Advances in Child Development and Behavior, Volume 3

ADVANCES IN CHILD DEVELOPMENT AND BEHAVIOR

VOLUME 3

Contributors to This Volume Robert J. Ellingson Raymond H. Hohle Herbert Kaye Howard H. Kendler Tracy S. Kendler Robert E. Klein Eleanor E. Maccoby Anne D. Pick Herbert L. Pick, Jr. Michael D. Zeiler

ADVANCES IN CHILD DEVELOPMENT AND BEHAVIOR edited by Lewis P. Lipsitt Department of Psychology Brown University Providence, Rhode Island

Charles C. Spiker Institute of Child Behavior and Development State University of Iowa Iowa City, Iowa

VOLUME 3

@

1967

ACADEMIC PRESS New York

London

COPYRIGHT 0 1967 BY ACADEMICPRESS INC. ALL RIGHTS RESERVED. NO PART OF THIS BOOK MAY BE REPRODUCED IN ANY FORM. BY PHOTOSTAT, MICROFILM, OR ANY OTHER MEANS, WITHOUT WRITTEN PERMISSION FROM THE PUBLISHERS.

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List of Contributors Numbers in parentheses indicate the pages on which the authors' contributions begin.

ROBERT J. ELLINGSON, Nebraska Psychiatric Institute, University of Nebraska College of Medicine, Omaha, Nebraska (53) RAYMOND H. HOHLE, Institute of Child Behavior and Development, University of Iowa, Iowa City, Iowa (225) HERBERT KAYE, Department of Psychology, Emory University,A tlanta, Georgia ( I ) HOWARD H. KENDLER, Department of Psychology, University of California, Santa Barbara, California(157) TRACY S. KENDLER, Department of Psychology, University of California, Santa Barbara, California (157) ROBERT E. KLEIN, Institute of Child Development, University of Minnesota, Minneapolis, Minnesota' ( I91) ELEANOR E. MACCOBY, Laboratory of Human Development, Stanford University, Stanford, California (99) ANNE D. PICK, Macalester College, St. Paul, Minnesota2(191) HERBERT L. PICK, JR., Institute of Child Development, University of Minnesota, Minneapolis, Minnesota ( I 91 ) MICHAEL D. ZEILER, Department of Psychology, Wellesley College, Wellesley. Massachusetts' (125)

Present address: Istituto de Nutricion de Centro American y Panama, Apartado Postal 1 1-88, Carretera Roosevelt, Ciudad Guatemala, Guatemala. %esent address: Institute of Child Development, University of Minnesota, Minneapolis. Minnesota.

I

'Present address: Institute of Child Behavior and Development, University of Iowa, Iowa City, Iowa.

V

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Preface In recent years, the field of child development and behavior has experienced enormous growth in the number of research and theoretical publications. Use of original sources by scientists and students in maintaining scholarly knowledge both within and outside their areas of specialization has become a most formidable task. The serial publication of Advances in Child Development and Behavior is intended to provide scholarly reference articles in the field and to serve two other purposes. On the one hand, it is hoped that teachers, research workers, and students will find these critical syntheses useful in the endless task of keeping abreast of growing knowledge in areas peripheral to their primary focus of interest. There is an indisputable need for technical, documented reviews which will facilitate this task by reducing the frequency with which original papers must be consulted, particularly in such secondary areas. On the other hand, the editors are also convinced that research in child development has progressed to the point that such integrative and critical papers will be of considerable usefulness to researchers in problem areas with which they are primarily concerned. No attempt is made to organize each volume around a particular topic or theme. Manuscripts are solicited from investigators conducting programmatic research on problems of current interest. The editors often encourage the preparation of critical syntheses dealing intensively with topics of relatively narrow scope but of potentially considerable interest to the scientific community. Although appearance in the volumes is ordinarily by invitation, unsolicited manuscripts will be welcomed for review if submitted first in outline form. We wish to acknowledge with gratitude the help of Joan Cantor, Rachel Keen Clifton, William J. Meyers, and Einar R. Siqueland, who assisted in the critical reading of manuscripts for this volume. We wish to thank Eunice Mabray, who has helped in the collating of materials and indexing. Appreciation is also expressed to our home institutions, Brown University and The University of Iowa, which generously provided time and facilities to produce these volumes. September, 1967

LEWISP. LIPSITT CHARLESC. SPIKER

vii

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Contents

L ~ s OF r CONTRIBUTORS ............................. PREFACE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CONTENTS OF P ~ ~ v r o VOLWS us

. . . . . . . . . . .

Infant Sucking Behavior and Its Modification

HERBERT KAYE

The Study of Brain ElectricalActivity in Infants ROBERT

..

2 6 17 49 50

53

..

61 81

90 91

ELEANOR E. MACCOBY

I. Statement of the Research Problem ................ I1. Age Trends in Selective Listening . . . . . . . . . . . . . . . . . I11. The Effects of Preparatory Set . . . . . . . . . . . . . . . . . . . . . IV. Individual Differences . . . . . . . . . . . . . . . . . . . . . . . . . V . Implications for the Development of Listening Skills in Childhood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.. ..

99 102 108 120

122 124

MICHAEL D . ZEILER

I . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I1. Definitions and Terminology . . . . . . . . . . . . . . . . . . . . . . ...................... 111. The Two-Stimulus Problem IV. The Intermediate-Size Problem . . . . . . . . . . . . . . . . . . . . . V . Choice Gradients for Individual Subjects . . . . . . . . . . . . . . VI The Determinants of Choice . . . . . . . . . . . . . . . . . . . . . . VII. Concluding Comments . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

..

J . ELLINGSON

I. Introduction; Methodology . . . . . . . . . . . . . . . . . . . . . . . I1. EEG Development in Infancy . . . . . . . . . . . . . . . . . . . . . I11. Brain Electrical Responses in Infancy . . . . . . . . . . . . . . . . IV. Conclusion .............................. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Selective Auditory Attention in Children

v vii xi

I . General Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . I1 . QuantitativeDescription ofthe Sucking Response . . . . . . . . . . I11. Experimental Procedures for Modifying The SuckingResponse . . . . IV. Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Stimulus Definition and Choice

.

126 126 128

..

132 141 149

155 155

CONTENTS Experimental Analysis of Inferential Behavior in Children

TRACY S. KENDLER AND HOWARD H . KENDLER

I . Theoretical Background . . . . . . . . . . . . . . . . . . . . . . . . I1. Initial Research on Inferential Behavior of Children . . . . . . . . I11. Development of Inferential Behavior in Children . . . . . . . . . . N . Infrahuman Reasoning . . . . . . . . . . . . . . . . . . . . . . . . . V . Influence of Experimental Variables on Inferential Behavior of Children . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VI. Pooled Developmental and Experimental Results . . . . . . . . . . VII . Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VIII. Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.. ..

157 160 166 170 175

..

183 186 189 189

HERBERT L . PICK. JR., ANNE D . PICK. AND ROBERT E. KLEIN

Perceptual Integration in Children

I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I1. Experimenter ComparisonofSenseModality Functioning ..... I11. Conflict of Sensory Input . . . . . . . . . . . . . . . . . . . . . . . . IV. Intermodal Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . V . Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

..

192 195 209 214 218 220

Component Process Latencies in Reaction Times of Children and Adults

RAYMOND H . HOHLE

I. Methods and Interpretations in Studies of Reaction Time I1. A Proposed Distribution Function for RTs . . . . . . I11. Studies of the Distribution Parameters . . . . . . . . N . Summary and Concluding Remarks . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . .

........ ......... .........

......... .......

225 235 242 257 259

AUTHORINDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

262

SUBJECr INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

269

X

CONTENTS OF PREVIOUS VOLUMES

Volume 1 Responses of Infants and Children to Complex and Novel Stimulation Gordon N. Cantor Word Associations and Children’s Verbal Behavior David S. Palermo Change in the Stature and Body Weight of North American Boys during the Last 80 Years Howard V. Meredith Discrimination Learning Set in Children Hayne W. Reese Learning in the First Year of Life Lewis P. Lipsitt Some Methodological Contributions from a Functional Analysis of Child Development Sidney W.BijouandDonaldM. Baer The Hypothesis of Stimulus Interaction and an Explanation of Stimulus Compounding Charles C. Spiker The Development of “Overconstancy” in Space Perception Joachim F. Wohlwill Miniature Experiments in the Discrimination Learning of Retardates Betty J. House and David Zearnan A U T H O R INDEX-SUBJECT

INDEX

Volume 2 The Paired-Associates Method in the Study of Conflict A Fred Castaneda Transfer of Stimulus Pretraining in Motor Paired-Associate and Discrimination Learning Tasks Joan H. Cantor

xi

The Role of the Distance Receptors in the Development of Social Responsiveness Richard H. Walters and Ross D. Parke Social Reinforcement of Children’s Behavior Harold W. Stevenson Delayed Reinforcement Effects Glenn Terrell A Developmental Approach to Learning and Cognition Eugene S. Gollin Evidence for a Hierarchical Arrangement of Learning Processes Sheldon H. White Selected Anatomic Variables Analyzed for Interage Relationships of the Size-Size, Size-Gain, and Gain-Gain Varieties Howard V. Meredith AUTHOR INDEXSUBJECT INDEX

xii

ADVANCES IN CHILD DEVELOPMENT AND BEHAVIOR

VOLUME 3

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INFANT S U C K I N G B E H A V I O R A N D ITS MODIFICATION'

Herbert Kaye EMORY UNIVERSITY

I. GENERAL INTRODUCTION

....................... 2 ... 6

11. QUANTITATIVE DESCRIPTION OF THE SUCKING RESPONSE A. THE PROCESS OF SUCKING IN THE NEWBORN INFANT

... 6

B. SUCKING PRESSURE . . . . . . . . . . . . . . . . . . . . . . . . 7 . . . . . . . . . . . . . . . . . . . . . . . C. SUCKING FREQUENCY 9 D. THE DEFINITION OF A SUCK AND A BURST OF SUCKS . . . 15 E. SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 111. EXPERIMENTAL PROCEDURES FOR MODIFYING THE SUCKING

................................ RESPONSE A. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . B. SUCKING DEPRIVATION . . . . . . . . . . . . . . . . . . . . . . C. FOOD DEPRIVATION AND STOMACH LOADING . . . . . . .............................. D. AROUSAL E. SUDDEN ONSET OF AN EXTERNAL STIMULUS . . . . . . . F. CONDITIONING . . . . . . . . . . . . . . . . . . . . . . . . . . . G. PATHOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . .

IV.

17 17 18 . . 20 25 . . 28 35 47 SUMMARY AND CONCLUSIONS . . . . . . . . . . . . . . . . . . . 49 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 '

'

I Studies of human infants which are presented for the first time in this manuscript were conducted under United States Public Health Service Grant Number NB 04268, to Dr. L. P. Lipsitt, while the writer was at Brown University. The author wishes to thank Dr. Lipsitt for his encouragement and support over a 6-year period. The work with infant monkeys was made possible in part by U.S.P.H.S. Grant Number MH 07136 to Dr. A. M. Schrier. The suggestions of Dr. Joan Cantor and Dr. Einar Siqueland also helped greatly in thepreparation of the final version. Dr. Siqueland also contributed ideas for the methodology used in the monkey studies.

1

Herbert Kaye

I. General Introduction In recent years there has been a renewed effort toward analyzing the ontogeny of learning in very young organisms of many species (Stanley, Cornwell, Poggiani, & Trattner, 1963;Zimmermann & Torrey, 1965: Lipsitt & Kaye, 1964). In light of the current data (Lipsitt, 1964; Kaye, 1966a; Siqueland & Lipsitt, 1966), it appears most parsimonious to approach learning in the human newborn, at least in the early stages of study, by utilizing paradigms similar to those employed in the study of mature humans and nonhuman animals. Although there are many subdivisions of design employed to study the learning process, two general models, the respondent and operant, have been considered adequate for the description of simple changes in behavior that occur with practice. A minimal commitment to these paradigms allows the researcher to deal empirically with a continuous series of interactions between the behaving organism and its environmental feedback by providing a terminology for dissecting a nonstatic (dynamic) situation. A recent review of learning in the first year of life (Lipsitt, 1964) has indicated that an understanding of these mechanisms during infancy is critical to the construction of a theory of behavioral development. Such an approach provides structure for many types of studies within a crosssection of time, and allows for developmental continuity. In addition to providing a conceptual framework for studying response acquisition and some classes of behavioral change, the respondent and operant learning models may also provide tools for assessing the psychophysical properties of the newborn. Recent studies with lower animals have demonstrated the effectiveness of these methods for analyzing the sensory abilities of nonverbal organisms (Blough, 1966). Although learning procedures have not as yet been employed in psychophysical studies of the human newborn, a number of other types of experimental procedures have focused on these problem areas. Some researchers have used the differential magnitudes and patterns of reflexive neural and motor responses to indicate the operational range of the infant’s sensory apparatus. For example, Zetterstrom (195l), and Barnett, Lodge, and Armington (1969, utilized the electroretinogram pattern and differential amplitudes of the ERG beta wave to explore the newborn’s response to photopic (color) stimulation; Bartoshuk (1964), and Steinschneider, Lipton, and Richmond (1966) studied differential heart rate acceleration to tones differing in amplitude; and Haynes et al. (1969, examined lens accommodation for targets varying in their distance from the infant’s eye. Other researchers have used habituation procedures which allowed comparisons

2

Infant Sucking Behavior and Its Modification

to be made between stimuli on the basis of their changing patterns of response elicitation with successive presentations. For example, Engen. Lipsitt, and Kaye (1963) used changes in the occurrence of breathing disruptions to examine the qualities of the olfactory response of the infant to different odors; Leventhal and Lipsitt (1964) used habituation of the startle response to tone stimuli to explore auditory localization and frequency discrimination in the newborn; and Bronshtein, Antonova, Kemenetskaya, Luppova, and Syrova (1958) used changes in the suppression of sucking to explore many sensory modalities. Researchers interested in problems of the newborn’s visual abilities have used various procedures which yield fixation times on parts or all of a visual display. For example, Salapatek and Kessen ( 1966) studied the newborn’s differential fixation patterns when facing a triangular line figure; and Fantz (1961), and Ames (1965) have recorded fixation times to patterns presented in paired comparisons or as successive stimuli. Although these investigators have provided a basis for specifying dimensional boundaries for certain sensory modalities, it may be argued that two important problems related to the psychophysical properties of the newborn infant require further converging operations which are “learning” based. The first problem concerns the nature of the response. It is possible that two stimuli within a given continuum could produce differential physiological or gross motor responses and not be able to be used as discriminative stimuli in an operant or respondent learning situation. Similarly, lack of stimulus differentation on the basis of some elicited response does not eliminate the possibility that these stimuli can be used as discriminative cues in, for example, a goal-seeking situation. The potential usefulness of a stimulus as a discriminative or conditional cue is an empirical question which can only be resolved through its use in that capacity. The second problem concerns the description of the effective stimulus dimension. A stimulus can be described by a series ofterms which denote its relative position on several continua. For example, a visual stimulus is physically described in terms of luminance, wavelength, and complexity, and may also include contour as a possible parameter. Since two or more of these parameters are always present in any visual stimulus, and the relationship of the physical dimensions described above to the psychological dimensions of brightness, hue, saturation, and form are not 1 : 1, procedures must be found which will help to partial out the contribution of each dimension of a complex eliciting stimulus. Procedures which have been found useful for this type of study are the transfer paradigms (see Shepp & Turrisi, 1966). In these, the S is shifted from a reinforcement seeking problem having multiple cues for solution, to one or more other problems in which the initially interrelated cues have been separated.

3

Herbert Kaye

However, before learning procedures can be utilized in the complex discrimination and transfer designs necessary to examine the above psychophysical questions in the newborn, it must be determined whether the basic qualities of the learned response can be predictably produced in this immature organism. Lipsitt ( 1964) has recently documented the progress made in this direction and has indicated that many gaps still exist in our understanding of the basic learning mechanisms in the newborn. Learning studies in infants have often been impeded by difficulties in defining the dependent variable in the experimental situation. The newborn human is both nonverbal and motorically immature, and his limited behavioral repertoire has given the psychologist little to work with in standard experimental manipulative designs. In addition to the small number of interdependent responses, there is the added problem of an extremely variable state of wakefulness (Brown, 1964; Bridger, Birns, & Blank, 1965). At the quiescent end of the continuum, this may mean suppression of almost all responding (as in sleep), and at the active end, movements accompanying crying may completely “inundate” the behavior being studied. Several attempts by Lipsitt and his co-workers to utilize such movements as foot withdrawal and the startle response as the dependent variable (reviewed in Lipsitt, 1964) have suffered because the low baseline rate, against which changes were to be measured, dictated that the infant be quiescent. Quite often the infant was (or appeared to be) asleep. This was apparently not the “ideal” state for conditioning. Recent attention has turned to the sucking response as a possible dependent variable in conditioning experiments. The sucking response has many positive attributes which recommend it as a dependent variable in studies of behavior modification: (1) It appears to be one of the few well-defined responses in the infant’s repertoire. (2) It has a generic definition in terms of millimeters of mercury (mm of Hg) negative pressure, a measure which provides an accurate representation of the organismic system producing it. (3) It is easily measured, either digitally (Levin & Kaye, 1964) or analogically (Kron, Stein, & Goddard, 1963; Sameroff, 1965), and it provides numerous primary measures, such as frequency, amplitude, burst-length, interresponse, and interburst intervals, and several second order measures, such as responses per burst, percentage change in rate with respect to baseline, and interresponse times per opportunity. (4) It may be used as a dependent variable over a wide range of activity states during which the infant is most attentive, and may even be of value in stabilizing the organism within these intermediate states (Rovee & Levin, 1966).

4

Infant Sucking Behavior and Its Modification

It would seem reasonable, in light of these qualities, to attempt to gain stimulus control over some aspects of the sucking behavior. By carefully choosing the infant population on the basis of number of previous feedings and perhaps parity variables, a more homogeneous sample can be obtained for study. The use of standard control groups is also critical. Historically, researchers on the newborn have considered the sucking response immutable. Feldman (1920) has pointed out that the physiological basis of the sucking response is potentially functional by the third month of fetal existence. The neural foundation for feeding behavior is apparently laid well in advance of its actual use. Herrick (1928) has stated “The mechanisms involved in these processes(food taking) are inborn and require no practice for their perfect performance. They are innate, invariable, and essentially similar in all members of a race or species.” Preyer (1901) adds further: “Sucking belongs to the earliest coordinated movements of man; it is associated directly with swallowing, and has been repeatedly perceived even before the child was fully born.” While neonatal sucking and the consummatory response are undoubtedly unconditioned (‘innate speciesspecific’) responses, observations (e.g., Piaget, 1952. Part I) have indicated that these behaviors undergo changes and vary from one infant to another with respect to certain measurable characteristics. It has been determined that these changes take place as a function of both immediate factors in the nursing situation and pretest experience.

McKee and Honzik (1962) have recently examined the broad clinical issues revolving around the phenotypic qualities of sucking and their relationship to the nature-nurture issue. They also explored the relationship of the sucking response to concepts of orality and the intervening variable “pleasure.” Their article, like Chapter 9 in Peiper’s “Cerebral function in infancy and childhood” (1963), is rich in historical commentary on the importance of the sucking behavior of the infant to initial health and subsequent normal development. The current review has been written to describe the usefulness of the sucking response as the dependent variable in experimental designs directed at examining the learning and sensory capacities of the newborn. For the most part, it concentrates on the human newborn, mentioning studies with lower animals when these are of value in understanding the human data, The general approach of the review is toward the description of functional relationships derived from experimentally controlled observations. The material is divided into two segments: first, the description of the response itself, with emphasis on the quantitative aspects of sucking prior to direct experimental manipulation; second, the description of experimental procedures employed to modify the response.

5

Herbert Kaye

11. Quantitative Description of the Sucking Response A. THE PROCESS OF SUCKING IN THE NEWBORN INFANT Throughout the past century there has been intermittent controversy over the mechanics by which sucking is carried out in the young infant. According to Jensen (l932), Auerback concluded after careful observations that there were two types of sucking: first, inspiratory suction, which was chiefly found in adults and consisted of a process identical to breathing in thtough the mouth; and second, suction as a result of enlarging the mouth cavity through lowering the jaw, while not allowing air to enter from the naso-pharyngeal cavity. The latter process decreases the pressure in the mouth, and, therefore, substances are pushed in by atmospheric pressure. Auerbach felt that the second type was present until about 3 years of age, at which time adult suction took over. Aurbach’s statement that the tongue did not play a very important role in sucking was opposed by Basch and Pfaundler (see Peiper, 1963;Jensen, 1932),who regarded changes in tongue pressure as important in the “expression” of milk from the nipple. Kashara (1916) distinguished four features of pressure change during the single nutritive suck. Although he did not enter the controversy concerning the importance of tongue movement, his schema seemed to indicate that pressure changes were critical. Recently Ardran, Kemp, and Lind (1958a,b) utilized cineradiographic techniques to obtain pictures of the response throughout successive stages of a single sucking cycle. Their data supposedly support the contention that the tongue plays an important role in at least two phases of the single suck. As described by Ardran and Kemp (1958): Emptying of the teat is associated with elevation of the tongue to the palate from before backwards, and simultaneously there is lowering forward movement of the back of the tongue, thus continuing to create suction; it is the latter movement which makes the cavity in which the milk accumulates prior to swallowing.

The photographs shown by the authors in support of the contention do not, however, appear conclusive. Since negative pressure exists at the nipple lumen, the stripping action of the tongue may simply open the lumen allowing milk to be forced by pressure differences into the back of the mouth cavity. Colley and Creamer (1958) utilized a different procedure to arrive at the conclusion that negative pressure is the critical factor in infant sucking. They measured negative pressure both within the nipple and at various distances from the nipple lumen. They found that experimentally produced changes in the flow rate of milk produced changes in the infant’s sucking

6

Infant Sucking Behavior and Its Modification

pressure at the nipple tip and along the side of the nipple but the pressure within the nipple remained constant. The sensitivity of the pressure to changes in flow rate supported their hypothesis that pressure played the major role in sucking. Differences in age, and therefore amount of sucking experience, however, may account for the differences between the findings of Colley and Creamer, and those of Ardran, Kemp, and Lind. In the former studies, the infants were from 5 to 35 weeks old; and in the latter, the infants were newborns. A study by Sameroff, to be reported below, has shown that the mechanics of sucking may be a function of the feeding contingencies. B. SUCKING PRESSURE Variable estimates have been given of the amount of negative pressure exerted by the young infant during sucking. Several factors contribute to these estimates. Halverson’s ( 1938) table of pressure estimates from earlier studies is reproduced below with all pressures converted to millimeters of mercury.

Investigator

Date

Pressure

Herz Basch F‘fauodler Creamer Barth

1865 1893 1899 1900 1914

3-14 mm Hg 3-10 mm Hg

7-52 mm Hg 43-104 m m Hg

&I50

mm Hg

The measurements vary markedly in both their absolute levels and in their ranges. B a h t (1948a,b) reports that individual sucks range from 3 to 11 mm Hg, but that the child may build up pressures of 150 mm Hg in the early stages of infancy, and as much as 590 mm Hg in later stages. Qualitative analysis of the early data by Halverson indicated that differences were partly determined by the type of feeding situation (bottle versus breast), the size of the nipple lumen (large versus small), the degree of hunger, and the age and size of the infant. Halverson’s own work showed that babies suck hardest at the breast, next at the easy (large-holed) nipple, next at the hard (small-holed)nipple, and with least pressure to a nonutritive nipple. Although the data are assessed from a sample with an age range of 1 to 43 weeks, they agree generally with Jensen’s (1932) observations on a younger sample. However, Colley and Creamer (1958) report that there

7

Herbert Kaye

were no age and weight effects in their sample (5 to 30 weeks) and, furthermore, that the estimated range of averages for infants sucking on the lowflow nipple was between 88 and 170 mm Hg, while that for the medium-flow nipple was between 44 and 118 mm Hg. This difference is an inversion in the order described by Halverson. One of the major problems with the estimates of the earlier observers is that they often did not separate the background pressure from the pressure exerted by the individual suck. Colley and Creamer( 1958)estimate the background pressure to be between I5 and 50 mm Hg. ThesCpressures seem to increase as a function of swallowing some of the air in the mouth along with the liquid. Kashara (1916) first reported that in sucking nonnutritively (on a pacifier) only a slight amount of pressure was built up, with the system stabilizing as air passed back and forth from mouth to nipple. This was corroborated and illustrated by Jensen (1932). Kron et al. utilized a closed pressure system connected to an air pressure transducer for the measurement of sucking. They examined sucking in infants during the first 5 days of life while feeding a 5% corn syrup solution through the same nipple from which they recorded their pressures. They found that the pressure ranged up to 300 mm Hg with averages between 30 and 60 mm Hg (average per minute) for forty subjects over a9-minute test period. Although there was an apparent increase in amount of pressure generated as a function of age (from 24 to about 96 hours of age), this trend was not significant. It should be mentioned that the individual sucking responses shown in their polygraph tracings are quite similar in form to those idealized by Kashara (1916). Sameroff (1965) recently designed equipment similar to that of Kron et al. (1963), but modified it so that tongue pressure and suction pressure could be recorded. The pressure signals were amplified and independently operated pumps which allowed liquids to be fed through the nipple. He recorded sucking pressures (Sameroff, 1966) between 50 and 200 mm Hg, with a mean of 104 mm Hg. The range of tongue pressure (called “expression” pressure) was between 15 and 80 mm Hg, with a mean of 48 mm Hg. It is difficult with Sameroff s data to be sure that “expression” pressure was not produced by the gums or lips rather than the tongue. Neither Kron et al. nor Sameroff mention background pressure, and in the tracings of an individual record shown by Kron et al., this characteristic is missing. It is difficult to know whether the background pressure noted by other researchers was absent because of their procedure, or if their recording systems were designed to filter out slower changes in pressure. It is quite apparent from the limited nature of the work so far completed that further basic parametric data should be collected on sucking pressures in groups varying with respect to such factors as size of nipple lumen (or rate of liquid flow), and shape and flexibility of the nipple. 8

Infant Sucking Behavior and Its Modification

C. SUCKING FREQUENCY As with the pressure variable, a few estimates of suckingrate are available from early studies. However, an immediate problem of interpretation arises from the fact that some experimenters determined rate on the basis of time actually sucking, while others took rates on the basis of total time that the nipple was in the mouth, that is, on the basis ofsuckingopportunitytime.The differences in estimates based on these two measurements are due to the fact that sucking occurs in “bursts” and pauses. Therefore, estimates made from periods actually spent sucking will be higher than those made from fixed periods of time during which both sucking and the pauses are included. Rates for the four conditions tested by Halverson are shown below. It should be noted that sucking rates and sucking amplitudes for these four conditions are inversely related.

Air Difficult nipple Easy nipple Breast

84-208 76-140 44-132 84-108

sucks per minute sucks per minute sucks per minute sucks per minute

Although it was not explicitly stated, these rates apparently were based on time actually sucking. Again it should be pointed out that Halverson’s sample ranges in age from 1 to 43 weeks. These rates are all given for infants with unspecified amounts of food deprivation. Peiper (1963) reports nutritive sucking rates of about 40to 90responses per minute in hungry babies. He states that initial rates are fairly continuous, but that as the infant is satiated, his rate falls and the number of pauses increases. B a h t (1948a,b) made some important distinctions in his analysis of rate. His data were collected during feeding, and sucking rates were analyzed in the unit of sucks per 10 seconds. An important general finding in his work was that sucking rates for actual sucking periods did not appreciably change over long periods of time, but that the interburst intervals increased, He distinguished four different types of sucking rate found in many subjects’ records. These are: N,, or basic frequency; R, or restart frequency; N?, or secondary frequency (occasional N, replacement); and Q , or quiver frequency. The N, frequency is the aversge rate found in the majority of an individual infant’s record. B a h t finds N, to range between 8 and 20 per 10 seconds. The rate for an individual infant is quite constant within and between sessions although there is a slow developmental drift toward higher frequencies. Tne “restart frequency” reflects the fact that when a pause has taken

9

Herbert Kaye

place, the first I or 2 seconds of the next burst of responses involve a much higher rate than is found throughout the remainder of the burst. These R frequencies range from 12 to 35 responses per 10 seconds. The N, frequency, found in a majority of infants (75% of Baht’s full term sample), is similar to the R frequency, or slightly lower, and may persist for 3 or 4 seconds at the beginning of a record. It also appears from time to time in the record as an alternative to the N, frequency. It is found most often in children who are sucking on a dry bottle after having finished the formula, sometimes during the last few minutes of finishing the formula. and occasionally in agitated children. B a h t estimates the ratio of N, : N, as about 3 : 2. The so-called Q , or quiver frequencies, are found by B a h t in about 53% of his sample. These are very low amplitude, high frequency responses. The response range, for all but two cases, was between 40 and 100 per 10 seconds. The two exceptions were in the range of 190 per 10 seconds. These extraordinarily high frequencies were found to occur usually before or after a burst of responses, and occasionally to be superimposed on the first few sucking responses of a burst. The Q frequency, like those ofN,, N,, and R,, is consistent within individuals. No analysis has yet been made of the mechanism behind these high rates, but it is most likely related to tongue quivering. Licking rates in lower animals, such as the rat, occur at similar frequencies. In a recent study by Kaye (1966b), records were examined for Q frequencies. These were found to occur in about 80% of the records, a figure slightly greater than found by B a h t . The pressures recorded for individual parts of these “microbursts” were between about 1 and 5 mm Hg. Similar to Baht’s findings, the Q frequencies occurred primarily in the few seconds before or after a burst of sucks, but were occasionally found superimposed on the sucking burst itself. Rates ranged from 6 to 1 1 responses per second. Rates, as well as position with respect to a burst, were found to be quite consistent within infants. Small differences between the findings of Kaye and those of B a h t may reflect the fact that the Kaye study was carried out with nonnutritive sucking. An actual tracing taken by Kaye of the Q frequency phenomenon is shown in Fig. I .

2 seconds

Fig. 1. Newborn sucking record showing the “Q”f r e q u e v before and a/ter a short burst of responses.

10

Infant Sucking Behavior and Its Modification

Kron et al. also measured sucking rates over the first few days of life for children 4 1/2 hours food deprived. Their test period was 9 minutes, during which time the infants could suck for 5% corn syrup mixture. For infantsin their second day of life (24 to 36 hours of age), rates were between Sand 30 responses per minute. Rates for the same children tested over the following 3 days averaged between 20 and 35 responses per minute. The lower limit for infants on the first day may reflect the general depression in responsiveness found by several researchers (Graham, Matarazzo, & Caldwell. 1956: Liositt & Levy, 1959; Kaye & Lipsitt. 1964). Increasesover days may indicate recovery from this depression or learning. These alternatives will be explored below. The sucking-rate studies based on sucking opportunity (with the exception of Kaye, 1966b) were all carried out under conditions of nutritive sucking, that is, sucking for liquid. In view of Halverson’s data, one would expect that rates while sucking for liquid would be lower than rates while sucking for air, but Halverson’s data did not take pauses into account. There have been no reports comparing sucking for liquids and nonnutritive sucking within the same recording system, although both Sameroff (1965) and Kron et al. (l963), have apparatus capable of pursuing this problem. Levin and Kaye (1964,1966)have conducted two experiments designed to explore some aspects of rate change as a function of time spent nonnutritively sucking. Their data measurements were computed on the basis of sucking opportunities, with pauses included. They used a nipple-covered microswitch device which gave digital records. Their procedure in the first study consisted of presenting the nipple for three 3-minute periods, each separated by 3 minutes of no nipple. They used forty-eight infants who were between 5 and 95 minutes food deprived, rating them for activity on a four-point, four-criterion scale. The test period consisted of three 3-minute sucking opportunities, separated by two 3-minute rest periods. Rates were found to range from only a few responses in the sleeping, recently fed infants, to over 600 for the highest responder over the 9 minute of sucking. Almost all the intermediate rates were represented. Their findings generally indicated that rate is positively correlated with food deprivation and arousa;, and that statements of rate without including information on these variables are relatively useless. (Deprivation, arousal, and several other factors will be discussed in the following section.) It was further noted that although individual subjects showed small minute-to-minute fluctuations, the partwhole ran k-order correlations between cumulative rates within the first minute of the first 3-minute segment of sucking and totals for either the first 3 minutes or for all 9 minutes quickly asymptoted at about .90(see Fig. 2). These correlations indicated that subject ranks were stable over at least short periods of time, but they did not describe possible changes taking

Herbert Kaye

.70-

/

.60-

Fig. 2. Part-whole correlation relating initial rate of nonnutritive sucking to total number of *esponsesfor Period I (broken line) and for periods I through IIl(solid line) (from Levin and Kaye. 1964).

place in absolute rates. Since there was a consistent intersubject ranking beginning with minute 1, subjects were divided into three groups on the basis of their first minute scores. The mean suckingrates are shown in Fig. 3. Both the low and medium rate infants show an essentially constant sucking rate within blocks of 3 minutes. However, the high responders (in this

o - - - c \ c . I

I

I

I

,

,

,

,

,

Infant Sucking Behavior and Its Modijication

sample, infants with rates of 28 or more in the first minute) show their highest response levels during the first minute of each 3-minute segment, with decreases in rate over the subsequent 2 minutes. To examine the factors which might be producing this “rest-recovery” and decrement, Levin and Kaye conducted a second study in which four groups of infants were examined who had sucking rates of 28 or more responses in the first minute. The treatments consisted of first giving 5 consecutive minutes of sucking opportunities to all groups. Following this, Group I received a second 5 minutes, continuous with the first. For Group I1 (the “touch” group), the nipple was withdrawn and replaced for 5 minutes as soon as the infant would accept it. Groups I11 and IV were given 1 and 5 minutes of rest, respectively, between the two 5-minute sucking opportunities. These groupings allowed the authors to examine whether the major factor contributing to the restrecovery was the stimulation attendant on the introduction of the nipple into the mouth, or whether, recovery was primarily a function of imposed rest. If the latter was the case, the authors could begin to examine the relationships of recovery to duration of rest with the data from the 1- and 5-minute groups. One factor which became apparent as the study progressed was that the arbitrary cut-off point for “high-responders” at 28 responses in the first minute was not adequate. Infants responding at less than 45 responses during the first minute showed subsequent increases in rate, whereas those above 45 responses showed decreases. The breakdown of the first 5-minute period is shown in Fig. 4 for groups separated on the basis of minute 1 scores. The sample for final analysis of the rest-recovery effect was therefore limited to infants with minute 1 rates above45. Figure 5 shows these subjects separated into four treatment groups. Group I and 11, the continuous and “touch” groups, showed little change from minute 5 to minute 6 . The two rest groups, however, gave minute 6 rates which were statistically comparable to their first-minute rates. This supported the conclusion that rest-recovery was a function of the interval between sucking opportunities and nut simply due to the stimulation produced by placing the nipple in the infant’s mouth. Furthermore, the lack of statistical differences between Groups 111 and IV indicated that recovery was apparently complete within the first minute of rest. The authors state that the role of tactile factors has not been independently tested. Anesthetization of the oral cavity in lower forms of mammals may help to complete the analysis of variables contributing to this effect. Very little can be said about the basic characteristics of the sucking burst, . . or what changes take place in it as a function of time. Asdescribed above, B a h t (1948b) has stated that the number of responses per burst in the feeding situation remains constant, but the interval between bursts lengthens. Peiper (1963, p. 420), however, states that sucking is continuous at the beginning of a session, and only as the baby becomes satiated do

13

Herbert Kaye

\ "9,\ \ '\

'\

2

I

3

4

5

Minutes

Fig. 4. Sucking rates over a 5-minute continuous sucking period for infants divided on the basis of minute I rates. The N for Groups I through 7 are 7, 6, 9, 12, 12, 11, and 6. respectively (from Levin and Kaye, 1966).

Minutes 6-10

0-4 *-d

I

2

Continuous Touch I min rest 5min rest

3

4

5 6 7 8 9 1 0 Minutes

Fig. 5. Eflects of four direrent treatments on decrement and recovery in sucking during minutes 1-5 andminutes 6-10 (from Levin and Kaye. 1966).

pauses begin to appear. Although not contradictory, the two statements emphasize different phases of the response over time. In part, the problem is specifying the interval during which burst length is to be examined. As 14

Infant Sucking Behavior and Its Modification

with direct measures of frequency per unit time, there have been no parametric studies of burst length comparing nutritive and nonnutritive sucking conditions. It has been unsystematically observed by the author, however, that the initial burst of nutritive sucking is consistently longer than that of nonnutritive sucking. Utilizing an inclusion criterion of 40 or more responses in the first minute, Kaye analyzed the data of 125 subjects given a 4-minute sucking opportunity on a pacifier. Looking only at the first two bursts in this period, 91 subjects gave more sucks during the first than during the second, the means for all subjects on the first and second bursts being 34.9 and 22.2 sucks, respectively. Of the 94 who had either greater or equal numbers of responses on the first as compared with the second burst, 30 had one or more other bursts during the 4-minute period which were longer than the first. The mean number of bursts for this sample was 4.00 for minute 1, 4.60 bursts for the average minutes 2-3, and 5.05 for minute 4. On the basis of these data, there seems t o be a trend toward an increasing number of bursts per minute over short (4-minute) periods. However, even in this fairly homogeneous sample, there is a great deal of variability. It is difficult to say whether the number of bursts per minute stabilizes after the second minute, as does the number of sucks per minute (Levin & Kaye, 1966), or whether there is a decrease in number. Again it should be cautioned in interpreting these data that they are based only on nonnutritive sucking. Observations made by B a h t and Peiper are on nutritive sucking. The rankorder correlation between number of bursts and number of responses for the 4-minute test period was approximately - .62, supporting the obvious fact that the longer the average burst, the fewer bursts are possible within a limited period of time. D. THE DEFINITION OF A SUCK AND A BURST OF SUCKS The problem of operationally defining both the suck and the burst ofsucks has been postponed until some of the general characteristics of what researchers have called sucking were explored. Four variables are apparently important in describing a suck, and one more is needed in describing a burst of sucks. For the suck these are: (a) over all base to peak amplitude; (b) rate of pressure decrease to peak; (c) rate of pressure recovery to base; and (d)response time, or length of cycle. The added temporal variable of interresponse time is needed in describing a sucking burst. The necessity for critical criteria1 analysis of sucking records has not been recognized because most early experiments were primarily concerned with gross qualitative distinctions. However, in some of the experiments discussed below, it will become apparent that the short-term probe procedures now in use require an exact frequency count, and 15

Herbert Kaye

differences of as little as plus or minus a single suck per burst may be of critical importance. The following criteria (Kaye, 1964) were designed for the description of nonnutritive sucking. It is felt that they may be employed in nutritive sucking as well, with only slight revisions. Before entering into a description of the suck and the burst, certain problems should be discussed. The most critical problem with the general acceptance of the absolute criteria to be described below would arise from small differences in the physical structure of the recording systems. Starting with the nipple, for example, it has been observed by the author that the utilization of a slit rather than a hole of fixed diameter produces a background pressure of increasing amounts. This is because the slit acts as a one-way valve, allowing air to escape from the nipple and transducer system, but not allowing it to return. This is a problem in cases in which the nipple is connected directly to the air transducer or in which the nipple is collapsible and is attached to a membrane which comprises one wall of a fixed-volume air reservoir. The solution to this problem is, as stated above, to have a hole of fixed diameter cut into the sucking stimulus, or to run a polyethylene (or some other rigid material) tube to the end of the nipple. This sort of system allows the air pressure in the transducer system to be equivalent to that in the mouth, but does not solve the problem of background pressure. Variable estimates of background pressure are given by some researchers (Colley & Creamer, 1958), and it can be assumed that in other cases, estimates of the amplitude of the single suck have included background pressure (Baht, 1948a). If one wishes to use amplitude of sucking as the dependent variable, it is undoubtedly the case that the background pressure has to be taken into account. It is reasonable to expect that greater effort will have to be made to produce a change of a given value when working against a large amount of negative pressure, than when working against a small amount. For example, it is presumed that it takes less physical effort to produce a 10-mm Hg change when the background pressure is essentially zero than it does to produce this same amount of change when the system is under the tension of a - 100-mm Hg background pressure. It is not possible at this point to predict what effects these different background pressures would have on other possible dependent variables, such as frequency. It is also difficult to predict how this interaction could be studied experimentally at this time. It is often the case that an intrasubject control is used with a dependent variable such as amplitude or burst length. It might therefore be best to build the pressure recording system so that slow changes in negative pressure are bled off and only the rapid changes associated with the individual sucks are utilized. Although this would artifactually decrease the signal output for any pressure change over time, the correction for the rapidly changing sucking response would be relatively small. 16

Infant Sucking Behavior and Its M o d i j k t i o n

The sucking criterion used by Kaye (1964) consisted of the following: ( a ) amplitude must exceed -7 mm Hg; (b) the change of -7 mm Hg must occur in 0.5 second or less; (c) return from peak negative pressure ( - 7 or

more mm Hg) must be at least 3.5 mm Hg in 1 second; and (d)a total response cycle from base to base (or from base to beginning of next suck) must not exceed 1.5 seconds. It should be stated here that, although these criteria appear quite stringent, they are sufficiently liberal to have required careful screening of no more than 5% of the individual record of any of the 120 subjects on which they were used. The added criterion for the burst can best be stated as follows: any two or more responses (defined as above) having an interresponse time of less than 2 seconds shall be considered a part of the same burst. Interresponse time may be recorded from peak to peak or from the point where the slope of the positive going pressure component becomes zero, to where it turns negative. As with the single suck, recent work has shown that less than 5x of an individual’s record requires careful screening.

E. SUMMARY From the work presented thus far, it is difficult to obtain a complete picture of the normal range of sucking behavior, because several independent variables such as number of previous feedings and time within the feeding cycle have not been explored. The two response measures which have dominated the small amount of research have been amplitude and frequency. This fact is not surprising since these are the most obvious characteristics of the behavior. However, there are many other apparently independent factors, such as burst length and interburst time, which have yet to be given adequate attention in highly controlled experimental settings.

111. Experimental Procedures for

Modifying the Sucking Response A . INTRODUCTION

The fact that the normal newborn infant is capable of engaging in the response called sucking does not, in any way, help to assess the factors controlling its occurrence. When a response system is dealt with operationally, as above, the choice of response measures is somewhat arbitrary and certainly tentative. If the parameters chosen for the description of the response are to be of greatest value, they must be related to controlled 17

Herbert Kaye

operations which produce systematic changes in their values. That is, although the ongoing sucking behavior has been partitioned into components such as frequency and amplitude, it is not known whether the breakdown is relevant to the factors that control sucking. It is possible, for example, that some combined response unit such as pressure per unit time sucking is related to amount of deprivation, and the description of frequency and burst length characteristics of the ongoing behavior would be of little consequence when describing the effects of feeding on sucking. Undoubtedly, certain experiential factors played a role in producing the range of values described in the studies reviewed in the previous section. Such factors were given only passing mention. Within the current conceptualization of the organization of sucking behavior, these factors have been labeled as follows: (a) sucking deprivation; (b) food deprivation; (c) variations in “arousal”; (d) sudden onset of an external stimulus; (e) conditioning; and u> physiological pathology. These factors and their possible interactions will be discussed below.

B. SUCKINGDEPRIVATION In 1934, Levy studied the effects on nonnutritive sucking of limited access to the nipple during feeding. This was a fairly controlled attempt to follow up earlier clinical observations (Levy, 1928) made on the effects of limited sucking in human infants on later thumbsucking. Levy observed that infants who were reduced to half their former amount of sucking spent more time sucking their fingersthan those provided with “normal” sucking opportunity. The differences were not attributable to the amount of food consumed, In the 1934 study, a litter of six pups of a collie bitch were utilized (Levy, 1934). These were divided into three groups of two each: two stayed with the mother; two were fed artificially through a small-holed nipple so that, over the 20 days of the experiment, they spent 1609and 1480minutessucking, respectively; and two were fed through a large-holed nipple, spending 278 and 264 minutes feeding. At the start, the pups weighed approximately the same but the bitch-reared pups showed greater weight gains over the test period. Although the four artificially(bottle) fed pups showed similar weight gains during this time, more food was required to produce these gains in the large-holed group than in the small-holedgroup. Levy used his finger covered with a nipple to test nonnutritive sucking, and examined amount and intensity differences before and after feeding. It was found that both groups of artificially reared pups sucked his finger vigorously just prior to feeding, but only those receiving the large-holed nipple sucked after the feeding. The latter group did this for a good portion of the period between feedings. The 18

Infant Sucking Behavior and Its Modification

data presented lend support to Levy’s contention that pups deprived of nutritive sucking spend more time in nonnutritive sucking. Sucking deprived animals were also more active, which most likely accounts for the weight gain differences and the food supplement necessary to bring about comparable weight gains. An incidental finding was that, when the artificially fed pups were returned to the bitch, there was difficulty both in getting them to feed from the breast when placed at it, and in getting the bitch to hold still for the feeding. Davis, Sears, Miller, and Brodbeck (1948), further pursuing the effects of sucking deprivation, worked with a sample of infants fed from birth by either cup, bottle, or breast. They tested two hypotheses concerned with whether the sucking drive was “inborn” or “acquired.” They hypothesized that if newborns fed by the cup from birth showed a comparatively larger amount of nonnutritive sucking and activity (indicators of tension) when compared to those infants fed by bottle and breast; this would support an “inborn” theory of sucking drive. However, if there were no differences, this would support an “acquired” drive theory; that is, sucking becomes a tension-reducing behavior as a function of its occurrence. They report that no differences were found between their cup-fed and bottle-fed groups. This is taken by them as a disconfirmation of Levy’s findings: in humans, sucking drive is not innate, and sucking deprivation does not lead to increases in nonnutritive sucking rate and vigor. Ross (1951) studied puppies to elucidate some of the factors which might be related to sucking deprivation. Although his final sample consisted of only six pups, the trends were definitely in favor of Levy’s findings. He used newborn pups fed either by the bitch, by an eye dropper, or by bottle. Two measures, sucking to a nipple attached to the experimenter’s finger, and pressure records of nonnutritive sucking, both yielded greater amounts for the dropper-fed and bottle-fed than for the breast-fed pups. It is assumed, although not explicitly stated, that the breast-fed pups were able to suck more than the artificially fed ones. Nutritional equality across the subjects was assumed from their weight gain curves. When the artificially fed pups were again placed with their mother, they showed agradual decrease in nonnutritive sucking rates and pressures. Ross points out that the whole test procedure was applied on pups in the first 2 weeks of life, whereas Levy’s test was carried out over several weeks. Therefore, Levy’s finding that the artificially reared infants would not attach to the bitch is not necessarily contradicted by Ross’ opposite findings. However, Rossdid find that sucking deprivation leads to additional nonnutritive sucking, in support of Levy’s results, and in opposition to those of Davis et al. In his summary, Ross raised the possibility that there are species differences in the role that experience plays in compensatory nonnutritive sucking in the presence of nutritive sucking deprivation. 19

Herbert Kaye

c. FOODDEPRIVATION AND STOMACH LOADING In 1932, Jensen noted some relationships between food deprivation and sucking which he had seen during his extensive testing. He asserted that, in general, the hungrier the baby, the more vigorous its sucking. He went on to say, however, that when sucking disruption is used as the indication of taste and oral tactile discrimination, the moderately satiated baby is a better discriminator than the hungry infant. It is apparent that, within Jensen’s design, hunger can so elevate the occurrence of the sucking response that it overrides the aversive properties of the solution being ingested. “The changes in the sucking curve which occur with satiety” he continues, “show that the infant makes different responses to a full and to an empty stomach, and that food alone is not the complete stimulus for sucking’’ (p. 469). He then lists five aspects of the sucking situation which are indicative of satiety: (1) frequent occurrence of rest periods; (2) decreased amplitude of the sucking response curve; (3) decreased or even released pressure; (4) disorganization of the sucking reponse; and ( 5 ) difficulty in acceptance of the nipple. In a brief review of the literature, James (1957) pointed out that little had been done to examine the fine parametric aspects ofthe relationship between sucking and nutrition. James considered this one of the weak points of both the Levy (1934) and Ross (1951) studies, and he initiated a study of the effects of stomach loading on sucking in pups during the first 25 days of life, using nineteen pups from three litters. The animals were loaded with milk 1 to 3 hours after being separated from the dam. The experiment was begun when the pups were 3 to 4 days of age, and litter mate controls were used. After stomach loading, the pup was returned to its mother and, after variable intervals, testing was begun. Several measurements were obtained, including frequency of sucking, weight gain during the test period, and average time of sucking. These showed no difference between the stomach loaded animals and their controls. In a second experiment, no differences were found in animals who were bottle-fed or dropper-fed in comparison to the bitch-fed pups. His conclusion from the first experiment was that milk intake had little if any effect on sucking. Inhibition of the sucking response, according to James, was related to some form of reflex fatigue. He stated that arousal of the pups led to more sucking, but he did not explore the interaction of arousal and reflex fatigue. (The test of the independence of sucking rate and stomach loading, and of the effective decrease of sucking through reflex fatigue could be tested in pharyngeal-fistulated pups, wherein sucking and swallowing could be explored independently of stomach loading.) In a later study using older pups (30 to 46 days), James and Gilbert (1957) obtained no differences in stomach loaded versus “hungry” animals, sup20

Infant Sucking Behavior and Its Modification

porting his findings with younger animals. His data, therefore, show no relationship between stomach factors and sucking, although they do not directly attack the problem of nutrition and sucking which he set out to explore. Further work with older pups (James, 1959) supported the independence of stomach loading and sucking, when it was found that stomach loading decreases the amount of food consumed by licking and chewing, but would not affect the frequency or intensity of sucking. James’ work poses several methodological questions concerning loading procedures, time elapsing between loading and testing, criteria for sucking, and amount of time spent sucking (see below). These methodological issues make James’ data difficult to interpret. In a series of studies in which the procedures were fully detailed, Stanley and his associates attempted to reexamine the phenomenon reported by James. Satinoff and Stanley (1963) used two matched groups of fifteen pups each. After separation from the dam for from 7+ to 9+ hours, stomach loading procedures were carried out, each experimental animal receiving as much simulated bitch milk as it could hold. The loading took from 5 to 20 minutes, and the authors point out that a temporary inability of the pups to take more milk did not indicate that the stomach had attained its maximum capacity load. The ages used were 1,2,3, 4, 5, and 1 1 days. The test consisted of placing the pup with the bitch for 30 minutes and recording both amount of time spent sucking and weight gain during the test period. Results indicated that the nonloaded pups spent an average of 26 minutes sucking and gained an average of 3.6% of their body weight, while the loaded pups spent an average of only 7 minutes sucking and showed only 0.12 weight gain. The differences were essentially equivalent across age groups, although the younger pups sucked less when loaded. The authors point out several possibly critical differences between their procedure and that of James. First, James loaded with an average of less than half the amount of milk used by Satinoff and Stanley, most likely a function of James’ stopping the feeding when regurgitation occurred. Secondly, James waited variable periods between loading and testing, and Satinoff and Stanley indicated that a pup can be tube fed again as early as 45 minutes after his initial tubing. This was an interval within the range that intervened between tubing and sucking in some of James’ animals. Satinoff and Stanley admit that by increasing the amount of time between separation of the pups from the bitch (73 to 93 hours), they were maximizing the differences. In a follow-up experiment, however, Stanley and Bacon (1963) found the same proportional differences between groups that were separated from the dam only long enough to stomach load. These animals, as would be expected, showed less weight gain and spent less time sucking than the 74 to 9+hour food deprived pups. These studies of pups by Stanley and his associates seem to be strong support for the role of stomach factors in sucking. 21

Herbert Kaye

Most human newborns do not have constant access to food, but are fed at regular or irregular intervals. During the lying-in period they are generally fed on a schedule. Irwin (1930) has shown that feeding is followed by a short period of high activity, a rapid decrease, and then a gradual rise in activity as the next feeding approaches, but little has been done to trace sucking activity during this period. Levin and Kaye (1964) have shown a similar nonmonotonic change in both sucking responses and activity state for several groups sampled individually at times ranging between approximately 10and 90minutes after feeding. Sucking rates and activity ratings for these groups are shown in Fig. 6. Although the groups showed a great deal of overlap, probably as a 400 7

-

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-

r

l

4

O

.

300 T In C In

g 200YI

c?

100 1

0-

il , I

8

,/

65 Minutes since end of feeding perad

38

-0

92

Fig. 6. Sucking rates and observed activity scores during approximately 90 minutesjollowing feeding (jrom Levin and Kaye. 1964).

function of the small differences in the time categories, there was asignificant over-all correlation of + .38 between sucking rates and time since feeding, and + .36 between activity rating and time since feeding. Pilot data collected by the author on seven children, who were probetested for 5 consecutive minutes every 15 minutes at various intervals before and after their morning feeding, yielded sucking rates with respect to the feeding as shown in Fig. 7.There was a large amount of variability in absolute numbers of responses, but the trends of individualsubjects generallyfollowed those of the group. The nonmonotonic shape of the sucking rate curve reflects, once again, a short active period following the feeding. Pratt, Nelson, and Sun (1930) also explored the sucking response in sleeping and awake babies, but they give no information on the time since previous feeding. They do report that sleeping infants show sucking behavior to stimulation about the mouth, and Balint (1948b) and Halverson (1938) also observed that spontaneous sucking movements are seen in sleeping babies. Bridger (1962) gives lower sucking rate figures for infants examined before and after feeding.

22

Infant Sucking Behavior and Its Modification

-60-45-30 -15 0 +15+X)+45+60+75+90+105 Minutes from feeding

Fig. 7. Sucking ratesfor seven

Ss &/ore and afrer ajeeding.

In a recent study, Kaye (1966b) examined the immediate effects of feeding on the suppression of subsequent nonnutritive sucking in human newborns. One hundred and twenty infants between the ages of 47 and 110hours were employed in two 3 x 4 factorial designs to determine the interactions of liquid amount given in prefeeding and the intensity of tones used to arouse the infant. The measure of the arousal effect of the tone was recovery from suppression. Different liquids were used in the two experiments, the first (Exp. I) using distilled water and the second (Exp. 11) using a 5% solution (by volume) of dextrose and water. In Exp. I, three groupsoftwenty infants received either no solution, 10 ml, or 20 ml of water. In Exp. 11, similar groups received either no solution, 20 ml, or 40 ml of dextrose and water. The procedure consisted ofgiving all infants a4-minute nonnutritive sucking period which served as the Baseline; a feeding period during which infants were removed from the stabilimeter and given the amount of liquid appropriate for their group; and finally, 20 consecutive minutes of sucking opportunity called the Test period. In Exp. I, the infants were allowed to suck 90 seconds of the 240-seconds feeding period, the remaining 150 seconds being used to remove the baby from the stabilimeter crib, burp him, and replace him for the Test period. In Exp. 11, the infants were allowed to suck for 210 of the 600-second feeding period. The longer feeding period was necessary in order to give the larger amounts of liquid (40 ml of dextrose solution). Infants within each experimental group were all given the same amount of sucking opportunity during the feeding interval; the no solution infants were given a blank pacifier or empty bottle. The same amount of time, 120 seconds, intervened between the end of actual sucking during the feeding period and the beginning of the test period for both experimental groups. The data were analyzed in terms of ( a ) average absolute rate and (b)the

23

Herbert Kaye

ratio of average Test rate to average Baseline rate. The latter measurement had the advantage of normalizing the population with respect to their Baseline rates. The ratio was expressed in terms of percentage of Baseline. The data for the two experiments are shown in Fig. 8: A represents the

Amount of liquid (in ml)

I

I

Fig. 8. Mean sucking rates over a 20-minute period following differential amounts offeeding. Experiment I = solid line; Experiment I1 = broken line. A: Mean absolute rates based on total number of sucks in 20 minutes B: Mean ratio ojresponses per minute during 4-minute prefeeding baseline (/;om Kaye. 19666).

average absolute rates and B the percentage of baseline for the different amounts of solution. With respect to absolute rates, Fig. 8A shows a negative monotonic relationship between the amount of solution given and the amount of sucking in Exp. 11. This was not the case for Exp. I in which the group receiving the largest amount of water showed the highest rate. A n examination of the baseline rates of all the groups, however, indicated that the 20-ml-water group was significantly higher in rate than the other groups. When the rates were reduced to percentage of baseline, as shown in Fig. 89, all groups came into line forming an over-all monotonic relationship between amount of liquid given and amount of suppression of nonnutritive sucking. Secondary differences between procedures in Exp. I and 11 were examined by comparing the two no-liquid groups and the two 20-ml groups. Lack of statistical differences between the no-solution groups indicated that different amounts of time allowed for ingestion (or sucking) during the feeding period did not have differential effects on subsequent sucking. Moreover. the lack of difference between the 20-ml groups indicated that

24

Infant Sucking Behavior and Its Modification

small differences in caloric value of the solutions given did not have differential suppressive effects. It is noteworthy for future experimental work that as little as 10 mi of liquid produces a suppressive effect during subsequent nonnutritive sucking. A further examination of the data indicated that suppression was almost immediate and remained relatively stable over the 20-minute test period for all groups except the 10-ml group, which started at the same level as the no-liquid group and slowly dropped off in rate over the remainder of the Test period. The data presented by Stanley and his associates with pups, and further supported by Kaye in human infants, strongly suggest that there is an inverse relationship between stomach loading and amount of sucking and, furthermore, the effects of feeding on suppression appear immediate. The data on time since feeding are not so controlled, but tend to support the same contention. Differences in ability of mothers to feed, in stomach capacity, and in rate of digestion by infants, make it difficult to decrease the variability in this latter relationship.

D. AROUSAI The concept of arousal has been used to describe the fact that the more complex organisms vary in their level of activity and alertness from some low point, labeled sleep, to a high point, variously labeled “aroused,” “activated,” or “mobilized.” The level of arousal is called the “state” of the organism, and the concept of state carries with it implications for all aspects of overt and covert responsivity. Several measurements have been employed to describe the state of the organism. Bindra (1959, p. 21 1) divides these measurements into three physiological categories: the autonomic nervous system (e.g., galvanic skin response), the somatic system (e.g., tactile thresholds), and the central nervous system (e.g., alpha-wave breakdown) but points out that these three categories probably do not reflect a single underlying process. Nevertheless, there is an interaction between the three systems which indicates some overlap such that raising the activity in one system is correlated with increases in activity of the others. The problems involved with working out the interrelationships are immense, because neither the behavioral nor physiological responses are easily scaled in such a way that comparisons between their measures are meaningful. There is currently no standard set of operations for describing state in the newborn. “State,” when not itself the dependent variable (as it rarely is), is taken care of through statistical controls designed to stabilize groups around some gross setting condition such as time in the feeding cycle or swaddling. For the current purpose, arousal will be positively equated either with activity of the autonomic nervous system, as indicated by changes in heart rate and

25

Herbert Kaye

skin conductance, or with activity in the somatic systems of all except the sucking response, and the interrelationship of sucking to these measures will be explored. Jensen (1932) suggested a positive relationship between arousal and sucking when he stated that, even though his Ss were moderately satiated and their sucking rates had fallen, he could increase sucking in 100% of those tested by either pinching their toes or pulling their hair. As will be recalled, James reported that if his sleeping pups were awakened, they began sucking, but if left alone, they would sleep and not suck. Bridger (1962) directly tested this hypothesis by taking individual infants before and after a meal and subjecting them to cold water foot stimulation. He found that recently fed infants, who started with an average of about 20 responses per minute, could be brought rapidly to about 38 responses per minute after a series of three cold water stimulations. This was also the asymptotic average level for the babies given similar stimulation prior to their feeding. The “hungrier” infants averaged about 29 sucks per minute before cold water stimulation. According to Bridger, heart rate changes after stimulation were, as expected, higher than prestimulus rates and paralleled changes in sucking rate. Bridger’s findings indicate that the suppression of sucking which accompanies feeding can be over-ridden by activating stimulation. Levin and Kaye, in the study (1964) cited above, found a rank order correlation of .69 between pretest observer-rated activity and total number of sucking responses during the 9-minute test period. They concluded that the relatively high correlation between sucking and activity, when compared with the correlations between sucking and food deprivation and between activity and food deprivation, suggests that an awake baby will suck when given the opportunity, regardless of his level of food deprivation. Although the relationship between activity and sucking seems reasonable, the implied connection between activity and feeding has been only casually studied in the Bridger and in the Levin and Kaye studies. As stated in the previous section, it is difficult to control all the relevant feeding factors. In the Kaye study reported above, in which infants were given probe tests for nonnutritive sucking rates before and after their morning meals, activity and skin conductance measurementswere also recorded. The activity measurements were continuous, and skin conductance was measured at approximately 10-minute intervals. It was generally found that sucking rates were directly proportional to both pre-sucking activity and skin conductance levels. Skin conductance levels, in line with earlier findings (Kaye, 1964), showed only slow changes in direction. Activity decreased markedly during the sucking periods for active infants. This depressive effect of sucking on activity, the “pacification” phenomenon, has been described recently by several workers (Rovee & Levin, 1966; Kessen, 1965), 26

Infant Sucking Behavior and Its Modijication

and will not be discussed here. However, the effect of pacification on subsequent sucking is relevant to the current topic. The process of pacification is one in which the act of sucking decreases the infant’s activity level. Using activity level as an index of arousal, it would have to be said that the pacified infant is less aroused. If there is a correlation between arousal level and sucking rate, it should be expected that sucking would decrease as a function of its own occurrence. That is, nonnutritive sucking should approach a zero rate over time. This, however, is not the case. Although sucking rates do drop over the first 2 minutes for infants starting with rates above 45 per minute, Levin and Kaye (1966) have shown that rates stabilize after about the third minute of sucking in a 10minute test. Kaye (1964) has extended the findings to 20 minutes. It may be interpreted from this that there is a minimal level of arousal which is possibly set by feeding or stomach factors, but that strong external stimulation may be used to raise this level. These activating operations lead to progressive increases in sucking rate. The studies reported thus far have dealt with long-range monitoring of arousal and the relation of sucking frequencies to slow drifts in “state.” In a recent article, Gottlieb and Simner (1966) found a relationship between the immediate heart rate change and the probability of the child initiating a burst of sucking. The age range they dealt with was 1 to 2 months. They used a standard pacifier linked to a closed air reservoir; one end of which was a rubber membrane. By forcing the membrane away from the infant, a small copper plate contacted a copper screw, thus completing a circuit. The sucking record was a digital blip produced by a polygraph writeout unit. Electrocardiograph tracings were simultaneously recorded. A beat-by-beat analysis of the ECG was measured for each infant on four to six 40-second periods of silence interspersed between periods of tone, and in which the infant showed no gross motor activity. Their first analysis showed a high correlation between heart-rate levels and amount of sucking; a correlation found between most motor activities and heart rate. The authors also report that there appeared to be a periodicity to the heart-rate fluctuations, thus allowing them to examine the correlation between sucking burst onset and heart rate acceleration or deceleration. The acceleration and deceleration frequencies were tabulated and yielded a significant X2,indicating that acceleration phases were followed by bursting much more regularly than were deceleration phases. Unfortunately, these authors do not report the pressure required to produce a recordable suck. Since their device is digital, only those sucks above the required threshold would be recorded. It has been this author’s experience that digital devices often do not record the first one or two sucks of a burst because they are below the threshold for activating the device. Since Gottlieb and Simner show records in which there is an acceleration only over the one or two beats prior to the burst, and since

27

Herbert Kaye

the heart rate may be, on the average, twice as fast as the maximum sucking rate, it would seem that information on the threshold for producing a recordable suck is critical for supporting their contention. Until this information is obtained, an alternative interpretation of the correlation would be that the heart rate acceleration is produced by an initial unrecorded suck.

E.

SUDDEN ONSET OF AN

EXTERNALSTIMULUS

The boundaries between the operations for the above independent variables has not always been clear. Sucking deprivation and food deprivation have not always been independently manipulated, and food deprivation has often been the operation used to manipulate the level of arousal. Similarly, the operations described as “sudden onset of an external stimulus” are those sometimes used for manipulating arousal level. Jensen’s statement about the effects of “toe pinching” and “hair pulling” were included in the previous section, although these operations would certainly satisfy many definitions of an “external stimulus.” To focus on the relevant aspects of a stimulus situation, a stimulus may be described as an event having at least two roles: the first concerns its cue or discriminative value, the second its activating effects. The organism, as a dynamic physiological system, presents a background “noise” level upon which sensory effects are superimposed, As a novel stimulus increases in intensity beyond its physiological threshold, certain behaviors are elicited, the so-called unconditioned responses. One class of unconditioned responses has been labeled orienting reflexes, and according to Sokolov’s interpretation (1963), these are the first reflexes put into operation by a stimulus. “The orientation reflex is the first response of the body to any type of stimulus. . . . It tunes the corresponding analyzer to ensure optimal conditions for perception of the stimulus.. . . The orientation reflex involves muscular activity resulting in specific movements of eyes, lids, ears, head and trunk, which together give the animal “the power to meet chance dangers’. . . . At the same time it inhibitsother unconditioned and conditioned reflexes. . . . Thus the orientation reflex manifests itself in the stimulation of some and the inhibition of other systems of the body.” (p. 11)

Within the sensory receptor system, adjustments take place known as the “adaptation reflexes”; these are a function of the intensity of the stimulus. In addition to these orientation and adaptation reflexes, still another set of reflexes comes to play a role as the intensity increases. When the intensity of the stimulus reaches a certain level rhedefence repex enters into operation. This reflex shows certain properties quite distinct from orlentatmn and adaptation reflex. The similarity of adaptation and defence reflexes lies in their coinmon object, namely limitation of the action of the stimulus. This object, however,

28

Infant Sucking Behavior and Its Modification is restricted to one analyzer only in the case of the adaptation reflex and concerns the body as a whole in the case of the defence reaction.” (p. 14)

In dealing (in this review) with the topic of arousal, attention wasdirected to the end of the stimulus intensity continuum which produces gross changes in activity, which Sokolov calls the “active defence reflex.” (There is also a “passive defence reflex” typified by “freezing” behavior.) The current section will be focused on the effects of stimuli which are toward the low end of the intensity continuum. Recently, a paper by Bronshtein et al. (1960) presented a new method for testing sensory capacities, or discriminative ability, in the human newborn. A pacifier was placed in the infant’s mouth, and stimuli were presented while the infant was sucking. According to Bronshtein et al., the first presentation of any stimulus (the operation defining novelty) produced a suppression of sucking proportional to the intensity of the stimulus. Successive presentations were said to produce habituation of the suppression (i.e., a decrease in disruption of the ongoing sucking behavior), while the presentation of a new stimulus reinstituted suppression. Bronshtein and his colleagues argue that these characteristics of the sucking response indicated that discrimination and generalization, intermodel comparisons, and absolute thresholds could be effectively analyzed using objective criteria related to the reestablishment of sucking suppression. Bronshtein et al. reported their data in terms of per cent of subjects giving suppression; and although this statistic did not seem to be the most efficient one which could be used, it offered promise for further analysis. Unfortunately, the criterion for s u p pression was not reported, although one record of complete cessation of sucking during a stimulus presentation was presented. Another unfortunate aspect of the analysis was that, although sucking records were obtained from newborns within an hour of birth, no indication of mean age or age range of their sample was reported. While it was implied that suppression was obtained from infants within the first few days of life, Brackbill (1962) reports that only 34.7% of the children in Bronshtein’s study between the ages of 1.5 hours and 17 days showed suppression. This is a rather large age span to include under one category, as has been shown by studies demonstrating rapidly changing thresholds during the first few days of life (Lipsitt & Levy, 1959; Lipsitt, Engen, & Kaye, 1963). Bronshtein’s work was done on children up to 5 months of age, and the data were apparently combined for presentation. There is little that can be said, therefore, about the quantitative and qualitative aspects of their analysis, nor is there anyway of evaluating the interaction of frequency of suppression within or between modalities as a function of age. Keen (1964) has recently reported a study of sucking suppression and sucking initiation as a function of tonal stimulation in newborns. Sucking suppression was defined as a pause of 2 seconds or more occurring within 2 29

Herbert Kaye

seconds after tone onset. Initiation consisted of two or more responses occurring within the first 2 seconds after tone onset, and at least 2 seconds from the previous group of responses. Tone presentations were time-locked, having either a 2-second or 10-second interstimulus interval. Tone stimulations, fifty in all, were either of 2- or 10-second duration, and were of either 400 or lo00 cps. One of the frequencies was presented for the first twenty trials, the other for the next twenty, and the original for the last ten. Fortyeight infants, twenty-four males and twenty-four females, between the ages of 3 and 5 days were randomly assigned to eight groups, representing the different combinations of stimulus duration, interstimulus interval, and order of frequency presentation. The procedure consisted of presenting a 2-minute no-tone period, fifty test trials of tone separated by appropriate intervals, and a final 2-minute, posttest, no-tone period. The nipple was kept in the infant’s mouth throughout the procedure. In the final analysis, the effects of sex of the infant and behavior change over trials were also evaluated. The design therefore consisted of four between-group and one within-group comparisons. One data analysis compared the number of spontaneous cessations and initiations occurring in the pretest period with those that appeared in the first 2 minutes of tone testing, in the last 2 minutes of testing and in the 2minute posttest period. The results were interpreted as indicating that the 2-second interval, 10-second duration (21- 10D) group and the 10-second interval, 2-second duration (101-2D) group both had significantly greater proportions of cessations and initiations during the first 2 minutes of tone stimulation than during the pretest period. The proportion of initiations and cessations for the 21-IOD and 101-2Dgroups were approximately + .47 and + .37, respectively. The group having a 10-second interval and tonal duration had a significantly lower number of combined cessations and initiations during the posttest period than during the pretest period. The proportion of cessations during the pretest period for all groups ranged between + .29 and + .31 indicating that approximately one-third of all cessations and initiations during this period fell within 2 seconds following what would have been the stimulus onset. Several points should be mentioned which make interpretation of these data difficult. First, the 21-2D procedure is not sufficiently long to allow for the first and last 2 minutes of the test period to yield independent data. There were ten tone presentations which were analyzed as parts of both the early and late tone periods. Second, significance levels were interpreted using a one-tail test, and it is therefore questionable whether the 101-2Dand 21-10D differences should be accepted according to current statistical convention. The third problem arises from the fact that the pretest period is made up of the first 2 minutes of sucking opportunity, the time during which the longest bursts of a continuous sucking opportunity are found. It

30

Infant Sucking Behavior and Its Modification

is therefore difficult to determine whether the proportions arrived at during this interval should be taken as a baseline, or as representative of the “expected” level of sucking during the later intervals. The fourth question relates to the possible changes in the pattern of bursts which might accompany a 16-minute test period of tonal stimulation (101-10D) as opposed to one of approximately 3+ minutes (21-2D), this difference in total length of the test period being confounded with the experimental variables. Keen performed a second set of analyses on the number of cessations for the different groups, examined in blocks of ten trials. In tallying the proportion of cessations, only those trials on which a cessation could have occurred were included. The results are said to indicate a significant duration effect over all trials, and a significant duration by trials effect. It is not clear from the graphs whether the latter effect is a function of the differences in trend of the combined duration groups or is a function of the great amounts of variability in the block-to-block means. Amongthe factors in these analyses which make further interpretation difficult is the lack of information on what percentage of trials of each block, for each subject, was actually utilized, and whether these percentages were significantly different for the 2-second and 10-second duration groups. The fact that the two 2D groups and the two 10D groups (respectively) had essentially identical proportions of cessation during the first ten trials would indicate that differences were not solely a function of the test interval length (the 21-10D, and 101-2D periods being temporally equivalent). In summary, although treatment differences were undoubtedly produced in the Keen study, it is difficult to interpret these effects in the context of the “Bronshtein” phenomenon. Kaye and Levin (1963) have tried unsuccessfully twice to reproduce the Bronshtein suppression phenomenon. In both cases they dealt with absolute numbers of responses per unit time, rather than adichotomousjudgement of suppression versus no suppression. In their first procedure, ten males and ten females 3 to 4 days of age received three tones of 15-second duration begun on the thirtieth, nintieth, and one-hundred and fiftieth second of a 180-second nonnutritive sucking test. Comparisons were made between the amount of sucking during the tone with that during the 15-second periods both before and after stimulation, dividing each of the periods into 7+second segments. A control group of ten males and ten females received no tones during a similar period of sucking and their sucking records were analyzed in the same manner as the tonal group. The stimulus was a 500-cps (base frequency), square wave tone of approximately 85 db. Differences between the groups did not appear. A slight and nonsignificant sucking decrease did occur in the experimental group during the first few seconds following tone presentation. An attempt was made to maximize this effect in the second study by using a 2-second, 95-db. tone on fifteen more experi-

31

Herbert Kaye

mental subjects. These Ss received a 1-minute pretest nonnutritive sucking trial in order to obtain a baseline measure, and to insure that Ss had high initial rates. Fifteen control Ss received the same treatment except that the tone was presented to the experimental Ss only once, this being on the third suck of the second burst of responses during the second sucking period. This period occurred 1 minute after the end of the pretest trial. Again no differences were found between the experimental and control groups, analysis being done this time on 2-second segments starting4 seconds before the tone and continuing for 12 seconds after the tone. Although there was a decrease in rate following the tone, there was asimilar decrease in the control record, a finding which points up the importance of using “no-tone controls” in such experiments. While these data do not disprove the suppression hypothesis, they do indicate that very special procedures may be required to demonstrate it. Positive results were reported by Haith (1966) using a somewhat different procedure. His study was done using forty-one infants for one session on their second, third, or fourth days of life. The infants were inclined in a chair to an angle of about 30°,facing a 1-foot square panel at a distance of about 7 inches on which were set two rows of red lights, four to each row. The lights circumscribed a rectangle, 2 x 8 inches. The lights in the rectangle could be operated successively from lower right clockwise back to lower right, each element being lighted an equal amount of time and completing the circuit in approximately 5 seconds. Each S was given twenty-four 10second sucking trials with intertrial intervals of approximately 10 seconds. Twelve trials were test trials and twelve were control; they were presented in random order with the restriction that no more than two experimental or control trials be presented in succession and that an equal number of each be present in each six-trial block. The nipple was placed in the infant’s mouth at the beginning of each 10-second trial and removed at the end. The trial was begun only when the infant began to suck. Experimental trials consisted of allowing the infant to suck for 5 of the 10 seconds in the presence of a stationary lower right-hand panel light toward which he was initiallyoriented; this orientation was held by the positioning ofthe nipple. During the second 5 seconds of experimental trials, the lights were activated successively as described. For control trials, both the first and second 5 seconds were carried out in the presence of the stationary light. Each S therefore acted as his own control within blocks of six trials, with the first 5 seconds beingthe baseline and the second 5 seconds being either the treatment or treatment-control segment. Difference scores were obtained for all subjects on each trial by subtracting the second 5-second rate from that of the first, and the means were separately computed for the three experimental and three control trials of each six-trial block. There were no differences in the first 5 seconds between the experimental

32

Infant Sucking Behavior and Its Modijication

and control trials, but the experimental trials showed small but reliably greater decrements during the second 5 seconds than the control trials. None of the other variables tested (sex, age, and blocks) was significant. No habituation was found over the blocks, an effect which is not surprising since the times between experimental trials varied; sometimes the trials were adjacent and other times they were separated by one or two control trials. One further bit of information not reported by Haith is the proportion of the individual experimental trials that showed decreases during the second 5 seconds. From the data presented in Haith (1964), the difference between difference scores for the experimental and zontrol trials averages less than one response per trial, and this fact coupled with the highlevel ofsignificance indicates a stable within-subjects phenomenon. Lipsitt (personal communication) has questioned whether we can assume from Haith’s procedure that it was visual movement which produced the apparent suppression. If the child was focused on the lower right hand corner only, as the procedure required, then during the second 5 seconds the effective stimulus would consist of a light which disappeared and then reappeared. This could be considered a single blinking stimulus rather than a moving stimulus. Kaye (1966~)conducted a series of studies in an attempt to replicate and extend the Haith findings. In the first series, ten infants between the ages of 2 and 4 days were run in each of three groups. Employing Haith’s discrete trial method, sixteen 10-second trials were used; the first 5 seconds were within-subject control periods, the stimulus being presented during the second 5 seconds, Interstimulus intervals were approximately 20 seconds. The stimuli used were two square-wave tones of about 94 db., with basic frequencies of 30 and 600 cps (called low and high, respectively.) One experimental group (labeled L-H) received the low tone during the first eight trials, followed by eight trials of high tone. Another group (labeled H-L) received the tones in reversed order. Additional Ss received tones between trials, but not during their sixteen 10-second sucking opportunities. Comparisons were made among the three groups using both absolute rates in the first and second 5-second segments and percentage change. The data are shown in Figs. 9 and 10. All groups showed a decrease during the second 5 seconds, as was found by Haith, but the differences between experimental and control groups with respect to the absolute scores, and the percentage change as well, were not significant. An attempt was made, therefore, to replicate the essential features of the Haith procedures. Three groups, each of five infants, were run in a twentytrial procedure, wherein each S had both stimulus and no-stimulus trials. These were randomly distributed throughout the twenty trials, with no more than two consecutive experimental or control trials delivered, and five of each in every ten trials. The stimulus was a 15-watt bulb mounted in an

33

Herbert Kaye

Fig. 9. Mean nrrniher of sucks per minute for 3 groups of 10 Ss during 10-second sucking opportunities. The .first 5 seconds nere used ns within S controls .for the e1fect.s of introducing a tone stiniirlus during the second 5 seconds. Group L.-H first received a lo\t, and then n high frequencv tone. group H-L received the opposite. The toms nere changed a j e r the eighth rriol. The control group received no tones during the suckinK periods lfronl Kaye* IY06hl. Trial 1-8

Trial 9 - 16

90 +

8

Before

During Before Period with respect to lone presentation

Durinc

Fig. 10. Mean per cent of hejhre-tone sucking ji)r 3 groups of 10 Ss during 10-second sucking n7th the second 5 seronh opportunities. Rate during the first 5 seconds u'as considered 100Q/,. being coniputed from the rutio of ntrrtlher of sucks during the second 5 seconds to numher during the first 5 sec0nd.Y. rimes 100. Groups are as in Fig. 9 I/rom kaye, IY66bl.

all white reflecting hemisphere approximately 10 inches in diameter and situated about 12 inches from the infant. The three groups were given one of the following conditions: (a) semidarkness for the first 5 seconds and flashing light during the second 5 seconds; (6) steady light for the first 5 seconds flashing light for the second 5 seconds; and (c) steady light for the first 5 seconds and moving light for the second 5 seconds. The moving stimulus was produced by linear movement of the light through about a 30degree distance from midline to the infant's left and back again within the 5-second period. The results here were comparable to the previous study, there being a significant decrease in responding from the first to the second

34

Infant Sucking Behavior and Its Modijication

5 seconds but no significant differences between groups or between control and experimental trials. It should be stated that the procedures utilized by Kaye did not exactly replicate those of Haith, and the apparatus used for the visual presentation was not as elaborate. However, sucking rates for the two experiments during the first 5 seconds appeared comparable, averaging about 8 to 10 for the different subgroups. This would indicate that infants in the two studies were probably equivalent with respect to “hunger” or arousal at the start of the task. Two differences may be critical in explainingthe differences in findings. The first is that Kaye used an interstimulus interval approximately twice as long as that used by Haith. Second, the background noise levels in the two laboratories were quite different; Kaye’s laboratory was higher than Haith’s (1965). Differences in intertrial interval may affect the length of successive bursts in such a way that those following longer intervals are themselves longer. However, there is currently no information available on these relationships. In conclusion, it would appear from these findings that the Bronshtein effect is at best a difficult phenomenon to establish in the newborn, and presently it has little value as a psychophysical tool for the establishment of absolute and differential response thresholds.

