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UBC Theses and Dissertations

Auditory-visual integration of temporal relations in infants Humphrey, Gary Keith 1979

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AUDITORY-VISUAL INTEGRATION OF TEMPORAL RELATIONS IN INFANTS by GARY KEITH HUMPHREY B,A, (Hons.)-. U n i v e r s i t y of New Brunswick, 1972 M.A. Un i v e r s i t y of B r i t i s h Columbia, 1976 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES (Department of Psychology) We accept t h i s t hesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA November, 1979. (c) Gary Keith Humphrey, 1979 In presenting th is thes is in p a r t i a l fu l f i lment o f the requirements for an advanced degree at the Univers i ty of B r i t i s h Columbia, I agree that the L ibrary sha l l make it f r ee ly ava i lab le for reference and study. I fur ther agree that permission for extensive copying of th is thes is for scho la r ly purposes may be granted by the Head of my Department or by h is representat ives . It is understood that copying or publication of th is thes is for f inanc ia l gain sha l l not be allowed without my writ ten permission. Department of Psychology  The Univers i ty of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date T]cnr.tZ m 9 6 i i . ABSTRACT Three experiments examined a u d i t o r y - v i s u a l i n t e g r a t i o n o f t e m p o r a l r e l a t i o n s by i n f a n t s . I n t h e f i r s t experiment i n f a n t s o f 3, 6 and 10 months o f age were p l a c e d midway between two f l a s h i n g v i s u a l d i s p l a y s . Tones, t e m p o r a l l y s y n c h r o n i z e d t o one o f the v i s u a l d i s p l a y s , emanated from c o n c e a l e d speakers p l a c e d midway between the v i s u a l d i s p l a y s d i r e c t l y i n f r o n t o f the i n f a n t s . The v i s u a l d i s p l a y s , and c o r r e s p o n d i n g t ones d i f f e r e d i n t e m p o r a l r a t e by a f a c t o r o f f o u r . No e v i d e n c e was found f o r d i f f e r e n t i a l l o o k i n g t o the s o u n d - s p e c i f i e d v i s u a l p a t t e r n i n any o f t h e t h r e e age l e v e l s t e s t e d . The 3-month-olds showed a s t r o n g r i g h t - l o o k i n g b i a s r e g a r d l e s s o f v i s u a l p a t t e r n o r t e m p o r a l r a t e o f the t o n e , w h i l e t h e 10-month-olds p r e f e r r e d t o l o o k a t the f a s t v i s u a l p a t t e r n r e g a r d l e s s o f p o s i t i o n o r tone r a t e . Both o f t h e s e b i a s e s i m p a i r e d t h e e f f e c t i v e n e s s o f t h e s i m u l t a n e o u s p r e s e n t a t i o n paradigm t o d e t e c t d i f f e r e n t i a l l o o k i n g r e l a t e d t o a u d i t o r y v v i s u a l synchrony. Experiments I I and I I I used an h a b i t u a t i o n methodology which e l i m i n a t e d any e f f e c t s o f p o s i t i o n and r a t e b i a s . O nly 4-month-old i n f a n t s were t e s t e d . I n each experiment, one group o f i n f a n t s was f i r s t p r e s e n t e d w i t h t e m p o r a l l y synchronous a u d i t o r y and v i s u a l s i g n a l s d u r i n g h a b i t u a t i o n t r i a l s and t h e n nonsynchronous s i g n a l s d u r i n g r e c o v e r y t r i a l s . Two o t h e r groups o f i n f a n t s , one i n each experiment, r e c e i v e d t h e o p p o s i t e sequence. I n Experiment I I the a u d i t o r y and v i s u a l s i g n a l s were s p a t i a l l y congruous, but t h e y were s e p a r a t e d by 90° i n Experiment I I I . S i n c e t h e p u l s e r a t e o f t h e v i s u a l s t i m u l i was changed f o r t h e nonsynchronous t r i a l s , a c o n t r o l group.was t e s t e d which r e c e i v e d o n l y the l i g h t d u r i n g h a b i t u a t i o n and r e c o v e r y t r i a l s . B oth groups i n i t i a l l y presented with synchronous signals showed habituation and recovery. Neither group presented with nonsynchronous s t i m u l i during habituation t r i a l s demonstrated recovery and only the group with the s p a t i a l l y separated sources habituated. The results suggest that 4-month-old infants are able to coordinate the temporal relations between auditory and v i s u a l signals. i v . TABLE OF CONTENTS Page A b s t r a c t i i L i s t o f T a b l e s v L i s t o f F i g u r e s v i Acknowledgements v i i I n t r o d u c t i o n - 1 Experiment I . . . 23 Method 24 R e s u l t s and D i s c u s s i o n 32 Experiment I I . . 35 Method 36 R e s u l t s and D i s c u s s i o n 40 Experiment I I I 43 Method A3 R e s u l t s and D i s c u s s i o n 44 G e n e r a l D i s c u s s i o n 47 F o o t n o t e s . . . 58 R e f e r e n c e Notes 60 R e f e r e n c e s 61 Appendix A 66 Appendix B.. 68 Y . LIST OF TABLES T a b l e Page I Types o f Amodal Correspondence 3 LIST OF FIGURES F i g u r e Page 1 Model o f s e n s o r y i n t e g r a t i o n r e s u l t i n g from the convergence o f s p e c i f i c s e n s o r y c h a n n e l s on t h e a s s o c i a t i o n c o r t e x 6 2 Three s t a g e s o f s e n s o r y d i f f e r e n t i a t i o n a c c o r d i n g t o Bower • (1974-a) 9 3 Schematic diagram o f d i s p l a y f o r Experiment I 25 4 P u l s e p a t t e r n s u s ed i n Experiment I 27 5 Schematic diagram o f l a b o r a t o r y arrangement 28 6 P r o p o r t i o n o f l o o k i n g t o r i g h t and l e f t 30 7 P r o p o r t i o n o f l o o k i n g t o f a s t and slow v i s u a l d i s p l a y s 31 8 Schematic diagram o f d i s p l a y f o r Experiment I I . . . . 37 9 P u l s e p a t t e r n s u s ed i n Experiments I I & I I I 39 10 Mean d u r a t i o n o f f i x a t i o n p e r t r i a l f o r groups S 1 and NS 1 41 11 Mean d u r a t i o n o f f i x a t i o n p e r t r i a l f o r groups S 0 and NS 0. . 45 v i i . ACKNOWLEDGEMENTS I would l i k e to give special thanks to Dr. Richard C. Tees and Janet Werker for giving so much assistance, encouragement and moral support throughout the project. Thanks are also due to Dr. El i n o r Ames and Dr. Tannis Williams for t h e i r w i l l i n g assistance during c r i t i c a l stages of t h i s project. Dr. Michael Chandler and Dr. John Gilbert must be thanked for serving as members of my committee. My appreciation to Janet Werker and Mary-Catherine Rooney for t h e i r attentive infant observations. I am indebted to Mary Ann King for her r e l e n t l e s s , i n t e l l i g e n t and good-natured skepticism concerning many of my ideas about infant perception. Brian Moorehead designed and b u i l t the pulse generator and display apparatus. Thanks to Ruth A l l a n for typing the manuscript. F i n a l l y , I must thank the many infants and parents who participated i n the experiments. Much of t h i s research was made possible by grants from the NSERC (PA-0179) and SSHRC(410-78-0222) of Canada to Richard C. Tees. This thesis i s dedicated to the memory.of my mother and father. 1. INTRODUCTION I n the course o f an i n d i v i d u a l ' s i n t e r a c t i o n s w i t h t h e normal environment many eve n t s o c c u r which r e s u l t i n s t i m u l a t i o n o f more t h a n one sense. Such m u l t i m o d a l s t i m u l a t i o n i m p i n g i n g on d i f f e r e n t s e n s o r y systems i s , i n some manner, c o o r d i n a t e d l e a d i n g t o a u n i f i e d p e r c e p t u a l e x p e r i e n c e o f o b j e c t s and e v e n t s . I t i s n o t c l e a r how and a t what stag e i n development the a b i l i t y t o i n t e g r a t e s e n s o r y i n f o r m a t i o n o c c u r s . A l t h o u g h s e v e r a l t h e o r i e s o f p e r c e p t u a l and c o g n i t i v e development c o n t a i n s p e c u l a t i o n s on the n a t u r e and development o f s e n s o r y i n t e g r a t i o n , s y s t e m a t i c e m p i r i c a l e v i d e n c e i s l a c k i n g , p a r t i c u l a r l y w i t h r e s p e c t t o the c a p a c i t y of i n f a n t s . The f o c u s o f t h e p r e s e n t i n v e s t i g a t i o n was t h e p r o c e s s i n g o f b i m o d a l i n f o r m a t i o n d u r i n g i n f a n c y . I n p a r t i c u l a r , the r e s e a r c h e x p l o r e d the i n f l u e n c e o f temporal synchrony and nonsynchrony o f a u d i t o r y and v i s u a l s t i m u l i on i n f a n t s ' c o o r d i n a t i o n o f t h e s e s t i m u l i . Some e f f e c t s o f s p a t i a l c o n g r u i t y and i n c o n g r u i t y between the a u d i t o r y and v i s u a l s t i m u l i were a l s o examined. A l t h o u g h t h e r e a r e numerous i n t e r r e l a t i o n s h i p s between t h e senses 1 2 i n g e n e r a l and between a u d i t i o n and v i s i o n i n p a r t i c u l a r , t h o s e o f most importance t o the p r e s e n t r e p o r t have been r e f e r r e d t o as i n t e r -s e n s o r y e q u i v a l e n c e ( T u r k e w i t z & McGuire, 1978; Lawson, 1979). Two t y p e s o f i n t e r s e n s o r y e q u i v a l e n c e have been e l a b o r a t e d . The most common c o n c e p t i o n o f i n t e r s e n s o r y e q u i v a l e n c e i s t h a t a p r o p e r t y s p e c i f i e d i n one m o d a l i t y i s t h e same as t h a t s p e c i f i e d by a n o t h e r m o d a l i t y . The p r o p e r t i e s a r e p h y s i c a l l y i d e n t i c a l but can be p e r c e i v e d t h r o u g h more than one m o d a l i t y . F o r example, a t e m p o r a l p a t t e r n can be p r e s e n t e d a u d i t o r i l y , v i s u a l l y and f a c t u a l l y . S i n c e t h e same t e m p o r a l p a t t e r n can be p r e s e n t e d t o each o f t h e s e senses i t i s p o s s i b l e t h a t t h e 2. t e m p o r a l p a t t e r n can be a b s t r a c t e d r e g a r d l e s s o f t h e mode o f s p e c i f i c a -t i o n . Such p r o p e r t i e s have been c a l l e d "amodal", d e f i n e d as " h i g h e r o r d e r r e l a t i o n a l s t i m u l a t i o n which i s n o t s p e c i f i c t o a m o d a l i t y ( G i b s o n , 1969; p. 219)." Amodal i n f o r m a t i o n can i n c l u d e a number o f s t i m u l u s dimensions i n c l u d i n g shape, t e x t u r e , movement, d u r a t i o n , l o c a t i o n and number. Some o f t h e most g e n e r a l t y p e s o f amodal r e l a t i o n s a r e d e p i c t e d i n T a b l e I. R e c e n t l y , i t has been s u g g e s t e d (Mendelson, Note 1; S p e l k e , Note 2) t h a t the common s t r u c t u r a l o r amodal p r o p e r t i e s o f human environments i n f l u e n c e p e r c e p t u a l a c t i v i t y i n v e r y young i n f a n t s . Furthermore, a c t i v i t y prompted by amodal f e a t u r e s may be a f o u n d a t i o n f o r l e a r n i n g more a r b i t r a r y r e l a t i o n s such as th o s e between p a r t i c u l a r sounds and p a r t i c u l a r v i s u a l events ( e g . , a mother's f a c e and v o i c e ) . T h i s r e l a t e s d i r e c t l y t o t h e second type:' o f i n t e r s e n s o r y e q u i v a l e n c e . I n t e r s e n s o r y e q u i v a l e n c e has a l s o been used t o r e f e r t o the p e r c e p t i o n t h a t q u a l i t a t i v e l y d i f f e r e n t p r o p e r t i e s o f an o b j e c t can be used i n t e r -changeably t o i d e n t i f y t h e o b j e c t (Lawson, 1979; T u r k e w i t z & McGuire, 1978). F o r example, as mentioned above, a f a c e and a v o i c e can i n d e p e n d e n t l y i d e n t i f y a p a r t i c u l a r p e r s o n . I n t h i s case t h e i n f o r m a t i o n i d e n t i f i e s a common source b u t the a t t r i b u t e s a r e p h y s i c a l l y v e r y d i f f e r e n t . Thus two types of i n t e r s e n s o r y e q u i v a l e n c e can be d i s t i n g u i s h e d ; one based on t h e common s t r u c t u r a l c h a r a c t e r i s t i c s o f i n f o r m a t i o n r e c e i v e d t h r o u g h d i f f e r e n t m o d a l i t i e s , t h e o t h e r i n which q u a l i t a t i v e l y d i f f e r e n t k i n d s o f i n f o r m a t i o n s p e c i f y a common s o u r c e . Both t y p e s o f e q u i v a l e n c e have l o n g been a t o p i c f o r t h e o r e t i c a l s p e c u l a t i o n and more r e c e n t l y a s u b j e c t f o r e m p i r i c a l r e s e a r c h . P h i l o s o p h e r s and s c i e n t i s t s f rom a t l e a s t t h e time o f A r i s t o t l e have s p e c u l a t e d on t h e i n t e r r e l a t i o n s o f t h e s e n s o r y systems (Marks, 1978). A r i s t o t l e d e v e l o p e d t h e n o t i o n o f a "common sense" which 3. T a b l e I Types o f M o d a l Correspondences (From Mendelson, Note l ) 1. VALUES ALONG CONTINUA a. Time - Onset - Independent o f Space b. Space - P o s i t i o n - Independent o f Time c. I n t e n s i t y - Independent o f Time and Space 2. DISCONTINUITIES a. Temporal E v e n t s - D u r a t i o n b. S p a t i a l E v e n t s - L o c a t i o n c. M o d u l a t i o n o f I n t e n s i t y - I n Time and/or Space 3. PATTERNS OF DISCONTINUITY a. Rhythm - P a t t e r n o v e r Time b. Form - P a t t e r n over Space c. Movement - P a t t e r n o v e r Time and Space -4. RATES OF PATTERN a. Tempo - Rate o v e r Time b. T e x t u r e - Rate o v e r Space c. Speed - Rate o v e r Time and Space 5. CHANGES OF RATE a. Change of Tempo - Change over Time b. T e x t u r e G r a d i e n t s - Change o v e r Space c. A c c e l e r a t i o n - Change o v e r Time and Space A. a p p r e c i a t e d t h e "common s e n s i b l e s " . The common s e n s i b l e s were t h o s e p r o p e r t i e s o f s e n s a t i o n r e p r e s e n t i n g g e n e r a l a s p e c t s o f t h e w o r l d which c o u l d be apprehended by any o f t h e sens e s . These common s e n s i b l e s i n c l u d e d motion, r e s t , number, form, magnitude and u n i t y . The common sense o c c u p i e d a h i g h e r " l e v e l " t h a n . t h e s p e c i f i c senses and was s e n s i t i v e t o q u a l i t i e s l i k e number o r shape w h i l e t h e s p e c i f i c senses were r e s p o n -s i v e t o p r o p e r t i e s l i k e c o l o u r o r odour. The d i s t i n c t i o n between t h e common sense and t h e s p e c i f i c senses i s s i m i l a r t o the o l d d i s t i n c t i o n between p e r c e p t i o n . a n d s e n s a t i o n . I n terms o f s t i m u l u s d e s c r i p t i o n t h e common s e n s i b l e s b e a r an obvious s i m i l a r i t y t o amodal i n f o r m a t i o n . More r e c e n t l y t h e i n t e r e s t o f p h i l o s o p h e r s i n i n t e r s e n s o r y i n t e g r a t i o n had l e d them t o ask whether a p e r s o n b o r n b l i n d and r e s t o r e d t o s i g h t i n a d u l t h o o d would be a b l e t o name forms p r e s e n t e d v i s u a l l y which 3 had p r e v i o u s l y been known o n l y b y t o u c h . S u c c e s s f u l naming would i m p l y v i s u a l d i s c r i m i n a t i o n o f t h e forms and t h e a b i l i t y t o . r e l a t e p r e v i o u s t a c t i l e i m p r e s s i o n s o r r e p r e s e n t a t i o n s t o t h e v i s u a l i m p r e s s i o n . A l t h o u g h modern r e s e a r c h on s e l e c t i v e r e a r i n g , p e r c e p t u a l d e p r i v a t i o n and c a t a r a c t o p e r a t i o n s has shown t h a t t h i s q u e s t i o n was somewhat n a i v e i n i t s i m p l i c i t assumptions, i t was one o f t h e f i r s t q u e s t i o n s asked about i n t e r s e n s o r y e q u i v a l e n c e which c o u l d l e a d t o e m p i r i c a l i n v e s t i g a t i o n s . Furthermore, i t was concerned w i t h t h e manner i n which our a b i l i t i e s t o p e r c e i v e t h e w o r l d d e v e l o p . Two g e n e r a l approaches t o t h e development o f i n t e r m o d a l r e l a t i o n s h i p s have been emphasized (McGurk & MacDonald, 1978). One approach d e s c r i b e s i n t e r s e n s o r y development, b o t h p h y l o g e n e t i c a l l y and o n t o g . e n e t i c a l l y , as i n c r e a s i n g i n t e g r a t i o n o f i n i t i a l l y s e p a r a t e s e n s o r y m o d a l i t i e s . ' A c c o r d i n g t o t h i s p o s i t i o n s e p a r a t e s e n s o r y systems m a x i m a l l y r e s p o n s i v e t o d i f f e r e n t t y p e s o f energy e v o l v e d a t an e a r l y s t a g e i n phylogeny. 