus) whereas the processing of an individual word (his) implicates the more superficial syntactic representation where recency determines accessibility. Of course, the existence of two defaults, topic and recency, might be peculiar to pronouns and not reflect general properties of two distinct representational/memory systems. Hence, we turn next to a different structure -- sluicing. Sluicing is a structure where an embedded interrogative complement is elided, as shown in (10). The overt wh- in the embedded complement must bind a trace (the empty object of likes in (10)). The antecedent for the elided IP (Joan likes someone) guides the construction of the elided IP; the variable bound by the whmust correspond to an indefinite, someone in (10), the "inner antecedent" (or to a sprouted trace in a syntactically legal position, see Frazier & Clifton, in progress).

211

In a self-paced reading study, Frazier & Clifton (in progress) investigated the processing of ambiguous (11a,b) and unambiguous (11c,d) sluiced sentences. (11) a. Some tourist suspected / that the hotelkeeper was hiding someone / guess who. / b. Some tourist discovered / that the hotelkeeper was hiding someone / guess who. / c. Some tourist suspected / that the hotelkeeper was hiding Madonna / guess who. / d. Some tourist discovered / that the hotelkeeper was hiding Madonna / guess who. / In the ambiguous forms, the matrix subject and the embedded object were both indefinite. Thus either indefinite phrase could serve as the inner antecedent of the trace in the elided clause. In the unambiguous forms (11c,d), the embedded object was replaced by a name. Thus only the matrix subject was appropriate as the inner antecedent for the trace. We hypothesized that focused material would serve as a tempting inner antecedent for the trace. Focused material is typically new or contrastive whereas nonfocused material is typically given or available from context. Since it is given material that is deletable, the processor may include unfocused material in the elided constituent and preferentially take focused material as the inner antecedent for the trace. We assumed that the highest subject serves as default topic in English. Further, in English focused material (e.g., the nuclear accent of a sentence) typically occurs in final position. Thus, we assumed that the highest subject would not be taken as focused whereas the embedded object would. Therefore we expected readers to favor the embedded object interpretation of the ambiguous sentences (11a,b) and to comprehend the ambiguous sentences (when the focused phrase may serve as inner antecedent) faster than the unambiguous ones (where the focused phase is definite and cannot serve as the inner antecedent). The self-paced reading results confirmed the prediction: (11a,b) were comprehended more quickly than (11c,d). An independent questionnaire study confirmed the prediction that readers preferentially assign the object interpretation. To check our focus-based account of the object preference in (11), we then performed an auditory study using the a-form of the experimental sentences and manipulating the position of a pitch accent (indicated by capitals in (11'). (11') a. SOME TOURIST suspected that the hotelkeeper was hiding someone. Guess who? b. Some tourist suspected that the hotelkeeper was hiding SOMEONE. Guess who? As expected, in the auditory questionnaire study, the highest subject was chosen as antecedent more often when it was focused (roughly 50%) than when the object was focused (roughly 25%). The significant effects of accent placement supports the

212

focus-based account of the results. However, notice that the object interpretation was chosen overwhelmingly when the object was focused but the subject was chosen only half the time when it was focused. This suggests that focus is not the only factor at play. What is the other factor favoring the object interpretation? Let's assume that it is recency. What this suggests is that the LF for a sluiced sentence (e.g., in (10)) can be influenced by the surface syntactic representation, where recency favors the object inner antecedent, and by the discourse representation, where focus favors the object as inner antecedent when the object is accented but favors the subject as inner antecedent when the subject is accented.2 In an attempt to distinguish the various component steps of processing a sluiced sentence, Clifton & Frazier (in progress) contrasted d-linked (12b,d) and non-d-linked (12a,c) interrogatives in ambiguous sluiced sentences in a written questionnaire. (12) a. Some girl saw that the principal hit some boy. Guess who. b. Who = which boy a. Who = which girl b. Some girl saw that the principal hit some boy. Guess which one. b. Which one = which boy a. Which one = which girl c. Some girl saw the principal who hit some boy. Guess who. b. Who = which boy a. Who = which girl d. Some girl saw the principal who hit some boy. Guess which one. a. Which one = which girl b. Which one = which boy

We hypothesized that d-linked phrases which one in (12b,d) would access a discourse representation (see Section II above), whereas non-d-linked interrogatives who in (12a,c) would not. We then placed the recent inner antecedent in a syntactically accessible complement position, as in (12a,b), or in a syntactically inaccessible (island) position, i.e., inside a relative clause, as in (12c,d). If non-d-linked interrogatives (who) do not access a discourse representation, then perceivers should assign fewer object interpretations in (12c) with a syntactically inaccessible object than in the sentence with a syntactically accessible object (12a). By contrast, for d-linked phrases (which N'), the syntactic accessibility of the object inner antecedent might not matter because the discourse representation of the object should be available. The results of the questionnaire supported these predictions. The most common response was the embedded object response for (12a) 62%, (12b) 60%, and (12d) 69% but, as predicted, not for (12c) 41%. To sum up, investigations of sluicing suggest that both syntactic representations and discourse representations influence the processing of a sluiced sentence -- even one with a non-d-linked interrogative (e.g., (1 1)). The processor checks both the syntactic and discourse representation for an inner antecedent. A preference for recent inner antecedents has been identified and attributed to the syntactic representation. A preference for

213

focused inner antecedents has been established. Plausibly it indicates a role for discourse representation in the construction of an LF for a sluiced sentence. In addition, the interrogative phrase itself may access a discourse antecedent, but only in the case of a d-linked interrogative. Hence the syntactic accessibility of an inner antecedent is of less importance for a d-linked interrogative than a non-d-linked one. The above picture of processing is reinforced by a recent study of gapping. Katy Carlson investigated gapped sentences where a verb in a second conjunct is deleted, possibly along with one or more of the verb's arguments. Carlson (1998) demonstrated a strong preference for the conjoined VP (or T’) interpretation (13a) sentences like (13) in a written questionnaire. (13) Josh visited Marjorie during the vacation and Sarah during the week. (conjoined VP) a. and Josh visited Sarah during the week. b. and Sarah visited Marjorie during the week. (gapped) In an auditory questionnaire with ambiguous prosody, comparable results were obtained. However, Carlson also tried to identify strongly biasing prosodies for the sentences. The prosody that facilitated the gapped structure (13b) required a contrastive pitch accent on the subject of the first clause and on the first constituent of the second clause. Carlson attributes the structural preference for the conjoined VP (13a) analysis to a minimal structure principle operative in syntactic processing. What's interesting for present purposes are her prosodic results. They support the notion that deleted material should correspond to unfocused material (the internal object in (13b)) and that overt material (the constituent following and) should contrast with another focused constituent. This pattern seems to obtain for both the sluiced sentences discussed above and for Carlson's gapping results (see Williams, 1997 for a linguistic account based on similar generalizations). Most interesting for the present purposes is the evidence Carlson's study provides concerning how focus enters into processing. It does not dictate the processor's first hypothesis. If it did, then focus should have overridden the structural bias. Instead she still found a preference for minimal structure, with focus acting like a mitigating factor much on a par with the discourse role it has been attributed in sluicing in discussion of the sentences in (1 1). The operation of two defaults can also be observed in the association of adjuncts or "nonprimary phrases" with the larger sentence structure. Studies of three-site attachment ambiguities indicate that PP modifiers, relative clauses and conjoined phrases preferentially attach to the lowest, most recent, permissible attachment site. For example, Gibson et al. (1996) studied the relative clauses in (14). In both Spanish and English, (14a) with low attachment was read most quickly. (14) a. the lamps near the paintings of the house that was damaged in the flood b. the lamps near the painting of the houses that was damaged in the flood c. the lamp near the paintings of the houses that was damaged in the flood

214

However, the next lowest or next most recent site (14b) is not preferred or processed more quickly than the phrases with high attachment. If anything, high attachment (14c) is better than the intermediate attachment in (14b). Imagine that the lowest most recent attachment site corresponds to the syntactically most accessible analysis - the syntactic default. The highest attachment on the other hand allows the adjunct to modify the highest argument, e.g., an argument of the main predicate. By hypothesis, the highest argument or an argument of the main predicate is a discourse salient phrase. Thus, the high attachment preference may be viewed as attachment to a discourse salient (topic/focus) phrase - the discourse default. Hemforth, Konieczny & Scheepers (in press) explicitly treat relative clause attachment in these terms. In German, the relative pronoun, e.g., in (15a), acts like a personal pronoun, they argue, and prefers attachment to whatever discourse salient phrase a corresponding personal pronoun, e.g., er in (15b), would preferentially take as its antecedent. (15) a. Jemand sah den Studenten des Professors, der im Labor war. Someone saw the student of the professor who was in the lab. b. Jemand sah den Studenten des Professors, als er im Labor war. Someone saw the student of the professor when he was in the lab. In English, Schafer, Clifton & Frazier (1996) explicitly manipulated the placement of a pitch accent, as indicated by capitals in (16). (16) a. The sun sparkled on the PROPELLER of the plane that the mechanic was so carefully examining. b. The sun sparkled on the PROPELLER near the plane that the mechanic was so carefully examining. c. The Sun sparkled on the propeller of the PLANE that the mechanic was so carefully examining. d. The sun sparkled on the propeller near the PLANE that the mechanic was so carefully examining. They showed that perceivers are more likely to take a phrase to be head of the relative clause if the phrase is focused (accented) than if it is not. Thus in attachment of adjuncts too there is evidence for two defaults - one based on recency and another based on information theoretic notions of salience (topic/focus). Neither default favors the intermediate attachment site (14b), which is systematically unpreferred in the processing studies performed to date. Many questions remain open concerning the processing of pronouns, sluiced sentences, and attachment ambiguities. But we have seen ample evidence that in each of these areas two distinct sets of salience properties are at play: recency and topic/focus. These factors come together in different particular ways in these three areas. In processing pronouns, apparently the processor either finds an antecedent in syntactic structure (e.g., with nonphrasal pronouns), resulting in a recency advantage, or it finds an antecedent in discourse structure (e.g., with phrasal

215

pronouns), resulting in a topic advantage. By contrast, in processing sluiced sentences, both factors seemed to be at play in the same sentence presumably because both the syntactic and discourse representation influence the assignment of a disambiguated LF structure. In attachment studies these factors probably come together in yet a different way. There is some indication that recency operates earlier than discourse factors (focus or, equivalently, the Relativized Relevance constraint, Frazier & Clifton, 1996). De Vincenzi & Job (1993) present data from Italian suggesting that recency influences immediate processing but that discourse factors favoring high attachment can be observed in processing the same sentences but at a somewhat later stage. Despite the arguments in this section, one might try to push the idea that a single verbal memory system subserves both the syntactic processing representation and the discourse processing representation. One would then need to derive the distinct salience properties associated with each from more general principles of memory. For example, perhaps recency advantages are strongest for earliest stages of processing and simply become progressively weaker at higher or later levels of analysis. This might explain why recency preferences are associated with syntactic levels of processing assuming that syntactic processing of an input item precedes discourse processing of that item. As for discourse salience (topic/focus), one might assume that it is reflected in the structure of the discourse representation, e.g., with the topic serving as the current pointer into the discourse representation and the focus serving as highlighted information. If one could successfully derive the salience properties of syntactic versus discourse representations, one might persist with the notion of a single verbal memory system. But even then, the claim of a single unified system would seem unilluminating and perhaps would not be desirable. At present it looks as if more follows from the hypothesis that distinct postlexical memory systems exist, each with it own distinct representations, tasks and salience properties than from the claim that only one verbal memory system exists. Ultimately, I suspect the real question is how and to what extent memory systems help explain representational/processing systems versus how and to what extent representational processing systems help explain the properties of memory systems. DISTINCTIONS WITHIN

THE

SYNTACTIC SYSTEM

From the discussion in earlier sections it already follows that capturing the resource requirements for processing a sentence involves more than a metric indexing how much material must be held in temporary storage for how long. The nature of the representation of an antecedent (syntactic versus discourse) and the linguistic form of an anaphor may influence the accessibility or ease of retrieving the antecedent. An antecedent for a phrase may be readily available in one representation but not another. Depending on the type of anaphor (e.g., pronoun, interrogative, etc.) the processor may be sent to the appropriate representation or not. For example, recall the difficulty of processing a pronoun when the only available antecedent for it was who in the study discussed in connection with (5a) and (6a) above. See Dickey (1996) for a similar analysis where traces access their antecedents in the syntactic

216

representation, whereas resumptive pronouns may access a discourse antecedent (see Seely, 1987 for a compatible view of processing parasitic gaps). Confining our attention to syntactic processing proper, it would still be inappropriate to identify resource requirements simply in terms of how much material (how many words or phrases) must be held for how long. The computations needed to identify a structure also contribute to the resource demands of processing a sentence. Though my point here is an obvious one, it is perhaps sufficiently important to be worth emphasizing. Consider the Russian sentence in (19). It is ambiguous between the two structures in (19a) and (19b) illustrated in (20a) and (20b) respectively. (19) Olja dumact urazet Ivana (Rating 2.83) thinks respect Ivana.' 'Olja-N-sg a. Olja thinks Masha respects Ivan. b. Masha thinks Olja respects Ivan.

In the a-form, two phrases (Olja, Masha) have been fronted and each binds a trace lower in the sentence. By contrast, in the b-form, only the first phrase has been fronted and binds a trace. The second phrase (Masha) serves as the preverbal subject of the following verb (thinks). In a small written questionnaire study of sentences like (19) with two initial NPs, Sekerina & Frazier (1998) found that (19) was rated as more acceptable than any of the sentences that required an analysis where both initial phrases moved from their base position. This rating, along with native speaker judgments that (19b) is the preferred analysis of (19), suggests that the processor has opted for the simpler syntactic structure where only one phrase has been fronted (19b). This is not surprising. The interesting point is that the memory requirements for the two analyses are identical: the processor must wait until the verb thinks before it can combine the verb and its subject for WHATEVER analysis the processor chooses. Thus, until the verb thinks is encountered, the processor must maintain both Olja and Masha regardless of whether it computes (20a) or (20b) as the structure. At the verb, one phrase or the other may be interpreted as subject of thinks. Hence, viewed simply in terms of how much material must be maintained for how long, the two

217

analyses impose an equal burden on memory. The preference for (20b) thus shows clearly that the resource requirements for processing a sentence must make reference to computational as well as memory requirements. (And, by the way, the example provides a challenge to views like that of Pickering & Barry (1991) where traces are not syntactically represented and thus the two analyses of (19) are structurally equivalent and do not differ in their syntactic complexity.) Further distinctions are needed to correctly characterize the role of memory in sentence processing. Foremost is a distinction between immediate processing of input and later access of material. There is evidence that similarity among items can facilitate immediate processing at least in cases where it increases the predictability of the input whereas similarity among items inhibits processing when the items must be stored for later access. Facilitation due to similarity derives from self-paced reading studies of parallelism in the processing of conjoined phrases. Consider (21)-(23). (21) a. b. c. d.

John walked slowly and carefully, avoiding the broken glass. John walked slowly and with great care, avoiding the broken glass. John walked carefully, avoiding the broken glass. John walked with great care, avoiding the broken glass.

(22) a. b. c. d.

Mary is a Republican and a politician Mary is a Republican and proud of her politics. Mary is a politician. Mary is proud of her politics.

(23) a. Hilda noticed a strange man and a tall woman when she entered the house. b. Hilda noticed a man and a tall woman when she entered the house. c. Hilda noticed a strange man and a woman with a dog when she entered the house. d. Hilda noticed a man and a woman with a dog when she entered the house. Frazier, Munn, & Clifton (in progress) showed that syntactically parallel conjuncts, the a- forms of (21)-(23), are read more quickly than nonparallel b-counterparts. The c- and d- forms serve as lexical controls. The advantage for syntactically parallel conjuncts holds regardless of whether it is parallelism in the category of the conjuncts themselves (21a, 22a) which in principle the grammar might regulate, or parallelism in the internal structure of the conjuncts, as in (23a). Since the grammar clearly does not regulate the internal structure of conjuncts, one may conclude that the parallelism effect is a processing effect, not a grammatical effect. Interestingly, parallelism in the form of the subject and object NPs in sentences like (24) did not reveal a facilitation effect. (24) a. A strange / man / noticed / a tall woman / yesterday/ at / Judi's. b. A man / noticed / a tall woman / yesterday / at / Judi's. c. A strange / man / noticed / a woman / yesterday / at Judi's. d. A man / noticed / a woman / yesterday / at Judi's.

218

The fact that an advantage for syntactically parallel forms is restricted to coordinate phrases suggests that it is not due to ‘priming‘ or reuse of a recently employed syntactic template but instead is due to the higher predictability of parallel forms in coordinate structures. Now, what about similarity among items that must be stored for later access? Does the similarity serve as a form of predictability, aiding performance? Stabler (1994) proposed the bounded connectivity hypothesis below. Bounded connectivity hypotheseis: There is a natural typology of linguistic relations such that the psychological complexity of a structure increases quickly when more than one relation of any given type connects a (partial) constituent (or any element of ) to any constituent external to . Basically when a phrase cannot be fully integrated into the phrase-marker, it must be held in temporary memory. A subset of linguistic primitives such as Causative or Case (Nom, ACC, etc.) participate in this process. Reusing the same primitive is costly and repeated use can rapidly result in unacceptability of the sentence. For example, in Bolivian Quechua the causative morpheme may be applied to its own output. However, causativizing a (morphological) causative results in a perceptually difficult phrase and three applications of the causative is awkward or impossible. Stabler (1994) also discussed Hindi, a language where multiple wh-fronting is grammatical. He noted that fronting two wh-phrases with the same case results in near unacceptability though fronting wh-phrases with distinct cases is fully acceptable. He presented (25) in support of his bounded connectivity hypothesis. ram-ne kisko2 t1 t2 kaha ki sar dard he (25) ??? kis-ko1 tell that head pain is who-DAT Ram-ERG who-DAT Who did Ram tell that who has a headache? In (25) two dative-marked wh-phrases have been fronted. The resulting question is at best only marginally acceptable. Radó (1997) investigated Hungarian, another language where multiple whfronting is grammatical. She noted that extraction of an embedded (Nominative) subject triggers a 'Nom-to-Acc' rule, where the subject surfaces as an Accusative in its moved position (26). However, if the matrix clause already contains an Accusative, as in (27), the result is ungrammatical whether the moved subject surfaces as a Nominative or Accusative. (26) a. *Kii mondta Jani, [hogy ti találkozott Juli-val]? Who-DAT / said /Jani / that / met / Juli-with Intended meaning: “Who did Jani say met Juli?” b. Ki-ti mondott Jani, hogy ti találkozott Juli-val? who-Acc “Who did Jani say that met Juli?”

219

(27) a. #Ki-ti ki-ti tud Feri, [hogy ti megtalált ti]? who-Acc / who-Acc / knows / Feri / that / found intended meaning: "Who does Feri know found whom?" b. #Ki-tj ti-tj tud Feri, [hogy ti metalált ti]? Notice that application of the Nom-to-Acc rule in (27) would create a configuration with two wh-phrases of the same case. Thus the prohibition on applying the Nom-to-Acc rule in Hungarian is reminiscent of Stabler's finite connectivity hypothesis, as Radó noted. One way to think about Stabler's and Radó's results is in terms of certain linguistic primitives creating memory or its access code. Though two fronted phrases with the same case might increase the 'predictability' of the features of the second of the fronted phrases (on a par with the second conjunct in coordinate structures), it might also increase the confusability of the two phrases at a later point in the sentence when a fronted phrase must be accessed to bind a trace. Thus the question of whether similarity among items in memory facilitates or inhibits performance may be fundamentally misguided. The answer may depend on what the processor must do with the items. In this section, I have restricted attention to the syntactic system, setting aside the discourse representation of a sentence. I have argued that resource requirements for processing a sentence are intimately tied to the processing operations the parser must compute. Separating memory for words and phrases from the operations performed on those words and phrases is unilluminating at best, misleading at worst. Memory burden and computational complexity are intimately bound together. For the Russian example in (19), the initial phrases must be held in memory whether both phrases are analyzed as having moved or whether only one is analyzed as having moved. The greater acceptability of the simpler structure indicates that it would be a mistake to identify the computational requirements of a sentence with memory requirements for holding individual words or phrase in a temporary store. Another indication that computational properties of a system are essential to characterization of the memory subserving the system derives from consideration of similarity between linguistic phrases. Whether it facilitates or inhibits processing apparently depends on whether it increases the predictability of an input during its immediate analysis or whether instead it increases confusability among items that later need to be retrieved. If the computational properties of the processor are not considered, mapping out the role of similarity in memory will lead to contradictory conclusions. CONCLUSIONS

To summarize, it has been argued that: (i) Ordinary sentence comprehension involves construction of a discourse representation even when a sentence is presented without a discourse context.

220

(ii) Distinct representations exhibit distinct 'salience' properties or defaults: a robust recency advantage is observed for operations on the syntactic representation and a topic and/or focus advantage is observed for operations on the discourse representation. Which representation or representations are consulted at any point in processing depends on the task (implicitly) defined by the expression being processed, e.g., by whether a pronoun is phrasal or not, whether a variable is a pronoun or a trace, whether an interrogative is d-linked or not. (iii) Resource requirements for processing a sentence depend in part on computational complexity not simply on how long the input must be held in memory. (iv)

Similarity among items in memory can facilitate immediate processing when it increases predictability of the input but it can interfere with later access of an item by increasing the confusability of items.

What do these observations reveal about verbal memory? Observation (i) is informative. Like the sluicing results (see Note 1), it suggests that the modularity of the human language system is not defined in terms of domains with the syntactic processor identified with sentence-level operations and the discourse processor identified with the relation to extrasentential context (see Marslen-Wilson & Tyler, 1987) for additional arguments against a domain-defined modularity). Instead, it appears that the vocabulary in which a representation is couched determines the division of the processor into subsystems (Frazier, 1985, 1990). A discourse entity and a phrase differ: they are different kinds of representations and they support different kinds of inferences, e.g., new phrases in the linguistic input do not necessarily introduce new discourse entities. With respect to verbal memory, the question is whether both kinds of representations count as "verbal." Clearly the syntactic representation is included in the intended extension of "verbal" in verbal memory. But what about the discourse representation? It appears to be an interface representation par excellence. On the one hand, it must represent actual entities and, in this respect, it is like a purely conceptual or nonlinguistic mental model of the entities and relations described in a discourse. On the other hand, certain linguistic properties are clearly preserved because it matters how a set of propositions was conveyed, e.g., what was topic and what was focus. Further certain hierarchical properties must remain to account, say, for modal subordination (when an entity may exist only within the scope of a modal operator). For example, it is alright "John might catch a fish. He would eat it for dinner." but not in "John might catch a fish. It was dinner." The observations in (ii) amount to a substantive proposal about how distinct representations are accessed and for what purposes. If, with further scrutiny, the proposal proves to be correct, it will strengthen the view that the architecture of the human language system is highly structured. The linguistic properties of the input implicitly define the tasks of the processor and the information that must be accessed to accomplish the task. This view differs radically from a view where language

221

processing is a purely content-driven unstructured inferencing task where the input just happens to be linguistic. Parsing is by definition the productive combination of elements. The elements are prestored but the combination is not. It may seem natural to view the basic role of memory in parsing as storing the items to be combined, as in the retention of a verbal label for the letter R (or r) in the verbal monitoring task of Smith & Jonides (1997). But this misses at least half the point. In sentence processing, memory for an item is not retention of that item so much as the relation of that item to other items within the same system AND the relation of the representations of that item across different systems, e.g., lexical, syntactic and discourse systems. By viewing memory as retention of an item we leave out the computational properties of the system - the essential properties for purposes of language comprehension. Observations (iii) and (iv) point to a similar conclusion. At the outset it seems natural to ask if similarity among items facilitates or inhibits retention of the item in verbal memory. But it has been argued here that this question is essentially wrong-headed because it leaves out the computational properties of the system. In short, memory for parsing is computational. Memory is not simple retention but processing guided by an implicit set of stable tasks that structure ordinary sentence comprehension. Put differently, in the absence of a computational view of memory, we won't have a clue whether the results of two memory studies are consistent or whether they contradict each other. Analyzing the experimental task demands is not sufficient to identify the actual demands of a natural or automatic system like the human language processing device.

222

NOTES 1Whether the grammar needs to ban sentences like (9c) depends on intuitions about examples like (i), where context provides evidence for the analysis in (9c).

(i)

Max and Oscar had a bet. Max claimed that their mothers weren't the hardworking saints that they appeared to be. He bet that both their mothers would go to the movies on a weekday afternoon. Oscar said his mother would never do that. Max almost camped out in the food court near the theater all week, waiting for them to show up. On Friday, it rained. Max saw his mother go to Titanic. Then he spotted Oscar's mother going in. He raced to the phone to call Oscar so Oscar could verify that his mother had been there. Oscar got there in time to see his mother leave the theater. Later, when they were relating the story to me, Max would vouch that he saw HIS mother enter the theater and Oscar would too.

If the crossed reading indicated in (ii) is alright in (i), then it is sufficient to account for the extreme difficulty of (ii) in terms of the parsing problems it poses. However, if (ii) is still unavailable in a strong context like (i), this might indicate that a grammatical constraint is needed (possibly one motivated by parsing factors). (ii) [Oscar would vouch that Max saw Oscar's mother enter the theater] 2 Does this proposal conflict with modular claims about the structure of the language processor. The answer depends on which modular claim one has in mind. I assume that LF is a syntactic representation which serves as the interface with discourse. In the case of intersentential deletion, this implies either that the syntactic processor is not defined by or limited to the domain of a simple sentence or that the language processor is not modular. What I believe is the former but defending that view goes beyond the scope of this paper (see Marslen-Wilson & Tyler, 1987, and Frazier, 1990).

223

REFERENCES

Carlson, K. (1998). Processing of gaps in a DP-PP frame. U Mass manuscript. Clifton, C., Frazier, L., & Deevy, P. (in progress). Feature manipulation in sentence processing. Clifton, C., &Frazier, L. (in progress). Processing d-linked phrases. De Vincenzi, M., & Job, R. (1993). Some observations on the universality of the late closure strategy. Journal of Psycholinguistic Research, 22, 189-206. Dickey, M. (1996). Constraints on the sentence processor and the distribution of resumptive pronouns. In M.W. Dickey & S. Tunstall (Eds.) Linguistics in the laboratory, 19, 157-192. Frazier, L. (1985). Modularity and the representational hypothesis. In S. Berman, J. Choe & J. McDonough (Eds.), Proceedings of the Northeastern Linguistics Society, 15, 131-144. Frazier, L. (1990). Exploring the architecture of the language processing system. In G.T.M. Altmann (Ed.) Cognitive models of speech processing: Psycholinguistic and computational perspectives. Cambridge, MA: MIT Press Frazier, L., & Clifton, C. (in progress). Comprehension of sluiced sentences. Frazier, L., Munn, A., & Clifton, C. (in progress). Processing coordinate structures. Gibson, E. (1998). Linguistic complexity: Locality of syntactic dependencies. Cognition, 65, 1-76. Gibson, E., Pearlmutter, N., Canseco-Gonzalez, E., & Hickok, G. (1996). Recency preference in the human sentence processing mechanism. Cognition, 59, 23-59. Hemforth, B., Konieczny, L., & Scheepers, C. (in press). Syntactic attachment and anaphor resolution: two sides of relative clause attachment. In M. Crocker, M. Pickering & C. Clifton, Jr. (Eds.) Architecture and mechanisms for language processing. Cambridge: Cambridge University Press. Marslen-Wilson, W., & Tyler, L. (1987). Against modularity. In J. L. Garfield (Ed.) Modularity in knowledge representation and natural language understanding. Cambridge, MA :MIT Press. Pesetsky, D. (1987). Wh-in-Situ: Movement and unselective binding. In E. J. Reuland & A. G. B. ter Meulen (Eds.) The representation of indefinites. Cambridge, MA: MIT Press. Radó, J. (1997). Processing Hungarian: The role of topic and focus in language comprehension. University of Massachusetts doctoral dissertation. Schafer, A., Carter, J., Clifton, C., & Frazier, L. (1996). Focus in relative clause construal. Language and Cognitive Processes, 11, 135-164. Seely, D. (1987). The dependence hypothesis: Toward a theory of processing parasitic gaps. Proceedings of WCCFL, 6, Stanford: Stanford Linguistics Association. Stabler, E. (1994). The finite connectivity of linguistic structure. In C. Clifton, Jr., L. Frazier & K. Rayner (Eds.) Perspectives on sentence processing (pp. 303336). Hillsdale, NJ: Laurence Erlbaum Associates. Smith, E. E., & Jonides, J. (1997). Working memory: A view from neuroimaging. Cognitive Psychology, 33,5-42.

224

Stromswold, K., Caplan, D., Alpert, N., & Rauch, S. (1996). Localization of syntactic comprehension by position emission tomography. Brain and Language, 52, 452-473. Williams, E. (1997). Blocking and anaphora. Linguistic Inquiry, 28, 577-628.

Part 4

CONSTRAINTS ON LANGUAGE: NEUROSCIENCE

This page intentionally left blank.

