the development of language in bonobos and chimpanzees

8/19/2019 The Development of Language in Bonobos and Chimpanzees

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P e r g a m o n

Language Communication, Vol. 15, No. 2, pp. 1 21-148, 1995

C o p y r i g h t © 1 9 9 5 E l s e v i e r S c i e n c e L td

Pr in ted in Grea t Br i ta in . Al l r ights reserved

0271-5 309/95 9 .50 + 0 .00

0271-5309 95)00001-1

T H E D E V E L O P M E N T O F L A N G U A G E S K I L L S IN B O N O B O A N D

C H I M P A N Z E E - - I . C O M P R E H E N S I O N

K A R E N E . B R A K K E a n d E . S U E S A V A G E - R U M B A U G H

T h e s p e c ie s m o s t c l o s e l y re l a te d t o o u r o w n a r e t h e b o n o b o

P a n p a n i s c u s )

a n d th e c h i m p a n z e e

P a n t r o g l o d y t e s ) , w ho d i ve r g ed f r om t he hom i n i d ev o l u t i ona r y pa t h a s l it tl e as f i ve t o e i gh t

m i l l io n y e a r s ag o ( D i a m o n d , 1 9 8 8 ; M i y a m o t o

e t a L ,

1988) . The t wo s pec i e s o f

P a n ,

in turn ,

s ha r ed a com m on an ces t o r t wo t o t h r ee m i l l i on yea r s ago ( Di am ond , 1988).

A l t h o u g h c h i m p a n z e e s a n d b o n o b o s h a v e d e m o n s t r a te d m a n y c o m p l e x c o g n i t iv e s k il ls ( e .g .

B o y s e n a n d B e r n t s o n , 1 9 90 ; P r e m a c k , 1 9 7 6; R u m b a u g h e t a l . , 1993 ; To t h e t a l . , 1993) , the i r

capac i t y t o acqu i r e and us e l anguag e ha s been a t op i c o f con t r ove r s y ( Te r r ace

e t a l . ,

1979;

Vau c l a i r, 1990). Pa r t o f the d i f f i cu l ty in a s s e s s ing l anguage s k i ll s i n apes a r i s e s f r om t he f ac t

t ha t t hey do no t s peak . Ev en i f t hey pos s e s s ed a l l o f the cogn i t i ve requ i s i t e s f o r l anguage , t he

s t r uc t u r e o f t he i r voc a l appa r a ti wo u l d no t pe r m i t a rt i cu la t e s peech ( D uch i n , 1990 ; L i ebe r m an ,

1991) . Thus , i n o r de r t o exam i ne l anguage p r oduc t i on i n t he g r ea t apes , i nves t i ga t o r s have

t u r ned t o s i gn ( Fou t s , 1973 ; Ga r dne r and Ga r dne r , 1969 ; Mi l e s , 1983 ; Pa t t e r s on , 1978) o r t o

a r t if i c ia l s ym bo l s ys t em s ( P r em ack , 1971 ; Rum baug h , 1977 ; Sava ge - R um baug h , 1986 ;

S a v a g e - R u m b a u g h

e t a l . ,

1986) , e ach o f wh i ch en t a i l m o t o r and / o r vocab u l a r y l im i t a t i ons f o r

t h e n o n - h u m a n s u b je c ts . M a n u a l s ig n s s u c h a s th o s e u s e d in A m e r i c a n S i g n L a n g u a g e ( A S L ) ,

f o r e x a m p l e , o f t e n r e q u ir e f i n e m o t o r c o o r d i n a ti o n t h at p r o v e s a w k w a r d f o r l es s d e x t r o u s a p e

hands . Al s o , ape s ub j ec t s u s i ng non- s i gn s ym bo l s a r e expos ed t o a t m os t s eve r a l hundr ed

s y m b o l s t h a t t h e y c a n p r o d u c e ( P r e m a c k , 1 9 7 6 ; S a v a g e - R u m b a u g h

e t a l . ,

1986) r a t he r t han t he

t h o u s a n d s o f w o r d s h e a r d b y m o s t c h il d r e n as th e y m a t u r e . E v a l u a ti o n o f t h e a p e s p r o d u c t i v e

s k i ll s i s i n l a r ge pa r t, t hen , d e t e r m i ned by m o da l i t y l i m i ta t ions .