5. The different phyletic levels exhibit different degrees of organization among each of the sensory systems. As the evolutionary scale i s ascended an increase i n the capacity for intersensory integration i s thought to occur. However, as McGurk and MacDonald (1978) have observed, comparative evidence supportive of th i s position i s hard to f i n d . In general, though, i t does seem that there i s increasing c o r t i c a l convergence of different afferent systems. As you ascend the phylogenetic scale increasingly more neural tissue p o t e n t i a l l y subserves intersensory r e l a t i o n s , p a r t i -c ularly i n the cerebral cortex. Variants of t h i s view have been i n f l u e n t i a l i n the recent history of psychology. For instance Diamond and H a l l (1969) have argued that''-the supposed expansion of the association cortex interposed between the sensory and motor zones f i t the view prevailing i n psychology i n the early twentieth century. According to t h i s view integration between the senses required a neurological process that r e l i e d upon having the neural counterpart of modality - s p e c i f i c sensation available. Two premises were important: l ) s p e c i f i c sensory channels were somehow represented i n the brain, and 2) that i n order for complex behavioural and cognitive tasks to be accomplished, a c t i v i t y of sensory areas must be associated i n some other areas of the brain (Diamond & H a l l , 1969, p. 252). The simple model envisioned i s presented i n Figure 1. In recent psychological theorizing Birch and Lefford (1963; 1967) have put forward a si m i l a r view which draws on p a r a l l e l s between phylogeny and ontogeny. They have stated that: as one ascends i n the vertebrate series from f i s h to man the unimodal sensory control of behavior comes to be superseded by multimodal and intersensory control mechanisms (1963, p. 3). Their position regarding perceptual development i n humans has been stated as follows: 6. Thalamic Association Cortex Fig.I. Model of sensory integration resulting from the convergence of specific sensory channels on the association cortex. 7. i n f o r m a t i o n d e r i v e d from p r o x i m o c e p t i v e i n p u t i s dominant i n c o n t r o l l i n g t h e a c t i o n s o f i n f a n t s . However, w i t h age, p r o x i m o c e p t i o n comes t o be i n c r e a s i n g l y r e p l a c e d by t e l o r e c e p t o r c o n t r o l systems. . . . S i m u l t a n e o u s l y w i t h the emergence o f t e l o -r e c e p t o r preeminance, a second mechanism o f i n p u t o r g a n i z a t i o n seems t o be e v o l v i n g . I t c o n s i s t s o f t h e i n c r e a s i n g tendency of t h e s e p a r a t e s e n s o r y m o d a l i t i e s t o i n t e g r a t e w i t h one a n o t h e r , and o f o r g a n i z e d and d i r e c t e d a c t i o n t o be s ubserved by i n t e r s e n s o r y o r m u l t i m o d a l p a t t e r n i n g r a t h e r t h a n unimodal p a t t e r n i n g . (1967, p. 5-6) The p o s i t i o n o f B i r c h and L e f f o r d i s an e x p r e s s i o n o f t h e c l a s s i c e m p i r i c i s t v i ew o f i n t e r s e n s o r y development ( F r i e d e s , 1974) i n which the i n p u t f r o m s e p a r a t e s e n s o r y m o d a l i t i e s form t h e b a s i c b u i l d i n g b l o c k s of p e r c e p t i o n . I n i t i a l l y t h e s e n s o r y m o d a l i t i e s a r e u n c o o r d i n -a t e d , b u t w i t h development t h e s e p a r a t e s e n s o r y systems become I n t e g r a t e d , l e a d i n g ^ u l t i m a t e l y t o a u n i f i e d p e r c e p t u a l w o r l d . An a l t e r n a t i v e p o s i t i o n t h a t t h e r e i s a p r i m i t i v e u n i t y of t h e senses has been p r e s e n t e d by Bower (1974a; 1974b; 1978). Development, b o t h o n t o g e n e t i c a l l y and p h y l o g e n e t i c a l l y , would thus p r o c e e d as a p r o c e s s o f d i f f e r e n t i a t i o n o f an i n i t i a l u n i t a r y "supra-modal" p e r c e p t u a l space. Bower (1974b) argues t h a t t h e p e r c e p t u a l system e v o l v e d t o r e s p o n d t o s i g n i f i c a n t a s p e c t s o f the w o r l d . The p e r c e p t u a l system does n o t r e s p o n d t o i n p u t s from s p e c i f i c senses as such, b u t r e sponds t o changes and p a t t e r n s o f changes which can be p r e s e n t e d t h r o u g h any m o d a l i t y . These amodal s t i m u l i i n c l u d e t r a n s i t i o n s , g r a d i e n t s of change and t e m p o r a l d i f f e r e n c e s . These are th e r e a l l y s i g n i f i c a n t f e a t u r e s s i n c e t h e y s i g n a l common s t r u c t u r a l p r o p e r t i e s o f t h e w o r l d . E a r l y i n development, o n t o g e n e t i c a l l y and p h y l o g e n e t i c a l l y , p e r c e p t u a l u n i t y i s p r i m a r y . S e n s o r y u n i t y d i f f e r e n t i a t e s w i t h development. Bower s t a t e s t h a t "as organisms e v o l v e d , and p a r t i c u l a r l y as t h e y began t o grow t h e i r p a r t s , a t d i f f e r e n t r a t e s and t o d i f f e r e n t - s i z e s , t h i s 8. e a r l y u n i t y had t o be abandoned. I t i s t h e f a c t o f growth, w i t h d i f f e r e n t growth r a t e s o f sense organs and e f f e c t o r organs t h a t makes u n i t y imposs-i b l e f o r mammals w i t h t h e i r complex s k e l e t o n s (1974b, p. 515)." The o n t o g e n e t i c problem i s one of a c c o u n t i n g f o r d i f f e r e n t i a t i o n and a r t i c u -l a t i o n o f t h e d i f f e r e n t m o d a l i t i e s a l t h o u g h , a c c o r d i n g t o Bower (1978, p. 101), "we have o n l y the v a g u e s t c l u e about t h e p s y c h o l o g i c a l events which cause d i f f e r e n t i a t i o n . " Bower's c o n c e p t i o n o f s e n s o r y d i f f e r e n -t i a t i o n i s i l l u s t r a t e d i n F i g u r e 2. To r e c a p i t u l a t e , t h e r e a r e two major hypotheses c o n c e r n i n g e a r l y p e r c e p t u a l development which p o s t u l a t e s i g n i f i c a n t changes i n p e r c e p t i o n as the organism matures. A c c o r d i n g t o one view t h e senses a r e i n i t i a l l y s e p a r a t e and development of p e r c e p t u a l c a p a b i l i t i e s o c c u r s as a r e s u l t o f t h e g r a d u a l c o o r d i n a t i o n o f i n p u t s from d i f f e r e n t m o d a l i t i e s . A second view suggests t h a t development p r o c e e d s as a p r o c e s s o f d i f f e r e n -t i a t i o n o f an i n i t i a l supramodal space which, i n i t i a l l y , "does not r e g i s t e r l i g h t s o r sounds o r s m e l l s o r t o u c h e s , o r any o t h e r o f t h e s p e c i f i c e n e r g i e s o f n e r v e s (Bower, 1978, p. 9 4 ) . " A t h i r d p o s i t i o n , which i s not r e a l l y a t h e o r y o f p e r c e p t u a l d e v e l o p -ment, stems from t h e t h e o r i z i n g o f J . J . Gibson- (1966) and has been a p p l i e d t o i n f a n t b i m o d a l p e r c e p t i o n by S p e l k e (Note 4 ) . A c c o r d i n g t o t h i s p o s i t i o n p e r c e i v i n g i s the d e t e c t i o n o f i n v a r i a n t s i n s t i m u l a t i o n . F o r i n s t a n c e , s i g h t s and sounds d i s p l a y s p a t i a l . a n d t e m p o r a l c o r r e s -pondences t o which our p e r c e p t u a l systems a r e a t t u n e d . Such c o r r e s p o n d e n c e s are g u a r a n t e e d by t h e n a t u r e o f t h e p h y s i c a l w o r l d and an i n v a r i a n t -d e t e c t i o n t h e o r y o f p e r c e p t i o n seeks t o s p e c i f y w hich o f t h e s e r e l a t i o n s h i p s a r e u s e d by t h e o b s e r v e r . The t h e o r y i s not d i r e c t l y c o ncerned w i t h p e r c e p t u a l development. Rather, t h e c o n c e r n i s w i t h what p e r c e p t i o n i s ; namely,, t h e d e t e c t i o n o f i n v a r i a n t s . The p o s i t i o n does not deny t h a t Visual input Tactual input Auditory input Visual i n p u t Visual analysis Supramodal object perception Tactual analysis Auditory analysis Auditory input Tactual input Visual behavior Auditory behavior Auditory analysis Auditory input Manual behavior Fig.2. Three stages of sensory differentiation according to Bower (1974a,R|2O):0\) birth -4.5 months;(B}4.5 "6.5 months;(C)6.5 months and on. 10. perceptual systems mature, but i t does deny that the nature of perception changes. The process i s always the same as the perceptual systems are inherently organized to detect invariants. Accordingly, the task for the developmental researcher i s to specify which invariants are used and when sensitivity to such invariants occur. According to Spelke (Note 4) young perceivers experience neither a world of unrelated visual and auditory sensations, nor a world of undifferentiated, hetero-modal impressions, but appear to perceive a world of objects and events much as adults do. As soon as one attempts to compare and evaluate the various theoreti-cal alternatives one is immediately beset with many problems. For instance, there i s the fact that not a l l types of intersensory equivalence are the same. For example, Davenport (1976) has reported on research which demonstrates cross-modal transfer of an intensity or pulse pattern discrimination i n prosimiams, rats and rabbits. No studies, however, have found evidence for visual-haptic object equivalence i n animals other than monkeys. These phylogenetie differences are probably reflected, at least to a limited degree, in ontogenetic development. Ideally the various types of intersensory integration might be ordered along some dimensions of complexity. These dimensions would include, for instance, the neural mechanisms involved, the kind and number of relevant stimulus dimensions, the relative adeptness of the modalities involved (Freides, 1974) and the role of abstract coding systems such as language. With such a descriptive system the, probably different, developmental histories of various types of intersensory equivalence could be delineated. Now, unless the theories are addressing the same or similar types of sensory coordination then direct comparison is d i f f i c u l t . For example, i t i s not unlikely that intersensory coordination as discussed by Bower, involving 11. temporal differences, gradients of change, etc. could be quite different from the cross-modal equivalence of complex geometrical forms as discussed by Birch and Lefford. Perhaps Spelke's (Note 4) programmatic proposal is a reasonable strategy to begin with. Accordingly, the investigator of infant perception might focus on a relatively limited domain i n order to assess sensitivity to various types of intersensory equivalence within that domain. Although, this would not necessarily lead to a well developed theory of intersensory integration, i n general, assuming a more limited approach could ultimately be more f r u i t f u l . If so, our best approach i s to begin by examining those aspects of auditory-visual integration that have been investigated to date. In general, the research indicates that the auditory and visual systems do not act independently i n infancy, but interact i n a variety of ways. Three main areas of research need to be described in some detail: the effect of auditory stimulation on visual localization behaviour, reactions to incongruous visual and auditory information from persons and objects, and the influence of common temporal patterns between visual and auditory events on perceptual activity. Spatial location would appear to be an amodal property par excellence. Although there are auditory, visual, proprioceptive and olfactory spaces they are at least roughly coordinated. We can ask, however, whether there are modality-specific spaces which undergo a process of translation when referring one sense to another or, alternatively, whether there i s one overall spatial framework which could be called a common space? Auerbach and Sperling (1974) provide psychophysical evidence which supports the common space hypothesis for visual-auditory location i n young human adults. In their study subjects had to discriminate the spatial direction of two sound stimuli, two light stimuli, and a 12. sound and l i g h t s t i m u l u s . Because t h e r e was no v a r i a b i l i t y i n judgements which c o u l d be a t t r i b u t e d t o t r a n s l a t i n g from one s p a t i a l r e p r e s e n t a t i o n t o a n o t h e r , i t was argued t h a t a u d i t o r y and v i s u a l s e n s a t i o n s were r e f e r r e d t o a common p e r c e p t u a l space. I n terms o f p h y s i o l o g i c a l e v i d e n c e , M o r r e l l (1972) r e p o r t e d t h a t 70/169 c e l l s r e c o r d e d f r o m areas 18 and 19 o f t h e v i s u a l c o r t i c e s o f c a t s were r e s p o n s i v e t o b o t h a c o u s t i c a l and v i s u a l s t i m u l a t i o n . The response was such t h a t t h e a c o u s t i c a l r e c e p t i v e f i e l d was "mapped onto" t h e r e c e p t i v e f i e l d o r g a n -i z a t i o n f o r v i s i o n as a s e r i e s o f v e r t i c a l l y o r i e n t e d s t r i p e s . Moreover, c e l l s s e n s i t i v e t o moving s t i m u l i were u s u a l l y s e l e c t i v e i n d i r e c t i o n and t h e d i r e c t i o n was t h e same f o r b o t h m o d a l i t i e s . W i c k e l g r e n (1971) o b t a i n e d s i m i l a r r e s u l t s r e c o r d i n g from the i n t e r m e d i a t e g r e y area:', i n the s u p e r i o r c o l l i c u i u s o f t h e a d u l t c a t . A l t h o u g h a few r e s e a r c h r e p o r t s o f t h i s k i n d h a r d l y p r o v i d e d e f i n i t i v e e v i d e n c e i n su p p o r t o f the common space h y p o t h e s i s t h e y a r e a t l e a s t s u g g e s t i v e . I f t h e r e i s some commonality between a u d i t o r y and v i s u a l space i n i n f a n t s , s t i m u l a t i o n i n one m o d a l i t y might i n f l u e n c e a c t i v i t y i n t h e o t h e r . S p e c i f i c a l l y , a u d i t o r y s t i m u l a t i o n c o u l d provoke v i s u a l l o c a l i z a -t i o n a ttempts. T h i s was demonstrated i n t h e c l a s s i c s t u d y by Wertheimer (1961). He found t h a t a newborn baby r e l i a b l y t u r n e d h e r eyes i n t h e same d i r e c t i o n as a c l i c k sound which was p r e s e n t e d randomly t o e i t h e r e a r . However, McGurk, Turnure and C r e i g h t o n (1977) o b s e r v e d n e o n a t a l o c u l o m otor b e h a v i o u r under v a r i o u s c o n d i t i o n s o f v i s u a l and a u d i t o r y s t i m u l a t i o n . They were not a b l e t o r e p l i c a t e Wertheimer's r e s u l t s and a l s o showed t h a t v i s u a l t r a c k i n g was not i n f l u e n c e d by t h e a d d i t i o n of moving o r s t a t i o n a r y a u d i t o r y s t i m u l i . They argued t h a t t h e i r r e s u l t s suggest t h e m o d a l i t i e s a r e i n i t i a l l y independent and hence "the d e v e l o p -mental problem i s one o f a c c o u n t i n g f o r s y n t h e s i s between p e r c e p t u a l 13. m o d a l i t i e s r a t h e r t h a n o f a c c o u n t i n g f o r t h e d i f f e r e n t i a t i o n o f systems t h a t a r e i n n a t e l y u n i f i e d " (McGurk e t a l . , 1977, p. 143). S i m i l a r l y , B u t t e r w o r t h and C a s t i l l o (1976) c o u l d n o t r e p l i c a t e Wertheimer's r e s u l t s but d i d f i n d t h a t most o f the eye movements were c o n t r a l a t e r a l t o the l o c u s o f a u d i t o r y s t i m u l a t i o n . N e v e r t h e l e s s , two r e c e n t s t u d i e s have c o n f i r m e d Wertheimer's o r i g i n a l o b s e r v a t i o n . I n a s e r i e s o f s t u d i e s u s i n g c o r n e a l r e f l e c t i o n photography (Mendelson & H a i t h , 1976) i t was shown t h a t v i s u a l a c t i v i t y i n neonates was i n f l u e n c e d by a u d i t o r y s t i m u l a t i o n . The r e l a t i o n was s p a t i a l l y r e l e v a n t i n t h a t l a t e r a l l y p r e s e n t e d sounds r e s u l t e d i n i n i t i a l f i x a t i o n s h i f t s toward the s o u r c e o f sound. I n a n o t h e r i n v e s t i g a t i o n o f ' l o c a l i z a t i o n . ( M u i r , F i e l d & S i n c l a i r , Note 3) neonates were p r e s e n t e d w i t h two r a t t l e s , one o p p o s i t e each e a r . The r a t t l e s were moved s i m u l t a n e o u s l y , b u t o n l y one produced sound. The i n f a n t s t u r n e d more o f t e n t o the n o i s y r a t t l e ( t h e y o b t a i n e d a s i m i l a r r e s u l t when t h e sound was p r e s e n t e d t h r o u g h speakers r a t h e r t h a n r a t t l e s ). There are i m p o r t a n t d i f f e r e n c e s between the s t u d i e s of Mendelson and H a i t h and M u i r and h i s coworkers and t h ose o f McGurk e t a l . which c o u l d account f o r the d i f f e r e n t r e s u l t s . Mendelson and H a i t h and M u i r e t a l . used r e l a t i v e l y c o n t i n u o u s a u d i t o r y s t i m u l a t i o n ; a 40-secohd . p r e s e n t a t i o n of a r e p e a t i n g 16 second l o o p o f a p e r s o n r e a d i n g a poem and t h e p r e s e n t a t i o n o f a n o i s y r a t t l e f o r 20 second i n t e r v a l s . McGurk e t a l . u s ed b r i e f c l i c k s as t h e i r a u d i t o r y s t i m u l i and o n l y r e c o r d e d eye movements which o c c u r r e d w i t h i n 3 seconds o f s t i m u l u s o n s e t . The b r i e f o b s e r v a t i o n p e r i o d and s h o r t s t i m u l u s p r e s e n t a t i o n made f o r a v e r y demanding t e s t o f l o c a l i z a t i o n , p a r t i c u l a r l y g i v e n the r a t h e r " s l u g g i s h " motor system o f the neonate. 