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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. C l i m a n B.Sc, McGill University,  A THESIS SUBMITTED  1971.  IN PARTIAL FULFILMENT OP  THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n t h e Department of Paediatrics D i v i s i o n o f A u d i o l o g y and Speech S c i e n c e s  We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e required standard  THE UNIVERSITY OF BRITISH. COLUMBIA < July,  1973  In p r e s e n t i n g 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 r e q u i r e m e n t s f o r an advanced degree a t the U n i v e r s i t y of B r i t i s h Columbia, I agree t h a t 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 r e f e r e n c e and  study.  I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g 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 by h i s r e p r e s e n t a t i v e s .  be g r a n t e d by the Head of my  Department or  I t i s u n d e r s t o o d t h a t c o p y i n g or  publication  of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t  my  written permission.  Department o f  P a e d i a t r i c s , D i v i s i o n of A u d i o l o g y and Speech Sciences  The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada  J u l y 13,  1973  ABSTRACT  I n the p r e s e n t s t u d y , d i c h o t i c l i s t e n i n g p e r f o r m a n c e o f t w o - y e a r - o l d c h i l d r e n was  investigated. Single pairs  of  words were p r e s e n t e d 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 tween GA  2-0-12 and  3-1-20. Each s u b j e c t  t o p i c t u r e s o f what he had  was  asked to  be-  point  h e a r d . F o r each p a i r o f words  presented, a subject  was  shown t h r e e p i c t u r e s , w h i c h  r e s p o n d e d t o the two  stimulus  words and  cor-  a f o i l word. D i f -  f e r e n c e s between number o f c o r r e c t r e s p o n s e s f o r each  ear  were e v a l u a t e d by means o f a t t e s t . Words p r e s e n t e d t o the r i g h t e a r were more ; e f f i c i e n t l y r e c a l l e d t h a n words p r e s e n t e d t o t h e age  group , w h i c h s u g g e s t s t h a t the  l e f t ear,  in this  l e f t hemisphere  has  a c h i e v e d some degree o f dominance f o r language by age No  two.  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  o f r i g h t e a r a d v a n t a g e , between males and studies using  school  age  and a d u l t  f e m a l e s . When  subjects  are compared, i t  a p p e a r s t h a t the r i g h t ear advantage does not n i t u d e o r d i r e c t i o n f r o m age two u n t i l Results  change i n mag-  adulthood.  of the present i n v e s t i g a t i o n are  discussed  i n r e l a t i o n to e x i s t i n g t h e o r i e s of  t h e development of  e b r a l l a t e r a l i z a t i o n . An a t t e m p t was  made t o r e l a t e e x p e r -  imental  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.,  s t u d i e s . L i m i t a t i o n s of t h e for  further research,  are  and  e x p e r i m e n t , as w a l l as discussed.  cer-  clinical suggestions  TABLE OP CONTENTS  Page ABSTRACT  i i  TABLE OP CONTENTS  i i i  LIST OP TABLES  v  LIST OP FIGURES  vi  ACKNOWLEDGEMENT  a  v i i  Chapter 1  INTRODUCTION  1  Chapter 2  LITERATURE: REVIEW  6  2.0  Introduction  2.1  The A u d i t o r y Pathways and C o r t i c a l Language A r e a s  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 Auditory Lesions  7  2.13  C o r t i c a l Areas W i t h Language  8  .6  Concerned  2.2  Dichotic Listening  1tf  2.3  Development o f 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 Studies With C h i l d r e n .  29  Chapter 3  STATEMENT OP PROBLEM  38  Chapter  METHOD  40  4  4.1  P r e p a r a t i o n o f 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 o f Tape Loops  40  i i i  4-.13  Chapter  Chapter  5  6  Preparation of Stimu l u s Tapes  Page 4-1  4-. 2  S t i m u l u s Words  4-3  4-.3  Subjects  4-5  4-.4-  Experimental Procedure.  4-6  RESULTS  4-9  5.1  Scoring  4-9  5.2  Subjects  4-9  5.3  Right versus L e f t Ears  50  5.4-  Sex  51  5.5  Age.  51  5.6  Age v e r s u s Sex  51  5.7  Handedness  54-  5.8  Linguistic Ability  54-  5.9  Counterbalancing  55  DISCUSSION  56  REFERENCES  64-  APPENDIX 1 APPENDIX 2 APPENDIX 3 APPENDIX 4-  Oscilloscopic Tracings of Word-Pairs L i s t 1, L i s t 2 and F o i l Words  71 77  D u r a t i o n ( i n msec.) o f Stimulus Word-Pairs.....  78  Order o f P i c t u r e P l a c e ment  79  iv  LIST OF TABLES Table  Page  5.1  S u b j e c t s by Age and Sex  50  5.2  T V a l u e s and Mean P e r c e n t REAs f o r P o u r Age-Sex Groups  55  Y  L I S T OF FIGURES  Figure  Page  2.1  N e u r o a n a t o m i c a l Schema f o r t h e Asymmetries  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 P a t h w a y s i n t h e Case o f R i g h t Hemispherectomy  15  Diagrammatic R e p r e s e n t a t i o n of A u d i t o r y P a t h w a y s i n t h e Case o f S e v e r e d Corpus Callosum  15  2.4  E a r S u p e r i o r i t y and Age Measures  23  4.1  P r e p a r a t i o n o f S t i m u l u s Tapes  5.1  I n d i v i d u a l S c o r e s Rank O r d e r e d t o Age  2.3  Auditory  According  vi.  to  Two  14  42 According  52  ACKNOWLEDGEMENTS  I w i s h t o t h a n k a l l t h o s e who had a p a r t i n t h i s thesis $ - t h e members o f my t h e s i s committee,  D r . John D e l a c k ,  D r . Juhn Wada, and e s p e c i a l l y , D r . John G i l b e r t . - a l l t h e 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 t i m e and c o o p e r a t i o n . - H e l e n , G i n n i , R a c h a e l and M a r i o n f o r t h e i r agement.  THE FAMILY CIRCUS  "Whisper on T H I S s i d e — I ' m left-eared."  vii  encour-  CHAPTER 1  INTRODUCTION  T h r o u g h o u t t h e c e n t u r i e s , man  has  struggled  s t a n d t h e r e l a t i o n s h i p s between b r a i n and b e h a v i o r w i t h a r e a s o f the b r a i n .  neurologists, psychologists lating.  I t i s evident  appreciate  the  and  has  to  correlate  retained  a wealth of r e s e a r c h  by  o t h e r s c i e n t i s t s i s accumu-  t h a t the more we  complexities  mind and  Modern man  t h i s f a s c i n a t i o n w i t h t h e b r a i n , and  to under-  l e a r n , t h e more  involved.  we  Language, o f t e n c i t e d  as t h e 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 insights into  t h e p r o b l e m o f c e r e b r a l l a t e r a l i z a t i o n and speech.  Dax  (1865) o b s e r v e d t h a t a p h a s i a r e s u l t s more o f t e n  from l e f t hemisphere hemisphere. 95$  localization for  l e s i o n s than from l e s i o n s i n the  More r e c e n t  e v i d e n c e c o n f i r m s t h a t , i n more than.  o f 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 f r o m  h e m i s p h e r e l e s i o n s ( L e n n e b e r g , 1970). b a s i s o f one  was  the  left  B r o c a ( 1 8 6 1 ) , on  aphasic p a t i e n t , s t a t e d t h a t the t h i r d  f r o n t a l convulution  right  the  left  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 the c e r e b r a l hemispheres e x i s t s .  asymmetrical nature  of  Geschwind.and L e v i t s k y  (1968)  have shown t h a t t h e a r e a b e h i n d H e s c h l ' s g y r u s , w h i c h forms p a r t of the temporal speech c o r t e x , i n 2/5  of the a d u l t b r a i n s  i s l a r g e r on t h e  s t u d i e d , and  1  l a r g e r on t h e  left  side  right  2  side i n only 11$.  There r e m a i n s l i t t l e doubt t h a t t h e 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 t h e l a n g u a g e f u n c t i o n than the r i g h t hemisphere.  T h i s i s true 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 , B r a n c h and Rasmussen, 1 9 6 4 ) . The has  development o f 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  received  adults.  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  I t i s g e n e r a l l y assumed t h a t , a t b i r t h and f o r an  u n s p e c i f i e d t i m e a f t e r , t h e two h e m i s p h e r e s a r e b o t h  involved  i n subsuming t h e language f u n c t i o n , and t h a t t h e r i g h t o r n o n dominant h e m i s p h e r e g r a d u a l l y f a d e s o u t i n i m p o r t a n c e ( Z a n g w i l l , 1960; L e n n e b e r g , 1967)-  The o n l y e v i d e n c e c i t e d  i s t h e l a c k o f a p h a s i c symptoms i n c a s e s o f i n f a n t i l e plegia.  The p r o b l e m s w i t h t h i s p o s i t i o n w i l l be  i n t h e l i t e r a t u r e survey.. for  the paucity  dominance.  I t i s not d i f f i c u l t  of d i r e c t research  hemi-  discussed  t o account  on t h e development o f  Lateralization i sdifficult,  i f not impossible,  t o o b s e r v e 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 a n a t o m i c a l d i s s e c t i o n are few. Furthermore, i t i s t h e funct i o n a l and n o t t h e a n a t o m i c a l d i f f e r e n c e s between t h e two h e m i s p h e r e s t h a t a r e most i m p o r t a n t .  The Wada Sodium A m y t a l  t e s t (Wada and Rasmussen, 1960) e n t a i l s t o o g r e a t research  p u r p o s e s w i t h young c h i l d r e n .  t a s k s , w h i c h w i l l be d e s c r i b e d  Dichotic  a risk for listening  i n d e t a i l , have p r o v e d t o be  s a f e and s i m p l e p r o c e d u r e s f o r d e t e r m i n i n g s i d e o f dominance for  language i n a d u l t s .  T h i s t e c h n i q u e has been a p p l i e d t o  c h i l d r e n as young as t h r e e  y e a r s o f age ( N a g a f u c h i , 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 semantic a p p r e c i a t i o n  a  o f t h e m a t e r i a l p r e s e n t e d , a f a i r de-  gree o f a t t e n t i o n , and e i t h e r a v e r b a l o r w r i t t e n r e s p o n s e , no  one has a t t e m p t e d t o adapt t h e p r o c e d u r e t o c h i l d r e n  younger t h a n The for  three.  age and p a t t e r n o f development o f c e r e b r a l dominance  language i s o f i n t e r e s t f o r s e v e r a l r e a s o n s .  is theoretical. and  The f i r s t  L i n g u i s t s h y p o t h e s i z e about t h e s t r u c t u r e  g r a m m a t i c a l r u l e s o f language t h a t s u p p o s e d l y r e f l e c t t h e  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 f o r m u -  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 , a t l e a s t , n o t c o n f l i c t w i t h what we know about t h e b r a i n . The  f u n c t i o n and s t r u c t u r e o f t h e b r a i n i s , u l t i m a t e l y , a  substrate  o f language competence.  The c h i l d ' s e v o l v i n g  l a n g u a g e competence must c o r r e s p o n d i n some way t o n e u r o l o g i c a l g r o w t h and m a t u r a t i o n .  Unfortunately,  we a r e a l o n g  way f r o m k n o w i n g 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 b e h a v i o r a l m i l e s t o n e s o f language a c q u i s i t i o n .  Nor do we know  what t h e b e h a v i o r a l m i l e s t o n e s o f l a n g u a g e l e a r n i n g a r e . U l t i m a t e l y , t h e s e w i l l have t o be d e f i n e d n e u r o l o g i c a l development. cuitous.  i n reference  This problem i s obviously  to cir-  However, t h e development o f n e u r o l o g i c a l i n d i c e s ,  s u c h as c e r e b r a l l a t e r a l i z a t i o n , w o u l d have tremendous t h e o r e t i c a l impact. Such a development w o u l d have c l i n i c a l a p p l i c a t i o n s as well.  I t i s w e l l recognized  a b n o r m a l , we must f i r s t  t h a t , i n order t o understand the  look a t the normal course o f  4  development.  Thus, i n o r d e r t o d e s c r i b e a c h i l d a s 'neuro-  l o g i c a l l y i m p a i r e d ' t o a c c o u n t f o r a language d e l a y , we must f i r s t have n o r m a t i v e d a t a on n e u r o l o g i c a l changes  during  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 t o 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 s l o w development o f dominance o r i n c o m p l e t e dominance.  C u r r y and G r e g o r y (1969) have s u g g e s t e d  t h a t s t u t t e r e r s show a l a c k o f c e r e b r a l dominance, on a d i c h o t i c word t e s t .  as t e s t e d  T a y l o r (1962) and B r y d e n (1970)  have s u g g e s t e d t h a t p o o r r e a d e r s a r e s i g n i f i c a n t l y l e s s ear  right  d o m i n a n t , and t h u s , by i n f e r e n c e , have i n c o m p l e t e domi-  nance f o r l a n g u a g e .  Somners and T a y l o r (1972) t e s t e d  language  d e l a y e d and n o r m a l 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  task  and f o u n d t h a t t h e l a n g u a g e d e l a y e d c h i l d r e n showed a s m a l l e r r i g h t e a r advantage (REA) f o r d i c h o t i c a l l y p r e s e n t e d 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)  s u g g e s t e d 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 p r e d o m i n a n t l y show a l e f t e a r advantage f o r v e r b a l d i c h o t i c stimuli.  On t h e o t h e r 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 e a r advantage c o m p a r a b l e t o n o r m a l s ( J o n e s and S p r e e n ,  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  intellectual  impairment, r a t h e r than a s p e c i f i c language problem.  The  above m e n t i o n e d s t u d i e s a r e by no means i r r e p r o a c h a b l e o r 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 t o s p e c u l a t e on t h e p o s s i b l e d i a g n o s t i c v a l u e o f a w e l l documented cerebral  dominance.  measure o f  5  A normative d e f i n i t i o n of the beginning the process  and t h e end o f  o f c e r e b r a l l a t e r a l i z a t i o n w o u l d a l s o have  prognostic value.  I f primary  language l e a r n i n g c a n o n l y  take  place 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 ( L e n n e b e r g , 1967)) t h e n s u c h 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 when a l a n g u a g e d e l a y e d terminate  c l u e s t o more a c c u r a t e p r e d i c t i o n o f c h i l d w i l l c e a s e t o p r o g r e s s , when t o  language therapy,  and w i t h n o r m a l c h i l d r e n , when t o  i n t r o d u c e i n s t r u c t i o n i n a second l a n g u a g e .  CHAPTER 2  LITERATURE REVIEW  2.0  Introduction 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  topic i s presented  i n four sections.  S e c t i o n 2.1  research describes  t h e 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 t h e c o r t i c a l language a r e a s .  S e c t i o n 2.2 r e v i e w s some o f t h e r e s e a r c h i n  dichotic listening.  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  with  L e n n e b e r g ' s s c h e d u l e f o r t h e d e v e l o p m e n t o f c e r e b r a l dominance f o r l a n g u a g e 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 S e c t i o n 2.4 d i s c u s s e s  schedule.  some o f t h e r e l e v a n t r e s e a r c h on t h e  development o f 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 t h e d i c h o t i c l i s t e n i n g technique.  I n t h i s l i t e r a t u r e r e v i e w and  t h r o u g h o u t t h e t h e s i s , t h e words l a t e r a l i z a t i o n and dominance w i l l be u s e d  2.1  interchangeably.  The A u d i t o r y P a t h w a y s and C o r t i c a l 2.11  Auditory  Language A r e a s  pathways  We w i l l omit d e s c r i p t i o n o f t h e o u t e r , m i d d l e and i n n e r e a r mechanisms and f o l l o w t h e c o c h l e a r p o r t i o n o f t h e e i g h t h c r a n i a l nerve from t h e c o c h l e a t o t h e a u d i t o r y c o r t e x . a r e f i v e n e u r o n s i n t h e pathway.  There  The p r i m a r y n e u r o n f r o m each  i n n e r e a r p r o j e c t s t o b o t h t h e 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 t h e same s i d e .  Prom h e r e , about 60$ o f t h e f i b e r s  cross 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 , while the  6  7  remaining  40$ p r o j e c t t o t h e i p s i l a t e r a l s u p e r i o r  Thus, e a c h c o c h l e a i s r e p r e s e n t e d each s i d e .  olive.  i n t h e a u d i t o r y pathway on  The f i b e r s , now f o r m i n g  the l a t e r a l  lemniscus,  p r o j e c t t o t h e i n f e r i o r c o l l i c u l u s , go t o t h e m e d i a l g e n i c u l a t e body o f t h e t h a l a m u s , and f r o m t h e r e , t o t h e p r i m a r y  auditory  r e c e p t i o n area o f t h e c o r t e x , t h e temporal gyrus of Heschl. Thus, d e s t r u c t i o n o f p a r t o f one a u d i t o r y pathway above t h e l e v e l of the superior o l i v e w i l l not destroy hearing side.  on e i t h e r  Even w i t h t h e r e m o v a l o f one c e r e b r a l h e m i s p h e r e , t h e  p u r e t o n e t h r e s h o l d s f o r e a c h e a r w i l l be u n a f f e c t e d .  2.12  Detection of central auditory lesions  I t i s e v i d e n t t h a t some f o r m o f a u d i o m e t r i c  t e s t i n g more  s e n s i t i v e t h a n p u r e - t o n e 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 t h e c e n t r a l p o r t i o n s o f t h e a u d i t o r y pathway.  