9W

WITH LIMITED MEMORY: SENTENCE COMPREHENSION IN ALZHEIMER’S DISEASE

ORKING

Daniel Kempler, Amit Almor, Maryellen C. MacDonald, and Elaine S. Andersen

INTRODUCTION

Patients with Alzheimer’s Disease (AD) have substantial impairment in many cognitive domains, including language processing. The most obvious and best studied language problems in Alzheimer’s patients are in production: the frequency and nature of word-finding difficulties in AD have been the subject of much research (e.g., Bayles, Tomoeda & Trosset, 1990; Huff, Corkin & Growdon, 1986; Kempler, Andersen & Henderson, 1995). By comparison, relatively little research has addressed the comprehension problems which also impair Alzheimer patients’ abilities to answer questions, follow instructions, and participate in conversations. Because the language comprehension problems in AD occur in the context of memory and other cognitive impairments, it is difficult to determine the underlying cause of the comprehension impairments. In particular, because of the early and pronounced short term and working memory deficits in AD (e.g., Baddeley, Della Sala & Spinler, 1991), it is possible that the comprehension deficit is not due to a language impairment at all, but rather to a memory problem. Recent research has assumed that well-constructed experiments can determine whether the comprehension deficits in AD are due to deficits in memory or language. There have been proponents of each. Grober and Bang (1995), for example, argue that AD patients’ comprehension impairment is due to a “genuine syntactic deficit” (p 95). Although the notion of a syntactic deficit conflicts with early descriptions of preserved syntactic production in this population (Kempler, Curtiss & Jackson, 1987; Schwartz, Marin & Saffran, 1979), there is now evidence that syntactic impairments, although subtle, do appear in even in production tasks (e.g., Altmann, 1997; Bates et al., 1995). For example, Altmann, Andersen & Kempler (1993), and Altmann (1997) have analyzed spontaneous and elicited speech of AD patients and found a significant number of morpho-syntactic errors, indicating that even relatively unconstrained production tasks, AD patients make more syntactic errors than control subjects. Grober and Bang extend the notion of a 227

228

syntactic deficit to account for comprehension problems. They cite evidence that AD patients have little difficulty comprehending non-reversible passives which can be understood on the basis of word meaning alone (e.g., “The package is carried by the boy.”), but make errors on reversible passives which require syntactic processing for accurate comprehension (“The boy is kissed by the girl.”). They further assert that the comprehension deficits in AD are not due to memory impairment because AD patients show this same comprehension pattern even when “storage demands are minimized” by allowing patients to view the stimulus sentences while selecting an answer (p 104). In contrast, Caplan, Waters and colleagues (e.g., Rochon, Waters & Caplan, 1994; Waters, Caplan & Hildebrandt, 1991; Waters, Caplan & Rochon, 1995) argue that AD patients do not suffer from a syntactic processing deficit, but rather that memory and other nonlinguistic deficits underlie sentence comprehension impairments in AD. These authors found that AD patients’ errors did not necessarily increase as syntactic complexity increases, as would be predicted by a syntactic deficit hypothesis. In their studies, AD patients performed no differently when comprehending simple active sentences (e.g., “The lion killed the elephant.”) versus syntactically more complex structures of equal length, such as truncated passives (e.g., “The pig was touched.”) Rather, AD patients had more difficulty interpreting sentences that contained more than one proposition. Waters et al. attributed this pattern of comprehension deficits to an impairment of “postinterpretive” processing. They proposed that AD patients can interpret sentences as they hear them, but have difficulty when required to perform a comprehension task, such as matching the sentence meaning to a picture. By this account, postinterpretive processes are considered nonlinguistic, and hinge on working memory (WM) in order to maintain an active representation of the sentence meaning while selecting a match from a picture array. Clearly this debate concerning the locus of impairment has important theoretical and clinical implications. The patterns of impairment and sparing of language and memory functions in AD provide important evidence concerning the relationship between language and memory. If AD patients truly show an impairment in one area (e.g., working memory) but not another (e.g., sentence comprehension), it could be argued that the two functions, memory and language, are handled by independent cognitive mechanisms. Moreover, from a clinical point of view, it would be useful to understand the cause of comprehension difficulty in order to plan appropriate intervention. For example, if the problem is due to working memory deficits, intervention strategies might include repetition of the input. On the other hand, if language deficits are uncovered, intervention might involve linguistic simplification of the input and/or alternative communication modalities (e.g., gesture). The research described in the remainder of this chapter was undertaken initially to try to resolve this debate. The basic plan was to use two kinds of language comprehension tasks, an off-line task and an on-line task, on the view that these two types of task create substantially different memory demands (e.g., Tyler, 1992a,b). Specifically, the off-line tasks require significant memory to perform adequately, while on-line tasks require relatively little memory to perform well. To

229

the extent that the comprehension problem is due to memory impairment, we expected to see poor performance off-line with relatively better performance on-line. To the extent that the comprehension problem is due to a language impairment, we expected to see parallel performance on off-line and on-line tasks. Therefore, comparisons between on- and off-line performance could shed light on whether the comprehension impairments in AD patients stem from memory or linguistic deficits. To foreshadow our conclusions somewhat, the data led us in a rather different direction, so that we now view the distinctions between on- and off-line tasks, and the distinctions between linguistic and memory impairments, as less helpful than we originally thought. We will describe our new position in the General Discussion, following the review of our research. STUDIES OF LANGUAGE COMPREHENSION IN ALZHEIMER’S DISEASE

We developed our off-line and on-line language comprehension tasks with several different goals in mind. The first stage of our research was carried out to in order to replicate previous findings of sentence comprehension deficits using a traditional off-line sentence-picture matching task. We aimed to establish the degree to which syntactic or other aspects of the task (sentence length, picture complexity) affect sentence comprehension. The second part of our research utilized an on-line crossmodal naming task. We tested patients in an on-line task because the standard offline sentence comprehension tasks typically require some sort of judgment from participants and thus involve significant meta-linguistic and memory requirements. For example, to demonstrate comprehension in a sentence-picture matching task, participants must interpret a sentence and then reflect on and maintain the meaning of the sentence while searching for a matching picture. Performance on this task may be difficult to interpret, as people can perform poorly because of language, memory, attention or visual deficits. Because making explicit judgments about pictures as required in the off-line tasks does draw on other processes beyond those of normal comprehension, one primary goal of the on-line experiments reported here was to use a task that assesses sentence comprehension while minimizing nonlinguistic - particularly memory - requirements. Off-line Auditory Sentence Comprehension Because of the range of discrepant findings concerning the patterns of language comprehension in AD (summarized above), we designed a study to further investigate the effects of different types of structural complexity on sentence comprehension. Thirty individuals diagnosed with Probable Alzheimer’s disease and 23 agematched healthy control participants were given a sentence-picture matching test (Kempler, Almor, Tyler, Andersen & MacDonald, 1998). Stimuli consisted of 24 sentences sampling four grammatical constructions: simple active, active with a conjoined noun phrase (NP), full passive, and subject relative clause (see Table 1). All sentences used common nouns and transitive verbs, but differed in (1) syntactic

230

complexity (i.e., whether a sentence contained non-canonical word order or embedding) and (2) number of participants (two vs. three). Because the number of participants in a sentence is an index of both the semantic density of the sentence and the complexity of the picture array, we assume that the comprehension of sentences containing a greater number of participants will place greater demands on workingmemory.

Table 1. Sample stimuli used in the off-line sentence-picture matching protocol.

Sentences in all conditions were reversible, in that the sentence participants’ roles could have been switched without affecting the plausibility of the sentence meaning. The distracter pictures represented syntactic foils: they depicted the same action as the target (pushing, carrying, kissing, etc.) and the same participants, but in different roles. For example, the item “The boy is kissed by the girl” was accompanied by the target picture (a girl kissing a boy) and the syntactic foil (a boy kissing a girl). On each trial, participants heard a spoken sentence and were asked to point at the line drawing that best depicted the meaning of the sentence. Two vertically arranged pictures (a target and a distracter) were presented in each trial. The correct picture was the upper one on half of the trials and the bottom one on the other half. The sentence structures illustrated in Table 1 allowed us to test the two main hypotheses about the source of AD patients’ comprehension deficits. If the AD patients have a syntactic processing deficit, then they should perform more poorly on syntactically complex sentences than on syntactically simple sentences of comparable length. If the patients suffer from a memory deficit (and not a genuine syntactic deficit), they should perform worse on sentences that contain more participants than on sentences that contain fewer participants, but equally well on syntactically complex and syntactically simple sentences that contain the same number of participants. The performance of the AD patients is presented in Figure 1 (Healthy elderly controls performed nearly perfectly, so their performance is not included in the graph). As in previous research (e.g., Grober, & Bang, 1995; Rochon et al., 1994; Small, Kemper & Lyons, 1997), patients in our study showed an overall sentence

231

comprehension deficit: AD patients' performance (77% correct) was significantly worse than control participants' (99% correct). Furthermore, separate analyses for each sentence type showed that AD participants performed worse than the normal elderly on all sentence types, including the simple active sentences. An additional analysis of performance with the different sentence types of only the AD participants found that: (1) Patients performed better with the simple actives than with any other sentence type (passives, conjoined NPs, and relative clause); (2) Patients were more accurate with passives than with relative clause items (although this difference was only marginally reliable, p < .07); and (3) Patients performed better with conjoined NP sentences than with relative clause items. In other words, patients performed best with the active sentences, worst on the relative clause sentences, and intermediately with the passive and conjoined NP sentences.

These results offer some support for both a syntactic and a general memory source for sentence comprehension impairments in AD patients. First, the syntactic deficit hypothesis is supported by patients’ worse performance on the two syntactically complex sentence structures than on the syntactically simple structures, which were matched for number of sentence participants (active vs. passive, both containing two participants; conjoined NP versus relative clause, both containing three participants). Second, the fact that patients’ performance was equivalent on the syntactically simple conjoined NP and syntactically complex passive items suggests either that (1) AD patients have both syntactic and memory deficits or that (2) AD patients have a general memory impairment that affects the comprehension of items that are complex by any (syntactic or other) measure. Thus our off-line data do not uniquely support either the syntactic deficit hypothesis or the working memory deficit hypothesis. This uncertainty in the results is in part due to the

232

methods used: it is very difficult to separate effects of syntactic complexity versus memory when the task itself requires significant memory. Therefore, we sought to assess sentence comprehension with a method that would allow us to minimize the role of memory. On-line Sentence Comprehension Although on-line methods have not been used extensively with AD patients, we felt that they could be especially useful for distinguishing syntactic and memory deficit hypotheses. We reasoned that if sentence comprehension deficits in off-line studies are caused by task related memory demands, then simpler sentence processing tasks, which do not pose extraneous memory demands, should elicit better or even unimpaired performance. To this end, we compared the comprehension ability of AD patients and age-matched healthy controls in an on-line language comprehension task, cross-modal naming, which capitalizes on AD patients' relatively preserved ability to read aloud throughout the moderate stages of the disease (Bayles, Tomoeda & Trosset, 1992). Using the cross-modal naming paradigm, we examined patients' processing of various kinds of linguistic information (grammatical, semantic, and discourse) that is necessary for successful sentence comprehension. In all of our cross-modal experiments, we presented participants with auditory context sentence fragments and then recorded latencies as they read words that were either "good" or "bad" continuations of the context. The good target words were sensible and grammatical continuations of the auditory context, while the bad targets contained some syntactic, semantic, or discourse violation; the exact kind of violation varied across experiments. Latencies for reading good versus bad target words in the two conditions indicated whether participants are sensitive to the constraints that determine the goodness of the target as a continuation for the preceding context. Slower naming of the bad compared to the good continuations is expected in normal participants, and indicates the normal processing of the sentence structure and content. Similarly, if comprehension impairments in AD are due to the extralinguistic working memory demands posed by off-line tasks, then AD participants should perform similarly to the controls in this on-line task, which poses only minimal working memory demands. However, if AD participants suffer from a genuine linguistic deficit independent of memory impairments, then they should show a reduced difference between naming latencies of good and bad continuations in some or all experiments. Seventeen AD and 15 control participants took part, although not all subjects participated in all experiments. The experiments were conducted over several sessions, with half of the items in each session appearing in the good continuation condition and the other half in the bad condition. To minimize irrelevant variations due to performance differences of individual participants in different sessions, and to allow a comparison between the performance of the AD patients and the NCs, we normalized the data by transforming them into z-scores based on each subject's mean and standard deviation for each sentence structure for each session. Here we report only the sensitivity effects for the two populations (separately for

233

grammatical, semantic and discourse items); these were calculated by subtracting the mean normalized response time (for all subjects from each population) for good continuations from the mean response times for bad continuations. Examples of the stimuli from each of the three constraint types (grammatical, semantic, and discourse) are shown Table 2. A detailed presentation of the methodology and the tasks can be found in Kempler et al. (1998), Kempler, Almor & MacDonald, (1998), and Almor, Kempler, MacDonald, Andersen & Tyler (1999). Healthy controls' and AD patients' performance are shown in Figure 2. We discuss the data Grammatical Constraints. Forty grammatical sentences were constructed and then altered to create ungrammatical counterparts by the substitution, addition or deletion of one word. Two types of grammatical violations were included: (1) subject noun-verb agreement errors and (2) errors of transitivity (see Table 2). Preliminary analysis of the subject-verb and transitive sentence structures did not demonstrate any effect due to construction type (F < 1), so the data from both constructions were combined for analysis. An ANOVA examining the grammaticality effect (within participants factor) in the two groups (between participants factor) showed a reliable effect of grammaticality, such that latencies to grammatical targets were shorter than to bad targets (F (1,18) = 80.19, p < .001), no effect of group (F < 1), and no significant interaction (F < 1) (Figure 2). These results demonstrate that AD patients and healthy controls were equally sensitive to grammatical violations when tested with this on-line task. Table 2.

Sample stimuli used in the on-line cross-modal naming experiments.

234

Semantic Constraints. Of course, full interpretation of sentences requires more than just understanding the grammatical relations conveyed by words. It also requires integrating the meanings across several words, in sequence, to build a complex sentential meaning. For example, when listeners hear “Many people wash their....” they have already built a significant semantic representation, with certain expectations about what words might follow. In this case an object that many people could possess and would want to wash (e.g., ears, cups and cars) would be appropriate. Contrast that sentence fragment with: “Many insects wash their...” Here the subject noun “insects” carries with it semantic implications for the rest of the sentence, and “ears, cups and cars” are no longer appropriate, but “wings” and “prey” might be. One hypothesis about the cause of sentence comprehension impairments in AD is that, even if patients with AD understand single words reasonably well (Kempler, 1988; Nebes, 1989), these patients may have difficulty integrating individual word meanings over time and combining them into larger, more complex sentence meanings. If semantic integration is problematic, we should find that the AD patients who showed sensitivity to grammatical violations that was comparable to normals will have reduced sensitivity to violations involving semantic information. In this experiment, we used the cross-modal naming paradigm to test the hypothesis that patients with AD have difficulty with semantic integration. Twenty sentence pairs were constructed, and the two members of each pair differed in how well the last word fit the preceding context. In half of the sentences,

235

the final word was grammatically and semantically appropriate. In the other half, the final word was anomalous due to a semantic (or pragmatic) violation (Table 2). The procedure and subject populations were identical to the grammatical experiment described above. A 2x2 ANOVA, Population (normal vs. AD) by semantic appropriateness (appropriate vs. anomalous) revealed no effect of group (F < 1), a strong effect of appropriateness (F (1,18) = 9.97, p < .005), and no group by sentence type interaction (F < 1) (Figure 2). This result indicates that as with the grammatical violations, the control and AD participants were equally sensitive to the semantic and pragmatic appropriateness of the continuation word in the sentence context. Discourse Referential Constraints. Given the patients’ success with grammatical and semantic information during sentence comprehension, our third experiment was designed to investigate even higher level integration processes involving pronouns and their antecedents across multiple sentences. Perhaps the single most obvious characteristic of AD patients’ speech is the overuse of pronouns and other “empty words” (‘thing’, ‘it’, ‘do’) (Kempler, 1995; Ripich & Terrell, 1988; Ulatowska, Allard & Donnell, 1988). Although such empty words are common in language (indeed most of them are high frequency words), their use is generally restricted to particular circumstances. For example, pronouns (e.g., ‘it’, ‘he’) are typically used when the referent is highly salient for both the speaker and the listener, while full noun phrases (NP; e.g., ‘the dog’), which are more informative, are used when the referent is not highly salient in the discourse (Almor, in press; Ariel, 1990; Gundel, Hedberg & Zacharski, 1993; Marslen-Wilson, Levy & Tyler, 1982). In contrast to the restricted use of pronouns in normal speech, the use of pronouns by AD patients is frequent and often inappropriate (Kempler, 1995; Ripich & Terrell, 1988; Ulatowska et al., 1988). Although proper use of pronouns is affected by many factors in the discourse and sentence context, successful processing of pronouns requires that the information conveyed in the pronoun is matched with information that occurred earlier in the discourse. For example, to process the pronoun he, a match is required with a prior occurrence of a single male referent. Processing pronouns in discourse then requires the ability to match referents (a linguistic skill) and attention or memory sufficient to maintain active mental representation of previously mentioned referents. A discourse processing impairment then could result from either a linguistic or memory impairment. The on-line discourse processing experiment was designed to assess the ability of AD patients to process pronouns in short discourses. All discourse/pronoun items in the cross-modal naming experiment consist of a full sentence followed by an incomplete sentence fragment. The first sentence always introduces two entities, one plural, and one singular (e.g., “The children loved the silly clown at the party”). The second sentence fragment mentions one of the entities and ends right before the other entity is likely to be mentioned (e.g., “During the performance, the clown threw candy to__”). This fragment precedes a visual target which is an appropriate co-referential continuation pronoun (e.g., ‘them’) in half of the trials and an inappropriate continuation pronoun (‘him’) in the other half. (The sentence couplet “The children loved the silly clown at the party. During the performance, the clown threw candy to __” would be more likely to end

236

with the co-referential pronoun “them” than with the pronoun “him”, which would be interpreted as introducing a new entity by virtue of incompatible number.) Because in similar experiments healthy young adults were slower to name an inappropriate pronoun than an appropriate one (e.g., Marslen-Wilson, Tyler & Koster, 1993; Tyler & Marslen-Wilson, 1982), we expected older NCs to also show a similar pronoun appropriateness effect in target naming times. However, if AD patients are impaired in their ability to maintain active representation of referents, they should exhibit reduced sensitivity to pronoun appropriateness, compared to NCs. Overall, the experiment had 2 factors-Population (AD, NC), and Pronoun Appropriateness (appropriate, inappropriate). The procedure was identical to that of the previous studies. A 2 x 2 ANOVA, Population by Visual Target Appropriateness, found a main effect of target appropriateness, F(1,18) = 64.9, p < .001, and also an interaction between population and target appropriateness, F(1,18) = 29.78, p < .001. As is evident in Figure 2, although AD patients were sensitive to the appropriateness of the visual target, they were much less so than the control participants. This finding supports the claim that AD patients have difficulty in maintaining representations during discourse comprehension. Length Manipulations. The experiments summarized above found a difference between AD patients‘ impaired performance with discourse and their intact performance with manipulations of grammatical and semantic constraints in a crossmodal naming task. Our first hypothesis to explain the decreased sensitivity to the discourse violations was their memory deficits. Memory impairments might affect performance on the discourse items because the pronoun target was not presented immediately after the antecedent but only after many words. This contrasts with the grammar and semantic items, where the target followed closely (within one or two words) after the crucial linguistic context. If the impaired performance on the discourse items was simply due to the number of words separating the visual target from the part of the context which determined whether it was a good or bad continuation, this would be consistent with a working memory impairment. Moreover, if the context-target distance is the crucial factor in determining performance, then we should be able to “induce” poor performance by increasing the context-target distance in other (non discourse) stimuli as well. To test this hypothesis we constructed stimuli to vary the number of words occurring between the context and the target for some of the grammar items on which patients had previously performed very well (Almor, Kempler, MacDonald & Andersen, 1998). Short subject-verb agreement stimuli were taken from the subjectverb agreement items described above (Table 2) and long stimuli were constructed by adding an intervening 10-15 word clause between the subject and the verb. For instance, the subject-verb agreement item “The young girl was/*were” was transformed into a longer item “The young girl, who improved greatly every day because of the excellent teaching and good books was/*were.” We controlled the number marking on the last word of the embedded clause (in this case “books”), because previous research has shown that the number marking on a noun in an embedded clause affects interpretation of long-distance subject-verb number agreement (Nicol, Forster & Veres, 1997). In all cases, the number on the

237

embedded noun was different than on the subject noun (in this case “books” is plural while “girl” is singular). Analysis of the results demonstrates that AD patients and healthy elderly adults showed comparable sensitivity to grammatical violations of subject-verb number agreement in the short and long sentences. Both groups showed somewhat decreased sensitivity in the long sentences compared to the short items, but the decrease in sensitivity was comparable for both Alzheimer and control groups. We suspect that this decline in sensitivity is due to either to the additional length and/or to the mismatching number of the nearby embedded noun (e.g. “books”). Previous research with young adults has shown that a nearby noun with mismatching number yields longer reading times on a subsequent verb (Nicol et al., 1997) compared to a condition in which the subject noun and the embedded noun have the same number marking, indicating that mismatching number creates processing difficulty at the verb. Whatever the ultimate explanation for all participants’ reduction in sensitivity to long-distance grammatical violations, our data clearly indicate that the AD patients, even with very restricted working memory abilities, are not impaired relative to controls in interpreting long distance subject-verb number agreement. This suggests that some factor other than memory impairment is responsible for poor on-line processing of other long distance (i.e., discourse) dependencies. Another hypothesis to explain these findings (which we explore in the General Discussion), is that our discourse stimuli differed from the grammatical and semantic materials in some other (unintentional) ways that led to impaired performance by the AD patients. GENERAL DISCUSSION

We started this investigation attempting to pinpoint the source of AD patients’ sentence comprehension impairments in either working memory or linguistic deficits. We expected that the combination of a series of off- and on-line studies would yield a pattern of results that would implicate one of these impairments in sentence processing deficits. Our expectations were not met. While each of our results could bear on the question separately, the combination of all our results together do not afford a clear answer to the origin of sentence processing impairments. We will first review these results and then consider their interpretation and their implications for the study of language and memory in AD. We will conclude with a brief comment about the clinical implications of this work. Our off-line study found that an increase in both types of complexity tested syntactic and number of participants in the sentence - affected sentence comprehension for AD patients. This result suggests that these patients did not have a purely syntactic deficit. Rather, when the stimuli became more complex, either in sentence structure, number of participants (or even possibly picture complexity), patients’ performance declined. This result, by itself, is generally consistent with a working memory deficit, since added stimulus complexity of any type in a memory intensive task such as this one would tax the already diminished memory capacity of the AD subjects.

238

Our on-line experiments, however, suggest a different picture. The crossmodal naming task was designed to assess linguistic processing with minimal working memory and extraneous task demands. Insofar as working memory deficits are responsible for the sentence comprehension impairment, we expected to see intact processing of sentence material on-line. This expectation was partially borne out. We found that AD patients showed preserved ability to integrate grammatical and semantic information over short and long distances. However, in contrast to their normal performance with grammatical and semantic dependencies, the AD subjects were impaired in their ability to maintain discourse (pronominal) dependencies over comparable distances. Importantly, the patients’ performance in the on-line task was not affected by the memory load imposed by the items (short vs. long distance dependencies) but seemed to be affected by the linguistic content of the items (grammar & semantics vs. discourse). In summary, neither the off-line nor the on-line results are exactly what we anticipated, and integrating the results of both off-line and on-line experiments is a challenge. In neither case do we find clear-cut evidence for linguistic or memory deficits causing the sentence comprehension impairment. If the problem were linguistic in nature, we would have expected a clear effect of syntactic complexity in the off-line task and some consistency between the off-line and on-line syntactic processing. Since we did not find convincing evidence of linguistic impairment, we turned to the alternative hypothesis that the language comprehension impairment can be attributed to memory deficits. While the off-line data could be interpreted along the lines of a memory deficit hypothesis, the on-line data are only partially consistent with this explanation. On the one hand, since AD patients performed “normally” on several on-line tasks when memory demands were diminished, it appears that memory deficits were interfering with their performance on the off-line language comprehension tasks. On the other hand, if the problem was only memory, patients should have (1) performed better on all on-line tasks which minimize memory demands compared to off-line tasks which tax memory, and (2) performed comparably with the on-line long-distance grammar and the on-line discourse since both required the same degree of memory. Neither of these predictions were borne out, thus casting some doubt on a memory deficit explanation for the sentence processing results. It seems clear to us the we cannot place responsibility for sentence comprehension squarely in the domain of either linguistic deficits or memory impairments. How then can we explain our results? One way to approach this puzzle is to ask what task demands are shared by the “hard” tasks and how do they contrast with the “easy” ones? That is, what do the on-line discourse and the off-line stimuli share that the on-line grammar and semantic stimuli do not? We have already established that the answer is not simply “memory” - or else we would have seen a parallel between the on-line long distance grammar and the on-line discourse items which all contain the same distance between the context and target. The off-line stimuli and on-line discourse items also do not share linguistic structure: the off-line stimuli are single sentences of varying syntactic structures and contain no pronouns, while the on-line discourse items are sentence pairs varying in pronoun appropriateness. What other factors might be involved? We believe the answer may lie in the degree to which the task required

239

full processing of the sentence. In the off-line task, subjects must process the meaning of the entire sentence and determine how each of the participants relate to one another. This is also true for the on-line discourse items: in order to determine whether the pronoun him or them was coherent in the discourse, patients would have to understand the entire discourse. However, full processing of the sentences was not necessary for the on-line grammar and semantic items: in the case of our on-line grammatical and semantic items (Table 2), patients could perform well on the task (i.e., shorter naming times of good vs. bad visual targets) by attending to only minimal information in the sentence concerning the relationship between verbs and nouns. Even when these items were not immediately adjacent in the input, simple, high frequency, predictable grammatical relations (e.g., subject-verb number agreement) or very general semantic relationships (people-wash-knives) are tremendously salient in the language. Patients could therefore do well on these tasks even if they understood very little of the broader sentence meaning. We therefore conclude that it is not uniquely memory demands or the linguistic content that determines what AD patients will have difficulty understanding. Rather AD patients will have difficulty understanding language when they must derive a complete sentence meaning (as in the off-line and discourse items), when they must use relatively less common structural contingencies for interpretation (e.g., passive voice and relative clause structures), or when a task is particularly taxing on memory (e.g., more pictures to scan; more participants in the sentence). On the other hand, they will excel, and demonstrate normal comprehension when the stimuli are simple, made up of high frequency contingencies, or when they can rely on partial or salient aspects of the stimuli. Theoretical Implications We return now to the theoretical and clinical issues raised at the beginning of this chapter. We began by asking theoretical questions about the relationship between working memory and language comprehension in Alzheimer’s disease, and by implication, about the relationship between these two cognitive domains in healthy adults. Many investigators have explored the relationship between working memory and language comprehension in young healthy (and sometimes older and even occasionally impaired) adults by examining the relationship between performance on language comprehension tasks and performance on working memory tasks. In general, these studies ask subjects to perform independent language and working memory tasks. The memory tasks typically are patterned after Daneman and Carpenter’s (1980) reading and listening span tasks, in which subjects must remember and manipulate linguistic information (Just & Carpenter, 1992; Waters & Caplan, 1996). Investigators often find a correlation between, for example, verbal working memory tasks and tasks of language processing, and conclude that working memory of a certain type is “used” in the language comprehension task. Although many researchers, including our own group (e.g., Kempler et al., 1998; Almor et al., 1999) have produced research within this paradigm, there are some inherent difficulties in this reasoning and methodology. For instance, because the working memory tasks and the language comprehension tasks generally involve

240

the same set of skills (comprehending linguistic input while simultaneously retaining unrelated verbal information), a correlation between a “comprehension task” and a “working memory task” may really be a correlation between two related comprehension tasks. To put it another way, since the working memory tasks all involve language processing, it is difficult to know how much variance in a task is due to the language comprehension versus the theoretically independent measure of working memory. In addition, even if we believe that a working memory task is successful at measuring some memory function independent of comprehension, the correlation does not necessarily indicate that working memory is “used” in the comprehension task. Correlations only indicate that two tasks have some components in common, and other data are needed to infer a causal relationship, in order to conclude that working memory capacity determines comprehension performance (see MacDonald & Christiansen, 1999, for more discussion of these issues). Finally, on the practical side, there is notably very little variability in reading span scores in a healthy population, and resulting correlations in a normal population are therefore fragile at best. Our work with AD patients summarized here demonstrates an alternative approach to the study of component cognitive skills. Rather than searching for correlations among healthy individuals (who all function relatively well on these tasks), we utilized a population who are characterized (in fact, diagnosed) by their striking impairment on any and all measures of working memory. This approach allowed us to avoid the sticky methodological issues of generating just the “right” working memory task and relying on fragile correlations from relatively small samples to ascertain the relationship between memory and language. Rather than looking to correlations, we asked a somewhat different question, “What language can one process with very little memory?’ In our research, we have answered that question by demonstrating that it really depends how language is tested. Our results suggest that whenever the combination of task and materials forced participants to comprehend linguistic material in a deep fashion that is similar to normal language comprehension, mild and moderately impaired AD patients of the sort we have tested here will be impaired relative to healthy elderly controls. When they can get by with more shallow processing, they will tend to look less impaired. Other factors, including complexity and frequency of each sentence structure will also have an effect. Importantly, our research has lead us to re-think some of the distinctions and assumptions we believed in at the outset, and that have largely framed the debate and the research methods surrounding language and memory for many researchers. For instance, we began our research with the notion that off-line tasks are rough gauges of language comprehension, contaminated by memory and extraneous task demands, while on-line tasks assess language processing in a more direct manner. Our finding that performance on off-line tasks parallels some on-line tasks (but not others) forced us to reexamine what and how these tasks assess language. We concluded that the crucial distinctions affecting language performance may not be whether the task is off- versus on-line, or involving memory or not, but rather whether the task requires a partial or full analysis of the sentence meaning. Therefore, we end up viewing the distinction between on- and off-line tasks to be