C o m p r e h e n s i o n m a y p r o v i d e a b e tt e r i n d e x o f a s p e c i e s c o m p e t e n c e f o r l a n g u a g e t ha n d o e s

p r oduc t i on . As f a r a s we know , no pe r i phe r a l ana t om i ca l l i m i t at i ons app l y to apes ab i l it y t o

c o m p r e h e n d h u m a n s p e e c h . T h e e a r s t ru c t u re a n d t h e s e n s o r y - p e r c e p t u a l a u d i to r y p a t h w a y s o f

t h e t w o g e n e r a a p p e a r t o b e v e r y s i m i l a r ( A n k e l - S i m o n s , 1 9 8 3 ) ; s p e e c h c o m p r e h e n s i o n

d i f f e r ences be t ween s pec i e s , t he r e f o r e , a r e l i ke l y t o r e f l e c t CNS f unc t i on i ng . By eva l ua t i ng

w h i c h o f t h e r e c e p t i v e c a p a c i t i e s u n d e r l y i n g l i n g u i s t i c c o m p e t e n c e a r e w e l l d e v e l o p e d i n

s p e c ie s c l o s e l y r e l a te d t o o u r o w n , a n d w h i c h a r e n o t, w e m a y b e a b le t o b e t t e r u n d e r s t an d h o w

hum ans cam e t o be t he adep t l ingu i s t ic c r ea t u r e s tha t we a r e .

L a n g u a g e c o m p r e h e n s i o n i n h u m a n s

D e v e l o p m e n t a l p s y c h o l o g i s ts a r e fa m i l ia r w i th t h e p r e m i s e th a t c o m p r e h e n s i o n l e a d s

p r o d u c ti o n ( G o l d in - M e a d o w e t a l . , 1 9 76 ; H u t t e n l o c h e r , 1 9 7 4 ) . C o m p r e h e n s i o n o f l a n g u a g e

C o r r e s p o n d e n c e r e l a t i n g to t h i s p a p e r s h o u l d b e a d d r e s s e d t o K a r e n E . B r a k k e , L a n g u a g e R e s e a r c h C e n t e r , G e o r g i a

S t a t e U n i v e r s i t y , U n i v e r s i t y P l a z a , A t l a n t a , G A 3 0 3 0 3 - 3 0 8 3 , U . S . A .

121


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122 KAREN E. BRAKKE and E. SUE SAVAG E RUMB AUGH

b e g i n s t o b e e v i d e n t a r o u n d 8 - 1 0 m o n t h s o f a g e ( B a t e s , 1 9 9 3 ) , a n d a c h i l d s r e c e p t i v e

vocabu l a r y ea r l y i n t he l anguage - l ea r n i ng p r oces s i s l i ke l y t o be l a r ge r t han i t s p r oduc t i ve

v o c a b u l a r y ( B a t es , 1 99 3; G o l d i n - M e a d o w e t a l . 1976 ; Snyde r e t a l . 1981) .

A l t h o u g h l a n g u a g e c o m p r e h e n s i o n b e g i n s t o a p p e a r e a r l y i n l i f e a n d d o e s n o t i n h e r e n t l y

r equ i r e t he f i ne m o t o r ab i l it ie s t ha t s peech and s i gn p r oduc t i ve s k il ls do , i t is by n o m eans a

s i m p l e o r a u t o m a t i c p h e n o m e n o n . T h e d e v e l o p m e n t o f r e c e p t iv e l a n g u a g e s k i ll s i n o u r s p e c i e s

r equ i r e s t ha t s eve r a l m i n i m a l cond i t i ons be m e t . Us i ng s poken l anguage a s an exam pl e , t he

i nd i v i dua l m u s t be ab l e t o d i s ti ngu i s h d i f f e r en t pho nem es , t hen r e l a te t hem t o on e ano t he r a s

w o r d s . M e a n i n g m u s t b e a t ta c h e d t o t h e w o r d s , a n d f i n a l ly t h e w o r d s m u s t b e s y s t e m a t i c a ll y

