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Dichotic speech perception in two-year-old children Climan, Ita A. 1973

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DICHOTIC SPEECH PERCEPTION IN TWO-YEAR-OLD CHILDREN by I t a A. Climan B . S c , M c G i l l U n i v e r s i t y , 1971. A THESIS SUBMITTED IN PARTIAL FULFILMENT OP THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of P a e d i a t r i c s D i v i s i o n of Audiology and Speech Sciences We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH. COLUMBIA < J u l y , 1973 In presenting t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study. I f u r t h e r agree that permission f o r extensive copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e s . I t i s understood that copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my w r i t t e n permission. Department of P a e d i a t r i c s , D i v i s i o n of Audiology and Speech Sciences The U n i v e r s i t y of B r i t i s h Columbia Vancouver 8, Canada J u l y 13, 1973 ABSTRACT In the present study, d i c h o t i c l i s t e n i n g performance of two-year-old c h i l d r e n was i n v e s t i g a t e d . S i n g l e p a i r s of words were presented d i c h o t i c a l y t o t h i r t y - o n e c h i l d r e n be-tween GA 2-0-12 and 3-1-20. Each s u b j e c t was asked to p o i n t t o p i c t u r e s of what he had heard. For each p a i r of words presented, a s u b j e c t was shown three p i c t u r e s , which c o r -responded to the two s t i m u l u s words and a f o i l word. D i f -ferences between number of c o r r e c t responses f o r each ear were evaluated by means of a t t e s t . Words presented to the r i g h t ear were more ; e f f i c i e n t -l y r e c a l l e d than words presented to the l e f t ear, i n t h i s age group , which suggests t h a t the l e f t hemisphere has achieved some degree of dominance f o r language by age two. No s t a t i s t i c a l y s i g n i f i c a n t d i f f e r e n c e s were n o t e d , i n degree of r i g h t ear advantage, between males and females. When s t u d i e s u s i n g s c h o o l age and a d u l t s u b j e c t s are compared, i t appears t h a t the r i g h t ear advantage does not change i n mag-nit u d e or d i r e c t i o n from age two u n t i l adulthood. R e s u l t s of the present i n v e s t i g a t i o n are d i s c u s s e d i n r e l a t i o n t o e x i s t i n g t h e o r i e s of the development of c e r -e b r a l l a t e r a l i z a t i o n . An attempt was made to r e l a t e exper-i m e n t a l r e s u l t s from d i c h o t i c l i s t e n i n g , . EEG., and c l i n i c a l s t u d i e s . L i m i t a t i o n s of the experiment, as wall as suggestions f o r f u r t h e r r e s e a r c h , are d i s c u s s e d . TABLE OP CONTENTS Chapter 1 Chapter 2 Chapter 3 Chapter 4 Page ABSTRACT i i TABLE OP CONTENTS i i i LIST OP TABLES v LIST OP FIGURES v i ACKNOWLEDGEMENT a v i i INTRODUCTION 1 LITERATURE: REVIEW 6 2.0 I n t r o d u c t i o n .6 2.1 The A u d i t o r y Pathways and C o r t i c a l Language Areas 6 2.11 A u d i t o r y Pathways....... 6 2.12 D e t e c t i o n of C e n t r a l A u d i t o r y L e s i o n s 7 2.13 C o r t i c a l Areas Concerned With Language 8 2.2 D i c h o t i c L i s t e n i n g 1tf 2.3 Development of L a t e r a l i z a t i o n . . 18 2.4 D i c h o t i c S t u d i e s With C h i l d r e n . 29 STATEMENT OP PROBLEM 38 METHOD 40 4.1 P r e p a r a t i o n of D i c h o t i c Tapes.. 40 4.11 Recording S t i m u l i 40 4.12 P r e p a r a t i o n of Tape Loops 40 i i i Page 4-.13 P r e p a r a t i o n of Sti m -u l u s Tapes 4-1 4-. 2 S t i m u l u s Words 4-3 4-.3 S u b j e c t s 4-5 4-.4- E x p e r i m e n t a l Procedure. 4-6 Chapter 5 RESULTS 4-9 5.1 S c o r i n g 4-9 5.2 S u b j e c t s 4-9 5.3 R i g h t versus L e f t Ears 50 5.4- Sex 51 5.5 Age. 51 5.6 Age versus Sex 51 5.7 Handedness 54-5.8 L i n g u i s t i c A b i l i t y 54-5.9 C o u n t e r b a l a n c i n g 55 Chapter 6 DISCUSSION 56 REFERENCES 64-APPENDIX 1 O s c i l l o s c o p i c T r a c i n g s of Word-Pairs 71 APPENDIX 2 L i s t 1, L i s t 2 and F o i l Words 77 APPENDIX 3 D u r a t i o n ( i n msec.) of Stimulus Word-Pairs..... 78 APPENDIX 4- Order of P i c t u r e P l a c e -ment 79 i v LIST OF TABLES Table Page 5.1 S u b j e c t s by Age and Sex 50 5.2 T Values and Mean Percent REAs f o r Pour Age-Sex Groups 55 Y LIST OF FIGURES F i g u r e Page 2.1 Neuroanatomical Schema f o r the A u d i t o r y Asymmetries 14 2.2 Diagrammatic R e p r e s e n t a t i o n of A u d i t o r y Pathways i n the Case of R i g h t Hemispher-ectomy 15 2.3 Diagrammatic R e p r e s e n t a t i o n of A u d i t o r y Pathways i n the Case of Severed Corpus Callosum 15 2.4 Ear S u p e r i o r i t y and Age A c c o r d i n g to Two Measures 23 4.1 P r e p a r a t i o n of S t i m u l u s Tapes 42 5.1 I n d i v i d u a l Scores Rank Ordered A c c o r d i n g to Age 52 v i . ACKNOWLEDGEMENTS I wish to thank a l l those who had a p a r t i n t h i s t h e s i s $ - the members of my t h e s i s committee, Dr. John Delack, Dr. Juhn Wada, and e s p e c i a l l y , Dr. John G i l b e r t . - a l l the c h i l d r e n who p a r t i c i p a t e d and t h e i r mothers f o r t h e i r time and c o o p e r a t i o n . - Helen, G i n n i , Rachael and Marion f o r t h e i r encour-agement. THE FAMILY CIRCUS "Whisper on THIS s ide—I 'm left-eared." v i i CHAPTER 1 INTRODUCTION Throughout the c e n t u r i e s , man has s t r u g g l e d to under-stand the r e l a t i o n s h i p s between b r a i n and mind and t o c o r r e l a t e b ehavior w i t h areas of the b r a i n . Modern man has r e t a i n e d t h i s f a s c i n a t i o n w i t h the b r a i n , and a wealth of r e s e a r c h by n e u r o l o g i s t s , p s y c h o l o g i s t s and o ther s c i e n t i s t s i s accumu-l a t i n g . I t i s e v i d e n t t h a t the more we l e a r n , the more we a p p r e c i a t e the c o m p l e x i t i e s i n v o l v e d . Language, o f t e n c i t e d as the c a p a b i l i t y t h a t d i s t i n g u i s h e s man from lower animals, holds a s p e c i a l f a s c i n a t i o n . The study of a p h a s i a p r o v i d e d the f i r s t i n s i g h t s i n t o the problem of c e r e b r a l l a t e r a l i z a t i o n and l o c a l i z a t i o n f o r speech. Dax (1865) observed t h a t a p h asia r e s u l t s more o f t e n from l e f t hemisphere l e s i o n s than from l e s i o n s i n the r i g h t hemisphere. More r e c e n t evidence confirms t h a t , i n more than. 95$ of r i g h t handed i n d i v i d u a l s , a p h a s i a r e s u l t s from l e f t hemisphere l e s i o n s (Lenneberg, 1970). Broca (1861), on the b a s i s of one aphasic p a t i e n t , s t a t e d t h a t the t h i r d l e f t f r o n t a l c o n v u l u t i o n was the seat of a r t i c u l a t e language. Recent a n a t o m i c a l evidence f o r the asymmetrical nature of the c e r e b r a l hemispheres e x i s t s . Geschwind.and L e v i t s k y (1968) have shown t h a t the area behind Heschl's gyrus, which forms p a r t of the temporal speech c o r t e x , i s l a r g e r on the l e f t s i d e i n 2/5 of the a d u l t b r a i n s s t u d i e d , and l a r g e r on the r i g h t 1 2 s i d e i n on l y 11$. There remains l i t t l e doubt t h a t the l e f t hemisphere i s more i n t r i c a t e l y i n v o l v e d i n the language f u n c t i o n than the r i g h t hemisphere. T h i s i s t r u e f o r almost a l l r i g h t handed i n d i v i d u a l s and a l a r g e p r o p o r t i o n of l e f t handed i n d i v i d u a l s ( M i l n e r , Branch and Rasmussen, 1964). The development of c e r e b r a l l a t e r a l i z a t i o n i n c h i l d r e n has r e c e i v e d l e s s a t t e n t i o n than c e r e b r a l l a t e r a l i z a t i o n i n a d u l t s . I t i s g e n e r a l l y assumed t h a t , at b i r t h and f o r an u n s p e c i f i e d time a f t e r , the two hemispheres are both i n v o l v e d i n subsuming the language f u n c t i o n , and t h a t the r i g h t or non-dominant hemisphere g r a d u a l l y fades out i n importance ( Z a n g w i l l , 1960; Lenneberg, 1967)- The o n l y evidence c i t e d i s the l a c k of aphasic symptoms i n cases of i n f a n t i l e hemi-p l e g i a . The problems w i t h t h i s p o s i t i o n w i l l be d i s c u s s e d i n the l i t e r a t u r e survey.. I t i s not d i f f i c u l t t o account f o r the p a u c i t y of d i r e c t r e s e a r c h on the development of dominance. L a t e r a l i z a t i o n i s d i f f i c u l t , i f not i m p o s s i b l e , t o observe d i r e c t l y i n young c h i l d r e n ; young b r a i n s f o r anato m i c a l d i s s e c t i o n are few. Furthermore, i t i s the func-t i o n a l and not the anat o m i c a l d i f f e r e n c e s between the two hemispheres t h a t are most important. The Wada Sodium Amytal t e s t (Wada and Rasmussen, 1960) e n t a i l s too great a r i s k f o r r e s e a r c h purposes w i t h young c h i l d r e n . D i c h o t i c l i s t e n i n g t a s k s , which w i l l be d e s c r i b e d i n d e t a i l , have proved t o be safe and simple procedures f o r d e t e r m i n i n g s i d e of dominance f o r language i n a d u l t s . T h i s technique has been a p p l i e d t o c h i l d r e n as young as three years of age (Nagafuchi, 1970). 3 However, s i n c e d i c h o t i c l i s t e n i n g g e n e r a l l y r e q u i r e s a semantic a p p r e c i a t i o n of the m a t e r i a l p r e s e n t e d , a f a i r de-gree of a t t e n t i o n , and e i t h e r a v e r b a l or w r i t t e n response, no one has attempted to adapt the procedure t o c h i l d r e n younger than t h r e e . The age and p a t t e r n of development of c e r e b r a l dominance f o r language i s of i n t e r e s t f o r s e v e r a l reasons. The f i r s t i s t h e o r e t i c a l . L i n g u i s t s h y pothesize about the s t r u c t u r e and grammatical r u l e s of language t h a t supposedly r e f l e c t the speaker's u n d e r l y i n g competence. These t h e o r e t i c a l formu-l a t i o n s , t o be v a l i d , must c o i n c i d e w i t h n e u r o l o g i c a l evidence o r , at l e a s t , not c o n f l i c t w i t h what we know about the b r a i n . The f u n c t i o n and s t r u c t u r e of the b r a i n i s , u l t i m a t e l y , a s u b s t r a t e of language competence. The c h i l d ' s e v o l v i n g language competence must correspond i n some way t o neuro-l o g i c a l growth and m a t u r a t i o n . U n f o r t u n a t e l y , we are a long way from knowing what n e u r o l o g i c a l i n d i c e s c o r r e l a t e w i t h be-h a v i o r a l m i l e s t o n e s of language a c q u i s i t i o n . Nor do we know what the b e h a v i o r a l m i l e s t o n e s of language l e a r n i n g a r e . U l t i m a t e l y , these w i l l have t o be d e f i n e d i n r e f e r e n c e to n e u r o l o g i c a l development. T h i s problem i s o b v i o u s l y c i r -c u i t o u s . However, the development of n e u r o l o g i c a l i n d i c e s , such as c e r e b r a l l a t e r a l i z a t i o n , would have tremendous t h e o r e t i c a l impact. Such a development would have c l i n i c a l a p p l i c a t i o n s as w e l l . I t i s w e l l r e c o g n i z e d t h a t , i n order to understand the abnormal, we must f i r s t l ook at the normal course of 4 development. Thus, i n order to d e s c r i b e a c h i l d as 'neuro-l o g i c a l l y i m p a i r e d ' t o account f o r a language d e l a y , we must f i r s t have normative d a t a on n e u r o l o g i c a l changes d u r i n g language a c q u i s i t i o n . S e v e r a l c l i n i c a l c o n d i t i o n s have been h y p o t h e s i z e d to be s p e c i f i c a l l y a s s o c i a t e d w i t h slow development of dominance or incomplete dominance. Curry and Gregory (1969) have suggested t h a t s t u t t e r e r s show a l a c k of c e r e b r a l dominance, as t e s t e d on a d i c h o t i c word t e s t . T a y l o r (1962) and Bryden (1970) have suggested t h a t poor readers are s i g n i f i c a n t l y l e s s r i g h t ear dominant, and t h u s , by i n f e r e n c e , have incomplete domi-nance f o r language. Somners and T a y l o r (1972) t e s t e d language delayed and normal s i x - y e a r - o l d c h i l d r e n on a d i c h o t i c t a s k and found t h a t the language delayed c h i l d r e n showed a s m a l l e r r i g h t ear advantage (REA) f o r d i c h o t i c a l l y p r esented d i g i t s than d i d the normal c h i l d r e n . W i t e l s o n and R a b i n o v i t c h (1972) suggested t h a t c h i l d r e n w i t h a u d i o - l i n g u i s t i c d e f i c i t s may predominantly show a l e f t ear advantage f o r v e r b a l d i c h o t i c s t i m u l i . On the other hand, r e t a r d e d c h i l d r e n seem t o show a r i g h t ear advantage comparable to normals (Jones and Spreen, 1967). T h i s f i n d i n g would concur w i t h a g e n e r a l i n t e l l e c t u a l impairment, r a t h e r than a s p e c i f i c language problem. The above mentioned s t u d i e s are by no means i r r e p r o a c h a b l e or c o n c l u s i v e ; however, i t i s i n t e r e s t i n g to spe c u l a t e on the p o s s i b l e d i a g n o s t i c v a l u e of a w e l l documented measure of c e r e b r a l dominance. 5 A normative d e f i n i t i o n of the be g i n n i n g and the end of the process of c e r e b r a l l a t e r a l i z a t i o n would a l s o have p r o g n o s t i c v a l u e . I f primary language l e a r n i n g can o n l y take p l a c e w i t h i n the c r i t i c a l p e r i o d d u r i n g which c e r e b r a l l a t e r -a l i z a t i o n i s o c c u r r i n g (Lenneberg, 1967)) then such i n f o r m a t i o n might e v e n t u a l l y p r o v i d e c l u e s t o more accurate p r e d i c t i o n of when a language delayed c h i l d w i l l cease t o p r o g r e s s , when to terminate language therapy, and w i t h normal c h i l d r e n , when to i n t r o d u c e i n s t r u c t i o n i n a second language. CHAPTER 2 LITERATURE REVIEW 2.0 I n t r o d u c t i o n A survey of the l i t e r a t u r e p e r t i n e n t to t h i s r e s e a r c h t o p i c i s prese n t e d i n f o u r s e c t i o n s . S e c t i o n 2.1 d e s c r i b e s the p e r i p h e r a l and c e n t r a l a u d i t o r y pathways and the c o r t i c a l language ar e a s . S e c t i o n 2.2 reviews some of the r e s e a r c h i n d i c h o t i c l i s t e n i n g . S e c t i o n 2.3 d e a l s s p e c i f i c a l l y w i t h Lenneberg's schedule f o r the development of c e r e b r a l dominance f o r language and ' a l t e r n a t i v e t h e o r i e s t o t h i s schedule. S e c t i o n 2.4 d i s c u s s e s some of the r e l e v a n t r e s e a r c h on the development of l a t e r a l i z a t i o n i n young c h i l d r e n u s i n g the d i c h o t i c l i s t e n i n g t e c h n i q u e . I n t h i s l i t e r a t u r e r e v i e w and throughout the t h e s i s , the words l a t e r a l i z a t i o n and dominance w i l l be used i n t e r c h a n g e a b l y . 