Bocca e t a l .  (1954) d e l i v e r e d l o w - p a s s f i l t e r e d s p e e c h (500 Hz) t o p a t i e n t s w i t h tumours o f one t e m p o r a l l o b e , who showed n o r m a l p u r e - t o n e thresholds b i l a t e r a l l y . t o each e a r .  The s p e e c h was d e l i v e r e d a l t e r n a t e l y  I t was f o u n d t h a t s p e e c h 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 t h e d i s c r i m i n a t i o n s c o r e s o f n o r m a l subj e c t s were s y m m e t r i c a l  f o r normal e a r s , although  subjects  with  l e s i o n s o f one t e m p o r a l l o b e showed a d e f i c i t o f 20-30$ on t h e e a r c o n t r a l a t e r a l t o t h e l e s i o n , w h e t h e r t h e l e s i o n was i n t h e r i g h t o r t h e l e f t hemisphere.  These s t u d i e s , w h i l e  d e m o n s t r a t i n g a s y m m e t r i e s i n t h e a u d i t o r y pathways i n t h e case  8  of t e m p o r a l 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 .  o n l y w e l l documented way mals i s to present  2.13  So f a r , t h e  to r e v e a l these asymmetries i n nor-  s t i m u l i to both ears,  C o r t i c a l areas concerned w i t h  Most o f t h e i n f o r m a t i o n now  dichotically.  language  a v a i l a b l e concerning  o r g a n i z a t i o n o f language i n t h e b r a i n has been g a i n e d the study  of aphasic  patients.  the through  Aphasia i s a multi-modal  language d e f i c i t , w h i c h r e s u l t s f r o m d e s t r u c t i o n o f b r a i n t i s s u e , usually following a cerebrovascular injury.  The  l e s i o n i s most o f t e n c e n t e r e d  lobe, although The  aphasia  aphasia  accident i n the  l e f t temporal  can r e s u l t f r o m r i g h t h e m i s p h e r e l e s i o n s .  i s o f t e n accompanied by r i g h t h e m i p l e g i a .  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 in linguistic  o r head  o r p s y c h o l o g i c a l t e r m s and  c o r r e l a t e these d e f i c i t s  The deficit  t h e n , p o s t mortem, t o  w i t h s i t e of l e s i o n .  O t h e r 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 b r a i n , and  the  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 o f t h e p r o b l e m s a s s o c i a t e d w i t h a l l  t h e s e 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 specifying  t h e r e l a t i o n s h i p between e l e c t r i c a l and n o r m a l 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  or the exact  s i z e and  s i t e of  lesion,  a r e a s t i m u l a t e d o r a b l a t e d , (4) s m a l l number o f  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 o f l e s i o n a t t i m e o f i n j u r y f r o m t h e s i z e p o s t 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 o f a b l a t i o n from  e f f e c t s of surgery.  I t s h o u l d be remembered t h a t a l m o s t  none o f t h e r e s e a r c h a v a i l a b l e c o n c e r n i n g t h e s t r u c t u r e o f language i n t h e 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 intact population. Despite t h i s state of a f f a i r s , information i s a v a i l a b l e concerning 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 l a n g u a g e .  A summary o f t h e i d e n -  t i f i e d a r e a s f r o m W h i t a k e r (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 a r e a s 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 a r e a s a r e :  a)  P e r i p h e r a l p r o d u c t i o n systems (1)  B r o c a ' s a r e a - L e s i o n s h e r e cause a p r a x i a o r l o s s o f motor c o n t r o l o f s p e e c h .  (2)  E x n e r ' s a r e a - L e s i o n s h e r e a r e t h o u g h t t o cause impairment of w r i t i n g  b)  ability.  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 a r e a and r e c e i v e s f i b e r s f r o m t h e m e d i a l g e n i c u l a t e body.  I t i s n o t 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 a r e a i n t h e dominant h e m i s p h e r e w o u l d , i n some way, (4)  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.  A n g u l a r g y r u s - T h i s a r e a i s l o c a t e d between t h e s o m e s t h e t i c , a u d i t o r y , v i s u a l and s p e e c h a r e a s 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 h e r e cause m a j o r i m p a i r m e n t s i n r e a d i n g and B.  The (5)  writing.  f o u r c e n t r a l language areas a r e : 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 t h e c o m p r e h e n s i o n o f spoken l a n g u a g e ,  and  t h e r e a r e o f t e n s e r i o u s e f f e c t s on s p e e c h p r o d u c t i o n as (6)  well.  S u p e r m a r g i n a l g y r u s - L e s i o n s i n t h i s a r e a seem t o u p s e t some a s p e c t s  (7)  o f grammar.  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 a r e a has been t e n t a t i v e l y c a l l e d t h e  'naming  c e n t e r ' by W h i t a k e r ; i t seems t o be i n v o l v e d i n t h e a b i l i t y t o name o b j e c t s .  However, l i t t l e more t h a n  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 o f t h i s a r e a must a w a i t more r e l i a b l e d a t a . i n t h i s a r e a a r e t h o u g h t t o cause amnesic word f i n d i n g d i f f i c u l t i e s and (8)  Arcuate  Lesions  aphasia,  syntactic errors.  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 lobe w i t h p a r t s of the temporal l o b e .  frontal  Lesions  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 t h e o r g a n i z a t i o n o f language i n t h e 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 conjecture than f a c t .  I t i s n o t y e t known what happens i n t h e  b r a i n d u r i n g language a c q u i s i t i o n , o r d u r i n g e n c o d i n g o r coding.  de-  Even i f t h e above a r e a s 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 t h e y were d e m a r c a t e d i n brain-damaged p o p u l a t i o n s , it  i s n o t known how t h e y c o r r e s p o n d  an i n t a c t dynamic l a n g u a g e s y s t e m . to  t o the functioning of New ways must be f o u n d  expose t h e 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 o f t h e  o r g a n i z a t i o n o f l a n g u a g e , i n l a r g e numbers o f n o r m a l s u b j e c t s .  2.2  Dichotic Listening B r o a d b e n t (195^) f o u n d t h a t when b o t h e a r s a r e s t i m u l a t e d  simultaneously  w i t h two d i f f e r e n t s e r i e s o f s t i m u l i ,  s e r i e s e l i c i t responses,  b u t t h e y do so one a f t e r t h e o t h e r . ( s u c h a s 716)  Thus, when t h r e e d i g i t s while three other d i g i t s opposite  both  ( s u c h a s 253)  a r e a p p l i e d t o one e a r axe a p p l i e d t o t h e  e a r , s u b j e c t s t e n d t o r e s p o n d e i t h e r 716253 o r  253716 b u t seldom 721563-  T h i s method o f s i m u l t a n e o u s  pre-  s e n t a t i o n o f d i f f e r e n t s t i m u l i t o e a c h e a r 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, t h e b a s i s f o r an i m p o r t a n t area of research. K i m u r a (1961a) compared t h e 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 o f p a t i e n t s w i t h e i t h e r l e f t o r r i g h t damage u s i n g B r o a d b e n t s method o f s i m u l t a n e o u s 1  of d i g i t s .  cortical  presentation  She f o u n d t h a t t e m p o r a l l o b e e x c i s i o n o f e i t h e r  side impaired the perception of d i g i t s a r r i v i n g a t the contral a t e r a l ear.  However, b o t h e a r s p e r f o r m e d e q u a l l y w e l l w i t h  monaural o r a l t e r n a t i n g e a r p r e s e n t a t i o n .  Kimura a l s o found  t h a t t h e o v e r a l l performance o f p a t i e n t s w i t h l e f t l o b e damage was p o o r e r  than that of p a t i e n t s with  t e m p o r a l l o b e damage.  This r e s u l t confirmed  temporal right  a general  12  assumption  t h a t t h e l e f t t e m p o r a l l o b e p l a y s a more i m p o r -  tant r o l e than the r i g h t i n the perception of v e r b a l  stimuli.  A t h i r d , and p e r h a p s 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 , received higher 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 task.  K i m u r a (1961b) a d -  m i n i s t e r e d t h e d i c h o t i c t a s k t o t h r e e groups: (1) l e f t  hemi-  sphere -dominant ( f o r s p e e c h ) p a t i e n t s ( a s c o n f i r m e d by t h e •Vada Sodium A m y t a l t e s t ) ,  (2) r i g h t hemisphere  dominant  p a t i e n t s , and ( 3 ) n o r m a l r i g h t - h a n d e d p e o p l e who p r e s u m a b l y were l e f t h e m i s p h e r e d o m i n a n t .  The f i r s t two groups had  epileptogenic lesions of various parts of the b r a i n . r e s u l t s i n d i c a t e d an REA f o r t h e l e f t h e m i s p h e r e p a t i e n t s and f o r t h e n o r m a l g r o u p .  The  dominant  For those p a t i e n t s with  s p e e c h r e p r e s e n t e d i n t h e r i g h t h e m i s p h e r e , t h e l e f t e a r was f o u n d t o be more e f f i c i e n t . K i m u r a (1961a) p o s t u l a t e d t h a t c o n n e c t i o n s between  each  h e m i s p h e r e and i t s c o n t r a l a t e r a l e a r a r e s t r o n g e r a n d / o r more numerous t h a n s u c h c o n n e c t i o n s t o t h e 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 c o n f i r m e d b o t h a n a t o m i c a l l y and p h y s i o logically  ( R o s e n z w e i g , 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 h e m i s p h e r e dominance f o r s p e e c h , a c c o u n t e d , she f e l t , f o r t h e g r e a t e r e f f i c i e n c y o f t h e r i g h t ear.  S i n c e b o t h e a r s p e r f o r m 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 , K i m u r a c o n c l u d e d t h a t an REA e x i s t s o n l y when t h e r e i s c o m p e t i t i o n between t h e two e a r s and, i n t h i s c a s e , 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-  nections.  K i m u r a ' s n e u r o a n a t o m i c a l scheme f o r t h e o b s e r v e d  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 o f hemispherectomized  and s p l i t - b r a i n s u b j e c t s .  found t h a t the l e f t ear scores of r i g h t  Kimura  (1961a)  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 d e p r e s s e d . i n t h i s c a s e t h e o n l y pathways a v a i l a b l e and c o n t r a l a t e r a l t o t h e l e f t h e m i s p h e r e ,  are those  ipsilateral  subcortical  s u p r e s s i o n can be assumed t o be t a l c i n g p l a c e . i s diagrammed i n F i g u r e 2.2.  Since  This situation  S i m i l a r l y , i t has been f o u n d  t h a t c a l l o s a l l y s e v e r e d p a t i e n t s a r e a b l e t o r e c a l l a l m o s t 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 (Milner,  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  contra-  l a t e r a l and one i p s i l a t e r a l pathway t o t h e speech a r e a a r e functional.  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 suppression i s a f a c t o r i n p r o d u c i n g t h e REA, factor.  i t i s d e f i n i t e l y not the o n l y  I t i s p r o b a b l e t h a t t h e c r o s s - c a l l o s a l r o u t e from  t h e r i g h t t o t h e l e f t hemisphere d i c h o t i c a l l y to the l e f t ear.  i s used f o r s t i m u l i p r e s e n t e d  I n such a case, the l e f t  ear  s i g n a l has one more synapse t h a n t h e r i g h t e a r s i g n a l and t h u s t h e REA  m i g h t be a c c o u n t e d f o r by e i t h e r e a r l i e r a r r i v a l o f  the r i g h t ear s i g n a l t o the speech a r e a or e l s e i n c r e a s e d  de-  g r a d a t i o n o f t h e l e f t e a r s i g n a l because o f t h e g r e a t e r d i s t a n c e t r a v e l l e d ( S p a r k s , G o o d g l a s s and N i c k e l , 1970). The d e p r e s s i o n o f t h e l e f t e a r s c o r e s i n c a s e s o f 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-  RIGHT HEMISPHERE  LEFT HEMISPHERE (DIGITS)  (MELODIES)  RIGHT EAR  LEFT EAR  F i g u r e 2.1  N e u r o a n a t o m i c a l schema f o r t h e a u d i t o r y asymmetries. (from  Kimura,1967,fig.2,p.174-)  15  LEFT HEMISPHERE  LEFT EAR F i g u r e 2.2  RIGHT EAR Diagrammatic r e p r e s e n t a t i o n o f a u d i t o r y pathways i n t h e c a s e o f 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 o f a u d i t o r y pathways i n t h e c a s e o f s e v e r e d c o r p u s callosum.  16  pathways t o t h e r i g h t hemisphere b e f o r e c r o s s i n g o v e r t o t h e l e f t hemisphere  language a r e a .  s u p p r e s s i o n was t h e o n l y f a c t o r ,  If contralateral-ipsilateral 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 p e r f o r m l i k e n o r m a l s , i n a dichotic who  task.  S p a r k s and Geshwind  (1968) t e s t e d one  had had t h e n e o c o r t i c a l commissures  ject recalled  sectioned.  T h i s sub-  100$ o f t h e words p r e s e n t e d t o each e a r  a u r a l l y , b u t showed 100$ e x t i n c t i o n l e f t ear i n the d i c h o t i c  situation.  subject  mon-  o f s t i m u l i coming i n t h e 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 t i m e s and t o l d t o c o n c e n t r a t e on t h e l e f t  ear  s t i m u l i , he was a b l e t o r e c a l l 100$ o f t h e r i g h t e a r s t i m u l i and 35$ "the  of the l e f t ear s t i m u l i .  l e f t e a r may  The a u t h o r s s u g g e s t t h a t  improve f r o m i t s i n i t i a l l y l o w e r 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 o r damage t o t h e r i g h t t e m p o r a l 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 " . ( S p a r k s and Geschwind, 1968, p . 15.)  I t i s evident that both contra-  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 t h e c r o s s - c a l l o s a l r o u t e f r o m t h e r i g h t t o t h e l e f t hemisphere must be a c c o u n t e d f o r i n a t h e o r e t i c a l model o f d i c h o t i c  listening.  Numerous s t u d i e s w i t h n o r m a l a d u l t s f o l l o w e d w h i c h c o n f i r m e d and e x t e n d e d K i m u r a ' s o r i g i n a l r e s u l t s .  Kimura  (1964)  f o u n d a s i g n i f i c a n t l e f t e a r advantage f o r t h e r e c o g n i t i o n o f m e l o d i e s , w h i c h c o n f i r m e d M i l n e r ' s (1962) f i n d i n g t h a t t h e 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.  F u r t h e r m o r e , 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 , m e l o d i e s were p e r c e i v e d more e f f i c i e n t l y by t h e l e f t e a r , t h e p o s s i b i l i t y t h a t t h e REA  found f o r d i g i t s concerned the  17  f a m i l i a r nature o f these s t i m u l i ( r a t h e r than the v e r b a l n a t u r e ) was n e g a t e d .  An REA was a l s o f o u n d f o r words and f o r  nonsense s y l l a b l e s ( K i m u r a , 1967; C u r r y , 1968)  and f o r back-  ward s p e e c h sounds ( o b t a i n e d by i n v e r t i n g a t a p e  containing  nonsense s y l l a b l e s and p l a y i n g i t b a c k i n t h e n o r m a l ( K i m u r a and P o l b , 1 9 6 8 ) .  direction)  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 o f s p e e c h sounds are n o t r e l a t e d t o m e a n i n g f u l n e s s , f a m i l i a r i t y , or c o n c e p t u a l c o n t e n t . ( K i m u r a and P o l b , 1968, p . 396) Studdert-Kennedy  and S h a n k w e i l e r (1970) p r e s e n t e d 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 t h e s y l l a b l e a t a t i m e .  A s i g n i f i c a n t REA f o r  t h e p e r c e p t i o n o f c o n s o n a n t s , b u t n o t o f v o w e l s , was f o u n d . These a u t h o r s have h y p o t h e s i z e d t h a t , w h i l e t h e a u d i t o r y system o f each hemisphere parameters  s u c h a s i n t e n s i t y , f r e q u e n c y and t i m e , o n l y t h e  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  inherent i n consonants. of  appears e q u a l l y capable o f e x t r a c t i n g  Studdert-Kennedy  t h a t , whatever  P e r h a p s most i m p o r t a n t , t h e r e s u l t s  and S h a n k w e i l e r ' s e x p e r i m e n t  demonstrated  t h e mechanism o f s p e e c h p e r c e p t i o n i n t h e  left  hemisphere,  i t i s s e n s i t i v e t o the p h o n e t i c content o f an  utterance.  Thus, t h e p e r c e p t i o n o f p h o 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 s e m a n t i c and s y n t a c t i c  levels.  The p e r c e p t u a l asymmetry e x p l a n a t i o n o f t h e REA p r o p o s e d by K i m u r a  (1961b) was w i d e l y c h a l l e n g e d . O t h e r s e x p l a i n e d i t  as a s y m m e t r i c a l d i v i s i o n o f a t t e n t i o n t o l e f t and r i g h t e a r  18  i n p u t s ( T r e i s m a n and G e f f e n , 1968)  or asymmetrical  short  t e r m memory s t o r a g e  and/or a t e n d e n c y t o r e p o r t t h e r i g h t  ear f i r s t  1965).  (Inglis*  N e i t h e r a t t e n t i o n a l n o r memory  a s y m m e t r i e s c o u l d be t h e s o l e d e t e r m i n e r (1)  o f t h e REA because  t h e r i g h t e a r i s s u p e r i o r on b o t h t h e f i r s t  channels reported  (Bryden,  and second  1 9 6 7 ) ; ( 2 ) t h e r i g h t e a r i s more  e f f i c i e n t t h a n t h e l e f t when o r d e r o f 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 t h e f r e e r e c a l l s i t u a t i o n ( B r o a d b e n t and G r e g o r y , 1964; S a t z , 1 9 6 8 ) ; and most i m p o r t a n t , is material  (3) t h e REA  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; K i m u r a , 1964; S p r e e n , S p e l l a c y and R e i d , 1970) environmental  sounds ( C u r r y , 1967) a r e p r e s e n t e d  a l e f t e a r advantage i s f o u n d .  or  dichotically,  An e x p l a n a t i o n b a s e d on  memory o r a t t e n t i o n a l f a c t o r s o n l y c a n n o t a c c o u n t f o r t h i s specificity  2.3  (Darwin, 1969).  Development o f 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 t h e b r a i n d e v e l o p s  i t s l a t e r a l i z a t i o n f o r speech. review  o f the scant  childhood,  Z a n g w i l l (1960)  i  b a s e d on a  l i t e r a t u r e o f hemispherectomy i n e a r l y  stated:  I t w o u l d t h e r e f o r e seem t h a t a t b i r t h t h e 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 g a r d t o t h e a c q u i s i t i o n o f l a n g u a g e 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 t h e p o s s i b i l i t y o f a s h i f t i n dominance — appear t o 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 t o 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 c a n 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 a p p e a r s t o e v o l v e p a r i p a s s u w i t h t h e development o f s p e e c h 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 t h e advent o f m a t u r i t y . ( Z a n g w i l l , 1 9 6 0 , p . 2)  19 The f i r s t p e r s o n t o t h e o r i z e about an upper and l o w e r (1966,  l i m i t t o t h e p r o c e s s o f l a t e r a l i z a t i o n was L e n n e b e r g 1967).  As h i s t h e o r i e s have r e c e i v e d wide a c c e p t a n c e i n t h e  l i t e r a t u r e , t h e y w i l l be d i s c u s s e d i n some d e t a i l . Lenneberg the  brain,  correlated three factors:  (1) m a t u r a t i o n o f  (2) t h e n o t i o n o f a c r i t i c a l p e r i o d f o r p r i m a r y  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 o f t h e s p e e c h function to the l e f t  o r dominant h e m i s p h e r e .  Parameters of  b r a i n m a t u r a t i o n s u c h as b r a i n w e i g h t , d e c r e a s e i n c e l l d e n s i t y , and n e u r o c h e m i c a l 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$ o f t h e i r a d u l t v a l u e s i n t h e f i r s t two y e a r s o f l i f e . of  Thus, age two a p p e a r s t o be t h e b e g i n n i n g  a p e r i o d d u r i n g w h i c h s t r u c t u r a l and c h e m i c a l changes d e -  celerate.  Prom age two t o a p p r o x i m a t e l y age t h i r t e e n ,  such  p a r a m e t e r s 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 a r e r e a c h e d a t around p u b e r t y .  T h i s t i m e p e r i o d between t h e ages  of  two and t h i r t e e n i s h y p o t h e s i z e d by Lenneberg  for  p r i m a r y language a c q u i s i t i o n and s i m i l a r l y  t o be  critical  the period i n  w h i c h s p e e c h 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 L e n n e b e r g , t h e two h e m i s p h e r e s p o t e n t i a l f o r t h e development  are equi-  o f language i n t h e f i r s t two  y e a r s o f l i f e , t h a t i s , b e f o r e t h e c h i l d has a c q u i r e d l a n g u a g e . L a t e r a l i z a t i o n t h e n t a k e s p l a c e as a r e s u l t o f a p r o g r e s s i v e decrease i n involvement o f the r i g h t hemisphere. the  By p u b e r t y  b r a i n has r e a c h e d i t s mature s t a t e and c e r e b r a l  alization i s irreversibly  established.  later-  20  Most o f L e n n e b e r g ' s e v i d e n c e i s b a s e d on B a s s e r ' s - (1962) r e v i e w o f c h i l d r e n who have s u s t a i n e d  unilateral lesions.  I n h a l f o f t h o s e c h i l d r e n who s u s t a i n l e s i o n s b e f o r e t h e onset o f speech, speech i s d e l a y e d . as o f t e n w i t h r i g h t as w i t h  However, t h i s d e l a y o c c u r s  l e f t h e m i s p h e r e damage, s u g g e s t i n g  c e r e b r a l dominance has n o t y e t been e s t a b l i s h e d . who s u s t a i n e d disturbed  In children  l e s i o n s between ages two and t e n , B a s s e r n o t e d  s p e e c h r e s u l t i n g from l e f t h e m i s p h e r e l e s i o n s  85$  o f t h e t i m e and f r o m r i g h t h e m i s p h e r e damage 4-5$ o f t h e t i m e . 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 o f t w e l v e and t h i r t e e n y e a r s o f age p r o d u c e d i r r e v e r s i b l e l a n g u a g e d i s o r d e r s to aphasia i n adults while  r i g h t - s i d e d lesions sustained  t h i s age a l m o s t n e v e r p r o d u c e d a l a n g u a g e The c r i t i c a l p e r i o d  comparable at  disorder.  f o r p r i m a r y 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 L e n n e b e r g , l i m i t e d by b o t h m a t u r a t i o n o f t h e b r a i n and c o m p l e t i o n o f c e r e b r a l l a t e r a l i z a t i o n ? l a n g u a g e l e a r n i n g by mere e x p o s u r e c a n n o t t a k e p l a c e b e f o r e t h e b r a i n has  reached a c e r t a i n maturational  l e v e l or a f t e r completion  o f l a t e r a l i z a t i o n o f f u n c t i o n and l o s s o f p l a s t i c i t y . In  summary,  . . . c e r e b r a l l a t e r a l i z a t i o n o f t h e 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 b e f o r e 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 o r t w e l v e d u r i n g w h i c h 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 p u s h e d back i n t o t h e r i g h t h e m i sphere i f t h e l e f t h e m i s p h e r e i s d i s t u r b e d . After puberty, l a t e r a l i z a t i o n i s normally f i r m l y establ i s h e d t o t h e l e f t , and t h e r i g h t h e m i s p h e r e 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 t o t h e r i g h t do n o t . ( L e n n e b e r g , 1966, p . 47)  21  U n t i l v e r y r e c e n t l y , Lenneberg's s c h e d u l e f o r t h e development o f l a t e r a l i z a t i o n h a s r e m a i n e d u n c h a l l e n g e d 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 ( B e r r y , 1969, p . 4 2 ; P e r k i n s , 1971, p . 119; p. 1129).  after.1967  W i n i t z , 1971,  Most c l i n i c a l t e x t s p u b l i s h e d b e f o r e  Biological  F o u n d a t i o n s o f Language make no m e n t i o n o f l a t e r a l i z a t i o n o f s p e e c h i n t h e i r d i s c u s s i o n s o f language a c q u i s i t i o n .  (1965), f o r example, s t a t e t h a t t h e f o u r f u n c t i o n s  and A r n o l d  e s p e c i a l l y important are: (3)  (1)  Luchsinger  f o r t h e n o r m a l development o f language  s e n s o r y d e v e l o p m e n t , (2)  motor d e v e l o p m e n t ,  p s y c h o m o t o r d e v e l o p m e n t , and ( 4 ) i n t e l l e c t u a l d e v e l o p m e n t . R e c e n t l y , however, b o t h t h e upper and l o w e r l i m i t s o f  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.  K r a s h e n and Harshman (1972) have p o s t u l a t e d  that  l a t e r a l i z a t i o n i s c o m p l e t e by age f i v e , r a t h e r t h a n p u b e r t y as s u g g e s t e d by L e n n e b e r g . sented:  (1)  Two t y p e s  o f evidence are p r e -  changes i n degree o f l a t e r a l i z a t i o n between t h e  ages o f f i v e and t e n , and (2)  the observed e f f e c t s o f u n i -  l a t e r a l b r a i n l e s i o n s on s p e e c h when s u c h l e s i o n s o c c u r b e tween f i v e and t e n y e a r s  o f 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 childhood u n t i l puberty,  t h e n one might e x p e c t t h a t t h e 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 a s s u b j e c t s r e p o r t a d e c r e a s e 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 a c c u r a c y . as t h e c h i l d ' s t o t a l s c o r e  Thus,  ( b o t h e a r s ) i n c r e a s e s , t h e mag-  n i t u d e o f t h e d i f f e r e n c e between e a r s w i l l d e c r e a s e .  I n the  22  l i m i t i n g c a s e , a c h i l d who r e c e i v e s a p e r f e c t s c o r e w i l l n o t e x h i b i t any e a r a d v a n t a g e .  Krashen  (1972), u s i n g a p e r c e n t o f  e r r o r s method o f a n a l y s i s , h a s a n a l y s e d d a t a f r o m t h r e e developmental  s t u d i e s ( K i m u r a , 1 9 6 3 ; Knox and K i m u r a ,  and G e f f n e r and Hochberg, 1971)  1970;  and h a s f o u n d no change i n  magnitude o f REA from t h e ages o f f o u r o r f i v e u n t i l n i n e . His analysis of the previous f i n d i n g s i s presented i n F i g u r e 2.4.  A n o t h e r 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 a c c u r a c y i s p r e s e n t e d i n Kuhn (1972). C l i n i c a l d a t a on t h e e f f e c t s o f b r a i n l e s i o n s on speech were a l s o r e - e x a m i n e d  by K r a s h e n  (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 t o t h e r i g h t h e m i s p h e r e a f t e r t h e y h a d a c q u i r e d s p e e c h . Of t h e s e , seven  ( o r 4-5$) e x h i b i t e d " d i s t u r b e d " s p e e c h .  However, a l l  seven o f t h e s e c h i l d r e n were b e l o w f i v e y e a r s c h r o n o l o g i c a l age, a d d i n g s u p p o r t t o t h e " l a t e r a l i z a t i o n by f i v e " e s i s o f Krashen  hypoth-  and Harshman (1972).  The b e s t t e s t o f t h e a b i l i t y o f t h e r i g h t h e m i s p h e r e to subserve  language  c a n be e v i d e n c e d i n p a t i e n t s who have  had t h e l e f t h e m i s p h e r e removed, s i n c e i t i s n o t known t o what e x t e n t language aged h e m i s p h e r e . ispherectomy  c a n be c o n t r o l l e d o r i n h i b i t e d b y a dam-  B a s s e r (1962) p r e s e n t e d 52 c a s e s o f hem-  i n c h i l d h o o d , w h i c h L e n n e b e r g (1967) c i t e s as  evidence t h a t t h e r i g h t hemisphere i s capable o f t a k i n g over language  f u n c t i o n b e f o r e p u b e r t y . When B a s s e r ' s d a t a i s more  c a r e f u l l y examined ( K r a s h e n , 1 9 7 2 ) , i t i s seen t h a t 4-2 o u t o f  23  <iod  4F i g u r e 2.4  5  6  7  8  9  age  E a r 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.  ( D a t a f r o m Kimura,1963, Knox and K i m u r a , 1970,Geffner and Hochberg,1971,  combined)  ( f r o m Krashen,1972,fig.3.1,P-28)  24  t h e 52 c a s e s d i s c u s s e d by L e n n e b e r g as " b e f o r e t e e n s " were a c t u a l l y u n d e r f i v e when damage was s u s t a i n e d , a f u r t h e r s u p p o r t f o r t h e " 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 .  It  w i l l be s e e n i n l a t e r d i s c u s s i o n on t h e e a r l y l i m i t o f l a t e r a l i z a t i o n t h a t L e n n e b e r g 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 B a s s e r ' s d a t a . The p r e c e d i n g c l i n i c a l e v i d e n c e does n o t e x c l u d e t h e t h e o r y o f " l a t e r a l i z a t i o n by f i v e " o r l a t e r for  either  lateralization,  i t i s f i r s t n e c e s s a r y t o show t h a t l e f t h e m i s p h e r e damage  a f t e r t h e age o f f i v e and b e f o r e p u b e r t y does cause permanent language d i s t u r b a n c e a n d , c o n v e r s e l y , t h a t r i g h t h e m i s p h e r e damage a t t h i s age d o e s - n o t .  Unfortunately, only three  left  h e m i s p h e r e p a t i e n t s i n t h i s age r a n g e 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 K r a s h e n ,  1972)  and none a r e  described i n s u f f i c i e n t d e t a i l to illuminate this problem. complete  theoretical  Thus, c o n c l u s i v e p r o o f o f c e r e b r a l l a t e r a l i z a t i o n by f i v e y e a r s o f 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 o b v i o u s i n c a p a c i t y t o l e a r n a l l b u t t h e most p r i m i t i v e b e g i n n i n g s o f 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 , a t l e a s t i n t u i t i v e l y , attributable to a general state of c e r e b r a l i m m a t u r i t y . ( L e n n e b e r g , 1967, p . 168) Thus, a l t h o u g h L e n n e b e r g d i s c u s s e s i n d e t a i l t h e v o c a l i z a t i o n s of  t h e p r e l i n g u a l c h i l d , he does n o t c o n s i d e r t h e f i r s t  or  two o f 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 .  year  Further-  more, h i s comments a p p e a r t o be ambiguous as t o when t h e a c t u a l a c q u i s i t i o n p r o c e s s b e g i n s ; a t t i m e s he e q u a t e s i t w i t h t h e a p p e a r a n c e o f t h e f i r s t word a t a p p r o x i m a t e l y  25  t w e l v e months, a t o t h e r t i m e s w i t h t h e f i f t e e n - m o n t h mark, and a t o t h e r t i m e s w i t h t h e second o r t h i r d y e a r o f l i f e , when he p r o p o s e s t h e p r o c e s s o f c e r e b r a l begins. off  However, t h e f i r s t y e a r o f l i f e cannot be p a s s e d  a s a t i m e when l i t t l e  place.  lateralization  o r no language  learning takes  I t i s a working hypothesis that receptive  p r e c e d e e x p r e s s i v e language  skills.  skills  Thus, b e f o r e a c h i l d  c a n use h i s f i r s t word m e a n i n g f u l l y , he h a s t o have been a b l e to  i s o l a t e t h i s word f r o m t h e s t r e a m o f speech he h e a r s , t o  f o r m an a s s o c i a t i o n between t h e 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.  This description i s obviously  oversimplified,  and we have o n l y j u s t begun t o r e a l i z e t h e 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 o f language. R e c e n t e x p e r i m e n t s s u g g e s t t h a t t h e i n f a n t may be capable o f 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 o f l i f e .  Eimas e t a l . (1971) t e s t e d one-  and f o u r - m o n t h - o l d b a b i e s on t h e a b i l i t y t o d i s t i n g u i s h between t h e v o i c e d and v o i c e l e s s s t o p c o n s o n a n t s / 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 o f t h e n o n n u t r i t i v e s u c k i n g r e s p o n s e as a measure. d i f f e r i n t h e onset o f the f i r s t second and t h i r d f o r m a n t s .  I n a c o u s t i c t e r m s , / b / and / p / formant r e l a t i v e t o t h e  L i b e r m a n e t a l . (1957) p r e s e n t e d  a s e r i e s o f 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  o f v o i c e o n s e t t i m e (VOT) and f o u n d t h a t  adult  l i s t e n e r s perceive the interphonemic but not the intraphonemic d i f f e r e n c e s , a l t h o u g h t h e a c o u s t i c v a r i a t i o n was t h e same i n  26  t h e two c a s e s ; categorical.  t h a t i s , t h e i r p e r c e p t i o n o f phonemes i s They f o u n d t h a t t h i s t y p e o f c a t e g o r i c a l p e r -  c e p t i o n does n o t o c c u r w i t h n o n - s p e e c h s t i m u l i and i s c h a r a c t e r i s t i c of perception  i n t h e s p e e c h o r l i n g u i s t i c mode.  Eimas e t a l . (1971) compared t h e a b i l i t y o f 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 s p e e c h sounds w h i c h were  separated  by f i x e d d i s t a n c e s o f VOT, but w h i c h l a y e i t h e r on t h e same o r on o p p o s i t e  s i d e s o f t h e a d u l t phoneme b o u n d a r y .  f o u n d t h a t b o t h one-  They  and f o u r - m o n t h - o l d i n f a n t s were a b l e t o  d i s c r i m i n a t e a VOT d i f f e r e n c e o f t w e n t y msec, when t h e two s t i m u l i l a y on o p p o s i t e  s i d e s o f t h e a d u l t phoneme b o u n d a r y ,  but n o t when t h e y b e l o n g e d t o t h e same phoneme The  category.  a u t h o r s c o n c l u d e 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  o f s p e e c h sounds s i m i l a r t o t h e p e r c e p t u a l a b i l i t y o f a d u l t l i s t e n e r s , and t h u s a r e p e r f o r m i n g  linguistic discriminations.  T h i s e x p e r i m e n t was r e p l i c a t e d u s i n g b o t h n a t u r a l and s y n t h e t i c s t i m u l i , and a l s o e x t e n d i n g  the  stimuli to include the  homorganic p a i r / d / and / t / by Trehub and R a b i n o v i t c h whose r e s u l t s c o n f i r m e d  (1972)  t h e f i n d i n g s o f Eimas e t a l . (1971).  