14. I t has been argued (Lawson, 1979; McGurk e t a l . , 1977) t h a t t h e s e l o c a l i z a t i o n r e s p o n s e s i n d i c a t e r e f l e x i v e o c u l o motor r e s p o n d i n g r a t h e r t h a n h i g h e r - l e v e l a u d i t o r y - v i s u a l i n t e g r a t i o n . Support f o r t h i s i n t e r p r e t a t i o n comes from s t u d i e s w i t h b o t h b l i n d and s i g h t e d i n f a n t s . With' s i g h t e d neonates i t has been demonstrated t h a t v i s u a l l o c a l i z a t i o n o f sound s o u r c e s can be e l i c i t e d whether an i n f a n t ' s eyes a r e open o r c l o s e d ( T u r k e w i t z , B i r c h , Moreau, Levy, & C o r n w e l l , 1966). F r a i b e r g (1977) has r e p o r t e d on r e f l e x - t u r n i n g of t h e eye toward a sound source i n a b l i n d i n f a n t a t two months o f age. A t s i x months, as was t r u e f o r o t h e r b l i n d i n f a n t s , the baby d i d n o t turn, toward a s o u r c e of sound. I t would appear t h e n t h a t t h i s i n i t i a l o c ulomotor b e h a v i o u r , which may be r e f l e x i v e , i s i n need o f v i s u a l i n p u t i n o r d e r t o be m a i n t a i n e d . N o r m a l l y , however, such b e h a v i o u r may have s i g n i f i c a n t consequences f o r " h i g h e r - l e v e l " a u d i t o r y - r v i s u a l c o o r d i n a t i o n . A s i g h t e d i n f a n t l o o k i n g i n t h e d i r e c t i o n o f a sound s o u r c e r e c e i v e s s i m u l t a n e o u s b i m o d a l i n f o r m a t i o n about t h e v i s u a l and a u d i t o r y c h a r a c t e r i s t i c s o f an e v e n t . T h i s b i m o d a l s p e c i f i c a t i o n may a s s i s t i n t h e e s t a b l i s h m e n t o f a "cross-modal d i c t i o n a r y " ( B r y a n t , 1974) between p a r t i c u l a r s i g h t s and sounds. As such, q u a l i t a t i v e l y d i f f e r e n t c h a r a c t e r i s t i c s of an o b j e c t c o u l d come t o i n d e p e n d e n t l y i d e n t i f y t h e o b j e c t . One o f t h e " o b j e c t s " w i t h which i n f a n t s have a g r e a t d e a l o f e x p e r i e n c e i s the mother. The r e c o g n i t i o n o f c e r t a i n c h a r a c t e r i s t i c s o f t h e mother has been demonstrated i n v e r y young i n f a n t s . I t has been shown t h a t i n f a n t s 20 t o 30 days o l d can d i s c r i m i n a t e between t h e i r mother's v o i c e and v o i c e s o f o t h e r females ( M i l l s & M e l h u i s h , 1974). Other r e s e a r c h i n d i c a t e s t h a t i n f a n t s as young as 2 weeks o f age can d i s t i n g u i s h t h e i r mother from i n a n i m a t e o b j e c t s o r from o t h e r female f a c e s ( C a r p e n t e r , 15. T e cce, S t e c h l e r , & Freedman, 1970). An i n t e r e s t i n g q u e s t i o n i s whether t h e s e c h a r a c t e r i s t i c s are u n i f i e d t o form a common s o u r c e . I n an e f f o r t t o answer t h i s q u e s t i o n s e v e r a l i n v e s t i g a t o r s have c o n c e n t r a t e d on i n f a n t s ' r e s p o n s e s t o t h e "break-up o f t h e l o c a t i o n o f mother's f a c e and v o i c e . T h i s can be a c c o m p l i s h e d e a s i l y w i t h microphone and speaker arrangements. Those employing t h i s paradigm have argued t h a t i f m u l t i -modal i n f o r m a t i o n a v a i l a b l e i n o b j e c t s i s i n t e g r a t e d by t h e i n f a n t t h e n t h e y s h o u l d be " s u r p r i s e d " o r " d i s t r e s s e d " by t h e break-up o f such i n f o r m a t i o n . I n a w i d e l y d i s c u s s e d r e p o r t , Aronson and Rosenbloom (1971) c l a i m e d t o have shown a p r i m i t i v e u n i t y o f v i s i o n and a u d i t i o n i n i n f a n t s as young as 30 days. They measured i n f a n t s ' r e a c t i o n s (number o f tongue p r o t r u s i o n s ) t o s p a t i a l l y c o i n c i d e n t and s p a t i a l l y s e p a r a t e d p r e s e n t a t i o n s o f mother's f a c e and v o i c e . Having o b t a i n e d some p o s i t i v e e v i d e n c e t h e au t h o r s s u g g e s t e d t h a t i n f a n t p e r c e p t i o n o c c u r s w i t h i n a common a u d i t o r y and v i s u a l space. McGurk and Lewis (1974) s u b s e q u e n t l y p o i n t e d out t h a t Aronson and Rosenbloom d i d not use a v a l i d a t e d r e s p o n s e measure and had an e x p e r i -m ental d e s i g n which l a c k e d c o u n t e r b a l a n c e d p r e s e n t a t i o n . U s i n g an improved methodology, McGurk and Lewis were u n a b l e t o r e p l i c a t e t h e Aronson and Rosenbloom stu d y . They c o n c l u d e d t h a t "the n a t u r e and development o f a u d i o v i s u a l c o o r d i n a t i o n d u r i n g e a r l y i n f a n c y remains an open q u e s t i o n " (McGurk &.Lewis, 1974, p. 650). More r e c e n t l y Condry, Haltom and N e i s s e r (1977) were a l s o unable t o r e p l i c a t e t h e Aronson and Rosenbloom f i n d i n g s . These "break-up" s t u d i e s have employed a method which i s based on the assumption t h a t i f i n f a n t s combine a u d i t o r y and v i s u a l i n f o r m a t i o n about t h e i r mother t h e y w i l l be d i s t r e s s e d o r s u r p r i s e d by a s p a t i a l 16. d i s c r e p a n c y . F a i l u r e t o o b t a i n p o s i t i v e r e s u l t s may mean t h a t t h e i n f a n t s do not combine such i n f o r m a t i o n o r t h a t t h e y a r e n o t d i s t r e s s e d o r s u r p r i s e d by such a break-up. The number of b e h a v i o u r a l measures s u p p o s e d l y r e l a t e d t o d i s t r e s s and/or s u r p r i s e makes assessment d i f f i c u l t . Such measures have i n c l u d e d tongue p r o t r u s i o n ( A r o n s o n & Roseribloom, 1971; Condry e t a l . , 1977), f r e q u e n c y o f s m i l i n g , v o c a l i z i n g , f r e t t i n g o r c r y i n g (.McGurk & Lewis, 1972). A l t h o u g h mothers u n d o u b t e d l y are v e r y s i g n i f i c a n t t o t h e i r i n f a n t s t h e s t u d i e s d e s c r i b e d above p r o v i d e l i t t l e i n f o r m a t i o n about t h e s t i m u l u s c h a r a c t e r i s t i c s which may be i m p o r t a n t i n l i n k i n g complex v i s u a l and a u d i t o r y e v e n t s . One d i m e n s i o n t h a t has o f t e n been i m p l i c a t e d i n t h e p e r c e p t i o n o f a u d i t o r y - v i s u a l correspondence i s the t e m p o r a l domain. C o n s i d e r f o r i n s t a n c e t h e r a t h e r d i s c o n c e r t i n g e x p e r i e n c e o f v i e w i n g a p o o r l y dubbed f o r e i g n f i l m . One's a t t e n t i o n i s c o n s t a n t l y drawn t o the t e m p o r a l r e l a t i o n s h i p between t h e movement o f t h e s p e a k e r s ' l i p s and t h e sounds o f speech. S i n c e we a r e accustomed t o a p r e c i s e c o rrespondence between speech sounds and mouth movements we f i n d t h e " s l i p p a g e " i n t h e dubbed f i l m annoying. T h i s p r o s a i c example i l l u s t r a t e s our s e n s i t i v i t y t o such b i m o d a l i n p u t and the r e s e a r c h o f Dodd (1977), McGurk and MacDonald (1976), and R i e s b e r g (1978) h a s shown t h a t th e i n f o r m a t i o n a f f o r d e d by l i p movements a s s i s t s i n t h e p e r c e p t i o n o f speech. U s i n g r e l a t i v e l y a b s t r a c t l i g h t and sound p a t t e r n s i t has a l s o been shown t h a t synchrony i s t h e most i m p o r t a n t v a r i a b l e f o r o b t a i n i n g r e c a l -i b r a t i o n o f a u d i t o r y and v i s u a l l o c a t i o n s (Radeau. & B e r t e l s o n , 1977). Demany, McKenzie and V u r p i l l o t (1977) and Chang and Trehub (1977) have shown i n a s e r i e s o f s t u d i e s t h a t i n f a n t s 2 1/2 and 5 months o l d , r e s p e c t i v e l y , are s e n s i t i v e t o t e m p o r a l g r o u p i n g s i n a u d i t o r y p a t t e r n s . . I n b o t h cases i n f a n t s were h a b i t u a t e d t o one t e m p o r a l p a t t e r n 17. and showed s i g n i f i c a n t d i s h a b i t u a t i o n t o a n o t h e r . There i s a l s o one r e p o r t i n t h e l i t e r a t u r e on a u d i t o r y - v i s u a l t r a n s f e r i n i n f a n t s . A l l e n , Walker, Symonds and M a r c e l l (1977) p r e s e n t e d two groups o f 7-month-old i n f a n t s w i t h a s t a n d a r d v i s u a l or a u d i t o r y t e m p o r a l sequence. A f t e r 15 h a b i u t a t i o n t r i a l s t h e i n f a n t s were d i v i d e d i n t o f o u r subgroups i n w hich the p r e s e n t a t i o n m o d a l i t y and/or t h e t e m p o r a l sequence remained the same or d i f f e r e n t . I n f a n t s showed g r e a t e r r e s p o n s e r e c o v e r y ( i n c r e a s e i n h e a r t r a t e o r s k i n p o t e n t i a l ) w i t h a d i f f e r e n t t e m p o r a l sequence r e g a r d l e s s o f t h e s e n s o r y m o d a l i t y i n which the t e m p o r a l sequences were p r e s e n t e d . Thus by seven months t h e i n f a n t s were c a p a b l e of p e r c e i v i n g e q u i v a l e n c e s and d i f f e r e n c e s i n t e m p o r a l sequence i n f o r m a t i o n w i t h i n and a c r o s s m o d a l i t i e s . S p e l k e (1976, Note 2, Note 4) and B a h r i c k , Walker and N e i s s e r (Note 5) have adopted an i n t e r e s t i n g v a r i a t i o n o f t h e p r e f e r e n c e paradigm f o r i n v e s t i g a t i n g i n f a n t s ' s e n s i t i v i t y t o i n t e r m o d a l r e l a t i o n s . These a u t h o r s have assumed t h a t i n f a n t s r e c e i v i n g i n f o r m a t i o n f r o m one m o d a l i t y w i l l e x p l o r e i n o r d e r t o o b t a i n i n f o r m a t i o n from a n o t h e r . F o r i n s t a n c e , an i n f a n t might seek v i s u a l i n f o r m a t i o n about a u d i t o r y events i n o r d e r t o f o l l o w t h e events i n two m o d a l i t i e s . The p r o c e d u r e has been t o p r e s e n t i n f a n t s w i t h two m o t i o n p i c t u r e f i l m s o f " n a t u r a l e v e n t s . " The f i l m s a r e s e p a r a t e d w i t h t h e s o u n d t r a c k o f one o f t h e f i l m s emanating from a speaker p l a c e d between the f i l m s . The i n f a n t i s p l a c e d midway between t h e f i l m s i n f r o n t o f t h e c o n c e a l e d speaker. V a r i o u s measures o f the i n f a n t ' s l o o k i n g a t each f i l m are u s e d t o a s s e s s t h e i n f a n t ' s s e n s i t i v i t y t o t h e r e l a t i o n s h i p between the s o u n d t r a c k and t h e r e l e v a n t f i l m . Measures of p r e f e r e n c e and s e a r c h b e h a v i o u r have i n c l u d e d mean l o o k i n g time,-- d i r e c t i o n o f f i r s t l o o k , l a t e n c y o f f i r s t l o o k and t h e number o f t r i a l s on which t h e i n f a n t l o o k e d f o r any d u r a t i o n t o t h e 18. r e l e v a n t f i l m w i t h i n a s p e c i f i e d time p e r i o d . I n one r e p o r t ( S p e l k e , 1976) i n f a n t s aged 4 months were shown two motion p i c t u r e f i l m s : one d e p i c t e d a woman p l a y i n g "peekaboo" and t h e o t h e r a wooden b a t o n s t r i k i n g a wood b l o c k o r tambourine r e p e a t e d l y and r h y t h m i c a l l y . R e s u l t s i n d i c a t e d t h a t t h e i n f a n t s l o o k e d p r i m a r i l y a t the event s p e c i f i e d by t h e r e l e v a n t s o u n d t r a c k . These r e s u l t s c o u l d have been o b t a i n e d , however, i f t h e i n f a n t o n l y l i n k e d the human v o i c e sound w i t h t h e motion p i c t u r e o f t h e woman: n o t an u n l i k e l y assumption g i v e n some r e c e n t r e s u l t s ( S p e l k e & Owsley, 1979). The l a t t e r a u t h o r s showed t h a t a t 15 weeks o f age i n f a n t s w i l l s e a r c h . v i s u a l l y f o r a p a r e n t who i s h e a r d t o speak i n such a p r e f e r e n c e s e t - u p . T h i s o c c u r s even when t h e r e i s not any s p a t i a l o r te m p o r a l i n f o r m a t i o n u n i t i n g f a c e and v o i c e . G i v e n t h i s r e s u l t i t might be t h a t i n f a n t s i n t h e S p e l k e (1976) stu d y would l o o k a t t h e woman upon h e a r i n g t h e v o i c e and t h e 'non-person' o t h e r w i s e . As such i t i s u n c l e a r whether S p e l k e answered the q u e s t i o n which prompted h e r r e s e a r c h ; " W i l l i n f a n t s e x p l o r e s i g h t s and sounds whose r e l a t i o n s h i p i s s p e c i f i e d by t h e i r i n t e r n a l s t r u c t u r e ? " ( S p e l k e , 1976, p. 554). T h i s c r i t i c i s m has been more t h a n met i n r e c e n t i n v e s t i g a t i o n s . B a h r i c k e t a l . (Note 5) found c o n s i s t e n t and s t r o n g p r e f e r e n c e s f o r sound r e l a t e d f i l m s by 4-month-old i n f a n t s . The a u t h o r s p r e s e n t e d i n f a n t s w i t h e v e r y p a i r - w i s e comparison o f t h r e e f i l m s ; a p a t t e r n o f h a n d c l a p s , t h e p l a y i n g o f a xylophone, and the movement o f a s l i n k y t o y . O nly the p a i r i n g o f t h e xylophone and t h e s l i n k y t o y f a i l e d t o r e a c h s t a t i s t i c a l s i g n i f i c a n c e when t h e sound o f t h e xylophone was p r e s e n t e d . S p e l k e (Note 4) has shown t h a t 4-month-old i n f a n t s can p e r c e i v e t h e r e l a t i o n s h i p between t h e r a t e o f sounds and t h e v i s i b l e impacts o f o b j e c t s even i f t h e sounds and impacts a r e not s i m u l t a n e o u s . 