2.1 The A u d i t o r y Pathways and C o r t i c a l Language Areas 2.11 A u d i t o r y pathways We w i l l omit d e s c r i p t i o n of the o u t e r , middle and i n n e r ear mechanisms and f o l l o w the c o c h l e a r p o r t i o n of the e i g h t h c r a n i a l nerve from the c o c h l e a to the a u d i t o r y c o r t e x . There are f i v e neurons i n the pathway. The primary neuron from each i n n e r ear p r o j e c t s to both the d o r s a l and v e n t r a l c o c h l e a r n u c l e i on the same s i d e . Prom here, about 60$ of the f i b e r s c r o s s over t o the c o n t r a l a t e r a l s u p e r i o r o l i v e , w h i l e the 6 7 remaining 40$ p r o j e c t t o the i p s i l a t e r a l s u p e r i o r o l i v e . Thus, each c o c h l e a i s r e p r e s e n t e d i n the a u d i t o r y pathway on each s i d e . The f i b e r s , now forming the l a t e r a l l emniscus, p r o j e c t t o the i n f e r i o r c o l l i c u l u s , go t o the med i a l g e n i c u l a t e body of the thalamus, and from t h e r e , to the primary a u d i t o r y r e c e p t i o n area of the c o r t e x , the temporal gyrus of H e s c h l . Thus, d e s t r u c t i o n of p a r t of one a u d i t o r y pathway above the l e v e l of the s u p e r i o r o l i v e w i l l not d e s t r o y h e a r i n g on e i t h e r s i d e . Even w i t h the removal of one c e r e b r a l hemisphere, the pure tone t h r e s h o l d s f o r each ear w i l l be u n a f f e c t e d . 2.12 D e t e c t i o n of c e n t r a l a u d i t o r y l e s i o n s I t i s ev i d e n t t h a t some form of audiometric t e s t i n g more s e n s i t i v e than pure-tone t e s t i n g , i s needed t o r e v e a l l e s i o n s i n the c e n t r a l p o r t i o n s of the a u d i t o r y pathway. Bocca et a l . (1954) d e l i v e r e d low-pass f i l t e r e d speech (500 Hz) t o p a t i e n t s w i t h tumours of one temporal l o b e , who showed normal pure-tone t h r e s h o l d s b i l a t e r a l l y . The speech was d e l i v e r e d a l t e r n a t e l y t o each e a r . I t was found t h a t speech d i s c r i m i n a t i o n was s i g n i f i c a n t l y poorer i n the ear c o n t r a l a t e r a l to the l e s i o n . Calearo and A n t o n e l l i (1963),using i n t e r r u p t e d and d i s t o r t e d v o i c e , showed t h a t the d i s c r i m i n a t i o n scores of normal sub-j e c t s were symmetrical f o r normal e a r s , although s u b j e c t s w i t h l e s i o n s of one temporal lobe showed a d e f i c i t of 20-30$ on the ear c o n t r a l a t e r a l t o the l e s i o n , whether the l e s i o n was i n the r i g h t or the l e f t hemisphere. These s t u d i e s , w h i l e demonstrating asymmetries i n the a u d i t o r y pathways i n the case 8 of temporal lobe tumours, f a i l t o r e v e a l the n a t u r a l asymmetries f o r the p r o c e s s i n g of speech i n normal s u b j e c t s . So f a r , the o n l y w e l l documented way t o r e v e a l these asymmetries i n nor-mals i s to present s t i m u l i to both e a r s , d i c h o t i c a l l y . 2.13 C o r t i c a l areas concerned w i t h language Most of the i n f o r m a t i o n now a v a i l a b l e concerning the o r g a n i z a t i o n of language i n the b r a i n has been gained through the study of aphasic p a t i e n t s . Aphasia i s a multi-modal language d e f i c i t , which r e s u l t s from d e s t r u c t i o n of b r a i n t i s s u e , u s u a l l y f o l l o w i n g a c e r e b r o v a s c u l a r a c c i d e n t or head i n j u r y . The l e s i o n i s most o f t e n centered i n the l e f t temporal l o b e , although aphasia can r e s u l t from r i g h t hemisphere l e s i o n s . The aphasia i s o f t e n accompanied by r i g h t h e m i p l e g i a . The u s u a l r e s e a r c h procedure i s to d e s c r i b e the language d e f i c i t i n l i n g u i s t i c or p s y c h o l o g i c a l terms and then, p o s t mortem, to c o r r e l a t e these d e f i c i t s w i t h s i t e of l e s i o n . Other methods of g a i n i n g i n f o r m a t i o n i n c l u d e e l e c t r i c a l s t i m u l a t i o n of the b r a i n , and a b l a t i o n of p a r t s of the b r a i n i n c o r r e l a t i o n w i t h language d e f i c i t . Some of the problems a s s o c i a t e d w i t h a l l these methods i n c l u d e : (1) d i f f i c u l t y i n g e n e r a l i z i n g from abnormal to normal p o p u l a t i o n s , (2) d i f f i c u l t i e s i n s p e c i f y i n g the r e l a t i o n s h i p between e l e c t r i c a l and normal s t i m u l a t i o n , (3) i m p r e c i s i o n i n s p e c i f y i n g the exact s i z e and s i t e of l e s i o n , or the exact area s t i m u l a t e d or a b l a t e d , (4) s m a l l number of cases a v a i l a b l e f o r study, (5) d i f f i c u l t y i n s p e c i f y i n g the s i z e of l e s i o n at time of i n j u r y from the s i z e post mortem, 9 and (6) d i f f i c u l t y i n s e p a r a t i n g e f f e c t s of a b l a t i o n from e f f e c t s of surgery. I t should be remembered t h a t almost none of the r e s e a r c h a v a i l a b l e c oncerning the s t r u c t u r e of language i n the b r a i n comes from c a r e f u l r e s e a r c h on a l a r g e i n t a c t p o p u l a t i o n . D e s p i t e t h i s s t a t e of a f f a i r s , i n f o r m a t i o n i s a v a i l a b l e c oncerning those areas of the l e f t temporal lobe which are f e l t t o be a s s o c i a t e d w i t h language. A summary of the i d e n -t i f i e d areas from Whitaker (1969) w i l l be p r e s e n t e d . Whitaker i d e n t i f i e s f o u r p e r i p h e r a l and f o u r c e n t r a l areas a s s o c i a t e d w i t h language. A. The f o u r p e r i p h e r a l areas are: a) P e r i p h e r a l p r o d u c t i o n systems (1) Broca's area - L e s i o n s here cause a p r a x i a or l o s s of motor c o n t r o l of speech. (2) Exner's area - L e s i o n s here are thought to cause impairment of w r i t i n g a b i l i t y . b) P e r i p h e r a l r e c o g n i t i o n systems (3) Heschl's gyrus - T h i s i s the primary a u d i t o r y p r o -j e c t i o n area and r e c e i v e s f i b e r s from the m e d i a l g e n i c u l a t e body. I t i s not r e a l l y known what e f f e c t s l e s i o n s i n t h i s area cause; although pure-tone t h r e s h -o l d s are u n a f f e c t e d , i t i s thought t h a t l e s i o n s i n t h i s area i n the dominant hemisphere would, i n some way, i n t e r f e r e w i t h the a u d i t o r y p r o c e s s i n g of speech. (4) Angular gyrus - T h i s area i s l o c a t e d between the somesthetic, a u d i t o r y , v i s u a l and speech areas and 10 r e c e i v e s a s s o c i a t i o n f i b e r s from these areas. L e s i o n s here cause major impairments i n r e a d i n g and w r i t i n g . B. The f o u r c e n t r a l language areas are: (5) Wernicke's area - Lesions i n t h i s area g e n e r a l l y a f f e c t the comprehension of spoken language, and t h e r e are o f t e n s e r i o u s e f f e c t s on speech p r o d u c t i o n as w e l l . (6) Supermarginal gyrus - L e s i o n s i n t h i s area seem to upset some aspects of grammar. (7) P o s t e r i o r p o r t i o n of the i n f e r i o r temporal gyrus -T h i s area has been t e n t a t i v e l y c a l l e d the 'naming c e n t e r ' by Whitaker; i t seems to be i n v o l v e d i n the a b i l i t y to name o b j e c t s . However, l i t t l e more than s p e c u l a t i v e d a t a e x i s t s and f u r t h e r c h a r a c t e r i z a t i o n of t h i s area must await more r e l i a b l e d a t a . L e s i o n s i n t h i s area are thought to cause amnesic a p h a s i a , word f i n d i n g d i f f i c u l t i e s and s y n t a c t i c e r r o r s . (8) Arcuate F a s c i c u l u s - T h i s i s p a r t of a bundle of a s s o c i a t i o n f i b e r s which connect p a r t s of the f r o n t a l lobe w i t h p a r t s of the temporal l o b e . L e s i o n s here are thought to a f f e c t p h o n o l o g i c a l o r g a n i z a t i o n d u r i n g speech p r o d u c t i o n . I t i s e v i d e n t t h a t what i s known about the o r g a n i z a t i o n of language i n the b r a i n i s h i g h l y s p e c u l a t i v e , b e i n g more c o n j e c t u r e than f a c t . I t i s not yet known what happens i n the b r a i n d u r i n g language a c q u i s i t i o n , or d u r i n g encoding or de-c o d i n g . Even i f the above areas c o u l d be d e l i n e a t e d e x a c t l y , 11 because they were demarcated i n brain-damaged p o p u l a t i o n s , i t i s not known how they correspond t o the f u n c t i o n i n g of an i n t a c t dynamic language system. New ways must be found to expose the f u n c t i o n a l and b e h a v i o r a l c o r r e l a t e s of the o r g a n i z a t i o n of language, i n l a r g e numbers of normal s u b j e c t s . 2.2 D i c h o t i c L i s t e n i n g Broadbent (195 )^ found t h a t when both ears are s t i m u l a t e d s i m u l t a n e o u s l y w i t h two d i f f e r e n t s e r i e s of s t i m u l i , both s e r i e s e l i c i t responses, but they do so one a f t e r the ot h e r . Thus, when th r e e d i g i t s (such as 716) are a p p l i e d t o one ear wh i l e t h r e e other d i g i t s (such as 253) axe a p p l i e d t o the opposite e a r , s u b j e c t s tend t o respond e i t h e r 716253 or 253716 but seldom 721563- T h i s method of simultaneous p r e -s e n t a t i o n of d i f f e r e n t s t i m u l i t o each ear came t o be known as " d i c h o t i c l i s t e n i n g " and formed, the b a s i s f o r an important area of r e s e a r c h . Kimura (1961a) compared the p r e o p e r a t i v e and p o s t o p e r a t i v e performance of p a t i e n t s w i t h e i t h e r l e f t or r i g h t c o r t i c a l damage u s i n g Broadbent 1s method of simultaneous p r e s e n t a t i o n of d i g i t s . She found t h a t temporal lobe e x c i s i o n of e i t h e r s i d e i m p a i r e d the p e r c e p t i o n of d i g i t s a r r i v i n g a t the c o n t r a -l a t e r a l e a r . However, both ears performed e q u a l l y w e l l w i t h monaural or a l t e r n a t i n g ear p r e s e n t a t i o n . Kimura a l s o found t h a t the o v e r a l l performance of p a t i e n t s w i t h l e f t temporal lobe damage was poorer than t h a t of p a t i e n t s w i t h r i g h t temporal lobe damage. T h i s r e s u l t confirmed a g e n e r a l 12 assumption t h a t the l e f t temporal lobe p l a y s a more impor-t a n t r o l e than the r i g h t i n the p e r c e p t i o n of v e r b a l s t i m u l i . A t h i r d , and perhaps most p r o v o k i n g , f i n d i n g was t h a t a l l p a t i e n t s , p r e o p e r a t i v e l y , r e c e i v e d h i g h e r scores f o r the r i g h t ear than the l e f t i n the d i c h o t i c t a s k . Kimura (1961b) ad-m i n i s t e r e d the d i c h o t i c t a s k to three groups: (1) l e f t hemi-sphere -dominant ( f o r speech) p a t i e n t s (as confirmed by the •Vada Sodium Amytal t e s t ) , (2) r i g h t hemisphere dominant p a t i e n t s , and (3) normal right-handed people who presumably were l e f t hemisphere dominant. The f i r s t two groups had e p i l e p t o g e n i c l e s i o n s of v a r i o u s p a r t s of the b r a i n . The r e s u l t s i n d i c a t e d an REA f o r the l e f t hemisphere dominant p a t i e n t s and f o r the normal group. For those p a t i e n t s w i t h speech r e p r e s e n t e d i n the r i g h t hemisphere, the l e f t ear was found t o be more e f f i c i e n t . Kimura (1961a) p o s t u l a t e d t h a t connections between each hemisphere and i t s c o n t r a l a t e r a l ear are st r o n g e r and/or more numerous than such connections t o the i p s i l a t e r a l e a r . I n c a t s , t h i s has been confirmed both a n a t o m i c a l l y and p h y s i o -l o g i c a l l y (Rosenzweig, 1951). T h i s c o n t r a l a t e r a l advantage, i n c o n j u n c t i o n w i t h l e f t hemisphere dominance f o r speech, accounted, she f e l t , f o r the g r e a t e r e f f i c i e n c y of the r i g h t ear. S ince both ears perform e q u a l l y w e l l when s t i m u l a t e d s e p a r a t e l y , Kimura concluded t h a t an REA e x i s t s o n l y when th e r e i s c o m p e t i t i o n between the two ears and, i n t h i s case, the c o n t r a l a t e r a l connections i n h i b i t the i p s i l a t e r a l con-n e c t i o n s . Kimura's neuroanatomical scheme f o r the observed 13 a u d i t o r y asymmetries i s shown i n F i g u r e 2.1. Evidence f o r s u b c o r t i c a l s u p p r e s s i o n comes i n d i r e c t l y from s t u d i e s of hemispherectomized and s p l i t - b r a i n s u b j e c t s . Kimura (1961a) found t h a t the l e f t ear scores of r i g h t hemispherectomized p a t i e n t s i n a d i c h o t i c t a s k were s e v e r e l y depressed. Since i n t h i s case the o n l y pathways a v a i l a b l e are those i p s i l a t e r a l and c o n t r a l a t e r a l t o the l e f t hemisphere, s u b c o r t i c a l s u p r e s s i o n can be assumed to be t a l c i n g p l a c e . T h i s s i t u a t i o n i s diagrammed i n F i g u r e 2.2. S i m i l a r l y , i t has been found t h a t c a l l o s a l l y severed p a t i e n t s are able t o r e c a l l almost no v e r b a l m a t e r i a l presented to the l e f t ear i n a d i c h o t i c t a s k ( M i l n e r , T a y l o r and S p e r r y , 1968) and, a g a i n , o n l y one c o n t r a -l a t e r a l and one i p s i l a t e r a l pathway to the speech area are f u n c t i o n a l . T h i s s i t u a t i o n i s diagrammed i n F i g u r e 2 .3 . Although c o n t r a l a t e r a l - i p s i l a t e r a l s u p p r e s s i o n i s a f a c t o r i n p r o d u c i n g the REA, i t i s d e f i n i t e l y not the o n l y f a c t o r . I t i s probable t h a t the c r o s s - c a l l o s a l r o u t e from the r i g h t t o the l e f t hemisphere i s used f o r s t i m u l i presented d i c h o t i c a l l y t o the l e f t e a r . I n such a case, the l e f t ear s i g n a l has one more synapse than the r i g h t ear s i g n a l and thus the REA might be accounted f o r by e i t h e r e a r l i e r a r r i v a l of the r i g h t ear s i g n a l to the speech area or e l s e i n c r e a s e d de-g r a d a t i o n of the l e f t ear s i g n a l because of the g r e a t e r d i s -tance t r a v e l l e d (Sparks, Goodglass and N i c k e l , 1970). The d e p r e s s i o n of the l e f t ear scores i n cases of r i g h t -hemispherectomized and s p l i t - b r a i n s u b j e c t s makes i t c l e a r t h a t the l e f t ear s t i m u l i f o l l o w the s t r o n g c o n t r a l a t e r a l 14-LEFT HEMISPHERE (DIGITS) RIGHT HEMISPHERE (MELODIES) LEFT EAR RIGHT EAR F i g u r e 2.1 Neuroanatomical schema f o r the a u d i t o r y asymmetries. (from Kimura,1967,fig.2,p.174-) 15 LEFT HEMISPHERE LEFT EAR RIGHT EAR F i g u r e 2.2 Diagrammatic r e p r e s e n t a t i o n of a u d i t o r y pathways i n the case of r i g h t hemi-spherectomy. LEFT HEMISPHERE RIGHT HEMISPHERE LEFT EAR RIGHT EAR F i g u r e 2.3 Diagrammatic r e p r e s e n t a t i o n of a u d i t o r y pathways i n the case of severed corpus c a l l o s u m . 