F. CONDITIONING. With the exception of the data on sucking suppression and habituation presented above, the dependent variables reported thus far have had little relationship to the history of the infant. That is, the stimulus-response relationships were apparently “built-in,” species-specific characteristics. On the other hand, the topic of conditioning will deal with changes in stimulus response relationships as a function of experience. The models which will be considered as representative of the operations producing these changes are those of classical and instrumental conditioning. It is not always possible to describe the procedures used with reference to the simple Pavlovian and Skinnerian paradigms, however, and on occasion it is possible to interpret the procedures as either, or a mixture of both. Sucking conditioning has, in reality, consisted of bringing two types of response under control, although both types will be treated under the same heading here. The first consists of sucking movements in the absence of an actual sucking stimulus (such as a nipple). This has been called “anticipatory sucking.” The second has involved alteration of some aspect of sucking to an intra-oral stimulus. The latter, when obtainable, is probably preferable because the response can be more easily operationally defined and quantified.

35

Herbert Kaye

Marquis’ early experiment (193l), although lacking the rigor of measurement and sophistication of design one would expect in a modern study, seems to provide the earliest unequivocal data indicating the conditionability of sucking. She studied ten Ss from the age of 1 to 9 days. The conditioning procedure consisted of presenting a buzzer for 5 seconds before giving the baby its bottle for regular feeding. The buzzer was again sounded for the first 5 seconds of sucking. The bottle was removed and reintroduced from two to five times during each feeding, the procedure being the same each time. Marquis did this at every feeding during the 9 days of testing, for a total of over fifty experimental sessions per S and about 100 to 250 trials. She recorded anticipatory sucking movements as well as sucking movements during feeding via a balloon fastened under the chin of the infant and connected to a Marey capsule. Other records, such as activity, were also kept. The babies were fed milk obtained from the infant’s mother. The data for seven of the eight babies on whom complete data were available showed increases of both sucking and general mouth movements over the course of the 9 days. Although no statistics were reported, a control group run under a nonpaired tone and bottle situation showed no such increases. Up to this point, successful conditioning had not been shown in infants this young. Denisova and Figurin (1929), studying children as young as 10 days of age and using a relatively uncontrolled observational procedure, had not found anticipatory sucking when the child was placed in the feeding position until after the third week of life. Mirzoyants (see Brackbill, 1962), also using a Marey capsule for recording anticipatory sucking in infants as young as 2 weeks of age, found the first conditioned anticipatory sucking to a visual CS after about 10 days of training, partial stability after 25 days, and 100% performance after 45 days. During training, twelve to fourteen conditioning trials were given per day, using a 3-second CS-US interval. Unfortunately, the Russian experimenters have often reported the beginning of conditioning when the first few isolated responses have occurred contiguously with the CS,but they have not utilized the appropriate controls to exclude the possibility of these being simply random or chance occurrences of the response. A study by Lipsitt and Kaye (1964) on classical conditioning of anticipatory sucking has also yielded positive findings. They used twenty Ss 3 to 4 days of age, ten in the experimental group and ten in the control group. For the experimental Ss, five 15-second baseline tones were presented, during which sucking movements made to the tones alone were recorded by two observers independently. Following this, twenty-five trials were presented, each block of five trials containing four consecutive trials in which the tone was followed by a pacifier approximately 1 second after the tone onset. The fifth, tenth, fifteenth, twentieth, and twenty-fifth trials were CS-alone trials, used as tests of conditioning during training. These twenty36

Infant Sucking Behavior and Its Modijication

five trials were followed by a minimum of ten extinction trials of CS alone. The control group received the baseline trials, then twenty-five nonpaired CS and UCS trials, at an interstimulus interval of about 30 seconds. A significant treatments by trials interaction occurred (see Fig. 1 l), and

”

I ,ExDerimental V Experimentat

Fig. I I . Classical conditioning of the anticipatory sucking response: A , Per cent of trials on which at least one CR occurred; B, absolute number of CRs (from Lipsitt and Kaye. 1964).

significant differences were found between the two groups for two response measures: absolute number of responses during extinction, and percentage of trials in which at least one conditioned response took place. Several questions were raised as to the interpretation of the Lipsitt and Kaye findings. The first had to do with differences in length of experimentation for the two groups. Because the control group received the tone and the nipple unpaired, and a minimum of 30 seconds intervened between the end of one and the beginning of the other, the control group was tested over a period of time greater than that of the experimental group. It was assumed that this was apt to lead to more sucking for the control group because deprivation (time since last feeding) was greater. Second, since anticipatory sucking movements were only recorded during the 15-second intervals when the tones were presented, it was not known whether over-all rates went up more for the experimental than the control group. If rates were rising for the experimental subjects, then attributing the differences between the treatments to the pairing of the tone and the nipple was possibly gratuitous, and the effect could be handled more parsimoniously as a phenomenon other than “conditioning,” such as, “arousal” and/or sensitization. A third question, raised by Haith (1965), relates to the possibility that the pairing of the tone with sucking opporwnity may change the qualitative intensity of the tone. The proposition put forth was that if sucking decreases the apparent intensity of the tone, then the test period stimuli may “sound” louder, and may produce more sucking movements during the extinction trials.

37

Herbert Kaye

In a recent study by Kaye (1966a), appropriate measures were taken to control for the effects suggested above. Sixty infants similar to those used by Lipsitt and Kaye (1964) were divided into six groups of ten infants each. For all subjects the procedure ran 50 minutes. Anticipatory sucking movements were recorded throughout the total procedure. For the conditioning group (Group I), the Ss were given five baseline trials during which the tone (the same as that used by Lipsitt and Kaye) was presented for the first 20 seconds of each minute. During the next 25 minutes, each set of four conditioning trials was followed by a test trial. The conditioning trials consisted of pairing the 20-second tone with approximately 19 seconds of nipple in the mouth. Test trials consisted oftone alone. Following the fifth test trial, twenty trials of tone alone were presented in which the temporal sequence was identical to the baseline and test trials already given. The control group (Group 11) also received five 1-minute baseline trials but the tone was presented from the thirtieth to the fiftieth second of each minute. During trials comparable to the conditioning trials in Group I, the nipple was presented during the first 20 seconds of each minute, and 10 seconds following nipple withdrawal, the tone was sounded for 20 seconds. Again, every fifth trial during this period was a tone-alone trial. The twenty test trials following this were similar to the baseline and test trials given. Group 111 was a nipple-alone control; these subjects received the nipple at times comparable to Group I, but did not receive any tones. Group IV was a tone-alone group. receiving tones in a manner similar to Group I, but receiving no nipple stimulation. Group V (Sensitization-[) was tested to examine what decreases in tonal stimulation, rather than the complete absence of tones, would do to the patterning of anticipatory sucking movements. This group was given baseline and test trials identical to those of Group I, but no tones were sounded duringthe nipple presentation periods which again were identical to Group I. Group VI (Sensitization-11) received baseline and test trials similar to Group 11, but during the minutes in which the nipple was presented for the first 20 seconds (i.e., trials comparable to the conditioning control trials of Group II), no tones were sounded. (In Group I1 the tones were presented during these trials during the thirtieth to fiftieth seconds of each minute.) One analysis of results was done in a manner identical to that used by Lipsitt and Kaye (Fig. 12A, B). The grouping of the data represents mean percentage of trials on which a response occurred in each block of five trials (Fig. 12A), and absolute number of responses in each block (Fig. 12B). The treatment by trials effect was again significant for both measures, and in this experiment over-all treatments differences were also significant. The increased differences between groups can perhaps be accounted for on the basis of the more extensive pairing of tone and nipple for the experimental group in this study (20 seconds) as compared with the Lipsitt and

38

Infant Sucking Behavior and Its Modification

lA

Exp CI Cont -4

Base Test Extinction 1-5 1-5 1-5 6-1011-15 16-20 Triols

L Base Test

Extinction

1-5 1-5 1 5 6-1011-1516-20 Trials

Fig. 12. Classical conditioning of the anticipatory sucking response: A . Per cent of trials on which at least one response occurred; B , absolute number of CRs. The vertical line of Ext trials 6-10 indicates the cut-offpoint of the Lipsitt and Kaye (1964) graph (Fig. 11) (from Kaye. 1966a).

Kaye study (15 seconds). To answer the critical questions raised with respect to the earlier procedure, however, the data were further analyzed to determine what percentage of responses given in each block fell in the tonal period. If, as suggested above, the number of responses showed an over-all increase for the experimental group, then the effect described in Fig. 12A and B could be an artifact of this change. However, ifthepercentage of responses occurring in tone increased differentially for the two groups in the same direction as that shown in Fig. - 12A and B then the interpretation of the data as evidence for classical anticipatory conditioning would be strengthened. Figure 13A and B show this to be the case.

IA

-

Exp Cont *--a

Cont. ---a

L I , , , , , Base Test Extinction 1-5 1-5 1-5 6-10 11-15 16-20 Triols

Bose Test Extinction 1-5 1-5 1-5 6-10 1115 16-20 Triols

big. I J . Per cent oj responses given during the tonal portion of the test trials: A , Average absolute number of sucks in each minute summed over blocks af5minutes; B, ratio ofsucksduring tones to sucks for each test trial averaged over blocks ofjive trials Urom Kaye, 1966a).

The data presented in the two graphs within this figure were arrived at in slightly different ways. Those in Fig. 13A represent the mean ratios

39

Herbert Kaye

of the sum of responses for tone during a five-trial block divided by the total number of responses during the five-trial block. Figure 13B represents the mean ratios of total responses during tone on each 1-minute trial to total responses during that trial, for blocks of five trials; i.e., each point is the mean of five ratios for ten subjects. For minutes during which no responses occurred in either the tone or no-tone segments of a trial or block of trials, percentages were assigned on a time probability basis. Thus, each 20-second segment was considered to be the interval during which 33.3% of the responses would have occurred. The two methods for grouping the data could result in grossly different results in the event of there being many no-response trials. However, few infants showed no responding over blocks of five trials, and with few exceptions, the relationship between the groups and within each group for the two groupings of data in Fig. 13A and 13B were similar. It can be concluded from this analysis that the differential effects of the treatments are apparently specific to the tones. Differences between these two groups could be further compared for the 20-second periods on test trials during which no tones were sounded. For Group I this was the period involving seconds 31-50 and for the control group, Group 11, seconds 1-20. Differences between the groups in total number of responses during this period were not significant ( t < I), thus further supporting the contention that the pairing of the tone and the nipple increased the power of the tone to elicit anticipatory sucking. None of the other control groups showed curves similar to those of Group I. If the differential habituation suggested by Haith were operating, the effects should have shown up as similarities between Group I and Group V and VI, and they did not. These groups, however, did differ from Group 11. Group 111, the nipple-alone group gave approximately of its responding in each of the 20-second segments during the first 5-minute baseline period, in which the infant’s sucking movements were observed in the absence of tonal stimulation. However, it should be pointed out that responding in the presence of the tone during the first five baseline trials for all other groups showed an apparent initial suppression of sucking movements (below 33.370) and subsequent habituation. The phenomenon is illustrated in Fig. 14. The group trends represent much of the individual data. It may be suggested from this that the Bronshtein suppression phenomenon is present in the newborn; but in cases in which the infant is hungry and sucking rates are high, the sucking eliciting properties of the nipple override suppressive effects of the external stimulus. One final word should be said about the importance of measuring anticipatory sucking throughout the total test period. In analyzing the data in terms of percentage of trials on which at least one response was made (similar to the analysis used by Lipsitt and Kaye), some data were sacrificed. Although there was not great variability around the means for each block of

+

Infant Sucking Behavior and Its Modification

30 -

27 c

al

k

24-

0

2 21 -

I

I

2

3

4

5

Trials

Fig. 14. Average per cent of sucking movements found in the tonal portion of each of thejirst 5 min. (N = SO.) (from Kaye. 1966a).

trials, many individual subjects did not show over-all trends consistent with the means for the group. In addition, the absolute anticipatory sucking rates and base rates for these groups both showed large individual differences. The base-rate differences unequally weighted the contribution of some subjects. Both of these problems were partially solved by the percentage transformation used by Kaye. The results of the anticipatory classical conditioning procedures are quite promising. The recent studies have improved on earlier problems of statistical design and analysis, but the objectification of the response is still to be accomplished. It is difficult to predict at this point whether sufficiently stringent operational criteria for an “anticipatory” suck could be developed that would eliminate such mouth and jaw movements as those accompanying crying, burping, and “gapping,” without sacrificing “sucking” movements across the range of variability normally found in a population of newborns. A more convincing and valuable procedure, from the point of view of objectifying records of sucking and sucking change would be to measure changes in the infant’s response to the nipple or other sucking stimulus as a function of reinforcement contingencies. The recording of all sucking characteristics would give the researcher the added flexibility of pursuing several aspects of the response simultaneously.As mentioned above, current data do not adequately indicate which of the many attributes of the sucking response may be correlated with changes in reinforcement contingencies. However, several different approaches have recently emerged for studying conditioned responding to a definable sucking stimulus, and these will be of value in the future for making such decisions. Stanley et al. (1963) have recently published a study of conditioning of 41

Herbert Kaye

the sucking response in ne\\ born pups. Using tu enty-one pups divided into three groups and matched for titter and other relevant variables, testing was done over a 7-day period starting with an average age of 3 days, and ending at an average age of 10 days. All groups were given an initial period of 5 seconds of sucking on a tube connected t o a manometer, followed by a pause of 5 seconds and a final 12-15-second period of sucking. I n the final period, one group sucked simulated bitch milk, one sucked the manometer, and the third group sucked a quinine solution. The milk and quinine were delivered through a dropper, about .5 ml on each trial. Approximately ten trials were given each day. The test was the 5 seconds of manometer (CS) sucking that preceded each animal’s “reinforcement” condition. The results showed a significant increase in sucking to the CS over days when followed by milk, a slow decline in sucking when followed by the nonnutritive sucking, and a rapid decrease t o zero when followed by quinine. The same results were found in the analysis of only the first trial of each day, thereby averting the possibility that different trends were based on the immediate arousing and/or depressing effects of the reinforcement. Independent support for the effectiveness of the procedure comes from the fact that pups receiving quinine showed significantly more struggling in the experimental situation, as rated by the experimenters, than did those receiving either milk or no solution. The authors point out that the conditioned response occurred on only about 457( of the trials on the seventh conditioning day for the milk group, but that suppression occurred quite early in training in 100% of the subjects in the quinine group. They indicate that as conditioning progressed, the quinine animals struggled more than the milk or no-solution animals, so that often the tube could not be inserted for the manometer test. A major problem in using nipple sucking rates as the dependent variable in conditioning human infants is that the nipple itself elicits an extremely high base rate, imposing a ceiling on increases in such rates. Two solutions to this difficulty are: ( I ) to use a sucking stimulus which does not normally produce as high a rate as the nipple; and (2) to examine changes in one of the other characteristics of the response. A recent study by Lipsitt, Kaye, and Bosack (1966) has explored the possibility of conditioning increases in sucking rate to a “non-optimizing” sucking elicitor. This study will be reviewed after consideration of a prior study (Lipsitt and Kaye, 1965) which found differences in nonnutritive sucking rate to a piece of $-inch surgical tubing and a standard hospital nipple. Three g r o u p of ten infants were used. One received alternating blocks of five trials of nipple and five of tube for fifty trials starting with the tube. The second group received fifty trials of tube-alone, and the third fifty trials of nipple-alone. Trials were 10 seconds long and intertrial intervals were approximately 30 seconds long. Responses to both the nipple and tube

42

Infant Sucking Behavior and Its Modification

were counted independently by two observers, a procedure which resulted in high interobserver reliability. Figure 15 shows the results of the study. 21 20

1

Nipple alone

2 4 6 8 I0

15

20 25 30 35 Trlals

40 45

50

Fig. 15. Mean number of sucking responses on each 0ffiJ.v 10-second trials made b.v three groups of 10 Ss. Responses on nipple-presentation trials are represented by circles. The dark squares and circles for the nipple-alone and tube-alone groups are the pertinent control trialsfor effects of alternation in the tube-nipple group (jirom Lipsitt & Kaye. 1965).

Nipple rates were approximately twice those I’or the tube whether comparisons were made within or between subjects. I n addition, a within-blocks effect nas found such that sucking rates tended to increase L\ hen the nipple was administered but decreased when the tube was given. This is seen in Fig. 16 representing the mean number of responses on trials 1-5 of combined blocks 2-5. The nipple trials for the nipple-tube group are compared with those for the nipple-alone group, and the tube trials are compared with those for the tube-alone group. There is an increased rate for the nipple trials and a decreased rate for the tube trials as compared with the relatively stable performance of the nipple-alone and tube-alone groups. The authors interpreted the higher final rate in nipple sucking for the nipple-tube group as a “contrast” phenomenon whereby the nipple had greater effect after presentation of a weak sucking elicitor. A similar interpretation may be made of the decrease in sucking on tube trials of the nipple-tube group when compared with the tube-alone rates. The higher initial rates on tube trials of the nipple-tube group may indicate a perseverative effect of previous nipple experience.

43

Herbert Kaye

21r--/

Fig. 16. Mean sucking rates for each of the three groups. eliminating the first tnw blocks (trials 1-10) for all Ss. The upper graph compares mean sucking rate to the nipple of thenippletube (solid line) and the nipple-alone (broken line) groups. The bottom graph compares rate to the tube of the Nipple-Tube and Tube-Alone groups. Each point represents the average four trials often Ss. (e.g.. Trial I of block 2, 3, 4 and 5. etc.) (pornLipsitt ?L Kaye. 1965).

Since it was found that infants showed differential rates to different sucking stimuli, and that the tube did not elicit ceiling rates, an experiment was designed to produce conditioned increases in sucking rates to the tube (Lipsitt et al., 1966). Following the Stanley procedure, an experimental group was fed 1 ml of dextrose solution during the last 5 seconds of a 15 second tube-sucking trial. The control group received the tube for 15 seconds, but received the 1 ml of dextrose solution 30 seconds later through a syringe placed just inside the upper lip. The experimental group also received the syringe-on-the-lip stimulation 30 seconds after a tube trial but no solution was given. The procedure for the two groups during conditioning trials Tube trial

Syringe

n

5 % Dextrose

--

-One

trial -

-*,-

Tube

I

d

Fig. 17. Temporal arrangement of tube and liquid presentations for the experimental and control groups during the Conditioning and Reconditioning periods (from Lipsitt et al.. 1966).

44

Infant Sucking Behavior and Its Modijication is seen in Fig. 17. Ten infants were run in each group just prior to their morning meal. Responses were recorded during the first 10 seconds of each trial in a manner similar to that of the previous study. The sequence of trials consisted of six baseline (tube-alone) trials, ten conditioning (tubeliquid) trials, ten extinction (tube-alone) trials, five reconditioning (tubeliquid) trials, and five more extinction triak2 The data for the two groups are shown in Fig. 18. While the over-all difference between the groups was mConditioninq

'

Extinction

R e w M F

~.

1-7

1-5

6-iO

1-5 6-10

1-5

1-4

Trials

Fig. 18. Changes in sucking rate for experimental and control groups, represented as the mean ratio of number of sucks per trial in each of the periods divided by the number of sucks per trial during baseline period Vrom Lipsitt et al., 1966).

not significant, the trials by treatments effect was based primarily on the difference between the two groups during the second five trials of conditioning. These data offer preliminary support for the conditionability of sucking rates when nonoptimizing sucking elicitors are used. Stanley's (1965) work is currently directed at the experimental control of sucking amplitude through differential reinforcement of sucking pressures. Kron et al. (1963) found an increase in sucking rates as their infants increased in age. To determine whether the change was maturational or learned, they started testing a control group at an age similar to the second day of test for the original group, and found that the second-day rates of the original group were similar to the first-day rates of the control In analyzing the data, it was realized that the 10-second segment of each trial on which the frequency count was made should be influenced by the trial preceding it rather than the contingency following it. Accordingly, the final analysis was done on seven baseline trials (six original plus the first 10 seconds of the first Conditioning trial). ten original conditioning (trials 2-9 of conditioning plus the first of extinction), ten extinction (trials 2-9 original extinction plus the first of reconditioning), etc.

45

Herbert Kaye

group. Thus, they concluded, training within their procedure had not enhanced rates for their original group. However, since several feedings by the mother intervened between first-day and second-day tests on the original sample, and also preceded the first day of test for the control group, it is not possible to conclude that no conditioning had taken place. Sameroff (1966) has recently completed a study in which sucking “expression” pressures, or negative “suction” pressures could be differentially reinforced. “Expression” pressures were those caused by tongue movements, while “suction” pressures were a function of intraoral negative pressure. The initially high suction pressures and low cut-off point used by Sameroff made it difficult for the infants to show a significant increase in this parameter with contingent reinforcement, although the trends were in the appropriate direction. Differences between the contingent “expression” pressure group and its control showed a significant reinforcement contingency effect. Sameroff refers to the change as “adaptation” rather than “learning” and supports this distinction on the basis of there being no persistence of the effect as evidenced by a lack oftransfer between his two test sessions. But since no pretest data were collected for the second session, nor was any later testing done, this argument seems gratuitous. Sameroff does imply that extended testing of his groups will be necessary to test his conclusion adequately. The experiment by Sameroff is one of the few attempts to use the sucking response as an emitted operant rather than an elicited respondent. The sucking response has the characteristics of both, and this factor renders interpretation of sucking data of potential theoretical importance. Some studies on infant monkeys by Kaye and Seltzer (1966) also used the sucking response as an operant. The infants were taken at birth and reared in a situation which allowed each feeding to be used as a training or test session. The infants were required to suck in the presence of certain tones and not in the presence of others in order to receive their daily food. They were subsequently tested for generalization to tones surrounding the reinforced tone. The generalization data on one of the animals for both sucking rate and latency of approach to the nipple for a 30-second test period are shown in Fig. 19. This animal was initially reinforced for sucking in the presence of a 700-cps tone, and punished for approaching the nipple in the presence of the 900-cps tone. The data in Fig. 19 represent the average for fifty probes at each point, collected over fifty consecutive feeding sessions while discrimination between 700 and 900 cps was maintained. The infant was 45 days at the first of these sessions. Discrimination gradients were obtained on some animals as early as 14 days of age. These studies on infant nonhuman primates, and those by Stanley and his associates on pups promise to be valuable supplements to the work with human infants. 46

Infant Sucking Behavior and Its Modification

125

m 25n

g

I,: 20

% 20a, VI

c

-P

g

15

c

:

f

10

5: 0

I 600 650 700 750 800 850 900 950 (+I

Cycles per second

-J

0

I-)

Fig. 19. Mean number of sucking responses and mean lateniy to first response fbrfijiv consecutive sessions of generalization testing. SD was 700 cps and training SA was 900 cps (jrom Kaye & Seltzer. 19661.

G . PATHOLOGY3

There are several pathological characteristics which are found to interfere with the sucking response. Kashara (1916) found that premature infants often show irregular sucking records. This was also found in children who had had large weight losses. Both groups showed improvements as a function of weight gain. Certain diseases of the mouth or respiratory passage also produced irregularities in sucking but, again, these disappeared with improvement of the condition. Kashara also asserted that “idiots” always show irregularities in their sucking curves. Abt (1923) lists ten other factors that will interfere with sucking: ( I ) birth injuries to the face in babies delivered from a face or breech presentation; (2) injuries to the baby’s tongue in the Smelie-Veit extraction of the head; (3) birth injuries to the muscles of mastication; (4) injuries to the facial nerves causing temporary paralysis; (5) intracranial hemorrhages causing general somnolence; ( 6 ) drowsiness and fatigue due to general birth trauma without special localization; (7) cleft palate; (8) stomatitis; (9) acutely inflamed adenoids, and (10) the snuffles of congenital syphilis. One would gather from this that the sucking reflex is rather sensitive to pathological factors. Blanton (1917; p. 479) writes: “Nothing but the most marked retzrdation or injury seems to affect this reflex,” adding that swallowing would be more likely affected than sucking. JThe section on pathology is included primarily as source material for researchers ~ i s h i n gto pursue this area further, hut is not considered a complete review of theavailahle material.

47

Herbert Kaye

B a h t (1948a,b), after examining a sample which included a large number of infants suffering from intestinal disorders, stated that thereareessentially no differences between these and his normal subjects other than a tendency for secondary (N,) and restart (R)frequencies to be higher in the ill infants. Premature infants, he added, often do not show a restart or secondary frequency, and that the Q component is virtually absent in their records. Apparently the more subtle pathologically generated differences in the normal sucking pattern appear, if at all, only in the analysis of fine structure of the behavior, such as the change in pressure within a burst, or the ratio of responses per burst to interburst time. Further parametric work should document these relationships. However, pathological effects might be more profitably pursued in work designed to test more complex interactions. Nipple-tube alternation (Lipsitt & Kaye, 1965) or conditioning procedures (Lipsitt & Kaye, 1964; Kaye, 1966b) might yield more specific information on individual differences, and thus would be of value in categorizing the type of behavioral difficulties which would be correlated with physical affliction. A condition of temporary pathology may be said to exist in the behavioral depression accompanying treatment with certain medications. A study by Brazelton (1961) relates the effects of the prenatal application of drugs to the interaction of newborns with their mothers during feeding. The study dealt with the difficulty of breastfeeding as a function of the amount and type of analgesia and anesthesia given the mother prior t o and during delivery. The Ss were forty-one offspring of multiparous parents. The mothers had previous experience in breast feeding infants and were breast feeding for the second or third time. The infants were studied during the first 6 days of life. The mothers were asked to record their answers to two questions about the alertness of their children and the child’s willingness to nurse: (1) Did they nurse after 3 consecutive minutes of vigorous attempts at arousal?; and (2) were they alert and nursing for 3 minutes per nursing period in the first 2 days, and 5 minutes per period from days 3-5? A frequency count of babies reported to have met or not met these conditions was made. Averages were taken over all nursing periods for each day. The groups were divided on the basis of high and low premedication, and spinal block or inhalant anesthesia during delivery, four combinations thus being possible. The anesthesia differences over days were minimal, and the infants were therefore divided into two groups on the basis of whether their mothers had received large or small doses of premedication. The differences were significant. During the first day, 65% of the low-premedicated mothers reported their infants alert at feeding while only 30% of the highprernedicated mothers reported alertness or ability to sustain feeding. On day 2, the difference tias 6521to 259,,, respectively, the high-medicated mothers reporting essentially the same or poorer results. On day 3, the

48

Infant Sucking Behavior and Its Modification

differences were 757; and 35%; day 4, 87% to 55”,,: and on days 5 and 6 , the groups finally merged at about 8 5 ” ~The . author points out that several factors would have to be controlled before it could Ce concluded that the infants in the high-premedicated group were less responsive to the nursing situation. These are: (a) the effects of increased amounts of premedication on the mother’s ability to nurse; (b) the serial effect ofthe baby not sucking well on the first day, and thus delaying the mother’s production of milk; and (c) the physiological difficulties which might arise from the premedication in relation to both the mother’s ability to produce milk and the infant’s ability to utilize it. To these, perhaps, should be added the question of differences in reliability of observation and trends of judgment as a function of premedication. Regardless of the reservations, the large differences in the groups warrant further specific studies of the effects of drugs on the sucking response.

IV. Summary and Conclusions This review has dealt with an overview of parameters relevant to the sucking response and some of the enviror,mental factors which influence them. Several suggestions have been made as to how the sucking response can be used to explore further the sensory and learning capacities of the newborn. It should be cautioned that the use of the sucking response does not offer a panacea to the many methodological problems which still exist in studying newborn mammals. The response itself must receive a great deal of attention within highly controlled homogeneous populations if it is to be used as a dependent variable in manipulative psychological experiments. A problem in working with the newborn is the rapidity of shift in state of arousal; although the stability of sucking frequency indicates that this problem is partially overcome when the sucking response is used, a correlated physiological monitoring system would be valuable in helping to separate the effects of general arousal from reinforcement contingencies. I n conclusion, it would appear that concepts such as habituation, sensitization, activation, and classical and operant conditioning may be effectively employed in analyzing and predicting the occurrence of changes in some patterns of newborn sucking. Further work should extensively examine the changes in patterns of sucking during the first few days of life. It is during this period, when the child has had the least amount of experiential “contamination,” that the major contribution of individual physiological differences can be assessed. Similarly, having started with an experiential tabula ram, a more critical assessment can be made of the contribution of environmental factors.

49

REFERENCES Abt, I. A. Nutritional disturbances of infancy. Pediatrics, 1923. 3, 232-235. Ames. E. W . Paper read at Sac. Res. Child Develpm. meetings, Minneapolis, April, 1965. Ardran, G. M., & Kemp, F. H. Sucking in infants: A correspondence. Brit. Med. J . . 1958, 2. 634-635. Ardran, G . M., & Kemp, F. H., & Lind, J. A. Cineradiographic study of breast feeding.Brit. J. Radial., 1958, 31. 156162. (a) Ardran, G. M., Kemp, F. H., & Lind, J. A. Cineradiographic study of infant bottle feeding. Brit. J . Radial., 1958, 31, 1 I . (b) Balint, M. Individual differences of behavior in early infancy, and an objective method of recording them: 1. Approach and the method of recording. J . genet. Psychol., 1948. 73, 57-79. (a) Balint, M. Individual differences of behavior i n early infancy, and an objective method for recording them: 11. Results and conclusions. J. genet. Psychol., 1948, 73, 81-1 17: (h) Barnett. A. B.. Lodge, A., & Armington, J. C. Electroretinogram in newborn human infants. Science, 1965, 148. 651454. Bartoshuk, A. K. Human neonatal cardiac responses to sound: A power function. fsychon. Sci., 1964, I . 151-152. Bindra, D. Motivation. New York: Ronald Press, 1959. Blanton, M. G. The behavior of the human infant during the first 30 days of life. Psj*chol. Rev., 1917, 24, 456483. Blough, D. S. Psychophysical methods. I n W. Honig (Ed.), Operant hehavior: Areas of research and application. New York: Appleton-Century-Crofts, 1966. Brackbill, Y. Research and clinical work with children. In R. A. Bauer (Ed.), Some vieMI.7 on Soviet psychology. Washington, D. C.: American Psychological Association, 1962. Pp. 99-164. Brazelton, T. B. Psychophysiologic reactions in the neonate. 11. Effect of maternal medication on the neonate and his behavior. J . fediat., 1961,58, 513-518. Bridger. W. H. Ethological concepts and human development. Recent Advan. biol. fsychiar., 1962,4,95-107.

Bridger, W. H., Birns, B. M., & Blank, M. A comparison of behavioral ratings and heart rate measurements in human neonates. Psychosom. Med., 1965, 27, 123-134. Bronshtein, A. I., Antonova, T. G . . Kemenetskaya, A. G., Luppova, N. N., & Syrova, V. A . (On the development of the functions of analyzers in infants and some animals at the early stage of ontogenesis.) Problemy evolvutali jsiologicheskikh funktsii (Problems of evolution of ph.vsiologica1 functions.) Washinkton, D. C.: Office of Tech. Serv. Rep. No. 60-61066, 1960. Pp. 106-1 16. Moscow-Leningrad: Akad, Nauk, SSSR, 1958. Brown, J. L. States in newborn infants. Merrill-Palmer Quart. Behav. Develpm., 1964, 10, 313-327.

Colley, J. R. T., & Creamer, B. Sucking and swallowing in infants. Brit. Med. J., 1958, 2, 422424.

Davis, H. F., Sears, R. R., Miller, H. C., & Brodbeck, A. J. Effects of cup, bottle, and breast-feeding on oral activities of newborn infants. Pediatrics, 1948, 3, 549-558. Denisova, M. P.. & Figurin. N. L. The problem of the first associated food reflexes in infants. Vupr. Genet. Reg. Pedal. Mladen, 1929, 1 4 8 . Engen, T.. Lipsitt, 1 . P., & Kaye, H. Olfactory responses and adaptation in the human neonate. J. comp. physiol. Psychol., 1963, 56, 73-77. Fantz, R. L. The origin of form perception. Sci. Amer., 1961, 204, 459463. Feldman, W. M. The principles of ante-natal and post-natal child physiology. pure and applied. London: Longmans Green, 1920. Gottlieb, G., & Simner, M. L. Relationship between cardiac rate and non-nutritive sucking in human infants. J. comp. physiol. fsychol., 1966.61, 128-431. Graham. F. K., Matarazzo, R. C., & Caldwell, B. M. Behavioral differences between normal

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and traumatized newborns: I1 Standardization, reliability. and validity. Psychol. Monogr., 1956,70, No. 21. Haith, M. M. The response of the human newborn to visual movement. Unpublished doctoral dissertation, Univer. of California, Los Angeles, 1964. Haith, M. M. Personal communication, 1965. Haith, M. M. The response of the human newborn to visual movement. J. exp. ChildPsychol., 1966.3. 235-243.

Halverson, H. N. Infant sucking and tensional behavior. J. gene?. Psychol., 1938, 53, 365-430.

Haynes, H., White, 8 . L., and Held, R. Visual accommodation in human infants. Science, 1965,148,528-530.

Herrick, C. J. An introduction to neurology. (4th ed.) Philadelphia: Saunders, 1928. Irwin, 0. C. The amount and nature of activity of newborn infants under constant external stimulating conditions during the first ten days of life. Genet. Psychol. Monogr., 1930. 8. 1-92.

James, W. T. The effect of satiation on the sucking response in puppies. J. wmp. physiol. Psychol., 1957, 50, 375-380. James, W. T. A further analysis of satiation on the sucking response in puppies. Psychol. Rec., 1959, 9, 1-6. James, W. T., & Gilbert, T. F. Elimination of eating behavior by food injection in weaned puppies. Psychol. Rep., 1957,3, 167-168. Jensen, K. Differential reactions to taste and temperature stimuli in newborn infants. Psychol. Monogr.. 1932, 12, 363-479. Kashara, M. The curved lines of suction. Amer. J. Dis. Child., 1916, 12, 416435. Kaye, H. The effects of feeding and tonal stimulation on nonnutritive sucking in the human newborn. Unpublished doctoral dissertation, Brown Univer., 1964. Kaye, H. The conditioned anticipatory sucking response. Unpublished manuscript, Brown Univer., 1966. (a) Kaye, H. The effects of feeding and tonal stimulation on nonnutritive sucking in the human newborn. J. exp. Child Psychol., 1966. (b) Kaye. H. Some further attempts to document tonal suppression of sucking. Unpublished manuscript, Brown Univer., 1966. (c) Kaye, H., & Levin, G. R. Two attempts to demonstrate tonal suppression of non-nutritive sucking in neonates. Percept. mot. Skills, 1963, 17, 521-522. Kaye, H.. & Lipsitt, L. P. Relation of electrotactual threshold to basal skin conductance. Child Develpm., 1964, 35, 1307-1312. Kaye, H., & Seltzer, R. J. The use of the sucking response to examine auditory discrimination and generalization in the infant rhesus monkey. Paper read at meetings of East. Psychol. Ass., New York, April, 1966. Keen, R. Effects of auditory stimuli on sucking behavior in the human neonate. J. exp. Child Psychol., 1964, 1, 348-354. Kessen. W. Sucking and looking: Two congenitally organized patterns of hehavior in the human newborn. In H. W. Stevenson, E. H. Hess, and H. L. Rheingold (Eds.), Early Behavior: Comparative and Developmental Approaches. New York: Wiley, 1967. Kron, R. E., Stein, M., & Goddard, K. E. A method of measuring sucking behavior in newborn infants. Psychosom. Med., 1963, 25, 181-191. Leventhal, A., & Lipsitt, L. P. Adaptation, pitch discrimination, and sound localization in the neonate. Child Develpm., 1964, 35, 759-768. Levin, G. R., & Kaye, H. Nonnutritive sucking by human neonates. Child Develpm., 1964, 35, 749-758.

Levin, G. R., & Kaye, H. Work decrement and rest recovery during nonnutritive sucking in the human neonate. J . exp. ChildPsychol., 1966, 3 (2), 146154. Levy, D. Finger sucking and accessory movements in early infancy: A n etiologic study. Amer. J. Psychiat., 1928, 7, 88.

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Levy, D. Experiments on the sucking reflex and social behavior in dogs. Amer. J. Orthopsychiat., I934,4,203-224. Lipsitt, L. P. Learning in the first year of life. In L. P. Lipsitt & C. C. Spiker (Eds.). Advances in child development and behavior. Vol I . New York: Academic Press, 1964. Lipsitt, L. P., & Kaye, H. Conditioned sucking in the human newborn. Psychon. Sci., 1964, 1, 2%30. Lipsitt, L. P., & Kaye, H. Change in neonatal response to optimizing and non-optimizing sucking stimulation. Psychon. Sci., 1965,2,221-222. Lipsitt, L. P., & Levy, N. Electrotactual threshold in the neonate. Child Develpm., 1959, 30,547-554. Lipsitt, L. P., Engen, T., & Kaye, H. Developmental changes in the olfactory threshold of the neonate. Child Develpm., 1963.34, 371-376. Lipsitt, L. P., Kaye, H., & Bosack, T. Enhancement of’ neonatal sucking through reintorcement. J . exp. Child Psvchol. 4. 1966. 163-168. McKee, J. P., & Honzik, M. P. The sucking behavior of mammals: A n illustration of the nature-nurture question. In L. Postman (Ed.), Psychology in the making. New York: Knopf, 1962. Marquis, D. P. Can conditioned responses be established in the newborn infant? J. genet. Psychol., 1931,39,479492. Peiper, A. Cerebral function in infancy and childhood. New York: Consultants Bureau, 1963. Piaget, J. The origins of intelligence in children. New York: International Universal Press, 1952. Pratt, K. C..Nelson, A. K., & Sun, K. H. The behavior of the newborn infant. Ohio State Wniver. Stud., Contr. Psychol., 1930,No. 10. Preyer, W. Spezielle Physiologie der Em btyos. 190 I . Ross, S. Sucking behavior in neonate dogs. J. abnorm. SOC. Psychol., 1951,46, 142-149. Rovee, C.K., & Levin, G. R. Oral “pacification” and arousal in the human newborn. J. exp. Child Psycho/., 1966.3, 1-18. Salapatek, P.. & Kessen. W. Visual scanning of triangles by the human newborn. J. exp. ChildPwhol.. 1966.3.I5.S-167. Sameroff, A. J. An apparatus for recording sucking and controlling feeding in the first days of life. Pswhon. Sci., 1965.2, 355-356. Sameroff. A. J. The components of sucking in the human newborn. J . exp. ChildPsychol., 1966. Satinoff, E., & Stanley, W. C. Effect of stomach loading on sucking behavior in neonatal puppies. J. romp. phvsiol. Psvrhol.. 1963. 56. 6 M R . Shepp, B. E., & Turrisi, F. D. Learning and transfer of mediating responses in discriminative learning. I n N. R. Ellis (Ed.), International review of research in mental retardation. Vol. 2,New York: Academic Press, 1966.Pp. 85-121. Siqueland, E. R., & Lipsitt, L. P. Conditioned head turning in the human newborn. J. exp. Child Psvchol.. 3. 1966. 356316. Sokolov, Ye. N. Perception and the conditioned reflex. New York: Macmillan, 1963. Stanley, W. C. Learning, motivation and ingestive behavior in the neonatal dog. Paper read at 2nd Conf. on Learned and Unlearned Behav., Stillwater, Minn.. June, 1965. Stanley, W. C.,& Bacon, W. E. Suppression of sucking behavior in nondeprived puppies. Psychol. Rep., 1963,13, 175478. Stanley, W. C., Cornwell, A. C.. Poggiani, C., & Trattner, A. Conditioning in the neonatal puppy. J. comp. physiol. Psychol., 1%3, 56, 21 1-214. Steinschneider, A,, Lipton, E. L., & Richmond, J. B. Auditory sensitivity in the infant: Effect of intensity on cardiac and motor activity. Child Develpm., 1966,37, 233-252. Zetterstrom, B. The ERG in children during the first year of life. Acta Ophrhalmol., 1951, 29. 295. Zimmermann, R. R., & Torrey, C. C. Ontogeny of learning. In A. M. Schrier, H. F. Harlow, & F. Stollnitz (Eds.), Behavior in non-human primates. Vol. 11. New York: Academic Press, 1965. Pp. 405-447.

52

T H E STUDY O F BRAIN E L E C T R I C A L A CT I V I TY I N I N F A N T S

Robert J. Ellingson NFBRASKA PSYCHIATRIC INSTITUTE UNIVERSITY OF NEBRASKA COLLEGE OF MEDICINE

1.

II.

INTRODUCTION; METHODOLOGY

. . . . . . . . . . . . . . . . . . .

EEG DEVELOPMENT IN INFANCY . . . . . . . . . . A. EEGs OF ABORTUSES . . . . . . . . . . . . . . . . B. EEGs OF FETUSES IN W E R O . . . . . . . . . . . . C. EEGs OF PREMATURES . . . . . . . . . . . . . . . D. THE EEG DURING WAKEFULNESS FROM TERM

. . . . . . . . . ........ ........ ........

CONCLUSION REFERENCES

61 61 61 62

TO 1

................................. YEAR ..... E. THE EEG O F SLEEP AND DROWSINESS IN INFANCY F. EEG ABNORMALITIES IN INFANCY . . . . . . . . . . . . . . . . 111. BRAIN ELECTRICAL RESPONSES IN INFANCY . . . . . . . . . . . . A. NONSPECIFIC RESPONSES . . . . . . . . . . . . . . . . . . . . . . B. SPECIFIC RESPONSES . . . . . . . . . . . . . . . . . . . . . . . . IV.

53

................. . . . . . . . . . . . . . . .................. . . . . . . . . . . . . .

67 69 73 81 81 83

90 91

I. Introduction; Methodology This article will be concerned only with the development of brain electrical activity of the human fetus and infant to the age of 1 year post-term. I Supported by NIH Grants No. NB-OI 558 and NB-06486 from the National Institute of Neurological Diseases and Blindness and Grant No. HD-00370 from the National Institute of Child Health and Human Development.

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Robert J . Ellingson

Fortunately much of the electrical activity of at least the superficial portions of the brain can be recorded through the closed skull and scalp. Contact is made with the scalp of the subject by means of an electrolyte solution, jelly, or paste and metallic electrodes which lead to suitable high-gain amplifiers. The output ofthe amplifying system can be recorded by various means, but is most commonly recorded by an ink-writing oscillograph on moving paper tape. The resulting tracing is a continuous voltage-time graph, in which changes in voltage differences between any 2 electrodes occurring at rates of approximately 1-50 fluctuations per second are recorded as vertical deflections and time is represented in the horizontal dimension. Traditionally, and in most laboratories in the United States, 7 mm of vertical distance equals 50 ,uV and 30 m m of horizontal distance equals I second. Modern instruments are multichannel so that 8 or more voltage-time graphs, derived from as many pairs of electrodes, may be recorded simultaneously. In many research laboratories it is now also common practice to make a second simultaneous recording on magnetic tape for later computer processing. If necessary, “on-line” computer processing can also be done. Such recordings of voltage fluctuations occurring in the brain are called electroencephalograms (EEGs). It is common practice to record EEGs with the subject in a reclining position and relatively isolated from meaningful external stimulation. For many clinical purposes such EEGs are entirely satisfactory. Deviations from normal resting and sleep EEG patterns, which are useful in the evaluation of many brain disorders, may be thus observed. For some clinical and many research purposes, however, it is useful to introduce controlled stimuli or other independent variables, such as drugs. and to observe subsequent effects upon brain elctrical activity, behavior, and other dependent variables. Stimulation can result in changes in the pattern (frequency, amplitude, waveform) of ongoing EEG activity and/or in the occurrence of a transient voltage change ofspecific latency, waveform, and topographical distribution (evoked responses or potentials). It is often possible to relate such changes to behavior. Consequently the attention of behavioral scientists has been more and more drawn to the study of such dynamic aspects of brain electrical activity. It is necessary to be familiar with the resting EEG, however, because it provides the background against which brain electrical responses to stimuli from the internal and external environment occur. Early studies of the brain electrical activity of human infants were therefore naturally concerned largely with the EEG of the resting. relatively unstimulated infant, awake and asleep. The resting EEGs of infants will therefore be described first, then some aspects of EEG abnormalities in infancy and finally brain electrical responsiveness will be discussed. Preliminarily, however, some methodological matters require attention.

54

Brain Electrical Activity in Infants

I . Elecrrodes There is no agreement about the best type of electrodes to use with infants. Almost every type of electrode (solder disk, silver disk, silver-silver chloride saucer. copper disk, and pedestal and tripod) has been used, except that needle electrodes are generally avoided. Almost every type of electrolyte contact medium, from physiological saline solution to Bentonite paste and EKG ,jellies, has its advocates. Almost everv method of holding electrodes in place has been tried, rubber band head pieces, pastes, soft wax, collodion, etc. (Dreyfus-Brisac, Samson, & Fischgold, 1955; Ellingson, 1960a; Kagawa, 1962; Kellaway, 1952). Most of the techniques proposed work well in the hands of those experienced in their use. The skill and experience of the technician is of greater importance than minor variations in materials. I t is generally desirable to apply electrodes rapidly when working with infants because infants often do nottolerateprolongedexperimental sessions uell: excessive and prolonged manipulation of the head results in increasing irritability. and in the case of prematures and other fragile babies in isolettes the time the isolette is open for the application of electrodes must be minimal. Therefore a compromise must often be reached between speed on the one hand and number of electrodes applied and complexity of electrode application on the other. When rapid application is desirable, the author’s preference is for a thick electrolyte paste and solder or silver disk electrodes (gold electrodes also have recently become available) pressed onto the scalp and overlaid with cotton wool orgauze. When speed is not so important and a prolonged period of recording is anticipated and/or when low interelectrode resistances are essential, nothing compares with silversilver chloride saucer electrodes, fixed to the scalp with collodion and filled with a n EKG electrode solution or jelly. lnterelectrode resistances can ~isuallybe brought down to less than 5000 ohms by gently touching the scalp through a hole in the electrode with a blunted needle. A common problem with infants, especially newborns, is that scalp resistance, and hence interelectrode resistance, tends to be high. Most methods of applying electrodes d o not overcome this problem. Scoring or puncturing the skin before applying the electrode may result in low resistances, but are hardly desirable. The collodion-attached electrode described above will, in the author’s experience, consistently yield low interelectrode resistances, but it is one of the more difficult and time consuming electrodes to apply. In any case, interelectrode resistances should be measured and recorded at the beginning of every recording session, and again whenever the effectiveness of an electrode contact becomes suspect.

2 . Electrode Arra.vs and Montages Definitions: Array refers to the topographical distribution of a specific 55

Robert J . Ellingson

number of electrodes on the scalp. A derivation is a recording from one pair of leads (electrodes). A montage is a combination of a number of derivations simultaneously recorded (Storm van Leeuwen et al., 1966). In recent years an attempt has been made to adopt a universal electrode array for electroencephalography, called the International 10-20 System (Jasper, 1958). It involves the application of nineteen electrodes fixed to the scalp in carefully measured positions plus two “reference” electrodes on the earlobes. Although more laboratories each year are adopting the 10-20 System, it is still not universally used. Almost no one has used the full 10-20 System array for infants. To apply nineteen electrodes on a small head takes considerable time and requires rather close placement, which can easily result in electrode bridging and other technical problems. Hellstrom, Karlsson, and Mussbichler (1963) have suggested a modified 10-20 array. Another simple modification is to use only the prefrontal (Fp,, Fp,), rolandic (C3,C+), occipital (O,, 02), midtemporal (T?,T4), and earlobe (A,, A,) electrodes of the 10-20 System. This provides a close approximation to arrays used by many workers over the years, and also resembles the widely used Gibbs array (Gibbs & Gibbs, 1950). The author and others have also used an array of twelve electrodes on the scalp for full-term and older infants (Ellingson, 1958).Additional electrodes often have to be placed in specific positions for certain experimental purposes. Too many electrode placement systems have been used over the years to describe any more of them here. Suffice it to say that the principal matters to be considered in selecting an array are adequate coverage of the brain areas of interest, precision in the placement of electrodes (measured placements are highly desirable), and adequate interelectrode distances. Derivations from pairs of electrodes that are too close together over an extensive field of activity will tend to yield tracings showing little or no activity duu to the push-pull feature of the amplifying system (see below). It is not necessary, however, to maintain as great absolute interelectrode distances with infants as with adults to obtain satisfactory results. There are two classes of montages: unipolar (or monopolar) and bipolar. In the former the recordings are derived from pairs of electrodes, one of which is on the scalp over active brain tissue (the “active” electrode) while the other is usually over a point which is relatively neutral with respect to brain electrical activity (the “reference” electrode). In most unipolar montages all active electrodes are usually referred to the same reference electrode (e.g., conjoined earlobe lead) or all those on one side of the head to one reference electrode and those on the other to another (e.g., to the ipsilateral or contralateral earlobe electrode). The relative value of unipolar and bipolar recording is controversial. In the first place there is no ideal reference lead, i.e., one which is both truly neutral with respect to brain electrical activity and at the same timedetects 56

Brain Electrical Activity in Infants

absolutely no noncerebral signals (artifacts). The most commonly used reference leads for unipolar recordings are the earlobe leads, which almost always pick up activity of the lateral and inferior portions of the temporal lobe. This must be remembered especially in recording EEGs of prematures, in whom the most prominent activity tends to arise in the posterior-temporal area. Earlobe unipolar recordings in such subjects, or any subject in whom there are prominent signals in the temporal areas, tend to give the impression of much greater diffuseness of the activity than is actually the case. Also EKG artifact is more common in such unipolar records than in those of older subjects. More distant reference leads are usually more subject to EKG and other artifacts. Similarly, the vertex lead is not a very desirable reference lead, because, especially during sleep, when the most prominent activity tends to arise from the vicinity cf the vertex, it tends to make the activity present appear much more diffuse and bilaterally synchronous than it is. For these reasons, the author prefers to use primarily bipolar recording with prematures and neonates and a combination of bipolar and unipolar recording with older infants.

3 . A mplijiers and Recording Instruments Standard EEG instruments employ high-gain, multi-stage, resistancecapacity coupled, push-pull amplifiers. It is essential to understand two features of these systems. First is the effect of resistance-capacity coupling. A n R-C coupled amplifier has a characteristic called theTime Constant (TC), which is equal to the product of the resistance (in ohms) and the capacitance (in farads) of the coupling resistors and capacitors. The TC (the value of which is given in seconds) represents the time it takes for 67% ofan applied charge to leak off to ground. It determines the lower frequency limit ofsensitivity ofthe amplibing system. In electroencephalography, it is customary to employ TCs of 0.1 to 0.3 or even 1.0 sec. With a 0.1 sec TC, signiticant amplitude distortion is seen at frequencies of approximately 5 Hz and below, and with a 0.3 sec TC at frequencies approximately 1 Hz and below. For work with infants where so much activity is 2/sec or slower, a TC near 0.3 sec is desirable. I n any case a T C shorter than 0.1 sec should not be used. For recording ultraslow phenomena, stable direct coupled (DC) amplifiers are available. The TC of these amplifiers approaches infinity. The upper frequency limits of conventional EEG recording systems are determined largely by the inertia of the ink-writing system, but electronic dampening of high frequencies is also used to eliminate unwanted highfrequency artifacts, such as muscle potentials. However, such damping also distorts the waveforms of cerebral activity with high frequency components, such as spikes, and should not be used unless absolutely necessary. The high frequency limits of EEG amplifiers themselves is in the range of loo0 to 10,OOO Hz. For accurate high frequency recording, a low inertia 57

Robert J . Ellingson recording instrument, such as a cathode ray oscilliscope, should be used. For commercially available instruments, amplitude-frequency curves at various TCs and high frequency control settings are usually given in the instrument manual. These should always be studied. EEG and most other physiological aniplifiers are constructed with mirror-image circuitry so that input signals of the same relative polarity (positive or negative) reaching opposite sides of the circuit result in output signals of opposite polarity. These are known as push-pull amplifiers. They are constructed in this way in order to reject 60-cycle and other external artifacts which tend to reach two recording electrodes simultaneously and would otherwise cause much greater interference in recordings than they do. Another result of the push-pull arrangement is that in-phase cerebral signals of equal amplitude detected simultaneously by two electrodes leading to the two sides of the amplifier also cancel, and the resultant record will show no signal. Furthermore, if a signal is detected by one electrode of such a pair while nothing is detected by the other, the recording device will deflect in one direction; but if the same signal is detected by the second electrode and nothing is detected by the first, the resultant deflection will be in the opposite direction. In most laboratories a negative signal applied to the “Grid 1” side of the amplifier will cause an upward deflection of the recording pen or cathode ray oscilliscope beam, and a positive signal will cause a downward deflection, while the opposite is true for signals supplied to the “Grid 2” side. Unfortunately, some laboratories use the opposite convention. It is necessary to check the methods section of research papers to ascertain which convention is being used. The concepts covered in this section appear to be very difficult to grasp, but are of utmost importance in understanding electrophysiological recordings. If this brief presentation has not been clear, see Walter and Parr (1963) and Walter (1963), or better yet, consult a biomedical engineer.

4.Problems of Recording Evoked Responses a. Electrode Placement. For most evoked response work the author prefers placement of the “active” (Grid 1)electrode overthe area wherethe response is expected and of the “reference” electrode over a distant and neutral area. The earlobes are relatively distant from the areas in which both specific and nonspecific responses to visual, auditory, and somesthetic stimuli occur. The forehead and nose are also distant, and are preferred by many for recording somesthetic responses. They are not good reference points for visual responses because eye movements tend to occur to visual stimuli, and these can be detected by such leads and duly recorded. If it is desired to record eye movements, they should be recorded in a different channel from that used for visual evoked responses. The vertex is not a good reference point for

58

Brain Electrical Activity in Infants specific evoked responses, because nonspecific responses (responses to stimuli in any modality) tend to occur there. In recording nonspecific vertex evoked responses for their own sake, an earlobe reference lead may be used. Far frontal or far occipital reference leads may also be used, except in the case of visual stimuli. b. Presentation of Stimuli. The parameters of stimuli should be independently variable. Evoked responses tend to vary with intensity, frequency, and other dimensions of stimuli. Differences in evoked responses between subjects and in the same subject from time to time cannot be compared unless stimulus conditions are uniform. Many differences in evoked responses recorded from different laboratories are due to differences in stimulus conditions. In recording evoked responses it is preferable to present stimuli in a random rather than a rhythmic temporal sequence. Rhythmic brain wave activity can become locked to rhythmically presented stimuli and can be confounded with evoked responses. However, it may be desired to study such time locked, rhythms, which are called “following” or “driving” responses, and then of course rhythmic presentation of stimuli is essential. In recording the evoked responses of infants, stimuli should be spaced at least 2 seconds, and preferably more than 3 seconds apart, due to the fatigability effect, which will be discussed in Section 111, B, 1, f. c. Summating and A veraging Techniques. Evoked responses are often masked by background brain wave activity of greater amplitude than the responses and hence are not visible in original recordings. Various methods of summing or averaging successive stimulus-response events have been devised over the years to extract such signals (evoked responses) from the background “noise” (brain wave activity). Currently, special purpose analog and digital computers are widely used for this purpose. Although the precise mechanisms of such devices differ, the operations are basically similar. A segment of the brain electrical recording immediately following thepresentation of the stimulus is stored. This segment may be varied in duration from a fraction of a second to one or more seconds, depending upon the situation. The next segment following the next stimulus is added algebraically to the first, and so on. Since evoked responses are time-locked to the stimulus and are of the same or similar polarity and waveform on each occurrence, they tend to sum in one direction. Background brain wave activity and other “noise” are randomly distributed in time with respect to the stimulus, and tend to add now in one direction now in the other as successive events are stored. As more and more events are stored, the random signals tend to sum algebraically to zero, and the time-locked evoked responses emerge from the previously masking background.

59

Robert J . Ellingson

A distinction should be made between summating and averaging devices. If the device simply sums over a given number (N) of stimulus-response events, it is a summator. If after having done so, it then divides the sum by N , it is an averager. If N is varied, the results of summators cannot be directly compared (separate calibrations must be run for each N), but the results of averages can be compared. Most special purpose computers for evoked response work are summators. There are several limitations of summators and averagers which must be kept in mind: ( 1 ) Response to response variation in evoked responses will not be detected. Programs for calculating these variables, however, can be written for larger general purpose computers. (2) If such variations occur, the summed or averaged response may not be representative of the individual responses. If latency variations in successive responses occur and are great, the average may fail to show a response entirely. (3) “Noise” is not always effectively averaged out, especially if N is small. (4)Rhythmic components of background activity may lock to rhythmically repeated stimuli and be included in the sum or average (see above). ( 5 ) As N is increased, noise decreases as l m and signal-to-noise ratio decreases Increasing N therefore will eventually cost more than it is worth. as Satisfactory results can usually be obtained with Ns of 50-100, but sometimes a higher N is required.

a.

d. Controls. As a control against fai1uf.e to average out background activity, a series of segments of brain electrical activity should be summed or averaged during which the stimulus is not presented or during which stimuli are presented randomly in time with respect to the segments being averaged. Some summed or averaged responses should be derived more than once to test the reliability of the technique, keeping in mind that responses will vary with the subject’s state of consciousness. Cross-correlations between repeated averaged responses can be calculated to provide a quantitative measure of reliability. Controls for noncerebral responses time-locked to the stimulus should also be employed; eye movement responses to visual stimuli have already been mentioned. Bickford, Jacobson, and Cody (1964) have demonstrated myoclonic responses which could be confused with cortical evoked responses. Various other workers have demonstrated that not all responses recorded from the scalp can be explained as movement responses however. For other papers dealing with this question see the New York Academy of Sciences symposium (Katzman, 1964), and for further references see Ellingson (1965, p. 58). In brief, controls should be employed so that noncerebral responses can be identified. These consist of such techniques as changing head position to stretch and relax muscles suspected of producing 60

Brain Electrical Activity in Infants

myoclonic responses, which should result in changes in the appearance of responses, recording from various electrode pairs to determine the focal points of suspected responses, etc. For a somewhat more detailed discussion of the problems presented in this section see Ellingson (1967).

11. EEG Development in Infancy The period under review is that from 1950 through 1965. Earlier papers have been cited in a previous article (Ellingson, 1958). A . EEGS OF ABORTUSES Several investigators have recorded the spontaneous brain electrical activity of abortuses (nonviable fetuses of less than 500 gm weight at delivery). Okamoto and Kirikae (1951) obtained recordings from six fetuses ranging from 26 to 380 gm, as well as from six older prematures and seven full-term infants. The electroencephalograms (EEGs) of the abortuses showed predominantly 0.2-2/sec activity of 1&90 pV amplitude with superimposed low voltage fast activity of frequencies up to 30/sec. Borkowski and Bernstine (1955) made similar observations on two abortuses, Aresin (1962) on ten, and Engel (1964a) on one. The superimposed fast activity observed by these workers was less persistent than that observed by Okamoto and Kirikae. These observations show that spontaneous electrical activity is present in the human brain before the end of the first trimester of pregnancy rather than appearing late in pregnancy as was once thought, but not much more can be concluded. The tracings reproduced in most of the papers leave much to be desired. It is often difficult to tell from which portions of the brain the activity has been recorded, and, in some instances, one wonders whether artifact might not be present. In any case, whether any ofthe activity recorded from the brains of these abortuses is typical of “normal” activity during early intrauterine life is questionable, since these fetuses were in various stages of the process of dying.

B. EEGS OF FETUSES IN UTERO Lindsley (1942) first demonstrated that the EEG of a fetus in utero could be successfully recorded through the abdominal wall of the mother. Later workers have tended to adopt Lindsley’s criteria for determining whether an in utero EEG has actually been obtained. The criteria are as follows: @)The

61

Robert J . Ellingson

activity recorded should correspond in frequency, amplitude, and pattern to that recorded from the heads of newborn infants. (6) The activity should be recorded from electrodes over the area where the fetal head can be palpated, and not from other electrodes. If the fetal head changes position, only the electrodes now near the head should detect the activity. (c) A similar pattern of electrical activity should be recordable from the same infant’s head postnatally (provided he survives, of course). If the fetal head has descended into the pelvis, recordings can be obtained from electrodes mounted on a vaginal speculum and inserted in the vaginal fornices, or if the cervix is dilated, directly on the fetal head; the presence of an intact amnion apparently presents no difficulties (Bernstine, 1961 ; Bernstine & Borkowski, 1956; Bernstine, Borkowski, & Price, 1955; Huhmar & Jarvinen, 1963). In utero recording presents certain difficulties and problems: Noncerebral potential (voltage) variations, such as maternal and fetal EKG, abdominal muscle potentials, and slow potentials due to uterine contractions, may be recorded and must be distinguished by the electroencephalographer. The precise positions of the recording electrodes in relation to the fetal head are usually unknown and symmetrical bilateral placements are virtually impossible, so that localization of brain electrical phenomena cannot be accomplished. EEG activity recorded in utero normally consists of somewhat irregular I-2/sec waves with some faster activity up to 22/sec superimposed. Unusually rhythmic activity is apparently abnormal and may reflect fetal hypoxia (Bernstine, 1961; Bernstine & Borkowski, 1956; Huhmar & Jarvinen, 1963). Although failure to record fetal EEGs has been reported in cases of intrauterine fetal deaths (Bernstine & Borkowski, 1956), such failure to detect EEG activity cannot be taken to indicate fetal death, because failure may be due to some other cause, principally inappropriate position of the fetal head.

C. EEGs OF PREMATURES For present purposes, all infants weighing between 500 and 2500 gm and born prior to the fortieth week2 of gestation will be considered prematures. (In some reports infants of less than 6 months conceptional age are called “fetuses.”) The literature on EEGs of prematures is now rather extensive (Canova ’Gestation is calculated from the first day of the mother’s last menstrual period (LMP), and term birth occurs at 40 weeks. In some reports, especially European. gestation is calculated from 2 weeks after the first day of the LMP. Conceptional age can therefore differ by 2 weeks, depending upon the method of calculation used.

62

Brain Electrical Activity in Infants

& Cossandi, 1956; Dreyfus-Brisac, 1957, 1962, 1964; Dreyfus-Brisac & Blanc, 1956; Dreyfus-Brisac, Blanc, & Kramarz, 1958; Dreyfus-Brisac, Dargassies, & Minkowski, I96 1 ; Dreyfus-Brisac, Flescher, & Plassart, 1962; Dreyfus-Brisac & Monod, 1960; Ellingson, 1964a; Mai & Schaper, 1953; Mai, Schiitz, & Miiller, 1951 ; Monod, Dreyfus-Brisac, Morel-Kahn, Pajot, & Plassard, 1964; Polikanina, 1962, 1963; Samson-Dollfus, 1955). French investigators, principally Dreyfus-Brisac and her co-workers, have conducted the most extensive studies of the EEGs of prematures. Rather than presenting the results of the various studies individually in detail, an attempt is made here to summarize them by describing typical EEGs observed at various conceptional ages. It is emphasized that the following summary is based on impressionistic descriptions of EEG activity by investigators who have observed large numbers of infant EEGs. The author has depended heavily upon his own observations and those of the Paris group (Dreyfus-Brisac and her colleagues). LF-C .

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Fig. I . EEG of a premature infant recorded 22 hours after birth at a conceptional age of 24 weeks: birth weight 880 grams. In this figure and in Figs. 2. 3. 4. and 6. illustrating EEGs of prematures, an 8-electrode array was used. The electrode letter code at the lefr of the tracings is as follows: L = left, R = right, F = .frontal. C = central. 0 = occipital, T = midtemporal.

I . The EEG at a Conceptional Age of 5 Months The EEG (Fig. I ) is characterized by bursts of iiiixed 0.3-5/sec waves occurring intermittently against a background of relative absence of voltage variation. The periods of silence between bursts may last from a few seconds to 2-3 minutes. The bursts are most prominent in the occipital areas. Occasional transients may be seen. Bursts of rhythmic waves at 8-15/sec and less than 30 p V amplitude may occur in association with the slower w'aves Lvhich may reach 10&300 pV in amplitude. This faster activity may be predominantly occipital, but is sometimes rolandic in location. The activity described may occur bilaterally or unilaterally, but bilateral synchrony and synchrony among various areas of the same hemisphere is generally poor. No change in the EEG associated with a wakefulness-sleep cycle can be detected.

63

Robert

J . Ellinzson

2 . The EEG at a Conceptional Age of 6 Months Polymorphism diminishes significantly. Rhythmic 4-6/sec bursts are seen, often superimposed on somewhat irregular delta waves, with intervening periods of relative silence. The bursts tend to be synchronous throughout one hemisphere, but the two hemispheres are virtually independent of one another at this stage (Fig. 2). The activity can often be recorded best

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by means of transcortical bipolar linkages of electrodes. Amplitudes reach 50-150 pV in tracings recorded from transcortical pairs of electrodes. 3. The EEG at a Conceptional Age of7 Months Some features of the EEG at 6 months may persist into the following month. Voltage variations, however, tend to become continuous rather than intermittent. At 30-32 weeks conceptional age (Fig. 3A) bursts of M / s e c and 8-1 Ysec waves and irregular 0 . 5 4 s e c waves may be seen diffusely, but are more prominent in the occipital or occipital-temporal areas. Random scattered sharp multifocal transients may be seen. The slower components may be up to 20OpV in amplitude. The fast components are more commonly 10-20 p V in amplitude. Asynchrony remains the rule. It is still difficult to detect EEG changes associated with the wakefulness-sleep cycle. Toward the end of the month, discontinuity has further diminished and prominent l/sec waves (diffuse or predominantly occipital or occipital-temporal) become common. These slow waves are often surcharged with bursts of low-voltage rhythmic activity at 12-20/sec (Fig. 3B). Dreyfus-Brisac (1962, p. 8) has characterized EEG activity during the fifth to the seventh intrauterine months as follows: “A discontinuous character and an occasional paroxysmal tracing, interhemispheric asynergy, a meager reaction to various stimuli or no reaction, and no difference between sleeping and waking tracings.”