19. That i s , i f i n f a n t s a r e shown two m o t i o n p i c t u r e f i l m s o f a t o y a n i m a l b o u n c i n g a t two d i f f e r e n t r a t e s t h e y can d e t e c t the common r a t e o f sound and v i s i b l e movement even though t h e y do n o t o c c u r s i m u l t a n e o u s l y . I n f a n t s c o u l d a l s o d e t e c t the s i m u l t a n e i t y o f sound b u r s t s and v i s i b l e impacts even when the s y n c h r o n i z e d and n o n - s y n c h r o n i z e d o b j e c t s moved at t h e same r a t e . The r e s u l t s o f t h e s e s t u d i e s were c o n s i d e r a b l y weaker t h a n t h e B a h r i c k e t a l . s t u d y p a r t i c u l a r l y w i t h r e g a r d t o . o v e r a l l p r e f e r e n c e . The most c o n s i s t e n t d i f f e r e n c e s were found i n measures o f " v i s u a l s e a r c h " which i n c l u d e d t h e d i r e c t i o n o f f i r s t l o o k , the number o f t r i a l s on which the i n f a n t s l o o k e d f i r s t o r second t o the s y n c h r o n i z e d and n o n - s y n c h r o n i z e d f i l m s , and t h e l a t e n c y o f l o o k i n g . These s t u d i e s s u p p o r t t h e n o t i o n t h a t i n f a n t s w i l l e x p l o r e s i g h t s and sounds whose r e l a t i o n s h i p i s s p e c i f i e d by t h e i r i n t e r n a l s t r u c t u r e . The main v a r i a b l e s p e c i f y i n g t h i s i n t e r n a l s t r u c t u r e has been t h e t e m p o r a l r e l a t i o n s h i p between-the f i l m e d o b j e c t s ' movements and the sounds t h u s produced. The i n f a n t s a r e s e n s i t i v e t o t h i s r e l a t i o n s h i p . S e v e r a l i n v e s t i g a t o r s (Lawson, 1979; S p e l k e , Note 2; Lyons-Ruth, Note 6) have asked whether i n f a n t s a s s o c i a t e v i s u a l and a u d i t o r y f e a t u r e s o f n o v e l o b j e c t s d u r i n g b r i e f exposures t o t h e o b j e c t s when t h e r e i s a t e m p o r a l and/or s p a t i a l . c o r r e s p o n d e n c e between t h e v i s u a l and a u d i t o r y e v e n t s . Lyons-Ruth (Note 6) f o und t h a t 4- and 5-month-old i n f a n t s (but. not 3-month-olds) who had b r i e f l y e x p e r i e n c e d an o b j e c t s p a t i a l l y and t e m p o r a l l y c o i n c i d e n t w i t h a sound showed d i s t r e s s ( i . e . , . a n . - i n c r e a s e i n l i mb and body movement) when t h e r e was s p a t i a l d i s l o c a t i o n between t h e sound and o b j e c t . I n a s e r i e s o f s t u d i e s S p e l k e (Note 2) has p r e s e n t e d e v i d e n c e t h a t 4-month-old i n f a n t s can r a p i d l y a c q u i r e knowledge o f b i m o d a l l y s p e c i f i e d events on the b a s i s o f t e m p o r a l synchrony between the v i s u a l and a u d i t o r y a s p e c t s o f t h e e v e n t s . I n the experiment 20. (Spelke, Note 2, Experiment III) that most clearly makes this point she used the same procedure as described previously. There were two phases to the experiment; a familiarization period, and a test period. During the familiarization period two films were projected side by side. One film was of a toy kangaroo, the other of a donkey, each "bouncing"' at a rate of one bounce per 2 seconds. When either of the two objects hi t the ground one of two sounds was heard; a gong, or a thump. During familiarization only the temporal structure of the sound united i t with one of the films of the moving objects. On test t r i a l s both films were projected and infants were given brief presentations of the sounds separated by intervals when a small light was used to centre their gaze between the films before another presentation of the sound. Infants were divided into Synchrony and Non-synchrony conditions for the test t r i a l s . For the Synchronized condition presentation of the sound was synchronized with the impact of the object i t had specified during familiarization t r i a l s . For infants i n the Non-synchrony condition the sounds were not i n phase with the objects to which they had previously been related. There were no significant differences during test t r i a l s between the conditions, and infants i n both groups searched reliably for the sound specified object. Spelke argued that the infants had detected the temporal invariance which united the optic and acoustic stimulation during familiarization. This formed the basis for the acquisition of knowledge which led to relevant search behaviour even when the temporal correspondence between the objects and sounds was lacking. Lawson (1979) also investigated some of-the factors responsible for.the establishment of the coordinated perception of the auditory and visual characteristics of a common object-. To this end she systemati-cally varied the degree of temporal and spatial congruity between the auditory 21. and v i s u a l c h a r a c t e r i s t i c s o f two s e p a r a t e o b j e c t - s o u n d p a i r s . I n the o n l y study which c l e a r l y showed c o o r d i n a t e d p e r c e p t i o n , 6-month-old i n f a n t s were f i r s t f a m i l i a r i z e d w i t h an o b j e c t t h a t moved i n synchrony w i t h a p e r i o d i c sound which emanated f r o m the o b j e c t . T e s t i n g c o n s i s t e d o f p r e s e n t i n g t h e f a m i l i a r and a n o v e l o b j e c t s i m u l t a n e o u s l y , w i t h e i t h e r the f a m i l i a r o r . a n o v e l sound coming f r o m a speaker midway between the o b j e c t s . I n f a n t s spent a s i g n i f i c a n t l y g r e a t e r p r o p o r t i o n o f t h e i r f i x a t i o n time and a s i g n i f i c a n t l y g r e a t e r d u r a t i o n o f f i x a t i o n , l o o k i n g a t t h e f a m i l i a r o b j e c t i n the p r e s e n c e o f the f a m i l i a r sound. I n t h e p r e s e n c e o f t h e n o v e l sound t h e y d i d not show d i f f e r e n t i a l f i x a t i o n . The o t h e r c o n d i t i o n s i n c l u d e d t e m p o r a l synchrony between t h e o b j e c t and sound b u t w i t h 9 0 ° s p a t i a l s e p a r a t i o n , and two c o n d i t i o n s o f s p a t i a l c o n g r u i t y c o u p l e d w i t h t e m p o r a l i n c o n g r u i t y . I n one c o n d i t i o n t h e o b j e c t moved c o n t i n u o u s l y w h i l e p r o d u c i n g a p e r i o d i c sound and i n the o t h e r c o n d i t i o n t h e r e was p e r i o d i c movement o f the o b j e c t w i t h c o n t i n u o u s sound. A l l t e s t r e s u l t s were n e g a t i v e except f o r one o b j e c t - s o u n d p a i r i n the s p a t i a l c o n g r u i t y c o n d i t i o n i n v o l v i n g c o n t i n u o u s o b j e c t movement and p e r i o d i c sound. The r e s u l t s o f t h e s e s t u d i e s i n d i c a t e t h e importance o f s p a t i a l and t e m p o r a l congruency i n the c o o r d i n a t i o n of a u d i t o r y and v i s u a l s t i m u l i . The s p a t i a l s e p a r a t i o n o f 90° between o b j e c t and sound was much g r e a t e r t h a n i n th e S p e l k e (Note 2) i n v e s t i g a t i o n . G i v e n S p e l k e ' s p o s i t i v e r e s u l t s w i t h temporal synchrony and a s l i g h t s p a t i a l d i s c r e p a n c y i t would seem t h a t t h e s p a t i a l f a c t o r might be a m a t t e r o f degree. I n g e n e r a l , t h e e m p i r i c a l r e s e a r c h i n d i c a t e s t h a t t h e a u d i t o r y and v i s u a l m o d a l i t i e s o f i n f a n t s i n t e r a c t i n a number of ways. The v i s u a l s e a r c h b e h a v i o u r o f young i n f a n t s i s i n f l u e n c e d by t h e s p a t i a l l o c a t i o n o f sound.sources. The degree o f s e n s i t i v i t y t o t e m p o r a l r e l a t i o n s b o t h w i t h i n and between t h e m o d a l i t i e s i s q u i t e i m p r e s s i v e . 22. S e n s i t i v i t y to these various amodal properties may f a c i l i t a t e the learning of more arb i t r a r y or sp e c i f i c cross modal associations (Mendelson, Note 1; Spelke, Note 2) and i t appears that some of these associations can be established quite rapidly. EXPERIMENT I As indicated earlier, i t has been shown that when 4-month-olds are presented with two films simultaneously on either side of a speaker, the infants look at the sound specified film (Spelke, 1976, Note 2, Note 4; Bahrick et a l . , Note 5 ) . Such results have been interpreted as demonstrating that infants detect the rhythmic stimulation which unites the visual and auditory events and that, given the opportunity, infants w i l l attempt to follow events i n two modalities. Typically, the stimuli used in.such studies are of a multidimensional nature, and i t i s not clear what characteristics are of assistance i n guiding the infant's visual attention. As a matter of fact, the most consistent incidence of preference behaviour has been obtained i n the case of film strips of highly dissimilar objects paired with correspond-ingly different soundtracks ( i . e . , Spelke, 1976; Bahrick et a l . , Note 5 ) . Indeed, when the films were of the same object but merely differed i n tempo, the preference for the sound related film was much weaker (Spelke, Note 4 ) . It i s not clear, therefore, whether infants would show such preferential looking when visual and auditory events are only linked by a common temporal relationship. In the present study the number of stimulus dimensions was kept to a minimum using simple light and sound patterns. A preference technique similar to that devised by Spelke (1976) was used, except that the pattern of elements of the two visual displays and the sound which accompanied the visual patterns were the same i n a l l respects, except for temporal rate. The study was designed to investigate whether infants would show preferential looking to the sound-related visual event when the visual and sound patterns differed only i n temporal rate. In order to detect possible developmental changes three age levels were tested. 24. METHOD S u b j e c t s F o r t y - t w o i n f a n t s p a r t i c i p a t e d i n t h e experiment. Data f o r 6 of t h e s e 4-2 i n f a n t s were not f u l l y c o l l e c t e d due t o equipment f a i l u r e o r excess f u s s l n e s s d u r i n g t e s t i n g and have been e x c l u d e d f r o m a n a l y s i s . The t h r e e groups o f 12 i n f a n t s had mean ages o f (Group 1 ) 3 months, 10 days (S.D. = 12 d a y s ) , (Group 2) 6 months, 19 days (S.D. = 19 days) and (Group 3) 10 months, 11 days (S.D. = 14 d a y s ) . I n f a n t s were r e c r u i t e d t h r o u g h a d v e r t i s e m e n t s i n t h e l o c a l newspapers. No attempt was made t o b a l a n c e o r c o n t r o l f o r r a c e , sex o r s o c i o e c o n o m i c s t a t u s . S t i m u l i The v i s u a l s t i m u l i were f i v e l i g h t e m i t t i n g d i o d e s ( L E D ' s ) , embedded i n c l e a r p l a s t i c (5 cm a p a r t ) and a r r a n g e d i n a c r o s s p a t t e r n ( s e e F i g . 3) . The v i s u a l a n g l e subtended by t h e p a t t e r n was a p p r o x i m a t e l y 7.2 deg. A r e d t r a n s l u c e n t p l a s t i c s heet was p l a c e d o v e r t h e d i o d e s i n o r d e r t o enhance t h e i r b r i g h t n e s s . Two such s t i m u l u s p a n e l s , s e p a r a t e d by 70 cm., were used; one p l a c e d t o t h e i n f a n t ' s r i g h t , t h e o t h e r t o t h e l e f t . A s m a l l g r e e n f i x a t i o n l i g h t was p l a c e d midway between t h e p a n e l s . The v i s u a l a n g l e between a p a n e l and f i x a t i o n l i g h t was a p p r o x i m a t e l y 2 6 ° a t the v i e w i n g d i s t a n c e used. A u d i t o r y s i g n a l s were produced by c o m m e r c i a l l y a v a i l a b l e . S o n a l e r t s (model SC628) manufactured by P.R. M a l l o r y Co. I n c . w i t h a n o m i n a l f r e q u e n c y r a t i n g o f 2900- 500 HZ. These were c o n c e a l e d and p l a c e d midway between the v i s u a l p a n e l s . Ambient n o i s e l e v e l measured at t h e i n f a n t ' s head was 52 db a c c o r d i n g t o a G e n e r a l R a d i o Company sound l e v e l meter (model 1551C). The sound l e v e l was 62 db w i t h t h e tone p r e s e n t . Fig.3. Schematic diagram of display for Experiment I ro 26. The s t i m u l u s p a t t e r n s were g e n e r a t e d b y a s p e c i a l l y c o n s t r u c t e d two c h a n n e l p u l s e g e n e r a t o r . Two t e m p o r a l r a t e s were c o n t r o l l e d by s e p a r a t e c h a n n e l s o f t h e s i g n a l g e n e r a t o r . The c y c l e time f o r t h e "slow" p a t t e r n was 1.-4 sec w i t h t h e s t i m u l i on f o r 1.0 sec and o f f f o r 0.4- s e c . F o r t h e " f a s t " p a t t e r n t h e c y c l e time was 0.35 seconds w i t h a 0.25 sec on p e r i o d and 0.10 o f f p e r i o d ( s e e F i g . 4 ) . D e s i g n and Procedure Three d i f f e r e n t age groups o f i n f a n t s were t e s t e d . Each i n f a n t r e c e i v e d two t r i a l s w i t h t h e " f a s t " a u d i t o r y p a t t e r n and two t r i a l s w i t h t h e "slow" a u d i t o r y p a t t e r n . Order o f f a s t and slow p a t t e r n s was randomized a c r o s s i n f a n t s . H a l f o f t h e i n f a n t s i n each group had t h e f a s t v i s u a l p a t t e r n on t h e i r r i g h t , and the slow v i s u a l p a t t e r n on t h e i r l e f t , w h i l e the o t h e r h a l f were p r e s e n t e d w i t h t h e o p p o s i t e arrangement. T e s t i n g took p l a c e i n a s p e c i a l l y c o n s t r u c t e d darkened e n c l o s u r e (1.2 x 1.3 x 1.9 m) i n a d i m l y l i t , q u i e t room. The i n f a n t s were h e l d by the mother a t a d i s t a n c e o f a p p r o x i m a t e l y 80 cm from a p o i n t midway between the v i s u a l p a n e l s . The i n f a n t s were viewed t h r o u g h a peephole midway between t h e v i s u a l p a n e l s . Both t h e mother and o b s e r v e r h e a r d music t h r o u g h headphones which masked t h e a u d i t o r y s t i m u l u s t h r o u g h o u t t h e t e s t i n g s e s s i o n . Only one o b s e r v e r was used throughout the exper-iment ( see F i g . 5 ) . The o b s e r v e r began t h e t r i a l when the i n f a n t o r i e n t e d t o the g r e e n f i x a t i o n l i g h t . A s m a l l l i g h t went o f f a t t h e end o f a t r i a l t o i n f o r m the o b s e r v e r o f t r i a l end. T r i a l d u r a t i o n was c o n t r o l l e d by a L a f a y e t t e V I I I Bank Timer (model 5431A) and was 60 s e c . When-ev e r t h e i n f a n t was judged t o be l o o k i n g a t - a v i s u a l p a n e l d u r i n g a t r i a l t h e o b s e r v e r d e p r e s s e d one o f two s w i t c h e s ; one s w i t c h f o r l o o k i n g I.OO ON. .40 OFF SLOW RATE .25 ON JO OFF •Tirinnniwinnrm FAST RATE FIG.4. PULSE PATTERNS USED IN EXP.I ro Fig. 5. Schematic diagram of laboratory arrangement 29. a t t h e r i g h t p a n e l , t h e o t h e r f o r l o o k i n g a t t h e l e f t . The s w i t c h e s a c t i v a t e d s e p a r a t e pens on a R u s t r a k Event R e c o r d e r model 92. Measures o f L o o k i n g Two b i a s e s i n t h e d a t a r e q u i r e d c o r r e c t i o n . I n s p i t e o f t h e c o n t r o l f o r p o s i t i o n b i a s between s u b j e c t s t h e r e was a s t r o n g tendency f o r t h e i n f a n t s , p a r t i c u l a r l y i n t h e two younger groups, t o l o o k more toward one s i d e t h a n t h e o t h e r ( s e e F i g . 6 ) . T h i s l o o k i n g b i a s was h i g h l y c o n s i s t e n t i n group 1 w i t h t h e i n f a n t s showing a s t r o n g r i g h t -t u r n b i a s . Group 3 demonstrated a s t r o n g p r e f e r e n c e f o r t h e v i s u a l p a t t e r n w i t h the f a s t e r t e m p o r a l r a t e , r e g a r d l e s s o f accompanying sound o r p o s i t i o n ( s e e F i g . 