A d i s c u s s i o n o f t h e m e t h o d o l o g y o f t h i s e x p e r i m e n t and o f whether t h e d i s c r i m i n a t o r y a b i l i t y o f 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 a r e beyond t h e scope o f t h i s review;  however, t h e f i n d i n g s o f numerous e x p e r i m e n t s do  seem t o i n d i c a t e t h a t i n f a n t s a r e b e g i n n i n g  t o make p e r -  c e p t u a l judgements f r o m v e r y e a r l y i n l i f e and p r o b a b l y birth.  from  27 Another experiment suggested t h a t seven-week-old can d i s c r i m i n a t e t h e a c o u s t i c cues f o r p l a c e and i n t o n a t i o n ( M o r s e , 1972).  infants  of a r t i c u l a t i o n  The a u t h o r compared t h e s e r e -  s u l t s with 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  stimuli.  This 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) •  M o f f i t t ( i 9 7 i ) f o u n d t h a t i n f a n t s o f t w e n t y - and weeks o f age were a b l e t o d i s c r i m i n a t e between  twenty-foursynthetic  s y l l a b l e s w h i c h d i f f e r e d o n l y i n d e g r e e o f second f o r m a n t t r a n s i t i o n and c o r r e s p o n d e d t o t h e p e r c e p t u a l  difference  between / b a h / and /gah/. Since receptive l i n g u i s t i c s k i l l s are being  established  throughout t h e 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 t h e dominant h e m i s p h e r e , i t cannot be assumed t h a t t h e two h e m i s p h e r e s a r e e q u i p o t e n t i a l f o r s p e e c h a t any t i m e .  I t i s l i k e l y t h a t , up  t o a c e r t a i n t i m e , t h e r i g h t hemisphere i s a b l e t o t a k e o v e r the  language f u n c t i o n i n t h e case o f l e f t hemisphere damage b u t  t h i s i m p l i e s organic  p l a s t i c i t y , n o t 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 a l m o s t a l l c h i l d r e n , language become c e n t e r e d  functions  i n t h e l e f t t e m p o r a l l o b e i m p l i e s t h a t i n some  way t h i s a r e a must be p r e p o t e n t f o r language development a t l e a s t from b i r t h .  Note t h a t t h i s p r e p o t e n c y does n o t r u l e  out some e a r l y p a r t i c i p a t i o n o f t h e r i g h t h e m i s p h e r e .  Further-  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 d e m o n s t r a t e an REA f o r t h e p e r c e p t i o n  o f stop  consonants (Studdert-Kennedy  28  and S h a n k w e i l e r , 1970).  These a u t h o r s c o n c l u d e d t h a t t h e  " p r o c e s s o r " s p e c i a l i z e d f o r speech i n t h e l e f t hemisphere i s s e n s i t i v e t o t h e p h o n e t i c c o n t e n t o f an u t t e r a n c e .  That  i n f a n t s a r e o s t e n s i b l y c a p a b l e o f 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 l e n d s f u r t h e r c r e d e n c e t o t h e 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 a r e f u n c t i o n a l v e r y 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 t h e dominant  hemisphere.  I t s h o u l d be n o t e d t h a t w h i l e B a s s e r d i v i d e s h i s c a s e s i n t o " b e f o r e t h e o n s e t o f s p e e c h " and " a f t e r speech h a s been a c q u i r e d " , Lenneberg  r e p o r t s t h e e v i d e n c e as " b e f o r e 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 c a s e s d i s c u s s e d by B a s s e r i n t h e second c a t e g o r y were between t h e ages o f one and t w o . There i s some e v i d e n c e 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 a t s e v e n t e e n months o f age may have permanent e f f e c t s on h e m i s p h e r i c s p e e c h dominance.  N e t l e y (1972) compared t h r e e  groups on a d i c h o t i c l i s t e n i n g t a s k : (2)  (1)  normal  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)  injured patients.  infantile  The average age o f i n j u r y i n t h e t h i r d  group was s e v e n t e e n months. performed  controls,  Hemispherectomies  on b o t h groups o f p a t i e n t s .  were  later  I t was f o u n d t h a t r e -  c a l l s c o r e s f o r t h e e a r i p s i l a t e r a l t o t h e r e m a i n i n g hemisphere were l o w e r f o r t h e l a t e - i n j u r e d group t h a n f o r t h e c o n g e n i t a l l y i n j u r e d group o r t h e non-dominant e a r o f t h e normal group.  I t thus appears t h a t t h e c o n g e n i t a l l y  injured  p a t i e n t s a r e b e t t e r a b l e t o u t i l i z e t h e i p s i l a t e r a l pathways  29  between t h e non-dominant e a r and  the r e m a i n i n g hemisphere  i n a DL t a s k t h a n i n f a n t i l e - i n j u r e d ' p a t i e n t s . of p a t i e n t s are c o n t r a s t e d who,  with c a l l o s a l l y severed  although having normal monaural r e c a l l  almost completely  B o t h groups adults  bilaterally,  s u p p r e s s v e r b a l m a t e r i a l coming i n t h e  l e f t e a r i n a DL t a s k  ( S p a r k s and  Geschwind, 1968).  These  p a t i e n t s are unable t o u t i l i z e the c r o s s - c a l l o s a l r o u t e l e f t - e a r d i c h o t i c s t i m u l i and suppression  for  a p p e a r t o have a l m o s t c o m p l e t e  o f t h e pathway t o t h e dominant h e m i s p h e r e f o r  dichotic stimulation.  Netley's  r e s u l t s support the view t h a t  t h e r e l a t i o n s h i p s between pathways f r o m t h e e a r t o t h e l o b e a r e e s t a b l i s h e d and  temporal  a c h i e v e some d e g r e e o f permanence  much e a r l i e r t h a n s u g g e s t e d 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, t h e 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 exercized.  I t should  a l s o be n o t e d t h a t N e t l e y  twelve hemispherectomized p a t i e n t s i n a l l . e v i d e n c e does c h a l l e n g e  studied  only  However, s u c h  the almost u n i v e r s a l l y accepted  that l e s i o n s sustained before  two  y e a r s o f age  do n o t  idea  have  permanent c o n s e q u e n c e s .  2.4  Dichotic Studies with  Children  A s m a l l number o f s t u d i e s have f o c u s e d on t h e ment o f l a t e r a l i t y f o r s p e e c h .  develop-  K i m u r a (1963) t e s t e d  c h i l d r e n between t h e ages o f f o u r and  nine  on a DL  task.  c h i l d r e n were r i g h t - h a n d e d and d e m o n s t r a t e d no h e a r i n g ment.  The  120 All  impair-  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 t h r e e p a i r s , a n d each c h i l d was a s k e d t o  r e p e a t what he had h e a r d i n any o r d e r he w i s h e d .  I t was  f o u n d t h a t each age group t e s t e d p r e s e n t e d more e f f i c i e n t r e c a l l o f s t i m u l i p r e s e n t e d t o the r i g h t ear than those p r e s e n t e d t o t h e l e f t ; t h a t i s , t h e mean number o f d i g i t s  cor-  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 t h e r i g h t , t h a n f o r t h e ear.  left  Thus, a t l e a s t by age f o u r , a r i g h t e a r advantage f o r  v e r b a l m a t e r i a l was o b s e r v e d . Kimura s 1  I t s h o u l d be n o t e d t h a t  a t t e m p t s 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 n o t e d by K r a s h e n (1972), t h e r e s u l t s o f K i m u r a ' s i n d i c a t e a d e c r e a s e i n t h e magnitude tween e a r s , w i t h i n c r e a s i n g age.  study  o f the d i f f e r e n c e be-  When t o t a l s c o r e s ( f o r b o t h  e a r s combined) were compared, i t was f o u n d t h a t f i v e - a n d s i x y e a r - o l d f e m a l e s were s u p e r i o r t o t h e i r male p e e r s , a l t h o u g h s i g n i f i c a n t d i f f e r e n c e s between s e x e s d i d n o t appear i n any o t h e r age g r o u p . . K i m u r a l a t e r r e p l i c a t e d t h e e x a c t 1963 p r o c e d u r e c h i l d r e n ages f i v e t o e i g h t i n a l o w e r t o m i d d l e c l a s s (SEC) a r e a ( K i m u r a , 1967).  with  socioeconomic  I n t h i s study, f i v e - y e a r - o l d  f e m a l e s d e m o n s t r a t e d a n REA whereas f i v e - y e a r - o l d m a l e s 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 o f s i x , seven and e i g h t y e a r s o f age  demonstrated  a s i g n i f i c a n t REA. K i m u r a s u g g e s t e d t h a t (1) t h e  l o w e r SEC c h i l d r e n were a t a n e a r l i e r s t a g e o f c o g n i t i v e f u n c t i o n i n g t h a n c h i l d r e n t e s t e d i n h e r 1963 s t u d y , and (2) t h a t males l a g b e h i n d f e m a l e s i n t h e development hemisphere  dominance f o r s p e e c h .  of l e f t  I n both these s t u d i e s ,  31  Kimura omitted d e t a i l s o f h e r stimulus  synchronization  procedures. The  development o f e a r asymmetry f o r b o t h v e r b a l and  n o n v e r b a l sounds h a s been compared i n c h i l d r e n f r o m f i v e t o eight years chronological  age (Knox and K i m u r a , 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 t o t h o s e u s e d by K i m u r a (1963,  1967), w h i l e t h e 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 o f common e n v i r o n m e n t a l sounds s u c h a s a d o g b a r k i n g , train whistle. while  c o u g h i n g , and a  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 g r o u p s ,  a l e f t e a r advantage f o r n o n v a r b a l sounds a p p e a r e d  only  a t 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 s e x e s i n  the t o t a l r e c a l l o f v e r b a l s t i m u l i .  However, more n o n v e r b a l  sounds were i d e n t i f i e d by boys t h a n by g i r l s . G e f f n e r and Hochberg (1971) s t u d i e d s o c i o e c o n o m i c c l a s s (SEC)  b o t h l o w and m i d d l e  children at chronological  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 .  age f o u r ,  They f o u n d a  s i g n i f i c a n t REA f o r a l l age g r o u p s w i t h i n the m i d d l e SEC w h i l e o n l y the REA.  s e v e n - y e a r - o l d c h i l d r e n i n the  I n f a c t , four-year-old  a s u b s t a n t i a l l y stronger children.  l o w e r SEG showed an  middle c l a s s c h i l d r e n demonstrated  REA t h a n d i d s i x - y e a r - o l d l o w e r SEG  This i s not too s u r p r i s i n g since the four-year-old  m i d d l e 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 e a r d i f f e r e n c e did  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 .  than  This f i n d i n g i s  a g a i n p a r t i a l l y dependent on the d i f f e r e n t a c c u r a c y l e v e l s w i t h i n the  age groups ( K r a s h e n , 1972).  No s i g n i f i c a n t d i f f e r -  ences were o b s e r v e d between s e x e s f o r r i g h t e a r e f f e c t .  32  O n l y one s t u d y has looked  appeared i n the l i t e r a t u r e  which  for cerebral l a t e r a l i z a t i o n i n three-year-old children.  N a g a f u c h i (1970) t e s t e d e i g h t y n o r m a l c h i l d r e n between t h e ages o f t h r e e and s i x on a DL t a s k ; handedness was not i n dicated.  S t i m u l i c o n s i s t e d o f t w e n t y d i s y l l a b i c , and t w e n t y  trisyllabic,  words.  y e a r s o f age,  N a g a f u c h i f o u n d t h a t , even a t t h r e e  a s i g n i f i c a n t r i g h t e a r advantage was e v i d e n t  i n b o t h boys and g i r l s .  Three-year-old  g i r l s achieved  t o t a l s c o r e s t h a n t h r e e - y e a r - o l d boys and,  higher  not s u r p r i s i n g l y ,  t h e magnitude o f t h e REA was l a r g e r f o r t h r e e - y e a r - o l d than f o r three-year-old p r o c e d u r e were  girls.  boys  No d e t a i l s o f s y n c h r o n i z a t i o n  reported.  B r y d e n (1970) s t u d i e d b o t h l e f t - a n d r i g h t - h a n d e r s i n g r a d e s two,  f o u r and s i x ( a p p r o x i m a t e l y  t w e l v e ) on a d i c h o t i c d i g i t s t a s k .  ages e i g h t , t e n and  The r e s u l t s were  i n number o f c h i l d r e n showing e i t h e r a r i g h t e a r or a l e f t ear advantage, r a t h e r than percent r e c t l y r e c a l l e d from each e a r . two,  advantage  of digits  cor-  B r y d e n f o u n d t h a t , i n grade  t h e r e were no d i f f e r e n c e s by sex o r handedness i n t h e  number o f c h i l d r e n showing an REA. right-handed  an REA d e c r e a s e d . right-handed  However, t h e p e r c e n t o f  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  t o grade s i x w h i l e t h e p e r c e n t  of left-handed  c h i l d r e n showing  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  g i r l s a p p e a r e d i n grade f o u r w h i l e t h e 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 six.  reported  boys a p p e a r e d o n l y i n grade  K r a s h e n (1972) h a s 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 b e f o r e n i n e y e a r s o f age (Belmont  33  and B i r c h , 1 9 6 3 ) , some o f t h e c h i l d r e n i n t h e  right-handed  group i n B r y d e n ' s s t u d y were n o t t r u l y r i g h t - h a n d e d d i d n o t show a r i g h t e a r a d v a n t a g e .  As s u c h c h i l d r e n would  n o t 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 n e s s w o u l d t h e n be e v i d e n t ) t h e p e r c e n t  w o u l d 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. of the left-handed  showed an REA. one  increased.  t o a more r e c e n t p a p e r (Benson and G e s c h w i n d , 1 9 6 8 ) ,  most r e s e a r c h e r s  40$  left-handed-  o f c h i l d r e n showing  an REA w o u l d seem t o i n c r e a s e as grade l e v e l According  and  Thus, i t i s s t r a n g e  that  grade s i x c h i l d r e n i n B r y d e n ' s  These c h i l d r e n a r e t w e l v e  only  study  y e a r s o f age and  w o u l d e x p e c t t h a t t h e y show t h e same d i s t r i b u t i o n o f  r i g h t e a r s u p e r i o r i t y as t h e a d u l t p o p u l a t i o n .  Satz,  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 of left-handed  73$  a d u l t s show an REA.  Since these s i x studies are the only reported  develop-  m e n t a l i n v e s t i g a t i o n s u s i n g t h e DL t e c h n i q u e ,  some  c r i t i c i s m s appear w a r r a n t e d .  the r e s u l t s of  F i r s t , although  general  a l l s t u d i e s a p p e a r t o s u g g e s t t h a t c h i l d r e n as young a s c h r o n o l o g i c a l age t h r e e o r f o u r y e a r s show an REA f o r v e r b a l s t i m u l i , few o t h e r g e n e r a l i z a t i o n s c a n be made about s e x , handedness, age o r s o c i o e c o n o m i c 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 f e m a l e s i n a DL t a s k have been s u g g e s t e d :  (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 t h e age a t w h i c h an REA c a n f i r s t be o b s e r v e d .  34  The r e s u l t s o f two s t u d i e s s u g g e s t e d 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 p e e r s . one s t u d y , t h i s d i f f e r e n c e appeared  However, i n  o n l y a t age t h r e e  ( N a g a f u c h i , 1970), w h i l e i n t h e o t h e r , t h e d i f f e r e n c e  appeared  o n l y a t ages f i v e and s i x , b u t n o t age f o u r ( K i m u r a , 1963). F u r t h e r m o r e , t h r e e s t u d i e s s u g g e s t e d t h a t t h e r e were no d i f f e r e n c e s between s e x e s 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 K i m u r a , 1970;  t h e s i x t h s t u d y ( B r y d e n , 1970)  K i m u r a , 1967)  while  does n o t p r e s e n t t h i s  infor-  mation. I f a s e x d i f f e r e n c e i n t h e age o f appearance c o u l d be r e l i a b l y d e m o n s t r a t e d ,  o f an REA  then t e n t a t i v e suggestions  about t h e o n s e t o f 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 t h e s t u d i e s r e ported.  While Kimura's  d i d not demonstrate  an REA, N a g a f u c h i ' s (1970) t h r e e - y e a r -  o l d males d e m o n s t r a t e d t h e i r female p e e r s .  (1967) l o w e r SEC f i v e - y e a r - o l d males a larger right  e a r advantage  than  None o f t h e o t h e r 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 evident t h a t t o t a l r e c a l l and magnitude o f r i g h t not independent one a n o t h e r .  e a r advantage a r e  factors but are i n v e r s e l y correlated with  As a c c u r a c y i n c r e a s e s , so a l s o w i l l t h e  d i f f e r e n c e between e a r s d e c r e a s e . I f we a r e s e e i n g t h e development o f t h e u l t i m a t e  adult  p a t t e r n o f r e c a l l i n a DL t a s k , t h e n i t i s l o g i c a l t o l o o k f o r changes i n t h e d i f f e r e n c e between e a r s 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 gradually being established u n t i l  55  p u b e r t y ( c f . L e n n e b e r g , 196?) and i f we assume t h a t t h e magnitude  o f t h e ear d i f f e r e n c e r e f l e c t s t h i s  lateralization  p r o c e s s , t h e n one would e x p e c t t o see an i n c r e a s e i n t h e r i g h t e a r 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, t h e r e s u l t s o f t h e p r e c e e d i n g e x p e r i m e n t s seem t o s u g g e s t t h e o p p o s i t e ; t h e magnitude the  c h i l d gets older.  