r e l a t ed i n o r de r f o r the i nd i v i dua l t o de r i ve t he agg r ega t e m ean i ng o f t he u t te r ance . Un de r l y i ng

t hes e l i ngu i s t i c s k i l l s a r e cogn i t i ve capac i t i e s s uch a s t he ab i l i t y t o i n t eg r a t e t em por a l l y o r

s pa t i a l l y d i s t i nc t p i ece s o f i n f o r m a t i on ( Ba t e s , 1993 ; Di am ond , 1991) , t o m en t a l l y r ep r e s en t

abs en t en t i t i e s ( P i age t and I nhe l de r , 1969) , and t o e s t ab l i s h pa r t - who l e r e l a t i ons ( Lange r ,

1 9 8 6 ) . T h e c o n t e x t o f t h e u t t e r a n c e a n d t h e c o m m u n i c a t i v e i n t e n t o f t h e s p e a k e r a r e a l s o

e s s en t i a l com pon en t s o f s ucces s f u l unde r s t and i ng o f o t he r s m e s s ages ( Br une r , 1983 ; Lo ck ,

1980) .

I n add i t i on t o cogn i t i ve r equ i si t e s, app r op r i a te env i r onm en t a l cond i t ions m us t a l s o be ex t an t

f o r l anguag e - l ea r n i ng t o occu r . T he i n f an t c ann o t l e a r n l anguage u n l e s s i t i s expos e d t o it. I t is

b e c o m i n g i n c r e a s in g l y e v i d e n t t h at t h e d e v e l o p m e n t o f la n g u a g e c o m p e t e n c e i s h e a v i ly

s uppor t ed by t he peop l e and cu l t u r e s u r r ound i ng t he i n f an t ( Br une r , 1983 ; Lock , 1980) . Us e

o f ch i l d - d i r ec t ed s peech ( Be r k o - G l eas on , 1989 ; Fe r gus on , 1964 ; Snow , 1977) and j o i n t

a t te n t io n r o u t in e s ( B a k e m a n a n d A d a m s o n , 1 9 8 4; B r u n e r , 1 9 7 5 ; T r e v a r t h e n a n d H u b l e y ,

1978) , f o r exam pl e , h i gh l i gh t t he com m u ni ca t i ve p r oces s and e ngage t he i n f an t s a t ten t ion .

Pa r en t s encour age ch i l d r en t o pa r t i c i pa t e i n and r e s pond app r op r i a t e l y t o u t t e r ances du r i ng

da i l y ac t i v i t i e s l ong be f o r e t hey expec t t o hea r s i m i l a r u t t e r ances f r om t he i n f an t s ( Br une r ,

1 9 8 3 ; G o l d i n - M e a d o w e t a l . 1976) .

C o m p r e h e n s i o n , t h e n , a r is e s i n h u m a n s d u r i n g n o r m a l d a y - t o - d a y in t e r ac t io n s b e t w e e n

i n f an ts and o t he r s . Ch i l d r en a r e no t t augh t l angu age by d r i ll i ng r epea t ed t ri a ls o f wo r ds i n

o r d e r to g e t a f o o d r e w a r d . T h i s m u s t b e c o n s i d e r e d w h e n s t u d y in g l a n g u a g e c o m p e t e n c y i n

o t he r p r i m a t e s . I n o r d e r t o eva l ua t e s k i ll s o f r e l a t ed s pec i e s a t a l eve l t ha t pe r m i t s co m p ar i s on

t o ou r own , we m us t p r ov i de r ea r i ng env i r onm en t s a s s i m i l a r a s pos s i b l e t o t hos e f ound i n

hum an cu l t u r e s . Th i s i nc l udes p r ov i d i ng l i ngu i s t i c and s oc i a l i npu t t ha t i s m ode l ed a f t e r t he

way hum an adu l t s i n t e r ac t wi t h i n f an t s a r ound t he wor l d .