64

-Brain Electrical Activitv in Infants

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of a premature infant at conceptional ages of ( A ) 30 weeks (65 hourv after birth: weight 1490 grams] and ( B ) 31 weeks (weight 1500 grams). Note sporadic sharp transienls und asynchrony between hemispheres in A . Note also the rapid shift in I week to a pattern typically wen at 33-36 weeks, as seen in B lfrom Ellingson. 1964a, with permission of the publishers ).

4. The EEG at a Conceptional Age of 8 Months A t a conceptional age of 36-37 weeks EEG changes associated with the transition from wakefulness to sleep are seen clearly for the first time. During wakefulness the EEG consists of continuous semirhythmic and irregular activity, largely a t 47/sec, with some low-voltage slower activity and occasional weak beta activity (Fig. 4). This activity is diffusely distributed, and the beginning of bilateral synchrony may be seen, first in the rolandic region and later in the frontal areas. This continues to be the predominant picture during wakefulness through the end of the first month

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the publishers).

65

Robert J . Ellingson

post-term. Patterns observed during sleep will be discussed in Section 11, E. 5. Discussion It must be emphasized that the above descriptive summaries are generalizations based upon the patterns most likely to be seen at each successive developmental period. As would be anticipated, there are considerable individual differences at any given conceptional age. Transitions from one pattern to the next seem to occur rapidly rather than gradually (DreyfusBrisac & Monod, 1960: Ellingson, 1964a). Just how rapidly is not known. We as well as others have recorded the EEGs ofprematures asoften asonce a week, but no one has recorded from any appreciable number of subjects at shorter intervals. A total transition from one pattern to the next can certainly occur within 1 week (Fig. 3). The pattern may then remain stable for as long as 4-5 weeks, and then before 1 more week has elapsed the next more mature pattern appears. A given baby may seem at one time to be lagging behind in EEG development, but then pass through the succeeding developmental stage or stages rapidly, catching up or even forging ahead and displaying a more mature pattern before the typical age. Thus, a baby cannot be considered immature with respect t o its brain electrical activity unless it consistently displays immature EEG patterns for its conceptional age over a period of time. When there is a discrepancy between the estimated conceptional age and the birth weight of a newborn, the EEG pattern corresponds more often to the estimated conceptional age than to the weight. This has been repeatedly emphasized by Dreyfus-Brisac (1957, 1964: Dreyfus-Brisac era/., 1962), and has been confirmed by Canova and Cossandi (1956). Our own observations are also in agreement. Studies of the neurological development of prematures tend to confirm the EEG findings. It is therefore suggested that, while birth weight may be a more reliable measure than estimated conceptional age, the latter probably provides a more valid basis for estimating the maturity of at least some neural functions. This underlines the importance of not using birth weight as the only index of prematurity. Dreyfus-Brisac (1964) has also pointed out the parallelism between in utero and in-incubator EEG maturation. Premature entry into the extrauterine environment neither seems to facilitate nor retard EEG development. The EEGs of babies born several weeks prematurely and developing normally in incubators to a conceptional age of 40 weeks do not differ from EEGs of normal full-term infants at birth, and subsequent developmental EEG milestones (e.g., appearance of prominent sleep spindles) are reached at the same ages. Although there has been considerable speculation about the anatomical structures from which the EEG activity of the premature brain arise, a satisfactory explanation cannot be given as yet. There is a widespread

66

Brain Electrical Activity in Infants

opinion that the phenomena are of largely subcortical origin (DreyfusBrisac. 1964: Mai et al., 1951: Polikanina, 1962; Samson-Dollfus, 1955). The temporal-occipital predominance of activity during some stages of development has also suggested origin in limbic structures. There is no direct evidence in humans for these conclusions however.

D. T H EEEG DURINGWAKEFULNESS FROM TERMTO 1 Y E A R Again, rather than presenting individually the results of the several studies describing the EEG during the first year of life post-term (Bartoshuk & Tennant, 1964; Dreyfus-Brisac, 1964; Dreyfus-Brisac & Blanc, 1956; Dreyfus-Brisac, et al. 1958a, 1962; Dreyfus-Brisac & Monod, 1960; Ellingson, 1958, 1964a; Engel, 1961 ; Fischgold& Berthault, 1953; Gibbs& Gibbs, 1950; Glaser, 1959; Kellaway, 1957; Liberson & Frazier, 1962; Monod eral., 1964; Parmelee et al., 1967a; Samson, Delange-Walter, & Misks, 1963; Samson-Dollfus, 1955; Samson-Dollfus, Forthomme, & Capron, 1964; Schroeder & Heckel, 1952; Shepovalnikov, 1962; Sureau, Fischgold, & Capdevielle, 1950), an integration and summary ofthe findings will be given. The EEG during wakefulness at term does not differ significantly from that typically seen in 8-month prematures. Some workers have described low-voltage rhythmic activity in the alpha frequency range in the first days of life (Liberson & Frazier, 1962; Shepovalnikov, 1962), but such activity occurs under conditions which suggest that it is likely tremor artifact, and that possibility has not been ruled out. The pattern seen at term birth continues relatively unchanged, with slightly increasing regularity of semirhythmic activity, especially in the rolandic area, until 3 4 months post-term when a predominantly occipital rhythm appears at a frequency of about 4/sec. Some investigators refuse to call the occipital rhythm in infants “alpha,” since it is less than 8/sec in frequency.’ Lindsley (1939) and others have shown, however, that it has all of the other characteristics of the alpha rhythm, and further, it increases gradually in frequency until it reaches the alpha range (8-13/sec). Whether the infantile occipital rhythm is called alpha or not is of little importance as long as it is clearly identified. During the fourth to the twelfth months there is a relatively rapid increase in frequency of the occipital rhythm (Fig. 5), which is usually 6-7/sec but may be as high as IO/sec by the end of the first year (Gibbs & Gibbs, 1950; Kellaway, 1957). Throughout the year there is abundant theta (4-8/sec) and some delta (slower than 4/sec) activity, randomly distributed. ‘Alpha rhythm: Rhythm, usually with frequency of 8-1Usec. of almost sinusoidal form, in the posterior areas, present during relaxation when the eyes are closed, attenuated during attention, particularly visual (Storm van Leeuwen er a/., 1966).

67

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Rhythmic 4-5/sec activity may be prominent in the rolandic region. Faster activity (13-30/sec; beta) is seen diffusely, but is of low voltage (less than 5 pV) in the first weeks. All activity tends to be of low voltage during the first weeks of life; only occasional delta waves reach even 50 p V . The occipital rhythm tends to be prominent (greater than 50pV)when it appears. During the second 6 months post-term high voltages (100 pV or more) may be attained. Bilateral synchrony appears first in the rolandic and then in the frontal areas, which show fairly good synchrony between the hemispheres at term in many babies, but asynchrony is not to be considered an abnormality at this age. Bilateral synchrony in the parietal-occipital region may be fair to good at birth, but is more commonly poor to fair. It should be good by the last half of the first year. Asynchrony between the temporal areas is the rule throughout the first year. Bartoshuk and Tennant (1964) have made quantitative observations confirming earlier impressionistic reports. The end of the third month of life is a period especially to be noted (Dreyfus-Brisac, 1958). At this time the occipital rhythm appears, lending a distinct topographical organization to the EEG, and the response of blocking of the rhythm to sensory or psychic stimulation becomes established. The photic following response (Section 111, B, 2) becomes more clear-cut than it has previously been, and the latency of visual evoked responses (Section 111, B, 1)achieves almost the adult level. On the behavioral side, primitive reflexes disappear, oculomotor coordination improves strikingly, prehension is developing, and smiling in social situations is established.

68

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E. THE EEG OF SLEEP AND DROWSINESS IN INFANCY Most of the papers cited in the preceding sections (11, C and D) deal in part with the EEG patterns of sleep as well as those of wakefulness. There are several additional papers which deal primarily with the sleep EEG in infancy (Delange, Castan, Cadilhac, 8i Passouant, 1962; Dreyfus-Brisac & Monod, 1965; Goldie, 1965; Kellaway, 1952; Kellaway 8i Fox, 1952: Parmelee et al., 1964, 1967b; Passouant, Cadilhac, & Delange, 1965; Roffwarg, Dement, & Fisher, 1964; Schaper, 1953a,b). 1. Sleep Reports published as late as 1950 indicated that there were no changes in the EEG patterns of neonates associated with the wakefulness-sleep cycle. Evidence now available indicates that differences between the EEGs of wakefulness and sleep begin to become apparent in prematures at 7 months conceptional age or a little earlier, and are usually clearly apparent by 36-37 weeks. In the full-term infant the onset of sleep is accompanied by an increase in the amplitude of the low frequency components, activity below 4/sec predominating (Fig. 4). Very slow waves (0.5-Vsec) surcharged with fast rhythmic activity in the occipital region (as described in Section 11, C, 3) are not uncommon. Bilateral synchrony is sometimes poor over all areas, but fair to good synchrony is frequently observed over the frontal-rolandic areas (Bartoshuk & Tennant, 1964). Scattered transients may be seen in occasional subjects. Recent EEG-polygraphic research (Delange ef al., 1962; DreyfusBrisac, 1964: Dreyfus-Brisac 8i Monod, 1965; Goldie, 1965; Monod ef al.. 1964; Parmelee et al., 1967a,b; Passouant et al., 1965) has established what was only hinted at in previous reports, that two distinct sleep states can be distinguished in the 8-month premature and in the neonate, identified as “active sleep” and “quiet sleep.” Active sleep is characterized by intermittent body movements, clusters of rapid eye movements (REMs), irregular respiration, and moderately rapid irregular heart rate. Quiet sleep is characterized by rare or no body movements, occasional sucking movements, rare or no REMs, slow regular respiration, and regular heart rate, slightly slower than during active sleep. During active sleep the EEG is dominated by more or less continuous irregular slow waves (0.5-3/sec) mixed with some 4-6/sec activity which tends to be more rhythmic, with lowvoltage faster activity superimposed. The slowest components tend to be most prominent over the posterior regions of the brain. During quiet sleep the EEG is characterized by bursts of similar activity alternating with periods of relative inactivity lasting 2 or 3 to 10 seconds, rarely longer. This pattern is called rraci alternant (Fig. 6). These states alternate with each

69

Robert J . Ellingson

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other 2 or more times during a neonatal sleep period, the periods of quiet sleep lasting 10-25 minutes and active sleep lasting 10-40 miniites(DreyfusBrisac & Monod. 1965: Monod ef al.. 1964). Prior to 36 weeks conceptional age, it is difficult to distinguish the two types of sleep, or sleep from wakefulness, by EEG pattern. Indeed it is difficult to decide whether early prematures are awake or asleep by behavioral observation. Using eye closure as the criterion of sleep, and polygraphic criteria of type of sleep (active, quiet, or transitional), Parmelee et al. (l967a) found the greatest amount of active sleep in prematures with the lowest conceptional ages. The amount of active sleep diminished with maturation, and the amount of quiet sleep increased. At 34 weeks conceptional age active sleep accupied 63x of a sleep period, 59% at 36 weeks. 52”/;; at term, 4 2 x at 3 months post-term, and 24% at 8 months. They concluded that their observations were consistent with the concept that active sleep is a more primitive sleep than quiet sleep. Observations by Roffwarg et al. (1964) are consistent with this view. They found that REM sleep constitutes 55430% of sleep in neonates, 40% in young infants, and drops to 20% at 3 4 years, with minor fluctuations occurring thereafter. Dreyfus-Brisac and Monod (1965) found that quiet sleep occupied 20% of a sleep period at 37 weeks conceptional age and 30% at term. Slow sleep waves (0.5-3/sec) increase greatly in prominence toward the end of the first month post-term, after which quiet sleep is characterized by continuous slow waves with intermittent spindle bursts. Low-voltage fast (2&30/sec) activity may appear in early sleep at 5-6 months post-term; increasing in voltage to 18 months, it then diminishes and is uncommon by 7 years (Kellaway & Fox, 1952; Kellaway, 1957; Samson-Dollfus etal., 1964). By the last 6 months of the first year, slow waves may attain very high voltages (IW300 p V ) in deep sleep (Fig. 7A). Bilateral synchrony 70

Brain Electrical Activity in Infants

A

B

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is good over the entire convexity of the head, but remains poor between the temporal areas. The most prominent and lowest frequency waves tend still to occur in the occipital region, where they are sometimes asymmetrical and asynchronous, giving the impression of a unilateral slow focus. Such foci must be interpreted with caution, since they can occur in normal children; unless there is some other independent evidence of occipital or subtentorial lesion or dysfunction, they should be discounted. Sleep spindle bursts, if seen at all in the neonatal EEG, are weak and evanescent (Fig. 4B). By 2 months post-term, they have become prominent. They are maximal in the precentral region, and asynchrony between the hemispheres is the rule. The frequency of spindle bursts may be 10, 12,or 14/sec. The IO/sec variety tends to be maximal in the frontal areas. Bursts of 2 or all 3 frequencies may occur in the same record. There is not a progressive increase in spindle frequency with age as in the case ofthe occipital rhythm during wakefulness (Ellingson, 1964a). Spindle bursts as well as slow sleep waves may reach very high voltages during the second 6 months postterm (Fig. 7B). They have largely become bilaterally synchronous by the end of the first year, but occasional unilateral bursts may still be seen. Sleep transients (sometimes called “humps”), like spindles maximal in the rolandic area (region of the vertex), appear between 4 and 9 months postterm and may attain very high voltages and very sharp contours by the end of the first year. They are usually temporally associated with spindle bursts. By the end of the first year, the EEG during sleep is similar to, but by no means identical with, that observed in adults, with high-voltage slow waves dominating quiet sleep, and REM sleep occupying about 40% of total sleep time.

71

Robert J . Ellingson

2. Drowsiness I n the 8-month premature and the neonate drowsiness is accompanied only by a slight accentuation of irregular slow components (usually 4-6/sec) in the EEG. Sometime after 3 months post-term, usually at 4-6 months, and certainly by 9 months a notable change develops. Rhythmic, relatively smooth-contoured. bilaterally synchronous 3-5/sec waves appear (Fig. 8). LF.AT

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This activity may be of maximal voltage over the anterior half of the head, especially in the rolandic region. or may be quite diffuse. The amplitude, persistence, and topographical distribution of this activity varies a good deal from subject to subject. Kellaway (Kellaway & Fox, 1952) has termed the pattern “hypnagogic.” More recently, the term “oscitant” has been introduced. The oscitant pattern tends to become very prominent (greater than 100 p V ) by 1 year post-term, and may remain so until 4-5 years. The frequency is usually 4-5/sec, increasing slightly with age. It gradually diminishes and disappears, usually by 7 or 8 years of age, but rarely may persist to 10-11 years. The evolution of oscitant activity and of sleep spindles has been plotted in detail by Gibbs and Gibbs (1950). The oscitant pattern must not be mistaken for seizure activity. The risk of doing so is especially great when sedation has been administered to induce sleep, resulting in prominent fast waves occasionally falling by chance into the troughs between the high voltage 3 4 s e c waves, giving an erroneous impression of spike-and-wave complexes. In infants and young children, it is common t o observe sustained oscitant activity in the EEG for many seconds t o minutes after arousal from sleep, during which period the child is obtunded and appears “dopey” to the observer.

72

Brain Electrical Activity in Infants

F. EEG ABNORMALITIES IN INFANCY The literature on EEG abnormalities in infancy is too extensive to review in detail here. The present discussion will be limited to (a) general descriptions of abnormalities in infants’ EEGs, (b) EEG effects of the birth process, and (c) the clinical prognostic value of neonatal EEGs. The details of EEG correlates of various clinical syndromes will not be covered. It is emphasized that this formulation must be tentative. Future research may alter present conclusions. 1. A bnormalities in Infants’ EEGs Since EEGs of infants, and especially of prematures, are so markedly different from those of older subjects, familiar standards of normality and abnormality applied to the latter are of very limited usefulness with the former. Furthermore, the EEG patterns of the perinatal period evolve so rapidly that standards of normality and abnormality change from month to month. “The pathological brain produces at each age the abnormal patterns of which it is capable” (Dreyfus-Brisac & Monod, 1960, p. 44). It is only within the time span covered by this review that it has become possible to specify with any confidence which EEG features are abnormal and which not, but even yet there are many phenomena, the abnormality of which cannot be asserted or denied with confidence. There are a few phenomena which occur in infants’ EEGs which may be considered abnormal at any age: (a) high-voltage spikes, but they must be distinguished from multifocal transients (Section 11, C) and from biparietal sleep transients or “humps” (Section 11, E); ( b ) spike-and-wave complexes (see below); (c) high-voltage, diffuse or focal, persistent or intermittent delta activity (but see Section 11, E, 1, paragraph 5); (d)extreme diffuse or focal flattening (that is, absence of electrical activity), but this must be persistent throughout the recording and preferably be observed on more than I recording day, since some normal infants may display a remarkably flat record on occasion; and (e) hypsarhythmia (Section 11, F, 1, d). On the other hand, several suspicious-appearing phenomena seen during infancy are probably not abnormal. ( a ) Multifocal transients are common in normally developing prematures. Their appearance at term or later might however be considered as abnormal, if they constitute a feature of a heterochronic record (see subsection a, below). ( b ) Persistent bilateral asynchrony is not abnormal up to 3 4 months post-term, even though most infants show at least fairly good frontal-parietal bilateral synchrony by that time. It must also be remembered that asynchrony between the right and left temporal areas is common until at least 4-5 years of age. (c) Posterior delta waves during sleep, even if bilaterally asynchronous and of higher voltage on one side, should be discounted in the absence of specific clinical correlates. (6)

73

Robert J. Ellingson

Long flat periods in track alternant sleep records are normal unless consistently well over losecondsin duration. Even then theirabnormality isnot definitely established.(e)Generalized or focal flatteningin the neonatal period cannot be considered abnormal, unless such flattening is extreme, persistent through the wakefulness-sleep cycle, and (preferaoly) seen in more than one recording session. Later, after 1-2 months of age, and surely after 3-4 months, when brain wave activity of increasingly high voltage is the rule, these features become highly significant. It is emphasized that these statements represent the author’s personal opinion. a. EEG A bnormalities in Prematures of less than 8 Months ConceptionalAge. High-voltage spikes and extreme flattening may be seen at any age, even in previable infants of 4-5 months conceptional age (Dreyfus-Brisac& Monod, 1960; Samson-Dollfus, 1955). Persistent rhythmic activity is rare in prematures, and when present would seem to be abnormal (Bernstine, 1961; Huhmar & Jlrvinen, 1963; Schulte & Herrmann, 1965). Frontal slow waves, monomorphic, notched, or polymorphic, continuous, or intermittent, with or without slow transients, are also considered abnormal (DreyfusBrisac & Monod, 1960). Paroxysmal bursts of highdvoltage mixed slow and rapid waves are felt to be abnormal (Samson et al., 1963; Samson-Dollfus, 1955), but must be distinguished from the track alternant stage of sleep. Dreyfus-Brisac (1964; Dreyfus-Brisac et al., 1962) has described a feature which she calls “heterochronism,” and which she states is the most common type of abnormality in prematures. Heterochronism is defined as the occurrence at different times in the same record of patterns identified with distinctly separate stages of EEG development, especially waking and sleep records of different developmental stages. Seizures in early prematures usually consist of brief episodes of clonus associated with salvos of slow spikes (that is, spikes of long period‘) in the EEG (Dreyfus-Brisac & Blanc, 1956). b. EEG Abnormalities in Infants of 8 to 12 Months ConceptionalAge.Highvoltage slow spikes or sharp waves, usually at frequencies of 0.5-2/sec (Dreyfus-Brisac & Blanc, 1956; Engel, 1964a, 1965; Harris & Tizard, 1960; Ribstein & Walter, 1958; Samson-Dollfus, 1955; Schroeder & Heckel, 1953a, b), with occipital foci being the most common (Dreyfus-Brisac & Monod, 1964; Samson-Dollfus et al., 1964; Smith & Kellaway, 1964), generalized flattening (Engel, 1964a, 1965;Samson-Dollfus, 1955; Schroeder & Heckel, 1953b; Schulte & Herrmann, 1965), paroxysmal bursts (Engel, 1965; Loiseau, Aussaresses, & Verger, 1960; Samson-Dollfus, 1955; ‘Period The time interval in seconds from the beginning to the end of a wave. By currently accepted definition only transients of less than 80 msec period should be called “spikes”; those of 80-200 msec period should be called “sharp waves” (Storm van Leeuwen et al., 1966).

74

Brain Electrical Activity in Infants

Schaper, 1953: Schulte & Herrmann, 1965), high-voltage diffuse or focal delta waves (Dreyfus-Brisac & Blanc, 1956; Harris & Tizard, 1960; Loiseau ef al., 1960; Samson et al.. 1963; Samson-Dollfus, 1955; Schroeder & Heckel, 1953b; Schulte & Herrmann, 1965), frontal monomorphic slow activity (Dreyfus-Brisac & hnonod, 1960; Samson et al., 1963; SamsonDollfus et al., 1964), and heterochronism (Dreyfus-Brisac, 1964; DreyfusBrisac ef al., 1962; Loiseau et al., 1960) are still very much in the picture. Lack of differentiation between sleep and waking records is also considered abnormal, the more so the older the infant (Dreyfus-Brisac, 1964;Schroeder & Heckel, 1953b). Less definite abnormalities are prolonged flat periods (well over 10 seconds duration) in the track alternant pattern, over-organization with 7-8/sec rhythrric activity (Samson ef af., 1963; Samson-Dollfus ef al., 1964), and interhemispheric asymmetry in the sleep record (Samson er al., 1964); in the last, Samson proposed that the side of lower voltage is more likely to be the abnormal side, especially if arousal reactions fail to occur on that side. Seizures in this age group are usually focal Hith focal spike discharges or rronorrorphic alpha-like or delta waves in the EEG (Dreyfus-Brisac & Monod, 1960, 1964; Passouant, Cadilhac, & Ribstein, 1959), but brieftonic fits are occasionally seen (Harris & Tizard, 1960). The spikes are usually, but not always, of long period. The discharges are most often of 2-3/sec frequency in the first week post-term, increasing to 7 4 s e c by the third week (Passouant et af., 1959; Ribstein & Walter, 1958). Tonic seizure activity at blO/sec may be seen, followed by isolated clonic discharges (Passouant et al., 1959). There may be one focus or several independent foci. Spread of seizure activity is usually confined to one hemisphere or to the area of the contralateral hemisphere homologous to the primary focus (Dreyfus-Brisac & Monod, 1964; Passouant et al., 1959).As in older patients, occasional seizures are accompanied only by flattening of EEG tracings (Dreyfus-Brisac & Monod, 1964; Harris & Tizard, 1960). Grand ma1 seizures rarely occur in the neonatal period, and when they do they are not precisely of adult pattern (Dreyfus-Brisac & hnonod, 1960; Harris & Tizard, 1960; Passouant e f a f . ,1959).Petit ma1 seizures never occur in the first year of life, nor do the classical diffuse 3hec spike-and-wave complexes associated with them (Dreyfus-Brisac & Blanc, 1956; DreyfusBrisac & Monod, 1960; Passouant et a f . , 1959). Slow (I-2/sec) spike-andwave discharges (the “Petit Ma1 Variant” complexes of Gibbs) are rare, but can occur (Passouant et af., 1959). Discharges associated with myoclonic jerks are rare and atypical, resembling more the paroxysms seen in subacute leukoencephalitis than the classical polyspike-and-wave discharges of older patients (Passouant et al., 1959). c. LEG‘ Abnormalities at 3-4 Months Post-Term. Spikes, focal or diffuse flattening, focal or diffuse delta activity, and paroxysmal bursts are abnormal

Robert J . Ellingson as always. Early partial hypsarhythmic patterns may be seen (DreyfusBrisac & Blanc, 1956; Dreyfus-Brisac et al., 1961; Samson-Dollfus et al., 1964). Slow spike-and-wave complexes are somewhat more often seen than previously (Samson-Dollfus et al., 1964). Persistence of neonatal patterns as late as the third month probably indicates serious developmental retardation (Dreyfus-Brisac, Monod, Salawa, Ducas, & Mayer, 196 I). Absence of occipital organization while the baby is awake (the dominant occipital rhythm should appear at 3 4 months) is a suspicious variation. Continuous spindles during sleep, which may persist after arousal, have been reported by Kellaway (1952) to be associated with cerebral palsy. This may be the same phenomenon that the Gibbses call “extreme spindles,” which they have found to be most often associated with mental retardation (Gibbs & Gibbs, 1962, 1964). Focal and diffuse seizure discharges of the types previously described become gradually better organized during this period. Full-blown generalized tonic-clonic seizures can be observed with EEGs almost like those of adults, except that the rapid activity during the tonic phase is usually of lower frequency than in older patients. d. EEG A bnormalities at 6-12 Months Post-Term. The features described in the preceding section are still to be seen. Slow spike-and-wave and polyspike-and-wave discharges become better organized (Passouant et al., 1959: Samson-Dollfus et al., 1964). The 6/sec component of the 14 and 6/sec positive spike phenomenon can be seen in infants under 1 year of age, primarily during moderate to deep sleep (Gibbs & Gibbs, 1964). That this has not been more widely reported is possibly due to the fact that most workers studying infant EEGs use predominantly the bipolar recording technique, which is not optimal for recording the phenomenon. Samson-Dollfus et al. (1964) describe abnormally high-voltage fast activity resembling the extreme spindles of Gibbs. appearing after 6-7 months of age. It should be kept in mind that fast activity must be discounted if sedation has been used to induce sleep. The same workers have also suggested that absence or exaggeration of oscitant activity may be a sign of abnormality in this age period. Full-blown hypsarhythmia is seen from 6 months post-term (DreyfusBrisac & Blanc, 1956: Gibbs & Gibbs, 1952;Gibbs, Fleming, & Gibbs, 1954; Passouant et al., 1959; Samson-Dollfus et al., 1964). This pattern has been described by the Gibbses (1952) as follows: “Random high voltage slow waves and spikes. These spikes vary from moment to moment, both in duration and location. At times they appear to be focal, and a few seconds later they seem to originate from multiple foci. Occasionally the spike discharge becomes generalized, but it never appears as a rhythmically repetitive and highly organized pattern . . .” (Fig. 9). Hypsarhythmia is 76

Brain Electrical Activity in Infants

X C

ImPV

Fig. 9. Hypsarhyihmia at I I monihs of age. The patient displayed massive myoclonic seizures, some of which were observed during ihe EEG. The paiient also exhibited multiple phy.yical mal/ormations and was leihargic and developmentally retarded.

most often associated with minor-appearing seizures (variously called head nodding seizures, seizures in flexion, infantile spasms, massive myoclonic seizures, etc.), but sometimes with generalized convulsions. The prognosis is grave with mental retardation being the most common sequela. Motor impairment and continued seizures are also common sequelae. The death rate of about loo< is not insignificant (Gibbs et al., 1954). In addition to the seizures associated with hypsarhythmia, focal seizures and generalized convulsions continue to be encountered. Seizure patterns in the EEG come progressively more to resemble those classical patterns seen in older children and adults, though frequencies on the average are still a bit lower. The classical 3-per-second spike-and-wave pattern of petit ma1 is still not seen, and probably does not occur before 18 months post-term. Even then it is rare. EEG seizure patterns do not fully attain the organization seen in adult seizures until about 3 years of age (Passouant et al., 1959). 2. EEG Effects of the Birth Process Monod, Dreyfus-Brisac, Ducas, and Mayer (1960) reported a higher incidence of atypical and irregular neonatal EEGs among 46 infants delivered from breech presentations than among a group of 44 selected controls delivered from cephalic presentations. They emphasized that the significance of such irregularities is probably slight in cases in which rapid “normalization” occurs. Ellingson (1958) found relatively immature records with multifocal transients in two of seven breech babies. Liberson and Frazier (1962) compared the EEGs of newborns with and without birth complications delivered by natural and cesarian routes. Unfortunately, they did not distinguish prematures from full-terms in their report. The patterns particularly attended to were the presence of ( a )9-per77

Robert J . E l h g s o n

second alpha-like activity, ( b ) pronounced alternation of delta activity and silence, and (c)complex waves with sharp components. The results suggested that newborns born by cesarian section, but who were free of complications, “seemed to have a more ‘ideal’ EEG than those born by ‘natural’ birth, also without complications.” Ellingson (1958) observed no significant features in the EEGs of five cesarian babies, and subsequent review of the immediate neonatal EEGs of others has revealed no differences between this group as a whole and babies delivered naturally. He also found no effects of normal variations in duration of the second stage of labor upon EEG patterns in normal full-term babies. Rosen and Satran (1965) found 23% abnormal EEGs among I74 high-risk newborns. “High-risk” included 1 13 breech. forceps, cesarian, and vacuum extraction deliveries plus 6 1 cases of spontaneous cephalic deliveries with various prenatal problems (first trimester bleeding, diabetes, anemia, etc.). The abnormality rate among twenty controls was 9.5%. Since all of the infants were clinically normal, the figure of 2304 abnormality is high. In an earlier pilot study (1964). they obtained an abnormality rate of 32%. Several of the abnormalities (presumably spikes) illustrated in these papers look rather like the sharp positive phases of normal rhythmic waves occurring in bursts. Such bursts of rhythmic waves presenting a “semi-rectified” appearance are common in EEGs of infants. Ducas, Monod, Dreyfus-Brisac, Pajot, and Mayer (1962) found a relationship between the duration of postnatal apnea and incidence of disturbed EEGs in a study of infants who had to be resuscitated at birth. Contrary to earlier reports, recent studies (Ellingson. 1958: Liberson & Frazier. 1962) indicate that no effect of maternal anesthesia or analgesia can be detected in the neonate’s EEG when standard doses are used.

3 . The Clinical Prognostic Value of Infants’ EEGs Estimation of the prognostic value of infants’ EEGs requires longitudinal studies, of which there have not been many. Some tentative generalizations will be offered at the end of this section. a. The Prognostic Value ofEEGs in Undgjerentiated Groups of Infants. Engel (1965) found 78 abnormal EEGs in a series of 1409 newborns, 66 of whom showed focal spikes or paroxysmal bursts, and 12 of whom showed depression of activity. Of the 70 upon whom follow-up data were available after 1-3 years, 3 1 displayed definite neurological abnormalities. Monod and Dreyfus-Brisac ( 1962) reported on the grave prognostic significance of neonatal paroxysmal EEGs, those showing periods of absolute flatness interrupted by irregular polymorphic bursts often asynchronous over the two hemispheres. In their study, no infants with this pattern developed normally, and mortality in the first postnatal year was high. Monod, Salama, 78

Brain Electrical Activity in Infants

and Dreyfus-Brisac ( 1 962) emphasized the significance of abnormal EEGs recorded at 3-6 months post-term; all infants in their series with important alterations during this period suffered from encephalopathy. Likewise, Rossler (1963) reported that normalization of an abnormal neonatal EEG by 3 months post-term is a favorable prognostic sign, whereas persistence of abnormality is unfavorable. Samson-Dollfus et al. (1964) reported generally poor outcomes aniong subjects who displayed deteriorated EEGs before the age of 1 year: of twenty patients who later died, sixteen had abnormal EEGs; of twenty-one patients with encephalopathies, fourteen had abnormal EEGs; and of thirty-nine who developed normally to school age only two had abnormal EEGs. Ducas et al. (1962) reported a relationship between severity of neonatal EEG abnormality and severity of subsequent neurological deficit among I85 children who had had to be resuscitated at birth. Prediction was least good in the group that showed moderate EEG abnormalities, many of whom had developed normally. Presumably the neonatal EEG abnormalities in many of those cases were attributable to perinatal cerebral insults of a transient nature. Rapid normalization of the EEG would tend to suggest such conditions. A different approach was taken by Ellingson et al. (Ellingson, 1964a; Ellingson, Dutch, & McIntire, 1964), who reported on a @-year follow-up of prematures whose EEGs had been recorded in the neonatal period. None of the neonatal EEGs had been abnormal. Of the hfty-eight subjects upon whom detailed follow-up data were available, ten had died, twelve displayed physical (including neurological) abnormalities of congenital origin, five were clinically normal but had shown EEG abnormalities at some time postnatally, and thirty-one had no history of EEG or significant clinical abnormality. In no case could a member of any of the first threesub-groups have been identified from his neonatal EEG. The incidence of frank abnormalities in the later postnatal EEGs of abnormally developing infants was, however, significantly higher than that among those developing normally, but in some cases such abnormalities did not develop until after clinical abnormalities had been noted. The authors concluded that they had no evidence that the immediate neonatal EEG is of value “in identifying babies with congenital defects in whom those defects are not clinically manifested at, or near, the time of EEG.” A similar analysis of a larger number of full-term subjects awaits completion. b. The Value of EEGs in Infants Displaying Seizures. The occurrence of seizures in an infant is always cause for serious concern, but many infants suffering neonatal seizures later develop quite normally. EEGs can yield useful information in such cases, but like other tests their value is limited. EEG abnormalities recorded immediately or shortly after a seizure are of

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Robert J . Ellingson

no diagnostic or prognostic value (Dreyfus-Brisac et a/., 1958a) but, ifthe interseizure EEG is abnormal, the prognosis is poorer than if the EEG is normal. In a follow-up study of patients who suffered neonatal seizures Tibbles and Prichard (1965) found that +of those who had had abnormal EEGs were dead and only -f- were developing normally, whereas of those with normal EEGs less than & were dead and f were developing normally. Figures for those with borderline EEGs were intermediate. In a similar follow-up study, Keith (1964) found that eleven of twelve patients who died had had abnormal EEGs, fifteen of seventeen mentally retarded patients had had abnormal EEGs, seven of sixteen patients who were alive and seizure-free had had normal EEGs, and eight of eleven mentally normal patients had had normal EEGs. Harris and Tizard (1960) found that patients with bilateral EEG abnormalities have significantly poorer outcomes than patients with unilateral abnormalities. All investigators agree that the prognosis is poorer in the presence of persistent EEG abnormality than if the EEG becomes normal. Fischgold and Berthault (1953) and Dreyfus-Brisac er al. (1961b) point out that persistence of EEG abnormality into the second quarter of the first year has grave significance, and the latter recommend a second EEG between 3 and 6 months of age. It is also generally agreed that history and clinical status are more important in prognosis than the EEG (del Mundo Vallarta & Robb, 1964; Harris & Tizard, 1960; Prichard, 1964). Persistence of seizures themselves is cause for still greater concern than persistence of EEG abnormality. Harris and Tizard found significantly poorer outcomes in patients whose neonatal seizures persisted for more than 2 days than among those whose seizures persisted for less than 2 days. Prichard (1964) found propbrtionately poorer outcome the longer neonatal seizures persisted, the outcome being especially grave if seizures persisted for more than 14 days. It should be noted that early death is not at all a rare sequela of neonatal convulsions. The occurrence of status epilepticus in newborns is a very grave sign. In a 1-year follow-up study Dreyfus-Brisac and Monod (1964) found that thirty of fifty-seven patients were dead, fifteen displayed severe neurological and behavioral sequelae, and only seven were normal. A history of intrauterine seizures is similarly grave. This diagnosis depends entirely upon the mother’s report (no EEGs have been recorded in utero on such patients as yet), and the question of reliability is an important one. Consequently only a handful of such cases have been reported (Badr El-Din, 1960; Dutch, 1966; Isler, 1964). The results are uniformly depressing. All of the nine patients reported displayed seizures postnatally, all showed neurological defects, all who survived early infancy were mentally retarded,

80

Brain Electrical Activity in Infants

and four had died by the time the reports were written. Of the five cases reported by Dutch, two had hypsarhythmic EEGs. c. Summary. The following tentative generalizations are offered. (a) A normal EEG in infancy is of limited prognostic value. (b) A n abnormal neonatal EEG may reflect either transient physiological disorder or permanent physiological disease or structural damage. Repeat EEGs should be done after a short interval, and again between 3 and 6 months of age. Rapid normalization is a favorable prognostic sign. Persistence of abnormality, especially beyond 3 months of age, is unfavorable. (c) If an infant has had seizures in the neonatal period, an abnormal interseizure EEG warrants a poorer prognosis than a normal EEG, and persisting EEG abnormality is of still graver significance. The more clear-cut and extensive the EEG abnormality the poorer the prognosis. (d)Hypsarhythmia is of very grave significance. (e) However, an abnormal EEG, even hypsarhythmia, never warrants hopelessness. v) Clinical history and status are more important in prognosis than the EEG or any other single test of brain function.

111. Brain Electrical Responses in Infancy Brain electrical responses can conveniently be divided into two categories: ( a ) nonspecific responses, or those responses which can be more or less readily elicited by stimuli of any modality, and which consist either of alteration of background brain wave activity (usually blocking of rhythmic or slow potentials) or of the appearance of transient potential (voltage) changes of definable form and topographic distribution, and (b) specific responses, or those which can be elicited by stimuli of only one modality, and which consist of the appearance of transient potential changes of definable form in the appropriate input system. In studying human subjects, the investigator is almost always restricted to recording from the surface of the head, which essentially means the cerebral cortex (however, see Goldring, Sugaya & O’Leary, 1964). A . NONSPECIFIC RESPONSES

Most reports concerning nonspecific responses in the EEGs of newborns have been casual, merely pointing out that such responses have been seen. Somewhat more detail has been given by Dreyfus-Brisac and Blanc (1956) and by Ellingson ( 1 958), but no extensive systematic studies have been done. In the neonate, somesthetic stimuli are most effective in eliciting non-

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Robert J . Ellingson

specific responses, auditory stimuli next, and visual stimuli least effective (Ellingson, 1960b). Dreyfus-Brisac and Blanc (1956) reported that no nonspecific responses to stimuli can be observed before 8 months conceptional age. After 8 months conceptional age, three types of responses occur following auditory stimuli: ( a ) generalized flattening with or without behavioral arousal, (b) diffuse bursts of poorly differentiated irregular potentials and (c) double responses consisting of an amplification of sleep potentials followed by flattening. Ellingson (1958) observed the first type of response in 50%, and the second and third types in 20%, of full-term neonatal records, but never to all stimuli presented during a record. The first type of response was also elicited by visual stimulation in 15% of his neonatal records. Engel (1961) obtained responses to auditory stimuli in 87”/,of full-term newborns and in 68x of prematures at latencies of 100-200 msec. The difference from Ellingson’s results is probably due to differences in stimulus intensity. From 3 months post-term, auditory or somesthetic stimuli during sleep elicit (a) an increase in the amplitude of sleep waves or (b) sharp slow negative transients, which in deep sleep may be followed by K-complexes (Dreyfus-Brisac & Blanc, 1956). At 1 year, diphasic vertex transients of high amplitude, slow frontal transients of moderate amplitude, and high-voltage diverse occipital slow waves may be elicited (Dreyfus-Brisac & Blanc, 1956). Ellingson (1958, 1964a) observed vertex negative transient responses to auditory stimuli with peak latencies of about 200 msec in 25%,of fullterm neonates. Barnett and Goodwin ( 1965) studied responses to auditory click stimuli of various magnitudes in eighteen 2-4-day-old full-term babies, employing a computer averaging method of recording. The responses, presumably of vertex origin, consisted of several minor voltage deflections followed by a major positive and then a negative wave. The average latency to the peak of the positive phase was 267 msec. The average peak-to-trough amplitude of the major positive-negative complex was 19 pV at 65 db above adult auditory threshold. Amplitude diminished as stimulus intensity decreased. Unless the subject is already awake and alert, another type of nonspecific reaction to stimuli is a shift of EEG pattern to one associated with a less profound level of the wakefulness-sleep cycle. This effect can occur whether or not a nonspecific response of the types described above occurs. For example, a tract! alternunt (quiet sleep) pattern may shift to a diffuse slow (active sleep) pattern. If the stimulation is sufficiently intense and the infant’s threshold is sufficiently low, he may awaken and show a low-voltage pattern if he is in the neonatal period, or first a hypersynchronous and then a low-voltage pattern if he is older (Kellaway, 1957).

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Brain Electrical Activity in Infants

B. SPECIFIC RESPONSES 1. Visual Evoked Responses Specific cortical visual evoked responses, which are readily elicited by brief flashes of light, can be observed in the vicinity of the occipital pole. If the light stimulus is of longer duration (some seconds), an “on response’’ will occur at the onset of the stimulus and an “off response” will occur after the termination of the stimulus (Ellingson, 1958). The latter has not been very extensively studied. Methods of recording cortical evoked responses in human newborns have been discussed by Ellingson (1964b, 1967). The recording of visual evoked responses from newborns was first reported by Ellingson (1957). Several subsequent reports have appeared (Dustman & Beck, 1966; Ellingson, 1958, 1960b, 1964a, b, 1966; Engel, 1961, 1964b, 1965; Engel & Butler, 1963; Ferris, Davis, Hackett, & Dorsen, 1966; Hrbek & Mares, 1964, 1965). Recording by a computer summating technique was first reported in 1964 (Ellingson, 1964a, b).

a. Time of Firs? Appearance. All normal full-term human newborns display visual evoked responses. They cannot always be detected against higher-voltage background activity in raw tracings, but if summating or averaging techniques are used, they are always seen (Ellingson, 1966b; Ferriss et al., 1966; Hrbek & Mares, 1964). Ellingson (1960b) has recorded responses in a premature of 28 weeks conceptional age and Engel (1964b) in one of 24 weeks. The most that can be said at present is that the response probably appears prior to the end of the second trimester of pregnancy. b. Waveform. When the response first appears in fetal life, it consists of a monophasic wave of negative polarity at the active (occipital) electrodes (Fig. IOA). Sometime between 32 and 41 weeks conceptional age, apositive wave appears before the negative wave (Fig. 10B).At 40 weeks conceptional age, only 22, of infants show the negative phase alone (Ellingson, 1960). In many subjects, the initial positive phase is double, or positive-negativepositive (Fig. 10D). Failure to record the earlier positive wave, which may be of very low voltage, may be due to insufficient sensitivity of the method employed. Ferriss et al. (1966) found the double positive phase in all responses recorded by a computer summating technique. Later, a still earlier negative wave appears, which is infrequently seen as early as 40 weeks conceptional age. By the end of the first year many subjects show a polyphasic response resembling that seen in the adult (Fig. 10E). Rarely, this pattern is seen as early as the first month post-term, but, on the other hand, it may not be seen until 2-3 years of age.

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Robert J . Ellingson

E

0

.

.

.

.

500

Msec

Fig. 10. Tracings of summated responses to brief light flashes, recorded by means of an analog summating computer, in five subjects. Each tracing represents the algebraic sum of sixty responses derived fiom a midoccipital-lefr ear lobe lead. Downward deflections signgy relative positivity at the occipital lead. A . Long-latency negative response commonly seen in the early premature: rare at term. B and C. Positive-negative responses commonly seen at term. D. Double-positive-negative response o/ien seen at term. E. Complex response very rarely seen at term but common by the end of the first year. The roman numeral designations are those of Cig&nek( I 961 I.

It is emphasized that there are considerable individual differences in waveform a t any chronological age. Furthermore. level of consciousness (Ferris er af., 1966) and variation of stimulus parameters, such as intensity (Ellingson, 1966b), can cause apparent changes in waveform by affecting the amplitudes of the various components of the evoked response differently. c. Amplitude. The amplitudes of the smallest components of the evoked response as recorded from the scalp can be as low as 1 p V , and can be detected only by summating techniques. The amplitude from the trough of the major positive deflection to the peak of the major negative deflection is often as great as 50 pV in the newborn and in a few may reach 100 pV (Ellingson, 1960b; Hrbek & MareS, 1964). Such amplitudes are rarely seen in adults. With such exceptions the amplitudes of evoked responses in infants at term are not higher on the average than those of older children and adults (Dustman & Beck, 1966). Judging from animal data (Ellingson, 1964b), response amplitudes are probably lower when the responses first appear

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Brain Electrical Activity in Infants

during fetal life, but that apparently occurs in humans at a conceptional age earlier than anyone has yet been able to record them. d. Topographical Distribution. The shorter latency components of the evoked response can be recorded only from the occipital area. This is also true of the longer latency components at term, but by 12 weeks they may be seen as far anteriorly as the rolandic area, where they may be confused with nonspecific vertex responses. These longer latency components are probably subserved by a separate and more diffuse input system than the shorter latency components. e. Latencv. Mean latency to the trough of the major positive wave of the visual evoked response is 185-190 msec at term (Ellingson, 1960b, 1966b; Ferriss et al., 1966; Hrbek & Mares, 1964). This is approximately twice the latency of these responses among adults. Engel has reported latencies of around 155 msec to the beginning of the major positive deflection (Engel, 1961. 1964b). Reported standard deviations are around 2&25 msec (Ellingson, 1960b, 1966b; Engel, 1964b; Hrbek & Mares, 1964). Engel (1965) has reported shorter latencies among non-whites than whites and among females than males (p < .001), based upon analyses of variance of data for newborns of 3 0 4 4 weeks conceptional age. Our data (unpublished) on newborns at term show means of 189.9 msec for males and 181.4 msec for females (p < .Ol), and means of 185 msec for whites and 183 msec for non-whites (not significant). Decrease of evoked response latency with age has been reported in detail by several investigators (Ellingson, 1960b, 1966b; Engel, 1964b, 1965; Engel & Butler, 1963; Ferriss et al., 1966; Hrbek & MareS, 1964). There is already a significant decrease in latency during the first few days after term birth (Ellingson, 1960b; Hrbek & Mares, 1964). Data from two of our studies are plotted in Fig. 1 1 . Among prematures, mean latencies to the peak of the major positive deflection are very close to 220 msec at 3 4 3 5 weeks conceptional age, 210 msec at 3&37 weeks, and 200 msec at 38-39 weeks. Mean latencies are 185 msec at 4 0 4 1 weeks conceptional age and 180 msec at 42-43 weeks. They then drop rapidly for the next month or more. Most of the decrease takes place before 13 weeks of age, but a further gradual decrease continues until sometime after the end of the first year of life. Standard deviations of the latency distributions increase from 20 msec at term to 30.msec during th; period of rapid latency decrease at 5-6 weeks post-term, and then decrease to less than 15 msec for the remainder of the first year (Ellingson, 1966b). The two-legged nature of the developmental curve for visual evoked response latency in man has been replicated by Ellingson (Fig. 11) and recently confirmed by Ferriss et al. (I 966). Engel has plotted similar curves for latency to the beginning of the major positive deflection for the period of 30-44

85

Robert J . Ellingson

220 200 -

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; ; 180-

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Fig. 11. Two plots of visual evoked response latency against age in infants to 52 weeks post-term. Latencies were measured to the trough of the major positive dejection of the response as recorded at the occiput. The solid dots and continuous line are a plot of data derived from ink-writer tracings (Ellingson. 19Wb). The open dots are a plot of’recent longitudinal data derived by means of a summating computer on twenty-one subjects. The open dorsjor 3 4 und 7-8 weeks are obsnrred because theyfall directly on top of closed dots. The vertical lines passing through the open dots signfi f l S.D.for the group of twenty-one subjects. Latency to a comparable component of the adult evoked response is shown at the far right for comparison.

weeks conceptional age (Engel, 1964b, 1965; Engel & Butler, 1963). The slope of his curves over that period is somewhat steeper than the slope of the corresponding segment of Ellingson’s curves. The latencies of prematures are significantly greater than those of fullterm babies at term and for several months thereafter (Ellingson, 1964b; Engel, 1965), but they catch up in the second 6 months post-term (Ellingson, 1964b). Visual evoked response latency has also been plotted against body weight (Ellingson, 1960b, 1966b; Engel, 1965; Hrbek& MareS, 1965). In Ellingson’s earlier report (1960b), it appeared that this relationship was not a monotonic one; but the later reports (Ellingson, 1966b; Hrbek & Mares, 1965) show an inverse linear relationship between latency and body weight up to 6 kg, after which point the curve is almost flat. Enael and Butler (1963) obtained a correlation of 0.49 between conceptional age and birth weight and one of -0.43 between conceptional age and evoked response latency, and suggested that evoked response latency is as good a predictor of conceptional age as birth weight is.

f. Fatigability. A striking characteristic of visual evoked responses in the newborn is their fatigability, by which is meant relative inability to respond to stimuli arriving soon after a preceeding stimulus (Fig. 12). 86

Brain Electrical Activity in Infants

FLASH

SE c

1

I

Fig. 12. Responses to repetitive light flashes at I j a s h per second, at a Conceptional age of 38 weeks, showing fatigability. Note the fluctuation of amplitude of responses subsequent to the first, full-amplitude response. Inion-vertex derivation. Downward deflection indicates relative positivity at the inion.

In some infants, especially prematures, 4-5 (or more) seconds must be allowed to elapse between stimuli lest the second and succeeding responses fail to occur. At 40 weeks conceptional age, one in ten infants will respond well at rates of I/sec; almost none will respond at 2/sec (Ellingson, 1960b). Hrbek and Mare5 (1964) point out that later components of the response may be affected at a rate of l/sec, even though earlier components may not be. Ability to respond at higher rates of stimulation improves rapidly after birth. The term “fatigability” may have been ill-chosen, implying as it does that the mechanism of the effect is the exhaustion of energy supply and/or the accumulation of toxic by-products of the reaction. Although not impossible, it seems unlikely that such is the mechanism. It also seems unlikely that end-organ (retinal) adaptation plays an important role, since the flicker electroretinogram in newborns will follow stimuli at much higher rates than will cortical evoked or “following” responses. Prolonged refractoriness of immature afferent axons (due to slow rates of membrane repolarization) or increased geniculate and cortical post-excitatory depression (hyperpolarization) in the immature system seem more likely mechanisms. If the latter were the explanation, the “fatigability” effect should be greater the more intense the stimuli, but the author knows of no data bearing on this point. A final mechanism could be an increased efferent inhibitory influence on the sensory end-organ and/or relay nuclei (Livingston, 1959). This too seems unlikely, because it would imply greater rather than less efficiency of a portion of the immature nervous system, and because of the aforementioned ERG data. It might have been better if the somewhat less specific term “habituation” had been adopted for this effect, but the term “fatigability” seems to have caught on in the developmental neurophysiology literature. g. Evoked Response Changes in Brain Disorders. Hrbek and MareS (1964) reported a reduced incidence of visual evoked responses among brain damaged infants. Engel and Butler (1963) found no differences in response latency between normal and abnormal newborns, and Ellingson (1964b) reported no differences in latency at birth between infants later displaying

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congenital abnormalities and those not doing so. The possibility that there may be differences in rates of habituation between normal and brain damaged infants has not been investigated.

h. Summary. Neonatal visual evoked responses in the human differ from mature responses in the following ways: (a) they are of simpler waveform, (b) they are of longer latency, (c)they display greater fatigability, and (4they tend to be topographically less widespread. The visual projection system undergoes its most rapid maturation during the period from term birth to 13 weeks. Development continues however at a more leisurely pace for some time. We cannot indicate as yet the age at which the system reaches full maturity, but it is not unlikely that, like the age of alpha maturation, it varies widely among individuals. Since there is not space to present the results of studies of the development of visual evoked responses in non-human species, it must suffice here to say that while there are some differences in details as would be expected among species, the pattern of evoked response development is in general very similar (Ellingson, 1964b). 2 . Photic Following Responses Another type of response of the cortex to repetitive photic stimulation is the so-called “following response” (also sometimes called the “driving response”), which consists of rhythmic potential fluctuations at the frequency of the stimulation. These are maximal in the occipital area, but may occasionally be more widespread. That they are not the same phenomenon as the evoked responses described in the preceding section is indicated by the fact that the latter can occur quite discretely while the rhythmic response is also present (Ellingson, 1960b; Glaser & Levy, 1965). Whether the afferent pathways involved in the production of the two phenomena partly overlap or are completely independent is not known. a. Incidence of Following Responses. Following responses have been studied in infants much less completely and extensively than evoked responses. Dreyfus-Brisac and Blanc (1956) reported that they do not occur before 3 months post-term. Ellingson (1960b) reported observing them in 5% of newborns. Glaser and Levy (1965) observed them in 4804 of healthy 1-6-dayolds and in 33% of “stressed” infants. Eichorn (195 1) found an incidence of 87% in infants 7-81 days old, and Mirzoyants (1961) an incidence of 17.5% in infants 14-30 days old. Hrbek and MareS (1964), using Dawson’s superimposition technique, reported incidences of 6 3 x in 1-day-olds, 852, in all prematures, and 90% in 4-6-day-olds. Why such great differences in results? All investigators are agreed that the following response is not easy to elicit in infants, and when seen is

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relatively weak and evanescent. Therefore, conditions of stimulation and recording methods are especially important, and these have varied greatly among studies. The most important factors appear to be stimulus frequency, stimulus intensity (eyelid position and distance of the light source from the eyes are important determinants of stimulus intensity), background illumination (a stimulus of moderate intensity may be effective against low but not against high background illumination), and sensitivity of the method of recording. It would seem a reasonable inference that if intense stimuli and a computer summating or averaging method of recording responses are used, the incidence of following, even in neonates, should be found to be high, if not lOOo/,. Recent data from the author’s laboratory indicate that this is indeed the case. b. Frequency of the Following Response. It seems agreed that the range of frequencies over which following will occur in the full-term neonate is 1-5/sec, and that the optimal frequency is close to 3/sec (Eichorn, 1951: Ellingson, 1960b; Glaser & Levy, 1965; Hrbek & MareS, 1964). Harmonic and subharmonic responses are rare (Ellingson, 1960b; Glaser & Levy, 1965). Mirzoyants (1961) reports that following at higher than usual frequencies can be induced by a procedure which might be called “priming.” The subject is first stimulated at a low frequency (e.g., 3/sec) which will elicit following; once the following response is established the stimulus frequency is suddenly changed to a high level (e.g., 20/sec), and following may then be seen at the higher frequency. c. Changes in Following Responses Related to Age. Eichorn (195 1) reported that the frequencies at which following can be elicited increase with age. Mirzoyants (196 1) reported optimal driving frequencies of 0.3-3/sec at 2-3 months of age, &7/sec at 4-9 months, and I&ll/sec at 8-12 months. Ellingson (1960b), however, found only a slight increase in optimal driving frequency from birth to 6 months (averages of 3.7/sec and 4.5/sec, respectively). It should be pointed out that in both studies only a few subjects displayed following. All that can be said from these reports, and by extrapolating from data on older children, is that there is a progressive increase in frequency of the following response with age. It has been pointed out that the optimum frequency of following tends to be closely related to the frequency of the dominant rhythm during wakefulness (Glaser & Levy, 1965; Mirzoyants, 1961). d. EEG Abnormalities Induced by Photic Stimulation. It is well known that abnormal EEG activity can be induced by repetitive photic stimulation (flicker) at certain frequencies in some persons, especially some epileptics. Samson et al. (1963) state that such responses are never seen before the age

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of 2-3 years. Ellingson (1964a) reported inducing spike-and-wave responses at the frequency of stimulation in five infants under 1 year old. These responses were always confined to the occipital area and never outlasted the stimulation. One of the subjects displayed spontaneous diffuse spikeand-wave discharges several years later, but none has ever had seizures.

3. Auditory and Somesthetic Evoked Responses As far as can be ascertained, no one has as yet successfullyrecorded primary auditory evoked responses (that is, those originating in the region ofHeschl’s gyrus) from the scalp in a human subject, even using summating techniques. It may be that the buried position of the primary auditory cortex will make such recording impossible. All reports to date have obviously dealt with nonspecific responses to auditory stimuli. Even the short-latency lowvoltage components of the responses reported by Barnet and Goodwin (1965) are unlikely to be primary responses in view of the loci of their recording electrodes, and the authors do not claim that they are. Primary auditory responses, if it should prove possible to record them, should be picked up from the near vicinity of electrodes T3 and T4 (International 10-20 System) and should have a latency of less than 25 msec in adults. There have been no reports of attempts to record somesthetic evoked responses in infants.

IV. Conclusion This review has concentrated upon descriptive aspects of the developmental electrophysiology of the human brain. Much relevant data derived from animal studies is also to be found in the literature, but space limitations have not permitted its introduction here. It remains for future investigations to relate such data systematically to anatomical development and other physiologicaland behavioral processes in the developing infant. For example, our extensive knowledge of the electrophysiological ontogenesis of the visual system can be related to the onset and development of visuomotor behavior (tracking, reaching for objects, etc.). Critical periods could be sought. For example, the available data suggest that at age 3 4 months the visual system is ready to participate in complex perceptual processes. It is the epoch during which the dominant occipital rhythm appears and just prior to which the latency of visual evoked responses approaches the adult level; anatomical studies have shown striking development of occipital cortical neurons between birth and 3 months (Conel, 1939, 1947). It should be possible to devise or adapt test situations involving a range of visual-motor performances from the simplest to the more complex with which to measure the capacity of the infant visual

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system before, during, and after this probable critical period (Cantor, 1963, pp. 5-13; Lipsitt, 1963). Further information is obviously needed on the physiological development of the auditory and somesthetic sensory systems as well as of high level motor functions. Developmental relationships among the conventionally designated “systems” of the brain, and the development of interaction among these systems, have been little studied. Such studies will be of great importance, since complex behavior, such as conditioning and learning, necessarily involve constant interaction of widespread portions of the nervous system. At the same time, more sophisticated methods must be developed for analyzing brain electrical data of infants. Since modern recordingtechniques generate much more data than can be conveniently managed, data reduction is essential. Some of the analytical methods applied to adult human and animal brain electrical activity can be adapted to the study of the infant brain (Adey, 1965; Brazier, 1965). However, it must be kept in mind that, unless the investigator is wary and selective, computers can themselves generate unlimited quantities of derivative data, which may be less illuminating than the raw data from which they are derived, and at the risk of straying rather far from the realities of physiology. The ultimate goal is integration ofknowledgein the fieldsofdevelopmental neuroanatomy, neurophysiology, neurochemistry, neurology, and psychology. The recent increase of interest in these areas (Himwich & Himwich, 1964: Kellaway & Petersen, 1964; Minkowski, 1966; Purpura&SchadC, 1964; Sobotka, I96 I), and the interdisciplinary character of that interest, give promise that much more will soon be known about brain development and function in the perinatal period.

REFERENCESJ Adey, W. R . Computer analysis in neurophysiology. In R. W. Stacy %I B. D. Waxman (Eds.), Computers in biomedical research. Vol. I . New York: Academic Press, 1965. 4. 223-263. Aresin, L. Beitrag zur embryonalen Elektroenzephalographie. Conj6nia Neurol., 1962, 22, 121-1 27. Badr El-Din, M. K. A familial convulsive disorder with an unusual onset during intrauterine life. J. Pediat., 1960, 56, 655-657. Barnett. A. B.. & Goodwin. R. S. Averaged evoked electroencephalographic responses to clicks in the human newborn. Electroencephalog. din. Neurophysiol., 1965, 18,441-450. Bartoshuk. A . K.. & Tennant, J. M. Human neonatal EEG correlates of sleep-wakefulness and neural maturation. J . psychiat. Res., 1964, 2, 73-83. ’This is a selected, rather than an exhaustive, list of references. Abstracts and brief articles have been omitted if more comprehensive reports of the same data appeared later. Reports which have contributed no significant new information have also been omitted.

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Robert J . Ellingson Bern stin e , R . L . Fetal electrocardiography and electroencephalography. Springfield, I I I. : Charles C. Thomas, 1961. Bernstine, R. L., & Borkowski, W. J. Foetal electroencephalography. J . Obstet. Gynaecol. Brit. Empire. 1956, 63, 275-279. Bernstine, R. L., Borkowski, W. J., & Price, A. H . Prenatal fetal electroencephalography. Amer. J. Ohstet. Gynecol.. 1955, 70, 623-630. Bickford, R. G., Jacobson, J. L., & Cody, D. T. R. Nature of average evoked potentials to sound and other stimuli in man. Ann. N. Y. Acad. Sci., 1964, 112, Art. I , 204-223.

Borkowski. W. J., & Bernstine, R. L. Electroencephalography of the fetus. Neurology, 1955, 5, 362-365. Brazier, Mary A. B. The application of computers to electroencephalography. I n R. W. Stacy & B. D. Waxman (Eds.), Computers in biomedical research. Vol. 1. New York: Academic Press, 1965. Pp. 295-315. Canova. G., & Cossandi, E. L’elettroencefalogramma nel neonato immaturo. Riv. clin. Pediat., 1956, 107, 271-276. Cantor, G. N. Responses of infants and children to complex and novel stimulation. I n L. P. Lipsitt & C. C. Spiker (Eds.), Advances in child development and behavior. Vol. 1. New York: Academic Press, 1963. Pp. 1-30. CigBnek. C. The EEG response (evoked potential) to light stimulus in man. Electroencephalog. clin. Neurophysiol., 1961, 13, 165-172. Conel, J. L. The postnatal development of the human cerebral cortex. Vol. I . The cortex of the newborn. Cambridge, Mass.: Harvard Univer. Press, 1939. Conel, J. L. The postnatal development of the human cerebral cortex. Vol. Ill. The cortex of the three-month infant. Cambridge, Mass.: Harvard Univer. Press, 1947. Delange, M., Castan, P., Cadilhac, J., & Passouant, P. Les divers stades du sommeil chez le nouveau-nt et le nourisson. Rev. Neurol., 1962. 107, 271-276. del Mundo Vallarta, J., & Robb, J. P. A follow-up study of newborn infants with perinatal complications. Neurology, 1964, 14,413424. Dreyfus-Brisac. C. Activitt tlectrique ctrtbrale du foetus et du trks jeune prtmaturt. Proc. 4th int. Congr. Eleciroencephalog. clin. Neurophysiol., 1957, 163-1 71. Dreyfus-Brisac, C. The electroencephalogram of the premature infant. World Neurol., 1962, 3, 5-15. Dreyfus-Brisac, C. The electroencephalogram of the premature infant and full-term newborn: Normal and abnormal development of waking and sleeping patterns. In P. Kellaway & 1. Peterson (Eds.), Neurological and electroencephalographic correlative studies in infancy. New York: Grune & Stratton, 1964, Pp. 186-207. Dreyfus-Brisac, C., & Blanc, C. Electro-enckphalogramme et maturation ctrtbrale. Enciphale. 1956,3, 205-245.

Dreyfus-Brisac, C., & Monod, N. Aspect kvolutif de I’klectrogkntse ckrtbrale chez I’enfant. Rapports Premier Congr. Europien Pido-Psychiat., 1960, 3%5 1. Dreyfus-Brisac, C.. & Monod, N. Electroclinical studies of status epilepticus and convulsions in the newborn. In P. Kellaway & 1. Petersen (Eds.), Neurological and electroencephalographic correlative studies in infancy. New York Grune & Stratton, 1964. Pp. 250-272. Dreyfus-Brisac, C., & Monod, N. Sleep of premature and full term neonatepolygraphic study. Proc. royalSoc. Med., 1965, 58.6-7. Dreyfus-Brisac, C., Samson, D., & Fischgold, H. Technique de I’enregistrement EEG du prkmaturt et du nouveau-nt. Electroencephalog. clin. Neurophvsiol., 1955, 7 . 429432. Dreyfus-Brisac, C:. Blanc, C., & Kramarz, P. etude klectroenckphalographique du sommeil spontant de I’enfant atteint de convulsions avant trois ans. Rev. Neurol., 1958, 99, 54-67. ( a )

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Brain Electrical Activity in Infants Dreyfus-Brisac, C., Samson, D., Blanc, C., & Monod, N. L’eltctroenctphalogramme de I’enfant normal de moins de 3 ans. Prudes Nio-Narales, 1958.7, 143-175. ( b ) Dreyfus-Brisac, C., Dargassies, S., & Minkowski, A. L’examen neurologique et I’electroencb phalogramme du foetus, base d’une neurologie du dkveloppment. Plzefisky Lekabsky Sbornik, 1961. Suppl. 3, 181-188. (a) Dreyfus-Brisac, C., Monod, N., Salama, P., Ducas, P., & Mayer, M. L’EEG dans les six premiers mois de la vie, aprks ranimation prolongte et ktat de ma1 nto-natal Proc. 5rh int. Cong. Electroencephalog. din. Neurophysiol.. Excerpta Med., Int. Congr. Ser., 1961, 37,228-230. (b) Dreyfus-Brisac, C., Flescher, J.. & Plassart, E. L’tlectroenctphalogramme: Critkre d’age conceptionnel du nouveau-nk h terme et prtmaturk. Biol. Neonatorum, 1962, 4, 154173.

Ducas, P., Monod, N., Dreyfus-Brisac, C., Pajot, N., & Mayer, M. Etude tlectroenctphalographique de 185 enfants rtanimts h la naissance. Aech. Framises Pediarrie, 1962, 1057-1085.

Dustman, R. E., & Beck, E. C. Visually evoked potentials: Amplitude changes with age. Science, 1966, 151, 10134015. Dutch, S. J. Prenatal convulsions: Clinical and electroencephalographic correlations. Electroencephalog. din. Neurophysiol., 1966. 21, 403. Eichorn, Dorothy H. Electrocortical and autonomic response in infants to visual and auditory stimuli. Unpublished doctoral dissertation, Northwestern Univer., 195 I . Ellingson, R. J. “Arousal” and evoked responses in the EEGs of newborns. Proc. Isr inr. Congr. neurol. Sci., 1957,3, 57-60. Ellingson, R. J. Electroencephalograms of normal, full-term newborns immediately after birth with observations on arousal and visual evoked responses. Elecrroencephalog. din. Neurophysiol., 1958, 10, 31-50. Ellingson, R. J. Suggestions on recording EEGs of newborns. Spike & Wave, 1960,9,9-12. (a) Ellingson, R. J. Cortical electrical responses to visual stimulation in the human infant. Elecrroencephalog. din. Neurophysiol., 1960, 12, 663-677. ( b ) Ellingson, R. J. Studies of the electrical activity of the developing human brain. In Williamina A. Himwich & H. E. Himwich (Eds.), Progress in brain research. Vol. 9. Developingbrain. Amsterdam: Elsevier, 1964. Pp. 26-53. ( a ) Ellingson, R. J. Cerebral electrical responses to auditory and visual stimuli in the infant (human and subhuman studies). In P. Kellaway & I. Petersen (Eds.), Neurologicaland elecrroencephalographiccorrelarive srudies in infancy. New York: Grune & Stratton, 1964. Pp. 78-1 16. ( b ) Ellingson, R. J. Regional physiology of the central nervous system. In E. A. Spiegel (Ed.), Progress in neurology andpsychiatry. New York: Grune & Stratton, 1965, Pp. 57-85. Ellingson, R. J. Development of visual evoked responses in human infants recorded by a response averager. Electroencephalog. d i n . Neurophysiol., 1966,21,40344. Ellingson, R. J. Methods of recording cortical evoked responses in human infants. In A. Minkowski (Ed.), Regional development of the brain in early life. Oxford: Blackwell, 1967, Pp.413435.

Ellingson, R. J., Dutch, S. J., McIntire, Matilda S. A longitudinal study of EEG development in human prematures. Elecrroencephalog. din. Neurophysiol., 1964, 17, 71 1-712. Engel, R. Evaluation of electroencephalographic tracings in newborns. Journal-Lancer, 1961, 81, 523-532.

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Goldie, L. Sleep cycles in premature infants. Develpm. Med. Child Neurol., 1965,7,317-318. Goldring, S.. Sugaya, E., & O'Leary, J. L. Maturation of evoked cortical responses in animal and man. In P. Kellaway & 1. Petersen (Eds.), Neurological andelectroencephalographic correlative studies in infamy. New York: Grune & Stratton, 1964. Pp. 68-77. Harris, R., & Tizard, J. P. M. The electroencephalogram in neonatal convulsions. J. Pediat., 1960,57, 501-520.

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Brain Electrical Activify in Infants Kellaway, P. Ontogenetic evolution of the electrical activity of the brain in man and animals. Proc. 4th inr. Congr. Electroencephalog. elin. Neurophysiol., 1957, 141-1 54. Kellaway, P., & Fox, B. J. Electroencephalographic diagnosis of cerebral pathology in infants during sleep. I. Rationale, technique, and the characteristics of normal sleep in infants. J. Pediat., 1952. 41. 262-287. Kellaway, P., & Petersen, 1. (Eds.) Neurological and electroencephalographic correlative srudies in infan?!. New York: Grune & Stratton, 1964. Liberson, W. T., & Frazier, W. H. Evaluation of EEG patterns of newborn babies. Amer. J . Ps)tchiat., 1962, 118, 112S-l131. Lindsley, D. B. A longitudinal study of the occipital alpha rhythm in normal children: Frequency and amplitude standards. J. genet. Psychol., 1939, 55, 197-213. I.indsley, D. B. Heart and brain potentials of human fetuses in utero. Amer. J . Psycho/., 1942, 55,412416. Lipsitt, L. P. Learning in the first year of life. In L. P. Lipsitt & C. C. Spiker(Eds.), Advances in child development and behavior. Vol. 1. New York: Academic Press, 1963. Pp. 147-195. Livingston, R. B. Central control of receptors and sensory transmission systems. In J . Field, H. W. Magoun, & V. E. Hall(Eds.), Handbookofphysiology.Sect. I: Neurophysiology. Vol. I . Washington, D. C.: American Physiological Society, 1959. Pp. 741-760. Loiseau, P., Aussaresses, M., & Verger, P. Essai de corrtlations klectroclinques dans la ptriode immkdiatement postnatale chez le prkmaturt. Rev. Neurol., 1960, 103.236242. Mai, H., & Schaper, G. Elektrencephalographische Untersuchungen an Friihgeborenen. Ann. Paediat., 1953, 180, 34S-365. Mai, H., Schutz, E., & Muller, H. W. lfber das Elektrencephalogramm von Fruhgeburten. Z. Kinderheilkunde. 1951.69, 251-261. Minkowski, A . (Ed.) Regional maturation of the nervous system in the foetus and thenewbom. London: Blackwell, 1967, in press. hdirzoyants. N. S.(Changes in the electrical activity of the brain in early childhood in response to a flicker stimulus.) Zh. Vysshei Nervnoi Deiatel‘nosti imeni Pavlova (Moskva), 1961, 11, 1005-101 I . Monod, N., & Dreyfus-Brisac, C. The paroxystic EEG of the newborn at term. Electroencephalog. din. Neurophysiol.. 1962. 14, 778. Monod, N., Dreyfus-Brisac, C., Ducas, P., Sr Mayer, M. L’EEG du nouveau-nthterme. Etude comparative chez le nouveau-nt en prtsentation ckphalique et en prtsentation de sitge. Rev. Neurol.. 1960, 102, 37S379. Monod. N.. Salama, D., & Dreyfus-Brisac, C. The EEG of the second trimester of life, its prognostic value and its relationship to the neonatal tracing. Electroencephalog. clin. Neurophysiol.. 1962, 14, 778. Monod. N., Dreyfus-Brisac, C., Morel-Kahn, F., Pajot, N., & Plassard, E. Les premitres ttapes de I’organisation du sommeil chez le prtmaturt et le nouveau-nC. Rev. Neurol., 1964. 110, 304305. Okamoto, Y., & Kirikae, T. Electroencephalographic studies on brain of foetus, of children of premature birth and new-born, together with a note on reactions of foetus brain upon drugs. Folia P.y.vchiar. Neurol. Japonira. 1951, 5, 135-146. Parmelee, A . H., Jr., Wenner, W. H., Akiyama, Y., Stem, E., & Flescher, Jenny. Electroencephalography and brain maturation. In A. Minkowski (Ed.), Regional development of the brain in early life. London: Blackwell, 1967,459-480(a). Parmelee, A. H., Jr., Wenner, W. H., Akiyama, Y., Schultz, M., & Stern, Evelyn. Sleepstates in premature infants. Develpm. Med. Child Neurol.. 1967, in press. (b) Passouant. P., Cadilhac, J.. & Ribstein. M. Epilepsie et maturution dribrale. Montpellier: Dehan, 1959.