As m e n t i o n e d  o f t h e REA d e c r e a s e s as earlier, this i s partly  due t o d i f f e r e n t l e v e l s o f a c c u r a c y between age g r o u p s . Thus,, u n l e s s a c c u r a c y i s a c c o u n t e d f o r i n t h e c o m p u t a t i o n s , it the  i s n o t p o s s i b l e t o draw c o n c l u s i o n s about t h e changes i n magnitude The  o f t h e REA w i t h i n c r e a s i n g a g e .  l a s t t e n y e a r s h a s seen a r a p i d i n c r e a s e i n s t u d i e s  c o n c e r n e d 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 t e n d t o be one o f two t y p e s .  Lower c l a s s  e i t h e r have (1) or  (2)  d e f i c i e n t language s k i l l s  d i f f e r e n t language s k i l l s o r d i a l e c t i c a l  ( L a b o v , 1967). or  (Bernstein,  1961)  differences  No s t u d y known t o t h i s a u t h o r h a s d e m o n s t r a t e d ,  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 ( n o t confounded differences).  of cerebral  a l i z a t i o n i n l o w e r c l a s s c h i l d r e n ( K i m u r a , 1967; Hochberg,  by r a c i a l  I n v i e w o f t h i s , one must be wary o f r e s e a r c h  p a p e r s t h a t s u g g e s t s l o w e r development  1971).  G e f f n e r and Hochberg  none o f t h e c h i l d r e n d e m o n s t r a t e d it  children  later-  G e f f n e r and  (1971) s t a t e d t h a t  s p e e c h and language  deficits;  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 d e v e l o p e d a l l t h e 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 o f t h e i r l a n g u a g e , would n o t d e m o n s t r a t e an REA w h i l e t h r e e - y e a r - o l d c h i l d r e n do ( N a g a f u c h i , 1970).  I t appears  more l i k e l y t o a c c o u n t f o r s u c h r e s u l t s i n terms o f d i f f e r e n t s t y l e o f 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 , p o o r e r r a p p o r t w i t h the examiner  (Labov, 1 9 6 8 ) ,  poorer motivation, or misunderstanding of the i n s t r u c t i o n s . F u r t h e r m o r e , a l t h o u g h G e f f n e r and Hochberg criteria  (1971) g i v e t h e i r  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 , t h e y g i v e no  d e t a i l s o f t h e r a c e o f t h e c h i l d r e n , how t h e 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 s u c h as grade academic  level,  a c h i e v e m e n t , and e x p e r i m e n t e r b i a s were a c c o u n t e d 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 , t h e younger t h e c h i l d , t h e l a r g e r t h e 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 l a n g u a g e , o v e r a g i v e n t i m e p e r i o d . In t h e . f i r s t year of l i f e ,  the c h i l d acquires one-half of the  m a j o r phonemes and some s i m p l e morphemes (Mussen, Conger, and Kagan, 1969). to  I n t h e s e c o n d y e a r , t h e average c h i l d b e g i n s  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 u s e words  m e a n i n g f u l l y ; h i s s p e e c h becomes more i n t e l l i g i b l e and h i s c o m p r e h e n s i o n  increases greatly.  and complex  The average one-  y e a r - o l d u n d e r s t a n d s o r u s e s 3 words; a t 15 months, t h e average i s 19; a t 18 months, 22 words; by 21 months, 118 words; by two y e a r s , 272 words, and by age t h r e e t h e e f f e c t i v e v o c a b u l a r y i f 896 words.  A t t h e same t i m e , r a p i d g a i n s i n o t h e r a r e a s  of p h y s i c a l and c o g n i t i v e growth a r e t a k i n g p l a c e . six  The above  s t u d i e s have grouped c h i l d r e n on t h e b a s i s o f 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, a l t h o u g h  there are large  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 t h e s e two children.  Such a g r o u p i n g  procedure, although l e g i t i m a t e  w i t h a d u l t s o r o l d e r c h i l d r e n , m i g h t o b s c u r e changes i n t h e p a t t e r n o f development o f c e r e b r a l l a t e r a l i z a t i o n i n v e r y young c h i l d r e n . The All  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.  s t u d i e s m e n t i o n e d g i v e few, i f any, d e t a i l s o f t h e i r  methods o f d i c h o t i c t a p e c o n s t r u c t i o n .  As w i l l be d e m o n s t r a t e d  b e l o w , d u r a t i o n o f word, s y n c h r o n i z a t i o n o f s t i m u l i and  onset,  s i m i l a r i t y o f i n i t i a l phoneme a l l e x e r t m e a s u r a b l e e f f e c t s  in  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 o f t h e t h r e e above c r i t e r i a .  No d e t a i l s a r e  g i v e n about e x a c t l y what p a r t o f t h e s p e c t r u m i s s y n c h r o n i z e d 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, against a voiced p l o s i v e .  Furthermore, three of the s i x  s t u d i e s m e n t i o n e d u s e d t h e i d e n t i c a l t a p e ; t h e one c o n s t r u c t e d by K i m u r a i n 1963, w h i c h 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 t h e f i n d i n g s . Techniques used i n t h e c o n s t r u c t i o n o f 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 t h e e a r l y e x p e r i m e n t s p e r f o r m e d and r e p o r t e d i n t h e literature.  CHAPTER 3  STATEMENT OP PROBLEM  D i c h o t i c l i s t e n i n g h a s p r o v e n t o be a r e l i a b l e ,  safe  and r e l a t i v e l y s i m p l e way t o i n v e s t i g a t e c e r e b r a l dominance for  language.  T h i s t e c h n i q u e has been shown t o c o r r e l a t e  w e l l w i t h sodium a m y t a l t e s t i n g ( K i m u r a , 1 9 6 1 b ) .  O n l y a few  i n v e s t i g a t o r s have a d a p t e d t h i s t e c h n i q u e t o s t u d y t h e development  o f c e r e b r a l dominance i n young c h i l d r e n .  main t h e o r e t i c a l p o s i t i o n on t h e development or  The  of  lateralizati  dominance i s t h a t o f L e n n e b e r g (1966, 1 9 6 7 ) .  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 t a b l i s h e d i n t h e l e f t h e m i s p h e r e , b e g i n n i n g a t age two o r t h r e e and r e a c h i n g c o m p l e t i o n a t p u b e r t y .  This process occurs  c o n c u r r e n t l y w i t h t h e 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 t o L e n n e b e r g , no language l e a r n i n g t a k e s p l a c e bef o r e age two o r t h r e e , and p r i m a r y language l e a r n i n g i s n o t possible a f t e r puberty.  Hov/ever, e v i d e n c e p r e s e n t e d e a r l i e r  has shown t h a t some f o r m o f language l e a r n i n g t a k e s p l a c e f r o m b i r t h ; i t t h u s seems r e a s o n a b l e t o assume t h a t s u c h l e a r n i n g i s associated with areas of the l e f t  hemisphere,  w h i c h a r e becoming f u n c t i o n a l i n t h e v e r y p r o c e s s o f language  learning.  The m a j o r i s s u e c e n t e r s on t h e p r o b l e m , the  l e f t hemisphere become dominant  f o r language  I n v i e w o f t h i s , t h e aims o f t h e p r e s e n t  38  "When does function?".  39  investigation (1)  were t o seek answers t o t h e  Do c h i l d r e n  following:  between t h e ages o f two and t h r e e , when  presented with a verbal dichotic  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 e a r advantage? (2)  Is there a c h a r a c t e r i s t i c  age-related p a t t e r n t o the  development o f l a t e r a l i z a t i o n between two and t h r e e y e a r s of (3)  age? Do t w o - y e a r - o l d boys p e r f o r m d i f f e r e n t l y i n d e g r e e o r  direction  o f e a r advantage t h a n t h e i r f e m a l e p e e r s ?  CHAPTER 4  METHOD  4.1  P r e p a r a t i o n o f D i c h o t i c Tapes 4-. 11  Recording  stimuli  A S c u l l y 280 t w o - t r a c k  s t e r e o t a p e r e c o r d e r was  r e c o r d a l l s t i m u l u s words. audiometric  Recordings  20 dBA.-,  were r e c o r d e d  on two  inches, per 4.12  Two  level  Kjaer  An A l t e c 681A microphone  used f o r r e c o r d i n g , a t approximately microphone d i s t a n c e .  IAC  Ambient n o i s e  as t e s t e d by a B r u e l and  P r e c i s i o n s o u n d - l e v e l meter.  a t 7#>  were made i n an  b o o t h , u s i n g a male s p e a k e r .  i n t h e room was  used t o  was  s i x inches mouth-to-  l i s t s o f words ( L i s t 1, L i s t  2)  tapes at normal c o n v e r s a t i o n a l l e v e l ,  second.  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 t a p e i n o r d e r t h a t t a p e l o o p s 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 e o r i g i n a l t a p e s were p l a y e d b a c k f r o m a Revox  this,  two-track  s t e r e o t a p e r e c o r d e r , onto t h e S c u l l y 280 t a p e r e c o r d e r , t o p r o d u c e a new interval.  t a p e w i t h s t i m u l i s e p a r a t e d by a  six-second  P r i o r t o r e c o r d i n g e a c h word, t h e p l a y b a c k  on t h e Revox was  level  a d j u s t e d so t h a t , a t r e s t , each word showed  a peak i n t e n s i t y o f 0 VU  on t h e r e c o r d head o f t h e  Scully.  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 recording time. c o n t a i n i n g one  T h i r t y - f o u r tape  loops of e q u a l l e n g t h , each  s t i m u l u s word, were t h e n 40  at  constructed.  4-1  4-. 13  P r e p a r a t i o n o f stimulus tapes  Three t a p e r e c o r d e r s were a r r a n g e d s u c h t h a t one c h a n n e l o f each o f t h e f i r s t two c o n n e c t e d t o c h a n n e l s 1 and 2 o f t h e t h i r d t a p e r e c o r d e r ( s e e F i g u r e 4- .1). r e p l a y e d from the S c u l l y .  L i s t 1 t a p e l o o p s were  L i s t 2 t a p e l o o p s were r e p l a y e d f r o m  an Ampex AG 4-4-OB f u l l t r a c k t a p e r e c o r d e r .  Playback  levels  o f t h e Ampex and S c u l l y were k e p t a t t h e same r e l a t i v e f o r a l l s t i m u l i , w h i l e t h e r e c o r d i n g l e v e l s f o r each  level  channel  o f t h e Revox were a d j u s t e d f o r each p a i r o f words so t h a t word showed a peak i n t e n s i t y o f 0 VU.  each  A d u a l c h a n n e l memory  o s c i l l o s c o p e was c o n n e c t e d between t h e S c u l l y and t h e Ampex so t h a t t h e e x p e r i m e n t e r c o u l d v i s u a l l y m o n i t o r t h e d e g r e e of synchrony o f s t i m u l i onset d u r i n g copying. Method o f c o p y i n g : approximate  The two t a p e l o o p s were p l a c e d i n  s y n c h r o n y b y s e t t i n g b o t h words on t h e p l a y b a c k  heads o f t h e Ampex and S c u l l y .  As t h e Ampex h a d a s l i g h t l y  f a s t e r r u n n i n g speed, t h e word on t h i s t a p e 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 b a c k f r o m t h e p l a y b a c k head and t h e two tape r e c o r d e r s s e t i n motion. was t h e n a c t i v a t e d .  The r e c o r d mode o f t h e Revox  As t h e p a i r s o f words were b e i n g r e -  c o r d e d , t h e d e g r e e o f s y n c h r o n y was s i m u l t a n e o u s l y o b s e r v e d on t h e o s c i l l o s c o p e .  T h i s p r o c e d u r e was r e p e a t e d 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 o f words f r o m 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 n e x t p a i r  S t u d d e r t - K e n n e d y , S h a n k w e i l e r and Schulman (1970) have i n d i c a t e d t h a t , when t h e l e f t - e a r s i g n a l l a g s b e h i n d t h e r i g h t e a r s i g n a l by 20 m s e c , t h e l e f t e a r becomes t h e dominant one. B e r l i n e t a l . (1973) shov/ed t h a t t h e REA d i s a p p e a r s when t h e l e f t - e a r s i g n a l l a g s by 30 msec. Beyond a 30 msec, t i m e 1  42  S c u l l y 280 p l a y b a c k mode L i s t 1 tape loops  Amp e x AG 440B p l a y b a c k mode L i s t 2 tape l o o p s  dual channel o s c i l l o s c o p e channel 1 channel 2  Revox s t e r e o t a p e 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 stimulus tapes  43  of  words was  t h e n r e c o r d e d i n t h e same way.  The t a p e r e -  c o r d i n g s from t h e Re vox v/ere l a t e r r e p l a y e d , and t h e b e s t s y n c h r o n i z e d example o f each p a i r o f words was aid  of the o s c i l l o s c o p e .  chosen with- t h e  E a c h o f t h e s e p a i r s was  then cut  f r o m t h e t a p e 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 t a p e  was  c o n s t r u c t e d from t h i s t a p e . On t h e a c t u a l s t i m u l u s t a p e u s e d i n t h e e x p e r i m e n t , i n t e r s t i m u l u s i n t e r v a l was words "Show me"  i n c r e a s e d t o t w e n t y seconds  the  and  the  were spoken by t h e o r i g i n a l s p e a k e r , b e f o r e  each p a i r of words.  A p h o t o g r a p h was  t a k e n o f each  oscillo-  s c o p i c t r a c e i n o r d e r t h a t o n s e t t i m e c o u l d be more p r e c i s e l y determined; these photographs  4.2  are p r e s e n t e d i n Appendix  1.  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 o f 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 o f mono-  s y l l a b i c words; f o u r p a i r s were c o m p r i s e d o f d i s y l l a b i c  words.  Of t h e two p r a c t i c e w o r d - p a i r s , one p a i r c o n t a i n e d monos y l l a b i c words and t h e o t h e r 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 t h e e x p e r i m e n t e r t o be w i t h i n t h e of  vocabulary of a two-year-old c h i l d .  range  Most o f t h e words  d i f f e r e n c e , t h e 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 t h e p r e s e n t 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 o f d i c h o t i c p a i r s and a c c e p t e d a d i f f e r e n c e i n o n s e t o f up t o 10 m s e c , because o f t h e d i f f i c u l t y i n m e a s u r i n g s m a l l e r t i m e i n t e r v a l s on t h e o s c i l l o s c o p e . The d i r e c t i o n o f o n s e t t i m e d i f f e r e n c e was random.  44  ( t h o s e s t a r r e d i n A p p e n d i x 2) were c h o s e n f r o m t h e b e g i n n i n g i t e m s o f t h e Peabody P i c t u r e V o c a b u l a r y T e s t  (PPVT).  The words w e r e . p a i r e d , s u c h t h a t t h e f o l l o w i n g were o b s e r v e d :  (1)  conditions  a m o n o s y l l a b i c word was n e v e r 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 o f e a c h word i n  a p a i r were e i t h e r b o t h v o i c e d p l o s i v e s , o r b o t h v o i c e l e s s p l o s i v e s , o r both n a s a l s ; of  (3)  o s c i l l o m i n k t r a c i n g s were made  e a c h 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 r a n g e d f r o m 500 t o 950 m s e c ; A p p e n d i x 3 g i v e s the  d u r a t i o n f o r e a c h 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 r a n g e d f r o m 30 t o 100 m s e c , of  with the exception  one p a i r o f words ("spoon" was 4-50 m s e c  partner,  longer than i t s  "fish".  The peak i n t e n s i t y o f e a c h word on t h e f i n a l t a p e 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 m e t e r . The t a p e was r e p l a y e d on t h e S c u l l y t a p e r e c o r d e r w h i c h was m a i n t a i n e d a t c o n s t a n t p l a y b a c k l e v e l ( t h e s i g n a l b e i n g maint a i n e d a t a p p r o x i m a t e l y 70 d B ) ; a l l t h i r t y - f o u r words were r e p l a y e d t h r o u g h t h e same T e l e p h o n i c 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  e a r t y p e 4-152 p l a c e d on t h e sound  C o n d i t i o n (2) n o t o n 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 c e d u r e s b u t h e l p e d t o 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 t o be p r e s e n t i n d i c h o t i c l i s t e n i n g . F o r example, Lowe e t a l . (1970) have shown t h a t , a t s i m u l t a n e i t y , v o i c e l e s s c o n s o n a n t s a r e 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 t h a n v o i c e d c o n s o n a n t s . As y e t , t h e e f f e c t s o f t e m p o r a l 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 n o t been s y s t e m a t i c a l l y examined. S p r e e n 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 o f up t o 60 msec, p r o d u c e no s i g n i f i c a n t e f f e c t s on t h e e a r 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 n o t been examined. S i n c e most s t u d i e s r e p o r t e d i n t h e l i t e r a t u r e u s e d 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 could not have been c o n t r o l l e d i n t h e s e s t u d i e s .  45  l e v e l meter.  The l a r g e s t  intensity difference  between  paired  words was 4 dBA;  however, t h i r t e e n o f t h e s e v e n t e e n 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 .  has shown t h a t  t h e 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 t h e i n t e n s i t y o f t h e s t i m u l u s d e l i v e r e d is  as much as 10 dB l e s s t h a n t h a t  Research  to the r i g h t ear  o f t h e l e f t e a r (Thompson  et a l . , 1972). The p l a y b a c k l e v e l s o f t h e two c h a n n e l s o f t h e S c u l l y were a d j u s t e d so t h a t t h e p a i r s o f words were p l a y e d back a t 72 dBA Bruel  (+ 2 dB) t h r o u g h t h e headphones ( a s measured by a and K j a e r P r e c i s i o n  t o n e p l a c e d on b o t h t r a c k s  sound l e v e l m e t e r ) .  