a n g u a g e c o m p r e h e n s i o n in b o n o b o s

A t t h e L a n g u a g e R e s e a r c h C e n t e r ( L R C ) , t w o b o n o b o s ( K a n z i a n d M u l ik a ) , l e a rn e d t o u s e

and und e r s t and s ym bo l s i n m an y d i f f e r en t com m uni ca t i ve capac i ti e s wi t hou t exp l i c i t t r a in i ng

( S a v a g e - R u m b a u g h e t a l . 1990 ; Sev c i k and Savage - R um baug h , 1994) . Th e i r i n s t r uc ti on was

m u ch l e s s s t r uc t u r ed than t ha t o f o t he r apes wh o w er e t augh t t o u s e s ym bo l s i n repea t ed - t r ia l

o r r ewa r d - bas ed pa r ad i gm s ( P r em ac k , 1971 ; Ru m b augh , 1977 ; Sava ge - Ru m b augh , 1986).

L a n g u a g e - l e a r n i n g b y t h e s e b o n o b o s i n v o l v e d o b s e r v a t io n o f h u m a n m o d e l s w h o u s e d t h e

s y m b o l s a s t h e y i n t e ra c t e d w i th t h e a p e s t h r o u g h o u t t h e d a y . T h e y o u n g b o n o b o s w e r e a s k e d

t o a t t end t o and pa r t i c i pa t e i n t he da i l y ac t i v i t i e s o f t he l abo r a t o r y ( i nc l ud i ng p l ay and

s t r uc t u r ed t a s ks ) , bu t we r e no t r equ i r ed t o p r oduce s ym bo l s i n o r de r t o r ece i ve f ood o r o t he r

r ewar ds .


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COMPREHENSION IN P N 23

T h e t w o b o n o b o s s p o n t a n e o u s l y d e v e l o p e d r e c e p t i v e l a n g u a g e s k i l l s a n d r e a d i l y

c o m p r e h e n d e d s e v e r a l E n g l i s h w o r d s u n d e r b l i n d t e s t c o n d i t i o n s ( S a v a g e - R u m b a u g h

e t a l .

1 9 9 3; S e v c i k a n d S a v a g e - R u m b a u g h , 1 9 9 4 ). T h e o l d e r o f th e s e b o n o b o s h a s , i n f a c t,

d e m o n s t r a t e d t h e a b i l i t y t o u n d e r s t a n d s e v e r a l h u n d r e d n o v e l c o m p l e x s p o k e n s e n t e n c e s

( S a v a g e - R u m b a u g h e t a l . 1 9 9 3 ) . F u r t h e r m o r e , t h e c o m p r e h e n s i o n o f s y m b o l s g e n e r a l i z e d t o

s y m b o l p r o d u c ti o n i n th e s e s u b j ec t s ( S a v a g e - R u m b a u g h

e t a l .

1990) . In shor t , the two

b o n o b o s w e r e r e a r e d m u c h l i k e c h i l d re n a n d t h e ir s y m b o l a c q u is i ti o n e v i d e n c e d m a n y o f t h e

s a m e c h a r a c t e ri s t ic s a s t h a t o f y o u n g h u m a n s .

L a n g u a g e - l e a r n i n g a n d r o u t i n e s

C e n t r a l t o th e b o n o b o s l e a r n in g o f n at u r a l la n g u a g e w a s p a r t ic i p a t i o n in i n te r i n d iv i d u a l

r o u ti n e s a c c o m p a n i e d b y a d u l t la n g u a g e u s e . A s o u t li n e d i n S a v a g e - R u m b a u g h

e t a l .

(1993) ,

t h e s e r o u t in e s a r e m o r e o r l es s r e g u l a r ly s e q u e n c e d s e t s o f i n t e ri n d i v id u a l i n t e r a c ti o n s t h a t

o c c u r in a r e l a ti v e l y s i m i l a r m a n n e r o n d i f f e r e n t o c c a s i o n s ( p . 2 5 ). T h e s e i n t e ra c t i o n s a r e

e m b e d d e d w i t h i n a l a r g e r c o n t e x t . F o r e x a m p l e , w i t h i n a n e v e n i n g c o n t e x t w h e n t h e l a b i s

q u i e t , t h e r e w i l l o c c u r r o u t i n e s i n v o l v i n g m i l k p r e p a r a t i o n , q u i e t p l a y , d i a p e r c h a n g i n g , a n d