241

rather different than it is often presented in the literature, in that both the task itself and the properties of the linguistic stimuli will determine the nature of performance. Our conclusion that the AD patients’ performance could only be understood as a result of task demands and stimuli, and not as a result of “linguistic” or “memory” impairment, has lead us to reexamine the very distinction that is often made between verbal working memory and language comprehension. We suggest that a more precise account of AD patients’ performance, and by extension, the relationship between language and memory function in healthy adults, will emerge from a thorough scrutiny of the computational demands posed by particular combinations of task and stimulus material. On this view, impaired sentence comprehension is not likely to be easily traced either to a working memory impairment or a linguistic impairment but rather will be analyzed in terms of the computational demands confronting the patient (or subject) who performs the task. This more cautious approach may seem disappointing to those of us who hoped to solve the riddle of the origin of impaired comprehension, but we think this approach will ultimately yield a more satisfying account of language impairment in AD, and in the long run a more complete understanding of language comprehension in general. Clinical Implications The first practical implication is a general warning about the applicability of these or any test results to real verbal interaction. There are, at least among clinical researchers, several related, implicit assumptions about how well off-line and online comprehension tasks reflect what happens in natural discourse. Roughly stated these assumptions are: (1) off-line tasks are necessarily inaccurate in their ability to measure language ability because they are contaminated by non-linguistic (e.g., working-memory and other extraneous) task demands and (2) on-line tasks more accurately reflect “real” language processing as it takes place in verbal interaction. Because these assumptions color how clinicians interpret the results of language comprehension tests, and the advice provided to patients and caregivers, they need to be considered carefully. Our results suggests that these assumptions do not hold true across all tasks. We certainly agree that some off-line tasks (e.g., grammaticality judgments) are unnatural and unlike anything that is done in spontaneous verbal interaction and that such tasks may not be the best way to judge a person’s language ability. Many other off-line tasks (e.g., reading passages and answering comprehension questions) are very natural and are an excellent way to assess the type of language processing that people engage in every day. Therefore, we do not agree that off-line tasks are inherently impure, or even that the presence of non-linguistic demands makes a task unlike natural language processing. Instead we believe that normal processing often involves substantial memory demands, the integration of linguistic and visual information, and other features that are characteristic of off-line psycholinguistic tasks. We also do not think that on-line tasks are inherently preferable. For example, we suspect that our on-line cross-modal naming task may be very unnatural, insofar as it requires substantially less processing than normal language comprehension. That is, in the case of our short grammatical and semantic items in

242

the on-line experiments (Table 2), patients could perform well on the task by attending to only minimal information in the sentence concerning the relationship between verbs and nouns. As stated in the body of this chapter, simple grammatical relations (e.g., subject-verb number agreement) or general semantic relationships (people-wash-knives) are tremendously salient in the language, and patients could therefore do well on these tasks even if they understood little of the broader sentence meaning. Therefore, the first “take-home message” from these data is really an admonition to clinicians that they too, must carefully analyze the resource demands of clinical batteries and research protocols before concluding that a patient’s performance on one of these off-line or on-line tests is relevant to performance in live verbal interaction. In other words, just because AD patients performed well on some of our on-line tasks, does not mean they will understand what we say to them in conversation. Probably the most general practical finding of the work presented here is that successful comprehension depends on many factors, including the structure of the to-be-understood material (simple vs. complex sentences, short vs. long sentences) and they way in which successful comprehension is gauged – or how we ask people to “use” their comprehension. The first part of this point – the importance of the structure of the verbal inputhas long been realized by clinicians and caregivers. This notion has previously made its way to caregivers in the form of recommendations to simplify linguistic input to AD patients by using common words, simple sentence structures and repetition (e.g., Clarke & Witte, 1995; Gwyther, 1985; Mace & Rabins, 1991; Ostuni & Santo-Pietro, 1986; Rau, 1993). One can imagine a good rationale for many specific speech modifications: e.g., repetition might be most helpful if memory were severely impaired and causing comprehension problems; simpler sentence structures might be more effective if linguistic deficits were known to interfere with comprehension. Although many language modifications can simplify the comprehension process, it is still open to debate whether one speech modification might be more effective than another. One recent investigation (Small, Kemper & Lyons, 1997) found that repetition and paraphrase were both effective at improving comprehension in AD, suggesting that a range of modifications might be effective. From the data presented here, we would suggest that any strategy that makes the information more accessible, either through the use of simple, high frequency grammatical structures, repetition, or paraphrase (as long as the paraphrase is not structurally more complex than the original) should help. That is, any alteration that simplifies the input should reduce the resource demands of the task and be effective at improving comprehension. There is an additional point that is made by our data: it is not only the structure of the input that determines how successful comprehension will be, but also the task demands created by the context and the response requirements. At a very basic level, the linguistic and non-linguistic contexts will have an effect on comprehension. Busy or distracting contexts will make more demands on patients’ limited resources and leave less available to focus on the sentence comprehension aspect of the interaction. Therefore it is probably important to keep distractions to a minimum during verbal interactions. Most obviously, this means minimizing

243

irrelevant input such as other conversations within earshot or people carrying on unrelated activities during conversation. At a less obvious level, the way in which patients are asked to respond to auditory input also has an effect on the comprehension process. As with our studies, we can improve comprehension performance by asking the patients only to read a word aloud in order to indicate their comprehension, compared to requiring them to look at a picture array and point to a particular picture. While perhaps it is difficult to see the corollary of this comparison in the real world, every interaction constrains the potential responses. For instance, we can ask a patient to respond to a verbal question such as “What would you like to drink?” by either (1) making a verbal response, i.e., requiring them to activate a meaning from their mental dictionary and produce the phonology that accompanies it, or (2) reading aloud a choice from two written alternatives. Although the same question is presented in same manner in these two alternatives, the response requirements are drastically different. Comprehension is more likely to be demonstrated when the response requirements are simpler and within the patient’s preserved ability (word retrieval is often impaired, while reading aloud is often preserved). The important notion here is that to optimize comprehension, it is as important to simplify how comprehension is demonstrated (the output requirements) as it is to simplify the structure of the input. Finally, our data demonstrating that AD patients have particular difficulty processing pronouns in discourse suggest that increased explicitness and redundancy in reference would be of significant help. This reiterates advice given by Rau (1993) who suggests caregivers should adjust their vocabulary and use “concrete, specific and simple” words. She specifically recommends that caregivers avoid words such as ‘this,’ ‘these,’ ‘he,’ and ‘she.’ Our research indicates that these recommendations are appropriate and are likely to enhance patients’ comprehension.

244

REFERENCES

Almor, A. (in press). Definite noun-phrase anaphora and focus. The Informational Load Hypothesis. Psychological Review. Almor, A., Kempler, D., MacDonald, M.C., Andersen, E.S., & Tyler, L.K. (in press). Why do Alzheimer patients have difficulty with pronouns? Working memory, semantics, and reference in comprehension and production in Alzheimer’s Disease. Brain and Language. Almor, A., Kempler, D., MacDonald, M., & Andersen, E. (1998). Long distance number agreement in Alzheimer’s disease. Presented at the Academy of Aphasia, Santa Fe, November. Brain and Language, 65, 19-22. Altmann, L.P. (1997). Effects of Working Memory and Semantic Impairments on the Speech of Alzheimer’s Disease Patients. Unpublished doctoral dissertation, University of Southern California. Altmann, L.P., Andersen, E.S., & Kempler, D. (1993). Reevaluating syntactic preservation in Alzheimer’s disease. Presented at the Academy of Aphasia, October, Tucson. Ariel, M. (1990). Accessing noun-phrase antecedents. London; New York: Routledge. Baddeley, A.D., Della Sala, S. & Spinnler, H. (1991). The two-component hypothesis of memory deficit n Alzheimer’s disease. Journal of Clinical and Experimental Neuropsychology, 13, 372-80. Bates, E., Marchman, V., Harris, C., Wulfeck, B. & Kritchevsky, M. (1995). Production of complex syntax in normal aging and Alzheimer’s disease. Language and Cognitive Processes, 10, (5), 487-539. Bayles, K.A., Tomoeda, C.K. & Trosset, M.W. (1990). Naming and categorical knowledge in Alzheimer’s disease: The process of semantic memory deterioration. Brain and Language, 39,498-510. Bayles, K.A., Tomoeda, C.K. & Trosset, M.W. (1992). Relation of linguistic communication abilities of Alzheimer’s patients to stage of disease. Brain and Language, 42, 454-472. Daneman, M. & Carpenter, P.A. (1980). Individual differences in working memory and reading. Journal of Verbal Learning and Verbal Behavior, 19, 450-466. Clarke, L. & Witte, K. (1995). Nature and efficacy of communication management in Alzheimer’s disease. In Lubinski, R. (Ed.)., Dementia and Communication: Research and Clinical Implications (pp. 238-256). San Diego, CA: Singular Publishing Group. Grober, E., & Bang, S. (1995). Sentence comprehension in Alzheimer’s disease. Developmental Neuropsychology, 11, 95-107. Gundel, J. K., Hedberg, N., & Zacharski, R. (1993). Cognitive status and the form of referring expressions in discourse. Language, 69, 274-307. Gwyther, L.P. (1985). Care of Alzheimer’s patients: A manual for nursing home staff. American Health Care Association & the Alzheimers Disease and Related Disorders Association. Huff, F.J., Corkin, S., & Growdon, J.H. (1986). Semantic impairment and anomia in Alzheimer’s disease. Brain and Language, 28, 235-249.

245

Just, M. A,, & Carpenter, P. A. (1992). A capacity theory of comprehension: Individual differences in working memory. Psychological Review, 98, 122149. Kempler, D. (1988). Lexical and pantomime abilities in Alzheimer’s disease. Aphasiology, 2, 147-159. Kempler, D.(1995). Language Changes in Dementia of the Alzheimer Type. In R. Lubinski (Ed.) Dementia and Communication: Research and Clinical Implications. (pp. 98- 114). San Diego, California: Singular Publishing Group. Kempler, D., Almor, A., & MacDonald, M.C. (1998). Teasing apart the contribution of memory and language in Alzheimer’s disease: An on-line study of sentence comprehension. American Journal of Speech-Language Pathology, 7,61-67. Kempler, D., Almor, A., Tyler, L.K., Andersen, E.S., & MacDonald, M.C. (1998). Sentence Comprehension Deficits in Alzheimer’s Disease: A Comparison of Off-Line vs. On-Line Sentence Processing. Brain and Language, 64, 297-3 16, 1998 Kempler, D., Andersen, E.S., & Henderson, V. W. (1995). Linguistic and attentional contributions to anomia in Alzheimer’s disease. Neuropsychiatry, Neuropsychology, and Behavioral Neurology, 8,33-37. Kempler, D., Curtiss, S. & Jackson, C. (1987). Syntactic preservation in Alzheimer’s disease. Journal of Speech and Hearing Research, 30, 343-350. MacDonald, M.C. & Christiansen, M.H. (1999). Reassessing working memory: A reply to Just & Carpenter and Waters & Caplan. Manuscript submitted for publication. Mace, H.L., & Rabins, P.V. (1991). The 36-hour day: A family guide to caring for persons with Alzheimer’s disease, related dementing illnesses, and memory loss in later life (Revised Edition), Baltimore, MD: The Johns Hopkins University Press. Marslen-Wilson, W. D., Levy, E., & Tyler, L. K. (1982). Producing interpretable discourse: the establishment and maintenance of reference. In R. J. Jarvella & W. Klein (Eds.), Speech, place, and action, 339-378. Chichester: Wiley. Marslen-Wilson, W. D., Tyler, L. K., & Koster, C. (1993). Integrative processes in utterance resolution. Journal of Memory and Language, 32,647-666. Nebes, R.D. (1989). Semantic memory in Alzheimer’s disease. Psychological Bulletin 106, 377-394. Nicol, J., Forster K., & Veres, C. (1997). Subject-verb agreement processes in comprehension. Journal of Memory and Language, 36, 569-587. Ostuni, E. & Santo-Pietro, M.J. (1991). Getting through: Communicating when someone you care for has Alzheimer’s disease. Verb Beach, FL: The Speech Bin. Rau, M.T. (1993). Coping with communication challenges in Alzheimer’s disease. San Diego: Singular. Ripich, D. N., & Terrell, B. Y. (1988). Patterns of discourse cohesion and coherence in Alzheimer‘s disease. Journal of Speech & Hearing Disorders, 53, 8-15. Rochon, E., Waters, G.S., & Caplan, D. (1994). Sentence comprehension in patients with Alzheimer’s disease. Brain and Language, 46, 329-349.

246

Schwartz, M., Marin, O., & Saffran, E. (1979). Dissociations of language function in dementia: A case study. Brain and Language, 7, 277-306. Small, J.A., Kemper, S., & Lyons, K. (1997) Sentence comprehension in Alzheimer’s disease: Effects of grammatical complexity, speech rate, and repetition. Psychology and Aging, 12 (1), 3-11. Tyler, L.K. (1992a). Spoken Language Comprehension: An experimental approach to normal and disordered processing. Cambridge, Mass.: MIT Press. Tyler, L.K. (1992b). The distinction between implicit and explicit language function: Evidence from aphasia. In M. Rugg & D. Milner (Eds.) Neuropsychology of Consciousness. Academic Press. Tyler, L. K., & Marslen-Wilson, W. (1982). The resolution of discourse anaphors: some on-line studies. Text, 2, 263-291. Ulatowska, H. K., Allard, L., & Donnell, A. (1988). Discourse performance in subjects with dementia of the Alzheimer’s type. In H. Whitaker (Ed.), Neuropsychological studies in nonfocal brain damage, 108-131. New York: Springer-Verlag. Waters, G. S., & Caplan, D. (1996). The capacity theory of sentence comprehension: Critique of Just and Carpenter (1992). Psychological Review, 103,761-772. Waters, G., Caplan, D. & Hildebrandt, N. (1991). On the structure of verbal shortterm memory and its functional role in sentence comprehension: Evidence from neuropsychology. Cognitive Neuropsychology, 8, 81-126. Waters, G., Caplan, D., & Rochon, E. (1995). Processing capacity and sentence comprehension in patients with Alzheimer’s disease. Cognitive Neuropsychology, 12(1), 1-30.

247

ACKNOWLEDGEMENTS

This work was supported by a grant from the National Institutes of Health to Maryellen MacDonald (AG1177301). We wish to acknowledge the following for referring Alzheimer patients for this research: Dr. Victor Henderson, Professor of Neurology and Director of the Clinical Core of the Alzheimer’s Disease Research Center at the University of Southern California (NIH AG05142); Dr. Helena Chui, Co-Director, Alzheimer’s Disease Diagnostic and Treatment Center, Rancho Los Amigos Medical Center (DHS 94-20356), and Dr. Lee Willis, USC Department of Neurology and Geriatric Neurobehavior Center, Rancho Los Amigos Medical Center. We gratefully acknowledge the persistence and dedication of Lori Altmann, Mariela Gil, Laila Lalami, Karen Marblestone, Sarah Schuster and Karen Stevens who collected the data, and we would like to thank the subjects and their families for their participation.

This page intentionally left blank.

10 M

AGING? QUESTION: AN

EMORY OR

THAT'S

THE ELECTROPHYSIOLOGICAL PERSPECTIVE ON LANGUAGE Thomas C. Gunter, Sandra H. Vos & Angela D. Friederici

INTRODUCTION

In this chapter we discuss several experiments carried out in our laboratory which explored language, memory and aging from an electrophysiological perspective. We show that it is valuable to extend the traditional behavioral measures with more online electrophysiological ones. The first part of the chapter details some technical issues concerning the measurement of event related brain potentials (ERPs), describes several established ERP components which reflect different cognitive processes, and considers some relevant physiological changes in older persons. In the second part of the chapter we discuss three aging studies; two investigating semantic processing and one exploring syntactic processes. In the semantic studies one issue relates to the fact that several meta-analyses on aging have shown that the size of behaviorally measured semantic (priming) effects did not differ significantly between age groups although older adults often show a larger difference between related and unrelated contexts. Only data collapsed across many experiments revealed that the semantic priming effect is reliably different between young and older adults (e.g., Laver & Burke, 1993). It is possible that RT is less sensitive to age-effects than electrophysiological measures that allow information processing to be monitored much more on-line and independent of input and output stages. Another equally important issue relates to the question of whether aging in itself or memory capacity plays the main role in semantic processing. The third experiment investigating syntactic aspects of processing asks which part of the parsing process is affected by aging: first pass and/or second pass parsing. If first pass parsing is a relatively basic and automatic process (cf. Gunter & Friederici, 1999) it might be preserved in aging (cf. Salthouse, 1991). 249

250

ELECTROPHYSIOLOGICAL REFLECTIONS OF COGNITION

Event Related Brain Potentials Extracting event related brain activity from the spontaneous EEG. The EEG (Electroencephalogram) can be described as the electrical activity elicited in the brain due to synchronous activity of a large number of neurons which can be measured using electrodes placed on the scalp. In other words, the EEG can be viewed as a far-distance measure of brain activity of both cortical and sub-cortical structures. As early as 1875, Canton presented the first (animal) data which showed that electrical activity of the brain could actually be measured inside as well as on the surface of the brain. The first human recording of the EEG on the scalp was carried out by Berger in 1929. Since then a large body of research has focused on unraveling the functional meaning of the EEG. The early EEG-experiments explored the spontaneous background EEG. Such research showed that during complex task performance the normally dominant alpha rhythm (approximately 10 Hz) became desynchronized and higher frequencies in the beta range (approximately 13-25 Hz) appeared. During the early period of EEG-research some work showed that stimulation by light flashes or nerve stimulation (small electrical shocks) could be monitored in the EEG as tiny phasic brain responses which were superimposed on the spontaneous EEG itself. These event related brain responses are what we now call ERPs (Event Related Potentials). It is possible to extract these brain responses from the spontaneous EEG using the signal averaging technique developed by Dawson (1947, 1951). It was the practical problem of recording reliable somato-sensory ERPs in epileptic patients that led Dawson to use a superimposition technique of signal-to-noise enhancement in evoked potential recording. In order to get a cancellation of the noise (or random differences between the individual ERPs), Dawson (1951) carried out a paper and pencil averaging technique and demonstrated that signal averaging is effective in extracting ERPs from the EEG. Nowadays this technique is commonly performed by digital computers. In general, an ERP consists of several positive and negative deflections which are present at a particular point in time (the latency in milliseconds) with a particular strength (the amplitude in microvolt). The deflections, also called 'components', are typically named after their polarity and their peak-latency. For instance, the N 100 refers to a negative component with a mean latency of approximately 100 ms relative to stimulus onset. Sometimes ERP components are labeled after their polarity and ordinal position in the wave form (i.e., N1, for the first negative peak in the waveform after stimulus onset), or after the cognitive function the component is assumed to reflect (e.g. SPS for Syntactic Positive Shift or CNV for Contingent Negative Variation). ERP components are a reflection of patterned neural activity associated with informational transactions in the brain. Components which have a latency smaller than 10 ms, represent neural activity in the peripheral sensory pathways. Later components represent activity in subcortical (No, Po, Na, Pa, Nb) and cortical areas (P1, N1, P2, P300, N400). A more functional classification is the

251

use of the exogenous-endogenous distinction (cf. Donchin, Ritter & McCallum, 1978). An exogenous component is determined by the parameters of the physical stimulus rather than by a cognitive event, whereas an endogenous component is determined by a cognitive event rather than by the physical stimulus. In general, psychophysiologists are mainly interested in endogenous components which begin to become evident in the region of 50 - 100 ms after stimulus presentation. Note that the exogenous-endogenous distinction is by no means dichotomous and therefore only serve as a helping hand. The advantage of measuring ERPs in comparison to behavioral measures is that they provide information about cognitive processes without the need of an additional task like lexical decision. Beside the ‘unobtrusiveness’ of the measure, ERPs also provide information about the timing of cognitive stages (latency of the components) and a rough indication where these processes take place in the brain (scalp distribution of the amplitude of a component). Although these on-line characteristics of ERPs are a big advantage, it is important to note that we do not want to argue that behavioral measures are obsolete. It is clear that in many instances one wants to link ERPs with task and or memory performance. From this perspective, ERPs are an extension to and not a substitution of behavioral measures. Having said that we would now like to introduce several ERP-components and the cognitive processes they probably reflect. Early components P1, N1 and P2. In visual tasks, these early components are typically studied in selective attention studies. Several investigators in this field have argued that the early P1 (90 - 120 ms after stimulus presentation) and N1 (around 200 ms) component as elicited in visual attention tasks are evoked over the occipital scalp and appear to reflect modality-specific processing in the visual pathways that is sensitive to the direction of attention (e.g., Eason, 1981; Hillyard & Münte, 1984; Mangun & Hillyard, 1990). Both the P1 and N1 components are found to be enhanced in attended stimuli. This phenomenon is typically interpreted as a sign of a complementary process that enhances perceptual processing at the attended location (e.g., Hillyard, Luck & Mangun, 1994). In the aging studies presented in this chapter, the N1 component is assumed to reflect stimulus intake processes which take place in the occipital lobe (note that in the auditory modality similar components are elicited in the temporal lobe). This working hypothesis is strengthened by the fact that N1 amplitude has been found to depend on the strength of a visual stimulus. The functional significance of the P2 (around 250 ms) is still unknown although it is not directly affected by attentional manipulations. Stimulus updating: The P3b. One very well known and most extensively studied endogenous ERP component is the decision-related P3b. Over the last decade, a number of studies have investigated the reflection of memory comparison processes in ERPs. In such studies, the task of the participant is to memorize 1 to N items and to compare these items with a series of probe stimuli (cf. Sternberg, 1969). The ERP component of greatest interest is the P3b, a positive wave elicited approximately 500 ms post stimulus (for reviews see: Pritchard 1981; Verleger, 1988). Generally, it is found that P3b latency increases with larger memory set sizes (e.g. Strayer, Wickens & Braune, 1987) whereas its amplitude typically decreases with increased set sizes (e.g., Wijers, Mulder, Okita, Mulder, & Scheffers, 1989).

252

P3b latency in these kinds of task is presumed to reflect the time necessary for the build up of evidence about the presence or absence of a target (Donchin, 1981; Mulder, 1986) while P3b amplitude may be viewed as a reflection of processing resources that can be allocated to the task (e.g. Hoffman, Houck, MacMillan III & Simons, 1985). Because tasks with a high load on memory demand more processing, the P3b amplitude will become smaller depending on the memory set size. In general, it is found that P3b is delayed and smaller and has a different scalp distribution in older adults (Friedman et. al., 1993). Semantic processing: The N400. A negative component elicited around 400 ms after stimulus presentation, referred to as the N400, is of particular interest for language processing research since its amplitude has been shown to be sensitive to semantic processing (for reviews, see Kutas & Van Petten, 1988; Kutas & Kluender, 1991; Osterhout & Holcomb, 1995; Van Petten, 1995). More than two decades ago the first N400 experiments were carried out by Kutas and Hillyard (1980). They used sentences as linguistic material and found that, if the last word of a sentence was incongruent with the preceding context (e.g. 'She spread the bread with socks'), it evoked a large N400. On the other hand, if the last word was congruent with the preceding context (e.g. 'She spread the bread with butter' ) the amplitude of the N400 was reduced. These findings suggest that the N400 might be related to semantic processing. This interpretation was further supported in the experiment of Kutas, Lindamood and Hillyard (1984) which showed a semantically anomalous word to have a smaller N400 when it was related to the expected ending than when it was not (while the expected ending [eat] to the sentence stimulus The pizza was too hot to ... showed no N400, the ending drink showed some N400 effect but this was in turn much smaller than the unrelated ending cry). Additional research has shown that the N400 amplitude reduction depends on the preceding semantic context whether it be composed of a sentence fragment, a phrase or even a single word (Kutas & Hillyard, 1980; Neville, Kutas, Chesney & Schmidt, 1986; Bentin, McCarthy & Wood, 1985). Fischler, Childers, Achariyapaopan and Perry (1985) even showed that the N400 can be elicited by interpretable false statements. In their experiment, participants had to learn a set of statements such as 'Matthew is a lawyer'. False statements ('Matthew is a dentist' ) presented a day after the practice session elicited an N400. In an earlier experiment, Fischler, Bloom, Childers, Roucos and Perry (1983) showed that the N400 is more sensitive to the associative strength between entries in the mental lexicon than to the propositional content of a statement. Participants were asked to verify a set of simple semantic propositions (e.g. 'A robin is a bird' or 'A robin is not a car'). The truth of a statement did not affect the N400, the association between the two content words, on the other hand, did. All these data indicate that the N400 is related to semantic activation. Van Petten and Kutas (1990) showed that N400 amplitude to open class words is inversely correlated with the word's ordinal position in relatively simple English sentences. They interpreted this finding as a reflection of the build up of constraints imposed by a partial sentence upon individual succeeding words. More recently, it has been claimed that the N400 is related to lexical-semantic integration processes (Brown & Hagoort, 1993, see also Chwilla, Brown & Hagoort, 1995). That is, once a word has been accessed in the mental lexicon, its meaning has to be integrated into an overall representation of the current

253

word or sentence context. The easier this integration process is, the smaller the amplitude of the N400 becomes. Thus, changes in semantic processes can be measured using the N400 component. If one wants to investigate the effects of aging on these processes one must know whether or not the N400 is sensitive enough to be used as a measure. The effect of aging on the N400 was investigated for the first time by Harbin, Marsh and Harvey (1984). Young (mean of 21 years) and elderly (mean of 71 years) persons were presented with sequences of 5 words. The experimental task was to decide whether or not the fifth word matched the other four words which were all drawn from the same semantic category. In the case of a category mismatch, an N400 was elicited in both age groups. The latency of the N400 in the older group was delayed and, although not discussed by these authors, their data seem to suggest that the N400 amplitude was also reduced in this age-group. A study carried out by Hamberger and Friedman (1990) also showed clear aging effects on the N400 component during semantic processing. Their three age groups (young, middle aged and old) performed a semantic discrimination task in which they had to decide whether or not a particular word was animate or non-animate. The ERP-difference between animate and non-animate words was smaller and delayed for the two older age groups. More details regarding N400 age effects during sentence processing will be given later in this chapter (for a recent study on N400 effects across 6 decades see Kutas & Iragui, 1998). Syntactic processing: The (E)LAN & P600. More recently, interest has also focused on how syntactic processes are reflected in ERPs. Most research exploring syntax uses direct manipulations like syntactic violations.1 Generally speaking, two ERP-components have been directly correlated with the processing of syntactically anomalous sentences. A relatively early negativity (i.e. Left Anterior Negativity [LAN]; with a frontally or left anterior maximum) and a late centro-parietal positivity (i.e. P600 or the so-called Syntactic Positive Shift). The early negativities are typically elicited by elements that turn the sentence into an incorrect one. It is interesting to note that those studies that realized incorrect sentences by a word category error elicited a very early left anterior negativity (ELAN; around 200 ms; Neville et al., 1991; Friederici, Hahne, & Mecklinger, 1996; Friederici, Pfeifer, & Hahne, 1993; Hahne & Friederici, 1997) whereas studies in which the violation was realized morphosyntactically (i.e. inflectional), evoked a left anterior negativity between 300 and 500 ms (i.e. LAN; Münte, Heinze, & Mangun, 1993; Münte & Heinze, 1994; Osterhout & Mobley, 1995; Gunter, Stowe, & Mulder, 1997; Münte, Matzke, & Johannes, 1997; Penke, Weyerts, Gross, Zander, Münte, & Clahsen, 1997; Coulson, King, & Kutas, 1998a; Vos, Gunter, Kolk, & Mulder, 1998). A left anterior negativity in this latter time window was also found for targets violating a verb's argument structure (i.e. subcategorization violations; Rösler, Friederici, Pütz, & Hahne, 1993). This led Friederici (1995) to propose that the different latencies of these negativities may reflect a temporal hierarchy in the availability or use of the different types of information encoded in the lexical entry, with word category information being available first (i.e. first pass parsing; see below). P600s are found for both syntactically incorrect as well as syntactically infrequent structures (e.g. object relative clauses, see below). While the P600 is mostly preceded

254

by an early negativity in the case of incorrect sentences, it is not in the case of correct sentences with a non-preferred syntactic structure. Thus, a P600 which is often preceded by a negativity is found for morphosyntactic violations (e.g., subject-verb number disagreement: Hagoort, Brown, & Groothusen, 1993; Osterhout, McKinnon, Bersick, & Corey, 1996; Vos et al., 1998; other types of verb inflection violations: Gunter et al., 1997; case disagreement: Coulson et al., 1998a). Moreover, this LANP600 pattern is also observed with subjacency constraint violations (Neville et al., 1991) and with subcategorization violations (Osterhout & Holcomb, 1992; Rösler et al., 1993). A solitary P600 is found in different types of garden-path sentences (Osterhout & Holcomb, 1992; Osterhout, Holcomb, & Swinney, 1995; Mecklinger, Schriefers, Steinhauer, & Friederici, 1995; Friederici, Steinhauer, Mecklinger, & Meyer, 1998). The functional significance of the syntax related components is still under debate. Some researchers suggest that the P600 is the most robust syntax related ERPcomponent (Hagoort et al., 1993; Osterhout et al., 1996) whereas other researchers suggest a specific role of each of the two components in the parsing process. Friederici (1995) suggested that the ELAN (around 200 ms) observed in response to word category errors reflects first pass parsing processes whereas the P600 reflects second pass parsing processes like re-analysis or repair (cf., Frazier, 1987). Münte et al. (1997) proposed that the LAN (around 350 ms) reflects the actual detection of a morphosyntactic mismatch whereas the P600 reflects the necessary reprocessing of the sentence in order to make it semantically and syntactically meaningful. This suggestion was based on the observation that the LAN for subject-verb agreement violation is elicited by sentences containing real or pseudo-words whereas the P600 was only present in the case of real words. It is clear that the P600 reflects a controlled process. In experiments carried out in our laboratory it was found that the P600 was affected by a broad range of task variables such as semantics (Gunter et al., 1997), working memory load (Gunter et al., 1997; Vos et al., 1998), and probability of occurrence of a violation (Gunter et al., 1997; Hahne & Friederici, in press). This suggestion was also supported by a study in which a levels-of-processing approach showed the P600 to be smaller in a shallow task (upper-lower character distinction; Gunter & Friederici, 1999). Note that the recent discussion whether or not the P600 and the P3b originate from the same family (cf. Gunter et al., 1997; Coulson et al.; 1998 a & b, Münte, Heinze, Matzke, Wieringa, & Johannes, 1998; but see Osterhout et al., 1996; and Osterhout & Hagoort, in press) is relevant for this issue because the P3b can also be seen as the reflection of controlled processes. The (E)LAN is, in contrast to the P600, not affected by semantics (Gunter et al., 1997; Hahne & Friederici, in press), task instruction (Gunter & Friederici, 1999; Hahne & Friederici, in press), or probability of occurrence of a violation (Coulson et al., 1998a; Gunter et al, 1997; Hahne & Friederici, in press). Thus it appears that the two ERP-components observed in correlation with syntactic parsing differ along variousfunctionalparameters. Recently, there has been a debate in the literature over whether or not the LAN reflects a pure syntactic process or indexes working memory load (Kluender & Kutas, 1993). The Kluender and Kutas (1993) study showed that a LAN can also be found in sentences which are syntactically correct but make a heavy demand on working