A calibration  o f a t w o - t r a c k t a p e was u s e d t o  a l l o w t h e p l a y b a c k i n t e n s i t y o f t h e two c h a n n e l s t o be t h e same.  T h i s c a l i b r a t i o n p r o c e d u r e was r e p e a t e d on e a c h t e s t i n g  day. A f o i l word was c h o s e n and u s e d i n c o n j u n c t i o n v / i t h e a c h p a i r o f words.  S i m p l e b l a c k and w h i t e l i n e  were drawn s u c h t h a t  e a c h word p a i r and f o i l a p p e a r e d on one  page. and  4.3  illustrations  A random o r d e r o f p i c t u r e p l a c e m e n t was u s e d .  Stimulus  f o i l words ( o r d e r o f p r e s e n t a t i o n ) a r e g i v e n i n A p p e n d i x 4.  Subjects Children  were a l l between CA 2:0  and 3:2;  t h e i r ages on  t h e day o f t e s t i n g were r e c o r d e d i n y e a r s , months, and d a y s . The c h i l d r e n were g a t h e r e d by c o n t a c t i n g a m i n e r who had young c h i l d r e n . f e r r e d the i n v e s t i g a t o r  friends  of the ex-  These i n d i v i d u a l s t h e n r e -  t o o t h e r p a r e n t s o f young  children.  46  About o n e - t h i r d o f t h e c h i l d r e n were g a t h e r e d  through  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 . was  n o t b a s e d on s o c i o e c o n o m i c  class, linguistic  par-  Selection level,  handedness, handedness o f t h e p a r e n t s , b i r t h o r d e r o r  sex, develop-  mental h i s t o r y , a l t h o u g h 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 the mothers.  No  l e v e l , was  g a i n e d by i n t e r v i e w i n g  c h i l d showed any h i s t o r y o r i n d i c a t i o n  h e a r i n g l o s s , a l t h o u g h h e a r i n g t e s t i n g was  4.4-  Experimental T e s t i n g was  days.  The  first  not c a r r i e d  out.  Procedure c o n d u c t e d i n two  s e s s i o n s , on two  session lasted approximately  p r e - t e s t s e s s i o n , e a c h c h i l d was 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  In the  first  shown e a c h s t i m u l u s page a s k e d by t h e  examiner,  f o r each s t i m u l u s item i n t u r n .  o f t h i s p r o c e d u r e was  separate  twenty minutes  and t h e s e c o n d s e s s i o n , about t h i r t y m i n u t e s .  "Show me  of  The  purpose  t w o f o l d ; f i r s t , t o e n s u r e 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 t h e s t i m u l u s words  and,  s e c o n d , t o e s t a b l i s h a p o i n t i n g r e s p o n s e t o t h e words "'Show I f a c h i l d d i d n o t know a word, t h i s word c o u l d t h e n be by t h e e x a m i n e r .  Most o f t h e s t i m u l u s i t e m s , w i t h t h e  t i o n o f "queen" and D u r i n g the f i r s t  "gun"  were known by a l l t h e  s e s s i o n , t h e c h i l d was  t u n i t y to f a m i l i a r i z e M m s e l f / h e r s e l f and t h e headphones. day.  The- mother was  taught excep-  children.  a l s o g i v e n the  oppor-  w i t h t h e t e s t i n g room a l s o i n t e r v i e w e d on  me".  this  4-7  F o r t h e second s e s s i o n , a l l t o y s were removed from t h e room i n o r d e r t o m i n i m i z e d i s t r a c t i o n .  The c h i l d was s e a t e d  on h i s m o t h e r ' s l a p w i t h h i s back t o t h e t a p e r e c o r d e r .  One  headphone was removed f r o m t h e m o n i t o r h e a d s e t and was p l a c e d against the child's ear.  E i g h t s t i m u l u s items  ( f o u r from  each  c h a n n e l ) were p r e s e n t e d m o n a u r a l l y t h r o u g h t h e headphone and t h e c h i l d was a s k e d t o p o i n t t o t h e a p p r o p r i a t e p i c t u r e . purpose  The  o f 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 t h e p o i n t i n g  r e s p o n s e and t o accustom  e a c h c h i l d t o l i s t e n i n g o v e r head-  phones b e f o r e t h e more d i f f i c u l t d i c h o t i c t a s k was p r e s e n t e d . The u s e o f one headphone a l s o a l l o w e d t h e examiner and r e i n f o r c e t h e c h i l d  to reassure  auditorily.  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 t h e c h i l d , and t e s t i n g was commenced.  The examiner h e l d each s e t  o f p i c t u r e s b e f o r e t h e c h i l d , w h i l e a second examiner  removed  t h e o t h e r p i c t u r e s f r o m t h e c h i l d ' s v i e w and o p e r a t e d t h e t a p e recorder.  When o n l y one examiner was p r e s e n t , t h e t a p e r e -  c o r d e r was o p e r a t e d by a remote c o n t r o l d e v i c e . was  The examiner  a b l e t o m o n i t o r one c h a n n e l t h r o u g h t h e m o n i t o r  headset,  b u t was unaware t o w h i c h o f t h e c h i l d ' s e a r t h o s e words were being presented.  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 t o t h e  c h i l d by t h e e x a m i n e r .  Channel-by-ear  p r e s e n t a t i o n was a l t e r -  n a t e d between s u b j e c t s t o m i n i m i z e t h e e f f e c t s o f any d i f f e r ences between c h a n n e l s . A l t h o u g h most o f t h e r e s e a r c h w i t h d i c h o t i c  stimulation  has used v e r b a l r e c a l l a s a mode o f r e s p o n s e , v e r b a l i s n o t n e c e s s a r y t o produce  an REA i n n o r m a l a d u l t  recall  subjects.  4-8  A r i g h t e a r 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 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  ( S h a n k w e i l e r and S t u d d e r t - K e n n e d y , 1967; S h a n k w e i l e r , 1970), when s u b j e c t s t h e i r responses out of s e v e r a l Folb,  say, t h e i r responses S t u d d e r t - K e n n e d y and  were i n s t r u c t e d t o choose  l a t e r p r e s e n t e d ( K i m u r a and  1968; "Rroadbent and G r e g o r y , 1964-), and when  subjects  were i n s t r u c t e d t o t a p w i t h e i t h e r t h e r i g h t o r t h e l e f t ( T r e i s m a n and G e f f e n , 1 9 6 8 ) .  were  hand  I t was f e l t t h a t many t w o - y e a r -  o l d s would be u n a b l e o r u n w i l l i n g t o r e s p o n d v e r b a l l y t o d i chotic used.  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 r e s p o n s e was  CHAPTER 5  RESULTS  5.1  Scoring One p o i n t was g i v e n f o r each p i c t u r e c o r r e c t l y  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 . tween f i r s t and second  responses  chosen,  The d i f f e r e n c e s b e -  on e a c h t r i a l were d i s r e g a r d e d ;  however, t h e g e n e r a l r e s p o n s e p a t t e r n was one r e s p o n s e p e r trial,  t h e mean o v e r a l l a c c u r a c y s c o r e ( d e f i n e d a s t o t a l c o r -  r e c t responses  f o r b o t h e a r s 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 ) b e i n g 50.5$. e a r was 15« a t-test  T o t a l p o s s i b l e score f o r each  The d a t a were e v a l u a t e d t h r o u g h o u t  (Downie and H e a t h , 1959).  i n b o t h r a w form and i n POE form  The s c o r e s were t a b u l a t e d  , i n order t o c o r r e c t f o r  i n c r e a s e s i n accuracy w i t h i n c r e a s i n g age. experiment,  by means o f  However, i n t h i s  a c c u r a c y d i d n o t change w i t h age, i . e . , t h e mean  a c c u r a c y f o r c h i l d r e n b e l o w CA 2-6-30 b e i n g 4-9$, and f o r c h i l d r e n above CA 2-6-30 b e i n g 52$. f a c t o r was u n n e c e s s a r y ,  Thus, such a c o r r e c t i o n  and t h e r e s u l t s f o r b o t h measures  were n o t 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 ,  t h e t v a l u e s p r e s e n t e d a r e f o r raw d a t a .  5.2  Subjects Of t h e 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 s c o r e i s d e f i n e d a s t h e l e f t e a r ' s p e r c e n t a g e o f t h e t o t a l number o f e r r o r s ( K r a s h e n , 1972). 49  50  because t h e y w o u l d n o t t o l e r a t e headphones. by age and s e x i s p r e s e n t e d i n T a b l e 5.1• t e s t i n g ranged  The age on d a y o f  from CA 2-0-12 t o CA 3-1-20.  Males  Eemales  total  b e l o w CA  8  9  17  above CA  2-6-30  6  8  14  total  14  17  2-6-30  T a b l e 5.1  5.3  The s u b j e c t p o o l  Right  S u b j e c t s by age and s e x  versus Left  Ears  A c r o s s a l l s e x and age g r o u p s , t h e r i g h t e a r words were more e f f i c i e n t l y r e c a l l e d t h a n t h e l e f t e a r words ( t = 4.54, d f = 60, £ < 0.005, o n e - t a i l e d  test).  The mean $ REA f o r t h e  t o t a l group was 18$, a s c a l c u l a t e d  by t h e f o r m u l a : R-L / R+L  ( S h a n k w e i l e r and S t u d d e r t - K e n n e d y ,  1970;  1972).  The a d u l t v a l u e s g e n e r a l l y r e p o r t e d i n t h e l i t e r a t u r e  r a n g e between 2 and 8$ ( C u r r y , 1968; Kimura,  Z u r i f and R a m i e r ,  Z u r i f and R a m i e r ,  1967; S p a r k s , G o o d g l a s s and N i c k e l , 1970).  t h i r t y - o n e c h i l d r e n , twenty-four demonstrated demonstrated  1972;  Of t h e  an REA, s i x  an LEA, and one showed e q u a l p r e f e r e n c e f o r b o t h  ears.  The mean s c o r e f o r t h e r i g h t e a r was 8.97  left,  6.19.  and f o r t h e  51  5.4- Sex T h e r e 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 t h e degree  o f REA  ( d e f i n e d a s r i g h t minus l e f t e a r s c o r e s ) f o r males and f e m a l e s (t_ = 0.2856, d f = 29, n s ) , n o r were t h e r e d i f f e r e n c e s i n o v e r a l l a c c u r a c y ( m a l e s , 51.4$; f e m a l e s , 50.1$). The mean $ REA was 19«5$ f o r m a l e s , and 16.8$ f o r f e m a l e s .  Thus, boys demon-  s t r a t e d an REA w h i c h was s l i g h t l y l a r g e r , ( a l t h o u g h n o t s t a t i s t i c a l l y s i g n i f i c a n t ) t h a n t h e REA o f t h e f e m a l e s .  5.5  Age The i n d i v i d u a l s c o r e s r a n k o r d e r e d a c c o r d i n g t o age a r e  p r e s e n t e d i n F i g u r e 5.1• The d i f f e r e n c e between t h e s e v e n t e e n y o u n g e r c h i l d r e n (OA 2-0-12 t o 2-6-7) and t h e 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 n o t s i g n i f i c a n t ( t = 0.4868, df  = 29, n s ) .  The degree  o f REA d i d n o t show a s y s t e m a t i c  i n c r e a s e , o r d e c r e a s e , as a f u n c t i o n o f age ( r = -0.172; P e a r s o n p r o d u c t moment c o r r e l a t i o n , f r o m B r u n i n g and K i n t z , 1968, p . 1 5 2 ) . The mean a c c u r a c y l e v e l o f t h e y o u n g e r c h i l d r e n was 49.2$; mean a c c u r a c y l e v e l o f t h e o l d e r c h i l d r e n was  52.1$.  The mean $ REA was 19.9$ f o r t h e younger group  and 15.7$ f o r t h e o l d e r g r o u p .  5.6  Age v e r s u s S e x The t v a l u e s , a s w e l l as t h e mean $ REA, f o r t h e f o u r  age-sex groups i s p r e s e n t e d i n T a b l e 5.2.  I t c a n be seen t h a t  t h e o l d e r f e m a l e group d i d n o t a c h i e v e a s i g n i f i c a n t REA, w h i l e t h e o t h e r t h r e e groups d i d .  However, t h e s m a l l number  100  80  mean score ( t h i s study)  60  w  mean score o f 22 s t u d i e s analysed by Krashen (1972)  2  •p c <u  M a  40  20  2-6-30  Figure 5.1  I n d i v i d u a l scores rank ordered according t o age.  Raw Score N  L e f t Ear  Right Ear t ( one-tailed)  mean % REA  df  8  6.25  8.75  2.29 p<0.025  15.5  14  9  5.56  9.00  5.71 p<0.005  23.8  16  6  6.00  9.83  1.87 p<0.05  24.7  10  8  7.13  8.37  0.8 p^0.25 ns  8.95  14  males below CA 2-6-30  females below CA 2-6-30  males above CA 2-6-30  females above CA 2-6-30  Table 5.2  T values and mean percent REAs f o r four age-sex groups.  54  o f s u b j e c t s i n e a c h group r e d u c e s t h e i m p o r t a n c e o f t h e s e statistical  5.7  analyses.  Handedness B o t h t h e handedness o f t h e p a r e n t s and t h e mother's  o p i n i o n o f t h e c h i l d ' s handedness were r e c o r d e d .  The c h i l d r e n  were d i v i d e d i n t o two g r o u p s on t h e b a s i s o f h a n d e d n e s s ; 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 r i g h t - h a n d e d and who h a d two r i g h t - h a n d e d p a r e n t s .  I n the  second g r o u p , were 12 c h i l d r e n who were l e f t - h a n d e d o r ambid e x t r o u s o r who h a d a t 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 d e g r e e o f r i g h t e a r a d v a n t a g e between t h e s e two g r o u p s was n o t s i g n i f i c a n t  ( t = 0.06344, d f = 29, n s ) .  Because  t h e o n l y measure o f handedness u s e d i n t h i s s t u d y was j u d g e ment o f t h e m o t h e r , and because a p e r i o d o f i n s t a b i l i t y o f hand p r e f e r e n c e seems t o o c c u r between ages two and t h r e e ( O r t o n , 1934), we do n o t  f e e l j u s t i f i e d i n drawing conclusions  on t h e r e l a t i o n s between c e r e b r a l dominance and h a n d e d n e s s .  5.8  Linguistic  Ability  Of t h e 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 b e l o w t h e age o f 2-6-30, were n o t y e t u s i n g g r a m m a t i c a l s e n t e n c e s i n t h e i r speech.  Most o f them h a d j u s t r e c e n t l y begun u s i n g two and  t h r e e word u t t e r a n c e s a n d most o f t h e i r c o n v e r s a t i o n a l s p e e c h c o n s i s t e d o f s i n g l e words.  The mean r i g h t e a r s c o r e o f t h i s  group was 8.8 words and t h e l e f t e a r s c o r e was 5«87« t h e s e t w o - y e a r - o l d c h i l d r e n , who a r e a t an e a r l i e r  Thus,  linguistic  s t a g e , s t i l l d e m o n s t r a t e an REA c o m p a r a b l e t o t h e r e s t o f t h e g r o u p .  55  5.9  Counterbalancing S i x t e e n c h i l d r e n h e a r d c h a n n e l 1 and f i f t e e n  channel 2 i n the r i g h t ear. r i g h t e a r advantage nificant  The d i f f e r e n c e  between t h e s e two  ( t = 1.64-76, d f = 29,  ns).  children,  i n degree  conditions  of  was n o t s i  56  CHAPTER 6  DISCUSSION  I n summary, r i g h t e a r words were more e f f i c i e n t l y r e c a l l e d t h a n l e f t e a r words by t w o - y e a r - o l d c h i l d r e n . males demonstrated  a s l i g h t l y l a r g e r REA  younger c h i l d r e n demonstrated  Although  t h a n d i d f e m a l e s , and  a l a r g e r REA  than d i d older  c h i l d r e n , t h e s e d i f f e r e n c e s were n o t s t a t i s t i c a l l y  significant.  A c c u r a c y on t h i s t a s k d i d n o t change s i g n i f i c a n t l y a c r o s s t h e age range  studied.  The mean REA  f o r t h e t o t a l group  was  18$. The p r e s e n t r e s u l t s s u g g e s t t h a t , a t l e a s t by age two, an REA a c e r t a i n degree  chronological  f o r v e r b a l m a t e r i a l can be o b s e r v e d , and shows of s t a b i l i t y .  I f t h i s age marks t h e b e g i n n i n g  o f t h e s o - c a l l e d " l a t e r a l i z a t i o n " , t h e n , because c h i l d r e n show v a r i a b i l i t y i n r a t e o f n e u r o p s y c h o l o g i c a l m a t u r a t i o n , one would e x p e c t a l a r g e r number o f c h i l d r e n t o show an e q u a l p r e ference f o r both ears —  t h a t i s , t h o s e c h i l d r e n who  have n o t  y e t d e v e l o p e d c e r e b r a l dominance.  I n f a c t , 78$  i n t h i s study demonstrated  w h i c h i s i n c l o s e agreement  an REA,  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 ( K i m u r a and P o l b , 1968;  of the  children  children  B r y d e n , 1970).  S i m i l a r i l y , i f age two marks t h e b e g i n n i n g o f a change f r o m e q u i p o t e n t i a l i t y o f t h e two h e m i s p h e r e s ,  t o dominance o f  one, and i f t h i s p r o c e s s i s c o r r e l a t e d w i t h t h e development o f l a n g u a g e , t h e n one would e x p e c t t h a t c h i l d r e n o f an  "earlier  57  l i n g u i s t i c stage" nitude  m i g h t d e m o n s t r a t e a n REA. o f d i f f e r e n t mag-  or direction.  I n the p r e s e n t study, s i n c e only a  l i m i t e d number o f s u b j e c t s were t e s t e d , and t h e 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 simply was we  difficulty  as expressive  language  compounded by t h e 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  stages,  can o n l y s u g g e s t t h a t t h e s e c h i l d r e n do n o t d e m o n s t r a t e a  d i f f e r e n c e i n t h e d e g r e e o f magnitude o f REA. K i m u r a (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  tasks  were p e r f o r m e d by c h i l d r e n i n any e a r l y s t a g e o f d e v e l o p m e n t , a sex d i f f e r e n c e i n t h e d e g r e e o f c e r e b r a l dominance may be detected;  t h a t i s , s i n c e boys appear t o d e v e l o p language  more s l o w l y t h a n g i r l s  (McCarthy,  skills  1953), i t m i g h t be c o n c l u d e d  t h a t t h e y d e v e l o p c e r e b r a l dominance f o r language l a t e r . t h e p r e s e n t s t u d y , a l t h o u g h t h e r e were no s i g n i f i c a n t  In  differ-  e n c e s between s e x e s , boys d e m o n s t r a t e d 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 . conjecture  Such a f i n d i n g does n o t ,  of course,  about t h e l a t e r a l i z a t i o n p r o c e s s ,  allow  since 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 t h e d e g r e e o f l a t e r a l i z a t i o n does n o t  e x i s t , a s i t i s t h a t age two i s n o t t h e b e -  g i n n i n g o f the l a t e r a l i z a t i o n  process.  