g r o o m i n g u n t i l t h e i n f a n t fa l ls a s l e e p . E a c h o f th e s e r o u t i n e s , i n tu r n , i s m a d e u p o f a s e q u e n c e

o f a c ts o f c o m p o n e n t s s u c h a s - - f o r m i l k p r e p a r a t i o n - - p u t t i n g t h e li n in g i n t he b o t tl e , o p e n i n g

t h e m i l k f o r m u l a , p o u r i n g t h e f o r m u l a i n to t h e b o t tl e , a d d i n g w a t e r , p u t t in g t h e n i p p l e o n , a n d

f ina l l y d r i nk ing t he mi lk .

W i t h i n t h e s e r o u t i n e s , e a c h p a r t i c i p a n t h a s a r o l e t h a t f r o m d a y t o d a y s t a y s r e l a t i v e l y

c o n s i s t e n t b u t o v e r th e c o u r s e o f t i m e m a y s h i f t, w i t h t h e in f a n t b e c o m i n g m o r e a n d m o r e

ac t i ve i n in i t i a ti ng t he co m pon en t s o f the rou t i ne . I n i t ia l l y , how eve r , t he adu l t pa r t i c i pan t

d i r e c ts t h e f l o w o f t h e i n t e r a c t io n a n d a s s i g n s a r o l e t o t h e i n f a n t t h at c o n s i s ts o f p a y i n g

a t t en t i o n a n d i n d i c a ti n g r e a d i n e s s t o c o n t i n u e w i t h t h e n e x t c o m p o n e n t o f t h e r o u ti n e . S a l i e n t

c o m p o n e n t s o r t r a n si t io n s o f t h e r o u t i n e a r e b e h a v i o r a l l y a n d l i n g u is t i c al l y ( v i a s p e e c h a n d / o r

l e x i g ra m ) e n c o d e d b y th e a du l t. S u c h m a r k i n g o f t h e c o m p o n e n t s a p p e a rs to b e m o s t

e f f e c t i v e w h e n i t o c c u r s p r i o r t o t h e a c t u a l e v e n t ( S a v a g e - R u m b a u g h , 1 9 9 1 ) . T a l k i n g a b o u t

w h a t w e a r e g o i n g t o d o , b e f o r e w e d o i t, a l l o w s a l l p a r t ic i p a n t s t o p r e d i c t w h a t w i l l h a p p e n

n e x t . O n c e a b l e t o p r e d i c t u p c o m i n g e v e n t s , t h e i n f a n t c a n b e g i n t o e x e r t s o m e c o n t r o l o v e r

h o w t h o s e e v e n t s u n f o ld .

Q u i t e o f t en , c o m p o n e n t s o f a s t a n d a r d r o u t i n e w i ll b e a d d e d o r m o d i f i e d . If , w h i l e

p r e p a r i n g m i l k , f o r e x a m p l e , i t is d i s c o v e r e d t h a t t h e b o x o f b o t t le l i n e rs i s e m p t y , a n e w b o x

w i l l h a v e t o b e lo c a t e d a n d o p e n e d . L i n g u i s t ic m a r k i n g b e c o m e s e s p e c i a l l y i m p o r t a n t a t th e s e

t i m e s w h e n t h e r o u t i n e i s a l t e r e d . B y p r o v i d i n g i n f o r m a t i o n t h a t m i g h t o t h e r w i s e b e l a c k i n g ,

t h e v e r b a l i n f o r m a t i o n a l l o w s a l l o f t h e i n d i v i d u a l s i n v o l v e d t o c o o r d i n a t e t h e i r b e h a v i o r s o

t h a t c o n t i n u a t io n o f t h e r o u ti n e m a y p r o c e e d s m o o t h l y ( s e e S a v a g e - R u m b a u g h , 1 9 91 , f o r a f u l l

d i s c u s s io n o f t h e c o n t r i b u t io n s o f r o u t i n e s t o l a n g u a g e - l e a r n i n g i n a p e s a n d c h i ld r e n ).