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Robert J . Ellingson Passouant, P.. Cadilhac, J., & Delange, M. Le sommeil du nouveau-nt. Considerations sur la ptriode des mouvements oculaires. Arch. Franwises Pediat., 1965, 22, 1087-1092. Polikanina, R. 1. (Age modifications of the bioelectrical activity of the brain in prematurely born babies in early postnatal ontogenesis.) Zh. VyssheiNervnoi Deiatel'nosti imeni Pavlova (Moskva), 1962, 12,809-818. Polikanina, R. I. (Peculiarities of natural sleep in premature babies in early postnatal life.) Zh. Vysshei Nervnoi Deiatelnosti imeni Pavlova (Moskva), 1963, 13. 62-72. Prichard, J. S. The character and significance of epileptic seizures in infancy. In P. Kellaway & I. Petersen (Eds.), Neurologiml and electroencephalographic correlative studies in infanq. New York: Grune & Stratton, 1964. Pp. 273-286. Purpura, D. P., & Schadk, J. P. (Eds.) Progress in brain research. Vol. 4 . Growth and maturation of the brain. Amsterdam: Elsevier, 1964. Ribstein, M., & Walter, M. Convulsions du premier mois. Rev. Neurol., 1958, 99, 91-99. Rossler, M. EEG in newborn infants with damaged central nervous system. Electroencephulog. clin. Neurophysiol., 1963, 15, 168. Roffwarg, H. P., Dement, W. C.. & Fisher, C. Preliminary observations of the sleep-dream pattern in neonates, infants, children and adults. In E. Harms (Ed.), Problems ofsleep and dreams in children. Monographs on child psychiatty. No IT. New York: Pergamon Press, 1964. Pp. 6 7 2 . Rosen, M. G., & Satran, R. Neonatal electroencephalography: Results of a pilot study. Amer. J. Obstet. Gynecol., 1964, 89, 61%25. Rosen, M. G., & Satran, R. Neonatal electroencephalography. 11. The EEG of the high risk infant. Amer. J. Obstet. Gynecol., 1965, 92, 247-252. Samson, D., Delange-Walter, M., & Misbs, J. L'tlectroenckphalogramme de I'enfant. Rev. Neurol., 1963, 108, 138-141. Samson-Dollfus, Dominique. L'ilectro-enciphalogramme du prematuri jusqu'a luge de trois mois et du nouveau-ni 6 terme. Paris: Foulon, 1955. Samson-Dollfus, D., Forthomme, J., & Capron, E. EEG of the human infant during sleep and wakefulness during the first year of life. In P. Kellaway & I. Petersen (Eds.), Neurological and electroencephalographic correlative studies in infancy. New York:Grune & Stratton, 1964. Pp. 208-229. Schaper, G. Zum Hirnstrombild bei Schlafenden Fruhgeborenen. Mschr. Kinderheilkunde, 1953, 101. 149-151. (a) Schaper, G. Das Hirnstrombild des sclafenden Sauglings im 2. Trimenon. Mschr. Kinderheilkunde, 1953, 101,258-262. (b) Schroeder, C., & Heckel, H. Zur Frage der Hirtatigheit beim Neugeborenen, Geburtshilte und Frauenheilkunde, 1952, 12, 992. Schroeder, C., & Heckel, H. Zur Diagnose des Geburtstraumas beim Neugeborenen. Klinische Wschr., 1953, 31, 808-813. (a) Schroeder, C., & Heckel. H. Le diagnostic du traumatisme cranio-ctrtbral obstktrical chez le nouveau-nk par I'EEG. Rev. Neurol., 1953, 89.437. (b) Schulte, F. J., & Herrmann, Barbara. Elektrencephalographie beim Neugeborenen. Mschr. Kinderheilkunde, 1965, 113,457465. Shepovalnikov, A. (Rhythmic components of the electroencephalogram of suckling children.) Zh. Vysshei Nervnoi Deiatel'nosti imeni I . P. Pavlova (Moskva), 1962, 12, 797-808. Smith, J. M. B., & Kellaway, P. The natural history and clinical correlates of occipital foci in children. In P. Kellaway & 1. Petersen (Eds.), Neurological andelectroencephalographic correlative studies in infamy. New York: Grune & Stratton, 1964. Pp. 230-249. Sobotka, P. (Ed.) Functional and metabolic development of the central nervous system. Plzehsky Lekakskj Sbornik, 1961, Suppl. 3. 1-203. Storm van Leeuwen, W., Bickford, R., Brazier, M., Cobb, W. A., Dondey, M., Gastaut, H.,

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Brain Electrical Activity in Infants Gloor, P., Henry, C. E., Hess, R., Knott, J. R., Kugler, J., Lairy, G.C., Loeb, C., Magnus, 0.. Oller Daurella, L.. Petsche, H., Schwab, R., Walter, W. G.,& Wid& L. Proposal for an EEG terminology by the terminology committee of the International Federation for Electroencephalographyand ClinicalNeurophysiology.Electroencephalog. din. Neurophysiol., 1966, 20, 306-310. Sureau, M., Fischgold, H., & Capdevielle, G.L'EEG du nouveau-nb:Normal et pathologique. Electroencephalog. clin. Neurophysiol., 1950, 2, 1 13-1 14. Tibbles, J. A. R., & Prichard, J. S. The prognostic value of the electroencephalogramin neonatal convulsions. Pediatrics, 1%5,35,778-786. Walter, W . G.Technique-Interpretation. In D. Hill & G. Parr (Eds.), Electroencephalography. New York: Macmillan, 1963. Pp.65-98. Walter, W. G.,& Parr, G.Recording equipment and technique. In D. Hill & G.Parr(Eds.), Electroencephalography. New York Macmillan, 1%3. Pp.65-98.

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SELECTIVE AUDITORY ATTENTION IN CHILDREN'

Eleanor E. Maccoby STANFORD UNIVERSITY

............. .............. .............. B. FACTORS RELATED TO AGE IMPROVEMENT .......... THE EFFECTS OF PREPARATORY SET . . . . . . . . . . . . . . . .

1. STATEMENT OF THE RESEARCH PROBLEM 11. AGE TRENDS IN SELECTIVE LISTENING . A. STUDY A: DESIGN AND PROCEDURES

Ill.

A. PREVIOUS WORK AND THE CHOICE OF METHOD O F STUDY

99 102 102 103 108 108 110 113

B. STUDY B: PREPARATORY SET WITH SEQUENTIAL STIMULI . C. PREPARATORY SET WITH SIMULTANEOUS STIMULI . . . . . . D. THE ROLE OF SENSE-ORGAN ORIENTATION IN SELECTION BASED ON PREPARATORY SET (STUDY E) . . . . . . . . . . . 119 1V. INDIVIDUAL DIFFERENCES ...................... I20 V. IMPLICATIONS FOR THE DEVELOPMENT O F LISTENING SKILLS IN CHILDHOOD .............................. 122 REFERENCES

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124

I. Statement of the Research Problem Work on the development of perception has dealt more extensively with vision than with audition, although recent work on the development of 'The research underlying this paper was supported by NIH grants Nos. USPH 01092-01. USPH 0109242, and USPH 100744I.The author wishes to express indebtednessto Karl W. Konrad for efficient collaboration at all stages of the research; to T ~ o ~ K.M Landauer for valuable consultation on problems of design, analysis, and interpretation of the data: to Nathan Maccoby, Frederick D. Sheffield, and Norman Henderson, for helpful commentary and critique; and to Tom M.Jones for assistance in searching the literature.

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speech perception is beginning to close the gap. The processes underlying perceptual development are probably much the same for the two senses in many respects. Both, for example, require the learning of discriminations and the organization of discriminable parts into meaningful wholes. Complex auditory stimuli may even be thought of as having portions that are figural and portions that function as ground. There are at least two important respects, however, in which the two senses differ. The first is that while the parts of the visual field which are to be organized must be organized in space, the auditory field must be organized in time. The meaning of heard language is determined by the temporal order in which sounds arrive (e.g., kingdom vs. dumb king), and there is evidence that even when sounds arrive simultaneously, they are converted by the hearer into sequential patterns. Broadbent ( 1958)describes an experiment in which two different sets of digits were fed simultaneously to the two ears: when the subjects reported what they had heard, they reported first the set which had come to one ear, then the set that had come to the other, rather than giving the two first-heard digits first, then the two second-heard, etc. He says: “We can take it as a quite common occurrence for information reaching the senses at the same time t o emerge from the effectors successively: to change, metaphorically speaking, from line abreast to line astern” (p. 216). Of course, some visual perceptual processes are also sequential in time. Reading is a notable example: it is a visual code for what was initially an auditory process (namely, spoken language) and preserves the temporal dimension of that process. But most visual displays have the same meaning regardless of the order in w:hich they are scanned. If we can take it as true that hearing is more time-bound than vision, then it follows that the role of memory (especially short-term memory) may be greater, or at least different, in hearing. A second difference between hearing and seeing has to d o with how stimulus selection is accomplished. In vision, the seer selects those portions of the available visual stimuli that are relevant to his on-going tasks by selectively orienting his eyes toward these stimuli. If his task requires only material to be retrieved from memory, he can shut out all external visual stimulation by the simple expedient of closing his eyes. Auditory inputs are not so easily regulated by selective orientations of the sense organs. While the listener can turn his head so as to maximize the utility of localization cues, he cannot easily prevent unwanted sounds from stimulating his ears. It may be taken as reasonably well established, through the work of Broadbent (1958). Hernandez-Peon, Scherrer, and Jouvet (l956), and others, that stimulus selection does indeed occur in audition, but that the selection processes tend to be central, Thus the two senses could be contrasted in terms of the fact that peripheral processes probably play a larger role in stimulus selection for vision than for audition. The role of sense100

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organ orientation in selective hearing has not been fully studied: however, the issue is an important one and it will be taken up again below. To speak of stimulus selection is to enter the realm of the phenomena which have historically gone by the name of “attention.” Woodworth and Schlosberg (1954) discussed the following topics in their chapter on attention: determiners of attention, shifts and fluctuations of attention, division of attention (doing two things at once), and span ofattention. They cite reresearch on these topics spanning nearly a hundred years, very little of which is developmental, although work has been done comparing ages with respect to attention span. Since their chapter was published, new findings and new points of view have appeared, but the old issues are still relevant, as will be evident when we being below to formulate a research attack upon the question of how selective attention develops during childhood. A modern point of view on selective attention which has been highly influential in recent research is that of Broadbent (1958) and his colleagues. It is not possible to present the original theory in detail here, nor to describe the work which has followed the publication ofthe I958 book. At this point, it will suffice to state in general (and oversimplified) form the aspect ofthe theory which has most bearing upon the work to be reported here. Broadbent views selective attention in terms of the operation of a successive set of ‘‘filters.” In this view, information, after reaching the sense organs, is sorted on the basis of one or more attributes, and only that information which is “passed” by the filter or filters receives further processing. If an individual has shut out certain information on the basis of a single perceptual quality of the stimulus (such as the identity of the voice in which it was spoken), nothing more about that stimulus will “register” further. Thus, the content of the excluded message would not be available to the individual in memory or as a determinant of performance. Broadbent has not been concerned with the developmental history of filtering processes. In the present report, we will consider the usefulness of this point ofview in describingthe changes which occur with age in selective auditory attention. The present paper deals with the development in childhood of one aspect of listening skills: namely, the ability to hear verbal messages and report them accurately in a situation where selection is necessary. In most of the studies to be discussed, subjects ranging in age from 5 to 12 have been presented with two voices speaking simultaneously, and have been instructed to report only one of them. The major questions to be discussed are: ( I ) Does selective listening skill increase with age? (2) If so, what are some of the factors that contribute to the improvement? (3) What is the role of preparatory set in selective listening performance? (4)If preparatory set improves selective listening, does it depend for its effectiveness on senseorgan orientation?

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Eleanor E. Maccoby A series of studies was undertaken to explore these questions. The detailed findings of the studies are being published elsewhere (Maccoby & Konrad, 1966, 1967). For the present report, the findings and procedures will be summarized, and shown with significance levels indicated, but without analysis of variance tables. The reader is referred to the more technical publications for details of the experimental procedures and statistical treatment.

11. Age Trends in Selective Listening The primary objective of the first study was to take a n initial reading on the magnitude of age ct~angesin selective listening skill. A second objective was to begin the study of factors which might underlie age improvement, if such improvement was found. In this study, these factors were the availability of an “earedness” cue for discriminating the messages, and variations in word length. A. STUDY A: DESIGN AND PROCEDURES

Thirty-two children each from kindergarten, second grade, and fourth grade classes were asked to listen over headphones to a two-track stimulus tape, One track carried a woman’s voice speaking a twenty-three-item series of single-syllable and multi-syllable words; the other track carried a man’s voice speaking a different twenty-three-item list of words. The two tracks were synchronized so that when both were played, the two voices spoke simultaneously, each pair of simultaneous words being followed by a pause long enough for the subject to respond. The first time through the tape, the subject was instructed to report only one of the voice:, and the second time through, the other voice. The order of report (whether the man’s or woman’s voice was asked for first) was counterbalanced. For each subject, on one run through the tape the voices were presented dichotically(separate1y to the two ears): on the other run through the tape, both voices came to both TABLE I STL’DY A: MEANNUMBERCORRECT (OUT OF TWENTY-THRFE ITEMS) BY GRADE A N D DICHOTIC VERSUS BINAURAL PRESENTATION ~

Dichotic Binaural N

I02

~~

~

Kindergarten

Second grade

Fourth grade

7.5 3.9 32

11.2 6.4 32

12.7 1.4 32

Selective Auditory Attention in Children ears, and the order of this experimental variation was also counterbalanced. There was a clear improvement with age in the subject’s ability to report correctly the word spoken by the asked-for voice (see Table I) from a n average of about six correct out of twenty-three for the kindergarten children to ten for the fourth graders. There was also a progressive decline in the number of “intrusive errors”, i.e. reports of the word spoken by the voice \\ hich was not asked for. (Henceforward we will refer to this voice as the “masking voice.”) B. FACTORSRELATEDTO AGE IMPROVEMENT 1. Strategy for identifying Underlying Factors; Methodological Issues Hour can factors which underlie age improvement be identified? It is not sufficient to know that a factor which might be related to listeningskill, such as memory span, also increases with age, for both might be independent outcomes of a third factor, and functionally unrelated to one another. In the present studies, the following strategy has been adopted: Experimental variations in the conditions of stimulus presentation or stimulus content have been applied at successive age levels. If a given treatment has more effect on listening performance at older than younger ages, the inference is made that the factor which was varied is functionally related to age improvement in listening. Beyond this, it is possible to detect factors producing age improvement even if they d o not interact with age in these studies. If it could be shown, for example, that listening is more accurate for familiar than unfamiliar words, and there is independent information that older children are familiar with more words, then it is reasonable to infer that older children’s greater listening skills derive in part from their increasing familiarity with the language. There is a methodological difficulty in determining whether a given experimental treatment has more effect at one age than another. If the baseline performance level increases with age, then an experimental treatment is superimposed upon a different point in the scale for different age groups, and changes in performance may be easier to produce at some points of the scale than others. This issue is especially acute when one is dealing with a limited scale-that is, when performance has either a floor or a ceiling or both, due to testing with a limited number of items or an insufficient range in item difficulties. In this situation, the baseline performance for older groups is nearer the ceiling; if an experimental treatment is applied which improves performance, the older groups d o not have as much “room” in which to improve, that is, not as much opportunity to show the effects of the experimental treatment. In an attempt to solve this problem, Hovland et al. (1949) employed an “effectiveness index,”

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in \\ hich change was computed as a proportion of the number of scale points between the baseline and the ceiling-s a proportion of the scale distance available for improvement. If one does this, then lines which would be parallel for raw scores (as they would be for the figures in Table I) diverge for “effectiveness index” scores, and one finds that older children are shown as being more affected by the experimental treatment. There is another way of dealing with the problem of changing baselines for different groups: namely, to take improvement as a per cent of the baseline. This procedure treats a I-point improvement for a group which started with a mean score of 10 as equivalent to a 10-point improvement for a group which started with a mean score of 100. The assumption underlying this procedure is that, while units may not be equal along the scale on which the dependent variable is being measured, the size of the unit is inversely proportional to the magnitude of the scores. The reasoning here does not take ceiling effects into account. If, on the basis of this assumption, one uses per cent improvement scores, then lines which would be parallel for raw scores converge and older children are shown as being less affected by an experimental treatment, since any given amount of improvement is smaller in relation to their higher baseline scores than it would be for a younger group with lower baseline scores. There is a third approach: namely, to evaluate change produced by a n experimental treatment in terms ofthe variation of the baseline distribution. One asks. in effect, how many standard-deviation units did the experimental treatment shift the group? If ceiling effects are really operating for a highbaseline group. this will show itself through a reduction in variance of the scores and a small absolute change will be evaluated as larger in relation to this reduced variance. The procedures for carrying out this third approach are either to convert change scores into standard score units or transform scores in some other way (e.g., arcsin) so as to reduce ceiling effects and produce homogeneity of variance across age groups. We have taken the third position in the analysis of experimental effects across age groups. Ifvariances are homogeneous (not significantly different) then raw change scores are already equivalent in terms ofstandard deviation units: we, therefore, use raw scores and rely upon the interaction terms of the analysis of variance tables to show whether an experimental treatment has greater effect on one age group than another. If ceiling effects appear to be important (as indicated by significantly smaller variances for high baseline groups), we transform scores so as to reduce the discrepancy in variances from one age group to another and carry out the analysis of variance with these scores. In some instances, it is possible to test for the validity of age-curve comparisons by comparing them at two different levels of difficulty. If stimulus materials are subdivided into difficult and easy segments (as reflected in 104

Selective Auditory A ttention in Children

different baseline performance rates), and if an experimental treatment interacts in the same way with age regardless of the level of difficulty of the material, there is some assurance that the age effects are not simply a function of the changes in the baseline performance levels from age to age.

2 . Auditory Acuity Before considering the psychological factors which might account for the age improvement shown in Table I, we must inquire first whether there is any increase through the age range studied in auditory acuity based on physiological factors. Simple audiometer tests do reveal some increase through the age range 5 through 12 in the ability to detect faint sounds. The increase is greatest at the lower frequencies, and relatively slight (on the order of 5 decibels or less) for frequencies which are most important in the comprehension of speech (Eagles et al., 1963). These authors say: “The variation in hearing sensitivity with age is not completely understood. It has been suggested that this trend may be explained in part by the behavior of the child.” The performance of a child on audiometer tests, then, is thought to be a function not only of the state of development ofthephysiological mechanisms involved in hearing, but of the child’s ability to sustain attention during the test and shut out extraneous noise; the slight improvement in hearing acuity which occurs during the early school years, then, does not necessarily mean that the ears are functioning more efficiently in a physiological sense. In any case, it is doubtful whether the amount of improvement in acuity revealed in the audiometer tests is sufficiently large to account for the substantial improvement in selective listening shown in Table I. We turn to a consideration of other factors. 3. Language Facility There is evidence from our first study that older children’s greater efficiency in selective listening is related to their greater command of language. The first piece of evidence is that two-syllable words were more accurately reported than one-syllable words, and the advantage of twosyllable words was greater for older than younger children. When two voices are speaking at once, it is likely that the mutual masking effects are not uniform within and between words; that is, because of variations in pitch, stress, and other attributes of the stimuli, certain sound elements come through more clearly than others. The listener is therefore often in a position of having heard only part of a word. In normal selective listening situations, in which the speaker to be selected is speaking full sentences, the listener can fill in missing parts of the message on the basis of the context in which the gaps occur. In Study A, the stimuli were truncated by comparison with normal speech, but two-syllable words did provide more “context” than monosyllables. The results suggest that older children,

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having more knowledge of within-word sequential probabilities, can fill in poorly heard segments more accurately. This interpretation received support from an analysis of errors. Subjects sometimes reported that they had heard a different word than that spoken by either voice. This misreported word would sometimes be made up of sound elements taken from the two stimulus words. When the younger children reported such a “merged” or composite word, it tended to be a nonsense word-one which does not actually occur in English. When the older subjects gave a composite response, they almost never reported a nonsense word, but gave real English words. Their listening, then, was governed by a fairly narrow range of sounds known to be English words, while for the younger children, a considerably wider range of sound combinations appeared to be entertained as possible words. Whether these restrictions operated upon what the older children “heard” or only upon what they reported, we do not know. But it is likely that the narrower range of possibilities for older subjects increased their chances of guessing correctly when words were imperfectly heard. 4. Utilization of “Filter” Cues

Are there grounds for saying that a factor underlying improvement with age is an improved ability to “filter” out desired information in Broadbent’s sense? The task required subjects to select one voice on the basis of the sex of that voice. Previous work had demonstrated that children of kindergarten age could readily discriminate these two voices when asked to indicate whether a man or woman was speaking, when the two voices spoke separately. The fact that there may have been some improvement with age in the ability to use this readily discriminable cue as a basis for filtering is suggested by the declining rate of intrusive errors with age. Also the fact that the total number of merged responses (in which sound elements were taken from each of the two voices) declined with age would be consistent with the view that there is a growing efficiency in filtering processes. There was no improvement with age, however, in the ability to filter on the basis of which ear was being stimulated. Subjects listened in the one instance under conditions of dichotic presentation, while in the other instance both voices came to both ears. Under either condition, sex of voice was available as a cue for selection of the desired voice. Under dichotic listening conditions, there was another cue: the desired voice always came to a single ear. Presumably, in listening under these conditions, it would be possible for the subject to select the voice by listening only to one ear, as well as by listening only for one voice. One may ask whether one basis for the better performance of older subjects is their greater ability to take advantage of this cue for filtering. We have already seen that older subjects do make fewer intrusive errors, and fewer errors involving merging 106

Selective Auditory Attention in Children

of the two voices, so it is clear that they can shut out the masking voice more effectively on the basis of sex of voice. They do not appear to have an advantage in the use of the “earedness” cue, however. Subjects of all ages perform better under dichotic presentation. This superiority is probably at least partly due to other factors besides the availability of a sorting cue. Specifically, peripheral masking should be greater under mixed presentation conditions. But if part of the superiority of performance under dichotic conditions is due to the availability of an additional sorting cue, the cue appears to have been equally well employed for filtering by children of all the ages studied, since all age groups showed a similar degree of improvement with dichotic presentation (see Table I). Does the concept of “filtering” really help to explain the age improvement in selection? Are there other terms in which the improvement can be understood? In visual perception, figures which can be readily discriminated in simple form cannot be so easily discriminated when the quality of the stimulus is reduced, as in the case of dashed figures, or when the figure is surrounded by noisy elements, as in the case of embedded figures. There is an increase with age in both the ability to fill in incomplete figures, and to recognize them in an embedding context. Explanations of these age changes usually involve reference to an increasing ability to differentiate a stimulus field, or discriminate between elements in such a field. Analogously in hearing, identifying a voice as that of a man or woman is a somewhat different and more complex process when two voices are presented simultaneously than when they speak singly. In simultaneous presentation, the voice must be differentiated in a noisy surround. And in the instances where one voice actually masks the other, the desired voice is equivalent to a dashed figure in the recognition of visual forms: it is an incomplete stimulus, and must be filled in for recognition. A n analysis of age improvement in terms of the growing ability to discriminate or differentiate stimuli implies a different point of view about selective perception than an analysis in terms of filtering. If discrimination is emphasized, selective perception is viewed as a process in which everything about the stimulus that affects the sense organs is initially registered; the subject then discriminates the wanted from the unwaqted portions as well as he can, and reports only those parts that are wanted. The filtering point of view implies that the subject perceives initially only those aspects of the stimulus that bear upon whether the message is to be accepted or rejected; for the accepted message, more information is then recorded or perceived and its content becomes available for report. The findings of study A would be compatible with either of two points of view: that the ability to discriminate or differentiate complex stimulus patterns improves with age, or that the ability to use sex of voice as a basis for filtering out desired information improves with age. There is no basis 107

Eleanor E. Maccoby

for choice between the points of view in this set of data. We turn to study designs which have more direct bearing upon the issue.

111. The Effects of Preparatory Set A. PREVIOUS WORK AND THE C H O l C F OF METHOD OF S T U D Y

Study A demonstrated that older children can more accurately report one designated voice when two are speaking than can younger children. This finding does not reveal, however, whether they are more successful at selective perception in the narrower sense of this term. Perhaps all our subjects were handling the task by hearing both voices as well as they could and selecting one of them for subsequent report, rather than shutting out one of the voices at the time of initial perception. On first thought, it would seem that this possibility could be checked by asking subjects to report the words spoken by both speakers, and contrast this with the accuracy of report when only one voice was asked for in advance. If report of a given voice is as accurate when both voices are reported as it is when the subject is “set” for only one voice, it would appear that any “selection” in perception occurs in memory after the initial intake of all the material to be selected from. Unfortunately, it is not valid to do the experiment in this way because ofthe proactive inhibition exercised by the first-reported item upon later-reported items. Whatever was recalled second would be less accurately recalled, so that the total level of accuracy when the subject was asked to report both voices would be lower. This phenomenon (sometimes called “destructive read-out”) is illustrated in the ingenious experiment by Lawrence and Laberge (1956). These experimenters were concerned with whether subjects perceive a given attribute of a stimulus better if they are “set” in advance to perceive that attribute. Using brief tachistoscopic exposures, they presented visual displays each of which possessed three attributes: number, color, and nature of the objects pictured. Thus, one stimulus card might contain four green cars. In some instances the subjects were asked in advance to “concentrate” on one of these attributes. Under this condition, subjects reported the attribute in question more accurately than subjects who were simply asked to report what they had seen without having been alerted for an attribute. But in a third condition, the experimenter specified the order of report of a t t r i b u t e s that is, after the stimulus had been flashed, the subject was asked to report first either the color, or the number of objects, or the kind of objects that had been pictured. With this procedure, the first-recalled attribute \I as as accurately reported as it was if the subject had been asked to concentrate 108

Selective Auditory A ttention in Children

on it in advance. Later-reported attributes were not. This experiment, then, did not find evidence for selective perception in the sense of a preparatory set determining what is taken in, but did suggest that post-stimulus reporting is highly sensitive to order of report and that improvements in performance which have been attributed to pre-stimulus set or alerting may in fact be due to the fact that such sets specify the order of report. In another experiment with visual stimuli, Lawrence and Coles (1954) also failed to find evidence of improvement in performance with preparatory set. Sperling (1960), partially circumventing the order of report problem, used the technique of “post-stimulus samp1ing”asking subjects to report only a portion of what had been presented in brief visual displays. He was able to show that subjects initially take in more than they can subsequently report, and that this additional information is available for only a brief period after stimulation (approximately second). In the portion of his work that dealt with preparatory set, Sperling, like Lawrence and his colleagues, did not find clear evidence that pre-stimulus alerting improves the selection of certain elements of a complex array. He did hold, on theoretical grounds, that whether a pre-stimulus selective set improves performance should depend upon the amount of information in the stimulus array. If the stimulus array contains more information than the subject can report (more than his “span of attention”), then, Sperling argues, the subject must select out of what was initially taken in a portion to be retained and reported. Under these conditions, a prior signal indicating what portion is wanted should result in better reporting of that portion than will be possible if the subject does not know what portion is needed until after some of the initially available information has faded away. Is the problem of preparatory set and its effects comparable for audition and vision? We do not know whether there exists a brief “auditory afterimage” comparable to the visual one from which a subject can stillselect desired segments after stimulation has ceased. Furthermore, it is not possible to study auditory perception in relation to the same time intervals as those used in vision. Sperling and Lawrence’s work involve complex visual displays which are flashed so very briefly that the subject does not have an opportunity to scan the display and focus his eyes selectively upon desired portions. This narrows the problem of selective perception to the question of whether a preparatory set can enable the subject to select wanted portions of an array in any other way than through selective orientation of his sense organs. In hearing, it is difficult to present a complex stimulus, one that exceeds the subject’s span of apprehension, in a single moment. An array containing this many elements must be stretched out in time. If a subject is pre-set to report only certain kinds of items from a sequential list, and this set improves his performance by comparison with a post-stimulus signal indicating which items are to be reported, it

+

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Eleanor E. Maccoby

would probably be more accurate to describe the phenomenon as selective memory rather than selective perception. If the subject were listening, for example, to a successive series of words, some spoken by a man’s voice and some by a woman’s and was set in advance to report only one of the voices, he could perceive all the words as they were spoken, but cumulatively rehearse only those of the desired voice, thus improving subsequent recall of these words, without any differential initial perception having occurred. In selective listening to sequences of stimuli, then, performance ought to be a function of memory span. If the mixed list is sufficiently short so that it can be entirely held in memory, then recall of a specified segment should be near-perfect regardless of whether the subject is told before or after stimulus presentation what segment he is to report. As the list becomes longer, however, the advantage of the preparatory set over the after-signal ought to become greater, up to an asymptote set by memory span. Assuming that the subject is being asked for 50% of the items in a long list, for example, performance at the asymptote ought to be twice as good with a beforesignal as with an after-signal, since in both instances the total amount that can be reported will be limited by memory span, but with a preparatory signal all the items recalled should be of the desired kind, while with an after-signal only half of the items recalled (on the average) will be of the desired kind.

B.

STUDY

B:

PREPARATORY SET WITH SEQUENTIAL STIMULI

Some of these relationships were demonstrated in an unpublished study by Karl Konrad (1964). Konrad used a single voice speaking mixed strings of letters and numbers, delivered over a single loud speaker. The first four items were two-unit lists, the next four three-unit lists, and so on up to a block of four eight-unit items. On some trials, subjects were asked to report only the letters, on others, only the numbers, so that for every trial they were to report only half the units in the list. On half the trials, the subjects were signaled in advance whether numbers or letters were to be reported, and on half the trials this signal came after the stimulus list had been presented. Instructions were counterbalanced across subjects in such a way that for any given item, half the subjects were asked for letters, half for numbers, and half received a before-signal, half an after-signal. On all trials, the subjects waited till the entire stimulus string had been given before reporting back the selected portion. The subjects were second, fourth, and sixth grade children (twenty-four from each grade). Two predictions were made: (1) that the longer the stimulus string, the greater would be the superiority of before-signal over after-signal performance; and (2) that younger children would show a before-signal advantage 110

Selective Auditory A ttention in Children

on shorter lists than would older children. The latter prediction was based upon the fact that digit span increases somewhat through the age range being studied. The Stanford-Binet norms (Terman & Merrill, 1937) place repeating four digits at age 4,five digits at age 7, and six digits at age 10, so there should be an increase of slightly over one digit in the average digit span of children through the age range included in this study. First considering all age groups jointly: there was a clear relationship between the length of the string and the degree of advantage provided by TABLE 11 STUDY B: MEANNLIMLIER CORRECT, FROM LISTS OF VARYING LENGTHS, WHEN 50% OF THE ITEMS A R E ASKEDFOR, BY SET CONDITION A N D GRADE

Second grade Before signal After signal Fourth grade Before signal After signal Sixth grade Before signal After signal

Number of Items in List 4 5 6

2

3

.96 .92

1.42 1.40

1.87 1.65

2.02 1.75

.98 .96

1.50 1.44

2.00 1.92

1.00 1.00

1.50

1.98 1.87

1.48

7

8

2.29 1.77

2.56 1.96

2.85 1.98

2.29 2.13

2.85 2.21

3.15 2.35

3.27 2.40

2.42 2.25

2.92 2.52

3.10 2.52

3.56 2.50

the before-signal (see Table 11). With two-, three-, and four-unit strings (from which half were to be selected), performance was nearly perfect with or without a preparatory set. As the string became longer, the proportion of items correctly reported declined, and the decline was greater with an after signal. There was a tendency for younger subjects to show a greater decline under the after-signal condition for shorter lists, but variability was great within age groups, and whether the age effect was significant depended on the method chosen for measuring the divergence of before and aftersignal curves. In one analysis, each subject was given a score for the length of the items on which he first performed more accurately with a before than an after signal. The means for the three age groups on these scores were: second grade, 4.54:fourth, 4.88:sixth, 5.62. These scores mean that most of the second graders first showed a discrepancy between their before-signal and after-signal scores on either the four-unit or five-unit strings, while for the sixth graders, the superiority of a before signal tended to appear on either the five-unit or the six-unit strings. An analysis of variance for the age means (with 2 and 69 df.) yields and Fvalue of 3.86. For this analysis, then, the age effect .is significant at less than the .05 level. However, if one adopts a more stringent score, recording for each subject the length of the series on which he first has a higher before than after scorefor ~ W O S U C C ~ S -

111

Eleanor E. Maccoby

sive blocks of items, the means by grade are 5.79,5.87,and6.54, and the Fvalue is only 1.94, p between .I0 and .20. The age effect, then, must be regarded as of border-line significance. From this demonstration study, we can derive a positive conclusion and a negative one. In selective listening to material that is sequential in time, the degree of advantage of a preparatory signal specifying what is to be selected does depend upon the length of the list. It cannot be said precisely that the before-signal advantage depends upon the amount of information in the list, since Miller (1956) has shown that the amount recalled is not a function of the number of elements in a stimulus array but of the way the elements are grouped or chunked. In any case, the findings are entirely consistent with Sperling’s theoretical prediction concerning the conditions which should govern the utility of a preparatory set. The riegative conclusion is that the greater skill which older children display in selective listening cannot be attributed to any greater reliance upon, or ability to utilize, preparatory set.’ Indeed, the results suggest that in listening to sequential materials, older children may be better able to do without a preparatory signal, because of a slightly greater ability to retain a lengthy set of stimuli in memory long enough to make a post-stimulus selection. As noted above, a study in which stimuli are stretched out in time does not yield information on the effects of preparatory set on perception, but rather on rehearsal and memory. It is still important to know whether a preparatory set affects what is taken in at the time of initial stimulation, and whether there are age changes in the effects of such a set. There has been some previous work on the effects of a preparatory set (as compared with an after-signal) on the perception of simple brief sounds. Sumby (1962) reports that the probability of correctly perceiving aword in noise is increased if the subject is given a word set of one or two alternatives before presentation of a word stimulus from that set. Swets and Sewall (1959) find that giving subjects frequency information before the presentation of a signal improves the detection of the signal. These studies provide evidence that auditory perception is indeed selective on the basis of prior set rather than on the basis of response bias. However, these studies do not provide age comparison data, and they are not directly comparable to the experiments with vision reported earlier, in that they do not involve simultaneous inputs of a complex array of elements from which only a portion is to be selected. If an experiment is done on listening which is comparable to the visual experiments in that stimulation is multiple and very brief, the number of elements in the stimulus set must be within the immediate span of apprehension of the subjects, as this is usually measured. One cannot present eight or ten separate sounds simultaneously and expect them to be discriminated sufficiently well for selection. Therefore, small numbers of simultaneous

112

Selective Auditory A ttention in Children

stimuli must be used, and any advantage which subjects gain from a preparatory set will probably have a different basis from that seen in Study B. It should be noted that in the previously cited experiments on vision, there was precise control of the duration of stimulation. In experiments with audition, it is difficult to achieve this, if meaningful stimuli are used. Words differ in the time it takes to pronounce them, and speakers differ in the rapidity of their delivery. If single words of one or two syllables are used, their duration tends to be a second or less. By using taped stimuli, it is possible to achieve uniformity of timing across subjects, but not exact uniformity among stimulus words.

c. PREPARATORY SET WITH SIMULTANEOUS STIMULI 1. Study C: Effect of variations in word familiarity This study, like Study A , involved two voices speaking simultaneously, a man’s voice and woman’s voice. The voices spoke single words, which were systematically varied with respect to their familiarity. The voices came separately from two loudspeakers which were placed approximately 18 inches apart. One speaker was marked with the picture of a man’s face, the other with a woman’s. When the subject was to report the word spoken by the man’s voice, the man’s picture was lighted up; the woman’s picture was lighted for other trials; on some trials, the subject received this signal before the voices spoke, on other trials immediately after. There were thirtytwo trials (pairs of words), sixteen with a before signal, sixteen with an after signal. The subjects were twenty-four children each from the second, fourth, and sixth grades (the same children who served as subjects in Study

B). The study was intended to show first of all whether the before signal yielded better listening performance than the after signal, whether, that is, audition is selective on the basis of a prior set. A second objective was to determine whether, assuming an affirmative answer to the first question, the utility of a preparatory set changed with age. Third, the study explored the role of familiarity in the stimulus materials to determine whether the familiarity of the stimuli to be shut out, as well as the familiarity of the materials to be selected, affected performance. Table 111 shows the results in terms of the mean number of correct responses separately by grade level and by set condition. Total performance improved with grade ( F = 6.37, p < .01). Furthermore over all age groups, there was better performance with a preparatory signal ( F = 5 . 6 7 , ~< .025). This superiority of performance with a preparatory signal was found only at the younger two age levels, but the interaction of age and set condition was not significant ( p < .20). 113

Eleanor E. Maccoby TABLE 111 STUDY c MEANNUMBER CORRECT (OUT OF SIXTEEN ITEMS), BY GRADE, A N D SET CONDITION Grade Second Fourth Sixth

Before signal

After signal

N

7.27 8.23 8.60

6.08 7.21 8.75

24 24 24

There is evidence in this study, then, that auditory perception is indeed selective, in that a prior set to listen to only one portion of a complex stimulus improves the ability to report that portion (by comparison with post-stimulus signaling as to what segment is to be reported). There is a tendency for the advantage of the preparatory signal to be greater for younger subjects, suggesting that they may have more difficulty than older subjects in holding in mind the entire complex stimulus until an after signal permits them to select the desired portion. This is consistent with the trend in Study B for younger subjects to show an advantage of apreparatory signal with shorter stimulus lists; however, in both studies the age trend is weak. Familiar target words were more accurately reported than unfamiliar target words-this effect was large (F = 53.54, p < .001) and equally great at all age levels. This effect is consistent with previous work on stimulus conditions affecting listening accuracy (Savin, 1963; Dodwell, 1964). Perhaps more novel is the fact that the familiarity of the masking word (the word spoken by the unwanted voice) reliably affected performance as well (see Table IV) in an interactive way. When the target word was familiar, TABLE IV STUDYC: MEANNLWBER CORRECT (ow OF EIGHTITEMS), GRADE AND FAMILIARITY OF TARGET AND MASKING WORDS

BY

Familiarity of target: Familiarity of mask:

High

High

Low

Low

High

Low

High

Low

3.5 3.4 4.0

4.0 4.5 5.4

2.5 3.5 3.3

2. I 2.5 3.2

N

Grade

Second Fourth Sixth

24 24 24

performance was better if the masking word was unfamiliar. When the target word was unfamiliar, performance was better if the masking word was 1 I4

Selective Auditory Attention in Children

familiar. The F value for this interaction was 19.28, p c .001. These findings have some bearing upon filter theory. The fact that the familiarity of the target word accounted for considerably more of the variance in performance than the familiarity of the masking word does point to a process in which the hearer first selects the desired voice on the basis of sex of voice, then “hears” only what that voice is saying. The fact that the familiarity ofthe masking word does affect performance indicates that this “filter” is not perfectly efficient. The nature of the interactive effect indicates that there is no simple tendency for familiar masking words to “intrude”upon performance; they may be either easier or harder to shut out, depending upon the familiarity of the target word. It is as though familiarity is an attribute of the stimulus words on which they can differ, and the greater the disparity between target and masking word with respect to this attribute, the easier they are to distinguish and to select from. A technical problem was encountered in the preparation of stimulus materials for Study C. In any study comparing age groups, stimulus materials are needed which will not be too difficult for the youngest subjects nor too easy for the older subjects; it will be difficult to demonstrate the effects of experimental treatments if any age group is at either the “ceiling” or the “floor” on the task. Ceiling and floor effects are more likely to become a problem, of course, when scores are based on the number correct out of a fixed number of items or trials. In psychophysical studies, for example, in which scores represent the average error of adjusting a variable relative to a standard, ceiling effects on the error scores are minimal. In the listening tasks employed in this study, with a limited number of items in the stimulus lists, there was always the danger that with some experimental conditions for some age groups, ceiling or floor effects would be encountered. The initial stimulus materials prepared for Study C were too easy for the oldest subjects, with some pretest subjects turning in errorless performances. The task was therefore made more difficult by copying and re-copying the tape until the stimulus words were less distinct and performance was near the 50% level. There is a possibility that this method of increasing the difficulty of the task operated to reduce the utility of a preparatory signal. It seemed possible that there would be a more substantial effect of set if the signals employed were clear enough so that the to-be-selected voice could be very quickly identified. To check for this possibility, we wished to replicate Study C with a clearer set of stimuli. But if clarity were increased, it would be necessary to increase the difficulty of the task in some other way to avoid ceiling effects. To this end, two-word phrases were used in place of single-word stimuli. It is not necessarily true, of course, that longer stimuli are more difficult to hear (note the finding in Study A that two-syllable words were more accurately reported than one-syllable words). Two-word phrases should be more or I15

Eleanor E. Maccoby

less difficult to hear, depending upon the relationship of the two words to one another. It should be possible to produce two levels of difficulty within the stimulus materials by using some phrases whose two words had high probability of succeeding one another in English, and some phrases for which this probability was low. By including low-probability phrases, an experiment would provide data for testing the effects of preparatory set without encountering ceiling effects. 2. Study D: Effect of variations in sequential probability of phrases The procedures for this study were the same as for Study C, except for the stimulus materials. Subjects were again asked to report either the man’s or the woman’s voice, and sometimes the signal indicating which voice was wanted came before, sometimes after, the stimuli were presented. Stimuli were two-word phrases of either high or low sequential probability. (see Maccoby & Konrad, 1967, for the methods used in constructing these phrases.) On some trials, both voices spoke high-probable pairs; on some, both spoke low-probable pairs; and on some trials, the sequential probability of the phrases was different for the two voices, in some instances the target voice having a high-probable phrase while the masking voice spoke a lowprobable phrase, in other instances the reverse. This design permitted further investigation of the roles played by the characteristics of both the messages to be chosen and the messages to be shut out. The subjects for Study D included a kindergarten group, as well as children from the second, fourth, and sixth grades (twenty-four children from each). Kindergarten children had not been included in Study C because of the possibility that they would not be able to follow the experimental procedure, but pretesting revealed that they could do so. They were included in Study D partly in order to provide another data point free of ceiling effects. Figure 1 shows that there is a clear improvement with age in selective listening for two-word phrases. (The F value for grade is 42.) Listening is more accurate when the subject is signaled in advance which voice will be wanted ( F = 102.2). The degree of advantage provided by a preparatory set is uniform across all the age levels studied, and this is true for difficult (low-probable) as well as easy (high-probable) materials, so that the degree of advantage of a before signal is independent of the baseline level from which performance is measured. The findings of this study provide some evidence relevant to one of the historic issues discussed by Woodworth and Schlosberg: namely, the division of attention. Was it possible for the subjects to hear both voices at once? If they had heard only one voice, on the average this voice would be asked for 50% of the time in the after-signal condition and performance should therefore be at the 50”/, level or less. Performance of all groups except

116

Selective Auditory Attention in Children

40L

I

1

I

I

K

2

4

6

Grade

Fig. I . Study D: Selective listening for two-word phrases: number correct. by grade and before versus ajier signal (0 = before signal; 0 = afier signal)

the kindergarten-aged subjects was above this level with the after signal, so that older children did, to a degree, hear both voices. They did not hear them as well, however, as they did with a before signal, nor as well as they would undoubtedly have done if the voices had spoken separately, so in this respect there is a limitation on the ability to hear two voices at once.

3 . Role of Memory Span in Effects of Preparatory Set The selective nature of listening-its dependence upon preparatory s e t i s even more strongly demonstrated in Study D than in Study C. In Study C there was a suggestion that older children depend upon prior set less than younger children do, but there is no evidence whatever forthisagedifference in Study D. Is this because lengthening the stimuli to two-word phrases (four words in all on each trial) exceeded the immediate memory span of children at all the ages studied? This explanation is implausible for a number of reasons: 1. Four items do not exceed the normal memory span of subjects of ages 5-12. It is true that in Study D, the four items, involving two simultaneously presented two-word phrases, are presented in a much shorter time interval than would be used in a standard digit-span procedure, but there is no consistent evidence that speeding up the rate ofpresentation ofitemsreduces memory span. (For a review of the literature relevant to this point, see Postman, 1964.) Hence it is not necessarily true that four items presented rapidly would tax memory span when four presented slowly would not. 2. Operations which would normally affect memory spandid not influence I17

Eleanor E. Maccoby

the degree of advantage provided by a preparatory signal in Study D. High sequential probability phrases ought to be more easily “chunked,” and hence more easily retained in immediate memory, than low-probable phrases. On the basis of Sperling’s hypothesis, and the findings of our Study B, high-probable phrases should, therefore, benefit less from a preparatory signal if memory span were the determining factor in the utility of a set signal. In fact, high- and low-probable phrases benefited equally from a set signal. 3. There is a slight increase in memory span between the ages 5-12. Older children ought to show somewhat less difference between beforesignal and after-signal performance. In Study D, the difference was uniform across age groups. 4. In a study with an aged sample (ages 5 H 1 , data not reported here), in which the Study D stimulus materials and procedures were used, standard digit-span measures were taken. Digit span did not correlatewiththeamount of advantage of a before signal. These considerations suggest that memory overload was not the factor determining the advantage of a preparatory signal in Study D. Taking these results together with the findings of Study B, it seems probable that memory overload may be a sufficient but not a necessary condition for selectivity in auditory perception. It appears that when stimuli are simultaneous, even when the number of elements involved is sufficiently small to be within normal memory span, the subject cannot correctly perceive all the elements at once, and a preparatory set will determine, at least in part, which elements are perceived. TABLE V STUDY

D: MEANSCORE: TCTALCORRECI’, BY GRADE AND SEQUENIIAL PROBABILITY OF TARGET AND MASKINGPHRASES

Target voice: Masking voice:

High High

High Low

Low Low

Low High

Grade Kindergarten Second Fourth Sixth

27.12 36.76 39.96 41.36

27.72 36.68 38.76 41.00

24.00 30.04 3 1.92 33.48

24.20 31.72 33.56 36.04

4. Preparatory Set and “Filtering”

In Study D, there is some evidence that this selection is accomplished through a “filtering” process of the sort postulated by Broadbent. In this study, as Table V shows, the sequential probability level of the target phrase very substantially affected the accuracy of the response (F = 202.27), with high-probable target phrases being more accurately reported. The sequential probability of the masking phrase did not significantly affect the number of 118

Selective Auditoiy Attention in Children

correct responses. This suggests an almost perfectly efficient “filter” based on sex of voice. However, the sequential probability of the masking phrase did affect performance in one respect: it influenced the number of “intrusive errors’’ (the number of times the subject gave the phrase spoken by the voice which had not been asked for). When the target phrase was low-probable, then high-probable masking phrases were more easilv shut out, in the sense that they intruded less often as errors into the subject’s performance. However, the reduction of this form of error did not permit the subject to get a larger number of items correct. The data on intrusive errors indicate that the sex-of-voice filter was not perfectly efficient: it was nearly so, however.

D. THEROLE OF SENSE-ORGAN ORIENTATION IN SELECTION BASED ON PREPARATORY SET (STUDY E) It was previously noted that in vision, a primary mechanism for stimulus selection from a complex array is eye orientation toward thedesiredelement. While “pointing” the ears toward a particular source of sound will not so efficiently select that sound and exclude other sounds, it is still possible that at least part of the advantage of a preparatory signal derives from the fact that such a signal enables the subject to orient in advance toward the desired source of sound. While subjects were participating in experiments C and D, when the before signal was received, they characteristically looked at the speaker from which the signaled voice would come. This is not a very efficient method for maximizing the use of sound localization cues from the selected voice, since this puts the source of sound for that voice in the median plane with minimal phase differences between the two ears. Nevertheless, such orientation may aid selective listening in some way, and a n experiment was designed to determine the extent to which the effectiveness of a preparatory signal depended on the opportunity to orient toward a source of sound. For this study, Study D procedures and stimuli were used. In one condition, the two voices came from separate speakers, as had been done in the previous experiments. In another condition, the two voices came over a single speaker-a condition that precluded differential orientation. In both conditions. the before or after signals as to which voice was to be reported were again given by lighting up the man’s or woman’s picture. Subjects were forty third-grade and fourth-grade children attending summer school. The comparison of performance under the two conditions revealed that: ( 1 ) Listening was more accurate with separated speakers than with single-speaker presentation: (2) performance was better with a before than with a n after signal: and (3) the amount of gain from a preparatory signal (by comparison with an after signal) was the same regardless of whether the voices came over separate speakers or a single speaker. The utility of a prior

1 I9

Eleanor E. Maccoby

signal does not depend, then, upon ear orientation. The improved selection with a before signal must be based on more central processes.

IV. Individual Differences In part, interest in attention processes in children has stemmed from the assumption that “attentiveness” and its opposite, “distractability,” are fairly stable characteristics of individuals. Inattentiveness has been thought to be a frequent concomitant of brain damage and to be associated with reading difficulties: there has been discussion of the possible etiology of poor attentiveness, including the hypothesis that this difficulty stems from early institutional experience (Goldfarb, 1945). Wynn and Singer (1963) have studied the impairments in focal attention found among schizophrenic subjects in relation to the communication patterns which characterize the family or origin. Helen Bee (1964), working with a sample of normal children, studied the family interaction patterns which are associated with high or low levels of distractability in children, one of her findings being that the parents of distractable children tend to “take over” when their children are working on problems, giving such highly specific suggestions that they are in effect solving the problem for the child, while the parents of nondistractable children tend to suggest more general strategies which improve the child’s chances of hitting upon a solution for himself. Further work on the correlates and causes of attentiveness or inattentiveness could be much more sharply focused if more were known concerning the degree of intrapersonal stability of various aspects of attentive performance. Do certain children consistently perform wellorpoorly on a wide range of tasks which require the focusing of attention, or are there several narrower clusters representing fairly independent aspects of attentiveness? Are some kinds of attentive performance more diagnostic than others of a stable “trait” or “cognitive style”? In the studies discussed above, a fairly narrow range of attentive performance was studied. In the interests of contributing to future efforts to study the nature of “attentiveness” as a n individual attribute, some exploration was undertaken of the relation of performance on the selective listening tasks to other known characteristics of the subjects. In general, there has been only a moderate degree of intrapersonal stability in performance on the selective listening tasks. Performance is quite responsive to variations in experimental conditions (e.g., whether stimuli are presented split or mixed, whether the words spoken are familiar or sequentially probable, and whether there is a preparatory signal). Furthermore, performance consistently improves with age. But within age groups, it is not always possible to identify confidently individuals who are characteristically 120

Selective Auditory A ttention in Children

skillful or unskillful selective listeners. In Study D, a kind of split-half reliability for “total correct” and for the B-A score was computed, by correlating scores on blocks I , 3, and 5 with blocks 2, 4, and 6. Blocksof items were equated with respect to the representation of high and low sequential probability items, and before versus after signals, so the procedure of correlating odd versus even blocks (rather than items) insures that the two scores for each individual will be based on the same distribution of experimental conditions. The split-half reliabilities varied greatly from grade to grade, but no consistent pattern of increasing or decreasing stability with age could be discerned. For example, the split-half correlation for grade four, number correct (corrected with the Spearman Brown formula) was only .26, while for the kindergarten group it was 3 3 , and forthesixthgraders, .75. The usual level of reliability of the “total correct score” is about .65. The test then, in traditional terminology, is valid, in that it is highly responsive to variations in experimental conditions, but only moderately reliable. Another way to assess the degree of intrapersonal stability in selective listening performance is to examine the correlations between performances under different experimental conditions. Comparing scores under beforesignal conditions with after-signal scores, we again find great variations from grade to grade: the correlations range from - .01 to + .53,and an even greater range (with higher average figures) is found when one correlates scores on high-probability items with scores on low-probability items. In view of these findings, it is not surprising that the correlations between performance on selective listening tasks and general ability measures have been inconsistent from grade to grade. Ability measures were not available for the kindergarten children, but the older children had been tested with the California Test of Mental Maturity (CTMM). In Study A, the correlation between the CTMM scores and total correct was .29 for the second graders and - .47 for the fourth graders! In Studies B, C, and D these correlations ranged from - .24 to t .49, clustering in the low positive range, with no age trend apparent in the size or direction of the correlations. It is possible, of course, that the poor correlations with ability level stem from restriction of range. In Studies A through D, we were working with children of normal abilities, using primarily verbal stimuli which were well within the vocabulary level of all the subjects. It is possible that while selective listening performance is not diagnostic of intellectual abilities within a normal range, it might be so with special population groups. As a check on this possibility, we tested a group of poor readers, who were enrolled in a summer-school remedial reading program, comparing them with a same-aged group enrolled in a nonremedial summer-school program. These two groups did not differ, either on total performance or on the degree of improvement with a before signal.

121

Eleanor E. Maccoby T A B L E VI

SWY

D CORREI ATIONS BE” CTMM SCORES,A N D

BFFORE-MWS-AFI-ER

DIFFERENCE SCORES, GRADE

CHRONOLOGICAL AGE, BY

Age x CTMM

Grade

B-A Difference scores x CTMM

B-A Difference scores x age

Second Fourth Sixth

- .02 - .28 -.51

.I0

- .45

.I6

- .35 p.51

.46

With respect to the degree of advantage provided by a preparatory set (tne differences between before-signal and after-signal scores), Study D does provide some evidence that brighter children make less use of such a set. As Table VI shows, within each grade the children with higher CTMM scores tend to be younger. There is evidently some likelihood that a bright child will be advanced in grade level, or a dull child held back, in this school system. It is perhaps not surprising, then, that within each grade level (significantly only at the sixth) older children show larger B-A difference scores. As has been shown earlier, this is not true of a comparison across age levels-older children either derive the same advantage from a preparatory signal (Study D) or slightly less advantage (Studies B and C). The within-grade correlations, then, are probably a function of I.Q. rather than age. The correlation pattern seen in Table VI is not replicated for Studies B and C, however, so if there is any tendency for brighter children to be able to dispense with a preparatory signal, it is highly specific to the experimental conditions of Study D. These meager explorations of individual differences in “attentiveness” have been rather disappointing. There is a moderate degree of intrapersonal stability in selective listening performance. Insofar as individual children can be identified as having high or low attentive skills in these selective listening situations, their attentive abilities are only very slightly related to other standard ability measures. The tasks we have used have required the subject to maintain attention to a task only over fairly brief periods. Perhaps maintenance of set over a longer period of time may proveto beamore stable aspect of the person and more diagnostic of performance in a range of intellectual tasks.

V. Implications for the Development of Listening Skills in Childhood The ability to listen selectively (to select a wanted message when more

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than one message is available) increases with age through the range 5 through 12. It seems clear that an important factor in this increasing skill is the growth of language abilities. If the material to be selected is either familiar or sequentially probable, it is more successfullyheard and reported. Furthermore there is some evidence that familiarity or sequential probability of the material to be shut out helps selective listeningat least, if the target material is difficult to hear. Older children, having greater familiarity with probable sequences within words and between words in English, are in a better position to fill in poorly heard segments of a message on the basis of the context in which the ambiguous segment occurs. In the studies reported above, it was found that sequentially probable stimulus materials improved the performance of older children more than that of the younger ones. High word familiarity substantially improved performance at all age levels, and this fact indicates that older children’s larger vocabularies also constitute an advantage in listening. Children throughout the age range studied improve their performance when they are signaled in advance which segment of the message will be wanted. There was some suggestion (in two studies) that prior alerting was more important for younger than older children, but the effect was weak and was not replicated in a third study. In any case, it is clear that even the youngest children studied possess the ability to make use of a preparatory set if it is administered immediately before stimulation. Previous work on preparatory sets in reaction-time experiments (Elliott, 1964; Grim, 1967) has indicated that younger children are less able than older children and adults to hold a set when longer preparatory intervals are used than were used in the present series of studies. This fact suggests that in normallistening situations, younger children may be at a disadvantage whenever there is a slight delay between the cue that identifies which portion of a complex auditory array will be wanted and the arrival of the stimulus array. It should also be noted that in many listeningsituations, the alertingcueisnot external; rather, the subject must alert himself. It is quite possible that young children cannot so successfully administer their own preparatory sets, or continue to re-administer them through the course of a sequential task. If this were the case, their listening performance would be poorer, not because they are unable to make use of set in listening, but because their listening more often occurs in the absence of a set, so that they must take in too much initially and select afterwards, a procedure which we have seen to be relatively inefficient. There are formidable problems in designing research on selfadministered sets and their maintenance; nevertheless, it appears essential to pursue this topic if we are to further our understanding of attentiveness and distractability in children.

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Eleanor E. Maccoby REFERENCES Bee, H. L. The relationship between parent-child interaction and distractability in fourthgrade children. Unpublished doctoral dissertation, Stanford Univer., 1964. Broadbent, D. E. Perception and communication. New York: Macmillan (Pergamon), 1958. Dodwell, P. C. Some factors affecting the hearing of words presented dichotically. Cunad. J . Psychol., 1964, 18, 72-91. Eagles, E. L., Wishik, S. M., & Doerfler, L. G. Hearing sensitivity and related factors in children. Monogr. Amer. Acad. Ophthulmol. & Otolaryngol. St. Louis: Laryngoscope, 1963. Elliott, R. Physiological activity and performance. fsychol. Monogr., 1964.78, No. 10. Goldfarb, W. Psychological privation in infancy and subsequent adjustment. Amer. J . Orthopsychiat., 1945, 15. 247-255. Grim, P. F. A sustained attention comparison of children and adults using reaction time set and GSR. J. exp. Child Psychol, 5, 1967, 26-39. Hemandez-Peon, R., Scherrer, H., & Jouvet, M. Modification of electrical activity in cochlear nucleus during “attention” in unanesthetized cats. Science, 1956, 123, 33 1-332. Hovland, C. I., Lumsdaine, A. A., & Sheffield, F. D. Experiments on musscommunication. Princeton: Princeton Univer. Press, 1949. Lawrence, D. H., & Coles, G. R. Accuracy of recognition with alternatives before and after the stimulus. J . exp. Psychol., 1954, 47, 208-214. Lawrence, D. H., & Laberge, D. L. Relationship between recognition accuracy and order of reporting stimulus dimensions. J . exp. fsychol., 1956. 51, 12-18. Maccoby, E. E., & Konrad, K. W. Age trends in selective listening. J. exp. ChildPsychol., 1966,3, 113422.

Maccoby, E. E., & Konrad, K. W. The effect of preparatory set on selective listening: developmental trends. Monogr. SOC.Res. Child. Develpm.. 1967, in press. Miller, G. A. The magical number seven, plus or minus two. fsychol. Rev., 1956,63, 81-97. Postman, L. Short-term memory and incidental learning. In A. W. Melton (Ed.), Categories ofhuman learning. New York: Academic Press, 1964. Savin, H. B. Word frequency effect and errors in the perception of speech. J. ucoust. SOC.Amer., 1963,35,200-206.

Sperling, G . The information available in brief visual presentations. Psychol. Monogr., 1960, 74, No. I I . Sumby, W. H. On the choice of strategies in the identification of spoken words mixed with noise. Language & Speech, 1962,5,119-124. Swets, J. A., & Sewall, S. T. Stimulus versus response uncertainty in recognition, J. ucoust. SOC.Amer., 1959,31, 514-521. Terman, L. M., & Merrill, Maud A. Measuring intelligence. Boston: Houghton Mifflin. 1937. Woodworth, R. S., & Schlosberg, H. Experimentalpsychology. (Rev. ed.)NewYork: Holt, 1954. Wynn, L. C.,& Singer, M. T. Thought disorder and family relations of schizophrenics, I and 11. Arch. gen. Psychiat., 1963,9, 191-206.

124

STIMULUS DEFINITION AND CHOICE'

Michael D. Zeile? WELLESLEY COLLEGE

I. INTRODUCTION

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126

11. DEFINITIONS AND TERMINILOGY . . . . . . . . . . . . . . . . . . 126 A. THE TRANSPOSITION DESIGN . . . . . . . . . . . . . . . . . . 126 B. THE SPECIFICATION OF STIMULI . . . . . . . . . . . . . . . . 126 C. CHOICES AND THE STIMULUS CLASS . . . . . . . . . . . . . 127 111. THE TWO-STIMULUS PROBLEM . . . . . . . . . . . . . . . . . . . . 128

................ ................ ........................ B. SOME BASIC DATA CHOICE GRADIENTS FOR INDIVIDUAL SUBJECTS . . . . . . . . . A. INDIVIDUAL AND GROUP DATA ................ B. PROCEDURE FOR STUDYING INDIVIDUAL GRADIENTS ...

IV. THE INTERMEDIATE-SIZE PROBLEM A. SOME THEORETICAL QUESTIONS V.

C. IMMEDIATE AND DELAYED CHOICES .... D. LARGE, SMALL, AND MIDDLE-SIZED TRAINING VI.

......... ....... THE DETERMINANTS OF CHOICE .................. A. VARIABILITY IN CHOICE BEHAVIOR .............. B.

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TRANSPOSITION AND ABSOLUTE INSTRUCTIONS

C. VERBALIZATION AND CHOICE . D. SUMMARY OF THE DATA

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................... VII. CONCLUDING COMMENTS ...................... REFERENCES ..............................

155 155

Most of the research reported and the preparation of this chapter were supported by Grant MH08818 from the National Institute of Mental Health. *Now at the Institute of Child Behavior and Development, University of Iowa, Iowa City, Iowa.

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Michael D. Zeiler

I. Introduction This chapter summarizes the current status ofa research program designed to relate behavior in transposition experiments to its controlling antecedent conditions. For two reasons, there is no attempt to review all of the literature. Because most of the research on transposition has been oriented toward theory testing and has used a variety of procedures, the literature does not reveal much information of a systematic nature. Second, there is a comprehensive review of all of the relevant experimental and theoretical work available elsewhere (Reese, 1968). The emphasis, therefore, is on an integration of the research conducted in the writer’s laboratory rather than on a survey of the transposition literature.

11. Definitions and Terminology A. THE TRANSPOSITION DESIGN

The transposition experiment is divided into the training phase and the testing or choice phase. In training, responses to one stimulus, the positive training stimulus (S + ), are reinforced and responses to other stimuli are never reinforced. Generally, the training phase ends when the subject reaches a response-probability criterion based on the proportion of S + responses to the total number of responses. In the testing phase, new groups of stimuli are presented and the choices are observed. Choice, as the term is used here, refers to responses to the test stimuli and not to some process assumed to determine these responses. The need to distinguish between choice as an instance of observable behavior and as a process has been discussed by Skinner (1950).

B. THE SPECIFICATION OF STIMULI There are no limitations on the stimulus dimensions that may be used in the training and testing phases of the transposition design. This chapter, however, treats only the situation in which the stimuli of both the training and testing sets vary on the same physical dimension. Two important variables in the description of the stimulus conditions are the similarity of the components within a given set and that between the training and the test sets. Intra-set similarity is expressed by stating the quantitative relationship between the set members. For example, if one stimulus is 2 square inches in area and the second set member is 4 square 126

Stimulus Definition and Choice

inches, the relationship between the members of a set is such that they have an area factor of 2: 1. The difference between the training and the test sets, with respect to the relevant dimension, is referred to as the distance between the training and the test sets, with distance expressed in terms of steps. In order to describe between-set similarity in terms of steps, it is necessary that the intra-set similarity be the same in the training and the test sets. Given a series of stimuli in which each successive member differs from the preceding member by a constant factor, each successive step is constructed by substituting the next stimulus in the series for the member of the previous set that is the most different from it. For example, based on a training set composed of stimuli 2 and 8 square inches in area, the test set 1-step larger would contain stimuli 8 and 32 square inches, a 2-step larger test set would consist of stimuli 32 and 128 square inches, a 3-step larger test set would consist of stimuli 128 and 512 square inches, etc. It is also possible to have steps between sets. For example, using the training set made up of stimuli 2 and 8 square inches, a test set made up of stimuli 4 and 16 square inches, would be+ step removed from the training set, and one composed of stimuli 16 and 64 square inches would be I + steps removed. Note that in all of the examples the area factor of the training and the test sets is held constant at 4: 1. This terminology is not limited to the situation in which there are two stimuli used in the training and testing situations. The most common design using more than two stimuli is the three-stimulus intermediate-size problem in which the middle-sized training set member is the S + . If the training set consists of stimuli 1,4, and 16 square inches, a 1-step distant test set contains stimuli 4, 16, and 64 square inches, and a 2-step test set would have stimuli 16, 64, and 256 square inches. A +-step larger test set would consist of stimuli 2,8, and 32 square inches, and a I+-step distance test set consists of stimuli 8, 32, and 128 square inches.

+

c . CHOICES AND THE STIMULUS CLASS

The term “transposition” has been used to refer both to the type of experiment outlined in Section 11, A and to certain test choices. As a type of choice, transposition occurs when the subject responds to the test stimulus that has the same relationship to the stimuli of the test set as had the positive training stimulus to the members of the training set. The term “absolute choice” designates a selection of the test set member most like the positive training stimulus in physical dimensions. Usually, the most convenient way to present the data of transposition experiments is graphically, with the frequency of transposition or absolute choices plotted for each combination 127

Michael D. Zeiler

of training and test sets to produce either a transposition gradient or a gradient of absolute choice. Generalizations about the nature of the stimulus class (Skinner, 1935) controlling behavior are made from the shape of the gradients of transposition or absolute choice plotted asa function ofthetraining-test distances. If the transposition gradient is uniformly high, the same relationally defined stimulus was chosen in the training and in all of the testing conditions. Because the invariant property that these stimuli have in common is their relational aspect, the inference is that the relational characteristic of the positive training stimulus controlled behavior and is the relevant stimulus class. When it is the absolute choice gradient that is at a consistently high level because absolute choices occurred at every training-test distance, the conclusion is that the absolute property of the positive training stimulus was the essential aspect learned in the training phase of the experiment and that the physical dimensions of the stimuli are the relevant stimulus class. The problem of relating choices to observable stimulus properties becomes more complex when neither of these gradients is consistently high. Typically, in such cases, the gradients of transposition and absolute choice, when plotted on the same coordinates, cross to show that neither the relational nor the absolute aspects of the positive training stimulus was uniformly in control of the test behavior. Such data have been interpreted as suggesting that the stimulus class cannot be designated purely by reference to either absolute or relational stimulus properties acting in isolation, but must be described in terms of more complex determinants (James, 1953; Riley, 1958; Spence, 1937, 1942; Zeiler, 1963b). Although there are many intuitive and theoretical preconceptions about the nature of the relevant stimulus aspect, none of which is wholly satisfactory, the problem can be approached by taking the choice gradients as the dependent variables and proceeding inductively from a consideration of systematic relationships between these gradients and experimentally manipulated antecedent conditions. In this chapter, attention is focused on what appear to be key problems with special emphasis placed on developmental studies. Among these issues are the relationship of the patterns of choices to age level and the form of the gradients when the choices are plotted as a function of the distance between the training and the test sets.

111. The Two-Stimulus Problem In 1946, Kuenne reported an experiment in which the transposition design with two stimuli in the training and the test sets was used with children divided into four groups on the basis of age. The children were tested with

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Stimulus Definition and Choice

sets that were either 1 or 5 steps distant from the training set. Although all of the subjects transposed with the 1-step test set, with the 5-step distant test, transposition dropped off to approximately 50% for the youngest children and remained at almost lW?for the older children. On the basis of her data, which were replicated in their essential aspects by Alberts and Ehrenfreund (1951), Kuenne asserted that the stimulus class was qualitatively different for older and younger children. She hypothesized that verbal factors were the critical variables responsible for the differences in the choice behavior that were correlated with age. In tests of the subject’s ability to verbalize the relevant relational concept involved in the solution of the training problem, Kuenne found that, although all of the subjects could verbalize the relationship when asked, the most explicit statements about the relational aspect of the positive stimulus were made by the older children. Kuenne concluded that the older children, as opposed to her younger subjects, were controlled by the verbalized relational property of S+ . Kuenne’s emphasis on the critical role of verbal mediation has been quite influential in subsequent theorizing about developmental changes in various sorts of discriminative behavior (Reese, 1962). But the plausibility of the Kuenne hypothesis depends upon the generality of her experimental results, and an unambiguous relationship of overt verbalization to choice has not always been demonstrated. In a series of studies of the intermediate-size problem, subjects up to the level of adults consistently demonstrated both transposition and absolute choice whether or not they were able to verbalize the relevant relational principle (Zeiler, 1963b, 1964; Zeiler & Gardner, 1966b; Zeiler & Lang, 1966). Even in the two-stimulus transposition problem, the role of verbal mediation in choice has not always been clear. Rudel (1958) worked with 2-yearold children, who were not able to verbalize the relational solution to the problem at all, and with 3-year-old children who couldverbalize thesolution. The 3-year-old children were the same age as the youngest subjects in the Kuenne and the Alberts and Ehrenfreund studies. Rudel found that there was no difference between the “verbal” or “nonverbal” children in the amount of transposition at any training-test set distance. Rather, both groups of children showed a declining gradient of transposition as the distance between the training and test sets was increased. That verbalization per se had no obvious differentiating effects raises some question about the validity of any direct relationship postulated to exist between verbalization and choice, at least for very young children. The considerable differences that Kuenne and Alberts and Ehrenfreund found between the shapes of the transposition gradients of the younger and older children suggested that different aspects of the stimulus controlled the choice behavior depending on age level. But if there are basic differences in

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Michael D. Zeiler

underlying processes for younger and older children, the results from the intermediate-size problem are surprising, since they show that neither older nor younger children always transpose whether or not they can verbalize the relational solution. An examination of the Alberts and Ehrenfreund and Kuenne studies indicated that the research was identical in several respects: (1) withinset stimulus differences were large. Kuenne used stimuli with an area factor of 1.8:l and Alberts and Ehrenfreund used an area factor of 2: 1. (2) Both experiments used a fixed number of training trials per day and continued training until the subjects reached a certain number of errorless days. (3) The tests were not administered on the same day as the training set, but were given 24 hours after the criterion was reached in training. Although these procedural variables were identical for all of the children in the two studies, it seemed important to investigate the possibility that the results were due to methodological idiosyncracies. The pattern of test choices found with infrahuman subjects and children under 4 years of age appeared in a variety of experimental situations; many investigations showed a decreasing gradient when the frequency of transposition was plotted as a function of the distance between the training and test set. But the high level of transposition with 4- and 5-year-old children was reported only by Alberts and Ehrenfreund and Kuenne. A study was conducted to assess the generality of these findings (Zeiler, 1966a). The subjects were children who ranged in age from 4 to 6 years. The variables of intra-set difference (area factor) and the distance between the training and test set were combined in a 2 x 4 factorial design. The children were trained to respond to the larger of a set of two stimuli that differed from each other by an area factor of either 1.4: 1 or 1.96:1. Four groups of eight children were trained to a criterion of five successive correct choices with one of these training sets, and then were given one test set so that separate groups received a test set that was either 1, 2, 3, or 4 steps larger than the training set. The testing phase was conducted by giving ten trials with the test set with any response reinforced. Following the ten test trials, the ability of the subjects to verbalize the relationships of large and small was ascertained by asking the subject what each block in the test set was called. Figure 1 is the gradient of transposition on the first test trial for each intra-set area factor. There was a high percentage of transposition on both the first trial and the ten test trials with all of the test sets when the withinset differences were 1.96:1. The data were quite different, however, when the differences between the stimuli were 1.4: 1 . Under these conditions, the first test trial revealed a high level of transposition at 1 step and a declining frequency of transposition as the distance was increased from 2 to 3 to4 steps. All of the children verbalized the relationships of large and small. The few instances of spontaneous verbalizations of the relation between the positive 130

Stimulus Definition and Choice

I

2

3

4

Steps

Fig. I . Percentage of transposition by 4- and 5-year-oldchildren in rhe two-stimulus problem (fiom Zeiler. 1966a).

and the negative stimuli appeared to be uncorrelated with the choices in the tests. If attention is restricted to the groups that had the area factor of 1.96:1, this study replicated the uniform transposition found by Kuenne and Alberts and Enrenfreund for the same age group. But the decreasing gradient of transposition obtained with stimuli that differed by an area factor of 1 . 4 1 was a phenomenon that Alberts and Enrenfreund and Kuenne found only with the younger children, and that Rude1 reported with 2- and 3-year-old subjects. The mere fact of’ verbalization had little relevance to choice in this study. Although these data do not show whether it is necessary for the subjects to have the ability to verbalize the relation between the stimuli in order to obtain the gradient of consistent transposition found with the stimulus differences of 1.96: 1, they indicate that the size ratios of the stimuli are variables that determine the test choices. The results of this experiment raised the possibility that there is no real qualitative distinction between the choice behavior of younger “preverbal” children and older “verbal” children, and these results fit with others that questioned adirect causal relationship between verbalization ability and choice. Of possibly greater significancethan the relationship (or lack of a relationship) between verbalization and choice was the finding that the shape ofthe transposition gradient varied with changes in the stimuli. Under certain conditions of intra-set similarity, the chosen stimuli all had the same relational property; under other conditions, different choiceswere made. Rather than indicating the stimulus class to be some invariant property, as suggested by most workers who have considered the transposition design, this study suggests that the controlling stimulus class changes as the result of experimental manipulations. 131

Michael D. Zeiler

IV. The Intermediate-Size Problem A. SOMETHEORETICAL QUESTIONS A review of the literature on the intermediate-size problem (Zeiler, 1963b) indicated that neither an absolute nor a relational definition of the stimulus was adequate to deal with the data. An alternative interpretation, the ratio theory of intermediate-size discrimination, was offered to integrate these data (Zeiler, 1963b). The ratio theory was effective not only in deducing the data of the various studies of the intermediate-size problem but also in generating some new research. Zeiler (1963a) showed that for certain combinations of training and test sets, the ratio theory predicted that subjects would choose a test set stimulus that was previously an incorrect member of the training set, even though the previous S + was present and was the middle-sized member of the test set. For example, when subjects were trained to the middle-sized stimulus (5.6 square inches) of a training set composed of stimuli 4, 5.6, and 42.2 square inches, the ratio theory predicted that, for a test made up of stimuli 4,5.6, and 7.8 square inches, the subjects would choose the smallest test member (the 4-square-inch element). Under certain conditions, this type ofprediction was confirmed. Unfortunately, however, the results have been hard to replicate, and it has been impossible to determine the conditions under which the predicted results occur. Despite a series of parametric investigations instituted to establish when this phenomenon would appear, the general finding was that the prediction was confirmed only when the writer tested the subjects. Careful observations revealed no apparent differences in procedures, gestures, or instructions between the various experimenters. Of possible relevance to theabove puzzle wasan experiment that compared the effects of training with a two-stimulus set to that with a three-stimulus set with respect to subsequent choices with a test set composed of stimuli 4, 5.6, and 7.8 square inches. Some children were trained with a three-member set made up of stimuli 4, 5.6, and 42.2 square inches; others had a twostimulus set composed of stimuli 4 and 5.6 square inches; and a third group received a two-stimulus set composed of stimuli 5.6 and 42.2 square inches. In all of the conditions, the 5.6-square-inch stimulus was correct. All experimenters obtained different test choices with the training set made up of the 5.6 and 42.2-square-inch stimuli as compared to either of the other training sets. Whether there were differences in the test choices when training was with only the 4 and 5.6-square-inch stimuli as compared with the three-member set, however, depended on whether the writer or another experimenter tested the children. Why the large (42.2-square-inch) stimulus

I32

Stimulus Definition and Choice

played a more important role in the discrimination with one experimenter than with another remains a mystery, but the finding suggested that the ratio theory prediction was maintained only when the extreme training set stimulus played a significant role in the discrimination. Apparently, choices can be altered by changes in subtle experimental factors. In an investigation using a completely automated apparatus, pigeons did not behave in accord with the ratio theory predictions when they were trained and tested with three-element sets comparable to those that confirmed the ratio theory predictions with children as subjects. Instead, pigeons either continued to respond to the stimulus reinforced in training or showed some responses to the largest test-set member. Other studies (Zeiler, 1965a; Zeiler & Price, 1965) indicated that pigeons were always controlled by the absolute stimulus class. Although the data discussed above are the only ones that uniquely support the ratio theory as the proper view of the stimulus class, this theory does provide a parsimonious integration ofmuchofthedata.The reader interested in a more detailed discussion of the ratio theory and the current theoretical status of the intermediate-size problem is referred to the exchange of notes of Riley, Sherman, and McKee (1966) and Zeiler (1966b).