I t i s o f i n t e r e s t t o compare t h e d e g r e e o f r i g h t e a r 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 adult versus  p e r f o r m a n c e on d i c h o t i c v e r b a l t a s k s .  child  K r a s h e n (1972) h a s  p r e s e n t e d a r e v i e w o f t h e d a t a f r o m 22 s t u d i e s u s i n g t h e FOE method o f a n a l y s i s , and c o n c l u d e s t h a t t h e r e  is little  change  i n POE s c o r e f r o m age f o u r u n t i l a d u l t h o o d .  It i s chiefly  t h i s f i n d i n g which prompts him t o c l a i m t h a t  lateralization  58  i s c o m p l e t e by age f o u r o r f i v e .  The mean POE s c o r e f o r a l l  22 s t u d i e s p r e s e n t e d by K r a s h e n i s 58.5  and t h e mean POE  s c o r e o f t h e p r e s e n t e x p e r i m e n t (59.1) c l o s e l y a g r e e s w i t h  this.  I f one t h e r e f o r e assumes t h a t changes i n t h e d e g r e e o f REA r e f l e c t changes i n t h e d e g r e e o f l e f t hemisphere dominance f o r l a n g u a g e , t h e n on t h e b a s i s o f t h e p r e s e n t r e s u l t s , i t i s c o n 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 c o m p l e t e by age t w o . Such a s u g g e s t i o n i s c o n s i s t e n t w i t h t h e t h e o r y t h a t t h e two hemis p h e r e s a r e n e v e r e q u i p o t e n t i a l f o r t h e development o f l a n g u a g e . R a t h e r , t h e l e f t hemisphere always subserves language f u n c t i o n i n g , while f o r a c e r t a i n p e r i o d o f time the r i g h t  hemisphere  r e t a i n s t h e a b i l i t y t o t a k e over t h e language f u n c t i o n i n cases o f l e f t h e m i s p h e r e damage.  Perhaps the question t h a t  should  be a s k e d c o n c e r n s t h e t i m e l i m i t s w i t h i n w h i c h i t i s p o s s i b l e f o r t h e r i g h t h e m i s p h e r e t o assume l a n g u a g e f u n c t i o n s , f o r i t i s n o t known what a c c o u n t s f o r t h e p r o g r e s s i v e i n a b i l i t y o f t h e r i g h t hemisphere t o t a k e over language f u n c t i o n .  It is  d e b a t a b l e w h e t h e r 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) o r a p r o g r e s s i v e  e n t i a t i o n o f t h e r i g h t hemisphere f o r v i s i o - s p a t i a l  differ-  orientation  and o t h e r r i g h t - d o m i n a n t 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 t h e a c t u a l d e g r e e o f REA does n o t change f r o m age two t o a d u l t h o o d , s i n c e  later-  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 n o t appear t o change o v e r t h i s age r a n g e .  However, i t i s e q u a l l y  l i k e l y t h a t t h e r e l a t i o n s h i p between d e g r e e o f l a t e r a l i z a t i o n  59  and t h e d e g r e e o f REA i s e i t h e r o v e r s i m p l i f i e d o r 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 very simple g a t e a v e r y complex phenomenon.  technique  I t i s evident  used t o i n v e s t i that  language  i s b o t h 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 t h e 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 p a t h w a y s , b o t h i n t e r - and i n t r a - h e m i s p h e r i c , a s w e l l a s s u b c o r t i c a l . The  asymmetry f o u n d 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 f r o m asymmetry a t 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 p r o d u c t o f asymmetry a t a l o w e r l e v e l ; f o r example, i n B o t e z and B a r b e a u (1971)  the thalamus o r r e t i c u l a r f o r m a t i o n .  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 t h e l e f t d o r s a l thalamus, but n o t t h e r i g h t , and  t h e y emphasize t h e i m p o r t a n c e o f s u b c o r t i c a l mechanisms  i n s p e e c h and l a n g u a g e .  Moray (1970)  states:  . . . i t may w e l l be t h a t f o r t h e p h y s i o l o g i c a l c o r r e l a t e s o f c o n s c i o u s p e r c e p t i o n , we s h o u l d l o o k a t t h e a r o u s a l s y s t e m 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 t h a n a t t h e c o r t e x . The p r o b l e m i s t h a t i f t h e a r o u s a l system i s i n f a c t t h e c o n t r o l l e r o f 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 n o t merely t o a l t e r the gross o v e r a l l l e v e l o f r e sponsiveness o f t h e e n t i r e c e n t r a l nervous system but a l s o t o c o n t r o l t h e f l o w o f i n f o r m a t i o n o v e r q u i t e s p e c i f i c p a t h s , we a r e g o i n g t o have t o f i n d t h e a n a t o m i c a l l o c u s o f t h e " g a t e s " b e f o r e we c a n b e g i n t o a c c o u n t f o r p a r t i c u l a r phenomena i n t h e b e h a v i o r o f a n o b s e r v e r who i s a t t e n d i n g t o one s o u r c e o f 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 w i s h t o deduce w h e t h e r o r n o t a p a r t i c u l a r s t i m u l u s h a s been c o n s c i o u s l y p e r c e i v e d we s h o u l d look n e i t h e r a t t h e r e t i c u l a r system, n o r a t t h e c o r t i c a l a c t i v i t y , b u t a t t h e r e l a t i o n s h i p between t h e e l e c t r i c a l a c t i v i t y i n t h o s e two p a r t s o f t h e b r a i n a t l e a s t , and p e r h a p s a l s o a t t h e s i m u l t a n e o u s a c t i v i t y i n y e t other parts of the b r a i n .  (pp..175-176) F u r t h e r m o r e , c l i n i c a l s t u d i e s o f brain-damaged and h e m i s p h e r e c t o m i z e d p a t i e n t s may be no more h e l p f u l t h a n 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 i n speech and CNS  may  r o l e of s u b c o r t i c a l  structures  language, s i n c e damage a t a h i g h e r l e v e l o f  prevent expression  o f normal f u n c t i o n i n g  the  at a lower  level. A s c h e d u l e of the  c o u r s e of development of  dominance would u n d o u b t e d l y add and  when the  u n d e r s t a n d i n g of  b r a i n becomes l a t e r a l i z e d .  a r e , however, i n h e r e n t First,  to our  i n mapping out  cerebral  Several  limitations  such a s c h e d u l e .  as mentioned above, p e r c e n t a g e of REA  t a i n l y does not  how  almost  cer-  bear a d i r e c t r e l a t i o n s h i p to degree of dom-  i n a n c e , even s u p p o s i n g t h a t  "ear  a c c u r a c y , t a s k v a r i a b l e s , and f o r e , c a u t i o n must be  e f f e c t " was  unbiased  by  other extraneous f a c t o r s .  exercized  There-  i n generalizing dichotic  l i s t e n i n g r e s u l t s t o i m p l y changes i n degree of  lateralization  over t i m e . S e c o n d l y , i n most s t u d i e s , comparisons of c h i l d r e n based on c h r o n o l o g i c a l  age,  which might not  d i c a t o r of n e u r o l o g i c a l maturity. such as bone age,  be  the  r a t e o f growth o f the (Lenneberg, 1967), the  (Harrison  best  in-  A p h y s i o l o g i c a l measure  would u n d o u b t e d l y show a c l o s e r  t o growth o f the b r a i n  are  et a l . , 1964).  brain i s greatest  Since  the  e a r l y years  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 o f d i s c r e p a n c y between bone age  and  chronological  age.  younger the  i n the  correspondence  Thus, i n u s i n g  chronological  age  for  sample s e l e c t i o n , i t becomes n e c e s s a r y to have a l a r g e  enough  sample t o a l l o w  follows  f o r maturational  variability.  t h a t , when s e e k i n g changes over a s p e c i f i c  age  I t thus  range, i t i s  61  necessary age  t o have c h i l d r e n e v e n l y d i s t r i b u t e d a l o n g  r a n g e , i n o r d e r t o make v a l i d c o m p a r i s o n s .  this  This problem  o f adequate sample s i z e a t each age l e v e l i s a l i m i t a t i o n o f the present  research.  T h i r d l y , because o f 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 o n s e t t i m e s , and o t h e r 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 d e v e l o p m e n t a l c o u r s e of experiments,  b a s e d on a number  each d e a l i n g w i t h a p o r t i o n o f t h e age r a n g e .  On a more g e n e r a l n o t e ,  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 a g e s , even w i t h i n t h e same s t u d y , may n o t y i e l d  equivalent  r e s u l t s t o c o m p a r i n g a s e l e c t e d group o f c h i l d r e n i n a longitudinal  study.  Within the l i m i t a t i o n s of the present i n v e s t i g a t i o n , therefore, the f o l l o w i n g observations K r a s h e n ' s (1972) it  accrue.  Referring to  a n a l y s i s of d i c h o t i c studies with c h i l d r e n ,  c a n be s e e n t h a t t h e p r e s e n t  results f a l l  i n t h e lower  r a n g e o f ROE v a l u e s f o u n d f o r c h i l d r e n between t h e ages o f 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 s u g g e s t t h a t t h e mag-  n i t u d e o f t h e REA u n d e r g o e s l i t t l e nine.  change f r o m age two t h r o u g h  The d a t a a l s o i n d i c a t e t h a t t h e magnitude o f t h e REA  does n o t change between t h e age o f two and t h r e e .  Replication,  u s i n g a l a r g e r number o f s u b j e c t s , o v e r an e x t e n d e d age r a n g e , w o u l d be n e c e s s a r y  t o confirm these r e s u l t s .  were confirmed,, i t m i g h t be n e c e s s a r y  I f this  finding  t o rethink the t r a d i t i o n a l  v i e w t h a t dominance o f t h e l e f t h e m i s p h e r e 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 . r e s e a r c h on i n f a n t s and y o u n g e r c h i l d r e n , p e r h a p s  Further  utilizing  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  question.  The r e s u l t s o f t h e p r e s e n t i n v e s t i g a t i o n s u g g e s t  that a d i c h o t i c l i s t e n i n g study with eighteen-month-old c h i l d r e n m i g h t be p o s s i b l e . I f i t i s assumed t h a t t h e l e f t hemisphere i s a l w a y s domi n a n t f o r l a n g u a g e , how do we a c c o u n t f o r t w o - y e a r - o l d c h i l d r e n who show l a n g u a g e d i s t u r b a n c e s a f t e r r i g h t hemisphere damage ( B a s s e r , 1962)?  I t s h o u l d i m m e d i a t e l y be o b s e r v e d 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  child,  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 b e f o r e t h e onset o f speech; language " t e s t s "  :  f o r t h i s age range a r e o b v i o u s l y c r u d e . I t  i s a l s o a p p a r e n t 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 n o t 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 o f t i s s u e language f u n c t i o n . magnitude  I t i s p o s s i b l e t h a t damaS  e  underlying  of a certain  o r 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 d e v e l o p m e n t ; t h e e f f e c t s o f b r a i n damage on language a t t h i s age a r e n o t i n any way comparable t o e f f e c t s o f damage t o t h e f u l l y grown a d u l t s y s t e m . The i n n o v a t i v e u s e o f e l e c t r o e n c e p h a l o g r a p h i c (EEG) t e c h n i q u e s i s b e g i 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 o f normal s u b j e c t s o f a l l ages.  Recent  s t u d i e s w i t h n o r m a l 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  differ-  ence between t h e h e m i s p h e r e s 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 a n a l o g o u s non-speech g e s t u r e s , s u c h 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 s y m m e t r i c a l p o t e n t i a l s (McAdams and W h i t a k e r , 1971).  There a r e numerous r e p o r t s  b a s e s f o r development  o f EEG s i g n a l p a t t e r n s i n n o r m a l  establishing infants  63  (Hagne, 1972).  As y e t , however, o n l y one s t u d y u s i n g  this  t e c h n i q u e t o examine s p e e c h l a t e r a l i z a t i o n i n i n f a n c y , h a s appeared i n t h e p u b l i s h e d l i t e r a t u r e .  M a l f e s e (1972, a b s t r a c t  o n l y ) compared a v e r a g e d evoked r e s p o n s e (AER) wave forms from the  r i g h t and l e f t h e m i s p h e r e , i n r e s p o n s e t o s p e e c h  syllables,  words, music and n o i s e 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  f o u n d g r e a t e s t AER a c t i v i t y f r o m t h e 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 o f s u b j e c t s , w h i l e m e c h a n i c a l s t i m u l i e l i c i t e d l a r g e s t responses from t h e r i g h t hemisphere.  Such e v i d e n c e , when r e p l i c a t e d , w i l l u n -  d o u b t e d l y p r o v i d e s t r o n g e v i d e n c e f o r language asymmetry f r o m birth. Future r e s e a r c h w i l l undoubtedly u t i l i z e EEG t e c h n i q u e s .  more s o p h i s t i c a t e d  I t i s o n l y when c o h e s i o n i s b r o u g h t t o t h e o r y  and e x p e r i m e n t a l r e s u l t s f r o m a l l t h r e e l i n e s o f i n v e s t i g a t i o n (that i s , dichotic l i s t e n i n g , c l i n i c a l  s t u d i e s and EEG),  t h a t a more c o m p l e t e u n d e r s t a n d i n g o f how and v/hen l e f t s p h e r e d e v e l o p s dominance f o r l a n g u a g e w i l l emerge.  hemi-  64  REFERENCES Basser,  L. ( 1 9 6 2 ) . " H e m i p l e g i a o f E a r l y Onset and t h e F a c u l t y o f Speech w i t h S p e c i a l R e f e r e n c e t o t h e E f f e c t s o f Hemispherectomy," B r a i n 8 5 , 4 2 7 - 4 6 0 .  B e l m o n t , L. and B i r c h , H. ( 1 9 6 3 ) . " L a t e r a l Dominance and R i g h t - L e f t Awareness i n N o r m a l C h i l d r e n , " C h i l d  Development 3 4 , 257-270.  Benson, F. and Geschwind, N. ( 1 9 6 8 ) . " C e r e b r a l Dominance and I t s Disturbances," P a e d i a t r i c C l i n i c of North A m e r i c a 1J?, 7 5 9 - 7 6 9 . B e r l i n , C , L o w e - B e l l , S., C u l l e n , J . , Thompson, C. and L o o v i s , C. (1973). " D i c h o t i c Speech P e r c e p t i o n : An I n t e r p r e t a t i o n o f R i g h t E a r Advantage and T e m p o r a l O f f s e t E f f e c t s , " J . A c o u s t . S o c . Amer. 5 5 ,  699-709.  B e r n s t e i n , B. ( 1 9 6 1 ) . " S o c i a l C l a s s and L i n g u i s t i c D e v e l o p ment; a T h e o r y o f S o c i a l L e a r n i n g , " i n E d u c a t i o n , Economy and S o c i e t y , H a l s e y , F l o u d and A n d e r s o n , e d s . ( F r e e P r e s s , New Y o r k ) . B e r r y , M. ( 1 9 6 9 ) . Language D i s o r d e r s o f C h i l d r e n : t h e Bases and D i a g n o s e s ( A p p l e t o n - C e n t u r y - C r o f t s , New Y o r k ) . B o c c a , E. and C a l e a r o , C. ( 1 9 6 3 ) . " C e n t r a l Hearing Processes," i n J e r g e r , J . , Modern Developments i n A u d i o l o g y , (Academic P r e s s , New Y o r k and L o n d o n ) , 337-370. B o c c a , E., C a l e a r o , C. and C a s s i n a r i , V. (1954). "A New Method f o r T e s t i n g H e a r i n g i n T e m p o r a l Lobe Tumours," A c t a . O t o - L a r y n g o l . 4 4 , 219-221. B o t e z , M. and B a r b e a u , A. (1971). "Role o f S u b c o r t i c a l S t r u c t u r e s , and P a r t i c u l a r l y o f t h e Thalamus i n t h e Mechanisms o f Speech and Language,"  I n t . J . N e u r o l . 8 , 300-320.  B r o a d b e n t , D. (1954). "The R o l e o f A u d i t o r y L o c a l i z a t i o n i n A t t e n t i o n and Memory Span," J . E x p . P s y c h o l . 4 7 , 191-196. B r o a d b e n t , D. and G r e g o r y , M. ( 1 9 6 4 ) . "Accuracy o f R e c o g n i t i o n f o r Speech P r e s e n t e d t o t h e L e f t and R i g h t E a r s , " Quart. J . Exp. P s y c h o l . 1 6 , 359-360.  65  B r o c a , P. ( 1 8 6 1 ) . "Reraarques stir l e S i e g e de l a P a c u l t e d u Language A r t i c u l e , S u i v i e s d'une O b s e r v a t i o n d'Aphemie," B u l l , de l a Soc. Anatom. de P a r i s 6, 330-357, a s d i s c u s s e d i n S m i t h , A . , " H e m i s p h e r i c D i f f e r e n c e s i n Language and V i s u a l F u n c t i o n s , " C o r t e x 2, ( 1 9 6 6 ) , 109-126. B r u n i n g , J . and K i n t z , B. ( 1 9 6 8 ) . C o m p u t a t i o n a l Handbook o f S t a t i s t i c s ( S c o t t , Poresman and Company, G l e n v i e \ Illinois). B r y d e n , M. ( 1 9 6 7 ) . "An E v a l u a t i o n o f Some Models o f L a t e r a l i t y Effects i n Dichotic Listening," Acta Oto-Laryngol. 