16 pathways to the r i g h t hemisphere before c r o s s i n g over t o the l e f t hemisphere language a r e a . I f c o n t r a l a t e r a l - i p s i l a t e r a l s u p p r e s s i o n was the o n l y f a c t o r , then r i g h t hemispherectomized and s p l i t - b r a i n s u b j e c t s would perform l i k e normals, i n a d i c h o t i c t a s k . Sparks and Geshwind (1968) t e s t e d one s u b j e c t who had had the n e o c o r t i c a l commissures s e c t i o n e d . T h i s sub-j e c t r e c a l l e d 100$ of the words presented t o each ear mon-a u r a l l y , but showed 100$ e x t i n c t i o n of s t i m u l i coming i n the l e f t ear i n the d i c h o t i c s i t u a t i o n . When t h i s s u b j e c t was r e -t e s t e d s e v e r a l times and t o l d t o concentrate on the l e f t ear s t i m u l i , he was able to r e c a l l 100$ of the r i g h t ear s t i m u l i and 35$ of the l e f t ear s t i m u l i . The authors suggest t h a t "the l e f t ear may improve from i t s i n i t i a l l y lower l e v e l a f t e r c a l l o s a l s e c t i o n or damage to the r i g h t temporal r e g i o n , p a r t i c u l a r i l y i f s p e c i a l t r a i n i n g i s g i v e n " . (Sparks and Geschwind, 1968, p. 15.) I t i s e v i d e n t t h a t both c o n t r a -l a t e r a l - i p s i l a t e r a l s u p p r e s s i o n and the c r o s s - c a l l o s a l r o u t e from the r i g h t t o the l e f t hemisphere must be accounted f o r i n a t h e o r e t i c a l model of d i c h o t i c l i s t e n i n g . Numerous s t u d i e s w i t h normal a d u l t s f o l l o w e d which con-f i r m e d and extended Kimura's o r i g i n a l r e s u l t s . Kimura (1964) found a s i g n i f i c a n t l e f t ear advantage f o r the r e c o g n i t i o n of melodies, which confirmed M i l n e r ' s (1962) f i n d i n g t h a t the r i g h t hemisphere i s dominant f o r the p e r c e p t i o n of music. Furthermore, s i n c e v e r y f a m i l i a r , as w e l l as n o n f a m i l i a r , melodies were p e r c e i v e d more e f f i c i e n t l y by the l e f t e a r , the p o s s i b i l i t y t h a t the REA found f o r d i g i t s concerned the 17 f a m i l i a r nature of these s t i m u l i ( r a t h e r than the v e r b a l n ature) was negated. An REA was a l s o found f o r words and f o r nonsense s y l l a b l e s (Kimura, 1967; C u r r y , 1968) and f o r back-ward speech sounds ( o b t a i n e d by i n v e r t i n g a tape c o n t a i n i n g nonsense s y l l a b l e s and p l a y i n g i t back i n the normal d i r e c t i o n ) (Kimura and P o l b , 1968). These s t u d i e s p r o v i d e s t r o n g support f o r the suggestion t h a t the c r i t i c a l d i s t i n g u i s h i n g c h a r a c t e r i s t i c s of speech sounds are not r e l a t e d t o meaningfulness, f a m i l i a r i t y , or c o n c e p t u a l content. (Kimura and P o l b , 1968, p. 396) Studdert-Kennedy and Shankweiler (1970) presented CVC nonsense s y l l a b l e s d i c h o t i c a l l y , s y s t e m a t i c a l l y m a n i p u l a t i n g o n l y one sound w i t h i n the s y l l a b l e at a time . A s i g n i f i c a n t REA f o r the p e r c e p t i o n of consonants, but not of vowels, was found. These authors have h y p o t h e s i z e d t h a t , w h i l e the a u d i t o r y system of each hemisphere appears e q u a l l y capable of e x t r a c t i n g parameters such as i n t e n s i t y , frequency and time, o n l y the l e f t hemisphere i s able t o e x t r a c t the l i n g u i s t i c f e a t u r e s i n h e r e n t i n consonants. Perhaps most important, the r e s u l t s of Studdert-Kennedy and Shankweiler's experiment demonstrated t h a t , whatever the mechanism of speech p e r c e p t i o n i n the l e f t hemisphere, i t i s s e n s i t i v e t o the phonetic content of an u t t e r a n c e . Thus, the p e r c e p t i o n of pho n e t i c cues may i n v o l v e a process as " l i n g u i s t i c " I n nature as p e r c e p t i o n a t the semantic and s y n t a c t i c l e v e l s . The p e r c e p t u a l asymmetry e x p l a n a t i o n of the REA proposed by Kimura (1961b) was w i d e l y c h a l l e n g e d . Others e x p l a i n e d i t as asymmetrical d i v i s i o n of a t t e n t i o n t o l e f t and r i g h t ear 18 i n p u t s (Treisman and Gef f e n , 1968) or asymmetrical s h o r t term memory storage and/or a tendency to r e p o r t the r i g h t ear f i r s t ( I n g l i s * 1965). N e i t h e r a t t e n t i o n a l nor memory asymmetries c o u l d be the s o l e determiner of the REA because (1) the r i g h t ear i s s u p e r i o r on both the f i r s t and second channels r e p o r t e d (Bryden, 1967); (2) the r i g h t ear i s more e f f i c i e n t than the l e f t when order of r e c a l l i s c o n t r o l l e d , as w e l l as i n the f r e e r e c a l l s i t u a t i o n (Broadbent and Gregory, 1964; S a t z , 1968); and most important, (3) the REA i s m a t e r i a l s p e c i f i c ; t h a t i s , when m u s i c a l s t i m u l i ( M i l n e r , 1962; Kimura, 1964; Spreen, S p e l l a c y and R e i d , 1970) or environmental sounds ( C u r r y , 1967) are presented d i c h o t i c a l l y , a l e f t ear advantage i s found. An e x p l a n a t i o n based on memory or a t t e n t i o n a l f a c t o r s o n l y cannot account f o r t h i s s p e c i f i c i t y (Darwin, 1969). 2.3 Development of L a t e r a l i z a t i o n L i t t l e i s known about when and how the b r a i n develops i t s l a t e r a l i z a t i o n f o r speech. Z a n g w i l l (1960) i based on a revie w of the scant l i t e r a t u r e of hemispherectomy i n e a r l y c h i l d h o o d , s t a t e d : I t would t h e r e f o r e seem t h a t at b i r t h the two hemispheres are v i r t u a l l y e q u i p o t e n t i a l i n r e -gard t o the a c q u i s i t i o n of language and t h a t dominance may be r e a d i l y s h i f t e d i n consequence of e a r l y b r a i n i n j u r y . Although t h i s p l a s t i c i t y — and hence the p o s s i b i l i t y of a s h i f t i n dominance — appear to d i m i n i s h r a p i d l y w i t h i n c r e a s i n g age, i t s l i m i t s have y e t to be d e f i n e d w i t h p r e c i s i o n . A l l t h a t can be s a i d w i t h any c o n f i d e n c e _ i s t h a t c e r e b r a l dominance appears t o evolve p a r i passu w i t h the development of speech and t o be f u l l y e s t a b l i s h e d w e l l before the advent of m a t u r i t y . ( Z a n g w i l l , 1960, p. 2) 19 The f i r s t person t o t h e o r i z e about an upper and lower l i m i t t o the process of l a t e r a l i z a t i o n was Lenneberg (1966, 1967). As h i s t h e o r i e s have r e c e i v e d wide acceptance i n the l i t e r a t u r e , they w i l l be d i s c u s s e d i n some d e t a i l . Lenneberg c o r r e l a t e d t h r e e f a c t o r s : (1) m a t u r a t i o n of the b r a i n , (2) the n o t i o n of a c r i t i c a l p e r i o d f o r primary language a c q u i s i t i o n , and (3) l a t e r a l i z a t i o n of the speech f u n c t i o n t o the l e f t or dominant hemisphere. Parameters of b r a i n m a t u r a t i o n such as b r a i n weight, decrease i n c e l l d e n s i t y , and neurochemical i n d i c e s a l l show r a p i d change i n i t i a l l y , r e a c h i n g 60$ of t h e i r a d u l t v a l u e s i n the f i r s t two years of l i f e . Thus, age two appears t o be the begi n n i n g of a p e r i o d d u r i n g which s t r u c t u r a l and chemical changes de-c e l e r a t e . Prom age two t o approximately age t h i r t e e n , such parameters i n c r e a s e more s l o w l y and t h e i r a d u l t v a l u e s are reached a t around p u b e r t y . T h i s time p e r i o d between the ages of two and t h i r t e e n i s hypo t h e s i z e d by Lenneberg t o be c r i t i c a l f o r p r imary language a c q u i s i t i o n and s i m i l a r l y the p e r i o d i n which speech and language become g r a d u a l l y and i r r e v e r s i b l y e s t a b l i s h e d i n the l e f t hemisphere. A c c o r d i n g t o Lenneberg, the two hemispheres are e q u i -p o t e n t i a l f o r the development of language i n the f i r s t two years of l i f e , t h a t i s , before the c h i l d has a c q u i r e d language. L a t e r a l i z a t i o n then takes p l a c e as a r e s u l t of a p r o g r e s s i v e decrease i n involvement of the r i g h t hemisphere. By puberty the b r a i n has reached i t s mature s t a t e and c e r e b r a l l a t e r -a l i z a t i o n i s i r r e v e r s i b l y e s t a b l i s h e d . 20 Most of Lenneberg's evidence i s based on Basser's- (1962) review of c h i l d r e n who have s u s t a i n e d u n i l a t e r a l l e s i o n s . I n h a l f of those c h i l d r e n who s u s t a i n l e s i o n s before the on-set of speech, speech i s delayed. However, t h i s d e l a y occurs as o f t e n w i t h r i g h t as w i t h l e f t hemisphere damage, sug g e s t i n g c e r e b r a l dominance has not yet been e s t a b l i s h e d . I n c h i l d r e n who s u s t a i n e d l e s i o n s between ages two and t e n , Basser noted d i s t u r b e d speech r e s u l t i n g from l e f t hemisphere l e s i o n s 85$ of the time and from r i g h t hemisphere damage 4-5$ of the time. L e f t - s i d e d l e s i o n s i n c h i l d r e n of twelve and t h i r t e e n years of age produced i r r e v e r s i b l e language d i s o r d e r s comparable t o a p h asia i n a d u l t s w h i l e r i g h t - s i d e d l e s i o n s s u s t a i n e d at t h i s age almost never produced a language d i s o r d e r . The c r i t i c a l p e r i o d f o r primary language a c q u i s i t i o n i s , a c c o r d i n g t o Lenneberg, l i m i t e d by both m a t u r a t i o n of the b r a i n and completion of c e r e b r a l l a t e r a l i z a t i o n ? language l e a r n i n g by mere exposure cannot take p l a c e before the b r a i n has reached a c e r t a i n m a t u r a t i o n a l l e v e l or a f t e r completion of l a t e r a l i z a t i o n of f u n c t i o n and l o s s of p l a s t i c i t y . I n summary, . . . c e r e b r a l l a t e r a l i z a t i o n of the speech f u n c t i o n i s t o a c e r t a i n e x t e n t a p l a s t i c phenomenon. No l a t e r a l i z a t i o n seems t o be p r e s e n t before age two or t h r e e ; then t h e r e i s a p e r i o d t h a t l a s t s t o about age t e n or twelve d u r i n g which c e r e b r a l l a t e r a l i z a t i o n f o r speech i s g r a d u a l l y e s t a b l i s h e d but may s t i l l be pushed back i n t o the r i g h t hemi-sphere i f the l e f t hemisphere i s d i s t u r b e d . A f t e r p u b e r t y , l a t e r a l i z a t i o n i s n o r m a l l y f i r m l y e s t a b -l i s h e d t o the l e f t , and the r i g h t hemisphere i s no f u r t h e r i n v o l v e d i n speech f u n c t i o n s ; l e s i o n s t o the l e f t i n t e r f e r e w i t h speech, but l e s i o n s to the r i g h t do n o t . (Lenneberg, 1966, p. 47) 21 U n t i l v e r y r e c e n t l y , Lenneberg's schedule f o r the development of l a t e r a l i z a t i o n has remained unchallenged and has been w i d e l y quoted i n c l i n i c a l t e x t s p u b l i s h e d after.1967 ( B e r r y , 1969, p. 42; P e r k i n s , 1971, p. 119; W i n i t z , 1971, p. 1129). Most c l i n i c a l t e x t s p u b l i s h e d before B i o l o g i c a l  Foundations of Language make no mention of l a t e r a l i z a t i o n of speech i n t h e i r d i s c u s s i o n s of language a c q u i s i t i o n . Luchsinger and A r n o l d (1965), f o r example, s t a t e t h a t the f o u r f u n c t i o n s e s p e c i a l l y important f o r the normal development of language are: (1) sensory development, (2) motor development, (3) psychomotor development, and (4) i n t e l l e c t u a l development. R e c e n t l y , however, both the upper and lower l i m i t s of Lenneberg's c r i t i c a l p e r i o d f o r l a t e r a l i z a t i o n have been questioned. Krashen and Harshman (1972) have p o s t u l a t e d t h a t l a t e r a l i z a t i o n i s complete by age f i v e , r a t h e r than puberty as suggested by Lenneberg. Two types of evidence are p r e -sented: (1) changes i n degree of l a t e r a l i z a t i o n between the ages of f i v e and t e n , and (2) the observed e f f e c t s of u n i -l a t e r a l b r a i n l e s i o n s on speech when such l e s i o n s occur be-tween f i v e and t e n years of age. I f l a t e r a l i z a t i o n i s g r a d u a l l y e s t a b l i s h e d throughout c h i l d h o o d u n t i l p u b e r t y , then one might expect t h a t the REA would i n c r e a s e w i t h c h r o n o l o g i c a l age u n t i l p u b e r t y . However, most d i c h o t i c l i s t e n i n g s t u d i e s w i t h c h i l d r e n as s u b j e c t s r e p o r t a decrease i n REA w i t h i n c r e a s i n g age. T h i s f i n d i n g can i n p a r t be e x p l a i n e d by an i n c r e a s e i n accuracy. Thus, as the c h i l d ' s t o t a l score (both ears) i n c r e a s e s , the mag-ni t u d e of the d i f f e r e n c e between ears w i l l decrease. I n the 22 l i m i t i n