7 ) . The r a t i o n a l e b e h i n d such c o r r e c t i o n s , which have p r e v i o u s l y been used by Lawson (1979) and R u f f and B i r c h (1974), i s t h a t i f an i n f a n t has a s t r o n g r i g h t - l o o k i n g b i a s , t h e n l e f t - l o o k i n g time s h o u l d be g i v e n more weight because the s t i m u l u s on t h e l e f t has t o be e s p e c i a l l y a t t r a c -t i v e t o p u l l t h e i n f a n t ' s a t t e n t i o n from t h e p r e f e r r e d s i d e . The method o f c o r r e c t i o n c o n s i s t e d o f t a k i n g the l e n g t h o f l o o k i n g t o the r i g h t , f o r example, and f i n d i n g what p r o p o r t i o n t h a t time was o f t h e t o t a l r i g h t - l o o k i n g t i m e . F o r i n s t a n c e , i f an i n f a n t ' s t o t a l l o o k i n g time t o the r i g h t was 100 sec and t o t h e l e f t , 30 s e c , and i n a g i v e n t r i a l t h e i n f a n t l o o k e d t o the l e f t f o r 6 sec and t o the r i g h t , 25 s e c , t h e c o r r e c t e d p r o p o r t i o n s would be 0.20 and 0.25, r e s p e c t i v e l y . As mentioned above the measure o f p r e f e r e n c e was t o t a l l e n g t h o f f i x a t i o n t i m e t o each v i s u a l p a t t e r n . A measure o f " v i s u a l s e a r c h " u s ed by S p e l k e (Note 2; Note 4) was a l s o used. T h i s was l a t e n c y o f l o o k i n g , which was th e d u r a t i o n o f e l a p s e d time between the b e g i n n i n g o f a t r i a l IOO — RIGHT nm LEFT 80 O Z 5 60 O O O 40 z LU U at 20 l l l l l l l l ! GROUP GROUP 2 GROUP 3 FIG.6. PROPORTION OF LOOKING TO RIGHT AND LEFT (*• Significantly different from .50,1(10 = 2.30,E < .05, two-tailed ) o to o PERCENTAGE OF LOOKING TIME S o 00 o o o ST tn to" 3 < n Q 3 «<" O. .VI •o XI O -D O 70 O 3 | o 3 o . * 8 z — —1 7T 0 to r" o 5 Q < o to •o f— > -< o 70 o c O -z o TO w > c * z -° b o M JO m 6 I o TO O c CO UIU1IUU Trnn 'nTnnnnir f IIIIIII tn 31 O 0 1 3 32. and t h e i n f a n t ' s f i r s t l o o k t o t h e s y n c h r o n i z e d v i s u a l s t i m u l i and s i m i l a r l y , t o t h e n o n - s y n c h r o n i z e d s t i m u l i . A l s o , t h e number o f l o o k s t o each v i s u a l " . p a t t e r n was c a l c u l a t e d . Both o f t h e s e measures were a l s o c o r r e c t e d f o r p o s i t i o n and r a t e b i a s . RESULTS AND DISCUSSION Three s e p a r a t e between-groups ANOVA's were pe r f o r m e d on the mean l o o k -ing - t i m e , t h e average l a t e n c y t o t h e f i r s t l o o k , and the average number o f l o o k s . The groups d i d n o t d i f f e r on mean l o o k i n g time but', d i d so on l a t e n c y , F (2,33) = 4-34- p ^- .025, and number, o f l o o k s , F (2,33) = 9.74 p £- .001. Tukey ( a ) t e s t s (Winer, 1971, p. 198) i n d i c a t e d t h a t group 3 made s i g n i f i c a n t l y more l o o k s t h a n group 1 (p £- .005), and group 2 (p I- .01), w h i l e groups 1 and 2 d i d n o t d i f f e r from each o t h e r i n t h i s r e s p e c t . Tukey t e s t s a l s o showed t h a t l a t e n c y t o f i r s t l o o k was s i g n i f i c a n t l y g r e a t e r i n group 2 than group 3 (p £- .05). The d i f f e r e n c e i n l a t e n c y between group 1 and group 3 d i d n o t r e a c h s i g n i f i c a n c e u s i n g t h e Tukey p r o c e d u r e , b u t d i d w i t h a Newman-Keuls t e s t (p c .05). Groups 1 and 2 d i d not d i f f e r i n l a t e n c y t o f i r s t l o o k . A f t e r c o r r e c t i o n f o r b i a s the t o t a l p r e f e r e n c e f o r t h e sound r e l a t e d v i s u a l s t i m u l i was c a l c u l a t e d , f o r each i n f a n t , as t h e mean p r o p o r t i o n o f f i x a t i o n t o t h e s o u n d - r e l a t e d v i s u a l s t i m u l u s f o r t h e 2 sound c o n d i t i o n s . Two t_ t e s t s were performed on the d a t a f o r each group; one f o r t h e slow r a t e c o n d i t i o n and one f o r t h e f a s t . I n each case the p r o p o r t i o n o f l o o k i n g time t o t h e sound r e l a t e d v i s u a l s t i m u l u s was compared t o t h e p r o p o r t i o n e x p e c t e d by chance ( i . e . , 0.50). Not one o f t h e s e t e s t s r e a c h e d s i g n i f i c a n c e f o r t h e p r e f e r e n c e - m e a s u r e . 33. T h i s was a l s o the case f o r t h e number o f l o o k s measure and the l a t e n c y o f l o o k i n g measure. T h i s i s not s u r p r i s i n g , as a l l o f t h e s e measures are h i g h l y r e l a t e d . The P e a r s o n c o r r e l a t i o n between t h e b i a s c o r r e c t e d p r e f e r e n c e measure and the number o f l o o k s was 0.89 and between the c o r r e c t e d p r e f e r e n c e measure and the c o r r e c t e d l a t e n c y measure ( t o the s o u n d - r e l a t e d v i s u a l s t i m u l i ) was -0.78. The r e s u l t s o f t h e p r e s e n t s t u d y do not agree w i t h t h o s e from some p r e v i o u s i n v e s t i g a t i o n s u s i n g t h e m o d i f i e d p r e f e r e n c e methodology ( S p e l k e , 1976; B a h r i c k e t a l . , Note 5 ) . Even a f t e r c o r r e c t i o n f o r p o s i t i o n and t e m p o r a l r a t e b i a s t h e i n f a n t s f a i l e d t o show any c o n s i s t e n t p r e f e r e n c e f o r t h e s o u n d - r e l a t e d v i s u a l e v e n t s . T h i s was t r u e o f a l l measures employed. There a r e two p o i n t s o f i n t e r e s t i n t h e r e s u l t s o f t h e p r e s e n t experiment which, w h i l e not d i r e c t l y r e l a t e d t o a u d i t o r y - v i s u a l c o o r d i n a -t i o n , n e v e r t h e l e s s , p o i n t t o d e v e l o p m e n t a l d i f f e r e n c e s between the groups. The two s o u r c e s o f b i a s ; p o s i t i o n and temporal r a t e , show a developmental change from what i s p r o b a b l y a g r e a t e r c o n t r o l o f a t t e n t i o n by o r g a n i s m i c f a c t o r s i n the younger group t o s t i m u l u s f a c t o r s i n the o l d e r groups. P o s i t i o n b i a s has been n o t e d by o t h e r r e s e a r c h e r s , p a r t i c u l a r l y i n younger i n f a n t s (Cohen, 1976; Lawson, 1979; R u f f & B i r c h , 1974). The p r e f e r e n c e f o r the f a s t e r t e m p o r a l p a t t e r n i n the o l d e r i n f a n t s p r o b a b l y r e s u l t s more from the weakening of the p o s i t i o n b i a s t h a n from... a new b i a s f o r t h e f a s t e r p a t t e r n . Support f o r t h i s c o n t e n t i o n comes from a subsequent t e s t o f s u c c e s s i v e p r e f e r e n c e w i t h 10 f o u r - m o n t h - o l d i n f a n t s which i n d i c a t e d a m a r g i n a l l y s i g n i f i c a n t p r e f e r e n c e f o r t h e f a s t p a t t e r n ( s e e Appendix A ) . The o t h e r d e v e l o p m e n t a l change concerns t h e number of l o o k s and t h e l a t e n c y of t h e f i r s t l o o k . The o l d e r i n f a n t s l o o k e d more o f t e n and w i t h 34. shorter latency than the two younger groups. (The mean number of looks were 5.9 (S.D. = 3.6); 7.9 (S.D. = 2.3) and 13.8 (S.D. = 7.3) for groups 1, 2 and 3 respectively. Groups 1., 2 and 3 had mean latencies of 3.6 (S.D. = 2.4); 4 .0 (S.D. = 2.2) and 2.0 sec (S.D. = .7) respectively.) The groups did not differ, however, i n average fixation time. The infants i n the older group may have different processing strategies, perhaps resulting from maturation of central control and peripheral executive mechanisms. 35. EXPERIMENT I I The r e s u l t s o f Experiment I i n d i c a t e t h a t i n f a n t s do n o t show d i f f e r e n t i a l l o o k i n g toward sound r e l a t e d v i s u a l events when t h e o n l y d i f f e r e n c e between the p a t t e r n s i s t e m p o r a l r a t e . C o n s e q u e n t l y the h a b i t u a t i o n - r e c o v e r y paradigm ( e . g . , see Cohen, 1976) was used t o f u r t h e r i n v e s t i g a t e a u d i t o r y - v i s u a l p r o c e s s i n g i n i n f a n t s . By p r e s e n t i n g p a t t e r n s s u c c e s s i v e l y , p o s i t i o n b i a s i s c o n t r o l l e d . O nly one r a t e was used throughout the h a b i t u a t i o n and r e c o v e r y phases, t h u s c o n t r o l l i n g f o r r a t e b i a s . U s i n g a h a b i t u a t i o n p r o c e d u r e Demany e t a l . (1977) and Chang and Trehub (1977) have shown t h a t i n f a n t s o f 2-1/2 and 5 months o f age are s e n s i t i v e t o temporal g r o u p i n g s i n a u d i t o r y p a t t e r n s . Other h a b i t u a t i o n r e s e a r c h has i n d i c a t e d t h a t 7-month-old i n f a n t s a r e capable o f p e r c e i v i n g e q u i v a l e n c e s and d i f f e r e n c e s i n t e m p o r a l sequence i n f o r m a t i o n b o t h w i t h i n and a c r o s s t h e a u d i t o r y . a n d v i s u a l m o d a l i t i e s ( A l l e n e t a l . , 1977). Thus, the h a b i t u a t i o n methodology has been s u c c e s s -f u l l y employed t o i n v e s t i g a t e the p r o c e s s i n g o f t e m p o r a l p a t t e r n s by i n f a n t s . Two groups o f i n f a n t s were p r e s e n t e d w i t h synchronous and non-synchronous v i s u a l and a u d i t o r y s t i m u l i . In one c o n d i t i o n i n f a n t s were p r e s e n t e d d u r i n g h a b i t u a t i o n t r i a l s w i t h a s i m p l e p u l s e p a t t e r n i n which v i s u a l and a u d i t o r y s t i m u l i were s y n c h r o n i z e d . They were t h e n p u t o u t - o f - p h a s e f o r t h e r e c o v e r y p e r i o d . A n o t h e r group of i n f a n t s was g i v e n t h e o p p o s i t e sequence o f e v e n t s ; nonsynchronous s i g n a l s d u r i n g h a b i t u a t i o n and s y n c h r o n i z e d s i g n a l s d u r i n g r e c o v e r y . I t was h y p o t h e s i z e d t h a t t h e group r e c e i v i n g synchronous i n f o r m a t i o n d u r i n g h a b i t u a t i o n would show s i g n f i c a n t h a b i t u a t i o n and r e c o v e r y , and t h e o t h e r group would show l e s s h a b i t u a t i o n and no r e c o v e r y . These p r e d i c t i o n s f o l l o w from models o f h a b i t u a t i o n s i m i l a r t o t h a t p r o p o s e d by S o k o l o v (1963). 36. A c c o r d i n g t o such a model h a b i t u a t i o n depends upon s t i m u l u s e n c o d i n g . S u c c e s s f u l e n c o d i n g , o r r e p r e s e n t a t i o n , s h o u l d l e a d t o h a b i t u a t i o n and r e c o v e r y , w h i l e d i f f i c u l t y i n f o r m i n g a r e p r e s e n t a t i o n s h o u l d l e a d t o s l o w e r h a b i t u a t i o n and a p o s s i b l e l a c k o f r e c o v e r y . METHOD S u b j e c t s S i x t y - s e v e n i n f a n t s aged 3 months 23 days t o 4 months 17 days (mean age 4 months, S.D. 6 days) p a r t i c i p a t e d i n t h e experiment. Data f o r 7 of t h e s e 67 i n f a n t s were not f u l l y c o l l e c t e d due t o equipment f a i l u r e or e x c e s s i v e f u s s i n e s s d u r i n g t e s t i n g , and have been e x c l u d e d from t h e a n a l y s e s . I n f a n t s were r e c r u i t e d t h r o u g h a d v e r t i s e m e n t s i n t h e l o c a l newspapers. No attempt was made t o b a l a n c e o r c o n t r o l f o r r a c e , sex o r socioeconomic s t a t u s . S t i m u l i As b e f o r e , t h e v i s u a l s t i m u l u s was f i v e red. l i g h t e m i t t i n g d i o d e s ( L E D ' s ) , embedded i n c l e a r p l a s t i c (5 cm a p a r t ) , and a r r a n g e d i n a c r o s s p a t t e r n . The v i s u a l a ngle subtended b y th e p a t t e r n was a p p r o x i m a t e l y 7.2 deg. A u d i t o r y s i g n a l s were produced by c o m m e r c i a l l y a v a i l a b l e S o n a l e r t s . The S o n a l e r t s were c o n c e a l e d and p l a c e d i m m e d i a t e l y below the v i s u a l p a t t e r n ( s e e F i g . 8 ) . Ambient n o i s e l e v e l measured at the i n f a n t s head was 52 db a c c o r d i n g t o a G e n e r a l Radio Company sound l e v e l meter (model 1551C). The sound l e v e l was 62 db w i t h t h e tone p r e s e n t . The s t i m u l i were g e n e r a t e d by t h e s p e c i a l l y c o n s t r u c t e d p u l s e g e n e r a t o r . The t e m p o r a l p a t t e r n f o r synchronous l i g h t and sound was c o n t r o l l e d by a s i n g l e channel which se n t t h e same p u l s e r a t e t o t h e LED's and S o n a l e r t s . F o r the nonsynchronous s t i m u l i , s e p a r a t e channels Sonalerts Peephole Visual display Fixation light Fig.8. Schematic diagram of display for Experiment II 38. d e l i v e r e d d i f f e r e n t r a t e s t o the d i o d e s and S o n a l e r t s . C y c l e time f o r t h e synchronous p a t t e r n was 0.95 s e c , w i t h the s t i m u l i on f o r 0.68 sec and o f f f o r 0.27 s e c . F o r t h e nonsynchronous p a t t e r n , t h e c y c l e time f o r th e sound was t h e same as i n t h e synchronous c a s e , b u t , f o r t h e l i g h t , was 0.89 s e c , w i t h a 0.64- sec on and 0.25 sec o f f p e r i o d ( s e e F i g . 9 ) . T h i s produced an a u d i t o r y - v i s u a l t e m p o r a l r e l a t i o n s h i p which c o n s t a n t l y changed throughout each t r i a l . D e s i g n and Procedure Three groups o f i n f a n t s were t e s t e d . D u r i n g h a b i t u a t i o n t r i a l s one group r e c e i v e d synchronous v i s u a l and a u d i t o r y s t i m u l i (group S ^ ) . A f t e r 10 t r i a l s the l i g h t and sound were put out o f phase f o r 5 r e c o v e r y t r i a l s . A second group r e c e i v e d t h e nonsynchronous s i g n a l s d u r i n g h a b i t -u a t i o n t r i a l s and t h e synchronous s t i m u l i d u r i n g r e c o v e r y t r i a l s ( g r o u p NS^). S i n c e t h e c y c l e time o f t h e v i s u a l s t i m u l u s was d e c r e a s e d d u r i n g the nonsynchronous c o n d i t i o n , a t h i r d group o f i n f a n t s who o n l y r e c e i v e d t h e v i s u a l s t i m u l i was a l s o r u n as a c o n t r o l . H a l f o f t h e s e i n f a n t s r e c e i v e d t h e f a s t e r r a t e d u r i n g h a b i t u a t i o n and the s l o w e r r a t e d u r i n g r e c o v e r y t r i a l s (group V F ) , w h i l e the o t h e r h a l f r e c e i v e d t h e o p p o s i t e sequence of e v e n t s (group V S ) . T e s t i n g t o o k p l a c e i n t h e darkened e n c l o s u r e (1.2 x 1.3 x 1.9 m) i n a d i m l y l i t , q u i e t room. The i n f a n t s were h e l d b y t h e i r mothers a t a d i s t a n c e o f a p p r o x i m a t e l y 80 cm d i r e c t l y i n f r o n t o f t h e v i s u a l p a n e l . The i n f a n t s were viewed t h r o u g h a peephole 2 cm above t h e l i g h t p a n e l . A s m a l l , g r e e n i n c a n d e s c e n t f i x a t i o n l i g h t was p l a c e d 33 cm f r o m t h e c e n t r e of the v i s u a l p a t t e r n t o t h e i n f a n t ' s l e f t . Both t h e mother and o b s e r v e r , who were not i n f o r m e d o f t h e t e s t c o n d i t i o n , h e a r d music t h r o u g h headphones t h a t masked t h e a u d i t o r y s t i m u l u s . .68 ON_ .27 OFF U .68 ON_ .27 OFF SOUND LIGHT IN PHASE 15 SEC TRIAL .68 ON_ .27 OFF .64 ON A .25 OFF B SOUND LIGHT OUT OF PHASE A&C -MINIMUM PHASE DIFFERENCE B "MAXIMUM FIG.9. PULSE PATTERNS USED IN EXP'S. 2&3 40. The o b s e r v e r began t h e t r i a l when the i n f a n t s o r i e n t e d t o t h e g r e e n f i x a t i o n l i g h t . A s m a l l l i g h t went o f f a t t h e end o f a t r i a l t o i n f o r m the o b s e r v e r of t r i a l end. T r i a l d u r a t i o n was c o n t r o l l e d by a L a f a y e t t e V I I I Bank Timer and was 15 s e c . The d u r a t i o n o f the i n t e r s t i m u l u s i n t e r -v a l s was determined by t h e amount o f time i t t o o k f o r t h e i n f a n t t o o r i e n t t o t h e f i x a t i o n l i g h t ; t h e average i n t e r v a l was 6.9 s e c . D u r i n g a t r i a l t h e o b s e r v e r judged when the i n f a n t was l o o k i n g a t t h e v i s u a l p a n e l and d e p r e s s e d a s w i t c h which a c t i v a t e d a pen on t h e R u s t r a k Event R e c o r d e r . Two o b s e r v e r s were employed throughout the experiments ( I I & I I I ) ; t h e i n t e r o b s e r v e r r e l i a b i l i t y , c a l c u l a t e d as a P e a r s o n c o r r e l a t i o n on t o t a l l o o k i n g time p e r t r i a l f o r 135 t r i a l s , was 0.92. RESULTS AND DISCUSSION The d a t a were a n a l y z e d i n terms o f one major r e s p o n s e i n d e x ; l o o k i n g time p e r t r i a l . F i g u r e 10 shows the c o u r s e o f v i s u a l a t t e n t i o n f o r average t o t a l l o o k i n g t i m e s f o r t h e two main groups. A comparison o f t h e average l o o k i n g time d u r i n g t h e 10 h a b i t u a t i o n t r i a l s showed t h a t group NS 1 l o o k e d s i g n i f i c a n t l y l o n g e r t h a n S^, t_ (38) = 6.1, p .0005 ( o n e - t a i l e d ) ^ . The means f o r each o f T r a i l s 1 and 2 ( T . ^ , 9 and 10 ( T 2 ) and 11 and 12 ( T ^ ) were s u b j e c t e d t o a 2 x 3. A n a l y s i s o f V a r i a n c e i n which th e v a r i a b l e s were Group (S1 and N S ^ by T r i a l s ( T ^ T 2 , T ^ ) . B o t h t h e T r i a l s , F (2,76) = 25.33, P ^-.001, and Group by T r i a l s , F (2,76) -6.1, p z~ .003, e f f e c t s were h i g h l y s i g n i f i c a n t . A n a l y s i s o f s i m p l e main e f f e c t s showed t h a t t h e groups were n o t s i g n i f i c a n t l y d i f f e r e n t a t T 1 or Ty but were so a t T 2 , F (1,114) = 9.61, p 4- .005. T - t e s t s f o r c o r r e l a t e d samples r e v e a l e d t h a t group S-^  showed s i g n i f i c a n t d i f f e r e n c e s between T and T„, t (19) = 7.86, p ^..0005, ( o n e - t a i l e d ) , and s i g n i f i c a n t 10 (/> Q Z 9 o o LU 8 z 7 LU 6 »-NG 5 O 4 o _1 3 LU O < 2 UJ > 1 < J L ^ % G R O U P NS-, "X °~-"\ v G R O U P S 1 HABITUATION \ 0 ^ " o , , " " « o RECOVERY J I I • • ' ' ' J I J I 6 7 8 9 10 11 TRIAL N U M B E R 12 13 14 15 Fig/IQ Mean duration of fixation per trial for groups S-| and N S 1 . 