B. SOMEBASICDATA I . Four- and Five-year-old children The experiments reviewed in the next three sections suggested that choice behavior is a function of chronological age. All of the experiments employed similar procedures. Following the attainment of a criterion of five successive correct choices of the middle-size stimulus of the training set, subjects received a single test set. The stimuli were Masonite blocks with indentations cut on the underside so that a small plastic chip could be hidden under the correct block without being noticed. The spatial position of each block in the training set was varied on a random basis from trial to trial. All stimulus positioning was conducted with a screen interposed between the subject and the blocks. Reinforcement consisted only of finding the chip; the chips could neither be cashed in nor kept by the subject. Verbalization tests were conducted following the completion ofthe test trials. In all of these experiments, the dependent variable was the choice made by the subject on the first test trial (Figs. 2-5). Figure 2 summarizes the results of a series of experiments with 4- and 5year-old children that were reported by Zeiler (1963b). With an intra-set difference of 1.96:1, the children chose the middle-sized test stimulus with a step difference between the training and test set, and chose the stimulus closest in size to S + with a one step difference, maintaining choice of that

+

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Michael D. Zeiler lOOf

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Fig. 2. Transposition and absolute choices by 4- and 5-year-old children in the intermediatesize problem (from Zeiler, 19636).

stimulus at distances up to I + steps. A 1.4:1 area factor was studied more extensively. As seen in Fig. 2, middle-size choice was at a high level at 1-step, decreased very rapidly at the 2-step distance, and then tended to increase. The gradient of absolute choice was low at 1 step, peaked at 2 and 4 steps, and then tapered off. At 5 steps, the small and the large stimuli were chosen with about equal frequency. As opposed to the two-stimulus study summarized in Fig. I , in which a 1.4:1 area factor produced a declining transposition gradient and a factor of 1.96:l resulted in uniform transposition, the data presented in Fig. 2 showed no dramatic changes in the patterns of choice when intra-set similarity was manipulated, The effect of decreasing the area factor was to shift the gradients of transposition and absolute choice to the right and showed that any quantitative statements about the relationship of the distance between the training and the test sets of choice must include a specification of the area factor of the sets. If the choices are in some way controlled by the similarity of the training to the test sets, the similarity of these sets is a function of the differences within each set as well as the distance between sets. 2. A dults To establish a baseline from which toevaluate developmental changes, Zeiler (1964) studied the behavior of adults in the intermediate-size problem. Because of the preconceptions that adults would use the relational basis of learning the problem and would always transpose and that successive stimulus presentation would break up that type of learning, it wasdecided to compare the effects of giving simultaneous or successive training with the training set. The subjects in the successive group received the training set stimuli one at a time and those in the simultaneous group received the 134

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training stimuli all at once. I n this experiment, a five-stimulus intermediate size problem was used rather than the three-stimulus problem that was employed with the 4- and 5-year-old children. The area factor was 1.4: 1 and different subjects were tested with one set that was from 1 to 5 steps removed from the training set. There was definitely a difference in the test choices depending on whether training was with simultaneous or successive presentation of the stimuli. Whereas the successive training conditions produced the expected consistent absolute choices, the surprising data were those of the simultaneous training group. Rather than theexpected uniform gradient ofperfect transposition indicative ofrelationships as the stimulusclass, adultsdisplayed

r0t 60

I

2

3 Steps

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Fig. 3. Transposirion and absolute choices by adults in rhe inrermediate-size problem (from Zeiler, I964 1.

the choice gradients shown in Fig. 3. On the first test trial, the adultschose the stimulus closest in size to S + with a 1-stepdistance between the training and test set, and then had a decreasing gradient of absolute responses as the distance between the training and the test set was increased. The transposition gradient provided a mirror image ofthe absolute choicegradient with a low level of middle-sized responding witha 1-stepshift anda rising frequency of transposition as the distance was increased from 1 to 5 steps. These data were particularly striking since they were exactly the reverse of the gradients that had been found with children 4 and 5 years of age. Whereas the children had a falling gradient of transposition as the distance between the training and the test sets was increased, the adults revealed a rising gradient of transposition. A replication by Zeiler and Lang (1966) revealed that the adult data were due neither to the correction procedure used in the training phase of the 1964 study nor to the use of afive-stimulus problem. Zeiler and Lang found that adults produced essentially the same pattern of responding with either a correction or a noncorrection procedure and with either three or five stimuli. 135

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The most informative data of the experiment reported in Fig. 3 were provided because the research assistant wondered what would happen on the second test trial if on the first trial the adults were told that their response was wrong no matter which stimulus they chose. Practically all of the subjects switched the way in which they responded to the test set on the second trial. That is, if they had responded to the stimulus closest in physical size to the positive training stimulus first, they now switched to the middle-sized test stimulus. If on their first test trial they chose the middlesized test stimulus, they switched to the stimulus closest in size to the positive training stimulus. When the test set was sufficiently similar to the training set that the previously positive stimulus was contained in it, adults chose the previously positive stimulus initially, but switched readily to transposition on the second trial. When the test set was so far removed from the training set that neither the previously positive training stimulus nor any stimulus very much like it was contained in the test set, the adults transposed but chose the absolute stimulus on the second trial. A consideration of the first test trial alone provided choice gradients from which any inference about the stimulus would be tenuous, but the complete data gave the answer that adults had two ways of defining the stimulus. The testing conditions played a major role in determining whether the relational or absolute stimulus class determined the behavior. Whereas adults provided justification for inferring stimulus control by both the relational aspect and the physical size of S + , the children revealed no obvious existence of multiple control. One substantial difference between the behavior of children and adults in the first test trial choices was that adults always either transposed or chose absolutely, whereas children responded unsystematically when there were large differences between the training and the test sets. The major difference, however, was the diametrically opposed transposition gradients.

3 . Seven- and Eight- Year-Old Children At what age do children switch from the behavior typical of 4- and 5-year-old children to that found with adults? Research summarized by Kendler and Kendler (1962) on intra- and extra-dimensional shifts indicated that, at over 6 years of age, behavior occurred that remained stable up to the adult level, whereas prior to the age of 5, children responded as did lower organisms. To study the transition from the behavior of 4- and 5-year-old children to that of adults in the intermediate-size problem, Zeiler and Gardner ( 1966b) reasoned that the 7- to 8-year range would provide a good starting point. Zeiler’s (l966a) study of the two-stimulus problem, which showed differences in responding due to the area factor, indicated the necessity for

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studying more than one level of intra-set similarity. Therefore, in their study of the behavior of 7- and 8-year-old children, Zeiler and Gardner (1966b) used two different intra-set area factors. With a 1.4: 1 area factor, the test sets were from 1 to 5 steps removed from the training set, and with a 1.96:I area factor, the test sets were either +, 1, or I + steps removed from the training sets. loo

Transposition

I

loor

Absolute

I

6 601

20 i

4

t

;1

If

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Fig, 4 . Transposition and absolute choices by 7- and 8-year-old children in the intermediatesize problem (fromZeiler & Gardner. I966b).

The data of this study are presented in Fig. 4.Subjects transposed with a +-step difference between the training and test set with the 1.96: 1 area ratio and with a 1-step difference with the 1.4:lfactor. With all of the other test sets, the subjects chose the stimulus closest in size to the positive training stimulus. There was no sign either of the shifting to middle-size choice that was typical of adults nor of the inconsistent choices characteristic of 4- and 5-year-old children with large distances between the training and test set. As with the younger children, the changes in area factor served only to displace the choice gradients rather than to show basically different patterns of choice. How are these differences in developmental level to be explained? Is verbalization an adequate differentiator? In all of these studies, the ability of the subjects to verbalize the concept of middle-size was ascertained. Of the 4- and 5-year-old children, approximately 25-30% were capable of verbalizing the concept of middle size, whereas all of the 7- and 8-year-old children and the adults verbalized the concept. From the bare fact that the 7- and 8-year-old children and the adults, all of whom verbalized the solution to the problem, responded differently, it appears that verbalization does not have any simple relationship to choice behavior. In addition, a review of the data of the 4- and 5-year-old children showed no apparent differences between the behavior of those children that could and those that could not verbalize this relationship. Although it is tempting to speculate about the processes responsible for the developmental differences found in this series of experiments on the

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intermediate-size problem, such speculation is premature. Recall that the slight change in procedure of telling subjects that their choices were wrong, used to evaluate the behavior of adults by Zeiler (1964), produced a completely different idea of the nature of the stimulus class than that provided by the first test trial alone. Perhaps methodological changes would uncover patterns of responding in children different from those that had been found to date. To study this possibility, different experiments were conducted with children in which the time between the training and the testing phases and the number of training sets were manipulated. 4. Temporal Factors in Choice Rude1 (1957) manipulated the time interval between the training and the testing phases and found that a training-test set combination that produced absolute choices in an immediate test produced transposition when there was a delay. This finding could indicate that children learned both the absolute and relational aspects of S + , were controlled by the absolute stimulus class in an immediate test, but shifted to relational control with a delay between the training and the testing phases of the experiment. Such an interpretation of the effects of delay was made by Wertheimer (1959). The importance of this phenomenon lies in the possibility that, if Wertheimer’s interpretation is correct, young children are like adults in that their choices are determined by multiple classes with the controlling stimulus class dependent on the manner in which the testing conditions are presented. A shift to transposition is not unambiguous evidence for middle-size learning in the training phase of the experiment. The demonstration of middle-size control requires a uniformly high frequency of transposition regardless of the distance between the training and test set. If the choice behavior after a delay varied with the distance of the training from the test set, there is no clear justification for an inference about relational classes controlling behavior since other events might be occurring in time. For example, to obtain absolute choices, the training-test set distance might have to be increased beyond what is necessary with an immediate test, but this might reflect the effect of intervening events on the perceived stimulus similarity rather than a change in the controlling stimulus class. To investigate this question, Lang (1965) tested4- and 5-year-old children immediately and 24 hours after the training phase with sets that were either 1, 2, 3, or 4 steps removed from the training set. Each child was given a single training and test set and was tested both immediately and with a delay. Whereas the 1-step test set revealed absolute choices in an immediate test when there was a 1.96: 1 area factor, it produced middle-sized choice with a 24-hour delay. A smaller area factor (1.4: 1) resulted in predominant transposition at 1 step with both the immediate and the delayed conditions.

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These results replicated Rudel's finding. With test sets at 2,3, and 4 steps, however, there were predominant absolute choices in both the immediate and delay testing conditions with sets that had both area factors. This revealed that a delay did not make the middle-size relationship the defining stimulus class, but rather that unspecified variables in the intervening time period resulted in a 1-step shift of the point of decline or increase in the gradients of transposition and absolute choice respectively.

5 . Multiple Training Sets Some interesting data from the two-stimulus transposition design suggested a possible way of training young children to transpose consistently and thereby to establish relationships as the relevant stimulus class in the intermediate-size problem. Johnson and Zara (1960) and Sherman and Strunk (1964) showed that reinforcing the same relationally defined member of two different training sets used concurrently produced significantly more transposition than when either set was used separately. Would the same relationship hold in the context of the intermediate-size problem? As with the delay problem, a demonstration of uniform transposition would indicate that children's choice gradients were susceptible to change by a manipulation of antecedent variables. The starting point was a hypothesis about when two training sets would or would not have an effect different from that of a single set. The reasoning was that two training sets, presented randomly from trial to trial until criterion was reached, would have an effect on behavior different from that of a single set only if the learning of the problem required something different in the one- and two-set situations. This hypothesis reduces to the prediction that if the sets used as multiple training sets produce transposition when one is a training set followed by the other as a test set, their joint effect as training sets will be no different from that when either is used separately as a single training set. In this situation, choices will be reinforced in the two training sets that would be made without special training. Training sets, sufficiently different from each other so that one used as a training set would produce absolute choice if the other were the test set, should produce uniform middle-size choices in a test situation when they are both given as training sets because the middle-size relationship is emphasized. The least complicated way of learning this problem might be in terms of the common relational properties of the two sets of stimuli. To maximize reinforcements, therefore, the subjects need not alter the normal stimulus class in the first situation but could switch to the relational aspect of the positive training stimuli with the second type of training set. These predictions were confirmed in a study with adults (Zeiler & Paalberg, 1964). Following training on two sets that did not normally 139

Michael D. Zeiler

produce transposition from one to the other, adults consistently transposed in the testing phase of the experiment. When given two training sets that did result in transposition when given separately, the choices were the same as when only one of those sets were used in training. Adults, who had already revealed that they were controlled by multiple stimulus classes, could be taught to use the relational class uniformly by using certain combinations of training sets. The problem was not so easily investigated with children. Many children could not learn the multiple training set problem at all, and the singletraining-set control groups transposed so much that no significant increase could be demonstrated with two training sets. Although there was some degree of increased transposition with two training sets, the changes were not of sufficient magnitude to provide a satisfactory answer to the problem that the experiments were designed to study. Neither a delay between the training and testing phases nor multiple training sets produced uniform transposition with children under 6 years of age. 6. Comparison of Two- and Three-Stimulus Problems Generally, it has been assumed that studies of transposition using either two or three stimuli are related to each other and provide information about the same discriminative processes. There is now sufficient evidence to warrant a reevaluation of this assumption, at least as it pertains to the behavior of young children. With young children, there is a decrement in transposition with increased distance between the training and the test sets in both the two-stimulus and the intermediate-size problems. But there is a compelling difference between the two situations in the gradients of absolute choice. Although significantly more absolute choices than transposition routinely occur under some conditions in the intermediate-size problem, no investigations of the twostimulus problem have shown significantly more absolute choices than transposition. Second, an increase of the area factor of the stimuli within a set increases transposition in the two-stimulus problem (Zeiler, 1966a) and decreases the amount of transposition in the intermediate-size problem (Zeiler, 1963b; Zeiler & Gardner, 1966b). The third major difference stems from a comparison of the two-stimulus problem with a three-stimulus problem in which either the large or small stimulus is reinforced. Figure 5 presents the data of a study by Zeiler (1965b) in which 4- and 5-year-old children were trained to choose the large, small, or middle-sized member of a set with an area factor of 1.4: 1 and then were tested with a set either 1, 2, or 3 steps distant from the training set. Whereas middle-size training produced a declining gradient of transposition, training on large or small stimuli produced transposition regardless of the distance of the training set from the test set. Yet, with an area 140

Stimulus De$nition and Choice

f

2

3

Steps

Fig. 5. Percentage of transposition afrer training to the large, intermediate, and small test stimulus. Data for the large and small training conditions are combined (from Zeiler, 19656).

factor of 1.4: 1, Zeiler (l966a) found that children of the same age 4 to 5 years) yielded a declining transposition gradient following training to the largest of two stimuli. Here are data that demonstrate differences in twoand three-stimulus problems even when the same relationally defined stimulus is reinforced in both. The description of the Zeiler (1965b) experiment completes the presentation of data from studies in which different subjects were given one combination of training and test sets. The patterns of choices have been shown to change in various experiments depending on the number of stimuli in the training problem, the age of the subjects, the number of training sets, the time elapsing between the training and the testing phases, intraset similarity, and the particular stimulus reinforced in the training set. But since the effects of one level of one of these variables rarely have turned out to be constant, independent of particular levels of other variables, meaningful generalizations about stimulus definition are impossible. Perhaps the clearest finding has been that different patterns of choice occur under different conditions.

V. Choice Gradients for Individual Subjects A. INDIVIDUAL AND GROUPDATA

An assumption underlying many studies of stimulus definition is that subjects should be trained with a single set and tested with a single set in 141

Michael D. Zeiler

order to obtain valid information about the nature of the stimulus class. Underlying this assumption is the idea that response to the first test set is a function of what was learned about the positive stimulus in the trainingset, but response to subsequent test sets may reflect more than the influence of training. Responding to the second test set could be influenced by both the choice made and the reinforcement contingency encountered with the first test set. A related assumption is that the only really valid measure of test behavior is the response on the first test trial. Again, it is reasonable to assume that behavior on the very first appearance of a test set is controlled by what was learned about the preceding training set. But which stimulus the subject would choose on subsequent trials with a given test set could be influenced by what happened on the preceding test trials as well as on the training trials. In support of the second assumption are data which show that patterns of responding after several test trials are different from what they are on the first few test trials with a given set. In the two-stimulus transposition problem, the frequency of transposition increases slightly with an increased number of test trials (James, 1953; Zeiler, 1966a). If one is interested in evaluating what is learned about the positive stimulus during the training discrimination, the preceding argument leads to the assertion that the only valid measure is the choice on the first test trial with a single test set. Only then are the pure effects of what was learned about the positive training stimulus revealed. But this assertion has disturbing implications. If the behavior is irrevocably affected by one testing experience so that what is learned in training is lost forever, the test set has irreversible effects on behavior. Therefore, studies concerned with stimulus definition that have used only one training and test condition with each subject have done the only sensible thing. But, if that is the case, systematic functions between training sets and more than one test set do not represent behavior that could be generated by an individual. If they do not represent individual behavior, the puzzling question of what they do mean remains. A more comfortable situation would be one which found that the baseline established in training was of a more robust and longlasting nature. If there are no irreversible changes resulting from one test set or more than one test trial, or if these effects are relatively trivial, the data based on group functions are representative of individual behavior that occur under comparable conditions. Sidman ( I 952,1960) has presented a detailed analysis of the fundamental problem of whether curves obtained from subjects tested at a single point on a continuum represent true functional relationships between independent and dependent variables in the light of reversible and irreversible effects. The preceding discussion of data in the two-stimulus and intermediate142

Stimulus Definition and Choice

size problems dealt with choice gradients that were all based on the data of groups; that is, they represent mean effects or frequencies obtained by summing across different subjects. In none of these studies were the gradients of either transposition or absolute choice plotted for individual subjects. The question is open, therefore, as to whether the curves represent general behavioral possibilities or whether they hold only for the special case of subjects trained and tested at a single data point. The answer to this question requires experiments that study the choices of individual subjects, each of whom is given the full range of conditions.

B. PROCEDURE FOR STUDYING INDIVIDUAL GRADIENTS With the realization that it was essential to study individual behavior over a range of conditions, several problems arose. Not only was it important to be able to test the same individuals at various levels of training and test set similarity, it was also desirable to conduct more than one testing session with each individual so that the stability of the choices could be examined. The situation had to be one that would have the likelihood of generating stable behavior. The procedure that seemed best suited to meet these conditions required the use of intermittent reinforcement in the training phase of the experiment. If consistent choice of the positive stimulus was established with intermittent reinforcement, it was then possible to substitute test trials for the nonreinforced training trials. In this way, no test responses were reinforced, and the contrast between reinforcement contingencies in the training and testing phases was minimized by the frequent occurrence of nonreinforced training trials. This is quite similar to the Guttman and Kalish (1956) technique for studying stimulus generalization. The general design of the studies using intermittent reinforcement and extended testing of individuals consisted of the following. A simultaneous discrimination between two or three stimuli was used throughout each experiment. Initially, subjects were trained to a criterion of five successive correct choices of the positive stimulus with a plastic chip found under the correct block on every trial. After the criterion was reached with this contingency, the second phase of training began. Pennies, instead of the chip, were hidden under S t , but the reinforcement was administered on an intermittent rather than on a continuous basis. The pennies could be kept or could be used to buy toys or trinkets from an assortment displayed on a nearby shelf. The children were informed that they would be coming back for several days in a row and could save pennies from day to day so as to be able to buy more expensive or additional toys. With the intermittent schedule, occasionally two successive choices 143

Michael D. Zeiler

were reinforced, but sometimes as many as four successive correct choices were required to produce a penny. Stated formally, this was variable ratio reinforcement of correct responses with the ratio varying between 1 and 4. The mean value was 2.5. After each choice was made, a screen was interposed between the subject and the blocks and the positions of the stimuli were changed. The procedurc, in summary, used discrete trials with variable ratio reinforcement and a reinforcement technique similar to that described by Staats, Finley, Minke, and Wolf (1964). Once the intermittent reinforcement schedule was introduced and established, a criterion of four successive correct responses with the training set were required before a test set was introduced. Then the subjects were given one or more test trials, with no choices reinforced, followed by additional trials with the training set until they again attained the criterion. This sequence of training and test trials was repeated until the necessary tests were given. The number of test trials in an experimental session varied with the number of test sets employed in the study and the number of daily presentations of each set. Of interest is the effect that the reinforcement contingencies had on the child’s willingness to return on successive days. By the second or third day, the procedure had become routine and seemed to have lost much of its intrinsic interest. No subjects, however, showed any reluctance to come back the next day; their verbal behavior revealed that the economic system was the major allure of the experiment. In all of the various experiments with this procedure, errors with the training set were infrequent after the ratio reinforcement procedure was begun. Even when extinction tests were interpolated between the training trials, the number of incorrect choices was negligible.

c. IMMEDIATE

AND

DELAYED CHOICES

The first experiment with the above procedure (Zeiler & Salten, 1967) studied the effects of the time interval between the training and testing phases on the gradients of transposition and absolute choice for individual children. A sufficient number of subjects were used to permit the plotting of meaningful group gradients and to allow for a statistical analysis of the averaged data. In this way, the group and individual gradients could be compared. Children 5 to 7 years of age were trained with the middle-sized member of the training set as S + and were tested with stimuli that had an intra-set factor of either 1.4: 1 or 1.96: 1. With the 1.4: 1 area factor, the test sets were from 1 to 4 steps distant from the training set, and with the 1.96: 1 factor, the test sets were at either +, 1,2, or 3 steps. Different children were given 144

Stimulus Dejnition and Choice

the two area factors, but each child was tested at the four training-test set distances under both the immediate and the 24-hour delayed conditions. The first day of training was used to bring the subjects to criterion on the training set with the variable ratio schedule. At the beginning of each session, on days 2 to 5, the subject was given one test trial with each of the four test sets to determine the choices that occurred 24 hours after the last training trial. Following these four delayed test trials, the training set was presented until each child reached the criterion of at least four successive correct choices. Two trials with each test set were then interspersed among training trials for the rest of the session to constitute the immediate tests. Each day always ended with the number of training trials necessary for the child to reach the criterion of four successive correct choices, so that the initial trials on the next day would always follow a criterion performance with the training set. By the end of the experiment, there were a total of eight immediate trials and four delayed test trials with each set. Nine children were given the sets with the 1.4:1 area factor, and eleven had the sets with the 1.96:1 intra-set difference. When the data were averaged across subjects and plotted as group functions, an impressive amount of regularity appeared for both the immediate and delayed tests (Fig. 6). Analysis of variance conducted on these data showed a significant decline in transposition with increased trainingtest set distance and no effect of delay.

Steps

Fig. 6. Averaged data for immediate and 24-hour delayed tests Urom Zeiler & Salten. 1967).

A comparison of Figs. 2 and 5 with Fig. 6 shows that the group functions for the current experiment produced data quite similar to those found with children from 4 to 8 years of age. The relationship, therefore, between the amount of transposition or absolute choice on the one hand, and the distance of the training and the test sets, on the other, would appear to be an orderly and replicable one. The apparent generality of this relationship is increased by the fact that the earlier studies were based on data collected

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when each subject was tested with only one set, whereas the current study tested the same subject with all of the test conditions. The data for the delayed conditions were also in close correspondence with those from Lang’s (1965) study reported earlier which investigated the effects of a 24-hour delay on the amount of transposition. As seen in Fig. 6, the delay increased the frequency of transposition only with a one step test condition. The finding that changes in the frequency of transposition were limited to this condition, however, does not fit with Wertheimer’s (1959) hypothesis that delay results in the reliance of a subject on the relational aspect of the positive stimulus.

- 1.4: I

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:

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Fig. 7 . Representative individual data for the immediate tests. The upper nwnbers on each abscissa refer to steps for the 1.4:1 area factor; the lower numbers are the steps for the 1.96:1 area factor. Each graph presents the data for two subjects (from Zeiler & Salten, 1967).

An altogether different picture emerged from a consideration of the behavior of each subject individually. Figure 7 shows eight individual choice gradients that were fairly representative of the behavior of the various children. For each subject the percentage of transposition and absolute choice was computed for each training-test distance. There were considerable differences between individual children in the way that they responded under the different test conditions. Although few subjects had identical choices, gradients could be classified into the four broad general categories of uniform transposition, inconsistent choices, declining transposition gradient, and uniform absolute choices. For each of the two different conditions of intra-set similarity, there was nearly an equal division of the subjects into these four different categories. 146

Stimulus DeJinition and Choice

Inconsistent responders were those whose gradients of either middle size or absolute choices were U-shaped or revealed approximately equal frequencies of transposition and absolute choices. The declining transposition category was for children who showed a systematic decrease in transposition with increased training-test distance. Uniform transposition refers to the choice behavior of those subjects who transposed on practically all trials with all of the test sets. The uniform absolute choice category refers to the behavior of children who chose the stimulus closest in size to the positive training stimulus in all of the tests. Since two stimuli in the +-step test set were equally similar in size to the positive training stimulus (training set = 1-3-5, test set = 2-4-6; stimuli 2 and 4 are equally similar to stimulus 3), there are subjects in the absolute response category who most frequently transposed with the j-step test. Their classification as absolute responders is based primarily on their behavior with the other test conditions. The choice of a middle-size stimulus with test sets very similar to the training set for Ss who otherwise always choose absolutely can be attributed to the difficulty of discriminating S + from the middle-size stimulus of the test set. The data for the delay tests were classified into the same four categories. Just as in Lang’s (1965) experiment, there was some general tendency for delay to increase the amount of middle-size choice for the 1-step test set. With all of the other tests, however, there was either no effect of delay on the amount of transposition, or there were more middle-size choices with an immediate than with a delayed test. One surprising finding was that the significant declining transposition gradient produced by combining the subjects into groups (Fig. 6) was representative of the behavior of only three of the twenty subjects (Fig. 7, declining transposition category). Entirely different conclusions about the nature of behavior in transposition studies stem from different ways of analyzing the data. Whereas averaging data across different subjects (Figs. 2-6) repeatedly suggested that the relationship between choice and the training-test distance is described by a rather smoothly declining transposition gradient, the individual data showed that this was not the case. Instead of uniform choices related to training-test distance, there was a considerable amount of heterogeneity between different subjects, with the declining transposition gradient found in a relatively small percentage of individuals. An analysis of the data for the individual subjects indicated no systematic alterations in the way subjects responded from day to day or from trial to trial except for two of the children classified as inconsistent responders. One of these subjects had a consistent increase in the frequency of transposition and the other had increased absolute choices with each successive day. Since most of the subjects were consistent, however, the high degree of stability 147

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indicates that the heterogeneity between subjects was not produced by the effects of one test on the next. Several authors demonstrated that group curves may not correspond with those of the individuals in thegroup (Estes, 1964;Hayes, 1953;Sidman, 1952; Zeaman & House, 1963) and suggested various techniques for handling this problem such as backward learning curves or limiting the presentation of the data to the results for individualsubjects. The same considerations about group and individual data hold for the transposition experiment. In the light of the demonstration of a minimum of four distinctly different patterns of individual choices, it is evident that inferences about controlling stimulus classes based on group curves are of questionable validity. The results for the individual subjects presented a new picture of the type of behavior that occurs in transposition studies. Instead of some homogeneous patterns of choices as a function of the relationship between the training and the test stimuli, there is considerable variety in the behavior. This variety makes it impossible to assert that there is some direct relationship between patterns of choice and the level of similarity between the training and the test sets.

D. LARGE,SMALL, AND MIDDLE-SIZED TRAINING On the basis of the Zeiler (1965b)experiment reportedin Fig. 5, it appeared that between-subject behavior was less variable following training to the largest or smallest stimulus than it was after training to the middle-sized of three stimuli. Figure 5 showed practically uniform control of choices by the relational aspect of the positive stimulus after large or small training. Of interest, therefore, was the question of whether individual subjects would show less heterogeneity after large or small training than after middle-size training. In the next experiment (Zeiler & Gardner, 1966a), the effects of training to either the largest, smallest, or middle-sized of three stimuli was studied with 28 children ranging in age from 5 to 7 years. This study used three different area ratios: 1.2: 1, 1.44: 1, and 1.73:1. One group of nine children received the area ratio of 1.2: 1, another nine received the area ratio of 1.73: 1, and the other ten children were trained and tested with the area ratio of 1.44: 1. The tests were 1, 2, and 3 steps distant from the training sets with four trials with each of the test sets given on each day. On each day for each child a different member of the training set was correct. Whether the small, middle-sized, or large stimulus was correct on a given day was determined randomly. Each stimulus was positive on either 1 or 2 days. There was a great deal of variability in choices for subject to subject 148

Stimulus Definition and Choice

and from test to test with many subjects. Some subjects transposed under one condition and not under others; some transposed more the second time after undergoing a given training condition than they did the first time; and some transposed more the first time than the second. Approximately half of the subjects transposed on all of the test trials with the three different training conditions. All in all, the conclusions must be that the subjects were quite heterogeneous in their choices. When combined into groups, however, there was a declininggradient oftransposition for the intermediatesize training conditions and a flat gradient of approximately 75% transposition after training to the large or small stimulus. As opposed to the previous experiment in which the choices made by each subject remained quite constant throughout the experiment, several of the subjects of the current study were not consistent in the way they responded with repeated training and testing. This lack of consistency suggested that something happened that had an effect over successive training or testing conditions. The major difference between this study and the preceding one, which showed stable behavior throughout the experiment, is that in the current study the training conditions were altered from day to day, whereas in the first one they were the same on each day. These data suggested, therefore, that the effects of the reinforcement contingencies of one day were not completely cancelled by those of the subsequent days. Because of the instability of the behavior with the various conditions, no conclusive statement about the effects of large, small, or middle-size training are justified. Instead, there is strong evidence that the nature of the controlling stimulus class is influenced by the subjects’ experimental history with different reinforced stimuli. The isolation of just what about the situation caused the within-subject variability and why there were so many differences between individual subjects awaits further research. Certainly no firm statement is possible about the relative frequency of transposition in individual subjects following these different types of training.

VI. The Determinants of Choice A. VARIABILITY IN CHOICE BEHAVIOR

In both experiments dealing with individuals, there were between-subject differences in the choice patterns of the children. This heterogeneity indicates that major variables that determined the choice behavior were left uncontrolled. If the independent variables that must be imposed to make all individuals choose alike were isolated, they would explain why the 149

Michael D. Zeiler

subjects in the experiments discussed earlier differed in their choices. A complete explanation of choice depends on the specification of these variables and the demonstration that they can be brought under control. The next study reported initiated a program to isolate the important factors in choice behavior.

B. TRANSPOSITION AND ABSOLUTEINSTRUCTIONS The purpose of this experiment (Zeiler & Salten, 1966)was to reduce the variability between subjects in their patterns of choices. The hope was that choices could be influenced by verbal cues about the nature of the positive training stimulus. The question asked by this experiment was whether instructions could uniformly produce either transposition or absolute choice in children 5 to 7 years of age. Explicit verbal cues were used first in the attempt to reduce variability because, if effective, they could provide a starting point from which to investigate both experimenter-generated cues and the control of choice behavior by a subject’s own verbalizations. Two types of experimenter verbalizations, given after the training criterion was attained, served as stimuli designed to influence the way in which S + was defined. When instructions were provided intended to produce transposition, the subject was asked, with the training set out of sight, which block had been correct. When the subject indicated which stimulus it was by reference to the appropriate relationship, the instructions were to remember that, even ifthe blocks were changed. For the absolute instructions, the subject was told to remember how big the block was that had been correct. Two subjects were given an intermediate-size problem and four subjects received a problem in which the larger of two stimuli was correct. Half of the subjects given each problem had training and test sets that differed by an area factor of I .4:1, and the other subjects had sets with an area factor of 1.96:l.The 1.4:l area factor test sets were 1, 2, 3, and 4 steps removed from the training set, and the 1.96:1 area factor test sets were+, 1,2, and 3 steps distant from the training sets. The procedure in this experiment differed from that reported earlier in that the children were put immediately on an intermittent reinforcement schedule for correct responses to S + without a period of continuous reinforcement with the chip. The children were told that pennies would be hidden under the blocks and that they should try to find as many as they could choosing only one block on each turn. No other instructions were given until a number of trials had been completed. Of interest is the finding that none of the subjects reached criterion until they were told both that there was no way to find a penny on every trial and, that whenever there was a penny, it would always be found under the same block.

150

Stimulus Definition and Choice

Following the attainment of criterion on the first day, each test set was presented once after either transposition or absolute instructions. No training trials intervened between the four test trials. The child was then trained to criterion again, given the other set of instructions, and was again given each test set once. On days 2,3, and 4, the subjects were brought to criterion, were given either absolute or transposition instructions, and then had two test trials with each test set. They were then trained to criterion again, given the other type of instructions, and again had two test trials with each set. In some cases, test trials with no instructions were given as the first test series on a day. Intermediate sire problem

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Fig. 8. Choices afrer transposition (unfilled circles) and absolute (filled circles) instruciions. Each rectangle enclosed by the solid lines is the daia for an individual subject (/ram Zeiler & Salten. 1966).

The choice gradients for each subject produced by computing the percentage of transposition and absolute choices for each training-test set distance are shown in Fig. 8. The heights of the two-choice gradients differed 151

Michael D. Zeiler

depending on the experimenter’s verbalization. Of the two subjects given the intermediate-size problem, both showed more transposition after transposition instructions than after absolute instructions. Absolute choices were more frequent after absolute as opposed to transposition instructions. Clear alterations in the heights of the gradients were produced by different instructions even though neither subject was brought under the complete control of the verbalizations. In summary, the postcriterion instructions did change the frequencies of transposition and absolute choices. In the two-stimulus problem, the degree of control by the instructions differed, but, in general, there was a strong relationship between the instructions and the choices. Given transposition instructions, subjects showed either predominant transposition or a considerable decrement in the amount of absolute choices that occurred with absolute instructions. Although the failure to eliminate between-subject variability shows that the instructions did not establish complete control over the behavior, such verbal cues apparently did exert a strong effect on the way subjects chose in the tests. The instructions had the same general results on all of the subjects with transposition instructions increasing the amount of transposition relative to absolute choices and absolute instructions having the reverse effects. This study represents a starting point in the discovery of the independent variables that can be manipulated to bring choice under systematic control, since it has shown that an independent variable can exert similar control over the behavior of all of the individual subjects. The gradients of absolute choice following absolute instructions represent the first demonstration that clearly predominant absolute choices could occur in a two-stimulus problem with children as subjects. Other studies of two-stimulus problems have not revealed any significant amount of absolute choice, but always have shown either transposition or equal frequency of choices of the two stimuli in the test set. Although the instructions may have produced this behavior, it is important to note that this was the first experiment of the two-stimulus problem with children as subjects that studied the choices of individuals over a range of conditions. The experiment just reported showed that experimenter verbalizations could influence behavior but did not indicate whether the effects were due to the secondary cues for choice provided by the experimenter or were because of the externalization of verbalizations made implicitly by the subjects. Although no answer to this question is possible at this time, verbalizations of various types deserve further study because of their demonstrated importance in controlling human behavior in other contexts (e.g., Ayllon & Azrin, 1964). Much research has inferred verbalization as a relevant controller of behavior, but there is not an extensive literature in which verbal behavior has been manipulated directly. 152

Stimulus Definition and Choice

c.

VERBALIZATION AND CHOICE

Some additional data are relevant to the problem of the relationship between the overt verbalizations of children and their choices in a testing situation. In the Zeiler and Salten (1966, 1967) and Zeiler and Gardner (1966a) experiments, all of the subjects could point out and give the relational labels of the members of the test set followingthe final testing session. But if the subject was given the training set, was asked to identify verbally and point to one of these stimuli, and then given a test set larger than the training set, he was frequently confused when asked to indicate the middle-sized test stimulus. Under these conditions, the subject sometimes identified the stimulus that had been the middle-sized stimulus of the training set and was the small stimulus of the test set. Similar “errors” occurred when the child was asked to point to the large training stimulus and then the large test stimulus. This finding may clarify the apparent lack of a relationship between verbalization and choice that has been found in both the two- and the three-stimulus problems. If, for example, the subject learned the middlesized concept in training but was given the test set to assess verbalization ability, he may have wrongly identified the middle-sized stimulus with the result that he was classified as a non verbalizer. Yet, had the training set rather than the test set been given, the middle-sized stimulus would have been identified correctly. Depending on the nature of the conditions used to test for the presence of the concept, different conclusions about the relevance of verbalization to choice could result. This would tend to be true particularly in cases in which the subject had limited experience with any sets other than the training set, as when the child is trained to criterion with one set, and then is given one or very few trials with the single test set. Another related possibility is that if the subject implicitly verbalized the relational concept with regard to S+ and at the same time learnedits absolute size, this verbalization was relevant to what he has learned in training and yet was not manifested in choice. Perhaps the developmental sequence involves an increase in the generalization of the relational concept so that the verbalized training relationship comes to be more relevant to the test set with increased age. A third possibility, suggested by Zeiler and Gardner (1966b), is that the verbalization is a response that is produced to verbal stimuli that are not presented until after the test, If the subjects never verbalized to themselves in the course of the solution of the problem, the verbal responses made in the post-test period played no part in the discrimination. This would imply that a post-test estimate of verbalization ability is irrelevant to choice. To bring up a vaguely related point, there has been a curious tendency 153

for psychologists emphasizing the role of verbal mediation on choice behavior to equate verbalization with relationally defined choices. But there is no real necessity to assume that verbalizations are not equally as relevant to behavior when the choices are all absolute, since the only necessary difference is in what is verbalized rather than in whether or not verbalization occurs. Regardless of what may or may not be verbalized, and of the relationship of speech to behavior, the only way to get definitive answers about mediating verbal processes is to develop a procedure to externalize these hypothesized internal or implicit events.

D. SUMMARY OF THE DATA The experiments with individual subjects reported in this chapter raised questions about several conclusions from studies that have used group data. In particular, no statement involving the amount of transposition and the distance of the training from the test sets can be made that stands as a description of individual choice behavior. The most reliable empirical relationships are summarized below. ( I ) A general finding is that behavior can be controlled using intermittent reinforcement in a discrete trial situation. The accuracy of the discrimination of S + is not affected by the interpolation of unreinforced test trials. Observations of behavior under the conditions of intermittent reinforcement suggest that a strong reinforcing system, such as money backed up by toys, is necessary to maintain behavior under these conditions. (2) A delay interpolated between the training and the testing phases does not result in increased transposition except under very limited conditions. Both individual subjects and group averages showed little, if any, increase in transposition after a delay as compared to an immediate test. (3) A finding that cuts across the various studies of the behavior of individual children is that there is considerable heterogeneity in the way different children respond in the testing phase of the experiments. Apparently there are many parameters that operate to control choice in addition to the specific stimuli that are reinforced or not reinforced in the training phase of the experiment. (4)The third study using individual children revealed that verbal instructions considerably reduced variability. Since variability was not eliminated, however, there are obviously other factors in addition to verbal and stimulus factors that control behavior in this kind of situation. But the effects of these instructions were relatively uniform across all of the subjects. (5) Since systematic developmental changes in choice have appeared with grouped data based on the testing of individual subjects at a single point, the orderliness of these data require their consideration. Equally impressive, however, were the differences that occurred between children of the same age or even within the same children from the first to the second times they were trained and tested under certain conditions.

154

(6) Statements about the nature of a single defining stimulus class are impossible. What is learned varies with the situation.

VII. Concluding Comments The idea that the controlling stimulus classes change with a multitude of factors, including both those that are manipulated in an experiment and those that are part of the subject’s history at the time the experiment begins, was stated by Skinner in 1935 in his discussion of the nature of stimuli and responses. Although Skinner’s approach to stimulus definition was that expressed in the analysis of transposition in this chapter, the same approach has not been characteristic of all of the work in the area. A comparison of the discussions and rationales of several of the author’s experiments, when they were originally published, with the analysis of the same experiments in this chapter reveals the difference. Whereas the original approach was to infer the defining nature of the stimulus from the observed behavior, the current analysis defines the stimuli in terms of their observable properties and attempts to analyze the conditions in which different stimuli are chosen. The primary goal of the research program reported in this chapter is to explain choice behavior completely by means of a description of the relevant controlling conditions. As of now, the series of experiments has identified some of the variables that have a part in determining the controlling stimulus class. From this research, the conceptual and methodological paths to be followed in the next stages of the program have evolved.

REFERENCES Alberts, E., & Ehrenfreund, D. Transposition in children as a function of age. J. exp. Psyhol., 1951.41, 30-38. Ayllon, T., & Azrin, N. H. Reinforcement and instructions with mental patients. J. exp. am/. Eehuv., 1964.7, 327-33 I. Estes, W. K. Probability learning. In A. W . Melton (Ed.), allegories o f h learning. New York Academic Press, 1964. Guttman, N., & Kalish, H. I. Discriminability and stimulus generalization. J. exp. Psyhol.. 1956. 51. 79438. Hayes, K. J. The backward curve: a method for the study of learning. Psyahol. Rev., 1953,60, 269-215. James, H. An application of Helson’s theory of adaptation level to the problem of transposition. Psychol. Rev.,1953,46, 34S351. Johnson, R. C., & Zara, R. C. Relational learning in young children. J . romp. physiol. Psychol.. 1960,53,594-597. Kendler, H. H., & Kendler, T. S. Vertical and horizontal processes in problem solving. Psychol. Rev., 1962.69, 1-16. Kuenne, M. R. Experimental investigation of the relation of language to transposition behavior in young children. J. exp. Psyahol., 1946,36,471490. Lang, J. The effect of delay in test and intra-set differences on the solution of the intermediate size problem by children. Unpublished manuscript, 1965. Reese, H. W. Verbal mediation as a function of age level. Psychol. Bull., 1962. 59,502-509.

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Reese, H. W . The perception of stimulus relations: Discrimination learning and transposition. New York: Academic Press, 1968. in press. Riley, D. A. The nature of the effective stimulus in animal discrimination learning; transposition reconsidered. Psychol. Rev., 1958.65, 1-7. Riley. D.A,, Sherman, M.. & McKee. J. P. A comment on intermediate size discrimination and adaptation level theory. Psychol. Rev., 1966,73,252-256. Rudel, R. G.Transposition of response by children trained in intermediate-size problems. J . comp. physiol. Psychol., 1957,50, 292-295. Rudel, R. G . Transposition of response to size in children. J. comp. physiol. Psychol.,

1958, 51, 386390. Sherman, M., & Strunk, J. Transposition as a function of single versusdouble discrimination training. J. comp. physiol. Psychol., 1964,58,449450. Sidman, M. A note on functional relations obtained from group data. Psychol. Bull. 1952,49,

26?-269. Sidman, M. Tactics of scientijfc research. New York: Basic Books, 1960. Skinner, B. F. The generic nature of the concepts of stimulus and response. J. gen. Psychol., 1935,12,4045. Skinner, B. F. Are theories of learning necessary? Psychol. Rev., 1950,57, 193-216. Spence, K.W. The differential response in animals to stimuli varying within a single dimension. Psychol. Rev., 1937,44,43W. Spence, K. W. The basis of solution by chimpanzees of the intermediate size problem. J . exp. P~ychol.,1942.31. 247-271. Staats, A. W.,Finley, J. R., Minke, K.A., & Wolf, M. Reinforcement variables in the control of unit reading responses. J. exp. anal. Behav., 1964,7,139-149. Wertheimer, M. On discrimination experiments: I. Two logical structures. Psychol. Rev., 1959,

66,252-266. Zeaman, D., & House, B. J. The role of attention in retardate discrimination learning. In N. R. Ellis (Ed.), Handbook ofmentnl deficiency. New York: McGraw-Hill, 1963. Zeiler, M. D.New dimensions of the intermediate size problem: Neither absolute nor relational response. J. exp. Psychol., 1963.66, 588-593. (a) Zeiler, M. D. The ratio theory of intermediate size discrimination. Psychol. Rev., 1963,70,

516533.(6) Zeiler, M. D. Transposition in adults with simultaneous and successive stimulus presentation. J. exp. Psychol., 1964,68,103-107. Zeiler, M. D.Solution of the intermediate size problem by pigeons. J. exp. anal. Behav., 1965, 8,263-268.(a) Zeiler. M. D. Transposition after training to the largest, smallest, or middle-sized of three stimuli. Paper read at meeting of the East. Psychol. Ass., Atlantic City, April, 1965.(6) Zeiler, M. D. Solution of the two-stimulus transposition problem by four and five year old children. J. exp. Psychol., 1966,7I,576579.(a) Zeiler, M.D. The stimulus in the intermediate size problem. Psychol. Rev., 1966,73,257-261.(LJ) Zeiler, M. D., B Gardner, A. M. Individual choice gradients after large, small, or middlesized training. Unpublished manuscript, 1966. (a) Zeiler, M. D., & Gardner, A. M. Intermediate size discrimination in seven and eight year old children. J . exp. Psychol., 1966.71, 203-207. (b) Zeiler, M. D., & Lang, J. Adults and the intermediate size problem, J. exp. Psychol., 1966,72,

3 I 2-3 14. Zeiler, M. D., & Paalberg, J. The effect of two training sets on transposition in adults. Psychon. Sci., 1964, 1, 85-86. Zeiler, M. D., & Price, A. E. Discrimination with variable interval and continuous reinforcement schedules. Psychon. Sci., 1965,3,299-300. Zeiler, M. D. & Salten, C. S. Verbal instructions and choices. Unpublished manuscript, 1966. Zeiler, M. D. & Salten, C. S. Individual gradients of transposition and absolute choice. J. exp. Child Psychol. 1967,5,NO.2.

156

EXPERIMENTAL ANALYSIS O F INFERENTIAL BEHAVIOR I N CHILDREN’

Tracy S. Kendler and Howard H. Kendler UNIVERSITY OF CALIFORNIA

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I. THEORETICAL BACKGROUND

11. INITIAL RESEARCH ON INFERENTIAL BEHAVIOR O F CHILDREN 111. DEVELOPMENT O F INFERENTIAL BEHAVIOR IN CHILDREN IV.

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INFRAHUMAN REASONING

INFLUENCE O F EXPERIMENTAL VARIABLES ON INFERENTIAL BEHAVIOR O F CHILDREN ...................... DISCUSSION REFERENCES

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VIII. SUMMARY AND CONCLUSIONS

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I. Theoretical Background In 1930 Hull wrote an article entitled “Knowledge and Purpose as Habit Mechanisms” in which he set out a scheme for how an S-Rlearning theory ‘The research on children described in this paper was made possible by a series of three successive grants from the National Science Foundation including grant numbers GB-277 and 68-1447. The preparation of this report was aided by Public Health Service Grant HD-01361 to the senior author. The authors are grateful to Barrie Butler, Martha Carrick, May DAmato. Zena Pearlstone, Stanley Plisskoff, and Dons Wells for their expert assistance in the conduct of some of the experiments reported. We would also like to note our appreciation of the helpful cooperation we encountered in the many schools in which this research was conducted.

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could encompass intelligent foresight. He defined foresight as the reaction to an event which may be impending but has not yet taken place. Foresight presents a problem to the S-R learning theorist, because an event that is not yet in existence is not yet a stimulus and therefore cannot evoke a response. Having formulated the problem, he proceeded to solve it by analyzing the events in S-Rterms and introducing the concept of the “pure stimulus act.” The essence of his theory was that the events of the external world can be characterized as a series of stimuli, each of which evokes a corresponding response. Thus sequences in the outer world evoke parallel reaction sequences in sensitive organisms. A “high-grade organism possesses internal receptors which are stimulated by its own movements” (Hull, 1930, p. 5 12). Accordingly, each response produces a characteristic stimulus complex. These internal stimuli become associated with ensuing responses. Once the first response is initiated the whole chain of responses can run off even if the external events are interrupted. In this way the world stamps its pattern on the organism, and in this sense the organism “knows” the external world. A sequence of such representative responses provides a mechanism for foresight if the tempo of the response chain is faster than that of the outer world sequence it parallels. For example, if the last stimulus is noxious and produces flight, foresight will result if the response series runs off quickly enough for flight to occur before the noxious stimulus impinges on the organism. The idea that the proprioceptive feedback of most if not all responses is an important source of stimulation for the organism led Hull to postdate a class of responses whose sole function is to serve as stimuli for other acts, namely pure stimulus acts. Since these acts could be cued by other acts of the organism, as in the case of foresight, this conception provided a modus operundi for an organism’s ability to cope with the “not-here” and the “notnow,” a mechanism for a rudimentary form of individual symbolism. Now, as an aside, note that if pure stimulus acts influence the behavior of any organism then these acts are synonymous with verbal behavior as defined by Skinner (1957) or communication behavior as it is generally conceived. But Hull, recognizing this, chose to avoid the inherent challenge for the time being because he believed that acts of social or linguistic communication involve special stimulus-response mechanisms too complex for consideration at that time. Up to this point the only property that was assigned to pure stimulus acts was that they must have feedback, but Hull took the conception further. Since pure stimulus act sequences have no instrumental function they can be reduced in magnitude to any degree compatible with the production of adequate stimulation. Biological economy would dictate that they will become minimal. In fact, it is conceivable that they will diminish until 158

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nothing but a neural vestige remains. Similareconomic consideration would also suggest that some parts of the sequence would drop out until what remains is the smallest functional unit compatible with biologically adequate function. Note that although a pure stimulus act may at some point be sufficiently gross to be directly observable it not only may but is likely to become reduced to almost any degree consistent with adequate feedback. With this conception, Hull showed why foresight should be widespread among organisms capable of fractionated pure stimulus acts. Subsequently Hull (1935,1952)extended the pure stimulus act to apply to aphenomenon variously called reasoning, insight, inference, intelligence, and other synonymous terms. To define the phenomenon more precisely, in language appropriate to his system, Hull described it as the joining of two behaviorchain segments previously learned on separate occasions so that together they solve a problem faced by the organism. To illustrate his definition and provide a vehicle for his theory he designed an experimental paradigm

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Fig. I . Diagrammatic representation of three locomotor paths suitablefor use in an experiment on behavioral inright (adapted from Hull. 1952. p. 310; reprinted with permission of Yale University Press).

utilizing the maze presented in Fig. 1. In the paradigm, an organism forms the locomotor habit J - L with a large food reward on one occasion; on another occasion the habit H - J with a small food reward; and on a third occasion the habit H - N with a similarly small food reward. Then the hungry animal is placed at H to determine which path he will choose and how smooth or rapid his responses will be. Although the maze is clearly designed for experimentation with rats, Hull offered some comments about species differences worth mentioning

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Tracy S. Kendler and Howard H. Kendler

here. “It is perfectly obvious,” he wrote, “that normally intelligent humans would choose path H-J-L rather than path H-N. How far down in the animal scale this capacity extends remains to be determined experimentally. We are at present far from knowing enough about individual and species differences to speak with any confidence on this matter from the theoretical point of view” (Hull, 1952, p. 309). Having assumed that some organisms can perform insightfully, that is, choose H-J and join it smoothly to J-L, Hull offered a theory about how this process occurs which, like foresight, depends on the pure stimulus act. In this instance, he used only that pure stimulus act which represents the goal events, namely, the fractional goal response (rg).The theory proposes that rg of the major goal moves back from L toward J and is presently evoked by J itself. When H-J is learned rg is brought forward to path H , . Since rg produces stimuli, these stimuli become associated with the overt RHi. Therefore RHi is conditioned to all of the stimuli to which R,, is conditioned plus the stimuli associated with rg.When the organism is placed at H and allowed to choose he will make the insightful choice because there are more associated connections to RHithan to RH2. Although the theory is formulated in terms of locomotor responses, Hull attempted to show that it may be extended, with some additions and modifications, to cover the insightful tool-using behavior observed in chimpanzees by Kohler (1925) and by Yerkes and Yerkes (1929) among others. The important point is that with this theory Hull tried to extend his behavioral analysis to cover a complex process like insight which was usually considered beyond the scope of S-R learning theories. In doing so, he sharpened the definition of the term, provided a set of operations for measuring the occurrence of insight, and offered a number of testable theorems.

11. Initial Research on Inferential Behavior of Children When we began to investigate problem solving in children Hull’s paradigm had never been used in an experiment but Maier had presumably demonstrated that rats could reason (1929). In fact it was Maier’s definition of reasoning as the ability to combine the essentials of isolated experiences that led Hull to invent his experimental paradigm and it was probably Maier’s research that made the paradigm take a form most appropriate to rats. In Maier’s experiments with rats, the apparatus consisted of three small tables joined together by three elevated pathways which met in the center. The rats were permitted to explore the pathways and tables freely. Then food was put on one of the tables. The animal was placed on this table. allowed to eat a small amount, and then placed on one of the other 160

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tables to see whether he would go directly to the food table. On subsequent days a similar test was given involving different combinations. In one representative study, Maier (1932) compared young rats (59-90 days old) with adult rats (over 120 days). The per cent of correct runs on 12 days exceeded chance for both groups but, the older rats performed more effectively than the younger. Maier also studied reasoning in children (1936) using essentially the same procedure except that the maze was shaped like a swastika and the goal was a toy windmill. The results led him to conclude that in humans this ability is rather late in maturing since it is rarely developed before 6 years of age. It is immediately obvious that one of the important differences between the Hullian and the Maier paradigms is that the former is a one shot affair and the latter is more like a learning set procedure. Another more complex difference which we did not appreciate at the time, but which proved to be even more fundamental, will be discussed in a later section on infrahuman reasoning where its significance will be more apparent. Against this background, we started to investigate what could be learned about reasoning in young children and how far S-R behavior principles would go in accounting for what we found. Our intention was to begin by applying the Hullian paradigm in order to test a deduction from Hull's theory. The deduction was that inferential behavior should be influenced by the order in which the behavior segments are acquired. We reasoned that, if the occurrence of a correct initial choice hinged on the backward movement of r, from the major goal segment to the relevant minor goal segment, inferential choices should be more likely when training on the former preceded training on the latter. This variable is particularly interesting because a Skinnerian formulation would engender a similar prediction. The assembly of habit segments can be viewed as an exercise in chaining. In setting up behavior chains, it is qsually most efficient to start with the last link or segment. This enables the initiating (discriminative) stimulus of that segment to acquire secondary reinforcing powers which will in turn strengthen the relevant subgoal segment, Since the subgoal associated with the irrelevant subgoal segment does not acquire such additional reinforcing powers, the irrelevant initial choice should be less likely than the relevant, provided that training on the major goal segment precedes training on the relevant subgoal segment. The initial task was to design an experimental situation feasible for use with children and consistent with the Hullian paradigm. This task was more difficult than we had expected; in fact we have not yet completed it to our total satisfaction. The only relevant precedent was Maier's swastika maze, which was not suitable if only because our approach required relatively large numbers of subjects. This meant we needed a small portable apparatus 161

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that could be brought to schools in which subjects were plentiful but space was scarce. It is true that Piaget and Inhelder were studying reasoning in children using ingenious problems that required very simple apparatus. Moreover, these problems were better adapted to the human mode than locomotor mazes. But the responses they measured were primarily linguistic and we were seeking methods of experimentation that, like the Hullian paradigm, could ultimately be adapted to infrahuman organisms and to prelinguistic as well as “linguistic” humans. Our first apparatus (Fig. 2) closely resembled the maze in the Hullian I

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Fig. 2. Diagram of the first apparatus used to investigate inferential behavior of children (adapted from Kendler & Kendler, 1956. p . 31 1 ; copyright 1956 by the American Psychological Association and reprinted with permhion).

paradigm except that, instead of travelling through the paths to reach the reward in the goal box, the children remained outside of the apparatus and pulled a ribbon or a chain through the path to obtain the goal (Kendler & Kendler, 1956). Each child was trained on three separate behavior segments, designated as A-B (relevant subgoal segment), X-Y (irrelevant subgoal segment), and B-G (major goal segment). After training he was instructed to obtain the major goal, but the only responses available to him were those associated with the A-B and X-Y segments. In this, as in all subsequent experiments, the position of the A-B segment and the character of the subgoals were counterbalanced. To provide a pilot test of the effect of order of training, four out of the six possible orders (three segments taken three at a time) were used. The subjects were nursery school children between 3 and 6 years old. More of these children made the correct initial choice than would be expected by chance (72%), but no more correct initial choices occurred when B-G preceded A-B (62%) than when A-B antedated B-G (81%). In fact, the direction was opposite to that predicted! We also found that the apparatus was excessively large and clumsy, produced strong alternation responses which increased variability, and allowed for possible external orientation cues which obscured the issue. 162

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aperture

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1

Fig. 3. Diagram of the second apparatus used to investigate ir$erential behavior of children (adapted from Kendler el al., 1958. p . 208; copyright 1958 by the A m e r i m Psydrologial Association and reprinted with permission).

The next apparatus (Fig. 3), one step further removed from a maze, was a gray box-like structure with two levers, (A) and (X),projecting from its side. When either one of the levers was pushed it moved a box (B or Y) into the lower aperture. One of the boxes was square and yellow, and the other was red and triangular. For any given child, one of the boxes (B) was attached to the circular container (G) so that when B was pulled down through the lower aperture G emerged at the upper aperture. B and Y each held a single raisin and G a gold charm. This apparatus, which effectively eliminated any orientation cues or position preferences, was used in a series of experiments on nursery school children between 3 and 6 years of age (Kendler, Kendler, Pliskoff, & D’Amato, 1958). Each segment was acquired separately, and then a problem was presented which first required the response appropriate to the A-B segment followed by that appropriate to the B-G segment. Order of training was held constant. The variables under investigation were reinforcement during training and motivation during the test trial. The question was whether inferential behavior, similar to instrumental behavior, is influenced by these two basic variables. The answer appears to be affirmative, but to describe in sufficient detail how the variables were manipulated would take us too far from our present path. For present purposes the significant result was that in each of the experiments, under optimal reinforcement and motivation conditions, there was evidence that correct initial choices were significantly more likely than chance would allow. For all experiments combined, initial A choices were made by 65% of the children. But with the second apparatus another aspect of inferential behavior came under observation. We were somewhat surprised to find that during the test trial there were many children who, having made the initial correct 163

Tracy S. Kendler and Howard H . Kendler

choice and thereby placed B into position to obtain the major goal, nevertheless did nothing to obtain it. In order to get the charm they need merely to have pulled B down the lower aperture as they had previously done during B-G training, yet only 35% of those whose initial choice was A did so spontaneously in the test situation. Perhaps, we thought, this failure to achieve solution, when it was so obvious, was due to a lack of attention to the subgoal boxes. Perhaps the children attended only to the raisin and not to the shape and color of the containers which differentiated B from Y. To remedy this situation as well as to improve the mechanics of the apparatus still another one was constructed which, among other things, ensured that B and Y were not only attended to but discriminated as well. The third apparatus (a modification of which is shown in Fig. 4) no A- 8

8-G

x-Y

Fig. 4 . Photograph of apparatus used in the investigations of inferential behavior in children discussed in Sections I l l , V. and VI.

longer resembled a maze in any degree but maintained the essential character of Hull's paradigm. It consisted of a rectangular box with three distinct panels each 7 inches high by 6.25 inches wide. Each panel, which could be exposed to the subject's view singly or in combination with the others, corresponded to one habit segment. The center panel, which was yellow, provided for the B-G segment. On its surface, near the top, was a circular opening 1 inch in diameter, into which the subject could drop the small objects, a brass cube or a glass marble, that served as subgoals in this experiment. If the subject dropped the correct subgoal into the circular opening a pellet of candy (M&M) was propelled to an open tray 164

Analysis of Inferential Behavior in Children

near the bottom of the panel. The candy served as G, the major goal. If the incorrect subgoal was dropped into the aperture, no reward was delivered. During B-G training, the two subgoals were placed in front of the center panel. The two side panels correspond to the A-B and X-Ysegments. The left panel was red and the right panel was blue. Each of these panels was equipped with two manipulanda. Each manipulandum was shaped differently and required a different characteristic movement; “turn” and “toggle” on the left and “push in” and “push down” on the right. When the child responded appropriately to the correct manipulandum on either side panel, the appropriate subgoal was delivered. When he responded incorrectly, no subgoal was delivered. During training only one panel was open at a time. When the criterion on that panel was reached, the panel was closed and another opened. After the child was trained on all of the segments, all of the panels were exposed and he was instructed to get a candy. Now, however, the subgoals were not put in front of the B-G panel. A correct inferential solution required the child to make the response appropriate to the A-B segment and then drop the subgoal he obtained into the hole in the B-G panel. The next experiment used the third apparatus to provide a full scale test of the prediction that inference should be more likely if B-G preceded A-B than vice versa (Kendler & Kendler, 1961). The six possible orders in which the three segments could be presented are (1) B-G, A-B, X-Y; (2) X-Y, B-G, A-B; (3) B-G, X-Y,A-B; (4) A-B, B-G, X-Y;(5) A-B, X-Y,B-G; and (6) X-Y,A-B, B-G. The experimental design consisted of six experimental groups corresponding to the six orders of presentation; the subjects were preschool children between 30 and 65 months. The result failed to produce any statistically significant difference in either the per cent of correct initial choices or in the integration of the relevant segments between any of the six groups or between relevant combinations of the groups. On the whole, there was no indication whatever that order of presentation has a significant effect on the inferential behavior of young children. For a second time, empirical results were inconsistent with Hull’s theory of insight. One other result is pertinent. It is that this new apparatus, which required that the segments be learned and that the subgoals be discriminated, did not increase the probability that children would behave inferentially. There were, in fact, fewer inferential solutions in this experiment than in the others. The per cent of correct inferential solutions was so small ( 1 3%) that we had to wonder why the great majority of the children were unable to solve the problem. This “game” was more complex than the previous ones since it required 3 discrimination within each subgoal segment as

165

Tracy S. Kendler and Howard H . Kendler

well as between segments. Perhaps this increase in difficulty was more than enough to offset any advantage gained by the improved apparatus. But it was also the case that the children in this experiment were drawn from a day care center for working mothers in a low socioeconomic neighborhood while those in the previous experiments came from private nursery schools in upper-middle class neighborhoods. The difference between these samples might also have been due to differences in intellectual functioning. Plainly we had reached a stage where we had to take into account the level of intellectual development of our subjects.

111. Development of Inferential Behavior in Children Succeeding experiments took account of intelligence in two ways; chronological age served as a variable and the different age groups were matched for IQ as measured by the Peabody Picture Vocabulary Test (Dunn, 1959). These experiments dealt simultaneously with two sets of factors, experimental manipulations and developmental variables, but to make the line of argument clear the developmental variables will be dealt with first. The apparatus in these experiments was similar to the third apparatus but there were a few significant modifications (see Fig. 4). For one thing, each side panel had only one button instead of two manipulanda, thereby making the problem a little simpler. A steel ball bearing was substituted for the cube for mechanical reasons, and the major goal was a charm instead of a pellet of candy. Since we were no longer especially concerned with the order of training effect, a new training procedure was adopted which ensured that the child learned the connection between the response and the subgoal. Finally to decrease the possibility that the children would forget which subgoal produced the major goal, the last segment to be learned was the B-G segment. The procedure was also somewhat different. Since this procedure is basic to all of the rest of the experiments, it is described in some detail. As in the previous experiments, all subjects were run individually and completed in one experimental session. The session began with the administration of the Peabody Picture Vocabulary Test which took from 5 to 15 minutes and was followed immediately by training on the inference apparatus. One of the side panels was opened, and the S was told, “Press this button and see what happens.” When the subgoal was delivered, the S was instructed to pick it up, look at it. then return it to the experimenter so that he might have another turn. This side panel was closed. the other side panel opened, and the procedure repeated. After the S had one forced 166

Analysis of Inferential Behavior in Children

trial on each panel, the procedure was repeated with the order of the sequences reversed. Thus at this point in training the S had made two responses on the A-B and on the X-Y segments in the ABBA order. After these four forced trials, the doors of both side panels were opened and the S was shown one of the subgoals and directed to, “Press the button that will get one like this.” The procedure was repeated with each of the subgoals presented in an ABBA-BAAB order until the criterion of six successive correct responses was reached. The next step of the training started with the experimenter opening the middle panel (after closing the two side ones) and directing the attention of the S to a small window through which he could see a charm. He was told that it was a fairy-tale or nursery-rhyme charm which he would soon get an opportunity to examine closely. The aperture was pointed out and the S was informed that if he dropped “the right thing” into that hole, the charm would drop into the tray. Then the marble and the ball bearing were placed in front of the B-G panel and the experimenter said, “One of these two little things is the right thing. Take one of them and drop it in the hole to see if it makes the charm come out.” On the next trial the S was again instructed to drop in the one that would make the charm come out. After that, training proceeded until a criterion of four successive correct responses was reached. Ss who made two or less errors received no additional instructions while those who committed three or more errors were again urged to drop in the one that would make the charm come out. The relative positions of the marble and ball bearing (i.e., left and right) were varied in a random order after each correct response throughout the training on the B-G segment. After preliminary training the test trial was introduced with the following instructions: “Would you like to see another charm? Very well, this time I won’t put out any little things, but I will open all the doors. If you do what you are supposed to, you can make the charm come out. Go ahead.” The S was allowed 60 seconds in which to make any response that he chose. If he did not press the A or X button during this time, the experimenter said, “Which button should you press to help you get the charm? Go ahead.” After the S pressed either button, he was allowed another 60 seconds to complete the sequence by dropping either subgoal into the B-G aperture before the trial was terminated. Thus all Ss made either an A or X response, and the trial was terminated either when the S made a major goal response or when 60 seconds had elapsed since the subgoal had appeared. In order to minimize contamination from position and subgoal preferences, they were assigned in counterbalanced order: (a) half of the Ss in each experimental group had the right panel serve as the A-B segment while the left panel served as the X-Ysegment. The opposite arrangement applied to the remaining half. (b) For half of the Ss in each experimental group 167

Tracy S. Kendler and Howard H. Kendler

the marble was S, and the ball bearing S,; for the remainder the ball bearing was S, and the marble S,. The above procedure was used with the control groups of the next three experiments. The Ss in two of them were kindergarten and third grade children from Berkeley (T. S. Kendler & H. H. Kendler, 1962) and Santa Barbara (Kendler, Kendler, & Carrick, 1966), California public schools, respectively. The kindergartners ages ranged from 57 to 75 months with a mean of 68; the third graders from 84 to 118 with a mean of 104. Within each of these experiments, there were no significant IQ differences among the groups, nor was there any difference between the samples since the mean IQ of both was 108. The Ss in the third experiment were female Barnard College students (unpublished). No intelligence test was administered to the college students but they doubtlessly differed from the public school samples in IQ as well as CA. The obtained proportion of initial correct choices for each group, along with an estimated proportion adjusted for chance, are presented in Table I. The estimate adjusted for chance was derived as follows: TABLE I EACHEXPERIMENT WHOSE THE TESTTRIAL WAS CORRECT

PROPoRTlON OF CONTROL SUBJECTS IN CHOICE ON

NT Kindergarten, Berkeley Kindergarten,Santa Barbara Third grade, Berkeley Third grade, Santa Barbara College, Barnard

64 32 64 32 48

INITIAL

Obtained proportion correct

Estimated proportion adjusted for chance

.50

.oo

.53 .I3 .66 .96

.06 .46 .32 .92

Let pg = proportion of Ss who are guessing about their initial choices, pk = proportion who know the correct initial choice, and p, = obtained proportion of correct initial choices. Assume that, since there are only two choices, the “guessers” will be correct half of the time but “the knowers” will be correct all of the time: p, = .50 pg + 1.00 pk’ (1) Assume that all Ss are either “guessers” or “knowers”: p g + p & = 1.00 (2) To obtain an estimate of pk when only p, is known Equations 1 and 2 are solved simultaneously: p & = 2p0- 1.00 (3) The data in Table I show that the performance of the youngest groups 168

Analysis of Inferential Behavior in Children

did not differ significantly from chance, but that of the older children and, of course, the college students did. TABLE I1 TOTAL TESTBEHAVIOROF CHILDREN IN CONTROL GROWS AS A FUNCTIONOF GRADE LEVEL Proportion of subjects in each category

NT Kindergarten, Berkeley Kindergarten, Santa Barbara Third grade, Berkeley Third grade, Santa Barbara College. Barnard

32 32 32 32 48

Direct-correct Indirect-correct Incorrect No integration integration integration integration .06 .06

.50 33 .92

.44

.I2

.31 .38 .25 .08

.I5 .06 .13

.oo

.38 .47 .06 .09

.oo

A more complete picture of the test behavior is presented in Table 11, where the performance is described as falling into one of four mutually exclusive categories. The Ss in the first category made the correct initial choice (RA) and then, without making any other previously trained responses, picked up the relevant subgoal and dropped it into the hole in the center panel (R,). This kind of solution was very uncommon among kindergartners, became more common among third graders, and was typical of college students. The second category includes children who made an RA and an R, sometime during the test trial but also made one or more of the previously trained but now unnecessary responses between them. All of the college students in this category and some of the children erred only once, e.g., made an Rx either before or after R,. But some of the children continued to make these unnecessary responses repetitively. Some, for example, went through the entire training sequence, which consisted of pressing each of the buttons, then picking up each of the subgoals and handing them to the experimenter; some kept pressing one button and then the other alternately over and over again; and some just pressed one of the buttons repeatedly. One can say about this category that, however inefficient, it does constitute a solution and some of the kindergartners were able to reach such a solution without any help or prompting. This, however, is less surprising than the results in column 4 which show that a sizable proportion of the kindergartners never attained any solution. After all, one would expect that if the child just repeats all of his earlier responses he will, because there are so few alternatives, ultimately hit upon the solution. Yet what happened was that a goodly proportion of kindergartners never did solve it even though 2 minutes was allotted, and most of them (91%)at one point or another pressed the button that made the relevant subgoal 169

Tracy S. Kendler and Howard H. Kendler

available. It could, of course, be argued that the younger children were less motivated than their elders. However, if this were so, they should also have learned the individual segments more slowly, but in both public school experiments the kindergartners learned both the subgoal and major goal segments at least as quickly as the third graders. In fact, in both experiments the kindergartners made fewer errors on the B-G segment than the third graders. This difference was not statistically significant in the Berkeley study, but it was significant in the Santa Barbara one. It seems unlikely, therefore, that the younger children were less motivated or that the observed age differences in test trial performance are primarily motivational. We have skipped over column 3 of Table I1 which includes the children that made an integration response but used the wrong subgoal (Ry).This never happened in the college group, but did sometimes occur among the children. In all groups it was, however, much less likely than R,. In general these results indicate that when the Hullian paradigm is applied to young children, there is little or no evidence that reasoning or inference occurs. How far beyond this particular experimental situation such a statement can be generalized remains to be seen. But in this situation it now appears that most, if not all, young children cannot spontaneously organize a set of behavior segments into an efficient novel arrangement to solve a problem or attain a goal. With increasing maturity, this ability becomes more available until at the highest intellectual levels such simple problem solution is the typical response. If this is the case, to understand inferential behavior, we will have to know something more about what changes occur that make the older child perform better than the younger. As we pointed out earlier, Maier had long ago reported some related results. Using his paradigm, he found that both young rats and young humans were deficient relative to their elders in their ability to reason in a simple locomotor task. If the same developmental differences are found in the Hullian paradigm to apply to rats as well as children, explanation of the inferential process would have to include a developmental component common to both species. We shall, however, present what we believe to be convincing evidence that the Maier paradigm and the Hullian paradigm represent basically different processes, and that these processes have different developmental implications.