g case, a c h i l d who r e c e i v e s a p e r f e c t score w i l l not e x h i b i t any ear advantage. Krashen (1972), u s i n g a percent of e r r o r s method of a n a l y s i s , has analysed data from t h r e e developmental s t u d i e s (Kimura, 1963; Knox and Kimura, 1970; and Geffner and Hochberg, 1971) and has found no change i n magnitude of REA from the ages of f o u r or f i v e u n t i l n i n e . H i s a n a l y s i s of the p r e v i o u s f i n d i n g s i s presented i n F i g -ure 2.4. Another method t o s t a t i s t i c a l l y c o n t r o l f o r d i f f e r -ences i n accuracy i s presented i n Kuhn (1972). C l i n i c a l d a t a on the e f f e c t s of b r a i n l e s i o n s on speech were a l s o re-examined by Krashen (1972). Basser (1962) d i s c u s s e s f i f t e e n c h i l d r e n who s u s t a i n e d l e s i o n s to the r i g h t hemisphere a f t e r they had a c q u i r e d speech. Of thes e , seven ( o r 4-5$) e x h i b i t e d "disturbed"speech . However, a l l seven of these c h i l d r e n were below f i v e years c h r o n o l o g i c a l age, adding support t o the " l a t e r a l i z a t i o n by f i v e " hypoth-e s i s of Krashen and Harshman (1972). The best t e s t of the a b i l i t y of the r i g h t hemisphere t o subserve language can be evidenced i n p a t i e n t s who have had the l e f t hemisphere removed, s i n c e i t i s not known t o what extent language can be c o n t r o l l e d or i n h i b i t e d by a dam-aged hemisphere. Basser (1962) p r e s e n t e d 52 cases of hem-ispherectomy i n c h i l d h o o d , which Lenneberg (1967) c i t e s as evidence t h a t the r i g h t hemisphere i s capable of t a k i n g over language f u n c t i o n before puberty. When Basser's d a t a i s more c a r e f u l l y examined (Krashen, 1972), i t i s seen t h a t 4-2 out of 23 <iod 4- 5 6 7 8 9 age F i g u r e 2.4 Ear s u p e r i o r i t y and age a c c o r d i n g t o two measures. (Data from Kimura,1963, Knox and Kimura, 1970,Geffner and Hochberg,1971, combined) (from Krashen,1972,fig.3.1,P-28) 24 the 52 cases d i s c u s s e d by Lenneberg as "before teens" were a c t u a l l y under f i v e when damage was s u s t a i n e d , a f u r t h e r support f o r the " l a t e r a l i z a t i o n by f i v e " h y p o t h e s i s . I t w i l l be seen i n l a t e r d i s c u s s i o n on the e a r l y l i m i t of l a t e r a l i z a t i o n t h a t Lenneberg makes s i m i l a r g e n e r a l i z a t i o n s about c h r o n o l o g i c a l age when i n t e r p r e t i n g Basser's d a t a . The p r e c e d i n g c l i n i c a l evidence does not exclude e i t h e r the t h e o r y of " l a t e r a l i z a t i o n by f i v e " or l a t e r l a t e r a l i z a t i o n , f o r i t i s f i r s t necessary t o show t h a t l e f t hemisphere damage a f t e r the age of f i v e and before puberty does cause permanent language d i s t u r b a n c e and, c o n v e r s e l y , t h a t r i g h t hemisphere damage at t h i s age does-not. U n f o r t u n a t e l y , o n l y t h r e e l e f t hemisphere p a t i e n t s i n t h i s age range have been r e p o r t e d i n the l i t e r a t u r e ( f o r r e v i e w , see Krashen, 1972) and none are d e s c r i b e d i n s u f f i c i e n t d e t a i l t o i l l u m i n a t e t h i s t h e o r e t i c a l problem. Thus, c o n c l u s i v e p r o o f of c e r e b r a l l a t e r a l i z a t i o n complete by f i v e years of age has y e t t o be e s t a b l i s h e d . Lenneberg s t a t e s t h a t The i n f a n t ' s obvious i n c a p a c i t y t o l e a r n a l l but the most p r i m i t i v e beginnings of language d u r i n g h i s f i r s t f i f t e e n months i s , at l e a s t i n t u i t i v e l y , a t t r i b u t a b l e t o a g e n e r a l s t a t e of c e r e b r a l i m m a t u r i t y . (Lenneberg, 1967, p. 168) Thus, although Lenneberg d i s c u s s e s i n d e t a i l the v o c a l i z a t i o n s of the p r e l i n g u a l c h i l d , he does not c o n s i d e r the f i r s t year or two of l i f e as r e l e v a n t t o language a c q u i s i t i o n . F u r t h e r -more, h i s comments appear t o be ambiguous as t o when the a c t u a l a c q u i s i t i o n process b e g i n s ; at times he equates i t w i t h the appearance of the f i r s t word at approximately 25 twelve months, at other times w i t h the f i f t e e n - m o n t h mark, and at ot h e r times w i t h the second or t h i r d year of l i f e , when he proposes the proc e s s of c e r e b r a l l a t e r a l i z a t i o n b e g i n s . However, the f i r s t year of l i f e cannot be passed o f f as a time when l i t t l e or no language l e a r n i n g t akes p l a c e . I t i s a working h y p o t h e s i s t h a t r e c e p t i v e s k i l l s precede e x p r e s s i v e language s k i l l s . Thus, before a c h i l d can use h i s f i r s t word m e a n i n g f u l l y , he has to have been able to i s o l a t e t h i s word from the stream of speech he hears, to form an a s s o c i a t i o n between the word and i t s r e f e r e n t , and to l e a r n the oromuscular adjustments necessary f o r producing t h i s word. T h i s d e s c r i p t i o n i s o b v i o u s l y o v e r s i m p l i f i e d , and we have o n l y j u s t begun t o r e a l i z e the c o m p l e x i t i e s i n -v o l v e d i n the a c q u i s i t i o n of language. Recent experiments suggest t h a t the i n f a n t may be capable of v e r y f i n e p e r c e p t u a l d i s c r i m i n a t i o n s as e a r l y as the f i r s t month of l i f e . Eimas et a l . (1971) t e s t e d one-and four-month-old babies on the a b i l i t y to d i s t i n g u i s h between the v o i c e d and v o i c e l e s s stop consonants /b/ and /p/, u s i n g h a b i t u a t i o n and d i s h a b i t u a t i o n of the n o n n u t r i t i v e s u c k i n g response as a measure. I n a c o u s t i c terms, /b/ and /p/ d i f f e r i n the onset of the f i r s t formant r e l a t i v e t o the second and t h i r d formants. Liberman et a l . (1957) p r e s e n t e d a s e r i e s of s y n t h e t i c speech s t i m u l i which v a r i e d over a continuum of v o i c e onset time (VOT) and found t h a t a d u l t l i s t e n e r s p e r c e i v e the interphonemic but not the intraphonemic d i f f e r e n c e s , although the a c o u s t i c v a r i a t i o n was the same i n 26 the two cases; t h a t i s , t h e i r p e r c e p t i o n of phonemes i s c a t e g o r i c a l . They found t h a t t h i s type of c a t e g o r i c a l p e r -c e p t i o n does not occur w i t h non-speech s t i m u l i and i s char-a c t e r i s t i c of p e r c e p t i o n i n the speech or l i n g u i s t i c mode. Eimas et a l . (1971) compared the a b i l i t y of i n f a n t s t o d i s -c r i m i n a t e between s y n t h e t i c speech sounds which were separated by f i x e d d i s t a n c e s of VOT, but which l a y e i t h e r on the same or on opp o s i t e s i d e s of the a d u l t phoneme boundary. They found t h a t both one- and four-month-old i n f a n t s were able to d i s c r i m i n a t e a VOT d i f f e r e n c e of twenty msec, when the two s t i m u l i l a y on opposite s i d e s of the a d u l t phoneme boundary, but not when they belonged t o the same phoneme cat e g o r y . The authors conclude t h a t i n f a n t s show c a t e g o r i c a l p e r c e p t i o n of speech sounds s i m i l a r t o the p e r c e p t u a l a b i l i t y of a d u l t l i s t e n e r s , and thus are p e r f o r m i n g l i n g u i s t i c d i s c r i m i n a t i o n s . T h i s experiment was r e p l i c a t e d u s i n g both n a t u r a l and syn-t h e t i c s t i m u l i , and a l s o extending the s t i m u l i to i n c l u d e the homorganic p a i r / d / and / t / by Trehub and R a b i n o v i t c h (1972) whose r e s u l t s confirmed the f i n d i n g s of Eimas et a l . (1971). A d i s c u s s i o n of the methodology of t h i s experiment and of whether the d i s c r i m i n a t o r y a b i l i t y of one-month-old i n f a n t s can be c l a s s e d as l i n g u i s t i c are beyond the scope of t h i s r e view; however, the f i n d i n g s of numerous experiments do seem t o i n d i c a t e t h a t i n f a n t s are b e g i n n i n g t o make p e r -c e p t u a l judgements from v e r y e a r l y i n l i f e and p r o b a b l y from b i r t h . 27 Another experiment suggested t h a t seven-week-old i n f a n t s can d i s c r i m i n a t e the a c o u s t i c cues f o r p l a c e of a r t i c u l a t i o n and i n t o n a t i o n (Morse, 1972). The author compared these r e -s u l t s w i t h the a b i l i t y of the i n f a n t s t o d i s c r i m i n a t e between i s o l a t e d a c o u s t i c cues f o r p l a c e , t h a t i s , non-speech s t i m u l i . T h i s comparison suggested t h a t " i n f a n t s respond t o the a c o u s t i c cues f o r p l a c e i n a l i n g u i s t i c a l l y r e l e v a n t manner" (p. 4-77) • Moffitt ( i 9 7 i ) found t h a t i n f a n t s of twenty- and tw e n t y - f o u r -weeks of age were able to d i s c r i m i n a t e between s y n t h e t i c s y l l a b l e s which d i f f e r e d o n l y i n degree of second formant t r a n s i t i o n and corresponded to the p e r c e p t u a l d i f f e r e n c e between /bah/ and /gah/. Since r e c e p t i v e l i n g u i s t i c s k i l l s are being e s t a b l i s h e d throughout the f i r s t year of l i f e and, f o r normal c h i l d r e n , w i l l l a t e r be e s t a b l i s h e d i n a s s o c i a t i o n w i t h the dominant hemisphere, i t cannot be assumed t h a t the two hemispheres are e q u i p o t e n t i a l f o r speech at any time . I t i s l i k e l y t h a t , up to a c e r t a i n time, the r i g h t hemisphere i s able t o take over the language f u n c t i o n i n the case of l e f t hemisphere damage but t h i s i m p l i e s organic p l a s t i c i t y , not e q u i p o t e n t i a l i t y . The t r i v i a l p o i n t t h a t , i n almost a l l c h i l d r e n , language f u n c t i o n s become centered i n the l e f t temporal lobe i m p l i e s t h a t i n some way t h i s a rea must be prepotent f o r language development at l e a s t from b i r t h . Note t h a t t h i s prepotency does not r u l e out some e a r l y p a r t i c i p a t i o n of the r i g h t hemisphere. F u r t h e r -more, i t v / i l l be remembered t h a t a d u l t l i s t e n e r s demonstrate an REA f o r the p e r c e p t i o n of stop consonants (Studdert-Kennedy 28 and Shankweiler, 1970). These authors concluded t h a t the "processor" s p e c i a l i z e d f o r speech i n the l e f t hemisphere i s s e n s i t i v e t o the phonetic content of an u t t e r a n c e . That i n f a n t s are o s t e n s i b l y capable of making f i n e p e r c e p t u a l d i s c r i m i n a t i o n s among a d u l t phoneme c a t e g o r i e s lends f u r t h e r credence t o the h y p o t h e s i s t h a t speech p e r c e p t u a l mechanisms are f u n c t i o n a l very e a r l y i n l i f e and might be a s s o c i a t e d w i t h the dominant hemisphere. I t should be noted t h a t w h i l e Basser d i v i d e s h i s cases i n t o "before the onset of speech" and " a f t e r speech has been a c q u i r e d " , Lenneberg r e p o r t s the evidence as "before age two" and "age two t o t e n " . I n f a c t , at l e a s t t h i r t e e n of the t h i r t y cases d i s c u s s e d by Basser i n the second category were between the ages of one and two. There i s some evidence t h a t u n i l a t e r a l l e s i o n s s u s t a i n e d at seventeen months of age may have permanent e f f e c t s on hemispheric speech dominance. N e t l e y (1972) compared three groups on a d i c h o t i c l i s t e n i n g t a s k : (1) normal c o n t r o l s , (2) c o n g e n i t a l l y i n j u r e d p a t i e n t s , and (3) i n f a n t i l e i n j u r e d p a t i e n t s . The average age of i n j u r y i n the t h i r d group was seventeen months. Hemispherectomies were l a t e r performed on both groups of p a t i e n t s . I t was found t h a t r e -c a l l scores f o r the ear i p s i l a t e r a l t o the remaining hemi-sphere were lower f o r the l a t e - i n j u r e d group than f o r the c o n g e n i t a l l y i n j u r e d group or the non-dominant ear of the normal group. I t thus appears t h a t the c o n g e n i t a l l y i n j u r e d p a t i e n t s are b e t t e r able t o u t i l i z e the i p s i l a t e r a l pathways 29 between the non-dominant ear and the remaining hemisphere i n a DL t a s k than i n f a n t i l e - i n j u r e d ' p a t i e n t s . Both groups of p a t i e n t s are c o n t r a s t e d w i t h c a l l o s a l l y severed a d u l t s who, although having normal monaural r e c a l l b i l a t e r a l l y , almost completely suppress v e r b a l m a t e r i a l coming i n the l e f t ear i n a DL t a s k (Sparks and Geschwind, 1968). These p a t i e n t s are unable to u t i l i z e the c r o s s - c a l l o s a l route f o r l e f t - e a r d i c h o t i c s t i m u l i and appear to have almost complete sup p r e s s i o n of the pathway to the dominant hemisphere f o r d i c h o t i c s t i m u l a t i o n . N e t l e y ' s r e s u l t s support the view t h a t the r e l a t i o n s h i p s between pathways from the ear t o the temporal lobe are e s t a b l i s h e d and achieve some degree of permanence much e a r l i e r than suggested by Lenneberg. I n e x t r a p o l a t i n g from such r e s u l t s t o normal development, the same c a u t i o n t h a t a p p l i e s t o a l l c l i n i c a l d a t a must be e x e r c i z e d . I t should a l s o be noted t h a t N e t l e y s t u d i e d o n l y twelve hemispherectomized p a t i e n t s i n a l l . However, such evidence does ch a l l e n g e the almost u n i v e r s a l l y accepted i d e a t h a t l e s i o n s s u s t a i n e d before two years of age do not have permanent consequences. 