42. d i f f e r e n c e s between and 1^, t (19) = 3.12, p_Z- .005 ( o n e - t a i l e d ) , i n t h e p r e d i c t e d d i r e c t i o n s . However f o r group NS^ n e i t h e r t h e d i f f e r e n c e between and nor and 1^ r e a c h e d s i g n i f i c a n c e . A comparison o f t h e mean l o o k i n g t i m e s f o r group VF and VS o v e r the 10 h a b i t u a t i o n t r i a l s r e v e a l e d no s i g n i f i c a n t d i f f e r e n c e . A 2 x 3 ANOVA on Group (VF, VS) by T r i a l s ( T ^ , T 2 , T^) d i d n o t y i e l d any s i g n i -f i c a n t d i f f e r e n c e s . The r e s u l t s o f Experiment I I s u p p o r t the p r e d i c t i o n s . Group S-j^  showed s i g n i f i c a n t h a b i t u a t i o n and r e c o v e r y w h i l e group NS-^  showed n e i t h e r . Moreover, group NS^ showed s i g n i f i c a n t l y more l o o k i n g a t T^ t h a n group S^. These r e s u l t s cannot be a t t r i b u t e d t o the d e t e c t i o n o f o r p r e f e r e n c e f o r t h e f a s t e r l i g h t as t h e r e was no e v i d e n c e o f d i f f e r e n c e between the two v i s u a l groups. I t s h o u l d be n o t e d t h a t t h e t r i a l f a c t o r was not s i g n i f i c a n t i n t h e v i s u a l c o n d i t i o n i n d i c a t i n g a l a c k o f h a b i t u a -t i o n . I t appears t h a t 4-month-old i n f a n t s a r e a b l e t o c o o r d i n a t e the i n p u t from the m o d a l i t i e s and d i s p l a y a h i g h degree o f s e n s i t i v i t y t o 5 " the phase r e l a t i o n s h i p between the l i g h t and sound. 43. EXPERIMENT I I I The r e s u l t s o f Experiment I I were o b t a i n e d w i t h s p a t i a l c o n g r u i t y between t h e l i g h t and sound. Some r e c e n t r e s e a r c h (Lawson, 1979) has suggested t h a t i n f a n t s may need b o t h t e m p o r a l and s p a t i a l c o n g r u i t y i n o r d e r t o c o o r d i n a t e a u d i t o r y and v i s u a l i n f o r m a t i o n under some c o n d i t i o n s . A l s o , s i n c e t h e l i g h t and sound i n Experiment I were s e p a r a t e d by a p p r o x i m a t e l y 26°, t h i s may have made c o o r d i n a t i o n d i f f i c u l t . The q u e s t i o n o f i n t e r e s t i n the t h i r d experiment was t h e r e f o r e , whether i n f a n t s can "detect t h e p h a s i c r e l a t i o n s h i p s between l i g h t and sound when t h e s o u r c e s o f s t i m u l a t i o n a r e w i d e l y s e p a r a t e d . The groups were r u n as i n Experiment I I , but w i t h t h e l i g h t and sound s t i m u l i s e p a r a t e d . METHOD S u b j e c t s F o r t y - f i v e i n f a n t s aged 3 months 18 days t o 4 months 17 days (mean age 4 months 4 days, S.D. 8 days) p a r t i c i p a t e d i n t h e experiment. Three i n f a n t s were e x c l u d e d f r o m a n a l y s i s due t o f u s s i n e s s and 2, because o f equipment f a i l u r e . As i n the f i r s t two experi m e n t s , no attempt was made t o b a l a n c e o r c o n t r o l f o r r a c e , sex or soc i o e c o n o m i c s t a t u s . S t i m u l i The s t i m u l i and t e m p o r a l p a t t e r n s were t h e same as t h o s e used i n Experiment I I , except t h a t t h e S o n a l e r t s were p l a c e d a t a 90 a n g l e t o t h e i n f a n t s 1 ' l i n e o f r e g a r d a t t h e v i s u a l s t i m u l u s . H a l f o f t h e i n f a n t s i n each group had the a u d i t o r y s t i m u l u s on t h e l e f t , t h e o t h e r h a l f on t h e i r r i g h t . The S o n a l e r t s were a p p r o x i m a t e l y 60 cm f r o m the i n f a n t ' s e a r . 44. D e s i g n and Procedure Group S 2 r e c e i v e d t h e synchronous v i s u a l and a u d i t o r y s i g n a l s d u r i n g h a b i t u a t i o n and t h e nonsynchronous s i g n a l s d u r i n g r e c o v e r y . Group NS 2 r e c e i v e d t h e nonsynchronous s t i m u l i d u r i n g h a b i t u a t i o n and t h e synchronous s t i m u l i d u r i n g r e c o v e r y . H a l f o f t h e i n f a n t s i n each group had t h e S o n a l e r t s on t h e i r r i g h t , w h i l e t h e o t h e r h a l f had them on t h e i r l e f t . EESULTS AND DISCUSSION The major i n d e x o f a n a l y s i s was l o o k i n g time p e r t r i a l . The c o u r s e o f v i s u a l a t t e n t i o n f o r mean l o o k i n g time f o r t h e two groups i s i l l u s -t r a t e d i n F i g . 11. As t h e r e were no s i g n i f i c a n t d i f f e r e n c e s dependent upon t h e s i d e o f t h e sound s o u r c e , d a t a was combined i n t h e subsequent a n a l y s e s . A comparison of t h e average l o o k i n g time d u r i n g t h e 10 h a b i t u a t i o n t r i a l s showed t h a t group NS 2 d i d n o t d i f f e r s i g n i f i c a n t l y from group S^. Only t h e m a i n . e f f e c t f o r T r i a l s r e a c h e d s i g n i f i c a n c e , F (2,76) = 31.4, £ /i-.001, i n an AN OVA on Groups ( S 2 , NS 2) by T r i a l s ( T ^ , T 2 , 6 T ^ ) . Independent t - t e s t s i n d i c a t e d t h a t t h e groups were not s i g n i f i c a n t l y d i f f e r e n t a t T^, T 2 o r T^. T - t e s t s f o r c o r r e l a t e d samples demonstrated s i g n i f i c a n t d i f f e r e n c e s between T^ and T 2 f o r group S 2 , t_ (19) = 4.49, p Z-.0005, ( o n e - t a i l e d ) , and f o r group NS 2, t ( 1 9 ) = 4-4, p .001 ( t w o - t a i l e d ) . Group S 2 showed s i g n i f i c a n t r e c o v e r y , t _ ( 1 9 ) = 2.27, p ^- .025 ( o n e - t a i l e d ) , w h i l e t h e d i f f e r e n c e between T^ and T 2 d i d n o t r e a c h s i g n i f i c a n c e f o r group NS 2, t_ (19) = .510, p > .50 ( t w o - t a i l e d ) . The s i g n i f i c a n t h a b i t u a t i o n and r e c o v e r y f o r group S 2 s u g g e s t s t h a t s p a t i a l congruence between the v i s u a l and a u d i t o r y s t i m u l i i s not CO Q 11 10 9 O ° ft LU O CO 5 7 LU 5 6 z o o LXJ o < LU > < V G R O U P NSo G R O U P S 2 1 V -HABITUATION RECOVERY I I I L I 6 7 8 9 10 11 TR IAL N U M B E R 12 13 14 15 Fig.11. Mean duration of fixation per trial for groups S 2 and N S 2 . -IN- ' 4-6. a n e c e s s a r y c o n d i t i o n f o r c o o r d i n a t i o n i f t h e r e i s synchrony between t h e s t i m u l i . Group NS 2 showed h a b i t u a t i o n i n t h e same way as S 2 , but d i d n o t show r e c o v e r y . I t I s d i f f i c u l t t o know what t h e i n f a n t s were h a b i t u a t i n g t o i n t h i s c o n d i t i o n , a l t h o u g h i t i s p o s s i b l e t h a t t h e y were h a b i t u a t i n g t o one o f the components o f t h e compound s t i m u l u s . F u r t h e r r e s e a r c h c o u l d p o s s i b l y c l a r i f y t h i s . 47. GENERAL DISCUSSION I n Experiment I i n f a n t s were p r e s e n t e d w i t h two v i s u a l s t i m u l i d i f f e r i n g i n t e m p o r a l r a t e . The q u e s t i o n s o f i n t e r e s t were whether i n f a n t s would e x h i b i t d i f f e r e n t i a l l o o k i n g t o t h e s t i m u l u s t h a t was synchronous w i t h a sound and whether such l o o k i n g would change as a f u n c t i o n o f age. Such p r e f e r e n t i a l l o o k i n g has been demonstrated i n o t h e r i n v e s t i g a t i o n s when b o t h the a u d i t o r y and v i s u a l s t i m u l i have d i f f e r e d i n many dimensions ( S p e l k e , 1976, Note 2, Note 4; B a h r i c k e t a l . , Note 5). I n t h i s s t u d y the number o f dimensions was r e d u c e d t o one - . t e m p o r a l r a t e - i n o r d e r t o i n v e s t i g a t e whether l o o k i n g t o t h e s o u n d - r e l a t e d v i s u a l event would be demonstrable under such s t r i n g e n t c o n d i t i o n s . I n the case o f the p r e s e n t s t u d y t h e d i f f e r e n c e i n t e m p o r a l r a t e was o b v i o u s l y l a r g e ; that, i s , one p a t t e r n ' s c y c l e time was f o u r times g r e a t e r t h a n the o t h e r . However, no e v i d e n c e was f o u n d f o r d i f f e r -e n t i a l l o o k i n g t o t h e s o u n d - s p e c i f i e d v i s u a l p a t t e r n a t any o f t h e t h r e e age l e v e l s t e s t e d . I t i s u n l i k e l y t h a t t h e l a c k of d i f f e r e n t i a l l o o k i n g was t h e r e s u l t o f an i n a b i l i t y t o d i s c r i m i n a t e between the p a t t e r n s , as t h e f i n d i n g s o f t h e s u c c e s s i v e p r e f e r e n c e s t u d y (Appendix A) i n d i c a t e d t h a t 4-month-olds are p r o b a b l y a b l e t o d i f f e r e n t i a t e t h e p a t t e r n s . However, the e f f e c t i v e n e s s o f t h e s i m u l t a n e o u s p r e s e n t a t i o n e x p e r i m e n t a l s i t u a t i o n t o d e t e c t d i f f e r e n c e s r e l a t e d t o a u d i t o r y - v i s u a l synchrony was c l e a r l y i m p a i r e d by t h e d i f f e r e n t i a l l o o k i n g a s s o c i a t e d w i t h p o s i t i o n and t e m p o r a l r a t e b i a s e s . The younger i n f a n t s l o o k e d more t o t h e r i g h t , r e g a r d l e s s o f t h e t e m p o r a l r a t e o f sound o r l i g h t p a t t e r n , and t h e o l d e s t i n f a n t s l o o k e d more at the f a s t v i s u a l p a t t e r n r e g a r d l e s s o f p o s i t i o n o r a u d i t o r y r a t e . 48. Even w i t h c o r r e c t i o n f o r b o t h p o s i t i o n and r a t e b i a s , t h e r e was no d e m o n s t r a t i o n o f d i f f e r e n t i a l l o o k i n g t o t h e sound r e l a t e d ' v i s u a l p a t t e r n . Those i n v e s t i g a t i o n s which have shown p o s i t i v e r e s u l t s , i n the p a s t , have employed s t i m u l i which d i f f e r e d a l o n g a l a r g e number o f dimensions. The s t i m u l i used have been f i l m s t r i p s o f r e l a t i v e l y f a m i l i a r " n a t u r a l e v e n t s " ( S p e l k e , 1976; B a h r i c k e t a l . , Note 5 ) . Such events are c e r t a i n l y more complex t h a n those used i n t h e p r e s e n t s t u d y . F o r i n s t a n c e , the v i s u a l events d i f f e r e d i n c o l o u r and form, w h i l e t h e accompanying sounds d i f f e r e d i n s p e c t r a l f r e q u e n c y c o m p o s i t i o n . Furthermore, t h e rhy t h m i c r e l a t i o n s h i p between the a u d i t o r y and v i s u a l s t i m u l i was complex- and much l e s s r e p e t i t i v e t h a n i n t h e p r e s e n t s t u d y . A l l o f t h e s e d i f f e r e n c e s c o u l d have promoted d i f f e r e n t i a l l o o k i n g t o t h e s o u n d - r e l a t e d v i s u a l s t i m u l i . To date no r e s e a r c h has s o r t e d out t h e c o n t r i b u t i o n o f t h e s e v a r i o u s f a c t o r s t o such p r e f e r e n t i a l looking,, a l t h o u g h t h e r e s u l t s o f t h e p r e s e n t s t u d y , and some o f t h e r e s u l t s o f S p e l k e ' s (Note 4) s t u d y , suggest t h a t r a t e d i f f e r e n c e s themselves a r e not enough t o produce d i f f e r e n t i a l l o o k i n g t o t h e s o u n d - r e l a t e d v i s u a l e v e n t s . F a m i l i a r i t y . a l s o c o u l d have been a f a c t o r i n the i n v e s t i g a t i o n s t h a t have y i e l d e d p o s i t i v e r e s u l t s . I t c o u l d have had an i n f l u e n c e i n one o f two ways. F i r s t , i f one o f t h e p a i r o f s t i m u l i u s ed was more f a m i l i a r t h a n the o t h e r , p r e f e r e n t i a l l o o k i n g might be f a c i l i t a t e d . The p r e f e r e n c e shown i n S p e l k e ' s (1976) s t u d y , which p a i r e d a f i l m -s t r i p o f a woman p l a y i n g peekaboo with'one o f a wooden b a t o n s t r i k i n g a wood b l o c k , c o u l d have r e s u l t e d from such a d i f f e r e n c e i n ' f a m i l i a r i t y . The i n f a n t s may h a v e . l o o k e d t o t h e woman when .the sound o f a p e r s o n ' s v o i c e was h e a r d and t o the "non-person" when t h e o t h e r sound t r a c k was p r e s e n t e d . Such a p r e f e r e n c e would p r o b a b l y be based on p r i o r 49. a s s o c i a t i o n , r a t h e r t h a n the d e t e c t i o n o f t h e common a u d i t o r y - v i s u a l rhythm. F a m i l i a r i t y a l s o c o u l d be i n f l u e n t i a l i n a n o t h e r way. The f i l m - s t r i p s o f t h e o b j e c t s p r e s e n t e d t o i n f a n t s a r e r e p r e s e n t a t i v e o f a c l a s s o r c l a s s e s o f o b j e c t s w i t h which t h e y have had p r i o r exper-i e n c e . Both Lawson (1979) and S p e l k e (Note 2) have shown t h a t c r o s s -modal . a s s o c i a t i o n s can be formed v e r y r a p i d l y . Hence, i t i s not t o t a l l y u n r e a s o n a b l e t o suppose t h a t p r i o r e x p e r i e n c e w i t h a c l a s s o f o b j e c t s c o u l d have a s s i s t e d i n t h e p r o d u c t i o n o f d i f f e r e n t i a l l o o k i n g t o the sound r e l a t e d v i s u a l s t i m u l i . More r e s e a r c h i s n e c e s s a r y t o c l a r i f y the r o l e o f p r i o r e x p e r i e n c e . P o s i t i o n b i a s has been r e p o r t e d i n p r e v i o u s s t u d i e s which have used measures of v i s u a l p r e f e r e n c e (Cohen, .1976; Lawson, 1979; R u f f & B i r c h , 1974). F o r i n s t a n c e , Cohen (1976) r e p o r t e d on experiments i n which t h e r e were l o n g e r f i x a t i o n times t o the r i g h t , d e s p i t e the p r e s e n t a t i o n o f i d e n t i c a l p a t t e r n s on b o t h s i d e s . S i m i l a r l y , R u f f and B i r c h (1974) f o u