63, 595-604-. B r y d e n , M. (1970). " L a t e r a l i t y E f f e c t s i n D i c h o t i c L i s t e n i n g : R e l a t i o n s w i t h Handedness and R e a d i n g A b i l i t y i n C h i l d r e n , " N e u r o p s y c h o l o g i a 8, 443-4-50. C a l e a r o , C. and A n t o n e l l i , A. ( 1 9 6 3 ) . " C o r t i c a l Hearing Tests and C e r e b r a l Dominance," A c t a . O t o - L a r y n g o l . 56, 17-26. ~~ C a r t e r e t t e , E. (ed.) ( 1 9 6 6 ) . B r a i n F u n c t i o n , Volume I I I , S p e e c h , Language and Communication ( U n i v e r s i t y o f C a l i f o r n i a P r e s s , B e r k l e y and L o s A n g e l e s ) . C u r r y , F. ( 1 9 6 7 ) . "A C o m p a r i s o n o f L e f t - H a n d e d and R i g h t Handed S u b j e c t s on V e r b a l and N o n v e r b a l D i c h o t i c L i s t e n i n g Tasks," Cortex 34-3-352. C u r r y , F. ( 1 9 6 8 ) . "A C o m p a r i s o n o f t h e P e r f o r m a n c e s o f a R i g h t H e m i s p h e r e c t o m i z e d S u b j e c t and T w e n t y - f i v e N o r m a l s on F o u r D i c h o t i c L i s t e n i n g T a s k s , " C o r t e x 4_, 14-4--153. C u r r y , F. and G r e g o r y , H. (196 ). "The P e r f o r m a n c e o f S t u t t e r e r s on D i c h o t i c L i s t e n i n g T a s k s Thought t o R e f l e c t C e r e b r a l Dominance," J . Speech Hear. R e s . 12, 73-82. 0  Darwin, Dax,  C. ( 1 9 6 9 ) . A u d i t o r y P e r c e p t i o n and C e r e b r a l Dominance, U n p u b l i s h e d D o c t o r ' s T h e s i s , U n i v e r s i t y o f Cambridge.  M. ( 1 8 6 5 ) . " L e s i o n s de l a M o i t e Gauche de l ' E n c e p h a l e C o i n c i d e n t avec l ' O u b l i d e s S i g n e s de l a P e n s e e , " Gaz. Hebdom., S 2 , 1 1 , 259-260, a s quoted i n R o b e r t s , L . , " C e n t r a l B r a i n Mechanisms i n Speech," in Brain Function, Vol. I I I .  Downie, N. and H e a t h , R. (1959). B a s i c S t a t i s t i c a l Methods ( H a r p e r and Row, New Y o r k and E v a n s t o n ) .  66  E i m a s , P., S i q u e l a n d , E., J u s c z y k , p . and V i g o r i t o , J . (1971). "Speech P e r c e p t i o n i n I n f a n t s , " S c i e n c e 1 7 1 , 303-306. Galambos, R. and H i l l y a r d , S. (1970). " D e t e r m i n a n t s o f N e u r a l and B e h a v i o r a l P l a s t i c i t y : An O v e r v i e w , " i n S c h m i t t , P. ( e d . ) . The N e u r o s c i e n c e s : Second S t u d y P r o g r a m ( R o c k e f e l l e r U n i v e r s i t y P r e s s , New Y o r k ) ,  289-297.  G e f f n e r , D. and Hochberg, I . (1971). "Ear l a t e r a l i t y Performance o f C h i l d r e n f r o m Low and M i d d l e S o c i o e c o n o m i c L e v e l s on a V e r b a l D i c h o t i c L i s t e n i n g Task," C o r t e x 7,  193-203.  Geschwind, N. and L e v i t s k y , W. ( 1 9 6 8 ) . "Human B r a i n : L e f t R i g h t A s y m m e t r i e s i n T e m p o r a l Speech R e g i o n , " S c i e n c e 161, 1 8 6 . Hagne, I . (1972). "Development o f t h e EEG i n N o r m a l I n f a n t s During t h e P i r s t Year o f L i f e , " A c t a P a e d i a t r i c a S c a n d i n a v i c a , Supplement 232, 5-24-. H a r r i s o n , G.,V7einer, J . , T a n n e r , J . and B a r n i c o t , N. (1964-). Human B i o l o g y ; An I n t r o d u c t i o n t o Human E v o l u t i o n , V a r i a t i o n and Growth ( O x f o r d U n i v e r s i t y P r e s s , London). I n g l i s , J . (1965 ) • " D i c h o t i c L i s t e n i n g and C e r e b r a l Dominance," A c t a O t o - L a r y n g o l . 60, 231-238. J o n e s , D. and S p r e e n , 0. (1967). " D i c h o t i c L i s t e n i n g by R e t a r d e d C h i l d r e n : t h e E f f e c t o f E a r O r d e r and A b s t r a c t n e s s , " C h i l d Development 38, 101-105. K i m u r a , D. ( 1 9 6 1 a ) . " C e r e b r a l Dominance and t h e P e r c e p t i o n o f V e r b a l S t i m u l i , " Can. J . o f P s y c h o l . 1 5 ,  166-171*  K i m u r a , D. ( 1 9 6 1 b ) . "Some E f f e c t s o f Temporal Lobe Damage on A u d i t o r y P e r c e p t i o n , " Can. J . o f P s y c h o l . 1 5 , 156-165. K i m u r a , D. ( 1 9 6 3 ) . "Speech 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 as D e t e r m i n e d b y an A u d i t o r y T e s t , " J . Compar. P h y s i o l . P s y c h o l . £6, 899-902. K i m u r a , D. (1964-). "Left-Right Differences i n the Perception o f M e l o d i e s , " Q u a r t . J . E x p . P s y c h o l . 1 6 , 355-358. K i m u r a , D. (1967). " F u n c t i o n a l Asymmetry o f t h e B r a i n i n D i c h o t i c L i s t e n i n g , " Cortex 163-178.  67  K i m u r a , D. and F o l b , S. ( 1 9 6 8 ) . " N e u r a l P r o c e s s i n g o f Backwards Speech Sounds," S c i e n c e 161, 395-396. Knox, 0. and K i m u r a , D. (1970). " C e r e b r a l P r o c e s s i n g i n N o n v e r b a l Sounds i n Boys and G i r l s , " N e u r o p s y c h o l o g i a  8, 227-237.  K r a s h e n , S. (1972). "Language and t h e L e f t Hemisphere," UCLA Working P a p e r s i n P h o n e t i c s 2 4 . K r a s h e n , S. and Harshman, R. (1972). " L a t e r a l i z a t i o n and the C r i t i c a l P e r i o d , " UCLA W o r k i n g P a p e r s i n P h o n e t i c s  23, 13-21.  Kuhn, G. (1972). "The P h i C o e f f i c i e n t as an I n d e x o f E a r Difference i n Dichotic L i s t e n i n g , " Haskins Laboratories S t a t u s R e p o r t on Speech R e s e a r c h , SR-29/50, 75-82. Labov, W. (1967). "Some S o u r c e s o f R e a d i n g P r o b l e m s f o r Negro S p e a k e r s o f N o n - S t a n d a r d E n g l i s h , " New D i r e c t i o n s i n Elementary E n g l i s h , ( N a t i o n a l C o u n c i l of T e a c h e r s ) , 140-167. Labov, W. ( 1 9 6 8 ) . "The R e f l e c t i o n o f S o c i a l P r o c e s s e s i n L i n g u i s t i c S t r u c t u r e s , " i n Pishman, J . ( e d . ) , R e a d i n g s i n t h e S o c i o l o g y o f Language (Mouton, The Hague, P a r i s ) , 240-251. L e n n e b e r g , E. ( 1 9 6 6 ) . "Speech Development: I t s A n a t o m i c a l and P h y s i o l o g i c a l C o n c o m i t a n t s , " i n B r a i n F u n c t i o n , Volume I I I , 37-66. :  L e n n e b e r g , E. (1967). B i o l o g i c a l F o u n d a t i o n s o f Language ( W i l e y , New Y o r k ; . L e n n e b e r g , E. (1970). " B r a i n C o r r e l a t e s o f Language," i n The N e u r o s c i e n c e s : Second S t u d y urogram, 361-371L i b e r m a n , A. H a r r i s , K., Hoffman, H.• and G r i f f i t h , B. (1957). "The D i s c r i m i n a t i o n o f Speech Sounds W i t h i n and A c r o s s Fhoneme B o u n d a r i e s , " J . Exp. P s y c h o l . 54,  358-368.  Lowe, S., C u l l e n , J . j B e r l i n , C , Thompson, C. and W i l l e t t , M. (1970). " P e r c e p t i o n o f S i m u l t a n e o u s D i c h o t i c and M o n o t i c M o n o s y l l a b l e s , " J . Speech Hear. R e s . 13, 812. . L u c h s i n g e r , R. and A r n o l d , G. (1965). V o i c e - Speech Language (Wadsv/orth P u b l i s h i n g Company, I n c . , Belmont, C a l i f o r n i a ) . M o l f e s e , D. (1972). " C e r e b r a l Asymmetry i n I n f a n t s . , C h i l d r e n and A d u l t s : A u d i t o r y Evoked Responses t o Speech and Music S t i m u l i , " p r e s e n t e d a t 84th meeting o f Acousto Soc. Amer., 91 ( A ) .  68 McAdam, D. and W h i t a k e r , H. (1971)<> "Language P r o d u c t i o n : E l e c t r e n c e p h a l o g r a p h i c L o c a l i z a t i o n i n t h e Normal Human B r a i n , " S c i e n c e T£2, 4-99-501 0  M c C a r t h y , D. (1953). "Some P o s s i b l e E x p l a n a t i o n s o f Sex D i f f e r e n c e s i n Language Development and D i s o r d e r s , " J . P s y c h o l . 3£, 155-160o M i l n e r , B. ( 1 9 6 2 ) . "Laterality Effects i nAudition," i n I n t e r h e m i s p h e r i c R e l a t i o n s and C e r e b r a l Dominance, M o u n t c a s t l e , V., ed.' ( J o h n H o p k i n s , B a l t i m o r e ) . M i l n e r , B. ( 1 9 6 7 ) . " B r a i n Mechanisms S u g g e s t e d by S t u d i e s o f T e m p o r a l L o b e s , " i n B r a i n Mechanisms U n d e r l y i n g Speech and Language, M i l l i k a n , C. and D a r l e y , P., e d s . (Grune a n d S t r a t t o n , New Y o r k ) , 122-14-5. M i l n e r , B., B r a n c h , C. and Rasmussen, T. ( 1 9 6 4 ) . "Observations on C e r e b r a l Dominance," i n Language, O l d f i e l d , R. and M a r s h a l l , J . , e d s . (1968) / ( P e n g u i n ) , 366-378. Milner,  B., T a y l o r , L. and S p e r r y , R. ( 1 9 6 8 ) . "Lateralized Suppression of D i c h o t i c a l l y Presented D i g i t s a f t e r C o m m i s s u r a l S e c t i o n i n Man," S c i e n c e 1 6 1 , 184-186.  M o f f i t t , A. ( 1 9 7 1 ) . "Consonant Cue P e r c e p t i o n by 20 t o 24 Week O l d I n f a n t s , " C h i l d Development 4 2 , 717-731. Moray, N. (1970). A t t e n t i o n : S e l e c t i v e P r o c e s s e s i n V i s i o n and H e a r i n g ( H u t c h i s o n E d u c a t i o n a l , L o n d o n ) . M o r s e , P. ( 1 9 7 2 ) . "The D i s c r i m i n a t i o n o f Speech and Nonspeech S t i m u l i i n E a r l y I n f a n c y , " J . .Exp. C h i l d P s y c h o l . 14-, 4-77-4-92. Mussen, P., Conger, J . and Kagan, J . ( 1 9 6 9 ) . C h i l d Development and P e r s o n a l i t y , t h i r d e d i t i o n , ( H a r p e r and Row, New Y o r k , E v a n s t o n and L o n d o n ) . N a g a f u c h i , M. (1970). "Development o f D i c h o t i c and M o n a u r a l H e a r i n g A b i l i t i e s i n Young C h i l d r e n , " A c t a O t o - L a r y n g o l 69, 4-09-4-14-. N e t l e y , C. ( 1 9 7 2 ) . " D i c h o t i c L i s t e n i n g P e r f o r m a n c e o f Hemis p h e r e c t o m i z e d P a t i e n t s , " N e u r o p s y c h o l o g i a 1 0 , 233-24-0. O r t o n , 8. (1934-). "Some S t u d i e s i n t h e Language F u n c t i o n , " R e s . P u b l . A s s . N e r v . Ment. D i s . 1_3, 614--632, a s quoted i n Hecan, H. and A j u r i a g u e r r a , J . (1964) L e f t Handedness: Manual S u p e r i o r i t y and C e r e b r a l Dominance (Grune and S t r a t t o n , New Y o r k and L o n d o n ) . P e r k i n s , V/. (1971). Speech P a t h o l o g y : An A p p l i e d B e h a v i o r a l S c i e n c e , (C.V. Mosby Co., sh. L o u i s ) .  69 R o s e n z w e i g , M. (1951). " R e p r m e n t a t i o n s o f t h e Two E a r s a t t h e A u d i t o r y C o r t e x , " Amer. J . P h y s i o l . l o 7 , 14-7-  158.  S a t z , P. (1968). " l a t e r a l i t y E f f e c t s i n D i c h o t i c N a t u r e 218, 277-278. Satz,  Listening,"  Achenbach, K., P a t t i s h a l l . , E and F e n n e l l , E. (1965). "Order o f R e p o r t , E a r Asymmetry and Handedness i n D i c h o t i c L i s t e n i n g , " C o r t e x 1,' 377-396.  S h a n k w e i l e r , D. and S t u d d e r t - K e n n e d y , M. (1967). "Identif i c a t i o n o f Consonants and Vowels P r e s e n t e d t o L e f t and R i g h t E a r s , " Q u a r t . J . Exo. P s y c h o l .  19,  59-63.  Somners, R. and T a y l o r M. (1972). " C e r e b r a l Speech Domi n a n c e i n L a n g u a g e - D i s o r d e r e d and Normal C h i l d r e n , " C o r t e x 8, 224-232. S p a r k s , R. and Geschwind, N. ( 1 9 6 8 ) . "Dichotic Listening i n Man a f t e r S e c t i o n o f N e o c o r t i c a l Commissures, C o r t e x 4, 3-16.  II  S p a r k s , R.,.. G o o d g l a s s , H. and N i c k e l , B. (1970). "Dichotic L i s t e n i n g a f t e r Hemisphere L e s i o n s , " C o r t e x 6, 249-260. S p r e e n , 0. and B o u c h e r , A. (1970). E f f e c t s o f Low P a s s F i l t e r i n g on E a r Asymmetry i n D i c h o t i c L i s t e n i n g and Some U n c o n t r o l l e d E r r o r S o u r c e s , " J . Aud. Res. 10,  45-51.  S p r e e n , 0 . , S p e l l a c y , F. and R e i d , J . (1970). "The E f f e c t o f I n t e r s t i m u l u s I n t e r v a l and I n t e n s i t y on E a r Asymmetry f o r N o n v e r b a l S t i m u l i i n D i c h o t i c L i s t e n i n g , " N e u r o p s y c h o l o g i a 8, 245-250. S t u d d e r t - K e n n e d y , M. and S h a n k w e i l e r , D. (1970). "Hemisp h e r i c S p e c i a l i z a t i o n f o r Speech P e r c e p t i o n , " J . A c o u s t . Soc. Amer. 4 8 , 579-594. Studdert-Kennedy,  M., S h a n k w e i l e r , D. and Schulman, S. "Opposed E f f e c t s o f a D e l a y e d C h a n n e l on P e r c e p t i o n o f D i c h o t i c a l l y and M o n o t i c a l l y P r e s e n t e d CV s y l l a b l e s , " J . A c o u s t . Soc. Amer. 4 8 , 599-602. ~  (1970;.  T a y l o r , L. ( 1 9 6 2 ) . "Perception of D i g i t s Presented t o Left and R i g h t E a r s i n C h i l d r e n w i t h R e a d i n g D i f f i c u l t i e s , " Paper p r e s e n t e d a t Canadian P s y c h o l o g i c a l A s s o c i a t i o n m e e t i n g , H a m i l t o n , O n t a r i o , a s quoted i n B r y d e n , 1970.  70  Thompson, C , S t a f f o r d , M . , C u l l e n , J . , Hughes, L., Lowe-Bell,S. and B e r l i n , C. (1972). " I n t e r a u r a l I n t e n s i t y D i f f e r e n c e s i n D i c h o t i c Speech P e r c e p t i o n , " 8 $ r d m e e t i n g A c o u s t . S o c . A m e r , B u f f a l o , New Y o r k 0  0  Trehub, S. and R a b i n o v i t c h , S<, (1972) o "Auditory-Linguistic S e n s i t i v i t y i n E a r l y Infancy," Developmental Psychol-  ogy 6 , 74-77.  T r e i s m a n , A. and G e f f e n , G. ( 1 9 6 8 ) . " S e l e c t i v e A t t e n t i o n and C e r e b r a l Dominance i n P e r c e i v i n g and R e s p o n d i n g t o Speech Messages," Q u a r t . J . E x p . P s y c h o l . 2 0 , 139-  ~~  150o  Wada, J . and Rasmussen, T . ( 1 9 6 0 ) . "Intracarotoid Injection o f Sodium A m y t a l f o r t h e L a t e r a l i z a t i o n o f C e r e b r a l Speech Dominance: E x p e r i m e n t a l and C l i n i c a l Observ a t i o n s , J . N e u r o s u r g . 1£, 2 6 6 - 2 8 2 . W h i t a k e r , H. ( 1 9 6 9 ) . "On t h e R e p r e s e n t a t i o n o f Language i n t h e Human B r a i n , UCLA W o r k i n g P a p e r s i n L i n g u i s t i c s 12o Winitz, H  0  (1971 )<> " P s y c h o l i n g u i s t i c C o n s i d e r a t i o n i n Language Development," i n T r a v i s , L , Handbook o f Speech P a t h o l o g y and A u d i o l o g y , ( M e r e d i t h C o r p o r a t i o n , New Y o r k ) , 1113-1142. 0  S. and R a b i n o v i t c h , M. ( 1 9 7 2 ) . H e m i s p h e r i c Speech L a t e r a l i z a t i o n i n Children with Audio-Linguistic D e f i c i t s , " Cortex 8 , 412-426.  Witelson,  Z a n g w i l l , 0 . ( 1 9 6 0 ) . C e r e b r a l Dominance and I t s R e l a t i o n t o P s y c h o l o g i c a l F u n c t i o n ( C h a r l e s C. Thomas, S p r m g field, Illinois). Zurif, E  0  and R a m i e r , A ( 1 9 7 2 ) "Some E f f e c t s o f U n i l a t e r a l B r a i n Damage on t h e P e r c e p t i o n o f D i c h o t i c a l l y P r e s e n t e d jehoneme Sequences and D i g i t s , " N e u r o p s y c h o l o g i a 1 0 , 103-110. c  0  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 m s e c / s m a l l 0  division  hat nose  mommy apple  spoon fish  chair tree  doggie baby-  queen ccw  bird bed  cup clown  Appendix. 2 List  T, L i s t 2 and f o i l  List 1  List  2  words  F o i l Words  a.  hat  a.  nose  a.  sock*  b.  mommy*  b.  apple*  b.  wagon*  1;.  man  1.  mouse  1.  knife*  2.  ball*  2.  boy  2.  soap*  3.  bunny  3.  daddy*  3.  girl*  4.  pencil*  4.  candy  4.  bottle  5.  spoon*  5.  fish*  5.  pin*  6.  chair *  6.  tree*  6.  shoe*  7o  door.  7.  gun*  7.  key*  8.  kittie*  8.  cookie  8.  table*  9.  doggie*  9.  baby*  9.  icecream  10. queen  10. cow*  10. mouth  11. b o a t *  11. bus*  11. eye  12. b l o c k *  12. b e l l *  12. e a r  13. b i r d  13. bed*  13c f o o t  1 4 . cup*  14. c l o w n *  14. g l o v e  15. c a k e *  15. c a r *  15. b r u s h *  *words s t a r r e d were c h o s e n f r o m t h e PPVT„  Appendix 5 D u r a t i o n ( i n msec.) o f s t i m u l u s w o r d - p a i r s  List  List 1  2  a»  hat  660  a.  nose  780  b.  mommy  900  b.  apple  760  1.  man  760  1.  mouse  700  2.  ball  600  2.  boy  660  3.  bunny  500  3.  daddy  560  4.  pencil  900  4-„  candy  780  5.  spoon  960  5.  fish  480  6.  chair  620  6.  tree  660  7.  door  520  7.  gun  600  8.  kittie  580  8.  cookie  520  9.  doggie  680  9.  baby  760  1 0 . queen  64-0  1 0 . cow  680  11. boat  560  1 1 . 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. c l o w n  15. cake  600  '15. c a r  780 640  79  Appendix Order of p i c t u r e  4 placement  a.  hat  a.  nose  a.  (sock)*  b.  (wagon)  b.  apple  b.  mommy  1.  man  1.  (knife)  1.  mouse  2.  (soap)  2.  boy  2.  ball  3.  (girl)  3.  daddy  3.  bunny  4.  pencil  4.  candy  4.  (bottle)  5,  fish  5o  (pin)  5.  spoon  6.  tree  6.  (shoe)  6.  chair  7.  gun  7.  door  7-  (key)  8.  (table)  8.  kitty  8.  cookie  9.  (ice  9*  baby  9.  doggie  10.  (mouth)  10.  queen  10.  cow  11. boat.  11.  (eye)  11. bus  12.  (ear)  12. b l o c k  12. b e l l  13.  (foot)  13. b i r d  13. bed  14.  clown  14. ( g l o v e )  14. cup  15.  15-  15. cake  cream)  * f o i l words b r a c k e t e d .  (brush)  car  

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