2.4 D i c h o t i c S t u d i e s w i t h C h i l d r e n A s m a l l number of s t u d i e s have focused on the develop-ment of l a t e r a l i t y f o r speech. Kimura (1963) t e s t e d 120 c h i l d r e n between the ages of f o u r and nine on a DL t a s k . A l l c h i l d r e n were right-handed and demonstrated no h e a r i n g i m p a i r -ment. The s t i m u l u s m a t e r i a l c o n s i s t e d of d i g i t s i n groups 30 of one, two and three p a i r s , a n d each c h i l d was asked t o repeat what he had heard i n any order he wished. I t was found t h a t each age group t e s t e d p resented more e f f i c i e n t r e c a l l of s t i m u l i p resented t o the r i g h t ear than those p r e -sented to the l e f t ; t h a t i s , the mean number of d i g i t s c o r -r e c t l y r e p o r t e d was g r e a t e r f o r the r i g h t , than f o r the l e f t e a r . Thus, at l e a s t by age f o u r , a r i g h t ear advantage f o r v e r b a l m a t e r i a l was observed. I t should be noted t h a t Kimura 1s attempts t o t e s t t h r e e - y e a r - o l d s were u n s u c c e s s f u l . As noted by Krashen (1972), the r e s u l t s of Kimura's study i n d i c a t e a decrease i n the magnitude of the d i f f e r e n c e be-tween e a r s , w i t h i n c r e a s i n g age. When t o t a l scores ( f o r both ears combined) were compared, i t was found t h a t f i v e - a n d s i x -y e a r - o l d females were s u p e r i o r t o t h e i r male p e e r s , although s i g n i f i c a n t d i f f e r e n c e s between sexes d i d not appear i n any other age group. . Kimura l a t e r r e p l i c a t e d the exact 1963 procedure w i t h c h i l d r e n ages f i v e to e i g h t i n a lower to middle socioeconomic c l a s s (SEC) area (Kimura, 1967). I n t h i s study, f i v e - y e a r - o l d females demonstrated an REA whereas f i v e - y e a r - o l d males demonstrated o n l y a t r e n d towards b e t t e r r e c a l l from the r i g h t ear. A l l c h i l d r e n of s i x , seven and e i g h t years of age demonstrated a s i g n i f i c a n t REA. Kimura suggested t h a t (1) the lower SEC c h i l d r e n were at an e a r l i e r stage of c o g n i t i v e f u n c t i o n i n g than c h i l d r e n t e s t e d i n her 1963 study, and (2) t h a t males l a g behind females i n the development of l e f t hemisphere dominance f o r speech. I n both these s t u d i e s , 31 Kimura omitted d e t a i l s of her st i m u l u s s y n c h r o n i z a t i o n procedures. The development of ear asymmetry f o r both v e r b a l and nonverbal sounds has been compared i n c h i l d r e n from f i v e t o ei g h t years c h r o n o l o g i c a l age (Knox and Kimura, 1970). The v e r b a l s t i m u l i v/ere i d e n t i c a l to those used by Kimura (1963, 1967), w h i l e the n o n v e r b a l s t i m u l i c o n s i s t e d of common en-vi r o n m e n t a l sounds such as a dog b a r k i n g , coughing, and a t r a i n w h i s t l e . The r e s u l t s i n d i c a t e d an REA i n a l l age groups, wh i l e a l e f t ear advantage f o r nonvarbal sounds appeared only at ages s i x and seven i n g i r l s , and ages seven and e i g h t i n boys. There were no s i g n i f i c a n t d i f f e r e n c e s between sexes i n the t o t a l r e c a l l of v e r b a l s t i m u l i . However, more nonverbal sounds were i d e n t i f i e d by boys than by g i r l s . G e f f n e r and Hochberg (1971) s t u d i e d both low and middle socioeconomic c l a s s (SEC) c h i l d r e n a t c h r o n o l o g i c a l age f o u r , f i v e , s i x and seven on a d i c h o t i c d i g i t s t a s k . They found a s i g n i f i c a n t REA f o r a l l age groups w i t h i n the middle SEC wh i l e o n l y the seven-year-old c h i l d r e n i n the lower SEG showed an REA. I n f a c t , f o u r - y e a r - o l d middle c l a s s c h i l d r e n demonstrated a s u b s t a n t i a l l y s t r o n g e r REA than d i d s i x - y e a r - o l d lower SEG c h i l d r e n . T h i s i s not too s u r p r i s i n g s i n c e the f o u r - y e a r - o l d middle c l a s s c h i l d r e n a l s o showed a l a r g e r ear d i f f e r e n c e than d i d the s i x - y e a r - o l d middle c l a s s c h i l d r e n . T h i s f i n d i n g i s again p a r t i a l l y dependent on the d i f f e r e n t accuracy l e v e l s w i t h i n the age groups (Krashen, 1972). No s i g n i f i c a n t d i f f e r -ences were observed between sexes f o r r i g h t ear e f f e c t . 32 Only one study has appeared i n the l i t e r a t u r e which looked f o r c e r e b r a l l a t e r a l i z a t i o n i n t h r e e - y e a r - o l d c h i l d r e n . Nagafuchi (1970) t e s t e d e i g h t y normal c h i l d r e n between the ages of thr e e and s i x on a DL t a s k ; handedness was not i n -d i c a t e d . S t i m u l i c o n s i s t e d of twenty d i s y l l a b i c , and twenty t r i s y l l a b i c , words. Nagafuchi found t h a t , even at three years of age, a s i g n i f i c a n t r i g h t ear advantage was evid e n t i n both boys and g i r l s . T hree-year-old g i r l s achieved h i g h e r t o t a l scores than t h r e e - y e a r - o l d boys and, not s u r p r i s i n g l y , the magnitude of the REA was l a r g e r f o r t h r e e - y e a r - o l d boys than f o r t h r e e - y e a r - o l d g i r l s . No d e t a i l s of s y n c h r o n i z a t i o n procedure were r e p o r t e d . Bryden (1970) s t u d i e d both l e f t - a n d r i g h t - h a n d e r s i n grades two, f o u r and s i x (approximately ages e i g h t , t e n and twelve) on a d i c h o t i c d i g i t s t a s k . The r e s u l t s were r e p o r t e d i n number of c h i l d r e n showing e i t h e r a r i g h t ear advantage or a l e f t ear advantage, r a t h e r than percent of d i g i t s c o r -r e c t l y r e c a l l e d from each ear. Bryden found t h a t , i n grade two, th e r e were no d i f f e r e n c e s by sex or handedness i n the number of c h i l d r e n showing an REA. However, the percent of right-handed c h i l d r e n showing an REA g r a d u a l l y i n c r e a s e d up to grade s i x w h i l e the percent of l e f t - h a n d e d c h i l d r e n showing an REA decreased. A s i g n i f i c a n t d i f f e r e n c e between l e f t - a n d r i g h t - h a n d e d g i r l s appeared i n grade f o u r w h i l e the d i f f e r e n c e between l e f t - a n d r i g h t - h a n d e d boys appeared o n l y i n grade s i x . Krashen (1972) has commented t h a t s i n c e handedness i s not completely e s t a b l i s h e d before n i n e years of age (Belmont 33 and B i r c h , 1963), some of the c h i l d r e n i n the right-handed group i n Bryden's study were not t r u l y right-handed and d i d not show a r i g h t ear advantage. As such c h i l d r e n would not be i n c l u d e d i n an o l d e r sample ( s i n c e t h e i r l e f t - h a n d e d -ness would then be e v i d e n t ) the percent of c h i l d r e n showing an REA would seem to i n c r e a s e as grade l e v e l i n c r e a s e d . A c c o r d i n g t o a more r e c e n t paper (Benson and Geschwind, 1968), most r e s e a r c h e r s would agree t h a t handedness i s c o n c l u s i v e l y e s t a b l i s h e d by about age two. Thus, i t i s strange t h a t o n l y 40$ of the l e f t - h a n d e d grade s i x c h i l d r e n i n Bryden's study showed an REA. These c h i l d r e n are twelve years of age and one would expect t h a t they show the same d i s t r i b u t i o n of r i g h t ear s u p e r i o r i t y as the a d u l t p o p u l a t i o n . S a t z , Achenbach, P a t t i s h a l l and F e n n e l l (1965) have shown t h a t 73$ of l e f t - h a n d e d a d u l t s show an REA. Since these s i x s t u d i e s are the o n l y r e p o r t e d develop-mental i n v e s t i g a t i o n s u s i n g the DL te c h n i q u e , some g e n e r a l c r i t i c i s m s appear warranted. F i r s t , although the r e s u l t s of a l l s t u d i e s appear to suggest t h a t c h i l d r e n as young as c h r o n o l o g i c a l age three or f o u r years show an REA f o r v e r b a l s t i m u l i , few other g e n e r a l i z a t i o n s can be made about sex, handedness, age or socioeconomic c l a s s d i f f e r e n c e s . Two p o s s i b l e d i f f e r e n c e s between males and females i n a DL t a s k have been suggested: (1) a d i f f e r e n c e i n t o t a l r e -c a l l and (2) a d i f f e r e n c e i n the age at which an REA can f i r s t be observed. 34 The r e s u l t s of two s t u d i e s suggested t h a t males show poorer t o t a l r e c a l l than t h e i r female peers. However, i n one study, t h i s d i f f e r e n c e appeared o n l y at age three (Nagafuchi, 1970), w h i l e i n the o t h e r , the d i f f e r e n c e appeared only at ages f i v e and s i x , but not age f o u r (Kimura, 1963). Furthermore, three s t u d i e s suggested t h a t t h e r e were no d i f f e r e n c e s between sexes i n t o t a l r e c a l l ( G e f f n e r and Hochberg, 1971; Knox and Kimura, 1970; Kimura, 1967) w h i l e the s i x t h study (Bryden, 1970) does not present t h i s i n f o r -mation. I f a sex d i f f e r e n c e i n the age of appearance of an REA coul d be r e l i a b l y demonstrated, then t e n t a t i v e suggestions about the onset of l a t e r a l i z a t i o n might be p o s s i b l e . However, no c o n c l u s i v e d i f f e r e n c e s have been shown i n the s t u d i e s r e -p o r t e d . While Kimura's (1967) lower SEC f i v e - y e a r - o l d males d i d not demonstrate an REA, Nagafuchi's (1970) t h r e e - y e a r -o l d males demonstrated a l a r g e r r i g h t ear advantage than t h e i r female p e e r s . None of the other i n v e s t i g a t i o n s suggested a sex d i f f e r e n c e i n t h i s r e s p e c t . I t i s e v i d e n t t h a t t o t a l r e c a l l and magnitude of r i g h t ear advantage are not independent f a c t o r s but are i n v e r s e l y c o r r e l a t e d w i t h one another. As accuracy i n c r e a s e s , so a l s o w i l l the d i f f e r e n c e between ears decrease. I f we are seei n g the development of the u l t i m a t e a d u l t p a t t e r n of r e c a l l i n a DL t a s k , then i t i s l o g i c a l t o look f o r changes i n the d i f f e r e n c e between ears w i t h i n c r e a s i n g age. I f l a t e r a l i z a t i o n i s g r a d u a l l y b e i n g e s t a b l i s h e d u n t i l 55 puberty ( c f . Lenneberg, 196?) and i f we assume t h a t the magnitude of the ear d i f f e r e n c e r e f l e c t s t h i s l a t e r a l i z a t i o n p r o c e s s , then one would expect to see an i n c r e a s e i n the r i g h t ear advantage w i t h i n c r e a s i n g c h r o n o l o g i c a l age. However, the r e s u l t s of the preceeding experiments seem to suggest the o p p o s i t e ; the magnitude of the REA decreases as the c h i l d gets o l d e r . As mentioned e a r l i e r , t h i s i s p a r t l y due to d i f f e r e n t l e v e l s of accuracy between age groups. Thus,, u n l e s s accuracy i s accounted f o r i n the computations, i t i s not p o s s i b l e to draw c o n c l u s i o n s about the changes i n the magnitude of the REA w i t h i n c r e a s i n g age. The l a s t t e n years has seen a r a p i d i n c r e a s e i n s t u d i e s concerned w i t h language d e p r i v a t i o n and i t s r e l a t i o n s h i p t o s c h o o l f a i l u r e i n lower c l a s s c h i l d r e n . The t h e o r e t i c a l c o n s t r u c t s tend t o be one of two t y p e s . Lower c l a s s c h i l d r e n e i t h e r have (1) d e f i c i e n t language s k i l l s ( B e r n s t e i n , 1961) or (2) d i f f e r e n t language s k i l l s or d i a l e c t i c a l d i f f e r e n c e s (Labov, 1967). No study known t o t h i s author has demonstrated, or suggested, b i o l o g i c a l d i f f e r e n c e s i n the a b i l i t y t o l e a r n language between s o c i a l c l a s s e s (not confounded by r a c i a l d i f f e r e n c e s ) . I n view of t h i s , one must be wary of r e s e a r c h papers t h a t suggest slower development of c e r e b r a l l a t e r -a l i z a t i o n i n lower c l a s s c h i l d r e n (Kimura, 1967; G e f f n e r and Hochberg, 1971). Geffner and Hochberg (1971) s t a t e d t h a t none of the c h i l d r e n demonstrated speech and language d e f i c i t s ; i t seems q u e s t i o n a b l e t h a t s i x - y e a r - o l d c h i l d r e n who p r e -sumably have developed a l l the s y n t a c t i c and p h o n o l o g i c a l 36 r u l e s of t h e i r language, would not demonstrate an REA whil e t h r e e - y e a r - o l d c h i l d r e n do (Nagafuchi, 1970). I t appears more l i k e l y to account f o r such r e s u l t s i n terms of d i f f e r e n t s t y l e of approaching the t e s t i n g s i t u a t i o n i n lower c l a s s c h i l d r e n , poorer r a p p o r t w i t h the examiner (Labov, 1968), poorer m o t i v a t i o n , or misunderstanding of the i n s t r u c t i o n s . Furthermore, although Geffner and Hochberg (1971) give t h e i r c r i t e r i a f o r d e t e r m i n i n g s o c i a l c l a s s l e v e l , they g i v e no d e t a i l s of the race of the c h i l d r e n , how the c h i l d r e n were s e l e c t e d and whether o t h e r f a c t o r s such as grade l e v e l , academic achievement, and experimenter b i a s were accounted f o r . I t i s w e l l r e c o g n i z e d t h a t , the younger the c h i l d , the l a r g e r the changes w i l l be i n b e h a v i o r , p h y s i c a l growth, l e a r n i n g , and e s p e c i a l l y language, over a g i v e n time p e r i o d . I n t h e . f i r s t year of l i f e , the c h i l d a c q u i r e s one-half of the major phonemes and some simple morphemes (Mussen, Conger, and Kagan, 1969). I n the second year, the average c h i l d begins to a s s o c i a t e words w i t h t h e i r r e f e r e n t s and t o use words m e a n i n g f u l l y ; h i s speech becomes more i n t e l l i g i b l e and complex and h i s comprehension i n c r e a s e s g r e a t l y . The average one-y e a r - o l d understands or uses 3 words; at 15 months, the average i s 19; at 18 months, 22 words; by 21 months, 118 words; by two y e a r s , 272 words, and by age th r e e the e f f e c t i v e v ocabulary i f 896 words. At the same time, r a p i d gains i n ot h e r areas of p h y s i c a l and c o g n i t i v e growth are t a k i n g p l a c e . The above s i x s t u d i e s have grouped c h i l d r e n on the b a s i s of c h r o n o l o g i c a l y e a r ; t h u s , a c h i l d who i s 4- y e a r s , 1 month i s grouped w i t h a 37 c h i l d who i s 4 y e a r s , 11 months, although t h e r e are l a r g e d i f f e r e n c e s i n c o g n i t i v e and language a b i l i t i e s i n these two c h i l d r e n . Such a grouping procedure, although l e g i t i m a t e w i t h a d u l t s or o l d e r c h i l d r e n , might obscure changes i n the p a t t e r n of development of c e r e b r a l l a t e r a l i z a t i o n i n ve r y young c h i l d r e n . The l a s t c r i t i c i s m concerns s y n c h r o n i z a t i o n procedures. A l l s