255

memory (i.e. in filler-gap dependencies). A recent experiment of Kluender and coworkers (Kluender, Münte, Cowles, Szentkuti, Walenski & Wieringa, 1998) suggested, however, that this WM related LAN is a more phasic response with a longer duration than the LAN found in response to outright syntactic violations (see Vos et al., 1998). Thus, it seems that the more shorter LAN can be classified as syntactic in nature. To summarize, ERPs can give us a detailed insight into the processing of (language) stimulus material without the need for an overt response. In this chapter the N1 component is hypothesized to be an index for stimulus intake processing, the P300 for stimulus evaluation, the N400 for lexical integration, the (E)LAN for first pass parsing and the P600 for second pass parsing processes. As will be shown in the next paragraphs, ERPs are also sensitive to aging. Before describing these electrophysiological effects we discuss some general physiological factors related to aging in order to see these age related ERP-effects in the correct perspective. Aging Issues: Nerves, EEG and ERPs It is clear that information processing as measured by RT is slowed down in older persons. This delay might be explained by slowing down of input and/or output processing. It could be that stages in the information processing itself are delayed (as well). We will therefore first discuss, from an electrophysiological point of view, age changes in peripheral input and output processes. Then we turn to the issue of how information processing is reflected in the EEG. During later development, the rate at which nerve impulses are propagated along the peripheral nerves may slow down. Conductivity velocity of sensory nerves such as the median nerve slow down from about 42 meters/sec at age 20 to about 3 1 meters/sec at age 85 (LaFratta & Canestrari, 1966). Another nerve, the digital nerve, declines steadily from 57 meters/sec to 48 meters/sec while its amplitude drops from 43 to 21 µV, although the refractory period is unaffected (Schaumburg, Spencer & Ochoa, 1983). After approximately the age of 20, motor nerve conduction velocity slows at a rate of 1 meters/sec per decade. While consistent, these changes in conduction velocity are relatively small and it is clear that they cannot explain the large age effects found in, for instance, simple reaction time. In a study which compared 3 different response modes (foot, jaw and finger), Birren and Botwinick (1955) found a response mode independent delay of approximately 60 ms in older persons. This independence is particular striking since the neural pathway and musculature of each of the responses are very different. Such findings therefore point to more central processes being the major cause of the aging effect in cognitive processing. It is therefore important to turn our attention to age related changes in the EEG because this electrophysiological measure may give us an idea of what happens to central cognition. The EEG changes during life span. On the one hand, these changes might reflect 'real' age differences in information processing or, on the other hand, they may be in part due to neuronal changes (note that the volume conduction of the EEG changes due to, for instance, larger ventricles). The most consistent age-difference found in the 'normal' clinical EEG is the age-related decline in frequency of the dominant alpha rhythm (young: 10-10.5 Hz, 70 years: 9.0-9.5 Hz, and 80 years:

256

8.5-9.0 Hz; for reviews see Obrist, 1976; Prinz, Dustman & Emmerson, 1990). This well known phenomenon is, intriguingly enough, probably due to factors such as cardio- and cerebrovascular diseases. Studies that have rigorously screened for diseases have obtained smaller or minimal age differences in this parameter (for more details see Porges & Fox, 1986; Prinz et al., 1990; see also Obrist, 1979). Thus, in spite of its complexity, it seems that the clinical EEG does not contain identifiable features that reflect normal aging unconfounded by age-related disease states. Because the clinical EEG does not give reliable information about how information processing changes during life span it seems appropriate to explore how ERPs change over lifetime since they do reflect information processing reliably. As can be inferred from the age related deceleration in conductivity velocity of sensory nerves, ERP components provide evidence of age-related slowing at all functional levels of the brain. Most auditory brain stem potential studies (these potentials are elicited before approximately 10 ms) indicate age-related transmission delays which can be attributed to changes in peripheral auditory structures (Simpson, Knight, Brailowsky, Prospero-Garcia, & Scabini, 1985). Some brainstem studies also found significant slowing within the auditory brainstem (e.g. Chu, 1985). Conduction time from brainstem to cortex also appears to slow down with advancing age (e.g. Allison, Wood, & Goff, 1983). Klorman, Thomson, & Ellingson (1978) investigated ERP components between 20 and 300 ms which were elicited by auditory, somatosensory and visual stimuli. It was found that the later a particular ERPcomponent occurs (i.e. latency), the more it is influenced by aging. In general, one can conclude that the latency of early components (before 200 ms) is either not or is only minimally affected by aging whereas the latency of later components (after 250 ms) are markedly increased in older adults. In general, the amplitude of early components increased in older persons, whereas the amplitude of later components is decreased in this group (see Katzman & Terry, 1983, Klorman et al., 1978). One should be cautious when interpreting the delay of the later components in visual evoked potentials, however, since there is some indication to suggest that this effect might be due to age related visual loss. When stimulation is adjusted to compensate for visual loss, some studies have found no age related delay in later visual evoked potential components (e.g. Dustman, Shearer, & Snyder, 1982). Note that what Dustman et al. call 'later' components are not what are typically called 'endogenous components' (Cf. Donchin et al., 1978; see below) because they are not clearly related to any psychological process but are simply the response to checker boards or flashes. It is clear from the literature that endogenous components like the P300 are delayed in older persons (P300 about 1-2 msec/year from early age to adulthood: Prinz et. al. 1990). In relation to age effects on the amplitude of ERP components we have to discuss the so-called 'skull difference' issue. Sometimes it is argued that the age related amplitude changes in ERPs arise as a result of the elderly having thicker or calcified skulls. If this were the case, all ERP-components would show similar age related amplitude effects because this confounding factor would always be present. As described above, this is certainly not the case since early components increase their amplitude whereas later components show an age-related decrease. These

257

findings do not support a skull thickness explanation. The anatomical changes in the brain2 itself, on the other hand, may lead to age differences in the manifestation of ERPs on the skull. As has been noted by several investigators, ERP components, in particular endogenous ones (e.g. P300), exhibit different scalp distributions (e.g., Friedman et al., 1993). It is therefore important to be very circumspect when comparing age groups in an absolute manner. It is possible that the differences found are simply due to differences in scalp distribution. In this chapter, most age group comparisons will be made on the difference between two task-conditions for each age. While this will certainly not circumvent the problem totally, it is a more cautious approach than relying on an absolute comparison between age groups. The examination of ERPs can help us with the investigation of which processes or components of cognition (i.e., information processing) are actually affected with increasing age. This is what Salthouse (1991) calls the 'analytical approach to localization'. A general problem related to an information processing description of a task is whether one, two,....,N operations are actually involved. Another problem is that we do not know whether a particular task is carried out in a similar way by both young and old individuals. Perhaps older persons just insert an additional operation and are therefore slower. ERPs might help us to overcome such problems. Using ERPs one can establish whether or not the general patterns of results are similar between two age groups and, if not, at what point in time the ERPs from young and old adults start to deviate. If the ERP-patterns more or less match, one can argue that no processing operations were added or deleted. Next, it is useful to manipulate a task variable (e.g. memory load, semantic congruency, etc.) and see how this manipulation affects both age groups. If the manipulation has a different onset in the ERP-difference wave (e.g. congruent minus incongruent endings of a sentence) one could argue that the processing stage or stages associated with the manipulation are changed in one of the age groups. Age differences in ERP-patterns are rarely found. It is much more typical to see a similar pattern but that it is delayed after a certain moment in time. Thus, to put it differently, we are specifically interested in trying to estimate the actual point in time at which the aging process starts to become a burden on information processing. This point in time will probably be different for different kinds of tasks. Notice that the lower limit depends on the sample frequency used (in this case 100 Hz, limit 10 ms). Due to this time restriction we are not able to measure the slowing down of nerves or brainstem potentials because these phenomenon occur within 10 ms. SEMANTIC PRIMING: EFFECTS

OF

AGING

Behavioral Evidence The most fundamental way exploring the effect of context is to use a one word context. In such a priming situation, participants are typically presented with word pairs and have to make a word/non-word judgement on the second word, the target word. When the first word, the prime, and the target are semantically related/associated an enhancement of the reaction time (RT) is found for the lexical decision on target

258

words. According to Neely (1991) this facilitation or priming effect involves three different mechanisms, namely: automatic spread of activation (ASA), expectancy, and post-lexical priming mechanisms. While it is claimed that the first of these mechanisms (ASA) involves automatic processing the remaining two are viewed as requiring attentional processing. ASA plays a primary role in network theories of long term memory. Such theories (e.g. Anderson, 1983) assume that our knowledge of concepts consists of organized networks of concept nodes which are interconnected by relations or links (associations). If a particular word is encountered, not only does its memory node become temporarily activated, but this activation also spreads automatically through the links to associated nodes (i.e. ASA). The priming phenomenon can be explained by assuming that the second word (if it is an associated word) has just received some activation from the previous word and will therefore require less additional activation to bring it to a level above threshold. As a consequence, less time is required to make a lexical decision. The mechanisms underlying the propagation of activation in semantic networks may have important consequences for aging. Two major characteristics of semantic networks are of importance: The first is concerned with how activation spreads (i.e. which nodes are activated), the second addresses the time course of the spreading (i.e. how quickly nodes are activated). Behavioral explorations have shown that older persons probably have the same organization of concepts and therefore the same characteristics of semantic activation as younger persons have (e.g. Light, 1990). For instance, in a word association task, Burke and Peters (1986) found little change in the nature of word associations during adulthood, indicating that aging has little effect on the organization of knowledge. If older persons have a network structure similar to younger persons, the next question relates to the propagation of activation in the network itself. Howard, Shaw and Heisy (1986) showed, using a lexical decision task, that there is a possible slowing in the rise time of the spread of activation in older persons. Another important aspect concerning the spread is the time allowed to spread. In other words, the SOA used between prime and target might influence the characteristics of the spread. Balota, Black and Cheney (1992) investigated age differences in automatic and attentional mechanisms by manipulating SOA (250, 1000, and 1750 ms in Experiment 1 and 250, 1750, and 3250 ms in Experiments 2 & 3). Prime stimuli were visually available either for a short period of time (200 ms) or during the whole SOA. The automatic component (i.e. ASA), as measured in the 250 ms SOA was not clearly affected by aging. The attentional component (i.e. post lexical mechanisms like expectancy; SOA 1000, 1750, 3250), on the other hand, did show an age difference across SOAs. The attentional effect for the old participants first increased but then decreased at the longest SOA while the young participants showed a monotonic increase across the SOAs. Balota et al. (1992) argue that these findings are in accordance with the position adopted by Hasher and Zacks (1988), namely that older persons have difficulty in inhibiting irrelevant information. ERP evidence The priming data discussed so far was obtained by the use of a lexical decision paradigm. Investigating priming with ERPs has the advantage of being able to

259

monitor the cognitive processing related to priming without the need for an overt reaction. Moreover, ERPs allow the time interval before the classical overt response on the second word (i.e. the reaction elicited by the prime) to be investigated in detail. Since the majority of mechanisms leading to the priming effect take place during the interval between primes and targets, this is obviously an important possibility. One of the first single word studies investigating ERPs during priming was reported by Bentin et al. (1985). RT to target words presented in a wordlist showed the traditionally observed behaviorally priming effect. In the ERPs recorded during the lexical decision, targets showed a clear N400 whose amplitude was significantly larger for targets which were not preceded by a semantically related word. Later in this chapter, we will show that this N400-priming effect can also be elicited when no lexical decision has to be carried out. Holcomb (1988) was the first to report a direct reflection of differences in the processing of passively read primes in ERPs. The aim of his experiment was to explore ERP differences due to automatic and attentional processing of primes in young adults. He therefore manipulated the percentage of semantically related prime-target pairs in a particular list to either 12.5% in the automatic version or to 50% in the attentional version of the lists (SOA was always 1000 ms). In the ERPs recorded to the primes a significant difference was found between the two conditions: both the P300 (between 300 and 650 ms) as well as a negative going shift, which Holcomb called CNV (between 750 and 1150 ms), were larger in the attentional version of the list. The N400 effect elicited by targets was larger in the attentional version. In a recent study (Gunter, Jackson, & Mulder, 1998), we explored priming in young and middle aged academics. The association priming task used in this study involved the visual presentation of high and non-associated word pairs. The young (20 students, 20.5 years) and middle aged participants (20 academics; 57.2 years) were not required to respond during the presentation phase but were aware that on completion of a task block they would be asked to recall as many words as possible. A SOA of 700 ms was chosen, an interval which has previously been shown in behavioral studies to be sufficient to elicit a priming effect in elderly persons (i.e. Howard et al., 1986). This SOA also makes an analysis of the prime-target interval possible (faster SOA’s will disrupt the ERP-pattern; see Boddy, 1986). Memory processes were tentatively explored using recall scores. Results Recall performance. The analysis carried out on the recall scores indicated that the older participants recalled 6.5% fewer words than the younger participants and that highly associated words were approximately 20% better recalled than non-associated words. There were no interactions of age with any of the variables. ERPs. As can be seen in Figures 1 and 2, ERPs elicited by primes as well as targets elicited a N1 (Oz), a P2 (Fz) and a N400 (Cz). The N1 was faster for primes (8 ms) and showed no further effects, demonstrating that input processes are probably not affected by aging. The P2 showed clear effects of aging for its latency as well as its amplitude. The P2 for primes was 18 ms earlier and approximately 4 µV larger for the

260

older Ss. The P2 evoked by target words showed no age effect at ail in either latency or amplitude. The ERPs to the targets (see Figure 1) showed a clear N400 which was larger for the non-associated target for both age groups. Only the N400 for the non-associated targets was delayed (30 ms) and smaller (4 µV) in the older group. The association level effect (i.e. the electrophysiological priming effect as indicated by the difference between the ERPs elicited by associated versus not associated targets; see shaded areas) started approximately 150 ms later for the older group and was distributed differently: Neither the recordings at lateral nor the frontal electrode sites showed any association level effect in these older participants.

Figure 1: ERPs to primes for both age groups. The solid line shows the ERP for the young participants, the dashed line shows the ERP for the older participants. The shaded areas indicate a significant difference between both age groups.

261

ERPs elicited by prime words (see Figure 2) had a similar form for both age groups but were much more positive in the older participants. The shaded areas indicate in which intervals a significant main effect of age was found. The effect was enhanced at the midline electrodes but dominant at the anterior leads. At the time point when the target was presented (i.e. 700 ms after the presentation of the prime) the age groups no longer differed in their ERPs. It seems as if the N400-component of the older participants was smaller but elicited at the same time as the N400 of the younger participants. This impression was confirmed by analyses of the N400 peak latency and amplitude at the Cz electrode. No age effect was found for N400 latency but N400 amplitude was approximately 4 µV smaller in the older age group. Re-analysis on the basis of percentage recall. From each age-group 5 individuals with a high, and 5 individuals with a low recall score were selected As can be seen in Figure 3, the N400 for the young high recallers was most prominent. Their association level effect (shaded area) was (a) large in comparison to all other recall groups, (b) was present at both lateral electrodes, and (c) started to become significant after approximately 250 ms. The young low recallers had a much smaller association level effect which became significant approximately 120 ms later (i.e. 380 ms) than the high recallers in this age group. The older participants show approximately the same pattern as the young participants in that the high recallers had a much larger association level effect than the low recallers. In fact, the older low recallers did not show any significant association level effect at all. It seems as if the poorer recallers "activated" the target words less selectively than did the good recallers. In order to explore this suggestion more thoroughly we also re-analyzed the prime-data. Inspection of the ERPs on primes showed that there were indeed differences between the recall groups. To state it differently, the impact of the prime word was largest in the older high recallers. Discussion The experimental data presented here suggest that age differences are already evident at a very basic level of processing, namely in a passive priming task. While the N400 to non-associated targets was both delayed in latency and reduced in amplitude in the middle aged group, no age differences were apparent in the high associated targets. The effect of association level (high vs. low), as indicated by the difference wave, showed a delay of approximately 150 ms in the older group. This effect closely resembles the age related delay as found in a previous study with sentences (Gunter, Jackson, & Mulder, 1992). The fact that the N400 component elicited by highly associated targets showed no age difference indicated that this expected word was probably equally well and certainly sufficiently activated in both age groups. Otherwise, there would have been an ERP-difference between both groups around 400 ms (N400). The fact that non-associated targets showed a smaller N400 in the middle aged suggested an age difference in activation of this target category. Since the N400 amplitude is associated with semantic activation (the smaller the N400, the more activated a word is in semantic memory), the reduced N400 in the middle aged suggests a higher activation level of the non-associated targets in this age group. Both findings suggest that the activated semantic network of our middle aged participants had a larger/less

262

selective spread of activation than that of the young participants though the activated associated target word seemed similar for both age groups. ERPs elicited by primes were more positive in our middle aged group, suggesting either a better preparation for the word to come, or a different (probably better) use of context. Note that some earlier behavioral studies have also demonstrated that older individuals can and do utilize contextual constraints efficiently under certain conditions (Cohen & Faulkner, 1983; Burke & Yee, 1984). These data therefore suggest that middle-aged academics, particularly those who were more successful in the recall tasks, adopted compensatory strategies which, although not completely eliminating all age effects, certainly reduced them. The re-analysis of high and low recallers showed prime-target processing to be influenced by recall performance. It was found that middle aged high recallers in particular, had a larger positivity (P2) on prime words. Moreover, high recallers in general showed a much larger differentiation between low and high associated targets,

Figure 2.

ERPs to targets for both age groups. The solid lines show the highly associated targets, the dashed lines show the low associated targets. The shaded areas indicate a significant difference between both target categories.

263

as evidenced by a much larger N400 component elicited by low associated targets and a more positive ERP in the N400-region for the high associated targets. Thus, it seems that the highly expected targets were more activated in the high recall group while the low associated words were less activated in the high recall group. Thus, these data indicate that the dynamic range of semantic activation was much larger in high recallers or to reformulate in another way, low recallers may activate "fuzzier" semantic networks than do high recallers. Whatever the exact relationship between semantic processing and recall performance turns out to be, it is fairly safe to conclude that the memory system plays an important role in the elicitation of N400 effects. It therefore follows that at least part of the described age effects (i.e. smaller N400/association level effect) must be attributed to a general age difference in memory performance. Note, however, that the classical aging effects on N400 as measured on non-associated targets still remained when high recalling middle age participants were compared with low recalling young participants, indicating that memory differences can only account for a part of the aging effect. WORKING

MEMORY AND SEMANTIC PROCESSING:

EFFECTS

OF AGING

In the foregoing experiment, effects of (working) memory-capacity on language processing could only be explored tentatively because a 'real' WM-score was not available. Although it seems reasonable to assume that persons with a high recall score have a better (working) memory than persons with a much lower recall score, any analysis on the basis of recall runs the risk of being contaminated by variables such as individual strategies. In order to shed more light on the WM-issue, we will discuss an ERP-experiment (Gunter et al., 1995) in which 24 students (mean age 20.5 years) and 24 middle aged academics (mean age 57.5 years) were presented with sentences which were highly demanding of working memory. Before the experiment several memory measures were taken. They included word span; forward and backward digit span and a Dutch version of the Salthouse working memory task (L-span). In this test, participants were required to listen to a set of sentences and remember the last word of each sentence. Beside this memory task, they also had to answer a sentence related question after the presentation of each individual sentence. After all sentences of a particular set were presented, the to-be-remembered words had to be written down. The number of sentences per set varied from 1 to 7. Each set had 3 versions which used different sentences. The test started with the 3 sets containing 1 sentence. The next 3 sets contained 2 sentences etc. The test was terminated whenever a participant did not correctly answer all the questions or could not recall all last words correctly in at least two of the three sets of a particular condition. Instructions emphasized the need to answer the questions correctly. The experimental sentences (Dutch language) imposed either a high or low load on working memory. This memory load manipulation was accomplished by choosing two different syntactic structures: one in which a temporal subordinate clause was embedded within a main clause (high load) and the other in which the main clause followed the temporal subordinate clause (low load). The last word of each sentence was either a highly expected or an unexpected ending ('gered' [i.e. saved] was changed into, for instance, 'gevat' [i.e. understood]).

264

Figure 3. ERPs to targets for both high and low recallers, separately for both age groups on the central and both lateral electrodes. The solid lines show the highly associated targets, the dashed lines show the low associated targets. The shaded areas indicate a significant difference between both target categories.

Low load: " Terwijl een grote menigte stond toe te kijken, werd de kleine drenkeling door de held gered. " (A word by word translation into English would be: While a large crowd stood towards to look, was the small drowning-person by the hero saved.); High load: " De kleine drenkeling werd door de held, terwijl een grote menigte stond toe te kijken, gered. " ( The small drowning-person was by the hero, while a large crowd stood towards to look, saved.).

It is clear from the literature that working memory capacity plays an important role during the processing of complex sentence material like this. King and Just (199 1) for instance presented young adults, who had either a high or a low reading span, with sentences that imposed a low (subject relative sentences: ‘The reporter that attacked the senator admitted the error’) or a high (object relative sentences: ‘The reporter that the senator attacked admitted the error’) processing load. Though low and high span readers showed approximately the same performance on the less computationally demanding sentences, the object relative sentences were both comprehended more poorly and read more slowly by the low span readers.

265

Effects of WM-load on semantic processes can be measured by using the N400 component. If words are more difficult to integrate due to the higher load on memory, the N400 component will become larger than when integration is less difficult. Thus, in the case of our long sentences, one would expect that particularly the sentence with the central embedding shows the smallest N400-congruency effect. This is because at the end of this sentence type one has to retrieve the main clause out of memory before one can make sense out of this sentence. General reflections of memory processes in ERPs can be summarized as follows. With some caution one can conclude that prolonged positivities may reflect memory storage processes (cf. Rushkin, Johnson, Mahaffey and Sutton, 1988; Rushkin, Johnson, Canoune and Ritter, 1990; Rösler and Heil, 1991) and that slow negative waves are related to retrieval processes in long term memory (cf. Mecklinger, Kramer and Strayer, 1992; Rösler and Heil, 1993). Thus, an enhanced slow (i.e. long duration) negativity in a highly demanding situation, like our central embeddings, probably indicates retrieval effort. Results Memory tests. Only the working memory test (i.e. the L-span) showed a clear and significant age difference (young 4.15 vs. middle aged 2.75). Word span (4.9 vs. 4.7), digit forward (6.7 vs. 6.1) and digit backwards (5.4 vs. 5.3) did not differ between the age groups. ERPs. The ERP-data elicited by the sentence final words showed a clear N400 for incongruent words. The N400 of the older participants was delayed by 40 ms and smaller in amplitude (1.5 µV). The delay of the N400 was not due to input processes since the N1 component was not delayed in the older participants. Moreover, the congruency effect was smaller in the high WM-load sentences for young participants. In the middle aged the congruency effect was only present in the low load sentences. Interestingly enough, the syntactically more complex structure elicited a slow negative shift with a central maximum and a lateralization to the left. The shift was found for both the congruent and incongruent endings and started very early. Because of this early onset of the shift it was suggested that it must be related the processing of the preceding word and probably reflects retrieval operations needed during the parsing processes which were 'triggered' by the last word of the inserted subordinate clause in the high WM-load condition which actually always included a comma. Both age groups had this negativity although it was smaller in the older participants. Re-analysis on the basis of L-span. In order to explore the role of working memory capacity in these sentences in more detail, we re-analyzed our data for 4 sub-groups defined by age (young and middle-aged) and WM-capacity score (low and high). In each age group, 4 individuals with the highest and 4 with the lowest WM-score were selected and placed in the relevant subgroup. The mean memoryscores of each subgroup showed clear subgroup differences in L-span score (young: 5.6 vs. 2.8 older: 3.8 vs. 1.8) whereas the more traditional measures were the same. Since each subgroup only contained 4 participants, noise level was reduced by filtering the physiological data digitally (low pass, Fc=6Hz, 20dB). This procedure

266

will not affect the slow potential shifts in which we are interested since these signals are far below 6Hz. In Figure 4, a graphical representation of the congruency effect is given for all four subgroups in both the low and the high WM-load condition. Since the Cz electrode showed the maximal N400 and was highly representative for the congruency effects found in this analysis, discussion will concentrate on this position. The effects of congruency are straightforward. The young participants with a high WM-score show similar congruency effects in both WM-load conditions. However, the young participants with a low WM-score show clear effects of WMload: in the high WM-load condition their congruency effect almost disappears. Thus WM-capacity plays an important role in the data of the younger participants. The middle-aged participants with a high WM-score likewise show clear effects of congruency in the low WM-load condition. Although present, the congruency effect in the high WM-load condition did not reach significance. The middle-aged participants with a low WM-score showed no congruency effect in either load condition. Interpreting the data of the middle-aged participants must be done with care, since the low WM-group did not show any congruency effect at all. One could argue that a WM-score of 1.8 is really very low, perhaps so low that it impossible for such a participant to display an N400 in a long, complex sentence. In any event, WM-capacity also seems to play an important role in our middle-aged persons. As was discussed above, sentence endings in the high WM-load condition elicited a greater slow negative wave than the endings in the low WM-load condition. If this WM-load related negativity really depends on working memory, it follows that it should be different for the high and low WM-groups. In the reanalyses, clear interactions of WM-load and L-span score were found. The analysis carried out separately for young and middle-aged also showed clear WM-load by Lspan score interactions. Figure 5 shows the subtraction potential between high and low WM-load condition; the shaded area indicates where a significant interaction was found. As can be seen, the WM-load related negativity has a lateralization towards the left. The differences between high and low WM-span participants is maximal at the parietal electrode (shaded area). In both age groups, the high WMspan participants showed the largest effect. What is clear from the described data is that ERP-effects as found during sentence processing vary with WM-capacity as measured by the Salthouse working memory test, at least in the 2 sub-groups at the extremes of the distribution. In a situation where a high load on working memory is present, participants with a high WM-capacity display larger congruency effects as well as larger WM-related slow negative wave compared to those having a smaller WM-capacity. Although present, these effects were less pronounced in the middle-aged participants. Discussion Young participants showed clear effects of congruency with both high and low WMloads although the effect was smaller under high load. In contrast, middle-aged participants showed the congruency effect only under low load. One could argue that the disappearance of the congruency effect in the high load condition might be due

267

to the suspended interpretation and decay of the memory trace of the incomplete main clause in this condition. It is plausible that the overall smaller WM-capacity of the middle-aged group has played a role in this age related lack of congruency. Converging evidence supporting and extending this hypothesis was found in the reanalysis of data from participants with either a high or a low WM-capacity. Although less clear in the middle-aged persons, low WM-capacity participants showed a decrease in congruency effect in the high WM-load condition. High WMcapacity participants, on the other hand, show similar congruency effects in both WM-loads. Physiological data therefore reveal that individual differences in WMcapacity do in fact play an important role in the processing of complex syntactic structures. Moreover, this role is not confined exclusively to older individuals; young low WM-capacity participants showed a less clearly defined congruency effect than young participants with a high WM-capacity. Thus, age differences in sentence processing are therefore not simply a fact, they depend for a great deal on the memory capacity of a person.

Figure 4. ERPs as found on the Cz electrode elicited by congruent (solid line) and incongruent (broken line) sentence endings in the high and low WMload conditions for subjects with either a high or a low WM-capacity. The shaded areas indicate a significant main effect of congruency.