IV. Infrahuman Reasoning At about the time we were finding out that kindergarten children of average intelligence were, by and large, unable to solve our ostensibl simple problem, Koronakos (1959) published an article which reported t e first experiment to apply the Hullian paradigm to rats. He used a three-

J

170

I

Analysis of Inferential Behavior in Children

section maze, each segment corresponding to a behavior segment. The major goal contained a 2-gram food pellet. The two subgoals each contained a 1/2-gram pellet. The rats were given ten trials a day for 2 days on the major goal segment and on the next day twenty alternating trials on each subgoal segment. On the following day, they got ten trials in which they could choose to approach either subgoal. Exactly half of the rats approached one subgoal, and half approached the other. His intention, like ours, had been to test a deduction from Hull’s theory of reasoning. This intention was thwarted by finding no reasoning. On the face of it these results appear to contradict Maier’s, but more recently Gough (1962) and his students have performed a series of experiments which not only clarify the apparent contradiction but provide a basis for comparing the performance of rats with that of children in a Hullian paradigm. Gough was also interested in testing Hull’s theory, which by now must be credited with more heuristic than truth value. First he replicated Koronakos’ experiment with a change in the way the maze was painted because he thought this modification might improve the rats’ performance. The modification had no effect; in the test sihation his rats, like Koronakos’, performed at the chance level. Then he reasoned that perhaps theanimal becomes frustrated in the “correct” subgoal because it anticipates a large food reward which it is prevented from obtaining. During the test, it may avoid choosing the side that was associated with frustration and thereby decrease the tendency to make the inferential choice. So the experiment was repeated with a reversed order of training. The rats were trained first to run to the subgoals and then to the major goal. The result, as Gough describes it, was that “again 10 of the 20 animals turned in the predicted direction .” By now there were three experiments on rats using the Hullian paradigm, and in none of them was there any evidence that rats behaved inferentially, regardless of the order in which the segments were acquired. By this time Gough accepted these negative results but he continued to wonder, as we had before him, how they could be reconciled with the general impression in the literature that rats could “reason.” But instead of comparing his results to Maier’s he compared them to Seward’s (1949), perhaps because Maier’s research had been roundly criticized (e.g., Wolfe & Spragg, 1934) and Seward’s was widely accepted as valid. Seward, although he described his own experimental situation as so similar to Maier’s as to be its prototype, nevertheless considered that he was investigating latent learning, not reasoning. As we shall see this distinction is not merely semantic. Seward’s apparatus was a T-maze which effectively eliminated extramaze visual cues. One endbox was black, the other white. On 3 days, the rats were put in the maze five or six at a time and allowed to explore it for 30 minutes a day. No food was present in either endbox. On the fourth 171

Tracy S. Kendler and Howard H. Kendler day, each rat was individually placed directly into one endbox, through the roof, where for the first time there was food in the food cup. When it began to eat, the rat was lifted out and put in the starting box. Eightyeight per cent of the rats went directly from the choice point to the endbox in which they had been fed. The experiment was repeated, except that now the rats were placed in both endboxes but only one contained food. The results were essentially the same. In the broadest sense, it could be said that Seward had demonstrated that Maier was correct; most rats could combine isolated experiences to solve a problem. But the discrepancy between the Maier-Seward results and the Koronakos-Gough results required a closer examination of the difference between the kinds of “experiences” that were being combined, or more precisely, between the Maier-Seward paradigm and the Hullian paradigm. Gough and his colleagues conducted several more experiments to discover wherein these differences lay. Seward’s rats had 90 minutes free exploration while Gough’s had twenty discrete reinforced trials on each subgoal. So Gough did another experiment in which rats were allowed to explore the maze between the start box and the two subgoal boxes for 90 minutes before the forty reinforced trials. This time nine out of twenty rats conformed to prediction. Seward used a T-maze and Gough a V-maze. To satisfy himself that this was not the critical variable, Gough repeated Seward‘s experiment in the V-maze and replicated Seward‘s results; eighteen of the twenty rats chose the path leading to the arm in which they had just been fed. Most of these animals were able to respond differentially as a result of prefeeding in one of the subgoals. To carry the test further, another experiment was conducted by Smith, one of Gough’s colleagues. This time the major goal box was partitioned and a new group of animals was allowed to explore the entire maze. After the usual exploration period each animal was prefed in one of the partitions of the major goal box before being placed in the starting box. All twenty animals turned to the side which led to the goal box in which they had just been fed. It is by now apparent that the differences between the rat’s behavior in the Seward-Maier paradigm and in the Hullian paradigm do not reside either in strain differences between the rats, or in differences associated with the type of maze, or in degree of learning. As Gough points out, it looks rather more as though the important difference is that in the SewardMaier paradigm the behavior segments (the locomotor responses) required to reach the goal have been contiguously associated during the exploratory period. “Reasoning” in this case consists of choosing from among two or more previously connected behavior sequences the one that is appropriate to a newly introduced motivation-reinforcement contingency. In the case of the Hullian paradigm, a rational solution requires the 172

Analysis of Inferential Behavior in Children

integration of behavior segments that have not previously been integrated. This kind of problem solution is apparently beyond the rat. Gough cites two more experiments that make this conclusion even more convincing. In one experiment, the animals were given separate free exploration in the V and in the two terminal arms. In another, the animals were given separate free exploration in the V-maze and in one of the two terminal arms. In the test situation, both groups were prefed in the appropriate final goal box and returned to the start box. Neither group showed any preference for the arm which led to the final goal box and food reward. In other words, the rats could not spontaneously combine behavior segments to solve a problem if these segments had not previously been contiguously associated. There is some suggestion from Birch's (1945) experiment on the effect of previous experience on insightful problem solution that even chimpanzees may only be capable of the Maier-Seward kind of insight. Birch began with accepting that insight describes a distinctive kind of behavior but contended that there was no information about the effect of previous experience because the subjects of earlier observations were captured animals who may have had previous contacts with similar situations. The experimental problem Birch used was the hoe problem (Fig. 5 ) which required the subject

--

f0

Food

-Hoe

Fig. 5. Diagram of the hoe problem (adapted permission of the Williams & Wilkim Co.).

/ram

Birch, 1945, p . 372; reprinted with

to drag in the food by pulling on the handle of the hoe. The Ss were six young chimpanzees, between 4 and 5 years old, whom Birch considered naive with reference to the hoe problem but who had previously worked at a series of six patterned string problems. Since the patterned string problem also involves pulling in some food or other goal object placed beyond the reach of the animal, it is possible that even here total naivete was not established. Birch is careful to report that the animals lived in an outdoor enclosure in which all animals had theopportunityto handletwigsand branches but only one was observed doing so. In fact this animal, Jojo,"madearegular practice of stick using" and had frequently used a stick to reach out ofthe cage and turn the electric light switch on and off. None ofthe other animals had been observed to use the stick as a tool before the experiment began.

173

Tracy S. Kendler and Howard H. Kendler

The experiment consisted of a pretest on the hoe problem (Fig. 5 ) followed by a 3-day period of stick play in the enclosure and a retest on the hoe problem. In the pretest, Jojo and Bard solved the problem and the other four animals did not. Jojo’s solution was quick and direct, but this solution consisted of the application of a previously acquired set of behaviors to a new motivation-reward situation. Bard also solved the problem but in a different way. He began by making several futile attempts to reach the food with his hand. He desisted for a while to solicit the experimenter and then tried to reach it directly again. This time his arm accidentally brushed the stick, which moved the food slightly. Bard stopped reaching and looked carefully at the stick and food. Birch reports, “He then reached out deliberately and shoved gently at the side of the stick while he watched the food. The food moved. Bard then grasped the stick between two of his fingers, and pulled it in with the same technique as that which he had used in stringpulling, and after several tugs he brought the food into reach, took it up in his hand, and ate.” Bard’s solution required some generalization, but can also be attributed to prior training. In the usual string pulling training an animal is presented with two strings (S, and Sx), one attached to food and the other not. The way the strings are arranged makes it difficult to perceive which will bring the food within reach. If the animal pulls the wrong string, the food will not move; if he pulls the right one, it will. The animal therefore learns to respond to the moving food by hauling in the correct string. If no food movement occurs, he desists. In the hoe problem, Bard accidentally made the food move and so the problem was solved using the same kind of response he had previously learned. After the preliminary test the chimpanzees were provided with the opportunity to handle sticks during their play in the open air enclosure in which they lived. During this time, every S was observed on several occasions to reach out and touch some object with a stick. As Birch put it, they all “used the stick as a functional extension of the arm.” After this opportunity for stick-play, when the problem was again presented all of the chimpanzees pulled in the hoe and got the food. In other words, they adapted previously learned response sequences to new motivations. These data do not prove chimpanzees are no more capable than rats of spontaneously integrating behavior segments, but they do suggest that it is possible that chimpanzees’ insightful behavior, made famous by Yerkes and Kohler, may be closer to the adaptation of previously connected sequences of behavior to different motivation reinforcement contingencies, as in the MaierSeward paradigm, than to the novel combination of behavior segments that have not previously been connected, as in the Hullian paradigm. It would be very interesting to research this further. Whatever interpretation will ultimately be placed on the ability of chimpanzees to behave inferentially, there seems to be little doubt that such

174

Analysis of Inferential Behavior in Children

behavior is beyond rats’ capacity, as it is beyond that of very young human beings. The developmental changes that occur among humans as they mature, which make it more likely that they will display this capacity, is not shared by rats. Therefore, to understand the mechanisms of inferential behavior we need to understand both the essential differences between rats and humans with respect to this phenomenon and the changes that occur which make the older child perform differently than the younger. Our work on reversal and nonreversal shifts in the discrimination learning of rats (Kendler, Kendler, & Silfen, 1964) and children at various age levels (H. H. Kendler & T. S. Kendler, 1962; Kendler, Kendler, & Learnard, 1962) had suggested that one of the salient phylogenetic and ontogenetic developmental differences was the availability of relevant mediating response mechanisms. The remainder of the present report describes some experiments designed to determine whether related mechanisms affect the development of inferential behavior.

V. Influence of Experimental Variables on Inferential Behavior of Children We started this line of investigation by asking what happens at the point of integration between the A-B and B-G segment. One of the most unexpected results we had obtained was that when the younger children made the R, choice and S, emerged, it did not universally or even frequently evoke the R, response. This remained true even though the apparatus and procedure guaranteed that S, was both attended to and discriminated during both subgoal and major goal training. In fact, in both the Berkeley and Santa Barbara experiments, only 12% of the kindergartners who made an initial R, and obtained S , followed it directly with R,. Among the third graders, the percentages increased to 67 and 81 respectively in the two experiments. These findings made it plain that a-marble-in-the-left-hand-trough-preceded-by-a-button-press ( S , , ) is not the same stimulus constellation as a-marble-next-to-a-ball-bearing-in-front-of-the-center-panel (SBz). In the subgoal training, all of the children had learned to respond to S,, by picking up the marble and handing it to the experimenter. Then, after the experimenter made some manipulations, the next response the children made was to press a button again. In a great majority of the instances, the younger children responded to S,, in the test situation as they had in the subgoal training4hey either handed it to the experimenter or pressed another button. Yet few of the older children and none of the college adults did so. In the test situation, they responded to S,, as they had learned in the major goal training to respond to S,. So it seemed that there was some significant process that occurred among older children which had two important effects. 175

Tracy S. Kendler and Howard H. Kendler

It interrupted a previously learned chain of events at a critical point (e.g., before handing marble to experimenter) and enabled the S to generalize from SB,to S,. We supposed that this process consisted of one or more mediating events which laid the basis for a correct initial response and also served to mediate the generalization between the first and second stimulus constellation. A specific implication of this supposition is that the integration response is evoked, at least in part, by events associated with an implicit response. This implication was first tested in two experiments by attempting to separate the hypothetical internal events from the relevant external events. In one experiment (T. S.Kendler & H. H. Kendler, 1962), kindergarten and third grade children served as Ss, in the other, college students (unpublished). Half of the children (Berkeley sample) and half of the adults (Barnard sample) cited in the previously presented developmental results served as controls. The other half were trained in the same way as the controls but they faced a different test situation. For them the subgoals were surreptitiously interchanged after their training was completed and before the test trial began. If a child in this group made an initial R, (correct choice) he got an S, (irrelevant subgoal), if he made an initial R, (incorrect choice) he got S, (relevant subgoal). The experiment thus produced the four groups presented in Table 111. TABLE 111 PROPORTION OF SUEJFiClS AT EACHAGELEVELWHO MADEDIRECT INTEGRATIONRESPONSESAS A FUNCI-ION OF THE CORRECTNESS OF THE h l T U L RESPONSEA N D SUBCOAL

Subgoals

Constant Switched Switched Constant

Condition prior to integration response

RA-SB RX-SB RA-SY

RrS,

Kindergarten Prop. integr.

Third grade Prop. integr.

N,

.12 .I9

24

.67 .44

46

9

.oo

23 8

.35 .I2

46

N,

16 16 16 16

.12

I?,

2 2

College Prop. integr.

.96 1 .oo .20

.oo

The first column in Table 111 names the experimental group to which the Ss were preassigned at random. “Constant” refers to the control condition in which the subgoals were in the same position during both training and test; “switched” refers to the condition in which the subgoals were interchanged between training and test as described above. The second column describes the initial response of the S and the stimulus consequences of that response. For example, R, - S, means that the Ss in that row made an initial R, and obtained S,. The N, columns cite the total number of Ss exposed to each condition at each developmental level. The columns headed 176

Analysis of Inferential Behavior in Children

by Prop. Integr. cite the proportion of Ss in each condition who picked up the subgoal obtained after thejirst response, be it S, or S,, and dropped into the hole of the major goal panel. These proportions were used to determine whether the tendency to make an integration response was dependent on an initial correct choice or the occurrence of S, or both. For example, of the kindergartners in the first (R, - S,) condition, .I2 proceeded to use the S , to try to get the charm. The next row contains the children who made the wrong initial response but obtained the correct subgoal (R, - SJ. Since slightly more of these, .19, made the integration response there is no evidence here that whatever integration occurred depended on anything other than S,. The third group contains those who made an initial R, but got S,; none of them directly followed their initial response by trying to use S , to obtain the charm. Among the last group who made the wrong initial response and got the irrelevant subgoal, .I2used that subgoal to try to get the charm. Since the number of kindergartners who made any kind of integration is so small, any conclusions from their data would have to be very tentative; but if we compare the first two groups with the last two, we find that more integration occurs using S, than S,. In fact, if we anticipate ourselves somewhat, and make the same comparisons in the other developmental levels in the table, we find that this is true throughout, so we can safely conclude that at all age levels, the occurrence of the external stimulus common to the two segments contributes to the likelihood of junction. The question with which we were concerned was whether internal stimulation associated with “knowingly making the correct initial response” also contributes to junction. If this is so, then we should expect that junction would be more likely among Ss whose initial choice was R,. We should therefore get more integrations in the first condition than in the second; and in the third condition than in the fourth. Among the kindergartners there is no evidence of any contributions of such internal events. However, among the third graders the picture changes considerably. If S, appeared, the children at this level were more likely to use it to integrate the segments if their initial response was R,. Perhaps even more to the point, those children whose response produced S, were more likely to use it in an attempt to get the charm if their original choice was R, than if it was R,. Additional analyses showed that if we go beyond the data of Table I11 and extend this comparison to include all Ss who made any attempt at solution, direct or indirect, the effect of an internal stimulus component on the third graders’ junction behavior becomes even more apparent. In the total constant group only 6% dropped S,into the center hole; in the switched group this per cent increased to 56. In other words, the stimulation or direction associated with the inference that what they needed could be obtained by R, was sufficiently potent to compete successfully with the external stimulation for over half of the third graders. 177

Tracy S . Kendler and Howard H . Kendler

In the last pair of columns of Table I11 are the results of the same experiment with female college students as Ss. The important datum here is that one out of every five students in the switched group who made an initial R, used Sy to try to get the charm. A similar mechanism was apparently still operating even at this level. The data suggest that college students are less likely than third graders to use the incorrect subgoal, but the numbers are too small either to establish statistical reliability or to make the null hypothesis tenable. For at least some of the third graders and college students, the response at the junction of the two segments was determined by an anticipatory subgoal response. This is evidence of an anticipatory response mechanism akin to the one proposed by Hull which mediates both the correct initial choice and the junction response. But in this instance the mechanism follows more closely Hull’s theory of foresight than his discredited theory of insight. In the foresight theory, Hull wrote about representational responses which move forward in the behavior sequence and thereby serve to anticipate external consequences resulting in intelligent adaptive behavior. It is not difficult to formulate a theory about how anticipatory representational responses could produce inferential solutions in our paradigm. For example, we could assume that the Ss who solve the problem in the direct-correct manner covertly represent the relevant subgoal as rb and the irrelevant subgoal as ry during both subgoal and major goal training. The representations characterize some property of the stimulus. The representational responses may be idiosyncratic, they may be universal, they may or may not be linguistic, they may be central or peripheral. At this stage of theory building, there is no necessity to provide these responses with any properties other than the ability to become anticipatory and to influence overt behavior differentially. We could conjecture that in the initial training when the experimenter holds up the subgoal to show which one is to be obtained the S represents the subgoal and then makes the pressing response. Thus the stimulus consequences of rb (%) become associated with RAand those of ry (sy)become associated with R,. During major goal training, the events might take on something like this pattern: The experimenter opens the center panel and sets out S, and Sy; the subject orients to one of them, makes his representation, and then picks it up to drop in the hole. If he is correct, he is likely to repeat this string of events; if he is wrong, he is likely to change. Quite soon he is selecting S, and presumably making the relevant implicit representation (rb). This representation becomes anticipatory so that the experimenter need only to open the center panel to evoke it. As a consequence R, becomes associated with sb. By now sb has become associated with two responses, R, and R,. During the test situation the S is motivated to obtain the charm, he orients to the center panel which elicits r b , and the associated stimulation, s b tends to evoke RA and RE. Since there is no subgoal set out, R,is 178

Analysis of Inferential Behavior in Children

impossible. Both the side panels are now open and R, is possible and therefore occurs. The stimulation associated with the representational response persists in sufficient strength to produce the junction response, R,, and the problem is solved directly and correctly.2 While this theory is plausible, a rigorous test is impossible until methods are developed for experimentally manipulating the hypothetical covert mediating events. Our latest efforts have, in consequence, been directed more toward establishing experimental techniques for manipulating the hypothetical representational event than at testing a detailed model of inferential problem solving. Specifically, the last two experiments to be reported investigated the effect of overt representational responses on inferential behavior. For a number of reasons, the representational responses we chose were verbal labels. There was, for one, the obvious possibility that among humans the most important means of representing objects is linguistic; another is that the difference between younger and older humans lies in the tendency to make spontaneous, implicit, linguistic representations. Moreover, it was very easy to get the children to produce the labels without any other significant alterations in our experimental situation. And finally, there was by now some evidence that overt verbal labels do affect concept formation among kindergartners (Kendler, 1964). This is a good point at which to enlarge on the connection between concept formation and inferential behavior, We have already noted that kindergartners responded differently to the marble when it emerged from one of the side panels than when it was placed in front of the center panel. Since these are actually different stimulus constellations and since different responses were learned to these two constellations, this is exactly what we should expect unless the S actively singles out an attribute or element common to the two constellations and responds appropriately to it. Our approach implies that inferential reasoning requires a mechanism that produces this kind of abstraction. Since the stimulus situation at the end of one behavior segment is bound to be somewhat different than the stimulus situation at the beginning of another, part of the inferential process is the identification of a relevant common property. Our experimental situation was designed so that this element was very obvious to adults, but the problem could be made more difficult by making the common stimulus less obvious. In fact, so called “creative reasoning” consists in large measure of unusual, original, common identifications. William James had long ago come to a similar conclusion. He wrote *If this theory is to apply to rats in the Koronakos-Gough experiments, the representation would have to refer to the subgoal boxes which were different colors and shapes. Since it is difficult to conceive of a response system available to the rat that would Serve to represent differentially two colors or shapes, per se, it is to be expected that they would be incapable of inferential behavior in that particular experimental situation.

179

Tracy S. Kendler and Howard H.Kendler

(James, 1892, p. 353) that “It (reasoning) contains analysis and abstraction. Whereas the merely empirical thinker stares at a fact in its entirety and remains helpless, or gets ‘stuck,’ if it suggests no concomitant or similar, the reasoner breaks it up and notices some one of its separate attributes. This attribute he takes to be the essential part of the whole fact before him. This attribute has properties or consequences which the fact until then was not known to have, but which, now that it is noticed to contain the attribute, it must have , . , reasoning may then be very well defined as the substitution of parts and their implications or consequencesfor wholes. And the art of the reasoner will consist of two stages: First, sagacity, or the ability to discover what part. . . lies embedded in the whole . . . which is before him; Second, learning, or the ability to recall promptly (the part’s) consequences, concomitants, or implications.” Our hypothesis was that “sagacity” is aided and abetted by the occurrence of a relevant representational response. Specifically, we wanted to see whether we could increase inferential problem solution by requiring a common overt label for the stimulus event that potentially connected the A-B and B-G segment and, if so, whether the facilitating effect of the overt labels would be greater at the younger age levels. To answer these questions we ran another experiment on kindergarten and third grade children (Kendler et al., 1966). The procedure was similar to that of T. S. Kendler and H. H. Kendler (1962) except for the introduction of verbal labels during the training of the three segments for the experimental groups. There were three groups at each of the two grade levels. Let SB, refer to the relevant subgoal during the subgoal training and S , refer to the same object during the major goal training and let Syland , S refer similarly to the irrelevant subgoal object. The same label (SL) group learned to label SBl and Sa, with a common term (e.g., “glass marble”) and Syland ,S with another common term (e.g., “steel marble”) while learning the motor responses appropriate to each of the three segments. The different label (DL) group also used labels during training but the label for SBl (e.g., “glass marble”) was different than the label for Sb (e.g., “big marble”). Similarly the label for Syl(e.g., “steel marble”) was different than the label for ,S (e.g., “small marble”). The DL group was intended to determine whether there would be a general facilitating effect of verbalization which could be separated from the more specifichypothetical acquired mediation provided by the SL condition. The no label (NL) group was a control which was not required to do any overt labeling during training. The NL group appears in Table I as the Santa Barbara sample. The six experimental groups formed a 2 x 3 factorial design. The main effects were grade level (kindergartners vs. third-graders) and verbalization condition (SL, DL, and NL). 180

Analysis of Inferential Behavior in Children

We expected that the SL group would make more inferential solutions than the NL group at both age levelsbut the effectwould be more pronounced among the younger children. The expectations for the DL group were less clear. It seemed possible that requiring any kind of verbalization might have some general salutary effect; if so, then DL should also facilitate problem solution. However, if the overt verbalizations replaced the hypothetical covert representation then DL should interfere with solution, particularly among third graders. Since the theory was not sufficiently well developed to predict whether either or both of these factors would be operative, the DL condition was essentially exploratory. In Table IV, which presents the results, we see that the SL and DL groups made more correct initial choices than the NL groups at both grade levels. TABLE IV OF INITIALCORRECT CHOICES AND DIRECT-CORRECT INTEGRATIONS PROWRTION AS A FUNCTION OF GRADELEVEL AND THE USE OF LABELS

Experimental group

N,

Kinderg - NL Kinderg - SL Kinderg - DL

32 64 64

3rd - N L 3rd - SL 3rd - DL

32 64 64

Correct initial choice Obtained

Adjusted for chance

.53

3 3

.06 .16

.61

.22

.66

.32 .40 SO

.I0 .I5

Direct-correct integration

.06

.30 .19 .53 .4 1 .55

The differences were not statistically reliable, however. While neither set of labels had any demonstrable effect on initial choice, SL did have a significant effect on integration behavior. The result, in brief, was that there was no significant difference between DL and NL, but SL interacted significantly (p < .05)with both. Relative to NL and DL, SL increased the probability of direct-correct integration at the kindergarten level and decreased it at the third grade level. From the failure to obtain a significant difference between DL and NL, we can conclude that there is no evidence that labels, per se, affect integration. The significant interaction between verbal label and grade level is consonant with the expectation that a common label for SB1and S% would produce a greater positive effect at the kindergarten level than at the third-grade level. When the results for the kindergarten level were analyzed individually, the facilitating effect of SL, relative to NL, was significant (p < .05).We wanted now to be sure that this result could be replicated, particularly by a different experimenter. 181

Tracy S. Kendler and Howard H . Kendler

The prime purpose of the next experiment, the last to be reported, was to determine whether the SL condition would again produce more directcorrect integrations than NL among kindergartners when the experiment was conducted by a different experimenter. The secondary purpose was to determine whether the order in which the segments were trained would interact with the use of labels to increase inferential behavior. Perhaps because old loyalties die hard, the order variable was introduced to provide one more test of the prediction derived from Hull’s theory to the effect that training the B-G segment first should increase the proportion of correct initial choices. The justification for reintroducing this hypothesis lay in the discovery that for kindergarten children the stimulus produced by the relevant subgoal response (S,,) was significantly different than the stimulus that initiated the major goal segment (SE2).It could be argued that Hull’s theory, and the secondary reinforcement analysis as well, require that SBIand S, be identical, or at least similar enough for simple stimulus generalization to be effective. Following this theme we supposed that any variable that increases the generalization between SBIand SE2should also increase the effectiveness of the order variable. The experimental design was a 22factorial using thirty-two kindergartners in each cell. The procedure was similar to the one used in the previous experiment. Half of the children learned a common label for SEIand S, (SL group), and the other half used no labels (NL group). Half of each of these groups were trained on the B-G segment before they were trained on the subgoal segments (B-G first); the other half learned the subgoal segments first (B-G last). One of the predictions was that the facilitating effect of verbal labels on integration would be replicated. The other was that there would be an interaction between labeling and order which would result in the greatest proportion of correct initial choices in the SL-BG-first group. Again there was no indication in the results (Table V) that order had the predicted effect on initial choice. In fact, there was no statistically significant difference in the initial choice behavior attributable to either variable or to their interaction. On the other hand, the effect of labels on integration previously reported was replicated, i.e., there was significantly more directcorrect integrations in the SL than the NL condition (p < .05). In this experiment, the children in the NL groups made slightly more initial A choices and integration responses than the kindergartners of the preceding two experiments; this may reflect the fact that the experiment was conducted nearer the end of the school year than the others, and these children were consequently 5 months older, on the average, than those in the previous experiment. But these differences were small and statistically unreliable. On the whole, the results of the two experiments were rather similar, and the facilitating effect of labels was replicated.

182

A nalvsis of Inferential Behavior in Children TABLE V

DIRECT-CORRECT INTEGRATIONS AMONGKINDERGARTNERS A S A FUNCTION OF ORDER OF PRESENTATION AND THE USE OF LABELS PROPORTION OF INITIAI. CORRECT CHOICES AND

No Label

Order condition

Initial correct response Obtained

B-G First B-G Last

.h6 .59

Same Label Direct-correct integration

Estimated adjustment for chance

Obtained

.32 .I8

.I2 .12

Initial correct response Obtained

.59

.59

Direct-correct integration

Estimated adjustment for chance

Obtained

.I8 .I2

.25 .28

VI. Pooled Developmental and Experimental Results By now there were several experiments that testified that inferential solutions increased with age and that verbal labels interacted with age to affect such behavior. In each of these experiments, one or more of the experimental conditions was replicated; and in none was there a significant difference between replications when the experimental conditions and grade levels were similar. Note, for example, the similarity between the Berkeley and Santa Barbara NL samples in Tables I and I1 and between the kindergarten SL results in Tables IV and V. Since the results were so consistent, all of the available results on children who were trained and tested under similar conditions and who used no labels were pooled to form one large No Label Group. Similarly, all of the children in the SL conditions were pooled to form one large Same L abel Group. To provide a better picture of the developmental function with and without overt labels, each group was subdivided into five class intervals based on mental age. The mental age scores were derived from the Peabody Picture Vocabulary Test (PPVT) administered at the time of the experiments. The MAS were first tallied according to annual intervals and then organized into the following five classes: 3671 months, 7 2 4 3 months, 84-95 months, 96-131 months, and 132-167 months. The resulting developmental trends and the number of cases on which each representative point is based appear in Figs. 6,7, and 8. Figure 6 presents the developmental trends when no instructions about labels are provided. The college students are represented as points on the upper end of the scale. Because the PPVT was not administered to this sample. their M A is merely an estimate and consequently is not connected

183

Tracy S. Kendler and Howard H . Kendler 1.00

.90 .80 .70 u) +

g .60

q a

.50

.4-

5 .40 .c

k

2 a

.30

.20

Initial correct choice x-x

3

4

N;

5 32

6

7

33 35

8

10 II Mental age

12

9

43

23

Direct correct solution

13

14

15

16

17 18

48

Fig. 6. The proportion of’subjects who made initial correct choices and direct-correct solutions as a function of PPVT mental age in the no label condition. N, indicates the total number of subjects in the no label condition represented by each point.

to the rest. There are several interesting things to be noted in Fig. 6. One is that the probability of both a correct initial choice and adirect-correct solution increases monotonically with MA. Although the increase is consistent, the rate of increase seems to be greatest between 8 and 12. Another thing that can be gleaned from Fig. 6 is that the drfference between the two functions decreases steadily with increasing age. This indicates that, if children make the correct initial choice, the older they get the more likely they are to make efficient use of its product. Figure 7 compares the proportion of direct-correct solutions at each developmental level under no label and same label conditions. Here we see that labels increase inferential solutions at the lower developmental levels and decrease them at the upper levels. A multiple classification X 2 test of the corresponding frequencies (Sutcliffe, 1957) indicated that the interaction between MA and label condition is significant (p < .Ol). These trends are consistent with those found in the T. S. Kendler, H. H. Kendler, and M. Carrick experiment when grade level was the developmental index and only two points were measured. But the present analysis, which includes the results of that experiment along with others lends even more significance, statistical and otherwise, to the interference effect at the upper levels. Figure 8 compares the proportion of initial correct choices adjusted for chance under the two conditions. The effect of labels on initial choice are, unfortunately, not clear. If Figs. 7 and 8 are compared, the interactions 184

Analysis of Inferential Behavior in Children

1.00

.gOl 80

c

2

iiP

a

.40 .30

,001

3

4 N

5 37

8

7

6 53

41

10 I1 12 Mental age 45 16

9

S-S

Same label

N-N

No label

13

14

15

16

17 18

Fig. 7. Comparison between the obtained proportion of subjects who made direct-correct solutions in the no label and some label condition at each mental age. N, indicates the total number of subjects in the same label condition represented by each S point. The total number of subjects represented by each N point is the same as in Fig. 6. 1.00

.90 .80 2

.70

01

.60 ul 'c

O

-B c

._

.50 .40

g

.30

g

.20

Same label

.oat

No label

s:

.O 5

3

4

5

6

7

8

9 10 I1 Mental age

12

13

14

15

16

17

18

Fig. 8. Comparison between the estimated proportion o j subjects who made an initial correct choice adjusted for chance in the no label and same label condition at each mental age. The total number of subjects represented by each N and S point are the same as in Figs. 6 and 7. resoectively.

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Tracy S. Kendler and Howard H . Kendler

between the SL and NL functions appear very similar with one important exception. But for the lowest level, SL seems to interact with MA to increase initial correct choices at the lower levels and decrease them at the higher levels. At the lowest level, however, there is no evidence that SL improves foresight, a result consonant with the previous analysis when grade level served as the developmental index. Moreover, it is difficult to either accept or reject the implied interaction, because when a multiple classification x2 was applied to the data in Fig. 8, the statistical reliability of the interaction effect, though not significant (.05 < p < .lo), was too close to significance to accept the null hypothesis comfortably. This is another issue future research will have to resolve. In general, the pooled results show that the relatively crude relationships obtained in the several experiments between 2 or 3 grade levels are not only preserved but refined when presented in terms of MA. In fact, the MA analysis probably has more potential because it reduces variability and therefore provides a more efficient method of measuring developmental level. With greater efficiency, it will be feasible to determine more about the characteristics of the typical developmental changes for a particular behavior pattern (Fig. 6) and how experimental manipulations affect them (Figs. 7 and 8). The result could be better understanding and greater precision.

VII. Discussion Investigators have shown that rats do not solve problems that require the integration of separate habit segments. There may even be some question of whether infrahuman primates would be able to solve such problems, given appropriate experimental controls. When a similar experimental paradigm is applied to a cross section of human beings, we find that, if we use either grade level or MA as a developmental index, solutions are very infrequent at the lower developmental levels. However, as developmental level increases, solutions become increasingly frequent until, at the highest levels, they are the overwhelmingly dominant mode of response. Inferential behavior can be analyzed into two components; one of the components is the initiating behavior, and the other is the integration of the two segments, given that the potential connecting element is available. The probability that either component will occur is very unlikely at the lower MA levels but both become increasingly probable with increasing MA. A plausible hypothesis to account for the integration results is based on the recognition that the potential connector, the element common to the two segments, is embedded in different stimulus compounds in each seg186

Analysis of Inferential Behavior in Children

ment. Children at the lower developmental levels do not integrate the two segments at the first opportunity because they have learned to make different responses to these compounds. It would seem that oneofthe necessary conditions for integration is the abstraction of the relevant element. Our hypothesis is that as children in our culture mature they learn to make a representational response to the relevant element. Since this representational response is the same for both segments, it provides the basis for abstracting the common element and thereby mediates the generalization between the two stimulus compounds. To test this hypothesis, children were required to use a common obcrt label for the relevant element in both segments. To the extent that this overt label increased the probability of a common covert, or overt, representational response, where none would occur spontaneously, it should increase integration. Therefore, the greatest effect should occur at the lower MA levels. The result was that, with common overt labels, integration was increased among children with MAS below 9 or 10. If children at the upper MA levels are spontaneously making representational responses, overt labels should have little or no effect. The result was that at the upper MA levels common overt labels decreased direct-integration relative to the control. On the surface, this result appears contradictory to the hypothesis, but closer examination of the results suggests the opposite conclusion. To make this point clear, we must review the experimental procedure. In the Kendler, Kendler, and Carrick experiment, counterbalancing required half of the subjects to use “big” and “little” as labels and the other half to use “glass” and “silver” or “steel.” It is doubtless relevant that in research now in progress we find that, when children are permitted to choose their own labels, kindergarten children find it very difficult to provide a consistent set of labels. Third graders have ready labels but, to date, none of them has verbally differentiated the subgoals in terms of size. The labels they use most often refer to the materials of which the subgoals are composed, e.g., “glass” and “steel,” or “purie” and “steelie.” Similar results were obtained when subjects in the control No Label group in the Kendler, Kendler, and Carrick experiment were asked to describe the subgoals after the experimental session was completed. In light of these observations, it seemed possible that, if third graders were implicitly labeling the subgoals according to their composition, requiring that they be labeled according to size would produce a conflict that would reduce the effectiveness of both sets of labels. “Glass” and “steel,” being more compatible, should produce less interference. On the other hand, if kindergartners are unlikely to provide their own implicit labels, there should be relatively little difference between the two sets of labels. To test this hypothesis, the Same Label groups at both grade levels were 187

Tracy S. Kendler and Howard H . Kendler

subdivided according to the required label set and the results were compared with the relevant No Label groups. The result was that both sets of labels facilitated problem solution by kindergartners and there was practically no difference between the magnitude of their effects. On the other hand, for third graders, the effect was highly dependent on label set. The “glasssteel” set had practically no effect. All of the interference was produced by the size labels. The interaction implied by these results was statistically significant (p < .02). These results thus show that overt labels can facilitate, interfere, or have no effect on inferential problem solution. Which of these effects the labels have depends on both the developmental level of the subject and the labels used. If a set of overt labels is used which is consonant with the kind of representation third graders are likely to make spontaneously, the labels will facilitate integration at the kindergarten level and have little or no effect at the third grade level. This finding is in line with our original prediction. Although we had not anticipated that one of our sets of labels would produce active interference at the higher MA levels, having found that it is the kind of label which differs with the spontaneous representations of children at this level provides more confirmation than disconfirmation of the hypothesis about the role of covert representational responses in the integration of behavior segments. In fact, since there is evidence here of disruption by overt labels, these results could bear on the inner-outer speech formulation proposed by Vygotsky (1962). Our present hypothesis is that requiring the use of arbitrary overt labels interfered with problem solution at higher MA levels because it interfered with their inner speech, possibly because the inner and outer speech are not yet as differentiated as they will be at still higher stages of development. This explanation provides a number of interesting testable hypotheses. One of them is that allowingthird graders to choose their own labels should provide less interference than supplying them with arbitrary labels. The research in progress mentioned above indicates that when third graders provide their own labels their performance is slightly but not significantly better than the no label control. This work is still in progress so no substantiation of the hypothesis in terms of MA is yet available. Consequently this explanation, though provocative, must be considered tentative subject to further investigation. To forestall any misinterpretation, we should again make explicit that representational responses are not synonymous with linguistic labels. As far as we now know, any response with adequate feedback could serve the purpose. We used linguistic labels for reasons already enumerated. It also seems likely that, among articulate humans, verbal labels are among the most common responses used for representation simply because they are so well suited to this function. They are so available, discriminable, easily fractionated, can occur without interference with any other ongoing activity, 188

Analysis of Inferential Behavior in Children

and can so easily move forward in the behavior sequence. But in the present general formulation, any response that has the foregoing characteristics, even though in lesser measure, could theoretically servein thesame capacity. If this is so, there is no reason as yet to believe that infrahuman and nonspeaking humans cannot make either representational responses and/or inferential solutions, given the proper training. Apparently human beings either do not require special training to make such responses or, more likely. thev get this training during the course of their upbringing or education. But it is also possible that as research proceeds several classes of representational or mediating responses will be differentiated, and that these classes will have characteristics which fit more easily the requirements of some tasks than others and which are also more available in some species or in some stages of development than others.

VIII. Summary and Conclusions A series of investigations was presented which began with an attempt to use Hull’s experimental paradigm to verify his theory of insight. The result was that, while the paradigm provided a useful method for investigating the ability of children to form appropriate novel combinations ofhabit segments, the theory proved invalid. Our results and analyses, taken in conjunction with those obtained by other investigators, differentiated between the kind of insight which requires the adaptation of previously learned behavior sequences to new motivations from the kind which requires novel combination of previously learned behavior segments. The findings are that rats and very young children are not capable of the second kind of “reasoning” but that this ability develops in humans as they mature. We have offered a theory to the effect that ( I ) this ability is dependent on covert mediating mechanisms similar to those operating in human concept formation and (2) these mechanisms develop in human beings as they mature. Evidence was presented that these mechanisms have some connection with the labeling function of language along with some suggestions about the relationships between inner and outer speech mechanisms. The theory which was only partially corroborated must be considered tentative but it does suggest a direction that future research can take to elucidate this important process. REFERENCES Birch, H. G .The relation of previous experience to insightful problem-solving.J. comp. physiol. Psychol., 1945.38, 367-383. Dunn, L. D. Peabody Picture Vocabulary Test (P.P.V.T.1. Nashville, Tenn.: American Guidance Service, 1959.

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Gough, P. B. Some tests of the Hullian analysis of reasoning in the rat. Paper delivered at the convention of the Psychonomic SOC.,St. Louis, August, 1962. Hull, C. L. Knowledge and purpose as habit mechanisms. Psychol. Rev., 1930.37, 51 1-525. Hull. C. L. The mechanism of the assembly of behavior segments in novel combinations suitable for problem solutions. Ps.vchol. Rev.. 1935.42, 219-245. Hull, C. L. A behavior syytem. New Haven: Yale Univer. Press, 1952. James, W. Psychology (Briefer Course) 1892. Republ. by Cleveland: World, 1948. Kendler, H. H., & Kendler. T. S. Inferential behavior in preschool children. J. exp. Psychol., 1956, 51, 31 1-314. Kendler, H. H., & Kendler, T. S. Vertical and horizontal processes in problem solving. Psychol. Rev., 1962,69, 1-16. Kendler, H. H., Kendler, T. S., Pliskoff, S. S., & DAmato, M. F. Inferential behavior in children: 1. The influence of reinforcement on incentive motivation. J. exp. Psychol.. 1958, 55, 207-212. Kendler, T. S . Verbalization and optional reversal shifts among kindergarten children. J . verb. Learn. verb. Behav.. 1964, 3,428-436. Kendler, T. S. & Kendler. H. H. Inferential behavior in children. 11. The influence of order of presentation. J. exp. Psychol., 1961, 61, 4 4 2 4 8 . Kendler, T. S., & Kendler, H. H. Inferential behavior in children as a function of age and subgoal constancy. J . exp. Psychol.. 1962, 64, 460466. Kendler, T. S., Kendler, H. H., & Learnard, B. Mediated responses to size and brightness as a function of age. Amer. J. Psychol., 1962, 75, 571-586. Kendler, T. S., Kendler, H. H., & Silfen, C. K. Optional shift behavior of albino rats. Psychon. Sci., 1964, 1, 5-6. Kendler, T. S., Kendler, H. H., & Carrick, M. The effect of verbal labels on inferential problem solution Child Develpm., 37, 1966,74%763. Kohler. W. The mentality ofupes. (Trans. by E. Winter) New York: Harcourt, Brace, 1925. Koronakos, C. Inferential learning in rats: the problem-solving assembly of behavior segments. J . comp. physiol. Psychol., 1959, 52, 23 1-235. Maier, N. R. F. Reasoning in white rats. Comp. Psychol. Monog., 1929, No. 29. Maier, N. R. F. Age and intelligence in rats. Comp. Psychol., 1932, 13, Id. Maier, N. R. F. Reasoning in children. J. wmp. Psychol., 1936, 21, 357-366. Seward, J. P. A n experimental analysis of latent learning. J . exp. Psychol., 1949, 39. 177-186. Skinner, B. F. Verbal behavior. New York: Appleton-Century-Crofts, 1957. Sutcliffe. J. P. A general method of analysis of frequency data for multiple classification designs. Psychol. Bull., 1957, 54, 134-137. Vygotsky, L. S . Thought and language. Cambridge, Mass.: M.I.T. Press and New York: Wiley, 1962. Wolfe, T. B., & Spragg, S. D. Some experimental tests of “reasoning” in white rats. J. comp. Psychol., 1934, 18,455-467. Yerkes, R. M . , & Yerkes, A. W. The great apes. New Haven: Yale Univer. Press, 1929.

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P E R C E P T U A L I N T E G R A T I O N IN C H I L D R E N '

Herbert L. Pick, Jr., Anne D. Pick2, and Robert E. Klein3 UNIVERSITY OF MINNESOTA A N D MACALESTER COLLEGE

I. INTRODUCTION . . . . , . . . . . . . . . . . . . . . .. . . . . . II. EXPERIMENTER COMPARISON OF SENSE MODALITY

..

FUNCTIONING ............................. A. LOCALIZATION OF SOURCE OF STIMULATION . . . . . . . B. SHAPE PERCEPTION . . . . . . . . . . . . . . . . . . . . . . . C. HIGHER ORDER STIMULUS PERCEPTION ...........

. . . .

192 195 I96 199 205

111. CONFLICT OF SENSORY INPUT . . . . . . . . . . . . . . . . . . . . 209 . . . . . . . . . . . . . 209 A. IMMEDIATE RESPONSE TO CONFLICT B. RESPONSE AFTER PROLONGED CONFLICT . . . . . . . . . . . 213

. . . . . . . . . . . . . . .. . . . .. . . IV. INTERMODAL TRANSFER A. INTERMODAL MATCHING ....... .............. B. INTERMODAL TRANSFER OF TRAINING . . . . . . . . . . . . V. CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . REFERENCES . , . . . , , . . . , . . . . . . . . . . . . . . . . . .

214 215 217

218 220

I This work was supported in part by Grant MH 07631 from National Institutes ofHealth to the University of Minnesota and by the University of Minnesota Center for the Study of Human Learning. The authors are indebted to Drs. William Charlesworth and John Flavell for a critical reading of the manuscript. * Present address: Institute of Child Development, University of Minnesota, Minneapolis, Minnesota. Present address: Istituto de Nutricion de Centro American y Panama, Apartado Postal I 1 4 8 . Carretera Roosevelt, Ciudad Guatemala, Guatemala.

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I. Introduction Perceptual integration, interpreted broadly as the coordination of various sense modalities and sensory inputs, is an important part of any perceptual or perceptual-motor task. Yet a survey of current and historical literature indicates a lack of systematic study. This is not to say that the problem has been ignored since a variety of theoretical positions explicitly or implicitly deal with relationships among the senses. A consideration of some of these theoretical positions will provide a helpful context for the research which subsequently will be reviewed. The present chapter will not present an exhaustive treatment of the literature. Rather the purpose is to discuss selected investigations including those of the present authors, to search for trends, and to highlight persistent problems in intersensory development. The position with the longest history is that visual perception is based on prior tactual, kinesthetic, or proprioceptive experience. An early but strong proponent of one such view was Bishop Berkeley who argued, for example, that visual perception is based on sensing the degree of convergence of the two eyes. His position included the implication that the visual and proprioceptive input from the eyes are combined to form a unitary perception of depth and that the “meaning” of the unitary perception comes from the prior experience of reaching or walking toward visual objects, viewed with specific degrees of convergence. More recently Montessori, whose approach is currently undergoing a revival in this country, emphasized the importance of early tactual exploration in the subsequent development of visual perception: “I have already learned through my work with deficient children, that among the various forms of sense memory that of muscular sense is the most precocious. Indeed many children who have not arrived at the point of recognizing afigure by looking at it, could recognize it by touching it, that is by computing the movements necessary to the following of its contour. The same is true of the greater number of normal children., .” (Montessori, 1964, p. 198). Probably the most recent statement of the position that “touch teaches vision” was made by Zinchenko and his colleagues working in Zaporozhets’ laboratory at the Moscow Institute of Psychology (Zinchenko, 1957; Zinchenko, Lomov, & Ruzskaya, 1959). This point of view is like the classical Berkelean position in that haptic’ or active tactual perception is considered to be prior to visual perception and any given percept, for example of shape, is thought to be based on both visual and tactual or proprioceptive input. The mechanism proposed by these investigators differs from that of Berkeley. They suggest a two-stage process in which the external stimulus elicits a motor response which copies certain properties ‘Unless otherwise noted, haptic and tactual perception will be used to mean activetactual perception as compared with passive touch.

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of the original stimulus. The feedback from the copying response then serves as a basis for perception. This view, of course, implies that there is a proprioceptive component to all percepti~n.~ (Compare Pick, 1964 for a review of these studies and their theory.) It will be pointed out in the evidence reviewed in the present chapterthat there is no clear developmental sequence from tactual perception to visual perception in the handling of sensory information. For example, in most developmental studies in which conflicting visual and tactual information were presented simultaneously, vision was clearly dominant at all ages. Furthermore, in some studies in which tactual discrimination was compared with visual discrimination, the latter was better at the youngest ages. It would be surprising indeed if touch were to “teach” vision when visual discriminations are better than tactual discriminations and vision is dominant under conflict. Why then has the view that visual perception is based on the prior development of haptic perception been so persistent? One possibility is that casual observation of young children, even infants, usually reveals a great deal of tactual exploratory behavior. Piaget has emphasized the large amount of tactual exploratory behavior by noting how much object manipulation occurs in the early, sensory-motor stage of cognitive development. Such observations have been verified in studies by Boguslavskaya (cf. Zaporozhets, 1961) and by Schopler (1964). Boguslavskaya found that younger children engaged in more tactual exploratory behavior of novel objects than did older children. Schopler’s results seemed to confirm this by showing that younger children spent a greater proportion of their time in tactual exploration than did older children. However, the absolute amount of time spent in tactual exploratory behavior was approximately the same for the older and younger children. The extensive tactual exploratory behavior which does occur early in development might lead to the inference that tactual perception develops prior to and forms a basis for visual perception. This interpretation would be reinforced by superficial observation of the infant’s visual behavior which appears so random that, until recently, it was thought that young infants were unable to detect shapes but rather only “super” stimuli such as brightly colored or moving objects. However, the recent work of Fantz (1963), Hershenson (1964), Ames (Brennen, Ames, & Moore, 1966), and *It is to the credit of these investigators that their own studies led them to reject the original hypothesis that touch develops prior to vision (Zinchenko & Ruzskaya, 1960b). However, they have maintained their emphasis on the motor components of perception. Piaget, too, has found a motor component in perception (cf. Flavell, 1963, pp. 230ff.). However, in Piaget’s theory it is not proprioceptive feedback from the motor response which is important but where the stimulus is being scanned. Concentration of view or centration leads to overestimation of the viewed portion of the stimulus.

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others has shown that very young infants are able to make quite fine visual shape discriminations. There are, of course, other views of developmental relationships among the senses. The classical biological approach emphasizing increasing differentiation in development can be applied to the sense modalities. Such a view implies that the modalities operate increasingly independently as a function of age and is compatible with the differentiation theory of perceptual development held by the Gibsons (Gibson & Gibson, 1955). The Gibsons argue that perceptual discrimination becomes decreasingly variable as a function of age. (This decrease in variable error does not necessarily imply a decrease in constant error.) They suggest that underlying the increasing precision in perception is learning to detect or respond to new variables in the stimulation or an improvement in attention to the critical variables of stimulation. Applied to intermodal functioning, this position suggests an increasing ability to attend to the stimulation from asingle sense modality in the presence of input from several modalities. It is important to note parenthetically that the increasing differentiation referred to here is not between organism and environment, a distinction implicit in Witkin’s concepts of field dependence and independence (Witkin, Dyk, Paterson, Goodenough, & Karp, 1962). Rather it is differentiation among the sense modalities, perhaps developing out of a synesthesic unity of the senses in early childhood (cf. Werner, 1948, pp. 86 ff.). A differentiation theory must also provide for the increased integration found to be possible with increasing age. Thus, for example, E. J. Gibson, while advocating a differentiation position in general, has found evidence for a higher order intermodal perceptual unit-the grapheme-phoneme correspondence used in reading. Such cases pose no more problem for the differentiation position than does increasing integration within one modality (e.g. concept formation) as a function of age. Traditionally one distinguishes between primary and secondary generalization for intramodal functioning. Failure to make a discriminative response is not necessarily due to inability to differentiate but could be based on learned equivalence or secondary generalization. Failure to differentiate between sense modalities similarily could be based on a primary or secondary integration. The integration of differentiated sensory input could be provided for by a modification of Pollack’s position (1965), itself based on that of Piaget. Pollack has shown in a variety of situations that perceptual illusions which involve temporal integration increase with age. He hypothesized that these have a cognitive component and depend on information processing. On the other hand, illusions which do not involve temporal integration decrease age, and he hypothesized that these are more sensory in nature and depend on physiological and maturational aging processes. A good example illustrating Pollack’s position is the Miiller-Lyer illusion (Pollack, 1963). 194

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which decreases as a function of age and also as a function of decreasing contour detectability. Pollack asserts that the important age variable here is a decrease in contrast sensitivity and he provides evidence for such a decrease with age. [This should not be taken to mean that visual acuity in general decreases with age. Compare Eichorn (1963, p. 3 1) for a summary of evidence indicating increase in visual acuity with age.] In an ingenious experiment, Pollack (1964) showed that by modifying the Miiller-Lyer illusion so that it involves temporal integration, there is an increase with age in an illusory effect. (It should be noted that this illusory effect is in the reversed direction. The ordinarily overestimated segment is underestimated.) Furthermore, in this case, the magnitude of illusion was positively correlated with IQ, supporting the hypothesis that there is a cognitive component in the illusion. While Pollack has applied his theory only to temporal integration, it would seem natural to apply it to intermodal integration. The classical evidence of increasing size-weight illusion as a function of age might perhaps be explained in such terms since the size-weight illusion is itself intermodal. However, a recent careful and systematic study of that illusion by Robinson (1964) fails to confirm a developmental increase in the magnitude of that illusion. Of course, it is important to keep in mind that there are many other kinds of intermodal phenomena that must be explained as well as illusions. No contemporary theoretical view encompasses all of them. The present chapter is not organized around a specific theoretical position. It was felt that at the present stage of knowledge an empirical, problemoriented approach might prove as useful. Most investigations relevant to perceptual integration have employed three general experimental procedures which are termed respectively: experimenter comparison of sense modality functioning, conflict of input to two sense modalities, and intermodal transfer. In the sections that follow, research fitting these three kinds of experimental models will be reviewed.

11. Experimenter Comparison of Sense Modality Functioning One approach to the study of the development of perceptual integration involves comparisons of subjects’performance in separate intramodal tasks. For example, the same form perception task may be carried out visually and tactually and the investigator may then compare task performance under the two conditions. Of course, such comparisons of one intramodal task with another result in inferences about intermodal transfer and integration rather than direct analysis of the integration itself. It should be noted also that it is not always possible to speak of performance in one modality as being better or worse than in another; it may only be possible to speak of

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performance as being different. An example of this (discussed in detail in Section 11, B) is the preference shown by Ss for specific orientations of shape. There is no question of better or worse here. An interesting elaboration of the basic experimenter comparison procedure employs a design which examines the effect of experience in one modality on functioning in a second. This design is typified by a comparison of sighted and blind Ss on a tactual task and sighted Ss on the same task presented visually. Thus the basic design consists of three groups: blindtactual task, sighted-tactual task, and sighted-visualtask. In connection with such comparisons, it is of course the case that the result of intermodal transfer might be negative as well as positive. For example, it is quite conceivable that the effect of visual experience would be to cahse S to ignore a tactual difference that he would otherwise discriminate. Finally, it may be noted that groups of Ss with varying degrees of blindness or varying ages of onset of blindness may add to the power of this kind of experimental design by revealing the kind of visual experience that is necessary for such transfer to take place. The present section includes studies fitting the designs described above and is directed to the study of localization of sources of stimulation, shape perception, and finally, two examples of higher order stimulus perception. A. LOCALIZATION OF SOURCE OF STIMULATION It is well known that even young infants demonstrate the ability to localize sources of visual, auditory, and tactual stimulation. Graham’s (Graham, Matarazzo, & Caldwell. 1956) infant tests show that neonates are able to track moving lights; Papousek ( 1967) has found that neonates orient toward sounds; and the rooting response to a nipple is clear and common evidence that infants show tactual localization. Systematic quantitative study of this ability is hindered by the difficulties in finding a good dependent variable. In general, the infant’s responses are too crude to obtain high precision in the measurement of ability to localize. Whatever the precision of localizing in infants, it seems to be an ability which attains its maximum relatively early in life. Data obtained by the present authors on visual and proprioceptive localization show no improvement in precision over ages 9 to 16, and data for auditory localization show only slight improvement. Auditory and visual localization were measured by asking Ss to point at visual and auditory targets without visual feedback from their hand. Proprioceptive localization was measured by requiring Ss to use the index finger of one hand to indicate the position of the index finger of the other hand. This was done with the eyes closed and with the two hands on opposite sides of a board so as to preclude both visual

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Perceptual Integration in Children TABLE I ANGULAR PRECISION IN LOCALIZATION (DEGREES) Stimulus modality

Auditory Proprioceptive Visual

Age

9

13

16

10.5 5.7 3.6

6.7 7.1 3.0

5.4 6.2 3.3

and tactual feedback. The results are presented in Table I in terms of average error.6 These data indicate that between the ages of 9 and 16 only auditory localization improves in precision. Additional data for visual and auditory localization in adults suggests that there is no further change in this ability. Hence localization approaches its maximum precision by 9 years of age. How it develops and what factors are important in its development are just beginning to be studied systematically. The work of Burton White (1963; White, Castle, & Held, 1964) provides this beginning to the study of factors related to the development of the ability to localize visual targets. White has been studying the growth of visually guided grasping in infants. On the basis of a combination of observational and experimental studies, he suggests that visually directed grasping behavior occurs in infants at about the age of 6 months. The grasping is the culmination of a sequence of behaviors which includes visual attending to the hand and the target. The picture for tactual localization may be different from that for other types of localization. Before discussing tactual localization studies, though it is worth analyzing more carefully the nature of a localization task. A localization task requires S to respond to a source of stimulation of a specific modality. In comparing localization to different sources of stimulation, it is necessary to consider the modalities of response as well as the modalities stimulated. In the studies summarized in Table I, auditory, visual, and proprioceptive localization all were indicated by a proprioceptive response in the absence of vision (pointing the finger without looking at it). White’s task of grasping an object can be considered a proprioceptive response in the presence of vision. This distinction is important to the data next considered. A series of studies aimed at investigating developmental changes in modality dominance (Renshaw, 1930; Renshaw, Wherry, & Newlin, 1930; 6These data were collected as control measures for specific studies. The apparatus used for auditory and visual localization differed somewhat from that used for proprioceptive localization, so comparisons must be made with caution.

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Renshaw & Wherry, 1931) compared blind and sighted children and adults in their abilities to localize points on their hands and forearms. The localization task required S to touch a spot on his hand or forearm which E had just stimulated by touching. Sighted Sswere blindfolded for the task. I n asecond localization condition, sighted Ss were asked to perform similarly in the presence of vision. (The stimulation by E , of course, was again done u hile S was not looking.) The investigators considered this task one of visual localization. Sighted children were superior to sighted adults in tactual localization \\ ithout vision, but sighted adults ere superior to sighted children in the second localization task with vision. In localization without vision, congenitally blind adults performed at a similar level to sighted children and were superior to blind children as well as to sighted adults. Since Renshaw and Wherry considered the localization response H ith vision as a visual localization task, these data were interpreted as evidence for early tactual dominance followed by the development of visual dominance (a dominance which, of course, never develops in the congenitally blind Ss). The number of Ss in these studies is exceedingly small, and the studies badly need replication. Dunford (1930) did replicate the observation of at least some decreases in accuracy of tactual localization with increasing age. In his study, though, the Ss were never very accurate at the localizing task. Since there is mounting evidence contradicting the doctrine that “touch teaches vision” and that visual dominance emerges developmentally after tactual dominance, an alternative interpretation of Renshaw’s data might be considered. Renshaw stated that he \\as comparing tactual M ith visual localization. I n fact, both his tasks did require localization of tactual targets, but the localization response \\as visual in one case and proprioceptive in the other. The different results for blind and sighted children and adults may not represent developmental shifrs in dominance, but developmental differences in the functional nature of the target localized. Perhaps, in the visual response condition, Ss also fixed the target in memory by visualizing it, \\ hile being stimulated, and perhaps adults are better able to do this than children. The adults may have been able to visualize the location of the tactual target and respond to it visually, more accurately than children. Perhaps, u ith development, there is increasing integrated functioning among the sense modalities. Such a hypothesis u ould account for Renshau’s data and uould not contradict other evidence about development trends in visual as compared t\ ith tactual perception. Some additional support may be derived from a study by McKinney (1964) u ho used a slightly different type of localization task \\ ith young children 4 to 8 years. The S sat ith his eyes closed and his hand in a palm up position. The E touched a finger and instructed S to point to the finger iust touched. I98

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Generally, there was a marked decrease in errors as a function of age. In another condition, the S was asked to turn his palm over before pointing to the stimulated finger. This condition was intended to produce a conflict betnreen S’s ‘‘visual schema” of his hand, and its proprioceptively perceived inverted posture. Under such a condition, younger children were relatively less accurate than older. Thus, the older children seemed more able to integrate the “visual schema” and the inverted hand position to still respond accurately. These data seem to fit a hypothesis of a developmental increase in integrated functioning of modalities with age. It can be said in summary that sources of stimulation are localized in a variety of modalities early in development. Auditory, visual, tactual, and proprioceptive sources of stimulation are localized early and easily even without visual involvment in the localizing response. Accuracy of tactual localization may decrease with age, though the evidence for this is tentative. When vision is included in the response, accuracy of localization may improve.

B. SHAPEPERCEFTION A number of studies employ designs which allow for comparison of various aspects of tactual and visual shape perception. As part of investigations comparing intramodal and intermodal perception, Hermelin and O’Connor (1961), Rudel and Teuber (1964), and Zinchenko and his colleagues (Zinchenko & Ruzskaya, I960a, b; Zinchenko, Chzhi-Tsin, & Tarakanov, 1962; Lavrent’eva & Ruzskaya, 1960)compared visual matching of shape with tactual matching. The parts of these studies dealing with intermodal transfer will be discussed in Section I V , A ; in the present section the intramodal comparisons are of concern. Hermelin and O’Connor used unfamiliar Greek and Russian letters with 5-year-old normal children and 12-year-old imbeciles matched for MA. The normal children recognized these letters equally well visually and tactually. Tactual recognition by the imbeciles was significantly better than their visual recognition and better than either visual or tactual recognition by the normal Ss. There were no other significant differences. Rudel and Teuber, using geometric and nonsense three-dimensional forms with 3- to 6-year-old children, found decreasing matching errors as a function of age. Furthermore, visual-visual matching was most accurate and tactual-tactual matching least accurate over all the ages. Zinchenko and his colleagues, using two-dimensional nonsense shapes adapted from Gaydos (1956), found the visual matching to be easier than tactual for normal children from 3 to 7 years of age: per cent errors decreasing from 50 to 2 for visual matching and from 70 to 40 for tactual matching.

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Both these investigators and Piaget in similar studies were quite concerned about the exploratory manipulations made by the Ss and the degree to which these manipulations provided information about the objects being explored. For example, Piaget finds a trend from passive and unsystematic exploration to active and orderly exploration of objects presented for tactual identification to children from about 2+ to 7 years of age. He suggests that whether or not geometric forms or just familiar objects can be identified (recognized, matched, reproduced) on the basis of tactual stimulation alone depends on the type of tactual exploration of which a child is capable (Piaget & Inhelder, 1956, pp. 21ff.). On the basis of these studies as well as others to be discussed shortly, it appears that visual matching and identification of shape can be accomplished at an earlier age than tactual matching and identification. (The one exception to this is the study of Hermelin and OConnor.) Whether the later tactual development represents transfer from vision or just parallel development of the modalities is not answered by the present type of design. A further point to note is that in the Piaget and Zinchenko studies attention was focused on the perceptual behavior per se rather than just on age differences in perceptual errors. A second particularly valuable way to iwestigate sensitivity among sense modalities is to vary the stimulus dimensions in such a way that the bases for discrimination can be inferred from the errors in discrimination. Such a method has been used by two of the present authors (Pick & Pick, 1967) to investigate developmentally specific aspects of tactual shape discrimination. The study was a replication, in a different modality of a developmental study of visual discrimination conducted by the Gibsons (Gibson, Gibson, Pick, & Osser, 1962a). The original forms for visual presentation were black line drawings on a white background. The same forms for tactual presentation consisted of raised metal lines on a smooth metal background. In the present study subjects were asked to make “same different” judgments between pairs of the metal letter-like forms. Each pair consisted of a standard form and a transformation of that form. The transformations were of five types: line-to-curve changes, rotations and reversals, perspective changes (tilted views of standard form), topological changes (breaks or closes in standard form), and a size change. The subjects were normally sighted children 6 to I3 years and adults. The data are most meaningful when compared with the Gibson et al. developmental study of visual discrimination of the same forms. The data obtained by Pick and Pick indicate that, in general, tactual discrimination of these shapes is more difficult than visual. This is evidenced by a higher error rate even at the older ages for all the types of transformations. Furthermore, the decrease in errors as a function of age is more marked in the visual discrimination data than in the tactual data. Beyond these state-

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ments, it is not too meaningful to make comparisons of the absolute levels of performance between the two studies since there were procedural differences. What is probably useful is to examine the relative levels of difficulty of the types of transformation in the two studies. In the visual discrimination study of Gibson et al., the perspective transformations were most difficult, rotations, reversals, and line-to-curve transformations next in difficulty, and topological transformations easiest. In the present tactual discrimination study, the order was perspective transfmnations again most difficult, line-to-curve again in the middle, but rotations and reversals were just as easily discriminated as topological transformations. This drop in relative difficulty of tactual discrimination of rotations and reversals is quite reasonable when it is considered that tactual scanning is successive in nature. Rotations and reversals, then, may be functionally equivalent to the breaks and closes of topological transformations. To elucidate the role of prior visual experience in this kind of discrimination, two groups of blind Ss were used: a group of partially sighted (legally blind) Ss and a group of totally blind Ss. The partially sighted Ss all read Braille but had some residual vision varying from movement perception to crude shape perception. Both groups ranged in age from 6 to 21 years and had been visually handicapped since early infancy. These Ss performed the same tactual discrimination task with the metal letter-like forms. The order of difficulty of discriminations for the partially sighted Ss was the same as that for the sighted Ss performing tactually: perspective transformations most difficult, line-to-curve transformations second in difficulty, and rotations, reversals, and topological transformations equally easy. The totally blind Ss showed a slightly different order of difficulty. With these Ss only the perspective transformations were clearly more difficult than the other three types. The line-to-curve, rotations, reversals, and topological transformations were all approximately equally easy to discriminate. In the totally blind group, there was no decrease in errors as afunction of age. The low absolute level of the errors for all but the perspective transformations suggests that in totally blind Ss, of necessity all improvement in tactual discrimination occurred prior to 6 years of age. The shift in relative difficulty of line-to-curve discriminations in the totally blind may suggest that this is an important aspect of shape to be detected when touch is the only or dominant modality. When vision is dominant or when there is some visual capacity, it does not seem to be as easy a dimension of shape to detect tactually. Hunter (1954) compared directly thresholds of tactual discrimination of straight lines and curves in blind and sighted children. The S felt a flexible steel ruler 205mm in length and judged whether it was straight or curved. The performance of the two groups was compared in terms of the values in millimeters of curves judged straight and the blind Ss had a lower threshold 1.44mm) between straight and curved lines than the sighted Ss

(x=

20 1

Herbert L. Pick, Jr., Anne D. Pick, and Robert E. KIein

(x

= 2.37mm). This is in accord with the results of the study described just above in which tactual line-to-curve discriminations were easier, relatively, for blind Ss than for Ss having some vision. The blind Ss also showed less variability (SD = 3.03mm) than the sighted Ss (SD = 4.93). Hunter combined his blind and sighted Ss and compared three age groups 12-14 years, 14-17 years, and 17-19 years. He observed a significant decrease in variability of judgments as a function of age. It is not clear whether this was true of both the blind and sighted Ss. The curvature thresholds of older as compared with younger children did not differ. While a decrease in variability or other improvement in form discrimination as a function of age would not be unexpected, the factors responsible for such improvement must still be investigated. This was the purpose of a study conducted by one of the present authors (Pick, 1965). It involved comparisons of improvement in form discrimination in vision and touch and employed a transfer of training paradigm. The stimulus forms were some of the letter-like forms used in the studies just described. The Ss (all 5- and 6-year-olds) were trained to discriminate among a standard form and transformations of the standard form. Then, in a transfer task, they were asked to discriminate among either (a) the same standard form and new transformations or (b) a new standard form and the same types of transformations as in training or (c) a new standard and new transformations. All conditions involved intramodal training and transfer, and the design included one visual and two tactual experiments, one involving simultaneous comparisons and the other successive. The results suggested that the learning of stimulus differences or distinctive features (condition b above) is very important in improvement of discrimination of forms of this type. The stimulus shapes or prototypes (condition a above) seemed to be learned only to the extent that the comparison between the standard form and itsvariations was a successive rather than simultaneous one. The intramodal transfer conditions of the present experiment suggested that the nature of the comparison among stimulus forms (simultaneous or successive) is more important than the modality involved in determining what is learned in this type of training. Stimulus differences were learned in both modalities, touch and vision. Stimulus shapes were learned also, in either modality when the comparison task was a successiveone. A wider variety of shapes and stimulus dimensions might be used in further studies to investigate the generality of these results. (This experiment has been replicated in such a way as to look at intermodal transfer of improvement in form discrimination and is described in Section IV, B.) Thus far, studies of visual and tactual shape perception suggest that visual shape perception is easier earlier in development than is tactual shape perception, that some aspects of shape are more easily acquired by one or the other modality, and that the nature of stimulus exploration may be

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related to the relative ease or difficulty of a task in a given modality. Other aspects of shape would be usefully explored with the same paradigms. Orientation of form is another aspect of shape perception which can be compared in touch and vision. Lila Ghent and her colleagueshave observed that under visual presentation, children consistently label many twodimensional “nonsense” forms as “right side up” in one orientation, and “upside down” when inverted. These investigators (Ghent, 1960, I961 ; Ghent, Bernstein, & Goldweber, 1960) have systematically explored developmental trends in such orientation identifications and the characteristics of the forms which will elicit these identifications. A generally observed developmental trend is a decrease in the consistency of orientation identifications. In some cases, there seem to be reversals of the orientation response with increasing age. A form seen as upsidedown in one orientation by younger children is seen as right side up in that same orientation by older children. The present authors have investigated tactual as well as visual developmental trends in such form orientation responses (Pick, Klein, & Pick, 1966). The stimulus forms were the same letter-like forms described previously. They were chosen for the present study because of the developmental data already available. In the present study, a form and its up-down reversal were presented side by side to an S who was simply asked, “Which one is upside down?” The Ss ranged in age from 4 years to adults. Half the Ss in each age group were presented the 12 pairs of forms visually and half tactually. When the forms were visually presented, half of the pairs elicited consistent orientation identifications throughout the age range observed. This is in contrast to Ghent’s observations using different forms that such identifications tend to decrease with age. Tactual presentation conditions yielded markedly different results from the visual conditions. With tactual exposure, there were no more consistent orientation identifications exhibited in any of the age groups than would be expected by chance. However, a simple interpretation that form orientation identifications are purely visual is contradicted by data from blind Ss. A group of totally blind Ss and a group of partially sighted Ss, each ranging from 6 to 21 years of age, were asked to make orientation judgments under conditions of tactual presentation. These were the same groups of blind Ss as in the previously described form discrimination study. The partially sighted Ss were all legally blind but could perceive at least movement. Both groups had been visually handicapped since birth or early infancy. The results for the two groups differed. The totally blind group showed no consistent identifications while the partially sighted group did show such form orientation identifications. (There were not a sufficient number ofSs at any one age to compare different age groups separately, but the preferences shown were consistent throughout the entire group.) When these

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identifications were compared with those shown by normally sighted Ss with visual presentation, they were found to be the same. A comparison of all the modality and S conditions suggests some hypotheses about form orientation in touch and vision. First, under normal conditions intermodal transfer of orientation preferences does not always occur. Normally sighted Ss showed no evidence of transfer from vision to touch. Second, under abnormal conditions, intermodal transfer can occur. The partially sighted Ss showed the same preferences tactually as normally sighted Ss did visually. That these preferences represented some type of transfer, and not just increased development of the tactual modality, is suggested by the fact that only the partially sighted among the blind Ss manifested orientation preferences. Finally, one of the conditions, at least, under which this transfer may occur is the presence of some visual experience when vision is not the dominant modality. Further and more direct evidence about intermodal transfer and the conditions under which it occurs will be considered in Section IV. One additional study involves comparison of tactual shape perception in the presence and absence of visual experience. Hatwell (1959), observed sighted children, blind-born children, and children blinded after 4 years of age. In tasks of tactual recognition of geometric forms she found few, ifany, differences between the performance of the sighted children and the later blinded children. Both groups were superior to the blind-born children in performance on the experimental tasks. These Ss were 6 to 17 years old and Hatwell observed a general improvement with age on her tasks. Over the ages, however, the important differences were between the groups having visual experience and the blind-born Ss. This study does not give information about the extent of visual handicap of these children. However, the difference between performance of later blinded and early blinded children (which is a commonly observed difference) might be compared to the data of the present authors with partially sighted and totally blind Ss. Such a comparison would suggest that some aspects of shape perception (form orientation identification and Hatwell’s form recognition) are primarily relevant to the visual modality, but that some visual experience allows for transfer to the tactual modality when that is S’s dominant modality. Illusions of shape have been utilized to compare visual and tactual perception. Hatwell (1960) investigated some common geometrical illusions in blind children using tactual exploration. In some cases, performance of such children was compared with a comparable group of sighted Ss using visual exploration. Four illusions were studied: horizontal-verticai, Delboeuf, Muller-Lyer,and Halttre. Blind Ss showed a considerable horizontalvertical illusion. They also manifested a Muller-Lyer illusion, though somewhat less than a group of sighted Ss exploring the lines visually. Neither the 204

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Delboeuf nor Haltkre (which is like the Muller-Lyer, but with rectangles instead of arrows on the ends of the lines) elicited illusory judgments from the blind Ss. These different results are probably accounted for in terms of the nature of the tactual exploration of the specific forms. In exploring the horizontal-vertical illusion form, and perhaps to a lesser extent, the Miiller-Lyer illusion form, Ss necessarily felt the entire form, and specifically felt the sections necessary for the illusion to occur. In both the Delboeuf and Haltkre illusions, it is possible with tactual exploration to ignore the critical parts of the form-the two circles or the rectangles at the ends of the figure, respectively. With these illusions at least, to the extent that Ss must take in the critical stimulus information, the same illusion is manifest tactually as visually. This is also true of the size-weight illusion as will be discussed in Section 11, C. Hatwell used two age groups (8-12 years, 12-16 years) in her studies, but the only apparent differences were between sighted and blind Ss, and not between different age groups. With only one exception, the studies reviewed here document the early development of visual shape perception as compared with tactual shape perception. Still, many aspects of shape perception seem to be easily detectable in both modalities. Some dimensions though, may be especially relevant for one modality except under unusual circumstances. Orientation, for example, may be a type of information which is more appropriate for vision than touch. It will be recalled that orientation differences (rotations and reversals) are discriminated tactually like topological differences and such discriminations seem to be based on a small portion of the form. Consistent orientation identifications are made only visually except in blind Ss with some visual experience. On the other hand, tactual straight-curved discriminations seem to be made with much greater ease in blind than in sighted Ss. It would be useful, in studying the processes of vision and touch, to explore intermodally other dimensions which may have a special relevance for one or another modality. C. HIGHERORDERSTIMULUS PERCEPTION The size-u.eight illusion as typically studied involves two sense modalities, touch and vision, and two stimulus dimensions, size and weight. When the S picks up and looks at two objects to compare their weights, size information is provided both visually and tactually, while weight information is provided only tactually. The illusion consists of a misjudgment of the relative weights of two objects differing in size. For example, the larger oftwo equal weights will be judged lighter. Robinson (1964) studied the size-weight illusion in children from 2 to 10 years. He observed a decrease in the magnitude of the illusion w4th age, though no apparent change in the frequency of the illusion as a function of

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age. Robinson’s data suggested a relationship betc\,een the children’s ability to discriminate between different weights and the magnitude of the illusion. Specifically, the magnitude of the illusion approximated the limits of the Ss’ ability to discriminate weights. The method of experimenter comparison has been applied to the sizeweight illusion in three experiments (Pick & Pick, 1967). Developmental trends in the illusion elicited under threedifferent conditionswere compared. First, a developmental study of the illusion under standard exposure conditions was conducted. Children from 4 to 16 years and adults judged the relative weights of pairs of objects in which one member of the pair was larger in size than the other. The Ss held the objects in their hands while making their judgments. In a second study, a tactual form of the illusion was measured. Subjects of the same age range performed the same task while blindfolded, so stimulus information for size as well as weight was given only tactually. Finally, in a third study, the illusion was measured under conditions in wihich size information was obtained only visually. The Ss, again of the same age range, lifted pairs of objects by strings and, while looking at them, judged their relative weight. The results for the standard exposure condition showed an increase in the magnitude of the illusion with age, the main difference being between the 4-year-olds and all the older Ss. (The difference between these results and the decrease in magnitude of illusion found by Robinson may be, in large part, a function of the somewhat different age ranges in the two studies. Robinson’s decrease occurred primarily between the ages of 2 and 4, an age range which was not covered in the present study.) The tactual form of the illusion also showed an increase in magnitude as a function of age, the biggest increase occuring before the age of 10. In the third form of the illusion, in which size was given only visually, there was a marked decrease in magnitude of the illusion as a function of age, and nearly all of the decrease occurred between 4 and 6 years of age. The differences in developmental trends in the magnitude of the size\\eight illusion under the three conditions argues against a simple intermodal transfer hypothesis. It is also unlikely that the illusion operates independently in the two modalities. If this were the case, one would expect the magnitude of the illusion under normal conditions (with visual size and actual size information both present) to be the sum of the magnitudes ofthe illusion when visual size information alone and tactual size information alone were present. (The absolute magnitudes obtained also seem to rule out the possibility of these results simply being a ceiling effect.) Thus it would appear that the data for the size-weight illusion are more easily accounted for by an hypothesis of integrated functioning of the two modalities rather than by an hypothesis of separate independent functioning. The later importance of touch may reflect its later development, but the complex

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interdependence of the two modalities suggests an integrated process. A second higher order stimulus variable which has been investigated in relation to visual and tactual perception is the grapheme-phoneme unit. A grapheme-phoneme unit is itself an intermodal variable. It is based on the relationship of the spelling of the language to the sound of the language. Such units or correspondences are letter groups which have a single, regular pronunciation in the English language. For example, letter groups such as DINK, SLAND have high correspondence in English, but other arrangements of the same letters such as NKID, NDASL do not. The investigations of Gibson and her colleagues (Gibson, Pick, Osser, & Hammond, 1962b; Gibson, Osser, & Pick, 1963) showed that grapheme-phoneme correspondences function as grouping principles in the visual perception of printed material. Pseudo-words generated by rules of English grapheme-phoneme correspondence and presented tachistoscopically, were recognized more accurately by adults, third grade, and even first grade children than were pseudo-words not conforming to these rules. A recent study (Pick, Thomas, & Pick, 1966a) investigated the function of grapheme-phoneme correspondences in tactual perception. The Ss were a group of legally blind Braille readers from 9-21 years of age. They were asked to read as quickly as possible groups of pseudo-words written in Braille. The pseudo-words had either high or low grapheme-phoneme correspondence. The Ss spent a significantly greater amount of time and made more errors reading the low correspondence pseudo-words than the high correspondence pseudo-words. The results indicate that grapheme-phoneme correspondences function as grouping principles in tactual perception of Braille in much the same way as in the previously cited studies of tachistoscopic visual perception of printed material. These are probably not self-evident results, since there are obvious important differences between the manner in which information is obtained tactually and visually. The results of this study indicate that regardless of differences between visual and tactual scanning, the same variable can function as a grouping principle in visual and tactual perception. The mechanics of scanning apparently do not wholly determine the manner in which material in the two modalities is processed. At least complex material, of the sort involved in reading, seems to be processed in a similar manner in touch and in vision. The studies discussed in this section have been very diverse and tied together only insofar as they involved comparisons of perceptual functioning in separate modalities. The variables investigated here ranged from punctuate tactual stimuli to higher order stimuli, themselves defined by an intermodal relationship. Unfortunately the variation of stimuli over this range has not been as systematic as it has been diverse, and strong conclusions about intermodal development are not possible from these data.