t u d i e s mentioned gi v e few, i f any, d e t a i l s of t h e i r methods of d i c h o t i c tape c o n s t r u c t i o n . As w i l l be demonstrated below, d u r a t i o n of word, s y n c h r o n i z a t i o n of s t i m u l i onset, and s i m i l a r i t y of i n i t i a l phoneme a l l e x e r t measurable e f f e c t s i n a DL t a s k . When u s i n g d i g i t s as s t i m u l i , i t i s i m p o s s i b l e to s a t i s f y any of the th r e e above c r i t e r i a . No d e t a i l s are giv e n about e x a c t l y what p a r t of the spectrum i s synchronized when an i n i t i a l v o i c e l e s s f r i c a t i v e i s matched, f o r example, a g a i n s t a v o i c e d p l o s i v e . Furthermore, three of the s i x s t u d i e s mentioned used the i d e n t i c a l tape; the one c o n s t r u c t e d by Kimura i n 1963, which c o u l d p o s s i b l y l i m i t g e n e r a l i z a t i o n of the f i n d i n g s . Techniques used i n the c o n s t r u c t i o n of d i -c h o t i c s t i m u l i have become c o n s i d e r a b l y more s o p h i s t i c a t e d s i n c e the e a r l y experiments performed and r e p o r t e d i n the l i t e r a t u r e . CHAPTER 3 STATEMENT OP PROBLEM D i c h o t i c l i s t e n i n g has proven t o be a r e l i a b l e , safe and r e l a t i v e l y simple way t o i n v e s t i g a t e c e r e b r a l dominance f o r language. T h i s technique has been shown t o c o r r e l a t e w e l l w i t h sodium amytal t e s t i n g (Kimura, 1961b). Only a few i n v e s t i g a t o r s have adapted t h i s technique to study the development of c e r e b r a l dominance i n young c h i l d r e n . The main t h e o r e t i c a l p o s i t i o n on the development of l a t e r a l i z a t i or dominance i s t h a t of Lenneberg (1966, 1967). Lenneberg's p o s i t i o n i s t h a t language f u n c t i o n becomes g r a d u a l l y e s tab-l i s h e d i n the l e f t hemisphere, b e g i n n i n g at age two or three and r e a c h i n g completion at puberty. T h i s process occurs c o n c u r r e n t l y w i t h the language a c q u i s i t i o n p r o c e s s . Thus, a c c o r d i n g to Lenneberg, no language l e a r n i n g takes p l a c e be-f o r e age two or t h r e e , and primary language l e a r n i n g i s not p o s s i b l e a f t e r p uberty. Hov/ever, evidence presented e a r l i e r has shown t h a t some form of language l e a r n i n g t akes p l a c e from b i r t h ; i t thus seems reasonable t o assume t h a t such l e a r n i n g i s a s s o c i a t e d w i t h areas of the l e f t hemisphere, which are becoming f u n c t i o n a l i n the v e r y process of language l e a r n i n g . The major i s s u e c e n t e r s on the problem, "When does the l e f t hemisphere become dominant f o r language f u n c t i o n ? " . I n view of t h i s , the aims of the pr e s e n t 38 39 i n v e s t i g a t i o n were to seek answers to the f o l l o w i n g : ( 1 ) Do c h i l d r e n between the ages of two and t h r e e , when presented w i t h a v e r b a l d i c h o t i c l i s t e n i n g t a s k , demonstrate a s i g n i f i c a n t r i g h t ear advantage? (2) I s there a c h a r a c t e r i s t i c a g e - r e l a t e d p a t t e r n t o the development of l a t e r a l i z a t i o n between two and t h r e e years of age? (3) Do two-year-old boys perform d i f f e r e n t l y i n degree or d i r e c t i o n of ear advantage than t h e i r female peers? CHAPTER 4 METHOD 4.1 P r e p a r a t i o n of D i c h o t i c Tapes 4-. 11 Recording s t i m u l i A S c u l l y 280 two-track s t e r e o tape r e c o r d e r was used to r e c o r d a l l s t i m u l u s words. Recordings were made i n an IAC audiometric booth, u s i n g a male speaker. Ambient n o i s e l e v e l i n the room was 20 dBA.-, as t e s t e d by a B r u e l and K j a e r P r e c i s i o n s o u n d - l e v e l meter. An A l t e c 681A microphone was used f o r r e c o r d i n g , a t approximately s i x inches mouth-to-microphone d i s t a n c e . Two l i s t s of words ( L i s t 1, L i s t 2) were recorded on two tapes at normal c o n v e r s a t i o n a l l e v e l , a t 7#> inches, per second. 4.12 P r e p a r a t i o n of tape loops S t i m u l u s words were l a t e r c o p i e d onto a t h i r d tape i n order t h a t tape loops c o u l d be c o n s t r u c t e d . To e f f e c t t h i s , the o r i g i n a l tapes were p l a y e d back from a Revox two-track s t e r e o tape r e c o r d e r , onto the S c u l l y 280 tape r e c o r d e r , to produce a new tape w i t h s t i m u l i separated by a s i x - s e c o n d i n t e r v a l . P r i o r t o r e c o r d i n g each word, the playback l e v e l on the Revox was a d j u s t e d so t h a t , at r e s t , each word showed a peak i n t e n s i t y of 0 VU on the r e c o r d head of the S c u l l y . Thus, a l l s t i m u l u s words were matched f o r peak i n t e n s i t y at r e c o r d i n g t i m e . T h i r t y - f o u r tape loops of equal l e n g t h , each c o n t a i n i n g one s t i m u l u s word, were then c o n s t r u c t e d . 40 4-1 4-. 13 P r e p a r a t i o n of s t i m u l u s tapes Three tape r e c o r d e r s were arranged such t h a t one channel of each of the f i r s t two connected t o channels 1 and 2 of the t h i r d tape r e c o r d e r (see F i g u r e 4- .1). L i s t 1 tape loops were r e p l a y e d from the S c u l l y . L i s t 2 tape loops were r e p l a y e d from an Ampex AG 4-4-OB f u l l t r a c k tape r e c o r d e r . Playback l e v e l s of the Ampex and S c u l l y were kept at the same r e l a t i v e l e v e l f o r a l l s t i m u l i , w h i l e the r e c o r d i n g l e v e l s f o r each channel of the Revox were a d j u s t e d f o r each p a i r of words so t h a t each word showed a peak i n t e n s i t y of 0 VU. A d u a l channel memory o s c i l l o s c o p e was connected between the S c u l l y and the Ampex so t h a t the experimenter c o u l d v i s u a l l y monitor the degree of synchrony of s t i m u l i onset d u r i n g copying. Method of copying: The two tape loops were p l a c e d i n approximate synchrony by s e t t i n g both words on the playback heads of the Ampex and S c u l l y . As the Ampex had a s l i g h t l y f a s t e r r u n n i n g speed, the word on t h i s tape r e c o r d e r c o u l d be p l a c e d s l i g h t l y back from the playback head and the two tape r e c o r d e r s set i n motion. The r e c o r d mode of the Revox was then a c t i v a t e d . As the p a i r s of words were b e i n g r e -corded, the degree of synchrony was s i m u l t a n e o u s l y observed on the o s c i l l o s c o p e . T h i s procedure was repeated u n t i l i t was f e l t t h e r e were s e v e r a l p a i r i n g s of words from L i s t 1 and 2 s y n c h r o n i z e d w i t h i n 10 m i l l i s e c o n d s . The next p a i r 1 Studdert-Kennedy, Shankweiler and Schulman (1970) have i n d i c a t e d that, when the l e f t - e a r s i g n a l l a g s behind the r i g h t -ear s i g n a l by 20 m s e c , the l e f t ear becomes the dominant one. B e r l i n et a l . (1973) shov/ed t h a t the REA disappears when the l e f t - e a r s i g n a l l a g s by 30 msec. Beyond a 30 msec, time 42 S c u l l y 280 playback mode L i s t 1 tape loops Amp ex AG 440B playback mode L i s t 2 tape loops d u a l channel o s c i l l o s c o p e channel 1 channel 2 Revox ste r e o tape r e c o r d e r r e c o r d mode channel 1 channel 2 Figure4-.1 P r e p a r a t i o n of s t i m u l u s tapes 43 of words was then recorded i n the same way. The tape r e -cordings from the Re vox v/ere l a t e r r e p l a y e d , and the best synchronized example of each p a i r of words was chosen with- the a i d of the o s c i l l o s c o p e . Each of these p a i r s was then cut from the tape and s p l i c e d t o g e t h e r ; a f i n a l s t i m u l u s tape was c o n s t r u c t e d from t h i s t a p e . On the a c t u a l s t i m u l u s tape used i n the experiment, the i n t e r s t i m u l u s i n t e r v a l was i n c r e a s e d t o twenty seconds and the words "Show me" were spoken by the o r i g i n a l speaker, before each p a i r of words. A photograph was taken of each o s c i l l o -s c o p i c t r a c e i n order t h a t onset time c o u l d be more p r e c i s e l y determined; these photographs are presented i n Appendix 1. 4.2 S t i m u l u s Words The s t i m u l i c o n s i s t e d of f i f t e e n t e s t w o r d - p a i r s , as w e l l as two p r a c t i c e w o r d - p a i r s . E l e v e n p a i r s c o n s i s t e d of mono-s y l l a b i c words; f o u r p a i r s were comprised of d i s y l l a b i c words. Of the two p r a c t i c e w o r d - p a i r s , one p a i r c ontained mono-s y l l a b i c words and the other p a i r c o n t a i n e d d i s y l l a b i c words. The t h i r t y - f o u r words were a l l c o n c r e t e , p i c t u r a b l e , common nouns c o n s i d e r e d by the experimenter t o be w i t h i n the range of v o c a b u l a r y of a two-year-old c h i l d . Most of the words d i f f e r e n c e , the l a g g i n g message i n c r e a s e s i n i n t e l l i g i b i l i t y . I n the present r e s e a r c h , we aimed f o r s i m u l t a n e i t y of d i c h o t i c p a i r s and accepted a d i f f e r e n c e i n onset of up to 10 m s e c , because of the d i f f i c u l t y i n measuring s m a l l e r time i n t e r v a l s on the o s c i l l o s c o p e . The d i r e c t i o n of onset time d i f f e r e n c e was random. 44 (those s t a r r e d i n Appendix 2) were chosen from the begi n n i n g items of the Peabody P i c t u r e Vocabulary Test (PPVT). The words were.paired, such t h a t the f o l l o w i n g c o n d i t i o n s were observed: (1) a mono s y l l a b i c word was never matched a g a i n s t a d i s y l l a b i c word; (2) i n i t i a l sounds of each word i n a p a i r were e i t h e r both v o i c e d p l o s i v e s , or both v o i c e l e s s p l o s i v e s , or both n a s a l s ; (3) o s c i l l o m i n k t r a c i n g s were made of each word so t h a t d u r a t i o n c o u l d be measured e x a c t l y . Word d u r a t i o n ranged from 500 to 950 m s e c ; Appendix 3 g i v e s the d u r a t i o n f o r each word. D i f f e r e n c e s i n d u r a t i o n between p a i r e d words ranged from 30 to 100 m s e c , w i t h the e x c e p t i o n of one p a i r of words ("spoon" was 4-50 msec longer than i t s p a r t n e r , " f i s h " . The peak i n t e n s i t y of each word on the f i n a l tape was measured w i t h a B r u e l and K j a e r P r e c i s i o n sound l e v e l meter. The tape was r e p l a y e d on the S c u l l y tape r e c o r d e r which was maintained at constant playback l e v e l (the s i g n a l b eing main-t a i n e d at approximately 70 dB); a l l t h i r t y - f o u r words were r e p l a y e d through the same Telephonic TDH 39 headphone and B r u e l and K j a e r a r t i f i c i a l ear type 4-152 p l a c e d on the sound C o n d i t i o n (2) not on l y s i m p l i f i e d s y n c h r o n i z a t i o n p r o -cedures but helped to e l i m i n a t e p h o n e t i c e f f e c t s known to be prese n t i n d i c h o t i c l i s t e n i n g . For example, Lowe et a l . (1970) have shown t h a t , at s i m u l t a n e i t y , v o i c e l e s s consonants are more i n t e l l i g i b l e d i c h o t i c a l l y than v o i c e d consonants. As y e t , the e f f e c t s of temporal o f f s e t i n d i c h o t i c l i s t e n i n g have not been s y s t e m a t i c a l l y examined. Spreen and Boucher (1970) have shown t h a t d i f f e r e n c e s i n o f f s e t of up t o 60 msec, produce no s i g n i f i c a n t e f f e c t s on the ear asymmetry. However, l a r g e r d i f f e r e n c e s i n o f f s e t have not been examined. Since most s t u d i e s r e p o r t e d i n the l i t e r a t u r e used spoken d i g i t s as s t i m u l i , i t i s evident t h a t temporal o f f s e t c o u l d not have been c o n t r o l l e d i n these s t u d i e s . 45 l e v e l meter. The l a r g e s t i n t e n s i t y d i f f e r e n c e between p a i r e d words was 4 dBA; however, t h i r t e e n of the seventeen word p a i r s were w i t h i n 2 dB peak i n t e n s i t y d i f f e r e n c e . Research has shown t h a t the REA f o r v e r b a l m a t e r i a l i s o b t a i n e d even when the i n t e n s i t y of the s t i m u l u s d e l i v e r e d to the r i g h t ear i s as much as 10 dB l e s s than t h a t of the l e f t ear (Thompson et a l . , 1972). The playback l e v e l s of the two channels of the S c u l l y were a d j u s t e d so t h a t the p a i r s of words were p l a y e d back at 72 dBA (+ 2 dB) through the headphones (as measured by a B r u e l and K j a e r P r e c i s i o n sound l e v e l meter). A c a l i b r a t i o n tone p l a c e d on both t r a c k s of a two-track tape was used t o a l l o w the playback i n t e n s i t y of the two channels to be the same. T h i s c a l i b r a t i o n procedure was repeated on each t e s t i n g day. A f o i l word was chosen and used i n c o n j u n c t i o n v/ith each p a i r of words. Simple b l a c k and white l i n e i l l u s t r a t i o n s were drawn such t h a t each word p a i r and f o i l appeared on one page. A random order of p i c t u r e placement was used. Stimulus and f o i l words (order of p r e s e n t a t i o n ) are g i v e n i n Appendix 4. 4.3 S u b j e c t s C h i l d r e n were a l l between CA 2:0 and 3:2; t h e i r ages on the day of t e s t i n g were recorded i n y e a r s , months, and days. The c h i l d r e n were gathered by c o n t a c t i n g f r i e n d s of the ex-aminer who had young c h i l d r e n . These i n d i v i d u a l s then r e -f e r r e d the i n v e s t i g a t o r t o other p a r e n t s of young c h i l d r e n . 