268

Figure 5. Difference waves resulting from subtracting the ERPs of the sentence endings in the low WM situation from the ERPs in the high WMload condition (i.e. high load minus low load) for the high and low WM-capacity subjects (the solid respectively the broken line). The shaded areas indicate a significant interaction of WM-load with Lspan group. To sum up, both the priming and the sentence processing experiment showed that semantic processes, as measured by ERPs are clearly influenced by aging. In order to extract meaning (semantics) from sentences it is necessary that parsing processes are carried out correctly. The sole identification of the words, however, is not sufficient for sentence understanding. In order to identify the grammatical relation between these lexical elements, syntactic structures must be recognized. Guidance in this process is given by syntactic information such as word order, function words and inflectional elements. Some information is also encoded in the lexicon entry of the lexical elements themselves (e.g. syntactic category information: is a word a verb or a noun). It is clear that if the identification and/or the processing of syntactic related information is affected by aging this must have a fundamental impact on sentence comprehension itself. SYNTACTIC

PROCESSING:

EFFECTS

OF AGING

Behavioral evidence The few studies exploring syntactic processing in elderly have mostly used off-line production or comprehension tasks. Kemper (1986), for instance investigated the

269

effects of syntactic complexity on sentence imitation in the elderly. She presented young and older adults with sentences which varied in grammatical correctness and in length, position and type of embedded clause (e.g. left branching: "The dog who the woman who the boy watched owned chased after the ball"; right branching: "The child watched the woman who owned the dog who chased after the ball"). Participants were asked to repeat the sentences verbally. The older participants had more trouble responding to the ungrammatical sentences; had more difficulty in imitating the sentences with long embedded clauses correctly; showed few problems in imitating right branching sentences but appeared to be differentially affected by left branching sentences in which the embedded clause precedes or interrupts the main clause. These latter sentences are believed to place a greater burden on working memory. Kemper concludes that her results imply that the syntactic processing abilities of older adults are reduced as a result of attentional or memory limitations. Syntactic complexity of prose production also shows age-related changes. Kemper (1987) analyzed a collection of diaries. Although the older persons used less complex syntax in their prose, no age difference in the direction of branching of embedded constructions was found. Kemper suggested that writing may be less affected by different processing demands than oral speech production. Only recently a small number of studies have assessed syntactic aspects of language comprehension in older persons using more on-line tasks. Zurif, Swinney, Prather, Wingfield, and Brownell (1995) showed that older adults, in contrast to younger participants, did not reactivate a filler in filler-gap constructions when the distance between the filler and gap was large. To put it differently, there seems to be an age difference in the processing of sentences in which lexical elements are displaced from their normal, canonical, position. Zurif et al. (1995) attribute this age related difference to differences in memory capacity. A direct comparison between semantic and syntactic aspects of language processing in older adults was recently carried out by Friederici, Schriefers and Lindenberger (1998). Participants were presented with a semantic and a syntactic priming task. The prime was a small sentence fragment (e.g. ‘Der Apfel wurde’; ‘The apple was’). The targets were verbs which were written in upper case font (e.g. ‘GEGESSEN’; ‘EATEN’) and could either be correct or syntactically or semantically incorrect. The lexical decision on these targets showed, for uncorrected RTs, age differences for both types of violations. After logarithm transformation, however, only an age difference could be found for the syntactic violations. A cost-benefit analysis using a neutral baseline showed that the age influence on syntactic processes are particularly due to the cost component (incorrect vs. neutral) and that the benefit component (correct vs. neutral) is similar for young and older adults. To put it differently, when language input is syntactically correct there seems to be no age difference in syntactic processing. If, however, something syntactically goes wrong, aging kicks in. The specification of ‘what’ goes wrong is of course an important issue. As suggested above, syntactic errors can either occur in the first or in second pass parsing processes (cf. Frazier, 1987). Errors occurring in first pass parsing relate to the mismatch between syntactically expected and the actual (syntactic) word category. If such a mismatch is present, a phrase structure violation has occurred and the system

270

is in need of a re-analysis process, the so-called second pass parsing. Both of these processes can be measured using ERPs. Problems in first pass parsing will elicit an ELAN component whereas problems in second pass parsing will elicit a P600. Thus, if older participants are presented with a phrase structure violation and the ELANcomponent is affected, one can infer that the activation of very basic syntactic features (in the mental lexicon) like word category is problematic for this age group. If, on the other hand, the P600 shows age differences it can be concluded that older adults have a problem re-analyzing the syntactically unexpected word. Note that such a finding would, as was the case with semantic information, also point to an involvement of WM-processes. A syntactic re-analysis also has to be carried out in workingmemory. ERP Evidence We would now like to discuss new and unpublished data from a study carried out in the auditory modality which was specifically set out to explore the influence of aging on syntactic processes. In particular, the study explored whether first pass and/or second pass parsing processes are affected by aging. The German language material was similar to that used in earlier studies (Friederici et al., in press). Half of the sentences were correct, whereas the other half had either a semantic violation or a phrase structure violation. Correct: Semantic violation: Correct: Syntactic violation:

Die Tür wurde geschlossen (The door was being closed) Der Ozean wurde geschlossen (The ocean was closed) Der Laden wurde am Samstag geschlossen (The store was on Saturday closed) Das Geschäft wurde am geschlossen (The store was on closed)

The semantic violation was included in order to check if the participants showed the to-be-expected delay and reduction in the N400 component. Forty participants, 20 young (20-37, mean 27.8 years) and 20 older adults (40-59, mean 50.2 years) were presented with 192 sentences. After they heard a sentence they had to judge whether or not the sentence contained an error independently of the kind of violation. The behavioral data showed that the older participants were slightly less accurate than the young participants (88 vs. 92 %). Results The semantic violations showed an N400 which was earlier and larger for the younger participants (see Figure 6). The onset of the N400-effect was significantly delayed in the older group with approximately 100 ms (250 vs. 350 ms). The amplitude of the N400-effect was also much smaller in the older group. These data confirm what we have already seen in the foregoing experiments. As can be seen in

271

Figure 7, the ERPs elicited by syntactic violations showed a clear ELAN and P600 component. Interestingly enough the ELAN was not significantly different for the two age groups. The P600, however, was significantly smaller in the older participants. The onset of the P600-effect was elayed by 50 ms in the older group.

Figure 6. The left and middle panel show ERPs as found on the Cz electrode for semantically correct (solid line) and incorrect (dotted line) sentence final words for the young and older participants. The right panel shows subtraction waves (correct - incorrect) for the young (solid line) and the older (dotted line) participants.

Discussion The semantic violation elicited the to be expected age-difference in that the N400 was delayed and smaller in the older participants. One can therefore conclude that our participants are representative in their language performance for the described age range. The ERPs elicited by the syntactic violation showed that first pass parsing processes are spared whereas second pass parsing is affected by aging. Thus, the activation of the syntactic features of a word are age independent whereas syntactic re-analysis is performed more slowly because there was a 50 ms delay in the onset of the P600-effect. The smaller P600 amplitude in older participants probably indicates that the older participants had more difficulty in doing the syntactic reanalysis process. This difficulty probably relates to memory capacity. We know from the P3b-literature that the more complex or the more memory demanding a

272

task is, the smaller the P3b (cf. Parasuraman, 1990; Strayer et al., 1987; Wijers et al, 1989). Because there is growing evidence that the syntactic P600 and the P3b have similar characteristics, this memory related hypothesis for the observed late syntactic effect seems quite plausible. It is clear that older persons in general have a smaller memory capacity. The coupling of (working) memory capacity and P600 amplitude can not be made directly in the present experiment. We know, however, from several language ERP-experiments carried out on young persons that such a coupling seems to exists (Friederici et al, 1998; Mecklinger et al, 1995; Vos et al, 1998). In these studies it was found that the P600 (or in the case of Mecklinger et al. a P345) in low span persons was generally delayed in latency and smaller in amplitude. Thus inferring that our older participants did have a smaller (working) memory capacity there is, as was the case for semantic processing, an impact of memory capacity on syntactic processing. CONCLUSIONS

The experiments presented in this chapter explored age related changes in language processing. We were specifically interested in the investigation of semantic and syntactic processes independent of more peripheral input and output processes. Output processes were not involved because the experimental tasks were either postponed to the end of a task block (recall or recognition tasks) or delayed until 1000 ms after the sentence final word (grammaticality judgment). Input processes were not affected in our participants because the N1 and P2 components in the ERPs did not show any age-related slowing. Early syntactic processes were also not affected by aging. The ELAN, indicating first pass parsing, showed up with a similar latency and amplitude indicating that accessing syntactic features (i.e. the word category) of a word is independent of age. Accessing semantic features of a word, however, appears to be a completely different issue. As we have seen in the first two experiments reported here, the N400-data showed that although older persons activated the semantically associated/expected item correctly, the semantic network embedding this word is much larger for this age group (and for low span readers). We suggested that the inhibition of irrelevant associations might be a factor explaining this effect. Some of our most recent data exploring the use of inhibition in working memory points to a similar position (Gunter, Wagner, & Friederici, 1999). High and low span students were presented with German sentences which started off with an ambiguous word which was predisambiguated by a noun at the 5th position and finally disambiguated by a verb at the 6th position (example: predisambiguation is subordinate and final disambiguation is dominant: ‘The ball was by the dancer kicked and ...’). The ERP-data showed that there was a slight N400-difference between high and low span readers in processing the noun at 5th position. High span readers showed a bigger N400-component for the subordinated meaning than low span readers, suggesting that high span readers inhibited the subordinate meaning to a larger extent. When there was a switch from the subordinate to the dominant meaning between 5th and 6th position in the sentence, subjects with a high WM-capacity were found to suppress the irrelevant meaning very quickly, whereas subjects with a smaller WM-capacity had difficulties

273

inhibiting the dominant meaning. The results support the hypothesis that persons with a small memory capacity have problems with inhibiting irrelevant information. It was interesting to see that the data of all three experiments suggest that when no linguistic problem (semantic or syntactic) occurs older persons show no age difference at all. Similar ERP-responses were found for young and older participants for the expected words. When, however, a violation occurs, age differences in semantic integration and syntactic re-analysis occur. Both the N400 and P600 show a delay and an increase in amplitude.3 Our studies also showed that, although aging might be an important factor in eliciting N400 and P600 effects, it is certainly the case that the WM-capacity of a particular individual is also a very important contributor. For the semantic domain (N400) we have given sufficient evidence by

Figure 7. Effects of syntax as found for the young and older participants. As can be seen, both young and older participants showed a clear and comparable ELAN component (ATL-electrode). The P600 (Pz electrode) is smaller and delayed in the older age group.

274

now to make this conclusion. For the syntactic domain we can only conjecture, although experiments carried out on young adults (see above) indicate that this hypothesis is not implausible. To conclude, we have shown that ERPs are an useful addition to more traditional behavioral measures because they give the opportunity to monitor information processing on-line and independently of output parameters. In particular, we were able to demonstrate that both the WM-capacity and age of a person affects semantic integration and syntactic re-analysis during sentence processing. On the basis of the presented data we have raised the hypothesis that the observed effects of aging are due to a reduced memory capacity in old age.

275

NOTES

In rare cases the N400 is used to explore syntax (e.g. filler-gap assignments: Garnsey et al., 1989; Kluender & Kutas, 1993). In this type of experiment a specific syntactic structure gives a certain semantic expectancy at a specific point in a sentence. The position of this spot depends on the syntactic theory. Thus, in this type of research, syntactic processes are measured indirectly. 1

Atrophy of the brain occurring in normal aging is well documented in CT studies. Visual inspection of CT scans of normal older persons suggest that there is both cortical atrophy and ventricular enlargement (for references see Katzman & Terry, 1983). 2

3Note, that the delay of for instance the N400 is not always present in older persons. In the priming study, for instance, the N400 on primes and of associated targets showed no significant delay in the older participants.

276

REFERENCES

Allison, T., Wood, C. C., & Goff, W. R. (1983). Brain stem auditory, patternreversal visual, and short-latency somatosensory evoked potentials: Latencies in relation to age, sex, and brain size. Electroencephalography and Clinical Neurophysiology, 55, 619-636. Anderson, J. R. (1983). Cognitive psychology and its implications. San Francisco: W.H. Freeman and Company. Balota, D. A., Black, S. R., & Cheney, M. (1992). Automatic and attentional priming in young and older adults: Reevaluation of the two-process model. Journal of Experimental Psychology: Human Perception and Performance, 18, 485-502. Bentin, S., McCarthy, G., & Wood, C. C. (1985). Event-related potentials associated with semantic priming. Electroencephalography and Clinical Neurophysiology, 60, 343-355. Berger, H. (1929). Über das elektrenkephalogramm des menschen, Arch. Psychiat. Nervenkrankh., 87, 527-570. Birren, J. E., & Botwinick, J. (1955). Age differences in finger, jaw, and foot reaction time to auditory stimuli. Journal of Gerontology, 10, 429-432. Boddy, J. (1986). Event-related potentials in chronometric analysis of primed word recognition with different stimulus onset asynchronies. Psychophysiology, 32, 232-244. Brown, C. M., & Hagoort, P. (1993). The processing nature of the N400: Evidence from masked priming. Journal of Cognitive Neuroscience, 5, 34-44. Burke, D. M., & Peters, L. (1986). Word Associations in old age: Evidence for consistency in semantic encoding during adulthood. Psychology and Aging, 1, 283-292. Burke, D. M. & Yee, P. L. (1984). Semantic priming during sentence processing by young and older adults. Developmental Psychology, 20, 903-9 10. Canton, R. (1875). The electric currents of the brain. British Medical Journal, 2, 278. Chwilla, D. J., Brown, C. M., & Hagoort, P. (1995). The N400 as a function of the level of processing. Psychophysiology, 32, 274-285. Chu, N. S. (1985). Age-related latency changes in the brain-stem auditory evoked potentials. Electroencephalography and Clinical Neurophysiology, 62, 431436. Cohen, G. & Faulkner, D. (1983). Word recognition: Age differences in contextual facilitation effects. British Journal of Psychology, 74, 239-251. Coulson, S., King, J.W., & Kutas, M. (1998a). Expect the unexpected: Event-related brain potentials to morphosyntactic violations. Language and Cognitive Processes, 13,21-58. Coulson, S., King, J.W., & Kutas, M. (1998b). ERPs and domain specificity: Beating a straw horse. Language and Cognitive Processes, 13, 653-672. Dawson, G. D. (1947). Cerebral responses to electrical stimulation of peripheral nerve in man. Journal of Neurology, Neurosurgery, and Psychiatry, 10, 134140.

277

Dawson, G. D. (195 1). A summation technique for detecting small signals in a large irregular background. Journal of Physiology, 115, 2-3. Donchin, E. (1981). Surprise! ...Surprise? Psychophysiology, 18, 493-515. Donchin, E., & Coles, M. G. H., (1988). Is the P300 component a manifestation of context updating? The Behavioral and Brain Sciences, 11, 355-372. Donchin, E., Ritter, W., & McCallum, W. C. (1978). Cognitive psychophysiology: The endogenous components of the ERP. In E. Callaway, S. Tueting, & S. H. Koslow (Eds.), Event related brain potentials in man. New York: Academic Press. Dustman, R. E., Shearer, D. W., & Snyder, E. W. (1982). Age differences in augmenting/reducing of occipital visually evoked potentials. Electroencephalography and Clinical Neurophysiology, 54, 99-110. Eason, R. G. (1981). Visual evoked potential correlates of early neural filtering during selective attention. Bulletin of the Psychonomic Society, 18, 203-206. Fischler, I., Bloom, P. A., Childers, D. G., Roucos, S. E. & Perry, N. W., Jr. (1983). Brain potentials related to stages of sentence verification. Psychophysiology, 20, 400-409. Fischler, I., Childers, D. G., Achariyapaopan, T. & Perry, N. W., Jr. (1985). Brain potentials during sentence verification: Automatic aspects of comprehension. Biological Psychology, 21, 83-106. Frazier, L. (1987). Sentence processing. In M. Coltheart (Ed.), Attention and performance XII (pp. 559-586). Hillsdale, NJ: Erlbaum. Friederici, A. D. (1995). The time course of syntactic activation during language processing: A model based on neuropsychological and neurophysiological data. Brain and Language, 49, 259-281. Friederici, A. D., Hahne, A., & Mecklinger, A. (1996).Temporal structure of syntactic parsing: Early and late event-related brain potentials effects. Journal of Experimental Psychology: Learning, Memory, and Cognition, 22, 12191248. Friederici, A. D., Pfeifer, E., & Hahne, A. (1993). Even-related brain potentials during natural speech processing: effects of semantic, morphological and syntactic violations. Cognitive Brain Research, 1, 183-192. Friederici, A. D., Schriefers, H., & Lindenberger, U. (1998). Differential effects on semantic and syntactic priming. International journal of Behavioral development, 22, 813-845. Friederici, A. D., Steinhauer, K., Mecklinger, A., & Meyer, M. (1998). Working memory constraints on syntactic ambiguity resolution as revealed by electrical brain responses. Biological Psychology, 47, 193-221 Friedman, D., Simpson, G., & Hamberger, M. (1993). Age-related changes in scalp topography to novel and target stimuli. Psychophysiology, 30, 383-396. Garnsey, S. M., Tanenhaus, M. K. & Chapman, R. M. (1989). Evoked potentials and the study of sentence comprehension. Journal of Psycholinguistic Research, 1, 51-60. Gunter, Th. C., & Friederici, A. D. (1999). Concerning the automaticity of syntactic processing. Psychophysiology, 35, 126-137.

27 8

Gunter, Th. C., Stowe, L. A., & Mulder, G. (1997). When syntax meets semantics. Psychophysiology, 34, 660-676. Gunter, Th. C., Jackson, J. L., & Mulder, G. (1992). An electrophysiological study of semantic processing in young and middle aged academics, Psychophysiology, 29, 38-54. Gunter, Th. C., Jackson, J. L., & Mulder, G. (1995). Language, memory and aging: An electrophysiological exploration of the N400 during reading of memory demanding sentences. Psychophysiology, 32, 215-229. Gunter, Th. C., Jackson, J. L., & Mulder, G. (1998). Priming and aging: An electrophysiological investigation of N400 and Recall. Brain and Language, 65, 333-355. Gunter, Th. C, Wagner, S., & Friederici, A. D. (1999). Working memory and processing of semantically ambiguous words: inhibition or activation? In A. D. Friederici (Ed.), Annual report 1998, Leipzig: Max Planck Institute of Cognitive Neuroscience. Hagoort, P., Brown, C., & Groothusen, J. (1993). The Syntactic Positive Shift (SPS) as an ERP-measure of syntactic processing. Language and Cognitive Processes, 8, 439-483. Hahne, A., & Friederici, A. D. (1997). Two stages in parsing: Early automatic and late controlled processes. Experimental Brain Research, 117,47. Hahne, A., Friederici, A. D. (in press). Electrophysiological evidence for two steps in syntactic analysis: Early automatic and late controlled processes. Journal of Cognitive Neuroscience. Hamberger, M. J., & Friedman, D. (1990). Age-related changes in semantic activation: evidence from ERPs. In C.H.M. Brunia, A.W.K. Gaillard & A. Kok (Eds.). Psychophysiological Brain Research. (pp. 279-284). Tilburg: Tilburg University Press. Harbin, T. J., Marsh, G. R., & Harvey, M. T. (1984). Differences in the late components of the event-related potential due to age and to semantic and nonsemantic tasks. Electroencephalography and Clinical Neurophysiology, 59, 489-496. Hasher, L., & Zacks, R. T. (1988). Working memory, comprehension and aging: A review and a new view. In G.H. Bower (Ed.), The Psychology of learning and motivation (pp. 193-225). Orlando, FL: Academic Press. Hillyard, S. A., Luck, S., & Mangun, G. R. (1994). The cueing of attention to visual field locations: Analysis with ERP recordings. In H. J. Heinze, T. F. Münte & G. R. Mangun (Eds.) Cognitive Electrophysiology (pp. 1-25). Boston: Birkhäuser. Hillyard, S. A., & Münte, T. F. (1984). Selective attention to color and locational cues: An analysis with event-related brain potentials. Journal of Experimental Psychology: Human Perception and Performance, 17, 185-198. Hoffman, J. E., Houck, M. R., MacMillan, II, F. W., Simsons, R., & Oatman, L. C. (1985). Event-related potentials elicited by automatic targets: A dual-task analysis. Journal of Experimental Psychology: Human Perception and Performance, 1, 50-61.

279

Holcomb, P. J. (1988). Automatic and attentional processing: An event-related brain potential analysis of semantic priming. Brain and Language, 35, 66-85. Howard, D. V., Shaw, R. J., & Heisey, J. G. (1986). Aging and the time course of semantic activation. Journal of Gerontology, 41, 195-203. Katzman, R., & Terry, R. (1983). Normal aging of the nervous system. In: R. Katzman and R. Terry (Eds.). The neurology of aging (pp. 15-50). Philadelphia: Dares Company. Kemper, S. (1986). Imitation of complex syntactic constructions by elderly adults. Applied Psycholinguistics, 7, 277-288. Kemper, S. (1987). Life-span changes in syntactic complexity. Journal of Gerontology, 3, 323-328. King, J., & Just, M. A. (1991). Individual differences in syntactic processing: The role of working memory. Journal of Memory and Language, 30, 580-602. Klorman, R., Thompson, L. W. , & Ellingson, R. J. (1978). Event-related brain potentials across the life span. In: E. Callaway, P. Tueting, & S.H Koslow (Eds.), Event-related brain potentials in man (pp. 511-570). New York: Academic Press. Kluender, R., & Kutas, M. (1993). Bridging the gap: Evidence from ERPs on the processing of unbounded dependencies. Journal of Cognitive Neuroscience, 5, 196-214. Kluender, R., Münte, T. F., Wind Cowles, H., Szentkuti, A., Walenski, M., & Wieringa, B. M. (1998). Brain potentials to English and German questions. Poster presented at the CNS Fifth Annual Meeting, April, San Francisco, USA. Kutas, M. & Iragui, V. (1998). The N400 in a semantic categorization task across 6 decades. Electroencephalography and clinical Neurophysiology, 108, 456471. Kutas, M., & Hillyard, S. A. (1980). Event-related brain potentials to semantically inappropriate and surprisingly large words. Biological Psychology, 11, 99-1 16. Kutas, M., & Kluender, R. (1991). What is who violating? A reconsideration of linguistic violations in light of event-related brain potentials. CRL Newsletter, 6, 3-14. Kutas, M., Lindamood, T., & Hillyard, S. A. (1984). Word expectancy and eventrelated brain potentials during sentence processing. In s. Kornblum & J. Requin (Eds.), Preparatory states and processes (pp. 217-238). Hillsdale, NJ: Erlbaum. Kutas, M., & Van Petten, C. (1988). Event-related brain potential studies of language. In P.K. Ackles, J. R. Jennings, & M.G.H. Coles (Eds.), Advances in psychophysiology (Vol. 3, pp. 139-187). Greenwich, CT: JAI Press. Laver, G. D., & Burke, D. M. (1993). Why do semantic priming effects increase in old age? A meta-analysis. Psychology and Aging, 8, 34-43. LaFratta, C. W., & Canestrari, R. E. (1966). A comparison of sensory and motor nerve conduction velocities as related to age. Archives Physical Medical Rehabilitation, 47, 286. Light, L. L. (1990). Interactions between memory and language in old age. In J. E. Birren and K. W. Schaie (Eds.), Handbook of the psychology of aging (3rd ed., pp. 275-290). New York: Academic Press.

280

Mangun, G. R., Hillyard, S. A. (1990). Allocation of visual attention to spatial location: Event-related brain potentials and detection performance. Perception and Psychophysics, 47, 532-550. Mecklinger, A., Kramer, A. F., & Strayer, D. L. (1992). Event related potentials and EEG components in a semantic memory search task. Psychophysiology, 29, 104-119. Mecklinger, A., Schriefers, H., Steinhauer, K., & Friederici, A. D. (1995). Processing relative clauses varying on syntactic and semantic dimensions: An analysis with event-related potentials. Memory and Cognition, 23, 477-494. Miinte, T. F., & Heinze, H. (1994). ERP negativities during syntactic processing of written words. In H.J. Heinze, T.F. Miinte, & G.R. Mangun (Eds.), Cognitive Electrophysiology (pp. 21 1-238). La Jolla, CA: Birkhauser Boston, Inc. Münte, T. F., Heinze, H., & Mangun, G. R. (1993). Dissociation of brain activity related to syntactic and semantic aspects of language, Journal of Cognitive Neuroscience, 5, 335-344. Miinte, T. F., Heinze, H., Matzke, M., Wieringa, B. M., & Johannes, S. (1998). Brain potentials and syntactic violations revisited: No evidence for specificity of the syntactic positive shift. Neuropsychologia, 36, 217-226. Miinte, T. F., Matzke, M., & Johannes, S. (1997). Brain activity associated with syntactic incongruities in words and pseudo-words. Journal of Cognitive Neuroscience, 9, 318-329. Mulder, G. (1986). Memory search paradigms and practice effects. In W. C. McCallum, R. Zapolli, & F. Denoth (Eds.), Cognitive Psychophysiology: Studies in ERPs (pp. 57-63). Amsterdam: Elsevier. Neely, J. H. (1991). Semantic priming effects in visual word recognition: A selective review of current findings and theories. In D. Besner & G. Humphreys (Eds.), Basic processes in reading: Visual word recognition (pp. 264-336). Hillsdale, NJ: Lawrence Erlbaum Associates. Neville, H. J., Kutas, M., Chesney, G., & Schmidt, A. L. (1986). Event-related brain potentials during initial encoding and recognition memory of congruous and incongruous sentences. Journal of Memory and Language, 25, 75-92. Neville, H. Nicol, J. L., Barss, A., Forster, K. I., & Garret, M. F. (1991). Syntactically based sentence processing classes: Evidence from event-related brain potentials. Journal of Cognitive Neuroscience, 2, 151-165. Obrist, W. D. (1976). Problems of aging. In A. Remond (Ed.). Handbook of Electroencephalography and clinical Neurophysiology (pp.275-292). Amsterdam: Elsevier. Obrist, W. D., (1979). Electroencephalographic changes in normal aging and dementia. In F. Hoffmeister & C. Muller (Eds.). Brain function and old age (pp. 102-111). Springer Verlag, Berlin. Osterhout, L., & Holcomb, P. J. (1995). Event-related brain potentials and language comprehension. In M. D. Rugg & M. G. H. Coles (Eds.), Electrophysiological studies of human cognitive function, Oxford: Oxford University Press. Osterhout, L., & Holcomb, P. J. (1992). Event-related brain potentials elicited by syntactic anomaly. Journal of Memory and Language, 31, 785-806.

281

Osterhout, L., Holcomb, P. J., & Swinney, D. A. (1995). Brain potentials elicited by garden-path sentences: Evidence of the application of verb information during parsing. Journal of Experimental Psychology: Learning, Memory, and Cognition, 20, 786-803. Osterhout, L., McKinnon, R., Bersick, M., & Corey, V. (1996). On the language specificity of the brain response to syntactic anomalies: Is the syntactic positive shift a member of the P300 family? Journal of Cognitive Neuroscience, 8, 507526. Osterhout, L., & Mobley, L. A. (1995). Event-related brain potentials elicited by failure to agree. Journal of Memory and Language, 34, 739-773. Osterhout, L., & Hagoort, P. (in press). A superficial resemblance doesn’t necessarily mean that you’re part of a family: Counter arguments to Coulson, King & Kutas (1998) in the P600/SPS-P300 debate. Language and Cognitive Processes. Paller, K. (1990). Recall and stem-completion priming have different electrophysiological correlates and are modified differentially by directed forgetting. Journal of Experimental Psychology: Learning, Memory, and Cognition, 16, 1021-1031. Parasuraman, R. (1990). Event-related brain potentials and human factors research. In Rohrbaugh, J.W., Parasuraman, R., & Johnson, R. (Eds.), Event-related brain potentials: Basic issues and applications. Oxford: Oxford university press. Penke, M., Weyerts, H., Gross, M., Zander, E., Münte T. F., & Clahsen, A. (1997). How the brain processes complex words: An ERP-study of German verb inflections. Cognitive Brain Research, 6, 37-52. Porges, S. W., & Fox, N. A. (1986). Developmental psychophysiology. In M. G. H. Coles, E. Donchin and S. W. Porges (Eds.). Psychophysiology: Systems, processes, and applications (pp. 611-625). Amsterdam: Elsevier. Prinz, P. N., Dustman, R. E., & Emmerson, R. (1990). Electrophysiology and aging. In J. E. Birren & K. W. Schaie (Eds.). Handbook of the psychology of aging (3rd Ed., pp. 135-149). New York: Academic Press. Pritchard, W. S. (1981). Psychophysiology of P300: A review. Psychological Bulletin, 89, 506-540. Rösler, F., & Heil, M. (1991). Toward a functional categorization of slow waves: Taking into account past and future events. Psychophysiology, 28, 344-358. Rösler, F., & Heil, M. (1993). Monitoring retrieval from long-term memory by slow event-related brain potentials. Psychophysiology, 30, 170-182. Rösler, F., Pütz, P., Friederici, A., & Hahne, A. (1993). Event-related brain potentials while encountering semantic and syntactic constraint violations. Journal of Cognitive Neuroscience, 5, 345-362. Ruchkin, D. S., Johnson, J., Mahaffey, D, & Sutton, S. (1988). Toward a functional categorization of slow waves. Psychophysiology, 25, 339-353. Rushkin, D. S., Johnson, R, Canoune, H., & Ritter, W. (1990). Short-term memory storage and retention: An event-related brain potential study. Electroencephalography and clinical Neurophysiology, 76, 419-439.

282

Salthouse, T. A., (1991). Theoretical perspectives on cognitive aging. Hillsdale NJ: Lawrence Erlbaum. Schaumburg, H. H., Spencer, P. S., & Ochoa, J. (1983). The aging human peripheral nervous system. In R. Katzman & R. Terry (Eds.). The neurology of aging (pp. 111-122). Philadelphia: Dares Company. Simpson, G. V., Knight, R. T., Brailowsky, S., Prospero-Garcia, O., & Scabini, D. (1985). Altered peripheral and brainstem auditory function in aged rats. Brain Research, 348, 28-35. Sternberg, S. (1969). Memory-scanning: Mental processes revealed by reaction-time experiments. American Scientist, 57, 421-457. Strayer, D. L., Wickens, C. D., & Braune, R. (1987). Adult age differences in speed and capacity of information processing: 2 An electrophysiological approach. Psychology and Aging, 2, 99-110. Tyler, L. K. (1992). Spoken language comprehension: An experimental approach to disordered and normal processing. MIT press. Cambridge, Massachusetts. Van Petten, C. (1995). Words and sentences: Event-related brain potential measures. Psychophysiology, 32, 511-525. Van Petten, C., & Kutas, M. (1990). Interactions between sentence context and word frequency in event-related brain potentials. Memory & Cognition, 18, 380-393. Verleger, R. (1988). Event-related potentials and cognition: A critique of the context undating hypothesis and an alternative interpretation of P3. Behavioral and brain sciences, 11, 343-427. Vos, S. H., Gunter, Th. C., Kolk, H. H. J., & Mulder, G (manuscript submitted for publication). Working memory constraints on syntactic processing: An electrophysiological investigation. Wijers, A. A., Mulder, G., Okita, T., Mulder, L. J. M., & Scheffers, M. K. (1989). Attention to color: An ERP-analysis of selection, controlled search and motor activation. Psychophysiology, 26, 89-109. Zurif, E., Swinney, D., Prather, P., Wingfield, A., & Brownell, H. (1995). The allocation of memory resources during sentence comprehension: Evidence from the elderly. Journal of Psycholinguistic Research, 24, 165-182.