n d t h a t even though t h e y c o n t r o l l e d f o r p o s i t i o n b i a s , w i t h l e f t - r i g h t p a t t e r n r e v e r s a l s , t h e r e was a tendency f o r i n f a n t s t o l o o k more toward one s i d e t h a n the o t h e r . Caron (1967) found s i g n i f i -c a n t l y more "spontaneous" r i g h t head t u r n s t h a n l e f t head t u r n s and S i q u e l a n d (1968) r e p o r t e d more s u c c e s s f u l c o n d i t i o n i n g of a r i g h t head t u r n response t h a n a l e f t t u r n . T u r k e w i t z , Gordon and B i r c h (1968) have a l s o shown t h a t t o n i c - neck resp o n s e s i n neonates a r e d i r e c t e d t o t h e r i g h t about 80% o f t h e t i m e . The meaning o f s uch p o s i t i o n b i a s i s not c l e a r , a l t h o u g h some a u t h o r s have su g g e s t e d t h a t l a t e r a l d i f f e r e n c e s may r e f l e c t n e u r o b e h a v i o u r a l o r g a n i z a t i o n (Hammer & T u r k e w i t z , 1974). C e r e b r a l asymmetries are o f t e n i m p l i c a t e d i n such views o f n e u r o b e h a v i o u r a l o r g a n i z a t i o n . However, w h i l e a c e r e b r a l asymmetry i s e a s i l y l i n k e d t o hand p r e f e r e n c e ( B r e s s o n , Maury, 50. P i e r a n t - L e Bonniec & de Schonen, 1977; C a p l a n & K i n s b o u r n e , 1976) i t i s d i f f i c u l t t o see how t h i s would account f o r l o o k i n g p r e f e r e n c e s . The t e m p o r a l r a t e b i a s e x h i b i t e d by t h e o l d e s t group o f i n f a n t s i s i n a c c o r d w i t h the f i n d i n g s and s p e c u l a t i o n o f o t h e r r e s e a r c h e r s . The r e s u l t s o f Karmel e t a l . (1977) showed t h a t i n v e r t e d U-shaped f u n c t i o n s , w i t h s i m i l a r maxima, d e s c r i b e d v i s u a l a t t e n t i o n and s i g n a l s t r e n g t h / s e c o f t h e v i s u a l l y evoked p o t e n t i a l o f 3-month-old i n f a n t s t o t e m p o r a l l y modulated p a t t e r n s . T h i s f i n d i n g i s s u p p o r t f o r t h e view advanced r e c e n t l y t h a t t h e amount o f v i s u a l a t t e n t i o n t h a t a s t i m u l u s s t r u c t u r e e l i c i t s i s governed by the l e v e l o f - n e u r a l e x c i t a t i o n i t produces ( B o r n s t e i n , 1978; H a i t h , 1977; Karmel & M a i s e l , 1975).' That i s , v i s u a l a t t e n t i o n i s seen as b e i n g h i g h l y c o r r e l a t e d w i t h the " f i r i n g r a t e " o f neurons i n the v i s u a l c o r t e x . S t i m u l i t h a t produce 7 maximum f i r i n g ( t o an a s y m p t o t i c l e v e l ) w i l l e l i c i t most v i s u a l a t t e n t i o n . I n t h e p r e s e n t i n v e s t i g a t i o n t h e o l d e s t group (Experiment I ) and the 4-month-old i n f a n t s , t e s t e d s u c c e s s i v e l y (Appendix A) b o t h showed a p r e f e r e n c e f o r t h e f a s t e r v i s u a l p a t t e r n . T h i s i s c o n s i s t e n t w i t h the f i n d i n g s o f Karmel et a l . (1977.) and, a c c o r d i n g t o t h e above i n t e r p r e t a t i o n , t h i s p r e f e r e n c e s h o u l d be c o r r e l a t e d with, the l e v e l o f n e u r a l e x c i t a t i o n . The d i f f e r e n c e f o u n d between the o l d e s t (group 3) and younger (group 1 & 2) i n f a n t s i n l a t e n c y o f f i r s t l o o k was h a r d l y s u r p r i s i n g . Other i n v e s t i g a t o r s have a l s o f o u nd a d e c r e a s e i n l a t e n c y t o f i x a t i o n o f p e r i p h e r a l l y p r e s e n t e d t a r g e t s as a f u n c t i o n o f age ( A s l i n & S a l a p a t e k , 1975; De Schonen, McKenzie, Maury, B r e s s o n , 1978; T r o n i c k , 1972). However, the ages t e s t e d have been much younger t h a n t h o s e o f the p r e s e n t experiment and the measures and e x p e r i m e n t a l c o n d i t i o n s have v a r i e d . Such a d e c r e a s e i n l a t e n c y c o u l d r e s u l t from more e f f i c i e n t 51. eye and head c o n t r o l , an i n c r e a s e i n t h e ' s i z e ' o f the e f f e c t i v e v i s u a l f i e l d , a t t e n t i o n a l changes o r some c o m b i n a t i o n o f t h e s e f a c t o r s . A l t h o u g h i t i s n o t p o s s i b l e t o determine t h e c o n t r o l l i n g f a c t o r ( s ) on the b a s i s o f t h e p r e s e n t r e s u l t s , i t s h o u l d be n o t e d t h a t the f a s t e r r a t e p a t t e r n appeared t o be a p o w e r f u l " a t t e n t i o n - g e t t i n g " s t i m u l u s (Cohen, 1973) f o r the o l d e r i n f a n t s . That i s , th e o l d e r i n f a n t s , who had l e s s p o s i t i o n b i a s t h a n the younger i n f a n t s , were e s p e c i a l l y s e n s i t i v e t o s uch a p e r i p h e r a l l y p r e s e n t e d s t i m u l u s ; i t r e c r u i t e d t h e i r n o t i c e v e r y q u i c k l y . The i n f a n t s i n group 3 a l s o e x h i b i t e d a g r e a t e r number o f l o o k s t h a n t h o s e i n groups 1 and 2. T h i s c o u l d r e s u l t f r o m a more f u l l y d e v e l o p e d motor system, o r from d i f f e r e n t i n f o r m a t i o n - p r o c e s s i n g s t r a t e g i e s o r b o t h . The groups i n t h e p r e s e n t s t u d y d i d not d i f f e r i n average f i x a t i o n time. Hence the time p e r l o o k was g r e a t e r i n t h e younger groups. Such a d i f f e r e n c e i s s u g g e s t i v e o f more a c t i v e s c a n n i n g by the o l d e r i n f a n t s and i s r e m i n i s c e n t o f an o b s e r v a t i o n made by Ames and S i l f e n (Note 7, p. 6).: " I t appears t o us t h a t w h i l e t h e o l d e r i n f a n t may be c a p t u r i n g s t i m u l i w i t h h i s v i s u a l b e h a v i o u r , t h e young i n f a n t i s c a p t u r e d by t h e s t i m u l i " . I t remains t o be d e t e r m i n e d what such a s p e c u l a t i o n a c t u a l l y means i n terms o f the development o f p e r c e p -t u a l p r o c e s s i n g . ( F o r d i s c u s s i o n see Bronsdn,. 197-4; H a i t h , 1977; H a r r i s , 1973). S i n c e the p r e f e r e n c e methodology f a i l e d t o produce d i f f e r e n t i a l l o o k i n g r e l a t e d t o a u d i t o r y - v i s u a l synchrony,' t h e h a b i t u a t i o n paradigm was u s ed i n E x p e r i m e n t s • I I and I I I . The p r o c e s s i n g o f t e m p o r a l l y synchronous and nonsynchronous v i s u a l and a u d i t o r y s t i m u l i under c o n d i t i o n s o f s p a t i a l c o n g r u i t y and s e p a r a t i o n was examined. I t was h y p o t h e s i z e d t h a t t h e groups ( S ^ & S^) r e c e i v i n g synchronous a u d i t o r y and v i s u a l s i g n a l s d u r i n g h a b i t u a t i o n and nonsynchronous s i g n a l s d u r i n g 52. recovery t r i a l s would show s i g n i f i c a n t habituation and recovery. The groups (NS^ & NS 2) receiving the opposite sequence of signals, during habituation and recovery t r i a l s were predicted to show less habituation and no recovery. These predictions follow from models of habituation similar to that proposed by Sokolov (1963). According to such a model habituation depends on stimulus encoding. Successful encoding or representation should lead to habituation and recovery i f the stimulus i s changed, while d i f f i c u l t y i n forming a representation should lead to slower habituation and possible lack of recovery. There are a number of ways to encode the synchronous l i g h t and sound patterns -used i n Experiments I I and I I I , but the simplest would be to use a r e l a t i v e rather than an absolute code. An absolute code would involve, within some reasonable l i m i t s , the representation of the duration of the pulse.and inter-pulse i n t e r v a l . A r e l a t i v e code would require only that the synchrony between the l i g h t and sound be represented 8 and would not depend upon the encoding of absolute information . Accordingly, i t i s the constant relationship between the v i s u a l and auditory stimu l i which needs to be represented for habituation to occur. I t could be argued that the habituation and recovery demonstrated i n the case of the synchronous groups (S^ & S 2) resulted from the presumably successful encoding of the temporal r e l a t i o n between the l i g h t and sound, which was not influenced by the r e l a t i v e location of the stimulus sources. Also, the lack of habituation i n the conditions i n which the infants were only presented with the l i g h t pattern (groups VS and VF) further attests to the d i f f i c u l t y that may be involved i n represent-ing absolute temporal information. I t i s possible, however, that the coding of such temporal information may be more d i f f i c u l t for the v i s u a l modality than for the auditory modality. I t has been argued that the v i s u a l 53. m o d a l i t y i s more adept a t c o d i n g s p a t i a l l y p a t t e r n e d i n f o r m a t i o n , w h i l e t h e a u d i t o r y m o d a l i t y i s b e t t e r equipped t o d e a l w i t h t e m p o r a l i n f o r m a t i o n ( F r e i d e s , 1974). R e s e a r c h has demonstrated t h a t m a tching o f s i m p l e f r e q u e n c y r a t e s and rhythms i s more a c c u r a t e when done i n t r a m o d a l l y by t h e e a r , t h a n c r o s s - m o d a l l y by t h e eye and e a r ( C o l e , Chorover & E t t l i n g e r , 1961; Gebhard & Mowbray, 1959). Thus, a b s o l u t e a u d i t o r y t e m p o r a l I n f o r m a t i o n c o u l d p o s s i b l y be encoded. The i n f a n t s i n . t h e groups p r e s e n t e d w i t h nonsynchronous s i g n a l s d u r i n g h a b i t u a t i o n t r i a l s (NS.^ & N S 2 ) d i d not show ev i d e n c e o f r e c o v e r y . However, the group w i t h the l i g h t and sound s e p a r a t e d ( N S 2 ) h a b i t u a t e d , while, those p r e s e n t e d w i t h t h e l i g h t and sound s p a t i a l l y congruous (NS^) d i d n o t . The i n f a n t s i n t h e s e groups c o u l d have been a t t e m p t i n g t o encode the s t i m u l u s i n an a b s o l u t e o r i n a r e l a t i v e manner. An a b s o l u t e code c o u l d be used t o r e p r e s e n t t h e p u l s e r a t e o f t h e l i g h t or sound. But, i f s uch a code had been employed by the i n f a n t s i t would p r o b a b l y not have l e d t o h a b i t u a t i o n and c e r t a i n l y not t o r e c o v e r y . I n f a n t s i n t h e v i s u a l - o n l y c o n d i t i o n d i d n o t h a b i t u a t e o r r e c o v e r . I f t h e y had encoded any a b s o l u t e i n f o r m a t i o n , i t i s most l i k e l y t h a t i t was t h e a u d i t o r y p a t t e r n . I n t h a t case t h e r e c o u l d be no r e c o v e r y as the t e m p o r a l r a t e o f t h e a u d i t o r y s i g n a l was t h e same f o r b o t h h a b i t u a t i o n and r e c o v e r y t r i a l s . The i n f a n t s were p r o b a b l y a t t e m p t i n g t o c o o r d i n a t e t h e v i s u a l and a u d i t o r y i n f o r m a t i o n i n some manner, at l e a s t i n group NS^. The r e a s o n s f o r t h i s argument a r e , f i r s t , t h a t t h e i n f a n t s i n t h e synchronous groups d i d c o o r d i n a t e t h e i n f o r m a t i o n . More i m p o r t a n t l y , t h e r e were te m p o r a l r e l a t i o n s h i p s between the. s t i m u l i t h a t c o u l d have p r o v o k e d attempts a t c o o r d i n a t i o n . The l i g h t and sound p a t t e r n s had v e r y s i m i l a r p u l s e r a t e s . Other r e s e a r c h has shown t h a t i n f a n t s a r e s e n s i t i v e t o s i m i l a r t e m p o r a l rhythms between v i s u a l and a u d i t o r y 54. events even i f t h e y are not s y n c h r o n i z e d ( S p e l k e , Note 4 ) . The phase r e l a t i o n s h i p between the l i g h t and sound was such t h a t t h e s t i m u l i were m a x i m a l l y out o f phase i n the m i d d l e o f the t r i a l b u t appeared t o be i n phase a t the b e g i n n i n g and end o f t h e t r i a l ( s e e F i g . 9 ) . Such an " i n t e r e s t i n g l y " u n p r e d i c t a b l e p a t t e r n c o u l d have pr o v o k e d attempts at c o o r d i n a t i o n ; " F i n a l l y t h e l i g h t and sound s o u r c e s were s p a t i a l l y congruous f o r t h e NS^ group. The l a c k o f r e c o v e r y f o r b o t h non-synchronous groups s u g g e s t s t h a t t h e i n f a n t s were n o t a b l e t o form a r e p r e s e n t a t i o n o f t h e o u t - o f - p h a s e p a t t e r n which c o u l d t h e n be d i s c r i m i n a t e d from the synchronous p a t t e r n . The l a c k o f h a b i t u a t i o n i n t h e NS-^  group suggests t h a t t h e r e was c o n t i n u e d i n t e r e s t over t r i a l s i f t h e l i g h t and sound are s p a t i a l l y congruous. However, when t h e l i g h t and sound were s e p a r a t e d , as was t h e case f o r the NS 2 group, s i g n i f i c a n t h a b i t u a t i o n o c c u r r e d . T h i s i s p e r p l e x i n g , as i t i s d i f f i c u l t t o know what the i n f a n t s were h a b i t u a t i n g t o i n t h e N S 2 group. One s u g g e s t i o n i s t h a t w i t h s p a t i a l s e p a r a t i o n and l a c k o f t e m p o r a l synchrony between t h e s o u r c e s the sound became more s a l i e n t and the i n f a n t s were a b l e t o encode i t : T h i s - i s - - a h i g h l y ..tentative-s u g g e s t i o n which f u r t h e r r e s e a r c h c o u l d examine. What s o r t o f mechanism c o u l d a c c o m p l i s h a u d i t o r y - v i s u a l i n t e g r a t i o n o f the k i n d demonstrated i n Experiments I I and I I I ? One approach t o "mechanism" i s t o examine c e l l s , o r systems o f c e l l s , which c o u l d a c c o m p l i s h such i n t e g r a t i o n . A c c o r d i n g t o c u r r e n t n e u r o p h y s i o l o g i c a l t h e o r i z i n g c e r t a i n nerve c e l l s a r e e quipped t o r e s p o n d s e l e c t i v e l y t o p a r t i c u l a r " f e a t u r e s " o f t h e e x t e r n a l w o r l d ( s e e Barlow, 1972 f o r an extreme statement o f t h i s p o s i t i o n ) such as t h e well-known " s p o t " and " l i n e " d e t e c t o r s of t h e v i s u a l system. M i g h t some of the f e a t u r e d e t e c t o r s be multimodal? -Could each o f A r i s t o t l e ' s a t t r i b u t e s o f t h e 55. common sense - motion, r e s t , number, form, magnitude, d u r a t i o n - be r e p r e s e n t e d n e u r a l l y i n s i n g l e c e l l s ? Thompson, Mayers, R o b e r t s o n , and P a t t e r s o n (1970) have found a few c e l l s (5 out o f 500 sampled) i n the a s s o c i a t i o n c o r t e x o f c a t s which appear t o be " c o u n t i n g " c e l l s . Such a c e l l would f i r e o n l y i f a f i x e d number o f s t i m u l u s e v e n t s o c c u r r e d c o n s e c u t i v e l y . The c e l l would d i s c h a r g e r e g a r d l e s s o f m o d a l i t y , p r o v i d e d the c o r r e c t number o f s t i m u l a -t i o n s was-' p r e s e n t e d . The a u t h o r s c a u t i o n e d , however, t h a t " i t remains t o be demonstrated t h a t t h e s e ' c o u n t i n g ' c e l l s f u n c t i o n t o code number o f s t i m u l u s events under c o n d i t i o n o f normal b e h a v i o r (Thompson e t a l . , 1970, p. 273)." There has a l s o been some i n t e r e s t i n g S o v i e t r e s e a r c h on c e l l s w i t h "time - r e c e p t i v e f i e l d s " ( C h e l i d z e , 1975). These neurons ( a g a i n , a v e r y s m a l l p e r c e n t a g e o f t h o s e sampled) were found i n the v i s u a l c o r t e x o f the r a b b i t . They r e s p o n d s e l e c t i v e l y t o s p e c i f i e d i n t e r v a l s between f l a s h e s o f l i g h t . Other r e s e a r c h has shown t h a t t h e r e a r e c e l l s i n