46 About o n e - t h i r d of the c h i l d r e n were gathered through p a r -t i c i p a t i o n of t h e i r mothers i n a p r e - n a t a l c l a s s . S e l e c t i o n was not based on socioeconomic c l a s s , l i n g u i s t i c l e v e l , sex, handedness, handedness of the p a r e n t s , b i r t h order or develop-mental h i s t o r y , although a l l of t h i s i n f o r m a t i o n , w i t h the e x c e p t i o n of socioeconomic l e v e l , was gained by i n t e r v i e w i n g the mothers. No c h i l d showed any h i s t o r y or i n d i c a t i o n of h e a r i n g l o s s , although h e a r i n g t e s t i n g was not c a r r i e d out. 4.4- E x p e r i m e n t a l Procedure T e s t i n g was conducted i n two s e s s i o n s , on two separate days. The f i r s t s e s s i o n l a s t e d approximately twenty minutes and the second s e s s i o n , about t h i r t y minutes. In the f i r s t p r e - t e s t s e s s i o n , each c h i l d was shown each s t i m u l u s page c o n t a i n i n g t h r e e p i c t u r e s and was asked by the examiner, "Show me f o r each s t i m u l u s item i n t u r n . The purpose of t h i s procedure was t w o f o l d ; f i r s t , t o ensure t h a t each c h i l d c o u l d a u d i t o r i a l l y r e c o g n i z e the s t i m u l u s words and, second, to e s t a b l i s h a p o i n t i n g response to the words "'Show me". I f a c h i l d d i d not know a word, t h i s word c o u l d then be taught by the examiner. Most of the s t i m u l u s items, w i t h the excep-t i o n of "queen" and "gun" were known by a l l the c h i l d r e n . D u r i n g the f i r s t s e s s i o n , the c h i l d was a l s o g i v e n the oppor-t u n i t y t o f a m i l i a r i z e M m s e l f / h e r s e l f w i t h the t e s t i n g room and the headphones. The- mother was a l s o i n t e r v i e w e d on t h i s day. 4-7 For the second s e s s i o n , a l l t o y s were removed from the room i n order to minimize d i s t r a c t i o n . The c h i l d was seated on h i s mother's l a p w i t h h i s back t o the tape r e c o r d e r . One headphone was removed from the monitor headset and was p l a c e d a g a i n s t the c h i l d ' s e a r . E i g h t s t i m u l u s items ( f o u r from each channel) were presented monaurally through the headphone and the c h i l d was asked t o p o i n t to the a p p r o p r i a t e p i c t u r e . The purpose of t h i s t r a i n i n g was t o r e - e s t a b l i s h the p o i n t i n g response and t o accustom each c h i l d t o l i s t e n i n g over head-phones before the more d i f f i c u l t d i c h o t i c t a s k was prese n t e d . The use of one headphone a l s o a llowed the examiner t o reas s u r e and r e i n f o r c e the c h i l d a u d i t o r i l y . A f t e r t r a i n i n g , c i r c u m a u r a l headphones were p l a c e d on the c h i l d , and t e s t i n g was commenced. The examiner h e l d each set of p i c t u r e s before the c h i l d , w h i l e a second examiner removed the other p i c t u r e s from the c h i l d ' s view and operated the tape r e c o r d e r . When o n l y one examiner was p r e s e n t , the tape r e -corder was operated by a remote c o n t r o l d e v i c e . The examiner was able t o monitor one channel through the monitor headset, but was unaware t o which of the c h i l d ' s ear those words were b e i n g p r e s e n t e d . No v e r b a l i n s t r u c t i o n s were g i v e n to the c h i l d by the examiner. Channel-by-ear p r e s e n t a t i o n was a l t e r -nated between s u b j e c t s t o minimize the e f f e c t s of any d i f f e r -ences between channels. Although most of the r e s e a r c h w i t h d i c h o t i c s t i m u l a t i o n has used v e r b a l r e c a l l as a mode of response, v e r b a l r e c a l l i s not necessary t o produce an REA i n normal a d u l t s u b j e c t s . 4-8 A r i g h t ear s u p e r i o r i t y has been r e p o r t e d when s u b j e c t s were i n s t r u c t e d t o w r i t e down, r a t h e r than say, t h e i r responses (Shankweiler and Studdert-Kennedy, 1967; Studdert-Kennedy and Shankweiler, 1970), when s u b j e c t s were i n s t r u c t e d to choose t h e i r responses out of s e v e r a l l a t e r p resented (Kimura and F o l b , 1968; "Rroadbent and Gregory, 1964-), and when s u b j e c t s were i n s t r u c t e d to tap w i t h e i t h e r the r i g h t or the l e f t hand (Treisman and Geffen, 1968). I t was f e l t t h a t many two-year-o l d s would be unable or u n w i l l i n g to respond v e r b a l l y t o d i -c h o t i c s t i m u l a t i o n , and t h u s , a p i c t u r e p o i n t i n g response was used. CHAPTER 5 RESULTS 5.1 S c o r i n g One p o i n t was giv e n f o r each p i c t u r e c o r r e c t l y chosen, w i t h no p e n a l t y f o r i n c o r r e c t c h o i c e s . The d i f f e r e n c e s be-tween f i r s t and second responses on each t r i a l were d i s r e g a r d e d ; however, the g e n e r a l response p a t t e r n was one response per t r i a l , the mean o v e r a l l accuracy score ( d e f i n e d as t o t a l c o r -r e c t responses f o r both ears combined d i v i d e d by t o t a l p o s s i b l e s c o r e ) being 50.5$. T o t a l p o s s i b l e score f o r each ear was 15« The dat a were e v a l u a t e d throughout by means of a t - t e s t (Downie and Heath, 1959). The scores were t a b u l a t e d i n both raw form and i n POE form , i n order t o c o r r e c t f o r i n c r e a s e s i n accuracy w i t h i n c r e a s i n g age. However, i n t h i s experiment, accuracy d i d not change w i t h age, i . e . , the mean accuracy f o r c h i l d r e n below CA 2-6-30 being 4-9$, and f o r c h i l d r e n above CA 2-6-30 b e i n g 52$. Thus, such a c o r r e c t i o n f a c t o r was unnecessary, and the r e s u l t s f o r both measures were not s t a t i s t i c a l l y s i g n i f i c a n t . Unless otherwise s t a t e d , the t v a l u e s presented are f o r raw d a t a . 5.2 S u b j e c t s Of the t h i r t y - s i x c h i l d r e n c h o s e n , f i v e were r e j e c t e d The POE score i s d e f i n e d as the l e f t ear's percentage of the t o t a l number of e r r o r s (Krashen, 1972). 49 50 because they would not t o l e r a t e headphones. The s u b j e c t p o o l by age and sex i s presented i n Table 5.1• The age on day of t e s t i n g ranged from CA 2-0-12 t o CA 3-1-20. Males Eemales t o t a l below CA 2-6-30 8 9 17 above CA 2-6-30 6 8 14 t o t a l 14 17 Table 5.1 S u b j e c t s by age and sex 5.3 R i g h t versus L e f t Ears Across a l l sex and age groups, the r i g h t ear words were more e f f i c i e n t l y r e c a l l e d than the l e f t ear words ( t = 4.54, d f = 60, £ < 0.005, o n e - t a i l e d t e s t ) . The mean $ REA f o r the t o t a l group was 18$, as c a l c u l a t e d by the formula: R-L / R+L (Shankweiler and Studdert-Kennedy, 1970; Z u r i f and Ramier, 1972). The a d u l t v a l u e s g e n e r a l l y r e p o r t e d i n the l i t e r a t u r e range between 2 and 8$ ( C u r r y , 1968; Z u r i f and Ramier, 1972; Kimura, 1967; Sparks, Goodglass and N i c k e l , 1970). Of the t h i r t y - o n e c h i l d r e n , twenty-four demonstrated an REA, s i x demonstrated an LEA, and one showed equal p r e f e r e n c e f o r both e a r s . The mean score f o r the r i g h t ear was 8.97 and f o r the l e f t , 6.19. 51 5.4- Sex There was no s i g n i f i c a n t d i f f e r e n c e i n the degree of REA (d e f i n e d as r i g h t minus l e f t ear scor e s ) f o r males and females (t_ = 0.2856, d f = 29, n s ) , nor were there d i f f e r e n c e s i n over-a l l accuracy (males, 51.4$; females, 50.1$). The mean $ REA was 19«5$ f o r males, and 16.8$ f o r females. Thus, boys demon-s t r a t e d an REA which was s l i g h t l y l a r g e r , ( a l t hough not s t a t i s t i c a l l y s i g n i f i c a n t ) than the REA of the females. 5.5 Age The i n d i v i d u a l scores rank ordered a c c o r d i n g t o age are presented i n F i g u r e 5.1• The d i f f e r e n c e between the seventeen younger c h i l d r e n (OA 2-0-12 to 2-6-7) and the f o u r t e e n o l d e r c h i l d r e n (CA 2-7-11 t o 3-1-20) was not s i g n i f i c a n t ( t = 0.4868, d f = 29, n s ) . The degree of REA d i d not show a sys t e m a t i c i n c r e a s e , or decrease, as a f u n c t i o n of age ( r = -0.172; Pearson product moment c o r r e l a t i o n , from Bruning and K i n t z , 1968, p. 1 5 2 ) . The mean accuracy l e v e l of the younger c h i l d r e n was 49.2$; mean accuracy l e v e l of the o l d e r c h i l d r e n was 52.1$. The mean $ REA was 19.9$ f o r the younger group and 15.7$ f o r the o l d e r group. 5.6 Age ver s u s Sex The t v a l u e s , as w e l l as the mean $ REA, f o r the f o u r age-sex groups i s presented i n Table 5.2. I t can be seen t h a t the o l d e r female group d i d not achieve a s i g n i f i c a n t REA, wh i l e the other three groups d i d . However, the s m a l l number 100 80 60 w 2 •p c <u M a 40 20 mean score ( t h i s study) mean score of 22 studies analysed by Krashen (1972) 2-6-30 Figure 5.1 Individual scores rank ordered according to age. Raw Score N Left Ear Right Ear t( one-tailed) mean % REA df males below CA 2-6-30 8 6.25 8.75 2.29 p<0.025 15.5 14 females below 9 5.56 9.00 5.71 23.8 16 CA 2-6-30 p<0.005 males above CA 2-6-30 6 6.00 9.83 1.87 p<0.05 24.7 10 females above CA 2-6-30 8 7.13 8.37 0.8 p^0.25 ns 8.95 14 Table 5.2 T values and mean percent REAs for four age-sex groups. 54 of s u b j e c t s i n each group reduces the importance of these s t a t i s t i c a l a n a l y s e s . 5.7 Handedness Both the handedness of the par e n t s and the mother's o p i n i o n of the c h i l d ' s handedness were recorded. The c h i l d r e n were d i v i d e d i n t o two groups on the b a s i s of handedness; i n Group 1 were 19 c h i l d r e n c o n s i d e r e d by t h e i r mothers t o be right - h a n d e d and who had two right-handed p a r e n t s . I n the second group, were 12 c h i l d r e n who were l e f t - h a n d e d or ambi-dextrous or who had at l e a s t one l e f t - h a n d e d p a r e n t . The d i f f e r e n c e i n degree of r i g h t ear advantage between these two groups was not s i g n i f i c a n t ( t = 0.06344, df = 29, n s ) . Because the o n l y measure of handedness used i n t h i s study was judge-ment of the mother, and because a p e r i o d of i n s t a b i l i t y of hand p r e f e r e n c e seems t o occur between ages two and three (Orton, 1934), we do not f e e l j u s t i f i e d i n drawing c o n c l u s i o n s on the r e l a t i o n s between c e r e b r a l dominance and handedness. 5.8 L i n g u i s t i c A b i l i t y Of the t h i r t y - o n e c h i l d r e n , e i g h t , a l l below the age of 2-6-30, were not yet u s i n g grammatical sentences i n t h e i r speech. Most of them had j u s t r e c e n t l y begun u s i n g two and three word u t t e r a n c e s and most of t h e i r c o n v e r s a t i o n a l speech c o n s i s t e d of s i n g l e words. The mean r i g h t ear score of t h i s group was 8.8 words and the l e f t ear score was 5«87« Thus, these two-year-old c h i l d r e n , who are at an e a r l i e r l i n g u i s t i c s t a g e, s t i l l demonstrate an REA comparable to the r e s t of the group. 55 5.9 C o u n t e r b a l a n c i n g S i x t e e n c h i l d r e n heard channel 1 and f i f t e e n c h i l d r e n , channel 2 i n the r i g h t e a r . The d i f f e r e n c e i n degree of r i g h t ear advantage between these two c o n d i t i o n s was not s i n i f i c a n t ( t = 1.64-76, df = 29, n s ) . 56 CHAPTER 6 DISCUSSION I n summary, r i g h t ear words were more e f f i c i e n t l y r e -c a l l e d than l e f t ear words by two-year-old c h i l d r e n . Although males demonstrated a s l i g h t l y l a r g e r REA than d i d females, and younger c h i l d r e n demonstrated a l a r g e r REA than d i d o l d e r c h i l d r e n , these d i f f e r e n c e s were not s t a t i s t i c a l l y s i g n i f i c a n t . Accuracy on t h i s t a s k d i d not change s i g n i f i c a n t l y a cross the age range s t u d i e d . The mean REA f o r the t o t a l group was 18$. The p r e s e n t r e s u l t s suggest t h a t , at l e a s t by c h r o n o l o g i c a l age two, an REA f o r v e r b a l m a t e r i a l can be observed, and shows a c e r t a i n degree of s t a b i l i t y . I f t h i s age marks the b e g i n n i n g of the s o - c a l l e d " l a t e r a l i z a t i o n " , t hen, because c h i l d r e n show v a r i a b i l i t y i n r a t e of n e u r o p s y c h o l o g i c a l m a t u r a t i o n , one would expect a l a r g e r number of c h i l d r e n to show an equal p r e -ference f o r both ears — t h a t i s , those c h i l d r e n who have not  yet developed c e r e b r a l dominance. I n f a c t , 78$ of the c h i l d r e n i n t h i s study demonstrated an REA, which i s i n c l o s e agreement w i t h r e s u l t s o b t a i n e d w i t h a d u l t and s c h o o l age c h i l d r e n (Kimura and P o l b , 1968; Bryden, 1970). S i m i l a r i l y , i f age two marks the b e g i n n i n g of a change from e q u i p o t e n t i a l i t y of the two hemispheres, t o dominance of one, and i f t h i s process i s c o r r e l a t e d w i t h the development of language, then one would expect t h a t c h i l d r e n of an " e a r l i e r 57 l i n g u i s t i c stage" might demonstrate an REA. of d i f f e r e n t mag-n i t u d e or d i r e c t i o n . I n the present study, s i n c e o n l y a l i m i t e d number of s u b j e c t s were t e s t e d , and the d i f f i c u l t y i n d e f i n i n g " l i n g u i s t i c " a b i l i t y s imply as e x p r e s s i v e language was compounded by the d i f f i c u l t y i n d e f i n i n g l i n g u i s t i c s t a g e s , we can o n l y suggest t h a t these c h i l d r e n do not demonstrate a d i f f e r e n c e i n the degree of magnitude of REA. Kimura (1967) s t a t e d t h a t i f d i c h o t i c l i s t e n i n g t a s k s were performed by c h i l d r e n i n any e a r l y stage of development, a sex d i f f e r e n c e i n the degree of c e r e b r a l dominance may be de t e c t e d ; t h a t i s , s i n c e boys appear t o develop language s k i l l s more s l o w l y than g i r l s (McCarthy, 1953), i t might be concluded t h a t they develop c e r e b r a l dominance f o r language l a t e r . I n the present study, although there were no s i g n i f i c a n t d i f f e r -ences between sexes, boys demonstrated a s l i g h t l y l a r g e r REA, than d i d g i r l s . Such a f i n d i n g does n o t , of course, a l l o w c o n j e c t u r e about the l a t e r a l i z a t i o n p r o c e s s , s i n c e i t i s both e q u a l l y p o s s i b l e t h a t a sex d i f f e r e n c e i n the degree of l a t e r -a l i z a t i o n does not e x i s t , as i t i s t h a t age two i s not the be-g i n n i n g of the l a t e r a l i z a t i o n p r o c e s s . I t i s of i n t e r e s t t o compare the degree of r i g h t ear advantage r e p o r t e d i n the l i t e r a t u r e f o r a d u l t versus c h i l d performance on d i c h o t i c v e r b a l t a s k s . Krashen (1972) has presented a revi e w of the d a t a from 