11 A

EFFECTS ON THE FUNCTIONAL NEUROANATOMY OF SYNTACTIC PROCESSING IN SENTENCE COMPREHENSION

GE

David Caplan and Gloria Waters

There is very good evidence that language processing changes with age, but very little is known about the neural basis for these changes. To the extent that the changes reflect generalized changes in processing, such as cognitive slowing, their origins may lie in equally general neuronal processes, such as neuronal loss. However, to the extent that age-related changes in language processing are specific to certain language functions, such as difficulties with phonological lexical access, it is less plausible that they could be related to generalized neuronal processes. Such changes are more likely to reflect changes in specific neural systems. If there are such age-related changes in neural systems responsible for specific language processes, it is possible that there are overtly identifiable changes in the functional neuroanatomy of aspects of language processing associated with aging. In this chapter, we review data from our laboratory that begins to examine the question of whether the functional neuroanatomy of one aspect of language processing changes with age. The aspect of language processing that we have studied is syntactic processing in sentence comprehension; specifically, a set of operations related to assigning the syntactic structure and associated meaning of relative clauses. The technique we used to identify changes in functional neuroanatomy was positron emission tomography (PET) -- a method for measuring changes in regional cerebral blood flow (rCBF) that reflect changes in local neurophysiological activity. The results show differences in rCBF as a function of age in tasks that require syntactic processing. The interpretation of the results is not completely transparent, but we offer these studies as a first step in exploring this issue. METHODS

All studies reported here used the plausibility judgment task. In this task, subjects either read or listened to a sentence and made a speeded decision as to whether it was plausible (made sense) or not. In the activation condition, sentences that are 283

284

syntactically more complex were presented; in the baseline condition, sentences that are less complex were presented. We contrasted more complex subject-object (SO) sentences (e.g., The juice that the child spilled stained the rug ) with less complex object-subject (OS) sentences (e.g., The child spilled the juice that stained the rug ). There is considerable behavioral evidence that SO sentences are more difficult than OS sentences (Waters et al., 1987; King & Just, 1991). The higher demands made by the SO sentence are thought to be related to maintaining the head noun of a relative clause in memory while the relative clause is bring structured, computing the syntactic structure of the relative clause, relating the head noun of the relative clause to a syntactic position in the relative clause, relating the head noun of the relative clause to its position as the subject of the main clause, and interpreting the resulting syntactic structure semantically (Just & Carpenter, 1992; Gibson, 1997). In all experiments, implausible sentences were rendered implausible by virtue of an incompatibility between the animacy or humanness features of a noun phrase and the requirements of a verb, as in the example The book enjoyed the boy. Therefore, plausibility judgments did not depend upon subjects searching semantic memory for obscure facts but could be made on the basis of readily available semantic information. In all experiments, sentences were blocked by syntactic type, as is required by the PET technique. To reduce the possibility that subjects might habituate to more complex structures or develop non-syntactic strategies to make judgments regarding the status of a sentence in these blocks, we varied the animacy of nouns in grammatical positions in the sentences. The more and less complex sentences contained the same words and expressed the same content so that differences in lexical items and propositional meaning were not responsible for any rCBF effects. All nouns were common and were preceded by definite articles so as to make the same referential assumptions in the more and less complex syntactic conditions. The point of implausibility was varied throughout the implausible sentences of each syntactic type to force subjects to read or listen to each sentence in its entirety to make a judgment that it was plausible. Implausibility points were slightly earlier on average in the more complex sentences, biasing against the simple forms benefiting from the use of a strategy that judges a sentence to be acceptable when a certain point in the sentence had passed. All experiments in the PET scanner were preceded by behavioral testing in the psychology lab to ensure that there was behavioral evidence in the form of longer reaction times RTs and sometimes more errors that the more complex sentences were indeed more complex, and these measurements were repeated in the PET environment to be sure that these differences obtained there. Subjects in all experiments were strongly right-handed and had no first degree left-handed relatives. All had normal vision and hearing, and no history of neurological or psychiatric disease. PET techniques were ones in widespread use. PET data were acquired on a General Electric Scanditronix PC4096 15 slice whole body tomograph in its stationary mode in contiguous slices with center-to-center distance of 6.5 mm (axial field equal to 97.5 mm) and axial resolution of 6.0 mm FWHM, with a Hanningweighted reconstruction filter set to yield 8.0 mm in-plane spatial resolution

285

(FWHM). Subjects' heads were restrained in a custom-molded thermoplastic face mask, and aligned relative to the catho-meatal line, using horizontal and vertical projected laser lines. Subjects inhaled 15O-CO2 gas by nasal cannulae within a face mask for 90 sec, reaching terminal count rates of 100,000 to 200,000 events per second. Each PET data acquisition run consisted of 20 measurements, the first 3 with 10 sec duration and the remaining 17 with 5 sec duration each. Scans 4-16 were summed after reconstruction to form images of relative blood flow. The summed images from each subject were realigned using the first scan as the reference using a least squares fitting technique (Alpert et al., 1996). Spatial normalization to the coordinate system of Talairach and Tournoux (1988) was performed by deforming the contour of the 10 mm parasagittal PET slice to match the corresponding slice of the reference brain (Alpert et al., 1993). Following spatial normalization, scans were filtered with a two-dimensional Gaussian filter, full width at half maximum set to 20 mm. Data were analyzed with SPM95 (Friston et al., 1991, 1995; Worsely et al., 1992, 1996).

EXPERIMENTS WITH YOUNG SUBJECTS

We have conducted four experiments with young adults. In the first (Stromswold et al., 1996), we studied eight male subjects between the ages of 19 and 28 years. Behavioral results are shown in Table 1 and PET results in Table 2. There was an increase in rCBF in the pars opercularis of Broca's area when PET activity associated with OS sentences was subtracted from that associated with SO sentences. The second experiment (Caplan et al., 1998) was a replication of this study with eight female subjects, aged 21 - 3 1 years. Behavioral results are shown in Table 3 and PET results in Table 4. There again was an increase in rCBF in the pars opercularis of Broca's area when PET activity associated with OS sentences was subtracted from that associated with SO sentences. There was also activation in the medial frontal and cingulate gyri. The third experiment (Caplan et al., in press) was a replication of this study with auditory presentation. Sentences in condition 1 consisted of cleft object (CO) sentences (e.g., It was the juice that the child enjoyed ) and sentences in condition 2 consisted of cleft subject (CS) sentences (e.g., It was the child that enjoyed the juice ). We used cleft object and cleft subject sentences instead of the subject-object and object-subject sentences used in the previous research because preliminary testing of SO and OS sentences presented auditorily failed to demonstrate differences in RTs for end-of-sentence plausibility judgments. This is probably because the demands made by the embedded clause in SO sentences are over by the end of the sentence when the judgment is made. The cleft object and cleft subject sentences make the same contrast between object and subject relativization that the contrast between SO and OS sentences makes.

286

Table 1. Reaction time (RT) results for subject-object and object-subject sentences with visual presentation in Experiment 1 (N=8 young males).

Subject-object

Mean RT (msec)

Object-subject

4230

3719

Table 2. Areas of increased rCBF in Experiment 1 for subtraction of PET activity associated with object-subject sentences from subject-object sentence with visual presentation (N=8 young males).

Location

Left Broca's area pars opercularis

Max Z-score 2.7

Number of pixels 131

Location {X,Y,Z} -46.5, 9.8, 4.0

Table 3. Accuracy and reaction time (RT) results for subject-object and object subject sentences with visual presentation in Experiment 2 (N=8 young females).

Subject-object

Percent correct Mean RT (msec) (SD)

90.5% 2886 (1119)

Object-subject

94.4% 2548 (1011)

287

Sixteen subjects, eight male and eight female, ages 22 - 34 years, were tested. Behavioral results are shown in Table 5 and PET results in Table 6. There was an increase in rCBF in the pars triangularis of Broca's area when PET activity associated with cleft subject sentences was subtracted from that associated with cleft object sentences. There was also activation in the medial frontal gyrus and in the left superior parietal area. The fourth experiment (Caplan et al., under review a) investigated the possibility that the increases in rCBF in Broca's area in experiments 1 - 3 were due to increased rehearsal associated with the more complex sentences. Broca's area is involved in rehearsal (Vallar & Shallice, 1990; Smith et al., 1998), so this possibility must be considered. To address this issue, we repeated Experiment 1 under conditions of concurrent articulation. Concurrent articulation engages the articulatory loop and prevents its use for rehearsal (Baddeley et al., 1975). If the rCBF increase in Broca's area continued to be found under these conditions, it is highly likely that it is due at least in part to abstract psycholinguistic operations, not just to more rehearsal associated with the more complex sentences.

Table 4. Areas of increased rCBF for subtraction of PET activity associated with object-subject sentences from subject-object sentences in Experiment 2 with visual presentation (N=8 young females).

Eleven subjects, five male and six female, ages 19 - 35, were tested. Behavioral results are shown in Table 7 and PET results in Table 8. There was an increase in rCBF in the pars opercularis of Broca's area when PET activity associated with OS sentences was subtracted from that associated with SO sentences. There were also increases in rCBF in the dorsomedial nucleus of the left thalamus, the posterior cingulate, and the medial frontal gyrus.

288

Table 5. Accuracy and reaction time (RT) results for cleft object and cleft subject sentences in Experiment 3 with auditory presentation (N= 16 young males and females).

Table 6. Areas of increased rCBF for subtraction of PET activity associated with cleft subject from cleft object sentences in Experiment 3 with auditory presentation (N=16 young males and females).

289

Table 7. Accuracy and reaction time RT results for object-subject and subject object sentences in Experiment 4 with written presentation and concurrent articulation (N=11 young males and females).

Table 8. Areas of increased rCBF for subtraction of PET activity associated with object-subject sentences from subject-object sentences in Experiment 4 with written presentation and concurrent articulation (N=11 young males and females).

290

These four experiments all showed activation in Broca's area associated with more complex relative clauses. This activation persisted under concurrent articulation conditions. This suggests that Broca's area is an important locus of some aspect of syntactic processing associated with structuring more complex relative clauses. No other language regions were activated in these experiments. CBF was also increased in medial frontal lobe structures in several experiments, and in the centromedian nucleus of the left thalamaus in the articulatory suppression experiment, possibly the result of a non-domain-specific arousal and directed attention associated with increases in mental effort (Posner et al., 1988). EXPERIMENTS RELEVANT TO OLDER SUBJECTS

In a fifth experiment (Caplan et al., under review b), we replicated the Stromswold et al. (1996) and Caplan et al. (1998) experiment with 13 older subjects, ages 61 70. Results are shown in Tables 9 and 10. Unlike the young subjects studied in experiments 1 - 4, there was no increase in rCBF in Broca's area, but rather in the inferior parietal lobe. There was also an increase in rCBF near the midline of the superior frontal gyrus. Consideration of the behavioral results across these five experiments indicates that the older subjects performed less well than the young subjects, both in terms of reaction times and accuracy. (The longer RTs in the articulatory suppression experiment are a result of the concurrent task; cf., Waters et al., 1987.) It is possible that the differences in rCBF in the fifth experiment reflect performance proficiency, not age. We therefore studied a fifth set of young subjects who were matched in educational level to the older subjects studied in the fifth experiment. Eight subjects (4 males and 4 females, ages 19 - 28) participated. Behavioral results are shown in Table 11 and PET results in Table 12. The behavioral results showed no difference in reaction times for these two groups of older and young subjects. The only group effect was a significant three way interaction between age group, acceptability, and sentence type in the accuracy data, suggesting different response biases in the more complex condition (the older subjects made more errors on unacceptable SO sentences and the young subjects on acceptable SO sentences). The rCBF results showed an increase in rCBF in the superior parietal lobe near the midline, and in the superior frontal lobe. Differences in rCBF associated with subtracting OS from SO sentences were compared across age groups. The increases in rCBF in the inferior parietal and superior frontal lobes in the elderly were significantly greater than the changes in rCBF in these areas in the young subjects, and the increase in rCBF in the superior parietal lobe in the young subjects was significantly greater than the change in rCBF in this area in the older subjects. These two studies show different patterns of rCBF in older and young subjects matched for performance. They therefore suggest that the functional neuroanatomy of the brain for language changes with age. Comparing the rCBF pattern of the young subjects in this study with those in the first four experiments suggests that it may also change as a function of processing proficiency.

291

Table 9. Accuracy and reaction time (RT) results for subject-object and object subject sentences in Experiment 5 (N=13 older subjects).

Table 10. Areas of increased rCBF for subtraction of PET activity associated with object-subject from subject-object sentences in Experiment 5 (N= 13 older subjects)

GENERAL DISCUSSION

The results reported above for college aged young subjects appear fairly interpretable. Four experiments, involving both sexes and both modalities of language presentation, one of which reduced the possibility for verbal rehearsal, were associated with increased blood flow in Broca’s area when subjects processed sentences with more complex relative clauses. It is important to note the magnitude of the rCBF effects was small in each study; it is largely the consistency of this

292

Table 11. Accuracy and reaction time (RT) results for subject-object and object subject sentences in Experiment 6 (N=8 young subjects)

Table 12. Areas of increased rCBF for subtraction of PET activity associated with subtraction of object-subject sentences from subject-object sentences in Experiment 6 (N= 8 young subjects).

result across studies that encourages the conclusion that this region is involved in the aspect of syntactic processing highlighted in these studies. This conclusion receives support from studies of stroke patients; in particular, Swinney and his colleagues (Swinney et al., 1995, 1996; Zurif et al., 1993) have reported abnormal priming for the head noun of a relative clause in Broca’s aphasics, whose lesions involved Broca’s area, and not in fluent aphasics, whose lesions did not. The picture changes somewhat, but not significantly in our opinion, when we take into account the midline frontal activation seen in some of these first four

293

studies. We have suggested that this activation does not indicate that this region is involved directly in syntactic processing, preferring to attribute this activation to general activation and attentional control processes. We based this conclusion on the argument that lesions in these areas are not associated with disorders of syntactic comprehension, and that studies in other cognitive domains have shown activation in these regions that was attributed to these types of control processes. We also note here that an additional argument in favor of this analysis is that the activation in the left thalamus in the fourth experiment is also in a nucleus that is associated with attention and arousal functions. However, we think these arguments are far from definitive. The deficit-lesion literature is inconclusive because patients with anterior and superior frontal lesions have not been studied for their syntactic processing abilities, which require special tests to uncover and are not detectable on routine clinical or neuropsychological evaluations; therefore, we do not know that these patients do not have such deficits. The midline frontal activation seen in other studies has been in the cingulate and surrounding cortex -- inferior to that found in these studies. Lesions in the left thalamus produce language disorders; whether lesions restricted to the centromedial nucleus have these effects is not known. Finally, on the cognitive side, some researchers do not distinguish between attentional/processing resources used for “general” verbal purposes and those directed towards aspects of language processing (Just & Carpenter, 1992); in a single resource model, all activation related to verbal processing resource allocation has the same psychological origins. While we do not agree with this model (Caplan & Waters, 1999; Waters & Caplan, this volume), it remains a possibility. One can therefore with justification remain agnostic about the cognitive operations that are responsible for the increased rCBF in these regions. Perhaps this region is involved in syntactic operations. We note in passing that the analysis of the rCBF in Broca’s area as being related to syntactic processing is also affected by one of the considerations raised above -- the possibility that all activation related to verbal processing resource allocation has the same psychological origins. Were this to be true, we would not be able to ascribe the rCBF increases in Broca’s area to allocation of resources that are specific to syntactic processing. We would, however, still be able to consider a variety of other specific syntactic operations (e.g., relating the head noun of the relative clause to its position in the clause) as the source of this rCBF increase. The results of the last two experiments create problems for the relatively clean picture of the cognitive sources of rCBF increases in Broca’s area in the college educated, linguistically proficient, young subjects. As noted, the rCBF effects in the first four experiments were not large in any given study; confidence in their existence rests in large part on their having been replicated in four studies. The results with both the older subjects and the less proficient young subjects reduce confidence in this finding. However, at present, we may take refuge in the observation that there are clear differences in age and in processing efficiency in the two groups of subjects who did not show Broca’s area activation. Perhaps Broca’s area is the best site for this aspect of syntactic processing and its activity co-occurs with efficient syntactic processing. This post-hoc hypothesis is studiable: rCBF in Broca’s area should correlate inversely with syntactic processing efficiency.

294

A larger interpretive challenge posed by the results of the last two experiments is why the regions that were activated in these groups were activated. We omit discussion of the frontal activation, attributing it to attentional and control processes, as above. The inferior parietal activation in the older subjects is less troublesome. It is broadly consistent with what is known about the functional neuroanatomy of language processing and related cognitive functions. The increase in rCBF is in the inferior parietal lobe -- a part of the perisylvian cortex in which lesions lead to syntactic comprehension deficits (Caplan et al., 1996). The inferior parietal lobe is also involved in verbal STM (Valler & Shallice, 1990; Smith et al., 1998) and its activation in this experiment might reflect its role in meeting memory demands imposed by the more complex sentence type. The location of the increase in rCBF in the superior parietal lobe in the young subjects studied in Experiment 2 requires either an explanation in terms of nonlinguistic processing differences in the two sentence types or an extension of the region of the brain that we associate with language processing to the superior parietal cortex. Either account can be proposed. The superior parietal lobe is part of the dorsal visual pathway, and is involved in visually directed attention and mental imagery. Either could have been engaged to a greater degree in processing the more complex sentences. On the other hand, it is worth noting that this region was also activated in the auditory study reported by Caplan et al. (in press), so a unitary account in terms of visually directed attention is not possible. Also, as for anterior/superior frontal lesions, we do not know that patients with high parietal lesions do not have syntactic processing deficits; these studies remain to be undertaken. At this point, we can only note that this location of activation has now been found in two studies of syntactic processing, one in the auditory and one in the visual modality, and that this raises the possibility that this region of the brain may be involved in some aspect of syntactic processing or a related aspect of cognitive functioning in some subjects. If we accept the view that the parietal activations found in these two experiments reflect a role that portions of the parietal lobe play in syntactic processing, the results have implications for the neural basis for syntactic processing. They provide support for the hypothesis derived from off-line studies of syntactic comprehension disorders that a large number of cortical regions -including all parts of the dominant perisylvian association cortex -- can support syntactic processing (Caplan et al., 1996). The studies reported here point to several factors that might lead to variability in the functional localization of aspects of syntactic processing. A comparison of the studies with young subjects who differed in years of education and processing efficiency is consistent with the conclusion that the functional neuroanatomy for syntactic processing differs as a function of performance level. A comparison of the studies with young and old subjects is consistent with the view that it differs as a function of age, independent of performance level. These suggestions will need to be confirmed by additional studies. In summary, the experiments reported here provide evidence that the neural organization for syntactic processing differs in young and older subjects, and in subjects who perform more and less well on a syntactic comprehension task. The

295

rCBF patterns raise questions about the mechanisms involved in accomplishing the task, and about the effects of age and proficiency on cortical specialization for this function, which will require further research to answer.

296

REFERENCES

Alpert, N., Berdichevsky, D., Weise, S., Tang, J., & Rauch, S. (1993). Stereotactic transformation of PET scans by nonlinear least squares. In K. Uemura (Ed.), Quantifications of brain functions. Tracer kinetics and image analysis in brain PET (pp. 459-463). Elsevier Science Publishers, B.V. Alpert, N. M., Berdichevsky, D., Levin, Z., Morris, E. D., & Faschman, A. J. (1996). Improved methods for image registration. NeuroImage, 3, 10-18. Baddeley, A. D., Thompson, N., & Buchanan, M. (1975). Word length and the structure of short-term memory. Journal of Verbal Learning and Verbal Behavior, 14,575-589. Caplan, D., & Waters, G. S. (in press). Verbal working memory and sentence comprehension. Behavioral and Brain Sciences. Caplan, D., Hildebrandt, N., & Makris, N. (1996): Location of lesions in stroke patients with deficits in syntactic processing in sentence comprehension, Brain, 119, 993-949 Caplan, D., Alpert, N. & Waters, G.S. (1998). Effects of syntactic structure and propositional number on patterns of regional cerebral blood flow, Journal of Cognitive Neuroscience, 10, 541-552. Caplan, D., Alpert, N., & Waters, G. (in press): PET studies of sentence processing with auditory sentence presentation, NeuroImage Caplan, D., Alpert, N., Waters, G., & Olivieri, A. (under review a): Activation of Broca's area by syntactic processing under conditions of concurrent articulation. Caplan, D., Waters, G.S. & Alpert, N. (under review b). localization of syntactic comprehension by positron emission tomography in elderly subjects Friston, K. J., Frith, C. D., Liddle, P. F., & Frackowiak, R. S. J. Comparing functional (PET) images: The assessment of significant change (1991). Journal of Cerebral Blood Flow and Metabolism, 11, 690-699. Friston, K. J., Holmes, A. P., Worsley, K. J., Poline, J. B., Frith, C. D., & Frackowiak, R. S. J. (1995). Statistical parametric maps in functional imaging: A general approach. Human Brain Mapping, 2, 189-210 Gibson, E. (1997). Syntactic complexity: Locality of syntactic dependencies, Cognition, 68, 1-76 Just, M. A., & Carpenter, P. A. (1992). A capacity theory of comprehension: Individual differences in working memory. Psychological Review, 99, 122149. King, J., & Just, M. A. (1991). Individual differences in syntactic processing: The role of working memory. Journal of Memory and Language, 30, 580-602. Posner, M. I., Peterson, S. E., Fox, P. T., & Raichle, M. E. (1988). Localization of cognitive operations in the human brain. Science, 240, 1627-1631. Smith, E. E., Jonides, J., Marshuetz, C., & Koeppe, R. A. (1998). Components of verbal working memory: Evidence from neuroimaging. Proceedings of the National Academy of Sciences, 95, 876-882.)

297

Stromswold, K., Caplan, D., Alpert, N., & Rauch, S. (1996). Localization of syntactic comprehension by positron emission tomography. Brain and Language, 52, 452-473. Swinney, D., & Zurif, E. (1995). Syntactic processing in aphasia. Brain and Language, 50, 225-239. Swinney, D., Zurif, E., Prather, P., & Love, T. (1996). Neurological distribution of processing resources underlying language comprehension. Journal of Cognitive Neuroscience, 8, 174-184. Talairach, J., & Tournoux, P. (1988). Co-planar stereotaxic atlas of the human brain. New York: Thieme Medical Publishers, Inc. Vallar, G., & Shallice, T. (Eds.) (1990). Neuropsychological impairments of short tem memory, Cambridge: Cambridge University Press Waters, G., Caplan, D., & Hildebrandt, N. (1987). Working memory and written sentence comprehension. In M. Coltheart (Ed.), Attention and performance XII (pp. 531-555). London: Erlbaum. Worsley, K. J., Evans, A. C., Marrett, S., & Neelin, P. (1992). A three-dimensional statistical analysis for rCBF activation studies in human brain. Journal of Cerebral Blood Flow and Metabolism, 12, 900-918. Worsley, K. J., Marrett, S., Neelin, P., Vandal, A. C., Friston, K. J., & Evans, E. C. (1996). A unified statistical approach for determining significant signals in images of cerebral activation. Human Brain Mapping, 4, 58-73. Zurif, E., Swinney, D., Prather, P., Solomon, J., & Bushell, C. (1993). An on-line analysis of syntactic processing in Broca's and Wernicke's aphasia. Brain and Language, 45, 448-464.

ACKNOWLEDGEMENT

This work was supported by grant DC01198 from the National Institutes of Health.

This page intentionally left blank.

CONCLUDING OBSERVATIONS

Reinhold Kliegl and Susan Kemper

Language has long been recognized as one domain within which the varied patterns of aging present themselves almost in microcosmic detail. There is research evidence for decline, stability and even growth - as evidenced in the chapters of this volume. The task of research is to move beyond description of these patterns and determine the underlying principles and constraints that give rise to them. The authors who contributed to this volume undertook this task when they met for four days in Sedona, AZ, to discuss new and unpublished research, review existing models and findings, and outline research strategies for future investigations. In these concluding observations we want to highlight once more three current research topics and propose an agenda for future investigations of language and aging. Three issues recurred throughout our discussions and are examined at greater length in these chapters: the tension between general versus specific accounts of language and cognitive aging, the implications of off-line versus on-line methods for studying language and aging, and measurement problems affecting both language and cognition. The discussions at Sedona and in these chapters revealed points of agreement and disagreement and helped us move closer to a resolution of each issue. There were also some new themes which emerged in our discussions and which are echoed in several chapters; we predict these themes will shape discussion in the years to come: disentangling memory burden from computational costs of sentence processing, extending current research methods to the study of discourse, and developing a better understanding of compensations and tradeoffs, not only to enrich the theoretical debate but also to take our work into clinical and practical settings. CURRENT lSSUES

General versus Specific Accounts of Language and Cognitive Aging This issue has generated much debate in the field of cognitive aging, much less in psycholinguistics and cognitive psychology: Programmatic attempts to reduce all or 299

300

much of cognitive aging have sought a common explanatory principle, the three most prominent ones being "general slowing", "reduction of working memory capacity", and "inhibition deficit." Within this debate the status of age differences in language-related functions has achieved the status of a litmus test in several respects. First, it is clear that some aspects of language processing are age-invariant, most notably those related to lexical access and semantic memory, thereby reducing the explanatory scope of each of the three programmatic accounts. Several chapters in this volume suggest that age invariance may extend to syntax, or at least some aspects of syntactic processing, and to text-processing, or at least some aspects of text-processing, and that some aspects of syntax may be buffered against even the ravages of Alzheimer's disease. Burke (Chapter 1) refines this debate by contrasting information-universal and information-specific theories of aging. She argues that general theories or information-universal theories must predict a broad pattern of age-related decrements in language processing whereas information-specific theories can be tailored to account for specific patterns of age-spared and age-impaired processes. As Burke notes, there is evidence for age invariance on a considerable number of language tasks, but also considerable evidence that aging takes it toll on a fair number of other aspects of language. One general, information-universal hypothesis holds that syntactic factors interact with older adults' working memory limitations to affect processing of complex constructions (Kemper, 1992). Although Waters and Caplan (Chapter 5, in press) have heavily criticized this hypothesis and the research purporting to support it, other contributions to this volume have sought to more narrowly focus this hypothesis and offer new evidence in its favor: Aging appears to affect the processing of English embedded wh-clauses (Kemper & Kemtes, Chapter 4) and German main clauses with embedded relative clauses (Kliegl et al., Chapter 6) as well as detecting syntactic violations in Dutch (Gunter et al., Chapter 10). These effects are consistent with the working memory hypothesis but may also arise from a breakdown of inhibitory processes, or poor long term working memory retrieval structures, as suggested by Kemper and Kemtes, or executive control processes governing coordinative processes, as suggested by Kliegl et al. in Chapter 6. However, these age differences may be information-specific and arise from the nature of the language processing system itself. As Fanselow and his colleagues (Chapter 7) and Frazier (Chapter 8) remind us, the "laws of grammaticalization" need not mirror processing ease. Age differences in processing difficulty may arise, not from memory burden due to the temporary storage of linguistic elements, but from computational complexity reflecting the parsing operations which are required to establish syntactic relations within and across clauses. Hence, processing whclauses in English, embedded relative clauses in German, and syntactic violations in Dutch may lead to age differences, not because these structures impose a burden on working memory, but because information-specific aspects of the architecture of the parsing system affect how easily and rapidly the parser can compute anaphoric and pronominal references as well as other syntactic relations within and across clauses.

301

Off-line versus On-line Methods Research methodologies in psycholinguistics can be conveniently divided into offline versus on-line methods and each approach has attracted a devoted band of supporters. We note that the chapters in this volume take a refreshingly unideological stance. There is little doubt that the on-line techniques developed in the past decade have enriched our understanding and allow us to monitor the complexity of language processes in an ever increasingly ecologically valid way. The research reported in this volume relies on the auditory moving window paradigm, the decomposition of self-paced reading times, ERP, and PET technology. Nevertheless, language, at a minimum, involves comprehension, which is inextricably linked to memory. Therefore, an explanation of language The comprehension will always depend on so-called off-line assessment. advantages and disadvantages of each approach are delineated in several chapters, in particular in those of Wingfield and Tun (Chapter 2), Kemper and Kemtes (Chapter 4), and Kempler et al. (Chapter 9). There is one caveat we wish to express about the excitement of on-line measures: In most settings they reduce experimental control and invoke potential tradeoffs between interpretive and post-interpretative processes that may be difficult to trace. For example, in a self-paced reading study or a study measuring eye movements, it is up to participants to decide whether they want to allocate their processing resources immediately or at the end of sentences. It is unclear, however, whether the allocation policy we observe is an option or forced by limited resources. Age or individual differences in such strategies can be in the theoretical focus of research as in Stine-Morrow and Soederberg Miller (Chapter 3). The experimental control of presentation time - ideally allocated differentially to critical sentence elements and to groups of participants according to hypothesized time demands of underlying processes - could be used to disentangle optional versus constrained aspects of language processing. Even if such experimental manipulations of on-line processes appear to move us away from ecologically valid settings, they are of critical importance, for example, in order to understand age-related tradeoffs and compensatory strategies which we argue below is an emerging research trend in this field. Thus, the discovery of potentially compensatory strategies is the first step which may be greatly facilitated by on-line technology, as exemplified in the chapters by Stine-Morrow and Soederberg Miller (Chapter 3) and Gunter et al. (Chapter 10). It needs to be followed up, however, by experimental investigations controlling the allocation of processing time. Perhaps the common position that we agree on at this point is the one formulated by Kempler et al. (Chapter 9). They initially thought "off-line tasks are rough gauges of language comprehension, contaminated by memory and extraneous task demands, while on-line tasks assess language processing in a more direct manner" (p. 240). But results from the two types of tasks did not follow this distinction. They concluded "that the crucial distinctions affecting language performance may not be whether the task is off- versus on-line, or involving memory or not, but rather whether the task requires a partial or full analysis of the sentence meaning. Therefore, we end up viewing the distinction between on- and off-line

302

tasks to be rather different than it is often presented in the literature, in that both the task itself and the properties of the linguistic stimuli will determine the nature of performance." (p. 240). Measurement Problems affecting Language and Cognition There is one other issue that gathered much attention during our discussions in Sedona. It is exemplified in the chapter by Waters and Caplan (Chapter 5). How do we measure individual differences in language and cognition? A strong corollary of the hypothesis that working memory limitations constrain language processing has been that individual differences in working memory should be reflected in different patterns of language processing for subgroups of individuals defined by working memory capacity. This assumption received considerable support from the studies of Daneman and Carpenter (1984), King and Just (1991), and MacDonald, Just and Carpenter (1992) who defined the paradigm: measure working memory capacity, using a span test such as that devised by Daneman and Carpenter, dichotomize (or trichotomize) participants on the basis of this test, and then measure language processing using word-by-word reading times and/or comprehension accuracy. Yet the early findings supporting this corollary have not been supported by more recent finding, e.g., Kemtes and Kemper (1997), Waters and Caplan (1996, submitted). It was commonly assumed that those syntactic structures which involved movement or local ambiguities were good candidates for testing this corollary; however, we may have been looking at the wrong structures. Perhaps we should consider those structures that are information-specific, following Burke (Chapter 1), or those that involve establishing and maintaining inter- and intra-clausal reference, or those that are computationally complex, as suggested by Frazier (Chapter 8). Measuring working memory capacity has proven to be an equally complex problem. This topic has generated considerable debate in cognitive psychology as researchers have attempted to distinguish among working memory capacity, shortterm memory, executive function, and other sub-components. Span tasks have proliferated. And as Waters and Caplan (Chapter 5) note "groups that are chosen on the basis of performance on one measure of verbal working memory capacity (reading span), do not necessarily differ on other measures which are also thought to measure verbal working memory capacity" (p. 115). One solution is that adopted by Kemtes and Kemper (1997) who constructed a composite span score for each subject, differentially weighted by how strongly each measure loaded on a common factor. Another approach is that taken by Waters and Caplan: compare alternative measures of working memory capacity and processing efficiency. A danger of these approaches is that, as Kemper and Kemtes (Chapter 4) point out, there may be a threshold or critical region for span effects and our sampling strategies may yield high span groups that fall short of, or low span groups that exceed, this threshold. This issue is, therefore, not unrelated to the first two: As we move from general theories to more specific models and as we adopt increasingly sophisticated research tools, our efforts to relate individual differences in cognition to differential patterns of reading or listening times, eye movements, ERPs or PETs may flounder because neither language nor cognition has been appropriately measured.