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However, some generalizations and hypotheses to guide future systematic investigations are suggested by the work reviewed here. First there is improvement with age in approximately half of the perceptual processes studied. Furthermore there is additional documentation that visual perception approaches maturity earlier than tactual. In the perceptual processes which did not show improvement as a function of age, it may well be that the improvement occurred before the youngest ages included. A possible implication is that the most meaningful experimenter comparisons of modality functioning are not necessarily between Ss of the same age but rather between Ss operating at equivalent levels in the relevant modalities. Second, it is not true that all developmental trends are parallel in the modalities of touch and vision. For example, orientation identification and certain aspects of shape discrimination do not appear to show parallel trends in the two modalities. Another question is that of the conditions for intermodal transfer. A case in point is the fact that orientation identification shows transfer only under very special conditions. In order to elaborate such transfer conditions it will be necessary to examine very carefully specific stimulus dimensions and subject populations. A very tentative hypothesis about the trends which are and are not generally parallel in the two modalities is that the perception of simple variables, e.g., those involved in discrimination, orientation identification, and shape detection reflect modality characteristics such as mechanics of exploration, but more complex variables, e.g., grapheme-phoneme correspondences and to some extent those involved in the size-weight illusion are dealt with in some central integrating mechanism. Furthermore, as was suggested in relation to shifts in tactual localizing ability increasing integration in modality functioning may be a characteristic of development as well as of increasing stimulus complexity. Perhaps the different modalities improve in their ability to deal with the same information. In short, perception of more complex stimulus variables and perception by older Ss may reflect less the structural differences among modalities and more processes of integration common to information from the several modalities. This section has been concerned only with comparisons of a task performed in different modalities separately. The experimenter comparison design as it has been discussed here can be extended to allow comparisons of intramodal and intermodal functioning. This intramodal-intermodal design is typified by a matching task involving all combinations of two modalities such as vision and touch. In the matching task the standard stimulus is presented either visually or tactually, thus giving rise to four combinations of task: visual-visual, visual-tactual, tactual-visual, and tactual-tactual. Subjects are then compared on these four different comparisons. 208

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The simplest hypothesis describing the outcome of the intramodal-intermodal comparisons might be that intramodal tasks are easier and would result in better performance than intermodal tasks (as was hypothesized by Kelvin, 1954), or that visual presentation of the standard stimulus will result in better performance than tactual presentation. The latter hypothesis might be based on a view that matching tasks of this type involve an intermediate stage of storage or transfer and that visual stimuli are stored or remembered more easily than tactual stimuli. In that case a further study comparing simultaneous and successive matching tasks might be warranted. Whatever the case, simple hypotheses such as these are easily combined into more complex ones and the design seems a potentially useful one for testing such hypotheses about intermodal functioning. However, few investigators have employed the design (Hermelin & O'Connor, 1961; Rude1 & Teuber, 1964; Zinchenko & Ruzskaya, 1960a,b; Zinchenko et al., 1962; Lavrent'eva & Ruzskaya, 1960) and the intermodal comparisons of these studies will be discussed in Section IV, A along with other intermodal matching studies.

111. Conflict of Sensory Input The production of conflict between the inputs to two sense modalities provides a technique for direct observation of interrelations among them. Typically, S is required to respond to one of two conflicting stimulus values. For example, the size of an object may be optically distorted and thus a conflict created between visual and tactual size information. The Sjudges the true (or felt) size of the stimulus. Analogous conflicts may be created by distortion of location, orientation, and other properties, The sensory conflict technique has been employed with children in studies of immediate response in the presence of conflict and in studies of changes of response following a period of exposure to conflict. Studies of immediate response to conflict provide information about modality dominance. Investigations which focus on the changes of response following a period of exposure provide information about the relative flexibility and long-term integration of the sensory systems. In the present section, studies of these two types will be reviewed according to the type of distortion employed: orientation, location, size. and time. A. IMMEDIATE RESPONSETO CONFLICT Smith and Greene (1963) investigated the effects of visual orientation distortion on the performance of simple motor tasks. The Ss, boys between 9 and 13 years of age, were required to perform simple visual-motor tasks (e.g., 209

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draw matrices of dots, letters, and right angle triangles) under four conditions of visual feedback. The feedback conditions were (a) undistorted, (b) reversed (left-right), (c) inverted (up-down), and (d)inverted and reversed. The Ss viewed their responses through a television monitor and were required to reorient their movements such that writing, dotting, and drawing appeared to be normally oriented as they viewed the monitor. The authors report a striking age difference in the ability to perform under the distorted feedback conditions. Of the thirteen Ss under the ages of 12years, only one performed successfullyunder all four conditions, whereas eleven of the twenty-one older children performed successfully under all conditions. Developmental investigations of the effect of orientation distortions on perceived orientation have also been conducted by Witkin et al. (1962; Witkin, Lewis, Hertzman, Machover, Maissner, & Wapner, 1954). Two sensory conflict tasks used by these investigators are of interest here. One task required S to adjust his own body to upright. His chair and theroom could be tilted left or right independently of each other. A modification of this task required Sto adjust the room to upright. The second task requiredS to adjust a luminous rod to vertical. The rod was located within a square luminous frame in a darkened room. The rod and the frame and S’s chair could all be tilted independently. Successful performance in both ofthese tasks requires that S respond in relation to the sensed inclination ofthe body and disregard the erroneous visual directional stimuli (the tilted room or the tilted frame). Subjects who respond accurately in these tasks (i.e., respond in correspondence with proprioceptive, kinesthetic and vestibular cues) are termed “field-independent” whereas Ss whose responses are based on visual information are termed “field-dependent”. Data from cross-sectional (Witkin et al., 1954) and longitudinal (Witkin, 1960; Witkin et al., 1962) studies indicate that degree of field-independence, in general, is positively correlated with age. Field-independence increases rapidly between 8 and 13 years, gradually to age 17, and decreases slightly to 21 years. Witkin evaluates these data in terms of the concept of differentiation (cf. Section I). In this context field-independence is the result of the S’s growing ability to differentiate himself from his environment. A different type of orientation distortion investigated by Klein (1 966) also showed a developmental trend. In this study boys, 9 to 18 years of age, judged the felt orientation of their index finger.The Sviewed his index finger through a double dove prism. When S’s finger was pointed 20degrees below the horizontal, it appeared to be pointed 20 degrees above the horizontal. The S indicated the felt orientation of the viewed finger by adjusting his other index finger which was out of sight. The nature of this response may be important in interpreting the results as will be discussed later. The 18-year-old Ss were significantly less influenced by the distorted visual input than the 9- and 14-year-old groups. In general, it seemed the 210

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older Ss were better able to disregard the distorted visual stimuli and respond on the basis of the proprioceptive stimuli. Studies of orientation distortion are consistent in finding improvement in accuracy with age but reflect differences in the ages at which this improvement occurs. There have been several sensory conflict studies involving location distortions which have used adults as subjects. This type of distortion has been investigated developmentally by Klein (1966)who adapted for use with children (9-18 years) a sensory conflict task used by Hay et al. (1965). In this task a wedge prism laterally displaced the visual location of S’s finger. The S indicated the felt position of the index finger while viewing the optically displaced image. The Ss’ responses were very close to the optical location of the index finger and not to the true (or felt) location. In other words, for the most part Ss were unable to disregard the distorted visual information and respond to the proprioceptive information about location of the finger. Furthermore, response accuracy was approximately the same over all ages and was similar to response accuracy in adults tested by Hay et al. Two studies of auditory location distortion using adult Ss are presented here because these findings are similar to those for visual location distortion studies with both adults and children. Witkin, Wapner, and Leventhal(l952) investigated the effects of conflicting visual and auditory stimuli on the perceived position of a sound source. In this study, college students were asked to indicate when a speaker’s voice did not seem to be coming from the speaker’s mouth. The conflict was produced by controlling the degree of asynchrony in the energy arriving at S‘s ears from the speaker. The voice was started in the median plane and “moved” continuously until S signaledthat it did not seem to originate from the speaker’s mouth. The Ss tolerated angular deviations of the sound source of between 28 and 38 degrees before signaling that the source was to one side or the other. In a control condition, Ss were blindfolded and could receive only auditory position cues. Here the tolerance was approximately 18 degrees, significantly less than when the source was viewed. These results indicate that visual cues can modify the apparent locus of the source of auditory stimuli. Further evidence of the importance of vision in judgments of sound location comes from a study by Jackson (1953). Here Ss were seated before a series of steam-kettle whistles which had been modified so that steam could be emitted from a whistle independently of the whistling sound. When the real and apparent sound source deviated by 30°, 97% of the Ss were not aware of the visual-auditory conflict. A third type of distortion, visual distortion of size, has received attention in two studies, one with adults and one with children. Rock and Victor (1964) asked college students to view and feel a stimulus simultaneously and afterwards to judge its width. The stimulus was a square, and was viewed through 21 1

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a lens which compressed the visual image by one-half. The responses were very close to the optical size. rather than to the true (or felt) size of the

stimulus. Thus again the visual component of a conflict completely dominated the response. The Rock and Victor task was modified by Klein (1966) and used in a developmental study of responses to size distortion. Klein’s procedure required that S view and feel the stimulus and at the same time select a comparison stimulus from a nearby array. There were no age differences found in the range from 9 to 18 years. In fact, the Ss’ responses were only slightly affected by the visual component of the conflict rather than being completely dominated by it as in the Rock and Victor study. This may have been due to differences in procedure between the two studies. Rock and Victor’s Ss responded after viewing and feeling the stimulus whereas Klein’s Ss responded simultaneously with viewing and feeling the inspection stimulus. If visual stimuli are remembered more readily than haptic stimuli, then conflict tasks like Rock and Victor’s which use delayed responses might reflect more visual dominance than tasks which use simultaneous responses. In the studies discussed above, the sensory conflicts have involved distortion of the spatial qualities of objects (e.g., orientation, location, and size). Sensory conflict can also be produced by means of temporal distortions. Delayed auditory feedback (a delay in the arrival of the air-conducted component of a speaker’s voice at his own ears) can be viewed as a sensory conflict which involvesa distortion of the normal temporal relations between the tactual and proprioceptive components and auditory components of speech production. (Compare Yates, 1963 for a theoretical discussion of the issues involved in this interpretation.) The effects of delayed auditory feedback have been investigated with children by Chase, Sutton, First, and Zubin (1961). The Ss (ages 4-6 and 7-9 years) told stories and their speech was returned via earphones after a 200-msec time delay. The investigators report that the greatest changes under delay of auditory feedback were: (1) a decrease in rate of speech and (2) an increase in the number of prolonged syllables. Both changes were significantly greater for the older than for the younger Ss. In addition, almost all Ss detected a difference in their voices. However, the younger Ss generally described the changes as an increase in loudness, and none made reference to the temporal delay. On the other hand, half of the older Ss did make reference to the time disturbance. Apparently, only orientation and temporal relation distortions, of all those reviewed, show developmental trends. Distortions of temporal relation disturbed the performance of older Ss more than that of younger Ss. On the other hand, in the studies involving orientation distortion, the trends are consistent in that younger Ss are more disturbed than older ones. However, 212

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within these consistent trends, the particular age at which performance improves differs from study to study. Witkin, et al. found important changes between 8 and 13 years, Smith and Greene at 12 years, and Klein between 14 and 18 years. Two factors may account for these differences in the ages when improvement occurs. In the tasks used by Witkin et al.,Sresponds in the presence of grossly distorted visual referents (the tilted frame or tilted room). Thus the absolute values of the conflicting sensory cues change as a function of the response. It is possible that systematic changes in the magnitude of the conflicting cues, contingent upon s’s responses, help him register or attend to the distortion, and so enable him to overcome the sensory conflict at relatively early ages. Similarly, in the Smith and Greene study the distorted visual feedback of S’s own motor responses can also provide him with information about the distortion. Other evidence for the importance of motor responses is provided by studies of adaptation to prismatic distortion which indicate that such adaptation occurs rather quickly in the presence of response-produced stimulation (Held & Hein, 1958). In both the Witkin et al. and Smith and Greene studies, the development changes occurred relatively early as compared to the study by Klein. This difference might be accounted for if the distortion in the Klein study was less readily registered by the Ss. This might have occurred either because S did not view his own responses and thus had no opportunity to acquire information about the distortion from visual feedback or because S, by the nature of the task, produced no systematic change in the situation which might call attention to the distortion. Another reason that the distortion might not have been obvious in the Klein study is that, from the S’s point of view, only the target was distorted. In the other studies, there was distortion of a much larger portion of the visual field which could have provided the Swith more information about the nature of the distortion. B. RESPONSEAFTER PROLONGED CONFLICT All the studies considered so far have investigated immediate response to distortion. As indicated earlier, another currently popular method of studying sensory conflict is to look at response changes following periods of exposure to the conflict. (These periods may range from a few minutes to several weeks.) This procedure has been employed by Pick and Hay (1966) in a developmental study of adaptation to prismatic displacement. Wedge prisms with bases oriented left or right worn as spectacles displace the apparent location of objects laterally. After several minutes of exposure to such displacement an active S (cf. Held & Hein, 1958) will adapt to this distortion by localizing visual targets in their true location rather than in

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their apparent location. When Ss of 8, 12, and 16 years of age were subjected to this type of visual distortion for periods of 15 minutes, all manifested adaptation to an approximately equal degree. The type of adaptation which occurs as a consequence of prism exposure depends in some degree on the type of activity in which the person engages during exposure (Hay & Pick, 1966). If the S‘s vision is limited to his hand, the adaptation appears to be “proprioceptive” (i.e., manifest itself in pointing at sounds and straight ahead without vision, as well as at visual targets). If the S is permitted to view his whole body during exposure the adaptation appears to be “visual” (i.e., manifests itself in shifts in the apparent visual location of sounds as well as in pointing at visual targets). These effects of type of activity on nature of adaptation were replicated with the children, but there were no age differences (Pick & Hay, 1966). Thus whatever the processes responsible for adaptation to the prismatic distortion are, they are not dependent on age over the range studied. It is important to keep in mind that the prism distortion in question here is a lateral displacement. The consistent appearance of age trends in the studies of immediate response to distortion of orientation calls for a developmental study of prolonged exposure to this distortion. Although only the conflict situations involving orientation and temporal delay show significant age trends, the distortion technique offers an attractive possibility for the study of perceptual-motor development in young children. With the exception of the recent systematic work of White (1963; White et al., 1964), the study of perceptual-motor development has been primarily normative and descriptive (Halverson, 1931; Gesell & Thompson, 1934). Sensory conflict tasks studied developmentally provide a means of separating the perceptual and motor components in the development of perceptual-motor behavior.

IV. Intermodal Transfer Intermodal transfer will be used as a generic term to refer to tasks in which S uses information obtained in one modality to solve a task in another. Two such tasks will be discussed: intermodal matching, and intermodal transfer of training. Another type of intermodal task which does not involve the utilization of information by two modalities and which will not be considered in the present chapter is the situation in which S is asked to make a judgment in one modality while being exposed to extraneous stimulation in another modality. Werner, Wapner, and their colleagues have investigated a number of phenomena which show interactive effects under such conditions. For example, an auditory signal presented to one ear results in a shift in the

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judged vertical. The reader is referred to Wapner and Werner (1957, 1965) for an introduction to this literature.

A. INTERMODAL MATCHING

Studies of intermodal matching have dealt with a variety of stimulus dimensions: length, shape, duration, etc. However, there have been relatively few developmental intermodal matching studies, and the most frequent stimulus variable used in these studies has been shape. As pointed out in Section 11, B, the most useful information about stimulus dimensions in intramodal matching is obtained when the perceptual activity per se is analyzed or when the stimuli are varied systematicallyso as to be able to use the pattern of errors to infer what stimulus dimensions are important. This is equally true in the study of intermodal matching. Neither the studies of Hermelin and O’Connor (1961) and Rude1 and Teuber (1964) mentioned previously (cf. Section 11, B) nor an intermodal study of Birch and Lefford (1963) fitted these paradigms. Nevertheless, a consideration of them may provide useful clues for understanding intermodal processes. Birch and Lefford, using shapes from the Sequin form board test investigated three intermodal tasks: haptic (active touch)-kinesthetic (passive movement of S’s hand), visual-haptic, and visual-kinesthetic. A stimulus was presented simultaneously in the two modalities and S simply made a same-different judgment. Children ranging in age from 5 to 1 1 years served as Ss. As expected, the number of errors in all three tasks decreased with age.’ Errors of equivalence (calling different shapes the same) and errors of nonequivalence (calling same shapes different) were analyzed separately. In both cases, the haptic-visual transfer task showed fewer errors at all ages than the other two tasks. However, task comparisons cannot be interpreted meaningfully since order and type of task were confounded in the design. Although it was not the primary purpose of the study, the effect of specific shapes is described in a confusion matrix which includes the number of times each shape is confused with every other. There are frequent confusions between such pairs as diamond and hexagon, diamond and square, cross and star, etc. Similarity in number of turns or angles in the shapes seems to be a good predictor of likelihood of confusion. Unfortunately, frequency of confusion for specific pairs is not broken down by ages so it is impossible to tell if some types of errors dropped out faster than others as a function of age. Hermelin and O’Connor included tactual-visual and visual-tactual matching as part of their intramodal-intermodal design. The intermodal matching of the Greek or Russian letters was no better than the intramodal matching. i n fact, as previously noted (Section 11, B) only the tactual-tactual 215

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matching of the imbeciles was significantly better than any other condition. Rudel and Teuber (Section 11, B) used solid forms to study intermodal and intramodal identification with 3- to 6-year-old children. Performance improved with age, and at all ages performance on the intermodal tasks, tactual-visual and visual-tactual was better than the tactual-tactual task but worse than the easy visual-visual task. Changing the task from asuccessive to simultaneous comparison also reduced the difficulty. The series of studies carried out by Zinchenko and his colleagues (Zinchenko & Ruzskaya, 1960a,b; Zinchenko et al., 1962; Lavrent'eva & Ruzs'kaya, 1960) on children 3 to 7 years of age has the distinction of being the only developmental intermodal matching investigation in 'the current literature in which a careful analysis of the perceptual behavior was carried out. Again the general improvement with age was noted. In contrast with Rudel and Teuber's study, the Soviet investigatorsfound intermodal tasks to be more difficult than both the intramodal tasks. Also in contrast with Rudel's study, changing an intermodal task from successive to simultaneous made it more difficult. Zinchenko and his colleagues attributed this increased difficulty to the problem of attending to two aspects of the situation at once. These differences in results are surprisingsince the age range of children covered was nearly the same in Zinchenko's and Rudel's studies. The particular shapes used differed considerably; Zinchenko used amorphous cutout nonsense shapes while Rudel used solid forms. Zinchenko and his colleagues paid a good deal of attention to the hand and eye movements of the children as they explored the stimulus objects. Of most concern was the degree to which the exploratory movements conformed to the stimulus shape. When marked differences of performance appeared between two age groups, a difference in exploratory behavior was usually apparent; hand movements of the better performing children more closely conformed to the contour of the shape. There have been no developmental intermodal matching studies which systematically vary the dimensions of the stimuli to be matched. The letterlike forms constructed by Gibson might be a good starting point for such a study since there is a good deal of developmental data about intramodal discriminability of these forms. However, the stimulus dimensions along which these letter-like forms vary are probably more important for vision than for touch since their construction was based on analysis of printed English letters. It would be desirable to vary stimuli along dimensions meaningful to touch or to vision and touch. A good candidate for such a dimension might be surface texture. The work of J. J. Gibson has emphasized surface texture as an important visual dimension, and recently W. Schiff' has been exploring the possible relevance of surface texture for touch. Personal communication.

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B. INTERMODAL TRANSFER OF TRAINING There is not always a clear conceptual distinction between intermodal matching and intermodal frunsfer of alearneddiscrimination? An intermodal matching task may be in reality a transfer task in which thelearning occurred prior to the immediate experimental situation. Of course it is clear whether or not E teaches a discrimination and tests for transfer, but the operation does not guarantee a meaningful conceptual difference. Nevertheless, an intermodal transfer of training design yields information about the nature of the transferred material. The next experiments to be reviewed all are concerned with what it is that gets transferred. One study (Pick, Pick, & Thomas, 1966) has investigated whether something like prototypes are involved in intermodal transfer as opposed to distinctive features or dimensions of difference between stimuli. The letterlike forms described previously were used again. Six-year-old children were taught to discriminate tactually or visually between standard forms and particular transformations. The Ss were then tested for transfer in the other modality. The stimuli used in the original training and the transfer test were selected so as to be able to infer whether the children had learned the specific standard shapes in the original learning or had become sensitive to dimensions of difference. Results indicated that dimensions of difference are always learned and transferred in the tasks used. In addition, learning of standard shapes occurs and is transferred only under certain conditions of task difficulty. These results are similarto those ofthe study of intramodal improvement in discrimination described previously (Section 11, B). In another type of intermodal transfer task, S is trained to discriminate one signal from two signals. Blank and Bridger (1964) investigated transfer of such a discrimination from audition to vision and vice versa using 3- to 6-year-old children. A successive discrimination procedure was employed with a two-choice discrimination apparatus. On each trial, one or two signals were presented with one or theothermanipulandum being arbitrarily correct. The older children showed significant savings on the transfer task and their ability to verbalize the solution of the problem appeared to be a necessary (but not sufficient) condition for successful performance on the original as well as on the transfer task, Houck, Gardner, and Ruhl (1965) carried out a similar investigation of children’s ability to discriminate one signal from two. These investigators trained the discrimination visually or auditorily and observed transfer to touch. The general procedure was the same as that of Blank and Bridger, but age was eliminated as an independent variable by analyses of covariance. Savings in relearning in the new modality was also found in this study, but 8 For an excellent theoretical analysis of intermodal tasks and related issues see E. J. Gibson, Chapter VIII of Perceptual Learning and Development (in preparation).

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there was more savings for the visually trained Ss than for the auditorily trained Ss. (As the authors point out, this result may be an artifact oftheir procedure in which there was a possibility that the initial visual learning was better than the initial auditory learning.) The third type of intermodal transfer to be considered is transfer of practice effects resulting from repeated exposure to an illusion. The one relevant study is not developmental, but it is described here because the data bear on what it is that gets transferred. Rudel and Teuber (1963) found that the decrement in the Miiller-Lyer illusion which occurs on repeated presentation to adult subjects transferred from vision to touch and vice versa. Since Ss are unaware of the decrement of the illusion, the transfer of this decrement cannot be based upon verbalization. These studies of intermodal transfer of training have indicated that even in young children rather complex discriminations transfer from one modality to another. In some cases verbalization may play a role (Blank & Bridger, 1964), but in others it is not necessary (Rudel & Teuber, 1963). The fact that intermodal transfer may differ depending on the modalities involved (Houck, et al., 1965) and the fact that it does not seem to be an allor-nothing process argues against it being solely a conceptual transfer. Characteristics differing from modality to modality, such as patterns of exploratory behavior and attention, may serve as the basis for the initial discrimination and the subsequent intermodal transfer. The various studies of intermodal transfer unsystematically sample the universe of stimulus dimensions. Important stimulus dimensions such as size, texture, and spatial orientation have been completely neglected in developmental studies of intermodal matching. Studies of intermodal transfer of training typically have been demonstrations that something gets transferred rather than analytic studies of the transfer process. In this respect, Blank and Bridger’s series of studies exploring the role of verbalization is encouraging (Blank & Bridger, 1964, 1967). Sorely needed is a systematic approach to the general process of intermodal transfer and intermodal equivalence. Perhaps Gibson’s (in press) theoretical analysis can serve as a starting point.

V. Conclusions In the preceding pages, the discussion has been organized around the diverse experimental designs or tasks used in the investigation of children’s perceptual integration. The purpose of this synthesis has been to find trends and identify persistent problems. Our discussion made a specific attempt to focus on methodological problems in the study of intermodal integration, to indicate where there were gaps in present knowledge, and 218

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to suggest substantive generalizations or hypotheses. From a methodological point of view, the potential usefulness of intraintermodal experimental designs and sighted-blind comparisons was suggested. Presently available data using the intra-intermodal design are not always consistent from one investigator to another but this is probably due to procedural differences rather than a weakness of the design. The importance of the dependent variable was indicated in a number of contexts. Designs in which perceptual behavior, scanning, attending, etc. is studied directly were advocated, as were designs which included qualitative analysis of discrimination errors. It was further noted that in localization studies the nature of the response should be taken into consideration along with the nature of the stimulus. Viewing localization as an intermodal task emphasizes the importance of the response modality. The most general and severe gap in our present knowledge as was repeatedly observed is the lack of systematic data in practically all areas. Our ignorance about the functioning of different stimulus dimensions is a good example of this deficit. Shape has been the stimulus dimension which has been investigated intermodally most, frequently. On the one hand, shape is a good choice of stimulus dimension since it has some relevance for touch and proprioception as well as for vision. On the other hand, it is a poor choice since there is no generally good metric for shape. Stimulus dimensions vary from being equally relevant in several modalities, e.g., texture for vision and touch, to being specifically relevant to one modality, e.g., color for vision. The relations between sense modalities should be investigated with stimulus dimension relevance being treated as an independent variable. Perceptual-motor coordination which often involves integration of at least proprioception and vision has been rather neglected developmentally. Some types of localization tasks probably represent the simple extreme of perceptual-motor coordination and something is known about these developmentally. However, with the techniques available that are used in the study of tracking, it is surprising attention has not also been turned to the more complex kinds of perceptual-motor coordination. The problem of temporal integration has not been specifically discussed in this chapter. However, the results of a number of studies suggest the possible developmental importance of this variable. These include studies in which differences between simultaneous and successive discriminations occur as well as the study of delayed feedback. In addition, isolated developmental studies of apparent movement and metacontrast appear in the literature, but again there are few systematic data. Aside from areas in which our knowledge is simply lacking, there are questions raised by the results of the experiments themselves. Are the differences in results of intermodal matching tasks due to procedural and 219

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stimulus differences, and if so, what are these critical differences? What type of mechanism would account for the intermodal transfer of shape orientation preferences found in partially sighted Ss but not in sighted Ss, etc. Finally, what kinds of substantitive generalities about intermodal integration are possible? It is safe to say that some forms of intermodal coordination appear quite early. Ability to localize, for example, as manifested in various coordinations between eye, ear, and hand achieves precision at an early age. There is ample evidence that the development of perceptual process in the various sense modalities is not parallel even when the same stimulus discriminations are required. For example, different aspects of shape discrimination develop at different rates in vision and touch. And there is much evidence refuting the classical doctrine that touch teaches vision. This includes evidence of (1) the earlier development of visual discrimination as compared with tactual and (2) the dominance of visual information over tactual in sensory conflict situations. In concluding, a theoretical thread which appeared in several instances and is offered as ageneral hypothesis is that simple and higher order stimulus dimensions relate to different intermodal processes. The integration of simple dimensions reflects modality specific processes while the integration of higher order stimuli reflects more central processes common to the several modalities. REFERENCES Birch, H. G., & Lefford, A. Intersensory development in children. Monogr. SOC.Res. Child Develpm., 1963,28,No. 5 (Whole No. 89). Blank, M., & Bridger, W. H. Cross-modal transfer in nursery school children. J. cornp. physiol. psychol., 1964,58, 277-282. Blank, M., & Bridger, W. H. A comparison of deaf and hearing nursery school children on cross modal transfer. child Develpm., 1967,in press. Brennen, W. M., Ames, Elinor W., & Moore, R. W. Age differences in infants’ attention to patterns of different complexities. Science, 1966, 151,354-356. Chase, R. A., Sutton, S., First, D., & Zubin, J. A. A developmental study of changes in behavior under delayed auditory feedback. J. genet. Psychol., 1961,W. 101-1 12. Dunford, R. E. The genetic development of cutaneous localization. J. genet. Psychol., 1930, 37,499-513. Eichorn. D. H. Biological correlates of behavior. In H. W. Stevenson (Ed.), Child psychology, 62nd year b. wr. SOC. srud. educ. Chicago: Univer. of Chicago Press, 1963. Fantz, R. L. Pattern vision in new born infants. Science, 1963, 140, 296-297. Flavell, J. H.Developmenralpsychology ofJean Piager. Princeton, N. J.: Van Horstrand, 1963. Gaydos, H. F. Intersensory transfer in the discrimination of form, Amer. J. Psychol., 1956, 69. 107-110.

Gesell, A. E., Thompson, H. lnfunt behavior. New York: McGraw-Hill, 1934. Ghent, L. Recognition by children of realistic figures presented in various orientations. Cunad. J. Psychol., 1960, 14,249-256.

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Perceptual Integration in Children Ghent, L. Form and its orientation: A child’s eye view. Amer. J. Psychol., 1961,74,177-190. Ghent, L., Bernstein, Lily, & Goldweber, A. M. Preference for orientation of form under varying conditions. Percept. mot. Skills, 1960, 11,46. Gibson, E. J. Perceptual learning and development. Unpublished manuscript. Gibson, E. J. Perceptual development. In H. W. Stevenson (Ed.), Child psydology, 62ndyear b. rat. SOC. study. educ. Chicago: Univer. of Chicago Press, 1963. Gibson, E. J., Gibson. J. J., Pick, A. D., & Osser, H. A developmental study of the discrimination of letter-like forms. J. comp. physiol. Psychol., 1962,55, 897-906. (a) Gibson, E. J., Pick, A. D., Osser, H., & Hammond, M. The role of gaphemephoneme correspondence in the perception of words. Amer J. Psychol., 1962, 75, 554470. (b) Gibson, E. J., Osser, H., & Pick, A. D. A study in the development of graphemephoneme correspondences. J. verb. Leurn. verb. Eehav., 1963,2, 142-146. Gibson, J. J., & Gibson, E. J. Percqtual learning: Differentiation or enrichment? Psychol. Rev., 195562, 3241. Graham, F. K., Matarazzo, R. G., & Caldwell, B. M. Behavioral differencesbetween normal and traumatized infants. Psychol. Monogr., 1956,70, No. 427,428. Halverson, H. M. An experimental study of prehension in infants by means of systematic cinema records. Genet. Psychol. Monogr., 1931, 10, 107-286. Hatwell, Y. Perception tactile des formes et organisation spatiale tactile. J. Psychol., 1959,56,187-204.

Hatwell, Y. Etude de quelques illusions geometriques tactiles chez avengles. Annkpsychol., 1960,60, 11-27.

Hay, J., & Pick, H. L., Jr. Visual and proprioceptive adaptation to optical displacement of the visual stimulus. J. exp. Psychol., 1966, 71, 150-158. Hay, J., Pick, H. L., Jr., & Ikeda, K. Visual capture produced by prism spectacles. Psychon. Sci., 1965, 2, 215-216. Held. R..Rr Hein. A. V. Adaptation of disarranged hand-eye coordination contingent upon reafferent stimulation. Percept. mot. Skills, 1958, 8, 87-90. Hermelin, B., & O’Connor, N. Recognition of shape by normal and subnormal children. Brit. J. Psychol., 1961,52,281-284. Hershenson, M. Visual discrimination in the human new born. J. comp. physiol. Psychol., 1964,58,270-276.

Houck, E. V., Gardner, D. B., & Ruhl, D. Effects of auditory and visual pretraining on performance in a tactile discrimination task. Percept. mot. Skills, 1%5,20, 1057-1063. Hunter, I. H. L. Tactile-kinesthetic perception of straightness in blind and sighted humans. Quart. J. exp. Psychol., 1954,6, 14%154. Jackson, C. V. Visual factors in auditory localization. Quart. J. exp. Psychol.. 1953, 5, 52-65. Kelvin, R. P. Discrimination of size by sight and touch. Quart. J. exp. Psychol., 1954.6.23-34. Klein, R. E. A developmental study of perception under conditions of conflicting sensory cues. Unpublished doctoral dissertation, Univer. of Minnesota. 1966. Lavrent’eva, T. A., & Ruzskaya, A. G.Sravnitel’nyi analiz osyazaniyai areniya: Soobschenie V. Odnovremennoe intersensornoe sopostavlenie formy v doshkol’nom vosraste. (Comparative analysis of touch and vision: Communication V. Simultaneousintersensorycomparison of form at a preschool age.) Doki. Akad. Pehg. Nauk RSPSR, 1960,4 (4), 73-76. McKinney, J. P. Hand schema in children. Psychon. Sci., 1964, 1,99400. Montessori, M. The Montessori method. New York: Schocken Books, 1964. Papousek, H. Experimental appetitional behavior in human newborns and infants. In H. W. Stevenson, E. Hess, & H. L. Rheingold (Eds.), Early behavior: Conrparatiw and developmentalapprwches. New York: Wiley, 1967. Piaget, J., & Inhelder, B. The child’s conception ofspace. London: Routledge & Kegan Paul, 1956.

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Pick, A. D. Improvement of visual and tactual form discrimination. J. exp. Psychol., 1965, 69.33 1-339.

Pick, A. D., & Pick, H. L. Jr. A developmental study of tactual discrimination in blind and sighted children and adults. Psychon. Sci, 1966,6,367-368. Pick, A. D., Thomas, M. L., & Pick, H. L., Jr. The role of grapheme-phoneme correspondences in the perception of Braille.J. verb. Learn. verb. Behav., 1966.5,298-300. (a) Pick, A. D., Pick, H. L., Jr., & Thomas, M. L. Cross-modal transfer and improvement in form discrimination. J. exp. Child Psvchol., 1966,3, 279-288. (b) Pick, H. L., Jr. Perception in Soviet psychology. Psychol. Bull., 1964,62,21-35. Pick. H. L., Jr., & Hay, J. C. Visual and proprioceptive adaptation to optical displacement in children. In Perceptual development: Its relation to theories of intelligence and cognition. Bethesda: National Institutes of Health, 1966. Pp. 174-187. Pick, H. L., Jr., & Pick, A. D. A developmental and analytic study of the size-weight illusion. J. exp. Child Psychol., 1967, in press. Pick, H. L., Jr., Klein, R. E., & Pick, A. D. Visual and tactual identification of form orientation. J. exp. Child Psychol., 1966,4, 391-397. Pollack, R. H. Contour detectability threshold as a function of chronologjcal age. Percept. mot. Skills, 1963, 17,411417. Pollack, R. H. Simultaneous and successive presentation of elements of the Miiller-Lyer figure and chronological age. Percept. mot. Skills, 1964, 19, 303-310. Pollack, R. H. Intelligence and perceptual development in childhood. Paper presented at 73rd Ann. Meeting Amer. Psychol. Ass., Chicago, September, 1965. Renshaw, S. The errors of localization and the effect of practice on the localizing movement in children and adults. J. genet. Psychol., 1930, 38, 223-238. Renshaw, S., & Wherry, R. J. Studies on cutaneous localization: 111. The age of onset of ocular dominance. J. genet. Psychol., 1931.39.493496. Renshaw, S., Wherry, R. J., & Newlin, J. C. Cutaneous localization in congenitally blind versus seeing children and adults. J. genet. Psychol., 1930,28,239-248. Robinson, H. B. An experimental examination of the size-weight illusion in young children. Child Develpm., 1964.35.91-107. Rock, I., & Victor, J. Vision and touch: An experimentally created conflict between the two senses. Science, 1964, 143. 594-596. Rudel, R., & Teuber, H.-L. Decrement of visual and haptic Miiller-Lyer illusion on repeated trials: A study of crossmodal transfer. Quart. J. exp. Psychol., 1963, 15, 125-131. Rudel, R., & Teuber, H.-L. Crossmodal transfer of shape discrimination by children. Neuropsychologia, 1964,2, 1-8. Schopler, E. Visual versus tactual receptor preference in normal and schizophrenicchildren. Unpublished doctoral dissertation, Univer. of Chicago, 1964. Smith, K. U., & Greene, P. A critical period in maturation of performance with spacedisplaced vision. Percept. mot. Skills, 1963, 17,627439. Wapner. S., & Werner, H. Perceptual development. Worcester, Mass.: Clark Univer. Press, 1957.

Wapner, S.. & Werner, H. An experimentalapproach to body perception from the organismicdevelopmental point of view. In S.Wapner and H. Werner (Eds.), The body percept. New York: Random House, 1965. Werner, H. Comparative psychology of mental development. New York: Folliet Publishing, 1948.

White, B. L. Paper presented at Amer. Ass. Advance. Sci. Meetings, Cleveland, December, 1963.

White, E. L., Castle, P.. & Held, R. Observations on the development of visually directed reaching. Child Develpm., 1964,35, 34S364.

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Perceptual Integration in Children Witkin, H. A . Individuality in development. In B. Kaplan & S. Wapner (Eds.), Perspecrives in psychological theoty: Essays in honor of Heins Werner. New York: Int. Univer. Press, 1960. Pp. 335-361. Witkin, H. A,, Wapner, S., & Leventhal, T. Sound localization with conflicting visual and auditory cues. J. exp. Psychol., 1952,43, 58-67, Witkin, H. A,, Lewis. H. 8.. Hertzman. M., Machover, K., Maissner, P. B., & Wapner,S. Personality throughperception. New York: Harper & ROW,1954. Witkin, H. A., Dyk, E. B., Paterson, H. F., Goodenough, D. R.,& Karp, S. A. Psychological dgerentiation. New York: Wiley, 1962. Yates, A. J. Delayed auditory feedback. Psvchol. Bull., 1963,60,213-232. Zaporozhets, A. V. The origin and development of the conscious control movements in man. In OConnor (Ed.), Recenr Soviet psychology. New York: Liveright, 1961. Zinchenko. V. P. Nekotorya osobennosti orientirovochnykh dvizhenii ruki i glaza i ikh rol’ v formirovanii dvigatal’nykh navykov. (Some properties of orienting movements of the hands and eyes and their role in the formation of motor habits.) (Authorized summary of candidate’s doctoral dissertation.) Moscow: Institute of Psychology, 1957. Zinchenko. V. P. & Ruzskaya, A. G. Sravnitel’njli snaliz osyazaniya i zreniya: Soobschenie Ill. Zritel’no-gapticheskii perenos v doshkol’nom vozraste. (Comparative analysis of touch and vision: Communication 111. Visual-haptic transfer in preschool ages.) Dokl. Akad. Pedap. Nauk RSFSR, I%O. 4 (3), 95-98. (a) Zinchenko, V. P., & Ruzskaya. A. G. Sravnitel’nyi analiz osyazaniya i zreniya: Soobschenie VII, Nalichnjle urovenii vospriyatiya formjl u detei doshkonogo voqasta. (Comparative analysis of touch and vision: Communication VII. The observable level of perception of form in children of preschool age.) Dokl. Akad. Pedag. Nauk RSFSR, 1960, 4 (6). 85-88. (b) Zinchenko, V. P., Lomov, B. F., & Ruzskaya, A. G . Sravnitel’njli analiz osyazaniya i areniya: Soobschenie 1. 0 Tak nazivaem “simultanoe” vospriyatie. (Comparative analysis of touch and vision: Communication I. On so-called simultaneous perception.) Dokl. Akad. Pedag. Nauk RSFSR, 1959.3 (5). 71-74. Zinchenko, V. P., Chzhi-Tsin, V., & Tarakanov, V. V. Stanovlenie i razvitie pertseptivnjlkh deisfvii. (Formation and development of perceptive behavior.) Vop. Psikhol., 1962, 8 (3). 1-14.

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COMPONENT PROCESS LATENCIES IN REACTION TIMES OF CHILDREN AND ADULTS'

Raymond H . Hohle INSTITUTE OF CHILD BEHAVIOR AND DEVELOPMENT UNIVERSITY OF IOWA

I. METHODS AND INTERPRETATIONS IN STUDIES OF REACTION TIME A. STUDIES OF CHILDREN'S RT . . . . . . . . . . . . . . . . . . . . . B. PROCEDURES FOR IDENTIFYING COMPONENT PROCESSES . . . 11. A PROPOSED DISTRIBUTION FUNCTION FOR RTs . . . . . . . . . . . A. PROCEDURES FOR ESTIMATING COMPONENT PARAMETERS . . R . GOODNESS O F FIT TESTS . . . . . . . . . . . . . . . . . . . . . . . 111. STUDIES OF THE DISTRIBUTION PARAMETERS . . . . . . . . . . . . A. EFFECTS O F FOREPERIOD DURATION . . . . . . . . . . . . . . . B. NUMBER O F STIMULUS AND RESPONSE ALTERNATIVES . . . . . C. STIMULUS INTENSITY AND STIMULUS SEQUENCE . . . . . . . . . D. EFFECTS OF INTENSITY AND REPONSE MODE . . . . . . . . . . IV. SUMMARY AND CONCLUDING REMARKS .............. REFERENCES ...............................

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I. Methods and Interpretations in Studies of Reaction Time Studies of reaction latencies antedate, by more than half a century, the beginnings of experimental psychology. The well-known account of an I Data analyses reported in this paper were carried out using the facilities of the University of Iowa Computer Center. Funds for this purpose wsere provided by a grant from the Graduate College of the University of Iowa.

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astronomer’s dismissal of his assistant in 1796 because the latter persisted in recording observations of stellar transit times systematically different from his own stimulated considerable applied research on response latencies among astronomers. These studies were concerned primarily with determining constant latency differences between individual observers, but they also revealed the presence of substantial intra-individual variability. With the development of more objective methods of observation in astronomy in the second half of the nineteenth century, interest in reaction time (RT) shifted from matters of immediate practical concern to speculation and research on the psychological and physiological processes determining the magnitude and variability of reaction latencies. In keeping with this historical precedence of RT studies in experimental psychology, studies of children’s RT were undertaken considerably before an experimental approach was generally adopted in child psychology. A. STUDIES OF CHILDREN’SRT 1. Empirical Results One of the earliest and most extensive studies of RT of children was reported by J. A. Gilbert in 1894. Reaction times were obtained from twelve age groups from 6 to 17 years, with each group containing approximately 100 children. Each S was given 10 trials under each of two conditions: simple RT (key press at the appearance of a disc on the apparatus), and discrimination RT (key press only when a blue disc appeared in a sequence of blue and red discs). Median RTs were determined for both conditions comparing boys and girls and comparing groups, containing both sexes, classified into three levels of “general mental ability” by their teachers. Both simple and discrimination RT were found to decrease steadily with increasing age over the age range studied, with improvement in discrimination RT proceeding more rapidly. Reaction times of boys under both conditions tended to be slightly faster than those of girls at all ages, and children judged “dull” by their teachers showed slightly longer RTs than those judged “bright” or “average.” The average sex differences and differences associated with apparent intellectual levels were very small (on the order of 10-20 msec) and, in a single study such as Gilbert’s, could probably be attributed to sampling error; but differences of similar magnitudes have been obtained by a number of subsequent investigators. Comparable sex differences in simple RT to both visual and auditory stimuli, for example, have been reported by Bellis (1932-1933), Philip (1934), and by Goodenough (1935). And these studies, similar to Gilbert’s, indicated that the differences did not depend on age. Bellis, in fact, found a fairly constant difference in RT between males and females at all ages from kindergarten to 60 years old.

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On the other hand, Jones (1937) obtained data indicating the relatively slower RT of girls tended to disappear in late adolescence. He attributed this result to a procedure in his study whereby S was apprised of his performance after each trial and was urged to respond more quickly on successive trials. This procedure was interpreted as having an equalizing effect on the motivation of the older Ss, and accordingly, Jones suggested that “the superiority of boys in reaction time is a superficial difference depending primarily upon interest and upon a competitive urge in motor skills” (p. 193). Individual studies of the relation of RT to scores on various intelligence tests among relatively homogeneous groups have typically obtained very low, often statistically nonsignificant, negative correlations, i.e., higher test scores tend to be associated with faster RT(Lemmon, 1927; Philip, 1934; Goodenough, 1935). When statistically significant correlations have been found, they have tended either to be of such low magnitude as to provide essentially no basis for individual predictions of intellectual functions from RT (e.g., Lemmon, 1927),or have been obtained by comparing performance of highly diverse groups ofSs (Peak & Boring, 1926;Scott, 1940; Baumeister, Hawkins, and Kellas, 1965a, b). As an example of the latter type of study, Scott (1940) found that children with Stanford-Binet IQ scores from 120-200 showed significantly faster RTs than did children with scores in the range 63-94. But as Goodenough (1935) observed earlier, “one does not need a test to tell the genius from the idiot.. .” (p. 445). A marked decrease in RT with increasing age of children, as found by Gilbert (1894) has also been widely replicated (Miles, 1931; Luria, 1932; Bellis, 1932-1933; Philip, 1934: Goodenough, 1935; Jones, 1937).While this is intuitively not a very surprising result, a specific explication of the large average decreases in RT from, say, kindergarten age to late adolescence (on the order of 300 msec or more) is not easily formulated. That the improvement is not simply a matter of improved motor coordination is suggested by studies demonstrating variws motor skills and various somatic movement speeds to be essentially uncorrelated with RT within homogenous age groups (Slater-Hammel, 1952; Henry, 1952). Nor, apparently, can the improvement be attributed to differences in motivation between younger and older Ss: special motivating conditions lead to lower RTs by both children (Jones, 1937) and adults (Church & Camp, 1965), suggesting that in typical RT experiments, Ss of all ages tend not to respond at the limits of their capacities; but there is no evidence that any age group tends to approach this limit more closely than any other. In a direct comparison of adults and children with respect to effects of motivating conditions, Elliot (1964) obtained RTs from kindergarten and young adult Ss with and without monetary incentive payments for fast responses, and found that the incentive condition resulted in decreases in RT of about the same magnitude among adults as among children (about 10-15 msec).

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2. Strategy for Studying Development of the Reactive Process As part of a general schema purportedly describing the “neurodynamics” of human behavior, Luria (1932) proposed that the decrease in RT with age is one of a number of consequences of increasing differentiation of the child’s central nervous system. In the young child, neural excitation produced by the reaction stimulus spreads immediately to the child’s motor system, whereupon multiple diffuse somatic responses occur, interfering with the appropriate response designated by the experimenter. Later, a “functional barrier” develops that inhibits transfer of excitations to the motor system until some degree of organization has taken place in other neural centers. The result is controlled activation of the motor system in older children and adults, permitting specific, directed responses. The neurophysiological aspects of Luria’s formulation may be too general to have arly directly testable empirical consequences, but the diffuse behavior he described in children under, say, 7 or 8 years old in an RT experiment is readily observed. The young child appears at times unable to execute a simple response such as a finger movement without a good deal of hesitation and accompanying movements, even though he is apparently attending fully to the task. When he finally makes the designated response, he often does so with considerably more vigor than the task requires. Goodenough (1935) described similar behavior in her younger Ss, instructed to press a key upon onset of a buzzing sound: “often.. ., the increased tension of the muscles, not only of the arm and hand but of the entire body, is so great as to be plainly discernible to the experimenter. The child’s body stiffens, his eyes are fixed on the apparatus, the breath may be held for an instant and expelled in a sigh of relief when finally the reaction is accomplished. Accessory movements of the resting hand and even of the feet and legs are common” (p. 441). Thus there clearly are developmental changes, both quantitative and qualitative, in children’s RT. And these changes require some sort of explanation. A direct approach to such explanation, however4hat of postulating mechanisms to account directly for the developmental changesdoes not seem to be the most fruitful way to proceed. More enlightening perhaps, would be to explore a variety of laws relating RT to different stimulus and subject variables within age groups, whence it should be possible to account for the developmental laws in terms of some schema designed to accommodate these more “basic” relationships (cf. Spiker, 1965). The purpose of the present paper is to describe an approach of the latter sort. More specifically, concern here is with attempts to identify different components of the reactive process and determine latencies of these components under various experimental conditions. Such attempts might be classified into three types: (1) variation of the task of S such that different

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numbers of hypothetical component processes are involved, then comparing RTs under the different task conditions; (2) direct measurement of portions of total RTs: and (3) inferring components from statistical distributions of RTs.

B. PROCEDURES FOR IDENTIFYING COMPONENT PROCESSES 1. The Subtractive Procedure The earliest major effort to identify components of RT was by Donders (1868), who sought to obtain separate measures of reaction, discrimination, and choice times. The time for reaction was taken to be the average latency of a particular response to repeated presentations of a single stimulus, i.e.. simple RT. Discrimination time was then obtained by determining the difference between simple RT and the latency of a particular response to a particular stimulus presented in a sequence of different stimuli. Finally, “choice” time was derived by subtracting mean discrimination RT from observed response latencies under conditions of different responses prescribed for different stimuli. Wundt (e.g., 1874) accepted Donders’ assumption of additivity of components in the different types of RT and proposed an analysis of simple RT into five successive processes: sensory impulse, perception, apperception (attending to the perceived impression), will (the decision to respond), and motor impulse. There have been criticisms of the additivity assumption in general and the subtractive procedure of Donders in particular, notably by Kulpe (1895) and, later, by gestalt psychologists: these critics claimed that changes in the experimental task result in altered predispositions of the observer and thus affect the entire reactive process, not just individual parts of it. Nevertheless, as the discussions below will indicate, a considerable number of recent investigators have studied RTs as sums of independent (or nearly independent) component latencies, and some evidence has been compiled indicating that this is not an unreasonable assumption. Donders’ method of measuring the components by subtracting one type of RT from another has not yielded consistent results, and has not been widely accepted (however, see Taylor, 1966, and the discussion below under section 1. B. 3). Wundt (1874) very early pointed out that the recommended procedure for “discrimination” RT actually involved “choice” also. When a sequence of different stimuli are presented with a response prescribed for only one, each trial presents S with a choice or decision to respond or not to respond. A similar argument would seem to apply t o simple RT, for here too. a decision to respond must occur, but Wundt did not pursue this line of thinking. Instead, he proposed that discrimination time might be measured

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by subtracting simple RT from the response latency in a situation where a single response is prescribed for any of several stimuli presented in a random sequence. Other writers argued (e.g., Berger, 1886), and research verified (e.g., Cattell, 1886), that Wundt’s “discrimination” RT does not differ very much from simple RT, since the response does not actually depend on stimulus identification: the motor response can be initiated immediately upon reception of whatever stimulus is presented on a given trial. This generalization apparently does not apply if more than one sense modality is involved, however. Mathur (1966) found that mean RT to a light or to a tone presented repeatedly by itself was substantially faster than when the same response was prescribed for either the light or tone presented in a random sequence. The main problem associated with the subtractive procedure thus seems to be that it is difficult to devise experimental manipulations that introduce particular psychological processes unambiguously into the RT task.

2 . Direct Measurements of RT Components Various writers have proposed hypothetical schematic outlines of the sequence of events occurring in the stimulus-response interval in RT experiments. An analysis by Wundt was mentioned in the last section: a more recent proposal (Rosenblith & Vidale, 1962) includes the sequence: Stimulus-Afferent e v e n t e e n t r a l sensory e v e n t d e n t r a l decision eventsCentral motor events-Efferent events-Motor response. This sequence was intended to be a description of choice RT, but it seems to apply as well to less elaborate stimulus-response situations, including simple RT. Latencies of the central events in the more simple situations would, of course, be expected to be relatively short. Rosenblith and Vidale did not propose that the various events necessarily occur as discrete units, non-overlapping in time, but rather, that the outline provides a means of identifying those component latencies that are directly measurable and those that are not. Latencies of events produced by more peripheral mechanisms often can be assessed directly, while the proposed central events are constructs, postulated to account for residual latencies remaining when those of the peripheral events are subtracted from total RT. Probably the most unambiguously measured portion of RT has been the final motor response. This is achieved by recording initial action potentials from the muscles used in producing the response, and measuring the time from this event to completion of the effector response. If the response is a finger movement operating a delicate switch and muscle action potentials are recorded from the forearm, the average latency of the motor response is typically found to be about 40-60 msec. Bartlett (1963) obtained measurements of a sub-portion of motor time by recording times from initial application of force on a response switch to actual closure of the switch. This part 230

Component Process L ctencies in Reaction Times

of the response took a n average of about 25 msec, where the mean response time from a muscle action potential in the upper arm to switch closure was about 55 msec. Although stimulus intensity and foreperiod duration (i.e., the interval from a “ready” signal to stimulus onset) have been well established as having substantial effects on total RT, motor response time, defined as the interval from a relevant muscle action potential to an effecLor response, has been shown to be independent of both intensity (Allen & Sashin, 1960; Bartlett, 1963)and foreperiodduration(Weiss, 1965;Botwinick & Thompson, 1966). Latencies of the initial processes on the input side of auditory and visual systems also have been measured fairly accurately. Response times of the receptor organs appear to be very short. Rosenblith and Vidale (1962) report that latencies of responses in the auditory nerve of a cat to an auditory click varied from about 3 msec to 1 msec as stimulusintensity was increased from threshold up to 100 db, and studies recording electroretinograms (electrical changes in the eyeball) in humans (e.g., see Riggs, 1965) show similar latencies for the initial portion (a-wave) of the response to onset of a light. Further along the input channel, evoked potentials in the cortex provide another point at which response latencies can be recorded. These are recorded from humans by placing electrodes on the scalp and averaging electrical changes over repeated presentations of a stimulus. The observed changes using this method are presumably due to combined responses of populations of neural units. Records reported by Dustman and Beck (1966) indicate that the mean latency of an initial evoked potential taken from the occipital scalp, with a light flash of relatively low intensity (2.2millilamberts) as stimulus, was about 50 msec. This latency did not differ among Ss of age 6 to 60 years old, even though the form of the response changed markedly with age. That evoked potential latencies decrease to some extent with increasing stimulus intensity is suggested by findings of Rosenblith and Vidale (1962) that mean latencies of the cortical response to an auditory stimulus in a cat decreased from about 20 to 15 msec with an intensity increase of 100 db. In examining (occipital) cortical responses to sudden movement of a spot of light, Barlow (1964) found average latencies of 80-90 msec. The increased latencies under these conditions, compared to responses to onset of a light, suggests that evoked potentials in the cortex, as they have been measured, represent something more than simple arrival time of neural impulses from the receptors. A relatively simple psychophysical procedure was devised by May (1964) to measure “perceptual latency” as a function of stimulus intensity. Two clicks, separated by 1 second, were presented with a 10-msec light flash occurring at some point within this interval. The Ss were instructed to adjust the time of occurrence of the light flash to coincide with the apparent midpoint of the interval between clicks. Average settings of the stimulus onset

23 1

Raymond H.Hohle

by each of two Ss substantially preceded the actual midpoint of the interval even for the brightest flash (53,763 trolands), and as the intensity was reduced, the settings were moved increasingly towards the first click, until at 1.7 trolands the settings averaged about 55 msec earlier than for the highest intensity. The latencies measured by this method (which were not absolute times from stimulus onset, but were relative to the response to the highest intensity) were presumably times of events up to and including the “central sensory events’’ in the schema offered by Rosenblith and Vidale (1962). May’s results thus suggest that variation in RT as a function of stimulus intensity are due substantially, but not entirely, to effects on Ss sensory system, since the extreme intensities used in his study would probably produce a difference in RT of at least 100 msec (see, e.g., Woodworth & Schlosberg, 1954). It appears from the discussion above that a fairly large portion of simple RT can be accounted for by directly measurable physiological processes. consider, for example, a situation in which a simple response such as a finger movement is made to onset of a light. Mean RT of an appropriately motivated adult under such conditions would probably be in the neighborhood of 180 msec. It might now be estimated that the time to the first evoked potential in the cortex and the latency of the peripheral motor response would be roughly 50 msec each, and if we allow about 20 or 30 msec for efferent nerve conduction (Woodbury & Patton, 1960), not much time (50-60 msec) is left for intervening, central, events. But this argument holds only for optimal conditions where minimum RT is expected. If, instead of a single repeated stimulus, an ensemble of stimuli is introduced, and alternative responses are required to the different stimuli-r if S is 7 years oldthe total RT will be increased by as much as 2W300 msec or more. In view of available evidence, it is not reasonable to suppose that such marked effects are on the peripheral events; hence it appears that relationships of most empirical variables to RT are due to relations of these variables to the “central sensory, decision, and motor events” referred to by Rosenblith and Vidale (1962). Thus the processes underlying RT that are of greatest interest are also the least accessible for observation. The most common approach to studying these processes has been to determine average RT as a function of some other variable, then interpret the obtained relationship in terms of various hypothesized mechanisms. In recent years, however, there has been increasing emphasis on exploring effects of experimental variables on characteristics of RT distributions other than the mean and median.

3. Inferences from Statistical Distributions of RT This approach has been aptly described by McGill(1963), who regarded RT as an interval with boundaries marked off by an initiating stimulus event 232

Component Process Latencies in Reaction Times

and a terminating motor response: “These boundaries are said to straddle a statistical mechanism that grinds away during the silent interval. With repeated activity, the mechanism builds up its characteristic probability distribution, and, ideally, we hope that the shape of the distribution will be a kind of signature that will help us to identify the underlying process” (p. 31 I). A basic assumption in using this approach in the present paper is that an observed RT can reasonably be considered to be a sum of independent component latencies, each of which can be represented as a random variable with a characteristic distribution. Use of the term “random variable” here is intended to include the possibility of latencies with near-zero variance, i.e., “variables” that, for practical purposes, are constants. The assumption is not that the latencies of all conceivable component processes are independent, but rather, that there are statistically independent segments of total RTs which, in turn, may be sums of correlated sub-component latencies. In the discussion to follow it will be assumed that the same processes are operating on each trial of a given RT experiment, provided all experimental conditions are held constant, even though McCormack and Wright (1964) have suggested that this is not always the case. Recording muscle action potentials along with response latencies of a button-press at onset of a light, these investigators noted that on occasional trials a diminished muscle action potential (without an overt finger response) would occur just following onset of the light, and on such trials RTs tended to be abnormally long. From these data, the authors proposed that the positive skew typically observed in RT distributions may be due to similar incipient, interfering muscle responses occurring on some trials but not others. Activation of the response button used in McCormack and Wright’s study required excessive effort, however, and the RTs on trials showing the preliminary muscle action potentials were not at all typical: most of them were over 400 msec. It is quite possible. therefore, that, had the switch been less heavily loaded, the diminished muscle action potentials would have led to completed responses and would have been recorded as very short RTs. The authors acknowledged this possibility but argued that since the distribution of a set of faster RTs obtained subsequently with a lighter switch was also positively skewed, the same type of occasional double muscle action potentials (which could not be recorded) must have been present under these conditions also. Evidence supporting the additivity assumption is provided from a study by Taylor (1966) involving a modern version of Donders (1868) subtractive procedure. Four different experimental arrangements were devised purportedly requiring of S either both stimulus discrimination and response choice, choice only, discrimination only, or neither choice nor discrimination. The procedure involved presentation of a tone of variable duration,

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terminating Mith onset of either a red or a green light. The tour conditions Mere b: presentation of the red and the green light in an irregular sequence, requiring a different response for each (discrimination and choice); b’ : one color on half the trials, nothing on the other half, with a different response to each possibility (choice only); c: the two colors in a random sequence, with a response to one color only (discrimination only); and C: one color on half the trials, nothing on the other half, with a response to color only (neither discrimination nor choice). Taylor hypothesized that the latencies for discrimination and choice could be treated as random variables distributed independently of each other and of the remaining portion of the RTs. To test this hypothesis he made use of the well-known theorem from mathematical statistics that the mean, variance, and third central moment of a sum of independently distributed random variables are equal to the sums of the means, variances, and third central moments of the component variables. The first three moments of the hypothetical latency distributions for discrimination, choice, and discrimination plus choice could thereby be estimated by subtracting the obtained moments under condition C (neither discrimination nor choice) from the corresponding values obtained with conditions c, b’ and b, respectively. Then, according to the hypothesis, the relations (c - d) + (b’ - d ) = (b - C) should hold for all three moments except for sampling error. The results indicated that none of the three derived values, (c - c‘)+ (b’ - c), differed significantly from the corresponding obtained value for (b - c‘), though in each case the derived quantity was larger than that obtained directly. These data thus not only are consistent with the assumption of additivity of components of RT, but also suggest that the classical subtractive procedure proposed nearly a hundred years ago might yet have some utility. So far, nothing has been said about the actual form of the distributions either of total RTs or their components. Empirical distributions of total RT (and possibly those of some of the peripherally produced latencies) can be obtained experimentally, of course. The problem to be considered here is that of trying to specify reasonable hypothetical component distributions with properties such that they can be shown to combine to yield typically observed distributions. One distribution function that has been proposed to describe at least one component latency of RT is the exponential, or “waiting time” distribution. Christie and Luce (1956), for example, proposed that choice RTs might be considered sums of exponentially distributed “decision” times plus residual “base” times having an unspecified distribution; and McGill(l963) presented data showing that the upper portions of observed simple RT distributions are indeed shaped like exponential distributions. In contrast to the interpretation of Chiistie and Luce, however, McGill noted that the 234

Component Process Latencies in Reaction Times

shapes of the exponential-like portions of the RT distributions did not differ as a function of stimulus intensity, and on this basis concluded that the exponential component of RT must be the latency ofthe motor response. The possibility that RTs contain an exponential component is of special interest because, first, it would probably reflect the operation of a single process: there are no easily described variables with distributions such that their sum would have the exponential distribution; and second, a variable having this distribution is necessarily generated by a process with a particular property: let the variable consist of time from to until occurrence of a particular event, and suppose that time t has elapsed following towithout the event occurring; then the probability of the event occurring in the next instant is constant, independent o f t (see, e.g., Feller, 1957). While it is possible to make some inferences about the parameters of component distributions without knowing the precise form of distributions of total RTs (McGill, 1963; McGill & Gibbon, 1965; Taylor, 1965),this task clearly will be facilitated if the form of total RT distributions can be specified. One distribution function that has been found to fit a number ofobserved distributions of simple RT quite well is a convolution of the exponential and normal distribution functions (Hohle, 1965a). The present paper, in the sections below, will explore further the extent to which this function fits different types of RT distributions, and will examine relations of the parameters of the component distributions to several experimental variables.

11. A Proposed Distribution Function for RTs It can be shown that the sum of a large number of component random variables, regardless of the distributions of these components, tends to have a normal distribution unless the variance of one of the component variables is substantially larger than any of the others (Cramer, 1946). If one of the component variables does contribute disproportionately to the variance of the sum, then the distribution of the sum will exhibit some of the characteristics of the distribution of this dominant component variable. This immediately suggests a function for describing RT distributions. If it is assumed that RTs are sums of a number of component variables, a first guess might be that their distribution is normal; but since empirical distributions show some of the characteristics of both normal and exponential distributions, a better guess might be that an observed RT is the sum of a number of component variables with similar variances, plus an exponentially distributed variable with a greater variance than any of the others, If this is a good guess, then observed RT distributions should have the form described by a function representing the sum of an exponentially distributed

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variable plus a normally distributed variable. The probability density function describing such a sum, assuming the component variables are statistically independent, is as follows:

where the parameter a is the mean or expected value of the exponentially distributed component, p is the mean of the normally distributed component, and y is the standard deviation of the normal component. Equation ( I ) is actually an approximation, since its derivation involved restricting both the exponential and normal components to positive values. even though any real value should be permissible for a normally distributed variable. As the ratio of p t o y exceeds, say 3.0, however, as it nearly always does when applied to RT distributions, Eq. (1) rapidly approaches the exact density function. Two empirical questions might now be asked: (1) does the derived distribution function provide an adequate description of observed RT distributions, and (2) do the parameters representing aspects of the component distributions relate meaningfully and differentially to different experimental variables. Attempts to answer either question will require first a method of estimating the distribution parameters. A. PROCEDURES FOR ESTIMATINGCOMPONENT PARAMETERS

In a previous study (Hohle, 1965a), parameters of the distribution function under consideration here were estimated by programming a computer to carry out a systematic search for parameter values that minimized a chi square goodness of fit statistic for several observed RT distributions, A simpler method, the method of moments (e.g., see Deutsch, 1965) will be used for comparable analyses in the present paper. The method of moments consists of determining the parameters as functions of some of the moments of the theoretical distribution, then taking as parameter estimates, the corresponding functions of sample estimators of these moments. To apply this method for estimating the parameters a , p , and y in Eq. (I), consider first the theorem, mentioned earlier, that the mean, variance, and third central moment ofthe sum oftno or more independent random variables are equal to the sums of the means, variances, and third central moments, respectively of the component

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Component Process Latencies in Reaction Times

variables. Noting, then, that the mean, variance, and third central moment of the exponential component distribution are a,a,,and 2a3, and the corresponding moments of the normal component distribution arep, y2, and0, the population mean (p,), variance (p,), and third central moment (us)of the variable representing the sum of the two components (i.e., total RT) may be expressed pCI=a+P pUr= a2 y2 p3 = 2a3 0.

+

and + These equations can be solved directly to obtain the parameters as functions of the first three population moments. Substituting moment estimators s,, s, and s, for p , , p2, and p,, and substituting English letters a, b, and c for a,p , and y to denote sample estimates, the required set of parameter estimates are found to be

c = ds2- az,

and

where s,, s,, and s, are computed from a sample of n RTs as follows: Si =

--1 "

RT,,

i= I

and The quantities s2 and s, are slightly different from the second and third sample moments because the latter are biased estimators of ii., and II.,: i.e.. their means or expected values are not equal to the corresponding population moments. To obtain unbiased estimators, the second sample moment has been multiplied by n/(n- l), and the third by n2/(n- l)(n-2), where n is the sample size. It should be noted that the method of moments does not yield parameter estimators that maximize the correspondence between an observed distribution of RTs and the theoretical distribution function under consideration. The assumption could have been that a total RT is a sum of an exponentially distributed variable plus any variable with a distribution such that its third central moment is zero (which is true of any symmetrical distribution), and the parameter estimates would be exactly the same: a would still be an

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estimate of the mean of the exponentially distributed component, and b and c would be estimates of the mean and standard deviation of the remaining variable. The assumption that RTs contain a component that is normally distributed will nevertheless be retained, even though the method of moments will be used for all data analyses. Data provided in the next section appear to be consistent with this assumption.