22 s t u d i e s u s i n g the FOE method of a n a l y s i s , and concludes t h a t t h e r e i s l i t t l e change i n POE score from age f o u r u n t i l a dulthood. I t i s c h i e f l y t h i s f i n d i n g which prompts him to c l a i m t h a t l a t e r a l i z a t i o n 58 i s complete by age f o u r or f i v e . The mean POE score f o r a l l 22 s t u d i e s p resented by Krashen i s 58.5 and the mean POE score of the present experiment (59.1) c l o s e l y agrees w i t h t h i s . I f one t h e r e f o r e assumes t h a t changes i n the degree of REA r e f l e c t changes i n the degree of l e f t hemisphere dominance f o r language, then on the b a s i s of the p r e s e n t r e s u l t s , i t i s con-c e i v a b l e t h a t l a t e r a l i z a t i o n i s complete by age two. Such a sugg e s t i o n i s c o n s i s t e n t w i t h the the o r y t h a t the two hemi-spheres are never e q u i p o t e n t i a l f o r the development of language. Rather, the l e f t hemisphere always subserves language f u n c -t i o n i n g , w h i l e f o r a c e r t a i n p e r i o d of time the r i g h t hemisphere r e t a i n s the a b i l i t y t o take over the language f u n c t i o n i n cases of l e f t hemisphere damage. Perhaps the q u e s t i o n t h a t should be asked concerns the time l i m i t s w i t h i n which i t i s p o s s i b l e f o r the r i g h t hemisphere t o assume language f u n c t i o n s , f o r i t i s not known what accounts f o r the p r o g r e s s i v e i n a b i l i t y of the r i g h t hemisphere t o take over language f u n c t i o n . I t i s debatable whether t h i s p r o g r e s s i v e i n a b i l i t y i s due t o a l o s s of n e u r a l p l a s t i c i t y ( Z a n g w i l l , 1960) or a p r o g r e s s i v e d i f f e r -e n t i a t i o n of the r i g h t hemisphere f o r v i s i o - s p a t i a l o r i e n t a t i o n and other r i ght-dominant f u n c t i o n s (Galambos and H i l l y a r d , 1970). The p o s s i b i l i t y t h e r e f o r e e x i s t s , t h a t the a c t u a l degree of REA does not change from age two to adulthood, s i n c e l a t e r -a l i z a t i o n , as measured by d i c h o t i c l i s t e n i n g t a s k s , does not appear to change over t h i s age range. However, i t i s e q u a l l y l i k e l y t h a t the r e l a t i o n s h i p between degree of l a t e r a l i z a t i o n 59 and the degree of REA i s e i t h e r o v e r s i m p l i f i e d or n o n - e x i s t e n t . D i c h o t i c l i s t e n i n g i s a ver y simple technique used t o i n v e s t i -gate a ve r y complex phenomenon. I t i s evident t h a t language i s both a s t r u c t u r a l and f u n c t i o n a l e n t i t y i n the b r a i n , being an i n t e r r e l a t i o n s h i p between many s t r u c t u r e s and pathways, both i n t e r - and i n t r a - h e m i s p h e r i c , as w e l l as s u b c o r t i c a l . The asymmetry found i n d i c h o t i c l i s t e n i n g t a s k s , assumed t o r e s u l t o n l y from asymmetry at a c o r t i c a l l e v e l , may i n e f f e c t be a product of asymmetry at a lower l e v e l ; f o r example, i n the thalamus or r e t i c u l a r f o r m a t i o n . Botez and Barbeau (1971) have shown, f o r example, t h a t language d i s t u r b a n c e s may r e s u l t from l e s i o n s i n the l e f t d o r s a l thalamus, but not the r i g h t , and they emphasize the importance of s u b c o r t i c a l mechanisms i n speech and language. Moray (1970) s t a t e s : . . . i t may w e l l be t h a t f o r the p h y s i o l o g i c a l c o r r e l a t e s of conscious p e r c e p t i o n , we should look a t the a r o u s a l system and i t s f u n c t i o n a l r e -l a t i o n s r a t h e r than at the c o r t e x . The problem i s t h a t i f the a r o u s a l system i s i n f a c t the con-t r o l l e r of a t t e n t i o n and s e l e c t i v i t y , and a c t s not merely t o a l t e r the gross o v e r a l l l e v e l of r e -sponsiveness of the e n t i r e c e n t r a l nervous system but a l s o to c o n t r o l the f l o w of i n f o r m a t i o n over q u i t e s p e c i f i c p a t h s , we are going t o have to f i n d the a n a t o m i c a l l o c u s of the "gates" before we can begin t o account f o r p a r t i c u l a r phenomena i n the behavior of an observer who i s a t t e n d i n g t o one source of s t i m u l i and i g n o r i n g a n o t h e r . . . . i f we wish to deduce whether or not a p a r t i c u l a r s t i m u l u s has been c o n s c i o u s l y p e r c e i v e d we should look n e i t h e r at the r e t i c u l a r system, nor at the c o r t i c a l a c t i v i t y , but at the r e l a t i o n s h i p between the e l e c t r i c a l a c t i v i t y i n those two p a r t s of the b r a i n at l e a s t , and perhaps a l s o at the simultaneous a c t i v i t y i n y e t other p a r t s of the b r a i n . (pp..175-176) Furthermore, c l i n i c a l s t u d i e s of brain-damaged and hemi-spherectomized p a t i e n t s may be no more h e l p f u l than d i c h o t i c 60 l i s t e n i n g i n e l u c i d a t i n g the r o l e of s u b c o r t i c a l structures i n speech and language, since damage at a higher l e v e l of the CNS may prevent expression of normal fu n c t i o n i n g at a lower l e v e l . A schedule of the course of development of c e r e b r a l dominance would undoubtedly add to our understanding of how and when the br a i n becomes l a t e r a l i z e d . Several l i m i t a t i o n s are, however, inherent i n mapping out such a schedule. F i r s t , as mentioned above, percentage of REA almost cer-t a i n l y does not bear a d i r e c t r e l a t i o n s h i p to degree of dom-inance, even supposing that "ear e f f e c t " was unbiased by accuracy, task v a r i a b l e s , and other extraneous f a c t o r s . There-fo r e , caution must be exercized i n g e n e r a l i z i n g d i c h o t i c l i s t e n i n g r e s u l t s to imply changes i n degree of l a t e r a l i z a t i o n over time. Secondly, i n most studies, comparisons of c h i l d r e n are based on c h r o n o l o g i c a l age, which might not be the best i n -d i c a t o r of n e u r o l o g i c a l maturity. A p h y s i o l o g i c a l measure such as bone age, would undoubtedly show a c l o s e r correspondence to growth of the b r a i n (Harrison et a l . , 1964). Since the ra t e of growth of the b r a i n i s greatest i n the e a r l y years (Lenneberg, 1967), the younger the c h i l d r e n being tested, the l a r g e r i s the p o s s i b i l i t y of discrepancy between bone age and chronological age. Thus, i n using c h r o n o l o g i c a l age f o r sample s e l e c t i o n , i t becomes necessary to have a large enough sample to allow f o r maturational v a r i a b i l i t y . I t thus follows that, when seeking changes over a s p e c i f i c age range, i t i s 61 necessary to have c h i l d r e n evenly d i s t r i b u t e d a l o n g t h i s age range, i n order t o make v a l i d comparisons. T h i s problem of adequate sample s i z e at each age l e v e l i s a l i m i t a t i o n of the present r e s e a r c h . T h i r d l y , because of d i f f e r e n t s t i m u l u s m a t e r i a l s , v a r y i n g onset t i m e s , and other s i t u a t i o n a l v a r i a b l e s , c a u t i o n must be e x e r c i z e d i n mapping a developmental course based on a number of experiments, each d e a l i n g w i t h a p o r t i o n of the age range. On a more g e n e r a l note, comparing d i f f e r e n t c h i l d r e n of d i f f e r -ent ages, even w i t h i n the same study, may not y i e l d e q u i v a l e n t r e s u l t s t o comparing a s e l e c t e d group of c h i l d r e n i n a l o n g i t u d i n a l study. W i t h i n the l i m i t a t i o n s of the pre s e n t i n v e s t i g a t i o n , t h e r e f o r e , the f o l l o w i n g o b s e r v a t i o n s accrue. R e f e r r i n g t o Krashen's (1972) a n a l y s i s of d i c h o t i c s t u d i e s w i t h c h i l d r e n , i t can be seen t h a t the present r e s u l t s f a l l i n the lower range of ROE v a l u e s found f o r c h i l d r e n between the ages of f o u r and n i n e . These r e s u l t s t h e r e f o r e suggest t h a t the mag-n i t u d e of the REA undergoes l i t t l e change from age two through n i n e . The d a t a a l s o i n d i c a t e t h a t the magnitude of the REA does not change between the age of two and t h r e e . R e p l i c a t i o n , u s i n g a l a r g e r number of s u b j e c t s , over an extended age range, would be necessary t o c o n f i r m these r e s u l t s . I f t h i s f i n d i n g were confirmed,, i t might be necessary t o r e t h i n k the t r a d i t i o n a l view t h a t dominance of the l e f t hemisphere becomes g r a d u a l l y e s t a b l i s h e d over a p e r i o d of time d u r i n g c h i l d h o o d . F u r t h e r r e s e a r c h on i n f a n t s and younger c h i l d r e n , perhaps u t i l i z i n g 62 EEG, would h o p e f u l l y p r o v i d e a d d i t i o n a l c l u e s t o t h i s q u e s t i o n . The r e s u l t s of the present i n v e s t i g a t i o n suggest t h a t a d i c h o t i c l i s t e n i n g study w i t h eighteen-month-old c h i l d r e n might be p o s s i b l e . I f i t i s assumed t h a t the l e f t hemisphere i s always dom-i n a n t f o r language, how do we account f o r two-year-old c h i l d r e n who show language d i s t u r b a n c e s a f t e r r i g h t hemisphere damage (Basser, 1962)? I t should immediately be observed t h a t i t i s d i f f i c u l t t o i s o l a t e a language d i s o r d e r i n a young c h i l d , e s p e c i a l l y i f i n s u l t o c c u r r e d before the onset of speech; language " t e s t s " : f o r t h i s age range are o b v i o u s l y crude. I t i s a l s o apparent t h a t a sudden c e s s a t i o n i n t a l k i n g may not n e c e s s a r i l y be due t o d i r e c t d e s t r u c t i o n of t i s s u e u n d e r l y i n g language f u n c t i o n . I t i s p o s s i b l e t h a t damaS e of a c e r t a i n magnitude or s e v e r i t y anywhere i n a r a p i d l y d e v e l o p i n g system may cause a g e n e r a l d e l a y i n development; the e f f e c t s of b r a i n damage on language at t h i s age are not i n any way comparable to e f f e c t s of damage t o the f u l l y grown a d u l t system. The i n n o v a t i v e use of e l e c t r o e n c e p h a l o g r a p h i c (EEG) techniques i s begi n n i n g t o y i e l d i n f o r m a t i o n about speech a c t i v i t y i n the b r a i n of normal s u b j e c t s of a l l ages. Recent s t u d i e s w i t h normal a d u l t s have i n d i c a t e d a s i g n i f i c a n t d i f f e r -ence between the hemispheres i n EEG a c t i v i t y accompanying speech p r o d u c t i o n , w h i l e analogous non-speech g e s t u r e s , such as s p i t t i n g , e l i c i t e d b i l a t e r a l l y symmetrical p o t e n t i a l s (McAdams and Whitaker, 1971). There are numerous r e p o r t s e s t a b l i s h i n g bases f o r development of EEG s i g n a l p a t t e r n s i n normal i n f a n t s 63 (Hagne, 1972). As y e t , however, o n l y one study u s i n g t h i s technique t o examine speech l a t e r a l i z a t i o n i n i n f a n c y , has appeared i n the p u b l i s h e d l i t e r a t u r e . Malfese (1972, a b s t r a c t o n l y ) compared averaged evoked response (AER) wave forms from the r i g h t and l e f t hemisphere, i n response t o speech s y l l a b l e s , words, music and noise i n i n f a n t s , c h i l d r e n and a d u l t s . He found g r e a t e s t AER a c t i v i t y from the l e f t hemisphere was e l i c i t e d by v e r b a l s t i m u l i f o r a l l t h r e e groups of s u b j e c t s , w h i l e mechanical s t i m u l i e l i c i t e d l a r g e s t responses from the r i g h t hemisphere. Such evidence, when r e p l i c a t e d , w i l l un-doubtedly p r o v i d e s t r o n g evidence f o r language asymmetry from b i r t h . Future r e s e a r c h w i l l undoubtedly u t i l i z e more s o p h i s t i c a t e d EEG t e c h n i q u e s . 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Z u r i f , E 0 and Ramier, A c ( 1 9 7 2 ) 0 "Some E f f e c t s of U n i l a t e r a l B r a i n Damage on the P e r c e p t i o n of D i c h o t i c a l l y P r e -sented jehoneme Sequences and D i g i t s , " Neuropsych-o l o g i a 1 0 , 103-110. 71 Appendix 1  O s c i l l o s c o p i c t r a c i n g s of word-pairs SCALE: 20 msec 0/small d i v i s i o n hat nose mommy apple spoon f i s h chair tree doggie baby- queen ccw b i r d bed cup clown Appendix. 2 L i s t T, L i s t 2 and f o i l words L i s t 1 L i s t 2 F o i l Words a. hat a. nose a. sock* b. mommy* b. apple* b. wagon* 1;. man 1. mouse 1. k n i f e * 2. b a l l * 2. boy 2. soap* 3. bunny 3. daddy* 3. g i r l * 4. p e n c i l * 4. candy 4. b o t t l e 5. spoon* 5. f i s h * 5. p i n * 6. c h a i r * 6. t r e e * 6. shoe* 7o door. 7. gun* 7. key* 8. k i t t i e * 8. cookie 8. t a b l e * 9. doggie* 9. baby* 9. icecream 10. queen 10. cow* 10. mouth 11. boat* 11. bus* 11. eye 12. b l o c k * 12. b e l l * 12. ear 13. b i r d 13. bed* 13c f o o t 14. cup* 14. clown* 14. glove 15. cake* 15. c a r * 15. brush* *words s t a r r e d were chosen from the PPVT„ Appendix 5 D u r a t i o n ( i n msec.) of s t i m u l u s word-pairs L i s t 1 L i s t 2 a» hat 660 a. nose 780 b. mommy 900 b. apple 760 1. man 760 1. mouse 700 2. b a l l 600 2. boy 660 3. bunny 500 3. daddy 560 4. p e n c i l 900 4-„ candy 780 5. spoon 960 5. f i s h 480 6. c h a i r 620 6. t r e e 660 7. door 520 7. gun 600 8. k i t t i e 580 8. cookie 520 9. doggie 680 9. baby 760 10. queen 64-0 10. cow 680 11. boat 560 11. bus 600 12. b l o c k 760 12. b e l l 620 13. b i r d 520 1 3 . bed 460 14-. cup 680 14. clown 780 15. cake 600 '15. c a r 640 79 Appendix 4  Order of p i c t u r e placement a. hat a. nose a. ( s o c k ) * b. (wagon) b. apple b. mommy 1. man 1. ( k n i f e ) 1. mouse 2. (soap) 2. boy 2. b a l l 3. ( g i r l ) 3. daddy 3. bunny 4. p e n c i l 4. candy 4. ( b o t t l e ) 5, f i s h 5o ( p i n ) 5. spoon 6. t r e e 6. (shoe) 6. c h a i r 7. gun 7. door 7- (key) 8. ( t a b l e ) 8. k i t t y 8. cookie 9. ( i c e cream) 9* baby 9. doggie 10. (mouth) 10. queen 10. cow 11. boat. 11. (eye) 11. bus 12. ( e a r ) 12. b l o c k 12. b e l l 13. ( f o o t ) 13. b i r d 13. bed 14. clown 14. ( g l o v e ) 14. cup 15. cake 15. (brush) 15- c a r * f o i l words b r a c k e t e d . 

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