303

Moreover, in our attempt to establish reliable and valid constructs we can not ignore the standards set by individual-differences research with, for example, structuralequation modeling or hierarchical linear modeling which have proven to be valuable statistical tools to study other domains of cognitive function - even if this means that we inherit a new bag of problems. EMERGING ISSUES

Multiple Stores or Representations Memory research has delivered a set of reliable principles on the basis of list learning experiments. They range from proactive and retroactive interference, including issues of inter-item similarity and discriminability, the role of organizational factors, depth of processing, encoding specificity to distinctions between explicit and implicit memories. From the traditional perspective the comprehension of isolated sentences is based on a single postlexical representation and should be determined by how much material or uninterpreted structure has to be held in memory for how long. The problem is, as Frazier (Chapter 8) put it: "The assumption of one (active) verbal memory system gives rise to the expectation that it will reveal an advantage for recently presented material, or it won't. Similarity among items will facilitate (or inhibit) performance, or it won't'' (p. 204). We wish to highlight a novel proposal keeping a distinction between different types of representations in working memory. Wingfield and Tun (Chapter 2) present as the "questions to be answered" (p. 46f.) the possibility of multiple representations, potential interactions among them and with age, and their relation to one or more pools of resources or cognitive architectures. Their aim is to unpack the role of working memory in spoken language. They argue for distinguishing between acoustic, phonological, and conceptual traces, differing in duration but overlapping in time; these traces also differ in accessibility and susceptibility to interference. These authors show that there is age invariance across levels of task difficulty for the conceptual representation (similar to the conceptual short-term memory proposed by Potter & Lombardi, 1990) while at the same time they find age differences in other aspects of processing related to speech rate. This emphasis on processing limitations, as opposed to storage limitations, was also echoed by Frazier (Chapter 8). Frazier insists that temporary storage of intermediate stages of linguistic analysis be distinguished from computational demands and she suggests that there are potentially automatic triggers that give rise to more than one postlexical representation. Specifically, she distinguishes between syntactic and discourse representations where the latter can also be identified in processing of isolated sentences looking at subtle contrasts between questions with pronouns. Multiple representations for long versus short-term storage were also evoked by Gunter et al. (Chapter 10) to account for age differences and age similarities in ERP activation patterns. They distinguished between first-pass processing, concerned with the activation of syntactic features, and second-pass processing,

304

concerned with the detection of syntactic violations. They also link ERPs to different mnemonic processes, suggesting that long positive waves reflect storage processes while slow, negative waves indicate long term memory retrieval. Hence, ERP methodology may be useful in delineating different memory stores and tracking interactions among them, in order to answer Wingfield and Tun's (Chapter 2) questions. Formal Principles of Discourse A surprisingly number of these chapters discuss discourse, less in terms of a general add-on or extension of sentence processing that one eventually has to deal with anyway, than in terms of specific mechanisms that reach beyond the immediate context of isolated sentences. In other words, it appears that discourse processes will be increasingly cast in terms of formal principals. Such formal principles are likely to generate an interest in taking a "broader look" at discourse and aging. Burke (Chapter 1) links the communicative predicament of aging to her finding that tip-of-the-tongue states (TOTs) are more frequent in older adults. TOTs might be more frequent in older adults because they receive less speech input and produce less speech output. This reduction in speech activity leads necessarily to less phonological activation which in turn will weaken the links between lexical nodes and the phonological system. She also reconsiders discourse in her discussion of off-target speech and verbosity, emphasizing that age differences in discourse need not be equated with age deficits. Frazier (Chapter 8) presents three examples where perceivers were shown to establish a discourse representation via what she calls d-linked phrases. The examples comprise contrasts between phrasal and normal pronouns, sluicing, and 3site attachment preferences. This work suggests that it is time to move beyond descriptive accounts of discourse phenomena to the development of formal models of discourse. One such attempt to formalize discourse principles was adopted by Stine-Morrow and Soderberg Miller (Chapter 3) in their work on situation models. Less formal approaches to discourse are also evident in other chapters. Wingfield and Tun (Chapter 2) point out a number of parallels between fuzzy-trace theory and conceptual short-term memory including a concern for the gist of sentences and a continuum for storage ranging from fuzzy to verbatim. Older adults' primary concern with gist may be derived from a greater concern with the discourse as a whole, amounting to an age-related preference for global processing. Kliegl et al. (Chapter 6) present strong age differences in the comprehension of German object initial main clauses, results that are not easily reconciled with the assumption of age invariance for interpretive processes. However, this result might be related to a specific failure of older adults to generate the appropriate discourse context for this grammatical construction. The object MCs of this experiment involve pragmatic parameters such as the distinction between given or new information, or between presupposed and asserted parts of the clause. Whenever such factors play a role, post-interpretive processes in the sense of Caplan and Waters (in press) might be invoked because a full understanding of the content of the sentence presupposes a (re-)construction of a context situation in which a

305

sentence with the particular information structure could be uttered felicitously. Consequently, this perspective leads to the prediction of an age x S/O MC interaction. Kemper and Kemtes (Chapter 5) reach a similar conclusion in their study of wh-questions. Young and older adults apparently make different discourse-induced interpretations of wh-questions, reflecting in part memory limitations on the older adults' ability to retain multiple potential referents for the wh-words. Here, immediate sentence processing and post-interpretative discourse processing clearly diverge as the working memory constraints on immediate processing of whquestions give way to this age-bias in discourse processing. Finally, Kempler et al. (Chapter 9) show that there is little evidence that AD patients are sensitive to grammatical or semantic constraints. There is, however, evidence for a deficit in sensitivity to discourse constraints. A discourse processing impairment could result from either a linguistic or memory impairment. The on-line discourse processing experiment was designed to assess the ability of AD patients to process pronouns in short discourses. Although AD patients were sensitive to the appropriateness of the visual target, they were much less so than the control participants. This finding supports the claim that AD patients have difficulty in maintaining representations during discourse comprehension. Tradeoffs and Compensations A number of intriguing results are reported that fit the framework of tradeoffs and compensations. Stine-Morrow and Soederberg Miller (Chapter 3) remind us that being "slow" may be better than being "fast" in complex cognitive processes such as reading, driving home their point with a perfect analogy to kissing. If the experimental set-up leaves room for strategic choices of what to process, older adults apparently systematically pick the strategy that leads to more interesting results from a general perspective, a perspective that transcends the experimental context and connects the experiment with "real life" or pragmatic aspects of discourse. Examples of this phenomenon are reported in each of the first three chapters. In communicative settings, older adults are off-target with their speech more frequently than young adults. This off-target speech, however, generates systematically higher rankings of interestingness in what they are talking about both by young and older raters (Burke, Chapter 1). Given that off-topic speech has been taken as evidence of a cognitive deficit in inhibition, the positive evaluation of this performance in a broader context comes close to a Gestalt switch from an age deficit to an age advantage. In speech processing older adults are typically found on the "gist end" of the gist versus verbatim recall continuum (Wingfield & Tun, Chapter 2). The faster the presentation of syntactically coherent speech, the larger is the age difference in favor of older adults towards a semantic reconstruction of the content a pattern that remained after controlling for age differences in verbatim recall. And, finally, research on text processing probably provides the most elaborated conceptualizations about how the productive allocation of resources may help older adults to circumvent limits in working memory as well as maximize the utility of the

306

constructed representation. Stine-Morrow and Soederberg Miller (Chapter 3) discuss four conditions for which this appears to be true: comprehending narrative structure, contrasting comprehension goals, accessing situational models, and utilizing personal knowledge. They conclude that "it may be that their use of discourse-level features ... provides support to enable them to create a distinct and elaborated text-base on par with that of the young" (p.70). Finally, there are some suggestions coming from ERP studies that deserve closer scrutiny in follow-up research. Gunter et al. (Chapter 10) report the semantic network of middle-aged participants had a larger or less selective spread of activation than that of the young participants; the age groups did not differ in degree of activation for the associated target words. Moreover, ERPs elicited by primes were more positive for the middle-aged group; they interpreted this as indicating better preparation for the words to come or different (probably better) use of context. They conclude "that middle-aged academics, particularly those who were more successful in the recall tasks, adopted compensatory strategies which, although not completely eliminating all age effects, certainly reduced them" (p. 262). One "big question" to be answered about these results on tradeoffs and compensations (excepting the ERP results for now) is whether they reflect options or unavoidableconstraints. At least three issues need to be checked. First, is language processing in young and older adults mediated by different cortical sites, as suggested by Caplan and Waters (Chapter 11)? If so, some age effects may turn out be to due to functional neuroanatomy, rather than strategic processing differences. Second, if we instruct or train young adults to adopt these strategies, will age differences in favor of older adults disappear? And as a corollary, will young adults who deploy older adults' strategies suffer costs in their recall of detail-level information? Third, how will older adults respond if we prevent them from using these strategies, for example, by changing the experimental setup? Irrespective of the outcome of such manipulations the findings on tradeoffs and compensations come as close to a differentiated view on cognitive aging as we can imagine. Even if turns out that, in principle, young adults can emulate older adults' strategic choices, the results clearly suggest that young adults could, and actually should, learn something from older adults in this respect. CONCLUSION

There are many other perspectives one can take on language and cognitive aging. Obviously, we have not exhausted the list of topics that could be extracted from the contributions to this volume for concluding observations. The tantalizing pictures of age invariance on some and age differences on other tasks surely will motivate our research in future years.

307

REFERENCES Caplan, D., & Waters, G. (in press). Verbal working memory and sentence comprehension. Behavioral and Brain Sciences. Daneman, M., & Carpenter, P. A. (1980). Individual differences in working memory and reading. Journal of Verbal Learning and Verbal Ability, 19, 450-466. Kemper, S. (1992). Language and aging. In F. I. M. Craik & T. A. Salthouse (Eds.), Handbook of aging and cognition (pp. 213-270). Hillsdale, NJ: Erlbaum. Kemtes, K. A., & Kemper, S. (1997). Youngerand older adults' on-line processing of syntactic ambiguities. Psychology and Aging, 12, 362-371. King, J., & Just, M. A. (1991). Individual differences in syntactic processing: The role of working memory. Journal of Memory and Language, 30, 580-602. MacDonald, M., Just, M. A., & Carpenter, P. A. (1992). Working memory constraints on the processing of syntactic ambiguity. Cognitive Psychology, 24, 56-98. Potter, M. C., & Lombardi, L. (1990). Regeneration in the short-term recall of sentences. Journal of Memory and Language, 29, 633-654. Waters, G. S., & Caplan, D. (1996). The capacity theory of sentence comprehension: Critique of Just and Carpenter (1992). Psychological Review, 103, 761-772. Waters, G.S., & Caplan, D. (submitted). Verbal working memory capacity and online sentence processing efficiency in college students.

This page intentionally left blank.

INDEX

A Aaronson, D., 54, 55, 62, 71 Aberdeen, J. S., 31,51 Abrams, L., 5,6, 17,25 Achariyapaopan, T., 252,277 Ackles, P. K., 279 Adams, C., 59, 64, 70-71 Aging, iii, v, vi, xi, xii, xiii, xv, 1, 3, 5-13, 15-17, 19-28, 31, 33-34, 36, 38-44, 46, 48-54, 59-67, 6975, 79, 81-88, 90-99, 101-108, 111, 130, 133-135, 137-140, 142, 147, 155, 159-160, 162163, 165-167, 199, 244, 246, 249, 251-259, 263, 268-283, 299-300, 304-307 age deficits, 17, 53, 70, 97, 304 age differences, 5, 8, 10-11, 17-20, 22-23, 26, 32-34,41-43, 50-51, 59, 61-62, 64, 67, 71, 73-74, 86, 96, 103-105, 133, 137-149, 154165, 255, 257-258, 261, 263, 265, 267, 269, 273, 216-277, 282, 300, 303-306 age invariance, xiii, 138, 140-144, 160, 162, 200, 300, 303-304, 306 age x complexity interactions, 142, 163

old-over-young plots, 139-140, 146,161 slowing, 53 Albert, M. L., 134 Albertson Owens, S. A., 83, 103 Alexander, A. H., 36, 51 Allard, L., 235, 246 Allison, T., 256, 276 Allport, D. A., 30,48 Almor, A., vi, vii, 227, 229, 233, 235-236, 239, 244-245 Alpert, N., 203, 224, 285, 296, 297 Altmann, G. T. M., 223 Altmann, L. P., 227, 244, 247 Alzheimer's Disease, 227-243, 305 Ambiguity, 5, 20, 33, 35, 49, 87, 89, 95-96, 99, 103, 108, 134, 146, 167, 173, 175-176, 185, 200, 211-213, 216, 272, 277-278, 307 Anagnopoulos, C., 84,103, 134, 150 Andersen, E. S., vi, vii, 227, 229, 233,236,244,245 Anderson, P. A., 6, 24 Anderson, J. R., 152, 165, 258, 276 Anderson, S., 186, 199 Andrassy, J. M., 65, 73 Andres, D., 17, 23 309

310

Anes, M. D., 39,49, 108, 112, 133 Annon, T. A. K., 60,72 Antonis, B., 30,48 Aphasia, 48, 98, 105, 244, 246, 297 Aquino, M. R., 41,48 Arbuckle, T., 9, 17, 20, 22-23, 79, 101 Ariel, M., 235, 244 Atkinson, R. C., 30,48 Austin, A., 6, 19, 22, 24, 28, 79, 102

B Bach, E., 178, 199 Bäckman, L., 74, 146, 165 Baddeley, A., 3, 26, 31, 34, 45, 48, 81, 85, 101-102, 109, 133, 227, 244, 287, 296 Baldinelli, L., 60,73 Bales,P. B., 54, 71, 163, 165 Ball, H. E., 107, 133 Balota, D. A., 79-80, 101, 144, 165, 258, 276 Baltes, M. M., 54, 71 Baltes, P. B., 54,71, 163, 165 Bang, S., 227, 230, 244 Barry, G., 172, 200, 217 Barss, A., 280 Bartlett, F. C., 36, 44, 48 Bartolucci, G., xi, xv Bashore, T. R., 53, 71 Bates, E., 227, 244 Baum, S., 108, 133, 135 Bayles, K. A., 227, 232, 244 Benjamin, B. J., 82, 101 Bent, N., 3, 25 Bentin, S., 252, 259, 276 Berdichevsky, D., 296 Berger, H., 250, 276 Bersick, M., 254,281 Berwick, R. C., 110, 133 Besner, D., 280 Bever, T. G., 30,49 Birren, J. E., 25, 49, 74, 134, 165, 255, 276, 279, 281 Black, S. R., 258, 276

Blanchard, L., 46, 50 Blanchard-Fields, F., 74 Block, R. A., 45,49 Bloom, L., 80, 101, 252, 277 Bloom, P. A., 80, 101, 252, 277 Bock, K., 4, 17, 22-23, 79, 101 Boddy, J., 259, 276 Bolton, K., 23 Boruff, B., 84, 104 Botwinick, J., 110, 133, 255, 276 Bouma, H., 51 Bouwhuis, D. G., 51 Bower, G. H., 23, 56, 58, 73, 102, 278 Boyes, C., 5,25 Brailowsky, S., 256, 282 Brainerd, C. J., 45-46, 48, 73, 134 Brinley, J. F., 137, 165 Britton, B. K., 60, 68, 71 Broadbent, D. E., 30, 33,48 Brown, A. S., 252, 254, 276, 278 Brown, C. M., 6, 22, 252, 254, 276, 278 Brown, H. E., 7, 252 Bryan, J., 53, 71 Buchanan, M., 296 Burger, L. K., 4, 23 Burke, D. M., v, vii, xii, xiii, 3-7, 10, 12-16, 19-26, 79, 97, 101-102, 105, 134, 140, 166, 249, 258, 262, 276, 279, 300, 302, 304305 Bushell, C., 297 Butterworth, B., 39, 51

C Callaway, E., 277, 279 Campbell, J. D., 141, 165 Canestrari, R. E., 255, 279 Cannito, M. P., 5, 26 Canoune, H., 265, 281 Canseco-Gonzalez, E., 102, 223 Canton, R., 250, 276 Capacity see Working Memory

311

Caplan, D., vi, vii, xi, xii, xiii, xv, 3334, 48, 50, 98-99, 101, 105, 107-112, 114, 120, 125, 131133, 135, 137, 147, 165, 166167, 203, 224, 228-239, 245, 246, 283, 285, 287, 290, 293294, 296-297, 300, 302, 304, 306, 307 Capps, J. L., 65,73, 83, 103 Carlson, K., 199, 213, 223 Carlson, M. C., 97, 101 Carpenter, P. A., xi, xv, 31-33, 4850, 54-55, 71, 72, 88, 95-96, 101, 103, 105, 108-111, 113, 120, 125, 130-135, 239, 244246, 284, 293, 296, 302, 307 Carr, T. H., 27 Carter, J., 223 Cavigelli, S., 36, 5 1 Cerella, J., 26, 50, 137, 139-140, 165 Chantraine, Y., 20, 23 Chapman, R. M, 277 Charness, N., 67,72, 141, 165 Cheney, M., 258,276 Cheng, L., 185, 199 Cheung, H., 20, 24, 59, 74, 84, 87, 98, 103, 104, 134, 150, 166, 200 Chiesi, H., 67,72, 74 Childers, D. G., 252, 277 Chinen, A., 61, 72 Choe, J., 223 Christiansen, M. H., 240, 245 Chu, N. S., 256, 276 Chwilla, D. J., 252, 276 Clahsen, A., 253, 281 Clarke, L., 242, 244 Clifton, C., 172, 199, 205, 207-208, 210-212, 214-215, 217, 223 Cohen, A., 49 Cohen, G., 3, 6, 22, 65, 72, 97, 101, 262, 276 Coleman, E. B., 41,50 Coles, M. G. H., 277, 279-281 Coltheart, M., 49, 133, 135, 277, 297

Communication, x, xi, xii, xiii, xv, 24, 26, 101, 103-104, 106, 244245 Complexity computational complexity, 219220,300 coordinative, xv, 139, 141, 143, 146, 157, 159, 166-167 sequential, 139, 142, 146 Comprehension see Language processing, Connectionism, 4,7, 11, 180-182 Connelly, S., 97, 101 Conrad, R., 29,48 Cook, E., 199 Cooley, S., 6, 25 Coon, V. E., 141, 167 Cooper,P. V., 5, 18,22, 82, 101 Corey, V., 254, 281 Corkin, S. ,227, 244 Coulson, S., 253-254, 276, 281 Coupland, J., 19, 22 Coupland, N., 3, 19, 22,23 Craik,F. I. M., 24, 49, 51, 61, 72, 75, 102, 110, 133-134, 165, 199, 307 Crain, S., 85, 101 Crimmins, A., 60,73 Crocker, M., 223 Crystallized abilities, 69 Cuetos, P., 180, 199 Cunningham, A. E., 53,74 Curiel, J. M., 65, 73 Curry, C., 68,71 Curtiss, S., 227, 245

D Dagenbach, D., 27 Dahl, Ö., 209 Davies, D. R., 5 1 Davis, C. A., 107, 133 Davis, G. A., 82, 101 Davison, A., 101 Dawson, G. D., 250, 276, 277 de Villiers, J., 87, 101

312

Deevy, P., 208, 223 Dell, G. S., 4,22-23, 79, 101 Della Sala, S., 227, 244 Dementia, xi, xii, xiii, 98-99, 111, 244-246, 280 Denoth, F., 280 Deser, T., 6, 23 Dickey, M. W., 215, 223 Discourse, v, xiii, xv, 5, 9, 17, 19, 21-23, 26, 34, 35, 39, 50, 53, 55, 60, 67, 70-72, 74, 79, 81, 94, 101, 103-105, 205-206, 208-2 10, 2 12-2 15, 2 19-222, 232-233, 235-239, 241, 243246, 299, 303-305 distance effect, 56, 65- 67, 210 focus, xii, 3, 17, 45, 54, 61, 65, 73, 79, 81, 83, 107, 148, 153, 164, 174, 186, 189, 210, 212-215, 220-223,242, 244, 300-301 off-topic speech, 18-21, 305 reader goals, 54, 62 recency, 5, 7, 14,94, 102, 150, 210, 212, 214-215, 220, 223 situational model, 306 topic, 18, 20, 65, 187, 207-211, 214-215, 220-221, 223, 302 Dixon, R. A., 18, 23,74 Dobbs, A. R., 5,23 Donchin, E., 251-252, 256, 277, 281 Donnell, A., 235, 246 Dorosz, M., 59, 71 Duchek, J. M., 144, 165 Dustman, R. E., 256, 277, 281

E Eason, R. G., 251, 277 Elderspeak, xi, xv Electrophysiology, 249-250, 278, 280-281 (E)LAN, 253-255 EEGs, 250,255,256,280 ERPs, xiii, 249-282, 302,304, 306 N1,250-251, 255, 259, 265, 272 N100, 250

N400, 250, 252-253, 255, 259261, 263, 265-266, 270-271, 273, 275-279 P1, 71, 250-251 P2, 250, 251, 259, 262, 272 P300, 250, 255-257, 259, 277, 281 P3b, 251, 254, 272 P600, 253-255, 270-271, 273, 281 Ellingson, R. J., 256, 279 Ellis, A. W., 26, 101 Emery, O. B., 107, 133 Emmerson, R., 256, 281 Emonds, J., 178, 199 Engelkamp, J., 149, 166 Engle, R. W., 109, 132, 135 EPIC, 86 Ericsson, K. A., 67-68,72, 99, 102 Evans, A. C., 297 Event-related potentials see Electrophysiology

F Facilitation, 9, 55, 67, 74, 204, 217, 220, 258, 276, 303 Fanselow, F., vi, vii, xii, xiii, 137, 138, 149, 165, 167, 171, 173174, 176, 179-180, 199-200, 300 Faulkner, D., 6, 22, 65, 72, 262, 276 Fayyad, E. A., 53, 72 Feier, C. D., 107, 133, 150, 165 Fein, D., 134 Ferreira, F., 39, 49, 108, 112, 133, 207-208, 210 Ferres, S., 55, 62, 71 Fischler, I., 252, 277 Fitzgerald, J.M., 146, 165 Fleischman, D. A., 12, 23 Fleming, S. G., 5, 26 Fodor, J. A., 30, 49, 79, 80, 85-86, 102 Fodor, J. D., 79, 102 Forster, K. I., 236, 245, 280 Fox, N. A., 281,296 Fox, P. T., 256

313

Frackowiak, R. S. J., 296 Frazier, L., vi, viii, xii, xiii, 36, 49, 79-80, 85-86, 102, 149, 165, 172, 175, 178, 199, 203, 205, 208, 210- 217, 220, 222-223, 254, 269, 277, 300, 302-304 Freedman-Stern, R., 82, 105 Frensch, P. A., 141, 165 Friederici, A. D., vi, viii, 249, 253, 254, 269-270, 272, 277-278, 280, 281 Friedman, D., 252-253, 257, 277, 278 Friston, K. J., 285, 296, 297 Frith, C. D., 296 G Gabrieli, J. D. E., 12, 23 Garfield, J. L., 223 Garnsey, S. M., 275, 277 Garrett, M. F., 30, 49, 79, 102 Gathercole, S. E., 31, 48, 85, 102 Geary, D. C., 141, 165 Gerard, L., 65, 73 Gernsbacher, M. A., 30, 48-49, 58, 72, 80,97, 102, 133 Gerstman, L., 107, 133, 150, 165 Gibson, E., 81, 86, 102, 182, 199, 204, 213, 223, 284, 296 Giles, H., xi, xv, 3, 23 Glosser, G., 6, 23 Glynn, S. M., 71 Goff, W. R., 256, 276 Gold, D. P., 9, 17, 22-23, 79, 101 Goldinger, S. D., 38,49 Goldsmith, H. H., 58, 72 Goodglass, H., 29, 49 Gopher, D., 102 Gordon, P. C., 35,49 Gould, 0. N, 18, 23 Goulet, L. R., 163, 165 Goulet, P., 5, 17, 23 Gow, D. W., 35,49 Graesser, A. C., 54-56, 58, 62, 71-72, 75

Grammar, 1, iii, v, vi, xii, xiii, 29, 33, 38, 50-51, 59, 79, 81, 85, 92, 101-102, 134, 146, 148-149, 152, 155-156, 158, 162, 165166, 168-169, 171, 172, 174175, 180, 182, 186-187, 199200, 215, 223, 233, 244-245, 250, 253-254, 268-270, 273, 275, 278, 283, 296-297, 300, 303 Active Filler Strategy, 172, 194 active sentences, 6, 97, 147, 153, 172, 175, 194, 203-205, 228231, 235-236, 303 agreement, 4, 87, 147, 192, 233, 236-237, 239, 242, 244-245, 254, 299 animacy, 195, 284 antecedents, 83, 110, 206-212, 214-215, 236 cleft-object sentences, 109, 111 cleft-subject sentences, 109, 111 constraints, 236, 305 embeddings, 33,79, 80, 82, 83, 86, 90,99, 110, 149, 152, 159, 176, 180-181, 185, 191, 193, 205206, 210-212, 218, 230, 236237, 263, 265, 269, 272, 285, 300 frequency, 5,7, 13, 17, 23-24, 39, 49,55, 102, 112, 133, 180-181, 196-198, 227, 235, 239-240, 242, 255, 257, 282 gapping, 213 main clauses, 147, 149, 150, 152156, 158-162, 180-181, 193, 300, 304 movement, xiii, 39, 56, 171, 173, 175-188, 192-194, 200, 223, 302 object initiality, 149, 161, 176, 177, 179-184, 189-191, 193195, 198,304 object-subject sentences, 109, 111, 116, 284-287 ,289, 291-292 Optimality Theory, 178, 184, 199

314

passive sentences, 147, 153-154, 186, 203, 229-231, 239, 261 pronouns, 83, 148, 149, 150, 153, 206-209,214-215,220,235236, 238 relative clauses, 85, 108, 138, 147156, 158-166, 174, 176, 180, 212-214, 223, 229, 231, 239, 253, 280, 283-284, 290-293, 300 sluicing, 210, 212-213, 220, 304 subject initiality, 175-177, 180182, 184, 190-193, 195 subject-initial questions, 177 subject-object sentences, 109-111, 116, 173, 175, 187, 195, 197, 284-287, 289, 291-292 syntactic complexity, xiii, 49, 83, 99, 101-102, 104, 107, 113, 133-134, 137-138, 146-147, 148, 152, 154, 156-157, 160166, 199-200, 217, 228, 230, 232, 238, 269, 279, 296 syntactic complexity, xiii syntactic processing, xii, xiii, 83, 85-86,95-96,98-99, 109, 132, 134, 165, 199, 213, 215-216, 228, 230, 238, 253, 268-269, 272, 277-279 282-283, 290, 292-294, 296-297, 300, 307 syntactic system, 219 syntax, xiii, 29, 33, 38,50, 59, 92, 101, 146, 168, 171-172, 174175, 180, 182, 187, 199-200, 244, 253-254, 269, 273, 275, 278, 300, 303 traces, 29, 36-38, 42, 45-46, 83, 89, 110, 146, 172-174, 178, 210-211, 216, 219-220, 267, 301 violations, 84, 133, 233-237, 253255, 269-270, 276-277, 279281, 300, 304 wh-movement, 178-179, 185-187

wh-questions, 86, 88, 91-94, 96, 167, 180, 184, 189, 195-196, 199, 200, 305 Green, G., 101 Greenspan, S. L., 56,58,73 Gregora, A. W., 20,26 Grewendorf, G., 182, 199-200 Griffin, Z. M., 4, 17, 23 Grimshaw, J., 86, 102, 178, 184, 199 Grober, E., 227, 230, 244 Groothusen, J., 254, 278 Grosjean, F., 36,49 Gross, M., 253, 281 Growdon, J. H., 227, 244 Gruneberg, M. M., 24, 103 Gundel, J. K., 235, 244 Gunter, Th. C., vi, viii, xii, xiii, 249, 253-254, 259, 261, 263, 272, 277-278, 282, 300-301, 303, 306 Gwyther, L. P., 242, 244

H Haarmann, H. J., 110, 133 Hagendorf, H., 133 Hagoort, P., 252, 254, 276, 278, 281 Hahne, A., 253-254, 277, 278, 281 Hale, M., 175, 199 Hale, S., 53, 73, 139, 166 Hall, C. B., 161, 167 Hamberger, M., 253, 277-278 Hamilton, T., 71 Hargin, T. J., 253, 278 Harley, T. A., 4, 7, 8, 23 Harris, C., 244 Harris, J. E., 3, 26 Harrold, R. M., 6, 22 Harvey, M. T., 253, 278 Hasher, L., 8-9, 11, 18, 23, 27, 34, 51, 65, 73, 97, 101-102, 105, 258,278 Havinga, J., 24 Hawkins, J., 174, 199 Hayashi, M. M., 5,26 Hedberg, N., 235, 244