t h e s u p e r i o r c o l l i c u i u s ( W i c k e l g r e n , 1971) and the p a r a s t r i a t e and t h e s t r i a t e c o r t e x (Fishman & M i c h a e l , 1973; M o r r e l l , 1972) which are r e s p o n s i v e t o b o t h l i g h t and sound. Moreover, the v i s u a l and a u d i t o r y r e c e p t i v e f i e l d s o f t h e s e c e l l s a r e c l o s e l y a l i g n e d , h a v i n g t h e same h o r i z o n t a l b o u n d a r i e s . These few r e s u l t s a r e i n t r i g u i n g , .but none.of t h e s e kinds-,.of c e l l s ( e v e n i f t h e y r e p r e s e n t e d a l a r g e p r o p o r t i o n o f c e l l s p e r f o r m i n g s e n s o r y a n a l y s i s ) would be adequate t o the t a s k o f " e x p l a i n i n g " t h e a u d i t o r y - v i s u a l c o o r d i n a t i o n demonstrated i n t h e p r e s e n t s t u d i e s . A c c o r d i n g t o the i n t e r p r e t a t i o n o f t h e r e s u l t s o f Experiments I I and I I I some mechanism would have t o "measure" the time r e l a t i o n s h i p between the a u d i t o r y and v i s u a l s i g n a l s . The p r o c e s s i n v o l v e d would be a k i n t o 56. a t e m p o r a l c r o s s c o r r e l a t i o n o f t h e s i g n a l s i n which the time d i f f e r e n c e "between t h e a u d i t o r y and v i s u a l s i g n a l s was determined. M u l t i m o d a l c e l l s w i t h t i m e - r e c e p t i v e f i e l d s might p o s s i b l y p l a y some k i n d o f r o l e , a l t h o u g h such c e l l s would have t o be but one component i n a more c o m p l i -c a t e d n e u r a l system which u l t i m a t e l y l e d t o h a b i t u a t i o n a t a b e h a v i o u r a l l e v e l . Many d i f f e r e n t n on-sensory ar e a s o f t h e b r a i n appear t o u n d e r l i e ( s u c h as t h e hippocampus and t h e r e t i c u l a r system) t h e p r o c e s s o f b e h a v i o u r a l h a b i t u a t i o n ( S o k o l o v , 1975). The o t h e r components o f s u c h c i r c u i t s would have t o be h i g h e r -o r d e r i n t e g r a t o r s t h a t can p u t . t o g e t h e r i n f o r m a t i o n o v e r time and space and go beyond the d e t e c t i o n o f s i m p l e s t i m u l u s a t t r i b u t e s . A c c o r d i n g t o S o k o l o v (1975) t h e " n e u r o n a l model o f t h e s t i m u l u s r e g i s t e r s n ot o n l y t h e elementary, b u t a l s o t h e complex p r o p e r t i e s o f t h e s i g n a l , such as c o i n c i d e n c e or succession"' o f s e v e r a l s t i m u l i i n time ( p . 218)." Of c o u r s e , the p o s i t i n g o f such neurons i s h i g h l y s p e c u l a t i v e , and hazardous. The whole e x e r c i s e can become q u i t e p a i n f u l l y c i r c u l a r whenever one f i n d s o n e s e l f '.'fabricating" p a r t i c u l a r t y p e s o f f e a t u r e d e t e c t o r s t o p e r f o r m each and e v e r y p e r c e p t u a l t a s k ( s e e Dod w e l l , 1975) and t h e r e a r e a l t e r n a t i v e ways o f l o o k i n g a t p e r c e p t i o n , even a t t h e n e u r a l l e v e l . F o r example., W h i t f i e l d (1979). has. s u g g e s t e d t h a t a whole network o f n e u r a l elements i s r e s p o n s i b l e f o r each p e r c e p t u a l a c t . T h i s network i s d i s t r i b u t i v e and i s c o n t a i n e d i n many p a r a l l e l p a t h s . One s h o u l d n o t expect t o f i n d s i n g l e u n i t s o r even groups o f u n i t s , which a r e r e s p o n s i b l e f o r t h e p e r c e p t i o n o f o b j e c t s . M a f f e i (1977) has a l s o e x p r e s s e d a s i m i l a r n o t i o n : " I f one wants t o c o r r e l a t e n e u r a l a c t i v i t y w i t h t h e a c t u a l p e r c e p t i o n o f complex v i s u a l s t i m u l i , t h e c o n s i d e r a t i o n o f c o r t i c a l c e l l a c t i v i t y i n i s o l a t i o n from m i l l i o n s o f t h e i r n e u r a l n e i g h b o u r s seems t o me r a t h e r n a i v e .(p. 6 3 - 6 4 ) . " 57. Such a view does not n e c e s s a r i l y deny t h e e x i s t e n c e o f neurons t h a t a c t l i k e f e a t u r e d e t e c t o r s , but i t does deny t h a t f e a t u r e d e t e c t i o n , a t an elementary l e v e l , i s enough t o a c c o m p l i s h complex p e r c e p t u a l a c t s . Gf c o u r s e , i t i s p o s s i b l e t o t h e o r i z e about p e r c e p t i o n w i t h o u t a d e t a i l e d c o n s i d e r a t i o n o f u n d e r l y i n g n e u r a l mechanisms. A t a more g l o b a l l e v e l t h e r e s u l t s o f t h e p r e s e n t i n v e s t i g a t i o n c o u l d be seen as support f o r t h e s u g g e s t i o n t h a t our p e r c e p t u a l systems a r e s e n s i t i v e t o r e g u l a r i t y o r p a t t e r n and have a l i m i t e d c a p a c i t y t o absorb random or u n p r e d i c t a b l e events (Barlow, 1974). I n Experiments I I and I I I t h e synchronous s i g n a l s b e a r a s i m p l e and r e g u l a r t e m p o r a l r e l a t i o n s h i p t o each o t h e r , w h i l e t h e nonsynchronous s i g n a l s a r e e s s e n t i a l l y u npre-d i c t a b l e . An e a r l y s e n s i t i v i t y t o t h e i n v a r i a n t r e l a t i o n s h i p s between a u d i t o r y and v i s u a l i n f o r m a t i o n has o b v i o u s a d a p t i v e v a l u e and may p l a y an i m p o r t a n t r o l e i n p e r c e p t u a l development. As o t h e r s have s u g g e s t e d (Mendelson, Note 1; S p e l k e , Note 2) the d e t e c t i o n o f amodal p r o p e r t i e s which b e a r s t r u c t u r a l r e l a t i o n s c o u l d be t h e b a s i s ' f o r t h e a c q u i s i t i o n o f knowledge about s p e c i f i c a s p e c t s o f t h e environment such as which p a r t i c u l a r sounds 'go w i t h ' which p a r t i c u l a r s i g h t s . 58. F o o t n o t e s F o r i n s t a n c e , c o n s i d e r t h e many c r o s s - m o d a l i t y m a t c h i n g experiments which i n d i c a t e t h a t s t i m u l i p r e s e n t e d i n one m o d a l i t y can be p s y c h o p h y s i c a l l y equated, by s c a l i n g , t o s t i m u l i i n a n o t h e r m o d a l i t y . Or, more e s o t e r i c a l l y , t h e r e i s t h e phenomena o f s y n e s t h e s i a , i n which, f o r example, a p a r t i c u l a r sound may evoke v i v i d v i s u a l images. These a r e two o f many t y p e s o f s e n s o r y i n t e r r e l a t i o n which have been most r e c e n t l y and t h o r o u g h l y r e v iewed by Marks (1978). F o r example, i t has been shown t h a t changes i n t h e p h y s i c a l r a t e of a f l u t t e r i n g sound can cause changes i n the apparent f l i c k e r r a t e o f a s i m u l t a n e o u s l y viewed l i g h t , even though t h e p h y s i c a l r a t e i s h e l d c o n s t a n t (Regan & S p e k r e i j s e , 1977). T a y l o r and Campbell (1976) found t h a t the p r e s e n t a t i o n o f an i r r e l e v a n t n o i s e , d u r i n g a s v i s u a l r e a c t i o n time t a s k , d e c r e a s e d l a t e n c y t o r e s p o n s e . These are but two o f many i n v e s t i g a t i o n s which have shown t h a t s t i m u l i p r e s e n t e d i n one m o d a l i t y can i n f l u e n c e a c t i v i t y i n o t h e r m o d a l i t i e s . T h i s q u e s t i o n was o r i g i n a l l y posed by W i l l i a m Molyneux i n the e a r l y p a r t o f t h e e i g h t e e n t h c e n t u r y and was a d d r e s s e d t o t h e B r i t i s h p h i l o s o p h e r , John Locke. The i s s u e s r a i s e d by t h i s q u e s t i o n became t h e f o c u s o f some i n t e n s e p h i l o s o p h i c a l debate a t the time (see Morgan, 1977). O n e - t a i l e d t e s t s were u s e d f o r comparisons: f o r which t h e r e were • s p e c i f i c d i r e c t i o n a l p r e d i c t i o n s , o t h e r w i s e t w o - t a i l e d t e s t s were used. However a l l n o n - s i g n i f i c a n t r e s u l t s w i t h t w o - t a i l e d would n o t have r e a c h e d s i g n i f i c a n c e w i t h o n e - t a i l e d t e s t s and a l l s i g n i f i c a n t . r e s u l t s w i t h o n e - t a i l e d t e s t s would s t i l l be s i g n i f i -c a n t u s i n g t w o - t a i l e d t e s t s . 5. S t r i c t l y s p e a k i n g t h e t e r m 'phase' r e f e r s t o t h e t e m p o r a l r e l a t i o n -s h i p between two o r more s i g n a l s o f i d e n t i c a l period-.- I am u s i n g t h e t e r m i n a n o n - t e c h n i c a l manner f o r purposes o f e x p o s i t i o n . 6. A t t h i s p o i n t i t i s customary t o p r o c e e d no f u r t h e r w i t h p o s t hoc s t a t i s t i c a l a n a l y s e s n o t h a v i n g o b t a i n e d a s i g n i f i c a n t i n t e r a c t i o n . However, s i n c e a p r i o r i p r e d i c t i o n s were made T t e s t s were used t o f u r t h e r a n a l y z e t h e d a t a . A l s o , such t e s t s were seen t o a i d comparison o f t h e r e s u l t s w i t h t h o s e o f Experiment I I . 7. The importance o f t h e "meaning" o f t h e s t i m u l u s t o t h e i n f a n t i s b e i n g i g n o r e d f o r purposes o f e x p o s i t i o n . However f o r any f u l l a ccount o f i n f a n t v i s u a l b e h a v i o u r , p a r t i c u l a r l y a f t e r 6-8 weeks, t h i s i s a-most i m p o r t a n t f a c t o r ( s e e Bronson, 1974; H a i t h , 1977). 8. The s t r e n g t h s o f r e l a t i v e o v e r a b s o l u t e codes f o r s o l v i n g p e r c e p t u a l t a s k s have,been emphasized i n o t h e r c o n t e x t s as w e l l ( s e e B r y a n t , 1974). 60. REFERENCE NOTES 1. Mendelson, M.J. Amodal p r o p e r t i e s and a u d i t o r y - v i s u a l c o o r d i n a t i o n i n i n f a n c y . Paper p r e s e n t e d a t the I n t e r n a t i o n a l Conference on I n f a n t S t u d i e s , P r o v i d e n c e , March 1978. 2. S p e l k e , E.S. The i n f a n t s ' a c q u i s i t i o n o f knowledge o f b i m o d a l l y s p e c i f i e d e v e n t s . M a n u s c r i p t s u b m i t t e d f o r p u b l i c a t i o n , 1979. 3. M u i r , D., F i e l d , J . , & S i n c l a i r , M. 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J o u r n a l o f Comparative and P h y s i o l o g i c a l P s y c h o l o g y , 1968, 59, 189-192. ' ; Turkewitz,. G., & McGuire, I. I n t e r s e n s o r y f u n c t i o n i n g d u r i n g e a r l y development. I n t e r n a t i o n a l J o u r n a l o f M e n t a l H e a l t h , 1978, 7, 165-182. Wertheimer, M. Psycho-motor c o o r d i n a t i o n o f a u d i t o r y - v i s u a l space a t b i r t h . S c i e n c e , 1961, 134, 1692. W h i t f i e l d , I.C. The o b j e c t o f t h e s e n s o r y c o r t e x . B r a i n and B e h a v i o u r a l  E v o l u t i o n , 1979, 16, 129-154. W i c k e l g r e n , B.G. S u p e r i o r c o l l i c u i u s : Some r e c e p t i v e f i e l d p r o p e r t i e s o f b i m o d a l l y r e s p o n s i v e c e l l s . S c i e n c e , 1971, 173, 69-72. Winer, B.J. S t a t i s t i c a l p r i n c i p l e s i n e x p e r i m e n t a l d e s i g n . New Y o r k : M c G r a w - H i l l , 1971. Appendix A The o l d e s t group o f i n f a n t s i n Experiment I showed a s t r o n g p r e f e r -ence f o r the f a s t e r v i s u a l p a t t e r n , w h i l e t h e younger groups had a p o s i t i o n b i a s . The purpose o f t h e p r e s e n t experiment was t o check f o r p r e f e r e n c e s i n • 4—month-olds, andhhence a b i l i t y t o d i s c r i m i n a t e , between t h e f a s t and slow r a t e s u s ed i n Experiment I , when t h e r e was c o n t r o l f o r p o s i t i o n b i a s . T h i s was a c c o m p l i s h e d by p r e s e n t i n g the p a t t e r n s s u c c e s s i v e l y , r a t h e r t h a n s i m u l t a n e o u s l y . Method S u b j e c t s Twelve i n f a n t s p a r t i c i p a t e d i n the experiment. Data f o r 2 i n f a n t s were not f u l l y c o l l e c t e d due t o f u s s i n e s s d u r i n g t e s t i n g and have been e x c l u d e d f r o m t h e a n a l y s i s . The mean age o f t h e i n f a n t s was 4 months, 1 M a y (SD = 3 d a y s ) . I n f a n t s were r e c r u i t e d as b e f o r e . No attempt was made t o b a l a n c e o r c o n t r o l f o r r a c e , sex o r soc i o e c o n o m i c s t a t u s . S t i m u l i The s t i m u l i were the same as i n Experiment I , except t h a t t h e y were p r e s e n t e d f r o m a p o s i t i o n d i r e c t l y i n f r o n t o f t h e i n f a n t ( a s i n Experiments I I and I I I ) . The p a t t e r n w i t h t h e f a s t e r r a t e was always accompanied by t h e s y n c h r o n i z e d sound, as was t h e slower r a t e p a t t e r n . P r o c e d u r e Each i n f a n t was t e s t e d i n t h e e x p e r i m e n t a l . e n c l o s u r e as used i n a l l o f the exper i m e n t s . The p r o c e d u r e was i d e n t i c a l t o t h a t u s e d i n Experiment I I except t h a t t h e i n f a n t s r e c e i v e d o n l y 12 t r i a l s ; 6 w i t h t h e f a s t e r and 6 w i t h t h e sl o w e r r a t e , p r e s e n t e d i n a random o r d e r t o each i n f a n t . 67. R e s u l t s and D i s c u s s i o n A t_-test f o r c o r r e l a t e d samples was performed on t h e average l o o k i n g t i m e f o r t h e f a s t v s . t h e slow r a t e . The r e s u l t i n g t v a l u e ( t ( 9 ) = 1.93) was s i g n i f i c a n t a t t h e one-t a i l e d , but not t h e t w o - t a i l e d .05 l e v e l . The i n f a n t s demonstrated a m a r g i n a l p r e f e r e n c e f o r t h e f a s t e r r a t e p a t t e r n , as d i d group 3 i n Experiment I , when t h e i r l o o k i n g was c o n t r o l l e d f o r p o s i t i o n b i a s . Other r e s e a r c h e r s (Karmel, L e s t e r , M c C a r v i l l , Brown & Hoffman, 1977) have shown t h a t t h e v i s u a l a t t e n t i o n and o c c i p i t a l b r a i n r e s ponse o f 13 week o l d i n f a n t s t o temporal f r e q u e n c y c o v a r y , w i t h v i s u a l a t t e n t i o n and n e u r o p h y s i o l o g i c a l r e s p o n s e f u n c t i o n s h a v i n g s i m i l a r maxima a t 4.8 HZ and 5.8 HZ, r e s p e c t i v e l y . The i n f a n t s d i s p l a y e d l e s s v i s u a l a t t e n t i o n t o t e m p o r a l f r e q u e n c i e s b o t h h i g h e r and lower t h a n t h e maxima. A l t h o u g h , i n t h e p r e s e n t experiment, t h e f l a s h i n g l i g h t p a t t e r n was a l s o accompanied by sound and t h e o n - o f f p e r i o d s were not e q u a l , t h e r e s u l t s a r e complementary. A p r e f e r e n c e was found i n t h e same d i r e c t i o n as t h a t found by Karmel e t a l . 68. Appendix B Consent Form THE UiJIVERSITY OF BRITISH COLUMBIA 2075 Uesbr.ook H a l l VANCOUVER, B.C., CAUADA V6T 1U5 Department of Psychology • • CONSEHT FORM This experimental procedure has been requested by Keith Humphrey I have been informed of the procedures and understand them. I also understand that the procedures may be terminated at any time at my request. Procedure: The infant w i l l be held on his/her guardian's lap i n front of the t e s t i n g apparatus. The infant w i l l see and hear various patterns of l i g h t and sound. An i n v e s t i g a t o r w i l l watch the baby through a peephole and make a record of what the baby looks at. The baby w i l l be held by, and be under the c o n t r o l of, the guardian at a l l times. Uhenever the guardian desires there w i l l be a break i n or termination of the t e s t i n g session. Hy signature below c e r t i f i e s that I consent to the exoerimental procedure which has been described and which i s to be conducted on the iollowing date: i n the following place. Psychology Annex, U.B.C. and designated in the following manner: A s Above  D a t G:.: _ _ _ _ _ _ _ ilame: Signature: 

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