B. GOODNESS OF FIT TESTS In assessing the degree of correspondence between observed RT distributions and the probability density function in Eq. (l), a total of 240 distributions with either 96 or 100 RTs in each, were examined. One hundred fifty six of the distributions were of simple RTs to auditory stimuli of various intensities presented under various conditions, and 84 were sets of choice RTs obtained with various numbers of stimulus-response alternatives. Further details of these studies will be described in section 111. For each set of data, the three parameters were estimated using Eqs. (2). Before the theoretical function can be expected to fit a particular observed distribution of RTs, all observations in the distributions must be from the same population. This means each set of data must be obtained under constant conditions and, of course, observations from different Ss cannot be mixed. Despite efforts to keep conditions constant, however, Ss (particularly child Ss) are occasionally distracted by external events, with resultant abnormally long RTs, or begin responding just prior to onset of the reaction stimulus, and unrealistically short RTs are recorded. Even a single such stray observation, especially an extra long one, produces a serious bias in estimation of the third moment. In an effort to minimize the resilltine hias in the parameter estimates. a svstematic procedure was adopted whereby unusually short or long RTs (relative to the rest of the observations in the set) were discarded. If application of Eqs. (2) resulted in a negative value for the parameter a, the lowest RT of the set was discarded and all three parameter estimates were recomputed; and if the initially estimated value of b or c was negative (which would result if the third moment was excessively large relative to the mean or variance), then the highest RT of the set was discarded and the estimation procedure was repeated. Out of 23,664 observations in the 240 sets of data examined, this procedure resulted in rejection of 42 observations as too low and 140 as too high, for a total of .77% of the observations. No more than 7%) of the observations were discarded from any one set of data, and the percentage discarded was this high for only one of the 240 sets. After a final set of parameter estimates was obtained, values of the

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density function (1) and its integral (the cumulative distribution functions) were computed for 19 values of t ranging in a geometric series from b- I .5c to 3.9a (which are approximately the 1st and 98th percentile points of the theoretical distribution). The lower three and upper five of the twenty intervals formed by these points were then combined to make up the lowest and highest intervals, and expected frequencies in the resulting fourteen intervals were determined. Agreement between these expected frequencies and the observed frequencies in the same intervals was assessed for each set of data by means of the Pearson chi square goodness of fit statistic:

where f,. is the observed frequency in the jth interval, and ijis the corresponding expected frequency. The entire parameter estimation and goodness of fit test procedure was programmed to be carried out by an IBM 7044 computer system. Four examples of comparisons of Eq. ( I ) with observed distributions of RTs are presented in Fig. 1. These examples were selected to show the forms of Eq. ( I ) with a wide range of values for the three parameters, and to show varying degrees of goodness of fit. For any given interval on the abscissa of each graph, area under the curve represents the probability that, given the parameters indicated, a sample value o f t will fall in that interval, while the area covered by the histogram over the same interval represents the proportion of RTs that were observed in the interval. The intervals used for constructing the histograms are the same ones on which the goodness of fit statistics were based except that the two extreme intervals on the ends of the histograms were combined into single intervals before the statistics were computed. Unfortunately, the distribution of the goodness of fit statistic (under the hypothesis that the observed and expected frequencies differ only by sampling error) is not known precisely. Clearly, if the parameter values had been given a priori, the goodness of fit could be evaluated in relation to the distribution of a chi square variable with 13 degrees of freedom. At the other extreme, if the parameters had been chosen to minimize the statistic, then the statistic presumably could be compared to a chi square variable with 10 degrees of freedom. It thus appears that the least stringent test of the distribution model would be to reject the model only if obtained values of the goodness of fit statistic are too large to be consistent with the hypothesis that they have a chi square distribution with 13 degrees of freedom.

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Raymond H. Hohle ,0240

-

.OlW

D

,0120

100

no

180

r-

220

280

300

340

(1111

.ax0.o200-

a =5/.75 b-4425V

n.96

c =m.m r'e.72

.om0 .0120 -

I

n

t

= RT (muc)

Fig. 1. Observed distributions of RTs compared to plots of Eq. I(smooth curves), where values of the parameters in Eq. I were chosen such that the theoretimlandobserveddistributionshave the same first three moments. Plots (i)and (ii)are distributions of simple RT to tones of61 and82 db above threshold; (iii)and (iv) are distributions of choice RTs withfour andeight stimulus-response alternatives.

i 10

Goadnear of Fit Statlatic ( X * I

Fig. 2. Distribution of obtained goodness of fit statistics on 240 sets of data compared to the probability densityfunction of a chi square variable with 13 degrees offreedom.

240

Component Process Latencies in Reaction Times

The distribution of the statistic f over the 240 sets of data analyzed here, using the method of moments, is indicated in Fig. 2. The obtained distribution appears to be very nearly that of a chi square variable with 13 degrees of freedom, although a few too many large values of x2are indicated. The mean and variance of the obtained values were 13.33 and 35.05, which may be compared to a mean of 13 and variance of 26 for the chi square distribution with 13 degrees of freedom. The obtained variance of 35.05 is slightly too large to be attributable to sampling error. The occasional large values of the statistic may have been due to two conditions under which the observations were obtained in two studies from which 124 of the 240 sets of data were taken. In these two studies S was in a room isolated from E, which may have been conducive to occasional lapses in attentiveness of S, with a result that a few atypical distributions of RTs were obtained; and a relatively short, constant foreperiod (or intertrial interval) was used throughout, permitting S to respond, in some cases, to the time interval rather than the intended stimulus. In the two studies in which these two conditions prevailed, the means of the statistics were 12.81 and 14.85, and the obtained variances were 41.37 and 49.56, compared to means of 12.07 and 13.11 and variances of 20.13 and 19.46 in two other studies in which neither condition was present. That the statistic is sensitive to minor departures from the theoretical distribution is indicated by the results of an abortive study carried out recently in which 36 sets of simple RTs with 100 observations in each were obtained from six Ss under various experimental conditions. After the data had been collected, it was discovered that a part of the apparatus for producing pulses to start and stop the chronoscope was improperly grounded so that the chronoscope pulse was superimposed .on a stray 60-cps line voltage. The effect on the data, which was detectable only after plotting a distribution of all 3600 observations, was a slight but noticeable clustering of the recorded RTs at multiples of 16 tmsec (the period of a 60-cycle wave). The mean and variance of the goodness of fit statistic for these 36 sets of data were 21.84 and 174.37, compared to values of 12.81 and 41.37 subsequently obtained for 64 sets of data in an expanded version of the same experiment with similar Ss (see below, Section 111, C). It thus appears that if one does not adopt an overly strict criterion, it can be said that distributions of RTs, obtained under constant conditions, can be described quite accurately by a distribution function derived from the assumption that each RT is a sum of two component variables with exponential and normal distributions. The second question proposed in the beginning of this section was that of whether the parameters representing aspects of these component variables relate systematically to different experimental variables. Several studies attempting to determine such relationships will be described in the next section. 24 1

Raymond H.Hohle

111. Studies of the Distribution Parameters Before describing specific studies involving experimental manipulations of the distribution parameters, it will be useful to outline some kind of schema or model against which the data may be examined. Variations in set have often been invoked to account for differences in RT, though the term “set” is usually not very clearly defined. It has been used, generally, to refer to “those vaguely defined organic states, conditions or processes which are antecedent to some overt reaction-pattern and which run along with, and so exercise a selective and determining influence upon, that reaction” (Freeman, 1939, p. 30). Titchener (1910) distinguished, on the basis of introspection, between sensory and motor or muscular sets, and observed that if S was instructed in RT experiments to adopt a sensory set, his RTs would be substantially longer than if a motor set was emphasized. Both Titchener and, later, Woodworth and Schlosberg (1954), suggest that Ss usually adopt some kind of balance between sensory and motor preparatory sets. Woodworth and Schlosberg argue, however, that experimental conditions tend to determine which type of set receives greater emphasis regardless of instructions to S. If the stimulus is such that extra effort is required to detect it, for example, the set will be primarily sensory; whereas if a distinct stimulus is presented, with emphasis on fast RTs, a motor set will probably predominate. Implicit in both the Titchener and Woodworth and Schlosberg discussions is the notion that an emphasis on one type of set must be accompanied by a relative de-emphasis on the other. Davis (1940) proposed that set can be operationally specified in terms of patterns of incipient muscular and glandular activity. Supporting this proposal, Davis found that muscle tension changes in the forearm, measured electromyographically, were related to RT performance in ways similar to effects usually attributed to set: Tension was higher and RT shorter under conditions of a constant foreperiod compared to an irregular sequence of foreperiods, and, when the sequence of foreperiods was irregular, tension was highest and RTs shortest on trials where the foreperiod was near the average of the series. Presumably, the muscle tension measure is an indicant of motor set, and, accordingly, Davis offered the interpretation that sets with low muscle tension might be classed as sensory. A comparable physiological measure identified with sensory set does not seem to have been proposed. Knott (1939) did find that latencies of alpha rhythm blocking in electroencephalographic recordings were related to experimental conditions purportedly affecting S’s “mental set,” but Knott concluded from these experiments that the variations in blocking latency were peripherally determined. The concept of sensory set has thus been introduced either as an unobservable construct or has been defined in terms of Ss’ introspections. 242

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The notion of sensory set is retained here (as a construct), and the effects on R T that have been attributed to this type of set are interpreted in terms of operations of a hypothetical decision mechanism that discriminates a reaction stimulus from all other ongoing external and internal stimulation. Different versions of such a mechanism have been proposed by Christie and Luce (1956), Stone (1960), LaBerge (1962), Greenbaum (l963), McGill (1963), McGill and Gibbon (1965), and by Stilson (1966). In general, these models represent variations of the basic assumption of Signal Detection Theory (Swets, Tanner, and Birdsall, 1961; Hohle, 1965b). The assumption is that even when the stimulus is not present in adetection or RT experiment, S is faced with a continuous stream of randomly varying input, originating both from extraneous external stimulation and from internal activity of Ss perceptual system; and introduction of a designated signal stimulus simply augments this ongoing “noise” in the system. An S s task then consists of making a statistical decision whether the input he is receiving is only ongoing noise or is noise plus signal input. If the signal is very weak, as in a typical detection experiment,it may be impossibleto detect it with certainty, regardless of its duration. On the other hand, the relatively stronger or more distinct stimuli typically used in RT experiments can be detected and identified with near certainty (provided observation time is sufficient). This “sampling” time required to identify a stimulus with a given degree of certainty will be designated decision latency, or decision time. Decision latency presumably corresponds to the latency of the “central sensory events” in the schema proposed by Rosenblith and Vidale (1962) (see above, Section I, B, 2). In terms of this model, it would be reasonable to suppose that any factor operating to enhance the signal-to-noise ratio of sensory input would decrease decision latency. And probably the most obvious way to bring about an increase in the signal-to-noise ratio would be to increase the intensity or distinctiveness of the signal stimulus. Equally effective, however, would be to decrease the noise level. If we consider adoption of a sensory set by S in the RT situation to be an act of partial suppressionof ongoing activity in his perceptual system, an increase in signal-to-noise ratio, with a consequent reduction in decision latency, would be achieved by adoption of such a set. This is not to say that the model predicts faster total RTs with emphasis on a sensory set: it only predicts shorter latencies for that portion of RTs identifiedas decisiontime. Theassumptionmentioned above that conditions favoring a sensory set tend to be incompatiblewith a strong motor set leads to the empirically verified prediction of slowertotal RTs when a sensory set is emphasized. Another factor assumed here to influence decision latency is S s decision criterion, which reflects the degree of certainty demanded for the decision “stimulus x is present.” If emphasis is on quick identification, S will adopt a low decision criterion, whereby minimal information is required for

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a positive decision. Some accuracy might have to be sacrificed, of course, to achieve reduced decision times in this way. If, on the other hand. emphasis is on highly accurate identification, S must require more information, which takes more observation time. In terms of the model, he must raise his decision criterion. A working hypothesis adopted in analyzing the several studies in the following sections is that decision latency is the exponentially distributed component of RT described in Section 11. The remaining, normally distributed, component is hypothesized to include the latencies of all other processes such as receptor activation and neural conduction time, and latencies of central and peripheral motor processes.

A. EFFECTSOF FOREPERIOD DURATION

The speed of RTs obviously will depend on the readiness or set of S to receive the stimulus and execute the required motor response. The most common method of manipulating this set experimentally has been to vary the duration of the foreperiod or preparatory interval between a “ready” signal and the reaction stimulus. In general, RT is faster when the foreperiod is constant over blocks of trials rather than irregular over trials (e.g., Hohle, 1965a; Botwinick & Thompson, 1966), presumably because, under these conditions, it is possible for S to anticipate the approximate time of stimulus onset and thus be in a state of readiness to perceive and to respond. The often-cited results of Woodrow (1914) indicated that an optimal foreperiod for fastest RTs when the foreperiod is constant, was in the neighborhood of 2 seconds, but more recent findings of Karlin (1959), Botwinick and Brinley (1962), Hohle (1965a), and Botwinick and Thompson (1966) show that mean RT increases monotonically with foreperiod duration from as low as .5 second to 15 seconds. If different foreperiod durations occur in an irregular sequence over trials, RTs appear either to be at a minimum on trials with a foreperiod near the middle of the series (Davis, 1940; Botwinick, Brinley, and Robbin, 1959; Botwinick & Brinley, 1962; Botwinick & Thompson, 1966), or to decrease with longer foreperiods (Hohle, 1965a). Karlin (1959) obtained both monotonic decreasing, and non-monotonic curves relating mean RT to (irregular) foreperiod duration, depending on the range of foreperiods in the series. It has been widely assumed that effects of foreperiod duration on RT are due, in general, to effects on S’s set, and in particular, to effects on S’s peripheral muscular set (Freeman & Kendall, 1940; Davis, 1940: Teichner, 1954). Two recent studies, however (Weiss, 1965; Botwinick & 244

Component Process Latencies in Reaction Times

Thompson, 1966), have demonstrated that the portion of an RT from a muscle action potential in the responding limb, to completion of the motor response is independent of foreperiod duration, whether the foreperiods are presented in an irregular sequence or are constant for extended blocks of trials. The authors of both the latter studies conclude from their data that the locus of set as influenced by foreperiod duration is central rather than peripheral. Such a conclusion would not preclude the possibility that the origin of foreperiod effects are in S’s central motor system, of course. If it is supposed that effects of foreperiod duration on RT are indeed effects on S’s motor system (either central or peripheral), and ifthe schema outlined above is a reasonable one. then it should be predicted that the normally distributed component of RT (parameter b), but not the exponential component (parameter a), will be related to foreperiod duration. A study reported by Hohle (l965a) confirmed these expectations. The data from that study have subsequently been re-analyzed, however, using the method of moments to estimate the distribution parameters, with slightly different and more clear-cut results. The outcomes of the re-analysis will be described here. 1. Method Eight distributions of simple RTs with different foreperiod conditions were obtained from each of four 14-year-old female Ss, where the stimulus was a 62-db (re lo-’(‘ watt/cm2), IOOO-cps tone. Eight sessions of 100 trials (following thirty warm-up trials in each session) were given each S.During the first four sessions, foreperiods of 1.60, 3.20, 4.65, and 6.13 seconds occurred in an irregular (quasi-random) sequence. The same foreperiods were presented in the last four sessions, but within any given session, the foreperiod was constant. The distribution parameter estimates a, b, and c were obtained using Eqs. (2), and the goodness of fit statistic, X2,was computed for each of the 32 distributions of RTs.

2. Results and Discussion The mean and variance of the goodness of fit statistic were 12.08 and 20.13, indicating a reasonably good fit of the theoretical distribution function for describing these data. Analyses of variance indicated that the following effects, shown in Fig. 3, were statistically significant at the .05 level: Foreperiod sequence (random vs. constant) had significant effects on mean RT (F,? = 36.14) and parameter b (F,,*= 26.65); and the sequence X Forepenod interaction was significant for mean RT (F3,(‘= 20.37), u (F3,6 - 5.55), and b (F3,!= 15.01). The two Ss presented a descending series of foreperiods over sessions under the constant foreperiod condition also showed significantly faster RTs over-

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all than the other two Ss who received an ascending series, but this was considered to be due to sampling error because the same difference was found during both the first and last four sessions, even though all fourSs were run under identical conditions (irregular foreperiods) for the first four sessions. The parameter c was not significantly related to any of the experimental conditions. The relations of mean RT to foreperiod under the two presentation conditions are similar to those reported by other investigators. The curves for mean parameter b, however, look even more similar to typical curves reported for mean RT. When the foreperiod was constant over trials, b increased monotonically with foreperiod, whereas, if the foreperiodsappeared in an irregular sequence, this parameter was at a minimum for some intermediate value of foreperiod duration. In keeping with previous interpreta246

Component Process Latencies in Reaction Times

tions of the RT-foreperiod relationships then, it might be supposed that the mean of the inferred normally distributed component of RT(asmeasured by the b-parameter) contains latencies of operations of S’s motor system. The a-parameter, or mean of the inferred exponentially distributed component, was independent of foreperiod under the constant foreperiod condition, but unexpectedly showed a steady decrease with foreperiods presented in an irregular order. One interpretation of this finding is that, \+bile S is unable to anticipate onset of the stimulus under irregular foreperiod conditions, his uncertainty decreases as time passes following the warning signal; and with this increasing expectancy of the stimulus through the foreperiod, S tends to shift toward a sensory set, which, as assumed above, would decrease his decision latency. Consistent with this interpretation is the apparent rise in b with the longer foreperiods. This would be expected if a shift toward a sensory set is assumed to interfere with maintenance of an adequate motor set. Both a and bare highest fortheshortest foreperiod in the irregular sequence, suggesting that neither an adequate sensory nor a motor set is reached early in the foreperiod under these conditions. In view of the assumption that b and care the mean and standard deviation of a normally distributed variable, it is of some interest that c did not vary as a function of the experimental conditions while b did. This is consistent with the requirement that the mean and variance of a normally distributed variable are independent.

B. NUMBEROF STIMULUS AND RESPONSEALTERNATIVES Since the pioneering study of Merkel (1885) it has been well established that choice RT generally increases as the number of alternative stimuli in the set being presented is increased. The relationship usually observed is a linear one between RT and the logarithm of the number of equally probable alternatives. These results typically have been interpreted as an instance of a general linear relationship between RT and the Shannon (Shannon & Weaver, 1949) measure of information or uncertainty in the stimulus ensemble. Support for such an interpretation was reported by Hyman (1953), who found that the relationship holds when stimulus uncertainty is manipulated not only by varying the number of alternatives, but by varying the relative frequencies of the stimuli in the set or the sequential dependencies among the stimuli as well. A number of recent studies have demonstrated that under certain conditions, the RT-stimulusuncertainty relation tends to be greatly reduced, if not altogether eliminated. From these results, several investigators have made the generalization that if the stimuli are highly familiar andor stimulus247

Raymond H . Hohle

response compatibility is high-such as if the task involves identification of numerals (e.g., Brainard, Irby, Fitts, & Alluisi, 1962; Morin & Forrin, 1962) or letters of the alphabet (e.g., Davis, Moray, & Treisman, 1961)then RT is only slightly or not at all influenced by increasing the number of stimuli in the set. Fitts and Switzer (1962) pointed out that stimuli like numerals and letters normally appear in sets of fixed size (i.e., 10 digits and 26 letters), hence it is possible that S tends to adopt a “cognitive set” or “active memory” that includes the entire set, regardless of the size of a subset of items presented in a particular experimental series. It is not clear, therefore, whether stimulus familiarity and stimulus-response compatibility are critical factors in studies demonstrating a reduced correlation between RT and stimulus uncertainty where numerals or letters were used as stimuli. Suggestive evidence that stimulus-response familiarity is not an important determinant of this correlation when numerals are used as stimuli was reported by Morin and Fomn (1965). Series of two, four, or eight numerals were presented to first- and third-grade children for verbal choice RTs, and although the third graders showed considerably shorter RTs, neither group responded more slowly to the numerals appearing in the larger sets. Apparently, either the first-grade children already had sufficient practice in recognizing and responding to numerals to eliminate the usual RT-uncertainty relationship, or stimulus familiarity does not critically affect this relationship. One study, suggesting that strength of the stimulus-response associations does affect the relationship between RT and stimulus uncertainty when stimuli other than numerals or letters are used, was reported by Mowbray and Rhoades (1959). After more than 20,000 trials of practice over several months, differences in Ss’ choice RTs with initially unfamiliar responses (differential button pressing to different lights) with four and two alternatives were negligible. On the other hand, Pollack (1963) presented, for choice RTs, sets of five-letter words, with 2,4,8, 16, 100, or 1000 words in a set, to a group of Ss for 40 minutes a day, 5 days a week, for4 months, and still found that mean RT was clearly dependent on the size of the stimulus set at the end of the 4-month period. An absence of the familiarity effect was indicated by results of a study by Morin, Konick, Troxell, and McPherson (1965), who obtained vocal naming responses to a variety of highly familiar stimuli. Substantial, nearly linear, relationships were found between RT and stimulus uncertainty (log number of alternatives) when the stimuli were pictures of faces of close friends of S, animal pictures, colors, or geometric symbols, but this relationship was almost completely absent when the stimuli were English letters. Morin et al. (1965; see also Morin & Fomn, 1965) hypothesized that the most important difference between naming letters or numerals and naming 248

Component Process Latencies in Reaction Times

such stimuli as faces, geometric figures, etc., is that each of the latter stimuli might have a tendency to elicit a variety of responses, whereas a letter or a numeral is not likely to be strongly associated with anything but its name. The resulting response competition when one of the multiple-class stimuli is presented thus increases the latency of the prescribed response, with this effect multiplied when the stimulus is presented in larger sets of stimuli. In view of the studies described above, one might assume that two factors affecting the relationships of choice RT to size of the set from which the stimuli are drawn are ( I ) the discriminability or distinctiveness of the stimuli, which may be a consequence of familiarity of the stimuli, and (2) the extent to which multiple responses are associated with the stimuli. These factors do not appear at present to be operationally distinguishable, but since they can be described as separate phenomena in terms of the schema proposed in this paper for describing RT data, potentially they can be usefully distinguished empirically. In general, it might be supposed that, as the number of stimuli in a set being presented for choice RTs is increased, S would have to adopt a relatively more stringent decision criterion to avoid response errors, since the larger the set, the more likely it will be that some of the stimuli have similar characteristics. If the choice stimuli are highly distinctive, however, only a small adjustment of S’s decision criterion might be necessary, even when the number of alternatives is large: with sufficient redundancy in the differences among the stimuli, latency of the decision process may be little more than that of simple detection of the presence of the stimulus. If it is assumed that response competition as hypothesized by Morin et al. (l965), affects latencies of processes other than the sensory decision process-perhaps the latencies of “central decision events” of Rosenblith and Vidale (1962)-then it should be predicted that both the parameters representing means of the two inferred components of RT will vary as functions of stimulus uncertainty. The extent of variation of the parameter a (decision latency), of course, should depend on distinctiveness or familiarity of the stimuli, while b should depend on the degree of response competition present, relative to the prescribed responses. While data testing this prediction are not available, some experimental results obtained by Gholson and Hohle, (1966), described below, are not inconsistent with it. 1.

Method

Response latencies were obtained from three Ss in each of two age groups, 1 I and 16 years, responding orally, identifying printed four-letter words from two-, four-, and eight-word sets. The stimulus words were drawn randomly from the Thorndike-Lorge (Thorndike & Lorge, 1944) 2000 most frequently used words, with restrictions that none of the words were 249

Raymond H. Hohle

contractions, and no two words in the total pool of eight words contained the same letter in the same position. To ensure that S was cognizant at all times of the set from which the stimuli were being presented, the relevant list of two, four, or eight words was kept on display between trials. This was achieved by presenting the words in a two-field tachistoscope such that S’s response would turn off the field containing the stimulus word and reactivate the illumination of the second field on which the current word list was displayed. A cycling timer was set so that a new trial began every 8.5 seconds. On each trial, aclick signified to S that a new stimulusword would appear in 1 second. Times from onset of illumination of the stimulus word field to S’s vocalization of the word were recorded in milliseconds, and the recorded times were adjusted to compensate for relay lags in the apparatus. Instructions to the Ss emphasized that responses were to be made as quickly as possible, but that errors were to be kept at a minimum. Within each age group, two words, a different pair for each S, were common to all three lists, and a particular pair of words was common for all six Ss in the four- and eight-word lists. Each S was given 2 days of practice followed by 6 test days. At the beginning of each test session, S was given sixteen warm-up trials on the eight-word list, followed by sixteen trials on each stimulus word in each list, where the order of presentation of the different length lists was counterbalanced between Ss and across test days. There were thus fourteen distributions of RTs obtained from each S, with ninety-six observations in each. 2. Results and Discussion The mean and variance of the goodness of fit statistic over the eighty-four distributions of RT obtained in this study were 13.11 and 19.46. Since presentation of a printed familiar word would not be likely to elicit any responses other than saying the word, response competition was not expected to be a factor in determining RTs in this study. It was therefore expected that list length would influence the estimated parameter a, but not 6. Analyses of variance, with the mean responses to the two words common to all three lists as dependent variable, confirmed this expectation. The main effect of list length was significant (p < .05) for mean RT (F2*8= 9.30!, and for parameter a (F2,8= 9.62), but not for 6 (Fz,8=. 0.52). The obtained mean RT and mean estimated parameter values as functions of list length are shown in Fig. 4. The estimated values for the parameter c (the standard deviation of the inferred normally distributed component) unexpectedly was found to decrease significantly (FZ,* = l l .25) as a function of list length. A possible interpretation of this finding might be that, having adopted a more stringent decision criterion for the larger sets of words, S was less uncertain with 250

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respect to identity of the stimulus following the sensory decision, and hence was less variable in completing the response. A problem with this interpretation is that it suggests b also should have been smaller for the longer lists. There were no statistically significant differences between the I 1- and 16-year-old Ss on any of the measures, although mean RT and the mean values for all three parameters were higher for the 1 1-year-olds.

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c. STIMULUS INTENSITY AND STIMULUS SEQUENCE That RT decreases as a function of stimulus intensity has been known since studies of RT began. Wundt (1887) recommended that in studies of the RT-intensity relationship the individual intensities should be presented 25 1

Raymond H. Hohle

repetitively in blocks of trials because this procedure results in faster RTs than if the various intensities are presented in an irregular sequence. Until recently, Wundt’s “regular” procedure has generally been followed, even though H. M. Johnson (1923) pointed out that stimulus intensity, when it can be anticipated by S,will probably affect his “neuromuscular set” as well as his sensory system; and thus when the regular procedure is used, these two effects are confounded in the observed relation of RT to stimulus intensity. Jar1 (1958) further elaborated Johnson’s hypothesis, and proposed that “with irregular order or presentation, any variations in 0 ’ s adjustment will tend to affect RTs equally for all stimulus values in the series. Any dzrerentialeffects of the stimuli may then be ascribed to sensory or stimulus factors alone. Any change in these differential effects when preknowledge of the stimulus is added, may in turn be ascribed topreparatory or organismic factors” (p. 234). To test this “bi-factor” hypothesis, Jarl presented a series of low-intensity lights (.06, .18, and .85 foot lamberts) to a group of Ss, both in regular and irregular sequences. When the stimuli were presented in an irregular order, mean RT decreased linearly with increasing log intensity, but for the regular order, mean RT to the brightest light was greater than that to the middle intensity. Comparable results were reported by Grice and Hunter (1964) who found that decreases in RTs when the intensity of a tone was increased from 40 to 100 db were significantly greater when the two tones were presented in an irregular sequence than when each was presented repeatedly for extended blocks of trials. The schema proposed in this paper leads directly to the prediction that the exponentially distributed component of RT (i.e., parameter a) should decrease with increasing stimulus intensity. The study by May (l964), described above in Section I, B, 2, however, suggested that variations in RT as a function of intensity of a visual stimulus can be only partially accounted for by intensity effects on “perceptual latency”; therefore, it might be expected that b as well as a will vary’ with stimulus intensity. In view of the hypothesis proposed here that S‘s motor set affects the normally distributed component of RT, and the analyses of Johnson (1923) and Jarl (1958) indicating that a regular presentation procedure permits intensity to influence S s neuromuscular set, it should be expected that the relation of the parameter b to intensity will differ depending on whether the intensities are presented in a regular or an irregular order. And according to this analysis, the parameter a should be affected by the different presentation procedures only to the extent that changes in S’s muscular set produce reciprocal changes in emphasis on a sensory set. Data bearing on these predictions are described here (Hohle and Pederson, 1966).

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1. Method Four distributions of simple RTs with irregular presentation conditions and four with regular conditions were obtained from each of four 16-year-old and four 21-year-old female Ss. The reaction stimuli were intensity levels of 61, 69, 76, and 82 db (re watts/cmg)of a 500-cps tone, presented in a room with an ambient background noise level of about 59 db. The intertrial interval, measured from S’s release of the response button to onset of the next stimulus, was 3 seconds. No “ready” signal was used. Following an initial practice session of 60 trials, each S received two 128-trial sessions on each of 4 days. During one of these daily sessions, the four stimulus intensities were presented in an irregular order; during the other, a single intensity waspresented repeatedly, with the four intensities varied over days. Half the Ss in each age group were given the regular condition first each day, followed by the irregular condition, while the other half got the reverse order; and one S in each of these subgroups received an ascending order of intensities over days for the regular condition, with the other receiving a descending order. Only the last 100 trials of each session were retained for analysis, and the recorded RTs for these trials were adjusted to compensate for relay lags in the apparatus.

2 . Results and Discussion The mean of the goodness of fit statistic for the 64 sets of data was 12.81 and the obtained variance was 41.37. The mean is consistent with the hypothesis that this statistic has a chi square distribution with 13 degrees of freedom, but the variance is slightly too large. The data nevertheless seem sufficiently orderly to warrant evaluation (see Fig. 5). Neither mean RT nor any of the distribution parameter estimates differed significantly (p > .05) for the two age groups, nor did age show any interaction effects with either sequence (regular vs. irregular) or intensity. The main effect of sequence was also nonsignificant for all measures (cf. Wundt, 1887; Grice & Hunter, 1964), but stimulus intensity produced significant (p < .05) variations in mean RT (F3.18 = 38.52), a (F3,18 = 7.51), and b F3,’* = 9.w. The sequence X intensity interaction effect on bwasstatistically significant (F3,,8= 5.72), while this effect was not present for mean RT(F3,,, = 0.47), nor for a (F3,18 = 0.87). This interaction effect on b interpreted as the mean of the normally distributed RT component, is consistent with the notion that intensity, when it is not varied over trials, affects S‘s neuromuscular set (Johnson, 1923; Jarl, 1958),if it is assumed that b contains the mean latency of the motor processes in RT.It is of interest that the sequence Xintensity interaction is significant for b but not mean RT, even though mean RT contains b: this suggests that since mean RT = a + b, variations in b must

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have been accompanied by inverse variations in a, which should be expected in this study if it is assumed that changes in S’s motor set are accompanied by reciprocal changes in a sensory set. Unfortunately, for this interpretation, the requisite interaction effect on a was not statistically significant. As expected, in view of May’s (1964) results (see Section I, B, 2), both b and a decreased monotonically with increasing intensity when the different intensities were presented in an irregular order. Speculation on what processes other than sensory decision latency might be influenced by stimulus irftensity will not be attempted here. As was true in the study of RT as a function of foreperiod duration (111, A), estimates of the distribution parameter c were unaffected by any of the experimental manipulations.

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Component Process Latencies in Reaction Times

D. EFFECTSOF INTENSITY AND RESPONSE MODE In order to check the relations of the parameters to auditory intensity further, and to assess effects of different response modes on the parameters, a set of RTs were obtained using a fairly wide range of intensities (presented in irregular order) in which the prescribed response was either a finger or toe movement. It was expected that, if the parameter a reflects only sensory functioning, it probably would not vary with different modes of response. 1. Method Six female Ss, all 16 years old, were each given two series of 125 RT trials on each of 6 days. For three Ss the response (pressing a button operating a microswitch) was made with a toe during the first series each day, and during the second series the same button press was made with a finger, while the other three Ss got the reverse order. Two seconds following S's response on each trial, a flash of a small red light serving as a warning signal, preceded onset of the next stimulus by 1.5 seconds. The stimuli were intensity levels of 45, 65, 80, 90, and 95 db (re lo-"'watts/cm2)of an 800-cps tone from an audio generator producing a distorted sine wave. The five intensity levels were presented in a quasi-random sequence within each series, with each intensity appearing an equal number of times. All RTs, recorded automatically, were corrected for relay lags in the apparatus, and the last 100 trials of each series during the last 5 days of the experiment were retained for analysis. The final data thus consisted of 100 RTs with a toe response, and 100 with a finger response, to each intensity level for each of the six%.

2. Results and Discussion A mean of 14.85 and variance of 49.46 were obtained for the goodness of fit statistic in this study. Both of these values exceed the limits of sampling error (at the .05 level of significance) for the statistic to be accepted as having a chi square distribution with 13 degrees of freedom. This may have been due to the two conditions mentioned above (Section 11, B) as possibly contributing to poor fit of the theoretical distribution function, since both prevailed in the present study: a very short, constant foreperiod (1.5 seconds) was used, and E was not present in the experimental room with S during any of the sessions. Despite the somewhat unsatisfactory fit of Eq. (l), the obtained relations of the estimated parameters to stimulus intensity and response mode, as indicated in Fig. 6, were completely unambiguous. Differences in intensity = 112.12), a produced significant (p < .05) variations in mean RT (F4,16 (F4,16 = 6.16), b (F4s16 = 198.53), and in c (F4,16 = 8.71); and the finger

255

Raymond H. Hohle

260

I

I ~

6

0

7

0

8

0

9

0

Stimulur Intensity (dbl

Fig. 6. Mean RT and mean estimated parameters of Eq. I as Junctions of auditory stimulus intensity. where the response was either a finger or toe movement.

vs. toe effects were significant for mean RT (F,,4= 418.20), a(Fl, = 54.23), = 1.29). Whether Sresponded and tor b (F,,, = 198.53), but not for c (F,,, with a toe movement or finger movement during the first series each day did not affect any of the measures significantly. Although the effect of response mode on mean a was not expected, it can be accounted for in terms of the schema proposed above. When the Ss were instructed to press the response button as quickly as possible with a toe movement, this relatively unfamiliar and unpractised response probably required extra concentration, leading to heavy emphasis on a motor or muscular set. An assumed consequent de-emphasis on S's sensory set would then be expected to result in increased mean decision latency, which, by hypothesis, is measured by a. The obtained relations of a and b to intensity replicate the results of the

256

Component Process Latencies in Reaction Times

study described in the last section; but in this study, calso varied (inversely) with intensity. There does not seem to be any ready explanation why the effects of intensity on c differed in the two studies. The only apparent substantial differences in the two experimental procedures were that a somewhat wider range of intensities and a warning signal were introduced in the study described in the present section.

IV. Summary and Concluding Remarks A number of RT studies using child Ss were reviewed, and it was suggested that development of the reactive process might be better understood if more information were available on the underlying processes producing variations in RT. Three approaches were described, each directed toward identifying and determining the latencies of some of the various processes intervening between the stimulus and response in an RT situation: (1) variation of the task of S such that different numbers of hypothetical component processes are involved, then comparing mean RTs under the different task conditions; (2) direct measurement of portions of total RTs; and (3) inferring component latencies from statistical distributions of total RTs. The last of these approaches was developed in this paper. A specific distribution function was proposed to describe RT distributions, derived from the assumption that observed RTs can be represented as sums of two random variables, one having an exponential distribution, the other a normal distribution. A method of estimating the parameters of this function was described and the degree of correspondence was examined between fitted theoretical functions and 240 obtained distributions of RTs, taken from four different studies. While this correspondence was not completely satisfactory under all conditions, it seemed sufficiently close generally to warrant examination of the relations of the distribution parameters to several experimental variables. The parameter estimates included a, the mean of the hypothetical exponentially distributed component variable; b, the mean of the normally distributed component; and c, the standard deviation of the normal component. The parameter estimate Q (1) was found to be independent of foreperiod duration when the foreperiods were constant over blocks of trials, but varied inversely with foreperiod duration when the different foreperiods were presented in an irregular order over trials; (2) increased with the number of stimulus and response alternatives presented for choice reactions; (3) decreased with increasing stimulus intensity; and (4)was greater when the response was a toe movement rather than a finger movement. Parameter 6, interpreted as the mean of a normally distributed component

257

Raymond H.Hohle

of RT, ( I ) was, in general, lower when foreperiod durations were constant within blocks of trials than when the foreperiods occurred in irregular order: it increased monotonically with foreperiods of increasing duration under the regular condition, but when the various foreperiods were presented in an irregular order, b was highest for the shortest foreperiod, decreased to a minimum, then increased again for longer foreperiods. (2) This parameter appeared to be independent of the size of the set from which familiar four-letter words were presented for vocal choice RTs, but (3) varied inversely with stimulus intensity (provided that the different intensities were presented in an irregular order over trials), and (4) had higher values for a toe response than for a finger response. The standard deviation of the inferred normally distributed component, c, was uninfluenced by any of the experimental manipulations except that it decreased with larger numbers of stimulus word alternatives in sets presented for choice RTs; and, in one of two studies in which stimulus intensity was varied, c decreased with higher intensities. The results of the four studies were interpreted in terms of a model involving the assumptions (1) that the inferred exponentially distributed latency is “decision latency”, defined as the time required for a hypothetical decision mechanism to discriminate a reaction stimulus from all other ongoing external and internal stimulation; and (2) that the inferred normally distributed component is a sum of latencies of all processes other than the sensory decision process. In addition, the classical notions of sensory vs. motor set were adopted-including the assumption that emphasis by S on one type of set requires a relative de-emphasis on the other-and it was assumed that emphasis on a sensory set by S reduces decision latency, i.e., produces lower values of a, while emphasis on a motor or muscular set serves to diminish latencies of events in S’s motor system, thereby resulting in lower values of b. Details of this schema were deliberately left unspecified, with the expectation that further empirical studies can be designed specifically to provide the necessary elaborations. Further data, of course, may lead to more than filling in details: they might demand a complete re-structuring of the overall schema, or even require a new and quite different model. Whatever the fate of the schema proposed here, it appears, from the data described in Section 111, that the distribution parameters do relate differentially to various empirical variables, and hence can probably be interpreted as representing latencies of distinct processes underlying RT. Further research hopefully will provide a more detailed picture of the nature of these processes. And when this more detailed picture is attained, we should be in a better position to interpret the developmental studies of RT described in Section I. 258

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Raymond H. Hohle Gilbert, J. A. Researches on the mental and physical development of school children. Stud. Yale psychol. Lab., 1894,2, WIOO. Goodenough, F. L. The development ofthe reactive process from early childhood to maturity. J. exp. Psychol., 1935, 18,431-450. Greenbaum, H. B. Simple reaction time: A case study in signal detection. Unpublished doctoral dissertation, Columbia Univer., 1963. Grice, G. R., & Hunter, J. J. Stimulus intensity effects depend upon the type ofexperimental design. Psychol. Rev., 1964, 71, 247-256. Henry, F. M. Independence of reaction time and movement time and equivalence of sensory motivators of faster response. Res. Quart. Amer. Ass. Hlth, 1952, 23. 43-53. Hohle, R. H. Inferred components of reaction time as functions of foreperiod duration. J. exp. Psychol., 1965,69, 382-386. (a) Hohle, R. H. Detection of a visual signal with low background noise: An experimental comparison of two theories. J. exp. Psvchol., 1965,70,459463. (b) Hohle, R. H., and Pederson, D. R. Effects of stimulus intensity and stimulus sequenceon components of reaction times. Paper presented at Midwest. Psychol. Ass. Meetings, Chicago, May, 1966. Hyman, R. Stimulus information as a determinant of reaction time. J. exp. Psychol., 1953, 45, 181196. Jarl, V. C. Method of stimulus presentation as antecedent variable in reaction time experiments. Acta Psychol., 1958, 13, 225-241. Johnson, H. M. Reaction-time measurements. Psychol. Bull., 1923, 20, 562-589. Jones, H. E. Reaction-time and motor development. Amer. J. Psychol., 1937, 50, 181-194. Karlin, L. Reaction time as a function of foreperiod duration and variability. J . exp. Psychol., 1959,58, 185-191. Knott, J. R. Some effects of mental set upon the electrophysiological processes ofthe human cerebral cortex. J . exp. Psvchol., 1939. 24. 384405. Kiilpe, 0. Outlines of psychology. (Transl. by E. B. Titchener) New York: Macrnillan, 1x95. LaBerge, D. A recruitment theory of simple behavior. Psychometrika, 1962, 27, 375-396. Lemmon, V . W. The relation of reaction time to measures of intelligence. memorv. and learning. Arch. Psychol., 1927, No. 94. Luria, A. R. The nature of human conpicts or emotion. conflict and will. A n objective study of the disorganization and control of human behavior. W. H.Gantt, Transl. and Ed., New York: Liveright, 1932. McCormack, P. D., & Wright, N. M. The positive skew observed in reaction time. Cunad. J. Psychol., 1964, 18.43-51. McGill, W. J. Stochastic latency mechanisms. In R. D. Luce, R. R. Bush, & E. Galanter(Eds.), Handbook of mathematical psychology. Vol. 1. New York: Wiley. 1963. McGill, W. J., & Gibbon, J. The general-gamma distribution and reaction times. J. math. Psychol.. 1965, 2, 1-18. Mathur, V . K. Studies in reaction time: 4. Unpublished doctoral dissertation, Banaras Hindu Univer., Varanasi, India, 1966. May, M. J. A new method for studying visual latency. Vision Res., 1964, 4, 515-516. Merkel, J. Die zietlichen Verhaltnisse der Willensthiitigkeit. Phil. Stud., 1885, 2, 73-127. Miles, W. R . Measures of certain human abilities throughout the life span. froc. Na/.Acad. Sci. U.S. 1931, 17,627-633. Morin, R. E., & Forrin, B. Mixing of two types of S-R associations in a choice reaction time task. J. exp. Psychol., 1962, 64, 137-141. Morin, R. E., & Forrin, B. Information-processing: choice reaction times of first- and thirdgrade students for two types of associations. Child Develprn., 1965, 36, 713-720.

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Component Process Latencies in Reaction Times Morin. R. E., Konick. A.. Troxell. N., & McPherson, S. Information and reaction time for "naming" responses. J . exp. Psychol., 1965.70,309-314. hlowbray. G. H.. & Rhoades, hn. V. On the reduction of choice-reaction times with practice. Quart. J . exp. Psychol., 1959, 11, 16-23. Peak, H., & Boring, E. G . The factor of speed in intelligence. J. exp. Psychol., 1926,9.71-94. Philip, B. R. Reaction-times of children. Amer. J. Psychol., 1934.46, 379-396. Pollack, 1. Verbal reaction times to briefly presented words. Percept. mot. Skills, 1963, 17, 137-1 38.

Riggs, L. A . Electrophysiology of vision. I n C. H. Graham (Ed.), Vision andvisualperception. New York: Wiley. 1965. Rosenblith, W. A., & Vidale, E. B. A quantitative view of neuroelectric events in relation to sensory communication. I n S. Koch (Ed.), Psychology: A study ofa science. Vol. 4. New York: McGraw-Hill, 1962. Scott, W. S. Reaction time of young intellectual deviates. Arch. Psychol.. 1940, No. 256. Shannon, C. E. & Weaver, W. The mathematical theory of communication. Urbana: Univer. of Illinois Press, 1949. Slater-Hammel, A. T. Reaction time and speed of movement. Percept. mot. Skills Res. Exch., 1952,4, lWl13. Spiker, C. C. The concept of development: Relevant and irrelevant issues. Monogr. SOC.Res. Child Developm.. 1966. 31. Serial No. 107, No. 5. 40-54. Stilson, D. W. Neurophysiologically oriented computer simulation of reaction time and choice behavior. Paper presented at Sympos. on Mathematical Models of Behavioral Processes, Int. Congr. of Psychol., Moscow, August, 1966. Stone, M. Models for choice reaction time. Psychometrika, 1960, 26, 251-260. Swets, J. A., Tanner, W. P., Jr., & Birdsall, T. G. Decision processes in perception. Psychol. Rev., 1961.68, 301-340. Taylor, D. H. Latency models for reaction time distributions. Psychometrika, 1965,30, 157-164. Taylor, D. H. Latency componentsin two-choiceresponding.J. exp. Psychol., 1966,72,481-487. Teichner, W. H. Recent studies in simple reaction time. Psychol. Bull., 1954, 51, 128-149. Thorndike, E., & Lorge, 1. The reacher's wordbook30.000 words. New York: Columbia Univer., Bureau of Publications, 1944. Titchener, E. B. A text-book of psychology. New York: Macmillan, 1910. Weiss, A. D. The locus of reaction time change with set, motivation, and age. J. Geront., 1965, 20,6044.

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Woodworth, R. S., & Schlosberg, H. Euperimentalpsychology. (Rev. ed.) New York: Henry Holt, 1954. Wundt, W. Grundziige der Physiologischen Psychologie. Leipzig: Engelmann, 1874. Wundt, W. Grundziige drr Ph.vsiologischen Psychologie. 2ter Band. Leipzig: Engelmann, 1887.

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A U T H O R INDEX Numbers in italics indicate the pages on which complete references are given

A Abt, I. A., 41, 50 Adey, W. R., 91,91 Akiyama, Y.,67, 69, 70, 95 Alberts, E., 129, 155 Allen, J., 231,259 Alleuisi, E. A., 248, 259 Ames, E. W., 3,50. 193,220 Antonova, T. G., 3,29,50 Ardran, G. M., 6, 50 Aresin, L., 61.91 Armington, J. C., 2, 50 Aussaresses, M., 74, 75,95 Ayllon, T., 152, 155 Amin, N. H., 152,155

B Bacon, W. E., 21,52 Badr El-Din, M. K., 80,91 B a h t , M., 7,9, 13, 16, 22,48,50 Barlow, J. S.,23 1,259 Barnett, A. 8.. 2, 50, 82, 90,91 Bartlett, J. S., 230, 231,259 Bartoshuk, A. K., 2,50,67,68,69,91 Baumeister. A. A., 227, 259 Beck, E. C., 83, 84, 93, 231,259 Bee, H. L., 120,124 Bellis, C. J., 226, 227, 259 Berger, G. O., 230,259 Bernstein, L., 203,221 Bernstine, R. L., 61, 62, 74, 91 Berthault, F., 67, 80,94 Bickford, R. G., 56,60,67, 74,92,96 Bindra, D., 25,50 Birch, H. G., 173, f89.215.220 Birdsall, T. G., 243,261

Birns, B. M., 4,50 Rlanc, C.,63, 67, 74, 75, 76, 80, 81, 82, 88, 92 Blank, M.,4,50,217,218,220 Blanton, M. G., 47.50 Blough, D. S., 2,50 Boring, E. G., 227,261 Borkowski, W. J., 61,62,92 Bosack, T., 42,44,45,52 Botwinick, J., 231, 244, 245,259 Brackbill, Y.,29,36,50 Brainard, R. W., 248,259 Brazelton, T. B., 48.50 Brazier, M. A. B., 56,67, 74, 91,92, 96 Brennen, W. M., 193,220 Bridger, W. H., 4,22,26,50,217,218,220 Brinley, J. F., 244,259 Broadbent, D. E., 100. 101,124 Brodbeck, A. J., 19,50 Bronshtein, A. I., 3,29,50 Brown, J. L.,4,50 Butler, B. V., 83, 85, 86, 87,94 C

Cadilhac, J., 69, 75, 76, 77, 92, 95, 96 Caldwell, B. M., 1 I , 50, 196,221 Camp, D. S.,227,259 Canova, G., 63, 92 Cantor, G.N., 91,92 Capdevielle, G., 67, 97 Capron, E., 67,70,14, 75, 76, 79,96 Carrick, M.,168, 180, 190 Castan, P., 69, 92 Castle, P.,197, 214,222 Cattell, J. McK., 230,259 Chase, R. A,. 212,220 Christie, L. S., 234, 243.259 Church, R. M., 227,259

263

Author Index Chzhi-Tsin, V., 199,209, 216,223 Cighnek, C., 84, 92 Cobb, W. A., 56,67, 74, 96 Cody, D. T.R., 60,92 Coles. G. R., 109. 124 Colley, J. R. T., 6, 7, 8, 16,50 Conel, J. L., 96, 92 Cornwell, A. C., 2, 4 1,52 Cossandi, E., 63, 92 Cramer, H., 235,259 Creamer, B., 6, 7, 8, 16.50

D D’Amato, M. F., 163, 190 Dargassies, S., 63, 93 Davis, G. D., 83, 84, 85, 94 Davis, H. F., 19,50 Davis, R.,248,259 Davis, R. C.. 242, 244,259 Delange-”alter, M.. 67.69. 74. 75. 89, 92.96 del Mundo Vallarta, J., 80, 92 Dement, W. C., 69, 70, 96 Denisova, M. P., 36,50 Deutsch, R., 259 Dodwell, P. C., 114, 124 Doertler, L. G., 105, 124 Donders, F. C., 229, 233,259 Dondey, M., 56,67,74,96 Dorsen, M. M., 83, 94 Dreyfus-Brisac, C., 63, 64,66, 67, 68, 69, 70, 73. 74, 75, 76. 77, 78, 79, 80, 81, 82, 88, 92, 93, 95 Ducas, P., 76, 77, 78, 79, 80, 93, 95 Dunford, R. E., 198, 220 Dunn. L. D., 166,189 Dustman, R. E., 83, 84, 93,231,259 Dutch, S. J., 79, 80,93 Dyk, E. B., 194, 210,223

E Eagles, E. L., 105, 124 Ehrenfreund, D., 129, I55 Eichorn, D. H.. 88, 89, 93, 195,220 Ellingson, R. J., 55, 56, 60, 61, 63, 65, 66, 67, 71, 77, 78, 79, 81, 82, 83, 84, 85, 86. 87. 88, 89,93 Elliot, R.. 123,124,227,259 Engel, R., 61, 67, 74, 78, 82, 83, 85, 86, 87, 93,94

Engen, T., 3, 29,50,52 Estes, W.K., 148, 155

F Fantz, R.L., 3.X4193.220 Feldman, W. M.,5,50 Feller, W., 235,259 Ferriss, G. S., 83,84,85,94 Figurin, N. L., 36,50 Finley, J. R., 144, 156 First, D., 2 I 2,220 Fischer, C., 69,70,96 Fischgold, H., 55,67,80,92,94,97 Fitts, P. M., 248.259 Flavell, J. H., 193,220 Fleming, M. M., 76,77,94 Flescher, J., 63, 66, 67, 69, 70, 73,75,93,95 Fonin, B., 248,260 Forthomme, J., 67, 70, 74, 75, 76, 79, 96 Fox, B. J., 69, 70. 72, 95 Frazier, W. H., 67, 77, 78, 95 Freeman, G. L., 242,244,259

G Gardner, A. M., 129, 136, 137, 140, 148, 153, 156 Gardner, D. B., 217, 218,221 Gastaut. H., 56, 67, 74, 96 Gaydos, H. F., 199,220 Gesell, A. E.,214, 220 Ghent. L., 203,220.221 Gholson, B., 249,259 Gibbon, J., 235, 243, 260 Gibbs, E. L., 56.67, 72, 76, 77, 94 Gibbs, F. A., 56,67, 72, 76, 77, 94 Gibson, E. J., 194,200,217,221 Gibson, J. J.. 194,200. 207,221 Gilbert. J. A.. 226,227,260 Gilbert, T. F., 20.51 Glaser, G. H., 67, 88, 89, 94 Gloor, P., 56, 67, 74, 97 Goddard, K. E., 4, 8, I I , 51 Goldfarb, W., 120, 124 Goldie, L., 49, 94 Goldring, S., 81, 94 Goldweber, A. M., 203,221 Goodenough, D. R., 194,210,223 Goodenough, F. L., 226,227,228,260 Goodwin, R. S., 82, 90.91 Gottlieb, G., 27,50

Author Index Cough, I? B., 171, 190 Graham, F. K., II,50,196,221 Greenbaum. H. B., 243,260 Greene, P., 209,222 Grice, G. R.,252, 253,260 Grim, P. F., 123, 124 Guttman, N., 143, I55

H Hackett, E. R., 83, 84, 85, 94 Haith, M. M., 32, 33, 37, 51 Halvarson, H. M., 7, 22.51, 214, 221 Hammond, M., 207,221 Harris, R., 74, 75, 80, 94 Hartzman, M., 210,223 Hatwell, Y.,204,221 Hawkins, W. F., 227,259 Hay, J., 21 I , 213, 214,221,222 Hayes, K. J., 148, 155 Haynes, H., 2, 51 Heckel, H., 67, 74, 75, 96 Hein, A . V., 213,221 Held, R., 2. 51. 197. 213, 214, 221, 222 Hellstrom, B., 56, 94 Henry, C. E., 56,67, 74,97 Henry, F. M., 227,260 Herrnelin, B., 199,209, 215,221 Hernandez-Peon, R., 100, 124 Herrick, C. J., 5, 51 Herrmann, B., 74,75, 96 Hershenson, M., 193,221 Hess, R., 56, 67, 74, 97 Hohle, R. H.,235, 236, 243, 244, 245, 249, 252,259,260 Honzik, M. P., 5, 52 Houck, E. V., 217,218,221 House, B. J., 148, 156 Hovland, C. I., 103, 124 Hrbek, A., 83, 84,85, 86,87, 88, 89, 94 Huhmar, E., 62, 74, 94 Hull, C. L., 157, 158, 159, 160, 190 Hunter, I. H. L., 201,221 Hunter, J. J., 252, 253,260 Hyman, R., 247,260

I Ikeda, K., 21 I , 221 Inhelder, B., 200,221 Irby, T. S., 248, 259

Irwin, 0. C.,22,51 Isler, W., 80, 94 J Jackson, C. V., 211,221 Jacobson, J. L., 60,92 Jarvinen, P. A., 62, 74,94 James, H., 128, 142, 155 James, W., 180, 190 James, W. T., 20, 21,51 Jarl, V. C.. 252, 260 Jasper, H. H., 56, 94 Jensen, K., 6,7,8,20,26,51 Johnson, H. M., 252,260 Johnson, R. C., 139. 155 Jones, H. E., 227,260 Jouvet, M., 100, 124

K Kagawa, N., 5 5 9 4 Kalish, H. I., 143, I55 Karlin, L., 244, 260 Karlsson, B.. 56, 94 Karp, S. A., 194,210,223 Kashara, M., 6, 8,47,51 Kaye, H., 4, 10, 11, 12, 14, 15, 16, 17.22, 23, 24, 26, 27, 29, 31, 33, 34, 35, 36, 37, 38, 39, 41,42,43,44, 45, 46.47, 48, 50, 51,52 Keen, R.,29,Sl Keith, H. M., 80, 94 Kellas, G., 227,259 Kellaway, P., 5 5 6 7 , 69, 70, 72, 74, 76, 82, 94, 95,96 Kelvin, R. P., 209,221 Kemenetskaya, A. G., 3,29,50 Kemp, F. H., 6,50 Kendall, W. E., 244,259 Kendler, H. H., 136, 155, 162, 163, 165, 168, 175, 176, 180,190 Kendler, T. S., 136,155, 162, 163, 165, 168, 175, 176, 179, 180,190 Kessen. W., 3, 26,51,52 Kirikae, T., 61,95 Klein, R. E., 203,210,211, 212,221,222 Knott, J. R., 56, 67, 74, 97, 242, 260 Kohler, W., 160, 190 Konick, A., 248, 249,261 Konrad, K. W., 102, 116,124 Koronakos, C., 170,190

265

Author lndex Kramarz, P., 63,67,80, 92 Kron, R. E., 4, 8, I I, 51 Kiilpe, O., 229,260 Kuenne, M. R., 128,155 Kugler, J., 56. 67, 74, 97

L LaBerge, D. L., 108. 124,243,260 Lairy, G. C., 56,67,74,97 Lang, J., 129, 135, 138, 146, 147, 155, 156 Lavrent’eva, T. A., 199,209,216,221 Lawrence, D. H., 108, 109, 124 Learnard, B., 175, 190 Lefford, A., 215,220 Lemmon, V. W., 227,260 Leventhal, A., 3,51 Leventhal, T., 2 I I , 223 Levin, G. R., 4, 11, 12, 14, 15, 22, 26, 27, 31,51,52

Levy, D., 18,20,51,52 Levy, L. L., 88,89, 94 Levy, N., 1 1,29,52 Lewis, H. B., 210,223 Liberson, W. T., 61,77,78,95 Lind, J. A., 6,50 Lindsley, D. B., 61,67, 95 Lipsitt, L. P., 2, 3,4, 11, 29, 36, 37, 38, 39,42,43,44, 45, 48,50,51,52, 95 Lipton, E. L., 2,52 Livingston, R. B., 87, 95 Lodge, A., 2,50 Loeb, C., 56,67,74,97 Loiseau, P., 74,75, 95 Lomov, B. F., 192,223 Lorge, I., 249,261 Luce, R. D., 234,243,259 Lumsdaine, A. A., 103,124 Luppova, N. N., 3,29,50 Luria, A. R., 227, 228,260

91,

M

McCormack, P. D., 233,260 Maccoby, E. E., 102, 116, 124 McGill, W. J., 232, 234, 235, 243, 260 Machover, K., 210,223 Maier, N. R. F., 160, 161, 190 McIntire, M. S.,79, 93 McKee, J. P., 5,52, 133, 156

266

McKinney, J. P., 198,221 McPherson, S.,248. 249.261 Magnus, O., 56,67,74,97 Mai, H., 63.67, 95 Maissner, P. B., 210,223 Mares, P., 83, 84,85, 86, 87, 88,89, 94 Marquis, D. P., 36,52 Matarauo, R. G., 11.50, 196,221 Mathur, V. K.. 230,260 May, M. J., 231, 252. 254,260 Mayer, M., 76. 77.78, 79, 80, 93, 95 Merkel, J., 247,260 Merrill, M. A., 1 I 1, 124 Miles, W. R., 227,260 Miller, G. A., 112, 124 Miller, H. C., 19, 50 Minke, K. A., 144, 156 Min kowski, A .. 63, 93 Mirzoyants, N. S., 88, 89, 95 Misbs, J., 67, 74, 75. 89, 96 Monod, N., 63,66,67, 69, 70,73, 74, 75, 76.78, 79, 80.92, 93, 95

Montessori, M.. 192,221 Moore, R. W., 193,220 Morel-Kahn, F., 63. 67, 69, 70, 95 Morin, R. E., 248, 249,260,261 Mowbray, G. H., 248,261 Miiller, H.W., 63,67, 95 Mussbichler, H.. 56,94 Muray, N., 248,259

N Nelson, A. K., 22,52 Newlin, J. C., 197,222 0

OConnor, N., 199,209,215,221 Okamoto, Y.,61, 95 OLeary, J. L.. 81,94 Oller, D., 56, 67, 74, 97 Osser, H. A,, 200, 207, 221

P Paalberg, J., 139, 156 Pajot, N., 63.67, 69. 70, 78, 79, 93.95 Papousek, H., 196.221 Parmelee, A. H., Jr., 67.69, 70, 95 Pam, G., 58,97 Passouant, P., 69, 75, 76, 77, 92, 95, 96

Author Index Paterson, H. F., 194, 210, 223 Patton, H. D., 232, 261 Peak, H., 227,261 Pederson, D. R., 252,260 Peiper, A., 5, 6.9, 13, 52 Petsche, H., 56, 67, 74, 97 Philip, B. R., 226, 227, 261 Piaget, J., 5, 52, 200, 221 Pick, A. D., 200, 202, 203, 206,207. 217, 221,222 Pick, H. L., Jr., 193, 200, 203, 206,207, 21 I, 2i3,214,217,221,222 Plassard, E., 43,63,66,67,69.70, 73, 75, 93, 95 Pliskoff, S. S., 163, 190 Poggiani, C., 2, 41.52 Polikanina, R. I., 63, 67, 96 Pollack, I., 248,261 Pollack, R. H., 194. 195,222 Postman, L., 117, 124 Pratt, K. C., 22.52 Preyer, W., 5.52 Price, A. H.,62, 92 Price, A. E., 133, 156 Prichard, J. S.,80, 96, 97

R Reese, H. W., 126, 129,155, 156 Renshaw, S., 197, 198,222 Rhoades, M. V., 248, 261 Ribstein, M., 74, 75, 76, 77, 95, 96 Richmond, J. B., 2.52 Riggs, L. A., 231,261 Riley, D. A., 128, 133, 156 Robb, J. P., 80, 92 Robbin, J. S.,259 Robinson, H. B., 195, 205,222 Rock, I., 21 I, 222 Rossler, M., 78, 96 Roffwarg, H. P., 69, 70, 96 Rosen, M. G., 78.96 Rosenblith, W. A., 230,231, 232, 243, 249, 261 Ross, S., 19,20,52 Rovee, C. K.,4,26,52 Rudel, R. G., 129, 138, 156, 199,209, 215, 218,222 Ruhl, D., 217,218,221 Ruzskaya, A. G., 192, 193, 199,209,216, 221,223

S Salapatek, P.,3,52 Salarna, D., 95 Salarna, P., 76, 78, 79, 80,93 Salten, C.S., 144, 145, 146, 150, 151, 153, 156

Sameroff, A. J., 4,8, 11,46,52 Samson-Dollfus, D., 55,63,’67, 70, 74.75. 76, 79,89,92,% Sashin, D., 231,259 Satinoff, E.,21,52 Satran, R., 78, 96 Savin, H. B., 114, 124 Schaper, G.,63,69,75,95,96 Schcrrer, H., 100, I24 Schlosberg, H.,101, 124, 232, 242,261 Schopler, E., 193,222 Schroeder, C.,67,74, 75,96 Schlitz, E.,63,67,95 Schulte. F. J., 74, 75, 96 Schultz, M., 69, 95 Schwab, R.,56,67,74,97 Scott, W. S., 227,261 Sears, R. R.,19,50 Seltzer, R. J., 46,47,51 Sewall, S.T.,112,124 Seward, J. P., 171, I90 Shannon, C.E.,247,261 Sheffield, F. D., 103,124 Shepovalnikov, A., 67,96 Shepp, B. E., 3,52 Sherman, M., 133, 139,156 Sidman, M., 142, 148.156 Silfen, C.K.,175, 190 Simner, M.L., 27,50 Singer, M. T.,120, 124 Siqueland, E. R., 2,52 Skinner, 8. F., 126, 128, 155, 156, 158, 190 Slater-Harnrnel, A. T..227,261 Smith, K.U.,209,222 Smith, J. M. B., 74, 96 Sokolov, Ye. N.,28,52 Spence, K.W., 128, 156 Sperling, G.,109, 124 Spiker, C.C.,228,261 Spragg, S. D., 171,190 Staats, A. W., 144,156 Stanley, W. C.,2, 21,41, 45,52 Stein, M., 4, 8, 1 I , 51

267

Author Index Steinschneider, A., 2, 52 Stem, E., 67, 69, 70, 95 Stilson, D. W., 243, 261 Stone, M., 243,261 Storm van Leeuwen, W., 56, 67, 74, 96 Strunk, J., 139, 156 Sugaya, E., 81,94 Sumby, W. H., 112, 124 Sun, K. H., 22,52 Sureau, M., 67,97 Sutcliffe, D. P., 184, 190 Sutton, s., 212,220 Swets, J. A., 112, 124, 243,261 Switzer, G., 248,259 Syrova, V. A., 3,29,50

T Tanner, W. P., Jr., 243,261 Tarakanov, V., 199,209,216,223 Taylor, D. H., 229, 233,235,261 Teichner, W. H., 245,261 Tennant, J. M., 67,68, 69, 91 Terman, L. M., I I I, 124 Teuber, H.-L., 199, 209,2)5, 218,222 Thane, D., 60, 92 Thomas, M. L., 207,217,222 Thompson, H., 214,220 Thompson, L. W., 231,244,245,259 Thorndike, E., 249,261 Tibbles, J. A. R., 80,97 Titchener, E. B., 244.261 Tizard, J. P. M., 74, 75, 80, 94 Torrey, C. C., 2,52 Trattner, A., 2,52 Treisman, A., 248,259 Troxell, N., 248, 249,261 Turrisi, F. D., 3, 52

V Verger, P., 74, 75, 95 Victor, J., 21 I , 222 Vidale, E. B., 230, 231, 232, 243, 249, 261 Vygotsky, L. S., 188, 190

268

W Walter, M., 74, 75, 96 Walter, W. G., 56, 58, 67, 74, 91 Wapner, S., 210, 21 I , 215,222, 223 Weaver, W., 247,261 Weiss, A. D., 231, 244, 261 Wenner, W. H., 67,69,70.95 Werner, H.. 194,215,222 Wertheimer, M., 138. 146,156 Wherry, R. J., 197, 198,222 White, B. L., 2, 51, 197,222 White, E. L., 197, 214,222 WidCn, L., 56,67, 74,97 Wishik. S. M., 105, 124 Witkin, H. A., 194, 210, 211, 223 Wolf, M., 144, 156 Wolfe, T. B., 171, 190 Woodbury, J. W., 232,261 Woodrow, H., 244,261 Woodworth, R. S., 101, 124,232,242.261 Wright, N. M., 233, 260 Wundt, W., 229,251, 253,261 Wynn, L. C., 120, 124

Y Yates, A. J., 212,223 Yerkes, A. W., 160. 190 Yerkes, R. M., 160, 190

2 Zaporozhets, A. V., 193,223 Zara, R. C., 139, 155 Zeaman, D., 148, 156 Zeiler, M. D., 128. 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 144, 145, 146, 147, 150, 151, 153, 156 Zetterstrom, B., 2.52 Zimmermann. R. R., 2,52 Zinchenko, V. P., 192, 193, 199,209, 216, 223 Zubin, J. A., 212,220

SUBJECT I N D E X

A Acuity, visual, 195 Adaptation, to distortion, 210 Afferent events, 230 Age, 129-131, 133-138, 140 Age improvement in selective listening, factors related to, 103-107, see also Developmental trends Arousal in infants definition, 25-26 heart rate and sucking, 27-28 sucking and, 25-28 Attention auditory, 99-124 comparison of visual and auditory attention, 99-101 developmental trends, 102-103, 1 1 1-1 19 factors related to age improvement, 103108

Attentiveness, individual differences in, 120I22 Auditory acuity and selective listening, 105 Auditory attention, 99-124

B

Conflict of sensory input, 209-213 Contour detectibility, 195 Contrast sensitivity, 195 Cross-modal transfer, see Intermodal transfer

D Decision criterion, 243, 249 Degrees of freedom, 239 Developmental trends factors related to, 103-107 in selective listening, 102-103, 1 11-1 19 methodological issues in measurement of, 103-105

Dichotic listening, developmental trends in, 102-1 03 Differentiation theory in perceptual development, 194 Dimensions of stimulation, 200-201 Discrimination reaction time, 226, 229, 230 simultaneous and successive, 202 Distinctive features, 202, 217 Distortion of sensory input, 20912 I3 Distractability, see Attentiveness Dominance of sense modality, 197-198, 204

Blind subjects, 201, 207-208

E C

Central decision events, 230 Central motor events, 230 Central sensory events, 230 Choice, 126, 137, 147, 153-154 absolute choice, 127-128 instructions, 150-152 transposition, 127 variability, 149-150 Choice reaction time, 229 Component parameters, 236, 237 Concept formation in reasoning, 175-183

EEG, 51-97 abnormalities in infants, 73-81, 89-90 methodology, 55-58 of abnormal infants, 78-81 of abortuses, 61 of fetuses, 6142 of infants, 67-72 of prematures, 62-67 prognostic value of, 78-81 Efferent events, 230 Evoked responses, cortical auditory, 81-82,W

269

Subject Index methodology, 58-61 nonspecific, 81-83 visual, 83-88 Exponential distribution, 234

F Feedback, 210 delayed auditory, 212 proprioceptive, 193 Field dependence, 194,210 Filter theory of selective listening, 101.106I07 Food deprivation and sucking, 20-25 Foreperiod duration, 244 Foresight, 158-160, 178-179

Insight, see Inferential behavior Integration perceptual, 192 primary and secondary, 193 temporal, 192, 194 Intermediate-size problem, 132-1 55 multiple training sets, 13W40 Intermodal transfer, 203-204,215-218 matching, 209, 215-216 transfer of training, 217-218 Irreversibility, 142, 149

K Kinesthetic perception, 192

L C

Goodness of fit statistic, 238, 245, 250, 253, 255 distribution of, 240 Grapheme-phoneme correspondence, 194 Grasping, visually guided, 197

Language facility and selective listening, 105 Learning studies in infancy, difficulties, 4 Localization of source of stimulation, 196199.210-21 I

M Memory span and selective listening, 109-1 11, 117-1 18

H Haptic perception, 192 Higher order stimulus perception, 205-209 Hypsarhythmia, 76-77

I Illusions, 195,204-205 Delbouef, 204 Haltiere, 204 horizontal-vertical, 204 Muller-Lyer, 204 size-weight, 205 Individual and group data, 140-143, 146-148 Individual differences in selective listening, 1 2 w 22 Inferential behavior development in children, 166170,183486 effect of training on, 161-166, 175-183, 173-1 74 of verbal labels on, 180-182 in relation to chronological age, 168-170 to mental age, 183-186 representational responses in, 178-183 Information measure, see Stimulus uncertainty Information processing, 194

270

Mental age, relation to inferential behavior, 183-1 86 Method of moments, 236-237 Motor response, 230 Muscle action potentials, 230-231, 233 Muscle sense, 192

N Nerve conduction, 232 0

Orientation in infants, 28-29 of shape, 203-205,218 spatial, 210

P Perception cognitive development and, 193 differentiation theory, 194 motor components in, 193 selective auditory, %I24 sensory-motor stage, 193 Perceptual integration, 192-223 Perceptual latency, 231,252

Subject Index Photic following responses, 88-89 Preparatory set developmental trends in utilization of, 110-1 14, I 16-1 17 effect on selective listening, 108-1 19 role of sense organ orientation in utilization of, 119-120 Procedural variables, 130 delayed testing, 130. 128, 144 Proprioception, 192 Prototype, 202,217 Psychophysicsin newborn, 2-3 Pure stimulus acts, 158-160

R Ratio theory, 132-133 Reaction time, 225, see also Choice RT, Discrimination RT, Simple RT additivity assumption, 229, 233 age and, 227-228 distributions, 232, 240 intelligence and, 226-227 intensity and, 251 motivation and. 227 response mode and, 255-257 sex differences, 226 stimulus sequence and, 251-254 stimulus uncertainty and, 247-251 Reasoning, see also Inferential behavior concept formation in, 179-180 infrahuman, 170-174 Reinforcement, 143-1 54 intermittent, 143-154 monetary, 144-154 Representational responses, I 51160, I 7 1 182 Response mode, 255 produced stimulation, 213 Reversibility, 147

S Seizures, in infants, 75-77, 79-81 Selective listening, see also Auditory attention auditory acuity and, 105 correlations with ability measures, 121-122 developmental trends, 102-103, 11 1-1 19 effect of preparatory set on, 108-1 19 filter theory, 101, 106-107, 115, 118-1 19

individualdifferences in, 1 B 1 2 2 intrapersonal stability of, 120-121 language facility and, 105 role of sense organ orientation, 100-101, 119-120 sequential probability of stimulus phrases and, 116118 word familiarity and, 113-1 15 Sense organ orientation, role in selective listening, 100-101, 1 19-120 Sense modality, 192 dominance, 197-198.204 Sensory conflict, m 2 1 3 Sequential probability of verbal stimuli, 1 6 118 effect on selective listening, I Set, 245, see also Preparatory set motor, 242,252 sensory, 242-243 Shape, orientation, 203-205 perception, 199-205 Simple reaction time, 226, 229 Stimulation, localization of source, 196199 dimensions of, 200-201 Stimulus class, 127-129, 131, 147, 155 absolute characteristics, 128 relational characteristics, 128 Stimulus similarity, 126427 distance, 127 steps, 127 Stimulus uncertainty, 247 Stomach loading, 20-25 Subtractive procedure, 229-230 Sucking burst, 15-17 correlation with frequency, 15 definition, 15-17 Sucking deprivation, 18-19 Sucking response, 1-53 cineradiographic analysis, 6-7 conditioned, 3547 definition, 15-17 drug effects, 4849 frequency, 9-15 to nonoptimizing stimuli, 4245 under nonnutritive condition, 10-14 under nutritive condition, 9-1 1 historic references, 5 pathology, 47-50 positive attributes, 4 pressure, 7-8 pups, 18-21,4142 role of tongue, 6,46

27 1

Subject Zndex Sucking suppression, 2&35 Surface texture, 216 Synthesis, 194

T Tactual Perception, 192-223 Temporal distortion, 210 Temporal integration, 192, 194 Texture, surface, 2I6 Thumbsucking, 18 Touch, 192-223 Transportation design, 126-150 between-set similarity, 126127, 130, 133-134, 137-138, 140, 144,148, 150 within-set similarity, 126127, 130-131 133-134, 137-138, 140, 144,150 Transposition experiments, 125-127 comparison of two- and three-stimulus problems, 140-141

272

intermediate size problem, 132-155 transposition design, 126 two-stimulus problem, 128-131, 150-152 Two-stimulus problem, 128-131, IS152 procedural variables, 130

V Verbal factors, 129-131, 137, 152-154 Vestibular sensitivity, 210 Visual acuity, 195 Visually guided grasping, 197

W Waiting time distribution, see Exponential distribution Word familiarity and selective listening, 113-115