315

Hedrick, D. L., 82, 105 Heinze, H., 253-254, 278, 280 Heisey, J. G., 279 Heller, R. B., 5,23 Hemforth, B., 167, 200, 214, 223 Henderson, D., 74, 104 Henderson, J. M., 39, 49, 112, 133 Henderson, V. L., 82, 98, 104 Henderson, V. W., 227, 245,2 47 Henninghausen, E., 149, 166 Henwood, K., xi, xv Hess, T., 25,74 Hickok, G., 102, 182, 199,223 Hildebrandt, N., 99, 111, 135, 228, 246, 296, 297 Hillyard, S. A., 251, 252, 278-280 Hindman, J., 59, 64, 74 Hintzman, D. L., 45, 49 Hobart, C. J., 59, 71 Hoffman, J. E., 252, 278 Holcomb, P. J., 252, 254, 259, 279281 Holdredge, T. S., 68, 71 Holmes, A. P., 296 Houck, M. R., 252, 278 Howard, D. V., 6, 23, 258-259, 279 Howe, M. L., 73, 134 Hoyer, W., 26, 50 Huff, F. J., 227, 244 Huggins, A. W. F., 35, 49 Hulme, C., 79, 84, 102 Hulme, E., 19, 24 Hultsch, D. F., 11, 26 Hummert, M. L., xiv, 3, 20, 22-23, 26 Humphreys, G. W., 9, 12, 26, 280 Hupet, M., 20, 23

I Individual differences, xii, xv, 48, 49, 59, 74, 97, 101, 108, 133-134, 199, 244-245, 267, 279, 296, 301-302, 307 Inhibition, 4, 7-12, 16-19,22, 27, 95, 97, 99, 101-103, 105, 163, 176,

217, 219, 221, 272, 278, 300, 305 Inskeep, N. R., 45,49 Iragui, V., 253, 279

J Jackson, C., 227, 245, 259, 261, 278 Jackson, J. L., 227, 245, 259, 261, 278 Jagacinski, R. J., 53,72 James, L. E., 14, 15, 19, 23, 24, 79, 102 James, W., 6, 23 Jennings, J. M., 61, 72 Jennings, J. R., 279 Jescheniak, J. D., 17, 24 Job, R., 215, 223 Johannes, S., 253-254, 280 Johnson, J., 265, 281 Johnson, N. S., 55, 73, 81, 103 Johnson, R., 265, 281 Jones, G. V., 7, 24 Jonides, J., 203, 221, 223, 296 Junker, M., vi, viii, 137, 163, 165, 180, 199-201 Just, M. A., xi, xv, 31, 48-50, 54-55, 71-73, 95, 103, 105, 108, 132135, 176, 199, 239, 245-246, 264, 279, 284, 293, 296, 302, 307

K Kahn, H. J., 5, 23, 65, 73 Kahn, J., 5, 23, 65, 73 Kahneman, D., 30, 33, 49, 54, 72 Katzman, R., 256, 275, 279, 282 Keenan, J. M., 55, 72 Kemper, S., iii, v, vi, viii, xi, xii, xiii, xv, 3, 6, 19-20, 24, 26, 33, 36, 49, 55, 72, 79, 82-84, 86-88, 95-96, 98, 102-104, 107-108, 134, 149-150, 165-166, 168, 179, 199-201, 230, 242, 246, 268-269, 279, 299-302, 305, 307

316

Kempler, D., vi, viii, xii, xiii, 134, 227, 229, 233-236, 239, 244245, 301, 305 Kemtes, K. A., v, ix, xii, xiv, 20, 26, 33, 36, 49, 79, 86, 88, 95-96, 103, 106, 108, 134, 300-302, 305,307 Kerr, B., 30,49 Kieras, D. E., 86, 104 King, J., 132, 134, 176, 199, 253, 264, 276, 279, 281, 284, 296, 302, 307 Kintsch, W., 36, 50, 54-56, 62, 6769, 72-74, 79, 81, 99, 102-103 Kiparsky, P., 199 Klahr, D., 71 Kliegl, R., iii, vi, viii, ix, xi, xii, xiii, XV, 137, 139-141, 144, 146147, 149, 154-155, 157, 160161, 163, 165-168, 171, 173174, 176, 180, 199-200, 299300, 304 Klix, F., 133 Klorman, R., 256, 279 Kluender, R., 252, 254, 275, 279 Knight, G. P., 56, 73 Knight, R. T., 256, 282 Knopman, D. S., 12, 25 Koeppe, R. A., 296 Koh, C. K., 45, 51 Konieczny, L., 167, 200, 214, 223 Koriat, A., 102 Kornblum, S., 279 Koslow, S. H., 277, 279 Koster, C., 236, 245 Kotovsky, K., 71 Kramer, A. F., 265, 280 Krampe, R. Th., xi, xv, 138, 139, 140,166 Krems, J., 149, 166, 167, 173, 176, 200 Kritschevsky, M., 244 Kroll, J. F., 9, 24 Kutas, M., 252, 253-254, 275-276, 279-282 Kwok, H., 23

Kwong See, S., 97, 103 Kynette, D., 19, 24, 82-84, 102-104, 134, 150, 166, 200

L Labouvie-Vief, G., 59, 71 LaFratta, C. W., 255, 279 Lahar, C. J., 31, 39, 51 Laird, J. E., 86, 103 Language processing, xi, xii, xiii, 29, 31, 36, 47, 54, 67, 74, 79, 84, 93, 95, 97-99, 107, 109, 111, 166, 199, 221, 223, 227, 239241, 252, 263, 269, 272, 277, 283, 293-294, 300-302, 306 acoustic confusions, 36, 48 ambiguities, 36, 55, 79, 80,96, 103, 172, 176, 213-214, 302, 307 auditory moving window paradigm, 39, 109-110, 112, 119-120, 125, 133, 301 cognitive load, 176, 178 comprehension, v, vi, xi, xii, xiii, xv, 23, 29-31, 33-38, 45-51,56, 62-64, 66-67, 69-75, 79-81, 83, 85-86, 88,95-97, 100-105, 107-109, 111, 132-135, 137138, 147-149, 154-155, 160161, 165-167, 180, 193, 195, 203-204, 206, 220-221, 223224, 227-232, 234-246, 268269, 277-278, 280, 282-283, 293-294, 296-297, 301-307 conservative parser, 182-183 costs, xiii, 30, 145, 150, 154, 171, 175-182, 184-188, 192, 218, 299,306 cross-modal naming, 108, 229, 232-236, 238, 241 difficulty, vi, 13, 15, 17,20, 30, 34,39-40, 86, 115, 130, 137146, 149, 153, 155, 157, 160164, 171, 174-175, 177-179, 181-182, 185-188, 193,215,

317

222 ,228, 234, 236-237, 239, 243-244, 258, 269, 271, 300, 303, 305 discourse-level processes, 54, 55, 64 efficiency, vi, 19, 60, 97, 99, 107, 109, 111-112, 116, 120, 122, 125, 132, 162, 293 filler-gap constructions, 86, 159, 172, 216, 223 imitation, 95, 134, 165, 269, 279 immediate processing, 70, 98, 215, 217, 220, 305 naming, 5, 9-11, 17, 20, 23-26, 97, 104, 111, 177, 232, 236, 239, 244 off-line, 96, 108, 138, 149, 161, 228-232, 237-241, 268, 294, 299, 301 on-line, xii, 39, 41,49, 55-56,6061, 67, 70, 73-74, 86, 92, 95-96, 98, 99, 103-105, 107-109, 111112, 116, 120, 123, 130, 132, 134-135, 149, 161, 172, 200, 228-229, 232-233, 235,237238, 240-241, 245-246, 249, 251, 269, 274, 297, 299, 301, 305, 307 parsing, vi, xiii, 51, 81, 85-86, 102, 109, 166-167, 172-173, 175-176, 178, 182, 199- 200, 203, 221-222, 249, 253-255, 265, 268-272, 277-278, 281, 300 plausibility judgment task, 203, 283 post-comprehension processing, 95, 98, 100 primed competitor paradigm, 9-12, 16, 23, 25, 27 prior processing task, 13-14 processing efficiency, 111-112, 120, 122-124, 130, 132, 135, 137-138, 140, 200, 293, 294, 302, 307 processing models, 80-81, 171

production, v, xii, 3-6, 9-18, 20, 22-24, 26, 37, 42, 67, 73, 79, 82, 85-86, 95, 100-103, 105, 107, 138, 227, 244, 268-269 pronouns, 5,73, 103, 207-210, 214, 216, 223, 235, 238, 243244, 303, 304, 305 reading, xii, xiii, 35, 48, 53-56, 5960, 62, 64-67, 69, 71-74, 79, 83, 85-86, 88-92, 94-99, 101, 104, 108-111, 113, 115-117, 120, 121, 122, 125-127, 130-133, 135, 147, 149, 161, 176-177, 180, 182-184, 189-198,204209, 211, 217, 222, 232, 237, 239, 240-241, 243-244, 264, 278, 280, 301-302, 305, 307 resource requirements, 215-217, 219-220 segmentation, 38-39, 41-44, 49-50, 98, 99, 190, 193 sentence wrap-up, 55, 59, 62, 6465, 69 task demands, 30, 46, 65, 137, 204, 206, 221, 238, 240-242, 301 text base, 62, 63 text-level processes, 55 word finding, xii, 3, 5-7, 9, 12-16, 22-26, 304 word omissions, 36 word production, 3, 5-6, 16, 17, 20, 23, 27 word retrieval, xii, 3, 5-6, 16, 22, 23, 304 Languages Chinese, 185 Dutch, 165, 173, 199, 263, 300 English, xii, xiii, 17, 80, 111, 172, 173, 176, 185, 187, 209, 211, 213-214, 252, 264, 279, 300 German, xii, xiii, 138, 147, 149, 166-168, 173, 176, 178, 181183, 187, 189, 190, 192, 195, 196, 199-201, 214, 270, 272, 279, 281, 300, 304

318

Hindi, 185, 187, 218 Italian, 173, 199, 215 Japanese, 184-185 Kwakwala, 186, 199 Russian, 216, 219 Laurie, S., 3, 26 Laver, G. D., 7, 12, 24, 140, 166, 249, 279 Lawrence, A., 102 Lee, D. W., 60, 72 Lee, M-G., 42, 49 Leirer, V. O., 65, 73 Levelt, W. J. M., 4, 17, 24 Levin, Z., 296 Lewis, R. I., 81, 86, 103 Li, K. Z. H., 34, 51 Liao, M., 53, 72 Liddle, P. F., 296 Light, L. L., 6, 12, 22, 24, 26, 33, 49, 65, 73, 83, 103, 107, 134, 258, 279 Lima, S., 139, 166 Lindamoot, T., 252, 279 Lindenberger, U., 163, 166, 269, 277 Lindfield, K. C., 39,51,98, 105 Lloyd-Jones, T. J., 9, 12, 26 Logie, R., 109, 133 Lombardi, L., 36-38, 42, 44-45, 5051,303 Long term memory, 29, 45, 48, 68, 165, 258, 265, 281, 304 fuzzy traces, 45-46 Long-term working memory, 68, 72, 99,102 retrieval structures, 68-70, 99, 300 Lorch, R. F., 56, 73 Love, T., 297 Lovelace, E. A., 6, 25 Loveless, M. K., 10, 25, 59, 74, 98, 104 Lowe, D., 42, 51 Lubinski, R., 244, 245 Lucas, D., 7, 26 Luce, P. A., 37, 50 Luck, S., 251, 278 Luper, S. J., 9, 25

Luszcz, M. A., 53, 71 Lyons, E. A., 37, 50, 230, 242, 246

M Muller, G., 186, 200-201, 280 Macaluso-Haynes, S., 82, 105 MacDonald, M. C., vi, ix, 95- 96, 103, 132, 134, 180, 200, 227, 229, 233, 236, 240, 244-245, 247, 302, 307 Mace, H. L., 242, 245 MacKay, D. G., 4-6, 12, 17, 20, 22, 25,79, 103 MacWhinney, B., 147-150, 166 Mahaffey, D., 265, 281 Maki, P. M., 12, 25 Makris, N., 296 Manchester, J., 5, 25 Mandler, J. M., 55, 73, 81, 103 Marchman, V., 244 Marcoen, A., 155, 158, 167 Marcus, M., 171, 200 Marin, O., 227, 246 Marrett, S., 297 Marsh, G. R., 253, 278 Marshuetz, C., 296 Marslen-Wilson, W. D., 104, 108, 134, 220, 222-223, 235-236, 245-246 Martin, R. C., 33, 50 Massaro, D. W., 35, 50 Masson, M. E. J., 11, 26 Mattys, S. L., 35, 50 Matzke, M., 253, 254, 280 May, C. P., 97, 102, 105 Maylor, E. A., 3, 6, 25, 167 Mayr, U., vi, ix, xi, xv, 137, 139, 140-141, 144, 146, 157, 163, 166-167, 200 McCallum, W. C, 251, 277, 280 McCarthy, G., 252, 276 McClelland, J. L., 8, 12, 25, 79, 81, 103, 104 McDonough, J., 223 McDowd, J., xiv, 97, 103, 105

319

McFarlane, D. K., 112, 133 McFarlane, M. D., 39, 49 McInnes, L., 3, 25 McKinnon, R., 254, 281 Mecklinger, 253-254, 265, 272, 277, 280 Mecsas, C., 43, 50 Meier, R. P., 29, 50 Memory see Working memory see Short term memory memory burden, 204-205, 219, 299-300 memory stores, 34, 86, 203, 304 verbal memory, 33, 46, 204, 207, 215, 220-221, 303 Meneer, W. B., 3, 26 Meng, M., 173, 180, 200 Merikle, P. M., 31, 49 Meta-analysis, 24, 49, 166, 167, 279 Metalinguistic judgments, 84, 99, 102, 110, 112-113, 129, 216, 229, 284-285 grammaticality,241 ratings, 19, 87 Meyer, A. S., 24 Meyer, B. J. F., 81, 104 Meyer, D. E., 86, 104 Meyer, M., 254, 277 Miller, G. A., 29, 41, 50, 85, 104 Milner, D., 246 Mitchell, D. C., 180, 199 Miyaki, A., 31,48 Modularity Theory, 79, 99, 102, 137, 204, 220, 223 Mojardin, A. H., 46, 48 Monsell, S., 5, 9, 12, 27 Moore, B., 3, 25, 60, 75 Morris, E. D., 296 Morris, P. E., 24, 26, 103 Morrow, D. G., 54, 56, 58-59, 65, 73-74 Moscovitch, M., 144, 146, 166, 167 Muir, C., 84, 102 Mulder, G., 251, 253, 259, 261, 278, 280, 282

Munn, A., 217, 223 Münte, T. F., 251, 253-255, 278-281 Murphy, G. L., 45, 50, 53 Myers, J. L., 56, 73 Myerson, J., 53, 73, 139, 166

N Nebes, R. D., 234, 245 Neelin, P., 297 Neely, J. H., 258, 280 Nef, F., 20, 23 Nesselroade, J. R., 163, 165 Neurology, vii, 245, 247, 276 aphasia, 48, 98, 105, 244, 246, 297 brain, xv, 26, 29,48, 101, 105, 133, 146, 165-166, 224, 244246, 249-251, 256, 275-282, 285, 290, 294, 296-297, 307 Broca's area, 203, 285-293, 296297 cingulate gyrus, 287, 289 left hemisphere, 203 left thalamus, 287, 289, 293 medial frontal gyrus, 287 neuroanatomy, 283, 290, 294, 306 neuroanatomy, vi, 283 neuronal processes, 283 pars opercularis, 203, 285, 286, 287 pars triangularis, 287, 288 regional cerebral blood flow, 283295, 297 superior parietal lobe, 290, 294 Neville, H. J., 252-254, 280 Newell, A., 86, 103-104 Nicholas, M., 134 Nicol, J., 236-237, 245, 280 Nilsson, L.-G., 146, 165 Nimmo-Smith, I., 109, 133 Nix, L. A., 6, 22 Node Structure Theory, xii, 5, 6, 12, 160 Nohara-LeClair, M., 20, 22 Nooteboom, S. G., 49 Norman, D. A., 29, 50

320

Norman, S., 19, 24, 82- 84, 103-104, 107, 134, 150, 166, 179, 200 North, A., 25, 82, 105, 167 Nussbaum, J. F., 22-23,26 Nyquist, L., 59, 71

O Oatman, L. C., 278 Oberauer, K., 138, 163, 165, 168, 180, 199-201 Obler, L. K., 107, 134 Obrist, W. D., 256, 280 Ochoa, J., 255, 282 Okita, T., 251, 282 Olivieri, A., 296 Osterhout, L., 252-253, 254, 280-281 Ostuni, E., 242, 245

PQ

Paller, K., 281 Papagno, C., 31, 48 Parasuraman, R., 51, 272, 281 Parsing see Language processing Pearlmutter, N., 81, 102, 223 Pechmann, T., 24, 149, 166 Pedroza, M. J., 17, 25 Peled, M., 20, 22 Pena, C., 109, 135 Penke, M., 253, 281 Penland, M., 7 1 Perlmutter, M., 59, 71 Perry, N. W., 252, 277 Pesetsky, D., 205, 223 Peters, L., 6, 22, 258, 276 Peterson, L. R., 29,50 Peterson, M. J., 29, 50 Peterson, S. E., 296 Pfeifer, E., 253, 277 Pickering, M., 172, 200, 217, 223 Pléh, C., 149 Poline, J. B., 296 Pollatsek, A., 79, 104 Poon, L. W., 42, 51, 53, 73 Porges, S. W., 256,281

Porter, L. W., xiii, 24 Positron emission tomography, xiii, 203, 283-292, 296-297, 301 regional cerebral blood flow, 283, 296 Posner, M. I., 290, 296 Potter, M. C., 36-38, 42, 44-45, 50, 303 Pötter, U., 163, 166 Prather, P., 83, 105, 135, 269, 282, 297 Pratt, M. W., 5, 25 Prinz, P. N., 256, 281 Pritchard, W. S., 251, 281 Production see Language processing Prospero-Garcia, O., 256,282 Pushkar Gold, D., 9, 17, 20, 22-23, 79, 101 Pütz, P., 253, 281 Pye, C., 84, 87, 98, 104

R Rabbitt, P., 3, 25 Rabins, P. V., 242, 245 Radvansky, G., 56, 65, 73, 75 Raichle, M. E., 296 Rash, S., 19, 24, 82- 83, 102, 103, 107, 134 Rastle, K. G., 6, 12-13,26 Ratner, H. H., 60, 73 Rau, M. T., 242-243, 245 Rauch, S., 203, 224, 296, 297 Rayner, K., 79- 80, 101, 104, 223 Reading see Language processing Reading span see Language processing Reason, J. T., 7, 26 Reese, H. W., 163, 165 Representation, 5, 17, 31, 35-39, 5456, 59-60, 63, 65, 68, 70, 81, 94,99, 104, 108, 142, 148, 151, 168, 178, 179, 204-206, 209-

321

210, 212, 215, 220, 223, 228, 234-236, 253, 266, 303, 306 discourse, 205-206, 208-210, 212, 215, 219-220, 303-304 phonological representation, 5 postlexical, 204-205, 303 schema, 55, 59, 62, 81 situational model, 306 syntactic, 207-210, 212, 216, 220, 222 text, 54 text-base, 55, 60, 62, 65, 70, 306 Reuland, E. J., 223 Reyna, V. V., 45-46, 48 Reynolds, P., 30, 48 Ridderinkhof, K. R., 53, 71 Rinck, M., 56,73 Ripich, D. N., 235, 245 Ritter, W., 251, 265, 277, 281 Roberts, P. M., 82, 105, 186 Robertson, R. R. W., 58,72 Robins, S., 5,25 Rochon, E., 99, 105, 147-148, 166, 167, 228, 230, 245-246 Röder, J., 149, 166 Romani, C., 33, 50 Rosen, M. J., 42, 45-46, 50-51, 105 Rosenbloom, P. S., 86, 103 Rosenzweig, M. R., 24 Rösler, F., 149, 166, 253-254, 265, 28 1 Roucos, S. E., 252, 277 Ruchkin, D. S., 281 Rugg, M., 246, 280 Rugg, M. D., 246,280 Rumelhart, D. E., 8, 12, 25, 79, 81, 103 Ryan, E. B., xi, xv, 3, 26,97, 103 Rybash, J., 26,50

S Saffran, E., 227,246 Salthouse, T. A., 6, 24, 26, 38, 49-51, 53-54, 60, 72-73, 75, 79, 88, 102, 104, 110, 134, 137, 141,

165, 167, 199, 249, 257, 263, 266, 282, 307 Santo-Pietro, M. J., 242, 245 Scabini, D., 256, 282 Scarborough, H. S., 71 Schafer, A., 214, 223 Schaumburg, H. L., 255, 282 Scheepers, C., 214, 223 Schell, D., 60, 73 Schema, 55, 59, 62, 81 Schlesewsky, M., vi, ix, 138, 149, 165, 167-168, 171, 173-174, 176-177, 180, 189, 191, 199200 Schmidt, A. L., 252, 280 Schriefers, H., 24, 254, 269, 277, 280 Schutze, C., 102, 182, 199 Schwartz, M., 227, 246 Schwartzman, A., 17, 23 Schweickert, R., 84, 104 Search-depth functions, 138, 146, 163 Seely, D., 216, 223 Segrin, C., 20, 26 Seidenberg, M.S., 79, 104 Sekerina, I., 216 Semantics, 199 priming, 276, 280 semantic processing, xiii, 6, 14, 22, 166, 249, 252-253, 263, 265, 268, 272, 278 Shadden, B., 101 Shallice, T., 48, 287, 294, 297 Shaner, J., 20 Shankweiler, D., 85, 101 Shapiro, A. M., 45,50 Shaw, R. J., 88, 104, 258, 279 Shearer, D. W., 256, 277 Shewan, C. M., 82, 104 Shiffrin, R. M., 30, 31,48,50 Short term memory, 29, 31, 36, 45, 48, 50, 68, 88, 102-104, 246, 281, 296, 302 conceptual short term memory, 36, 303, 304 dual task interference, 30, 166

322

phonological store, 31,37,42 reconstruction, 36,42,44-45,51, 105, 172, 284, 305 resource pool, 30, 33,47 Siegel, G. M., 20, 26 Simpson, G., 256, 277, 282 Simsons, R., 278 Singh, A., 83, 103 Ska, B., 5,23 Sliwinski, M. J., 161, 167 Small, B. J., 11-12, 16, 26, 230, 242, 246 Smith, E. E., 203, 221, 223, 287, 294, 296 Smith, G. A., 53,73 Smith, M. C., 59, 71 Snyder, E. W., 256, 277 SOAR, 86, 103 Soederberg Miller, L. M., v, ix, xii, 53-54, 58-59, 61, 65, 67-69, 74, 301, 305-306 Solomon, J., 297 Sommers, M. S., 53,74 Speech, xv, 3-4, 6, 10, 15-20, 23-24, 26, 33-44, 49-51, 75, 79, 82, 98-99, 101-103, 105, 133, 135, 223, 227, 235, 242, 244-246, 269, 277, 303-305 perceptual window, 35, 54, 253 speech rate, 34, 37, 39, 41-45, 51, 98, 102, 246, 303 Spence, J. T., 48 Spence, K. W., 48 Spencer, P. S., 255, 282 Spilich, G., 67, 69, 72, 74 Spinnler, H., 244 Sprott, R., 82, 102, 134 Stabler, E., 218, 219, 223 Stanovich, K., 53,74 Staudacher, P., 168, 171, 182, 200, 201 Steinhauer, K., 254, 277, 280 Stemberger, J. P., 5, 8, 12, 26 Sternberg, S., 251, 282 Sternefeld, W., 200

Stine-Morrow, E. A. L., v, x, xii, xiii, 10, 26, 31, 39, 43, 50-51, 5354, 58-61, 64-65, 67- 68, 70, 73-75, 97-98, 104, 135, 301, 304-306 Storandt, M., 110, 133 Stowe, L. A., 172, 200, 253, 278 Streb, J., 149, 166 Stromswold, K., 203, 224, 285, 290, 297 Sunderland, A., 3, 26 Sutton, S., 265, 281 Svec, W. R., 4,23 Swinney, D., 83, 105, 135, 254, 269, 281, 282, 292, 297 Sykes, R. N., 24, 103 Syntax see Grammar

T Talairach, J., 285, 297 Talland, G. A., 110, 134 Tanenhaus, M., 199, 277 Tang, J., 296 ter Meulen, A. G. B., 223 Terrell, B. Y., 235, 245 Terry, R., 256, 275, 279, 282 Tesser, A., 68,71 Thiersch, C., 178, 200 Thompson, L. W., 279 Thompson, N., 296 Thomson, N., 84, 102, 256 Time-accuracy functions, xv, 137, 140, 141, 142, 161, 163, 166, 167 Tirre, W., 109, 135 Titchener, E. B., 33, 50 Tomoeda, C. K., 227, 232, 244 Tournoux, P., 285, 297 Trabasso, T., 79, 81, 104 Transmission Deficit model, 6, 7, 12, 13, 15, 16, 17 node activation, 5, 7 spelling errors, 17 Trosset, M. W., 227, 232, 244

323

Trovato, D., 3,26 Troyer, A., 144, 145, 146, 167 Tueting, S., 277, 279 Tun, P. A., v, x, xii, 6, 26, 29, 30, 33, 42-43, 45-46, 50-51, 60, 74, 105, 107, 135, 301, 303-305 Tunstall, S., 223 Turner, M., 109, 132, 135 Tyler, L. K., 220, 222-223, 228-229, 233, 235-236, 244-246, 282

UV Ulatowska, H. K., 5, 26, 82, 105, 235,246 Uszkoreit, H., 149, 166 Valencia-Laver, D., 6, 24 Vallar, G., 48, 287, 297 van der Molen, M. W., 53,71 Van Petten, C., 252, 279, 282 Vandal, A. C., 297 Vandeputte, D. D., 20,24,26 Veres, C., 236,245 Verhaeghen, P., 138, 141, 143, 145, 146, 155, 158, 161, 167 Verleger, R., 251, 282 Vesonder, G., 67, 74 Vitkovitch, M., 9, 12, 26 Vorberg, D., 24 Voss, J., 67, 72, 74

W Wade, E., 4,22 Wagner, S., 272, 278 Wagstaff, D., 53, 73 Waldstein, R., 108, 135 Walenski, M., 255, 279 Walker, V. G., 82, 105 Waters, G. S., vi, x, xi, xii, xiii, xv, 33-34, 48, 50-51, 98-99, 101, 105, 107-112, 114, 120, 125, 131-133, 135, 137, 147, 165167, 228, 239, 245-246, 283284, 290, 293, 296, 297, 300, 302, 304, 306-307 Watts, K., 3, 26

Waugh, N.C., 29,50 Wechsler, D., 82, 88, 105, 111, 127 Weeks Jr., P. A., 133 Weinberg, A., 110, 133 Weise, S., 296 Weiss-Doyle, A., 82, 105 Weissenborn, J., 187, 200 Welford, A. T., 165 West, R. L., 18, 27, 53, 74, 83, 146, 167 Westbrook, R. D., 68,71 Weyerts, H., 253, 281 Wheeldon, L. R., 5,9, 12,27 Whitaker, H., 246 Wickens, C. D., 30, 51, 251, 282 Wiemann, J., 3, 22-23, 26 Wieringa, B. M., 254, 255, 279, 280 Wijers, A. A., 251, 272, 282 Wiley, J. G., 24, 103, 141, 165, 245 Williams, E., 213, 224 Williams, J. N., 42, 49, 101 Wind Cowles, H., 279 Wingfield, A., v, x, xii, xiii, 6, 10, 26, 29-33, 36, 39, 42-46, 49-51, 54, 60, 74-75, 83, 98, 105, 135, 269, 282, 301, 303-305 Witte, K., 242, 244 Wood, C. C., 252, 256, 276 Woodworth, R. S., 7, 24, 27 Wooley, J. D., 54, 72 Working memory, xi, xii, xiii, xv, 20, 23, 25, 27, 31-34, 36, 48-51, 59, 65, 71, 74-75, 79, 81-88, 92-99, 101-105, 108-111, 113, 115, 117, 120-122, 126, 130135, 137, 139, 140, 142, 150, 157-158, 162-165, 179-180, 192, 199, 203-205, 223, 227228, 230-232, 236-241, 244245, 254, 263-266, 269-270, 272, 277- 279, 282, 296-297, 300, 302-303, 305, 307 alphabet span, 110, 112, 117, 130131 articulatory loop, 81, 85, 287

324

backward digit span, 82, 88,96, 97, 110, 112, 115, 117, 127, 130-131, 263 capacity, v, xii, xiii, xv, 29-31, 33, 35,49-51, 54, 60, 71,79, 81, 84-86, 93, 96-97, 99, 104-105, 107-111, 115, 117-118, 120, 122, 124, 130, 132-135, 162163, 179, 207, 237, 240, 245246, 249, 264, 265, 267, 269, 271, 273-274, 282, 296, 300, 302, 307 capacity limitations, 99, 207 composite Z scores, 120, 125-130 listening span, 79, 88, 239 L-span, 263, 265-266 missing digit span, 110, 112, 115, 117, 130-131 reading span, 88,96,99, 108-111, 113, 115-117, 120-122, 125127, 130-132, 135, 240, 264, 302 running item span, 110, 112, 117, 130, 131 word span, 32, 79, 84, 134, 263, 265 Yngve depth, 55, 82 Worsley, K. J., 296, 297 Worthley, J. S., 4, 22 Wulfeck, B., 244

XYZ Yee, P. L., 262, 276 Yngve, V., 55, 82, 85, 105 Yoon, C., 97, 105 Zacharski, R., 235, 244 Zacks,R., 8, 9, 11, 18, 23, 27, 34, 51, 65, 73, 97, 101-102, 105, 258, 278 Zander, E., 253, 281 Zapolli, R., 280 Zavis, D., 6, 24 Zerbst, D., 149, 166 Zurif, E., 83, 86, 105, 108, 135, 269, 282, 292, 297