S p e c i e s o r r e a r i n g d i f f e r e n c e s

P r i o r t o t h e s t u d y w i t h b o n o b o s a t t h e L R C , t w o m a l e c h i m p a n z e e s , S h e r m a n a n d A u s t i n ,

w e r e t a u g h t r e fe r e n ti a l u s e a n d c o m p r e h e n s i o n o f v i s u o g r a p h i c s y m b o l s ( l e x i g r a m s ) v i a

e x p l i c i t t r i a l- b a s e d p a r a d i g m s . E a c h c o m m u n i c a t i v e f u n c t i o n - - r e q u e s t i n g , l a b e l i n g , a n d

c o m p r e h e n s i o n o f o t h e r s u t t e r a n c e s - - w a s t a u g h t s e p ar a t el y a n d r e q ui re d m a n y r e p e a t ed t ri al s

f o r th e c h i m p a n z e e s t o m a s t e r . P r o d u c t i v e s k i l ls d i d n o t g e n e r a l iz e t o c o m p r e h e n s i o n w i t h o u t

e x p l i c i t t r a in i n g ( S a v a g e - R u m b a u g h , 1 9 8 6 ) , a n d c o m p r e h e n s i o n o f s y m b o l s , o n c e le a r n e d , d i d


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1 24 K A R E N E . B R A K K E a n d E . S U E S A V A G E R U M B A U G H

n o t e x t e n d t o s p e e c h ( S a v a g e - R u m b a u g h e t a l . 1 9 8 5 b ) . A l t h o u g h S h e r m a n a n d A u s t i n

a p p e a r e d t o u n d e r s t a n d s o m e v e r b a l r e q u e s t s p r e s e n t e d t o t h e m o n a r e g u l a r b a s i s , w h e n

c o m p a r e d o n a f o r m a l s i n g l e - w o r d r e c e p t i v e l a n g u a g e t a s k ( ' G i v e m e t h e x ' ) , t h e t w o

c h i m p a n z e e s d e m o n s t r a t e d n o c o m p r e h e n s i o n o f s p o k e n E n g l i sh d i v o r c e d o f c o n te x t u al

c u e s .

T h e d a t a f r o m S h e r m a n a n d A u s t i n o n o n e h a n d a n d K a n z i a n d M u l i k a o n t h e o t h e r

s u g g e s t e d a p o s s i b l e s p e c i e s d i f f e r e n c e in t h e a b i li t y to u n d e r s t a n d c o m p l e x s p e e c h ( S a v a g e -

R u m b a u g h e t a l . 1 9 8 5 a) . I f c o n f i r m e d , t h i s d i f f e re n c e w o u l d b e a p o i n t o f d i s t in c t io n b e t w e e n

t h e t w o s p e c i e s o f P a n a n d m i g h t p r o v i d e i m p o r t a n t c lu e s t o t h e e v o l u t i o n o f h u m a n

l a n g u a g e .

T h e c o m p a r i s o n b e t w e e n t h e b o n o b o ( K a n z i a n d M u l i k a ) a n d c h i m p a n z e e ( S h e r m a n a n d

A u s t i n ) s u b j e c t s w a s c o m p r o m i s e d b y t w o d i f f e r e n c e s in t h e ir r ea r i n g h i st o r ie s , h o w e v e r . T h e

c h i m p a n z e e s w e r e 1 t o 2 ' ~ y e a r s o l d w h e n t h e y st a r te d s y m b o l t ra i n in g , w h i l e th e b o n o b o s

w e r e 4 - 6 m o n t h s o ld w h e n t h e y w e r e f i rs t e x p o s e d to s y m b o l u se a n d E n g l i s h - s p e a k in g

c a r e g i v e r s . I t m a y b e t h a t e a r ly e x p o s u r e a n d a t t a c h m e n t t o h u m a n s i s a c ri t ic a l c o m p o n e n t f o r

d e v e l o p i n g s p e e c h c o m p r e h e n s i o n i n c h i m p a n z e e s .

T h e r e i s s o m e e v i d e n c e t h a t t h i s m a y b e t h e c a s e . F o u t s e t a l . ( 1 9 7 6 ) r e p o r t e d a p p r o p r i a t e

r e s p o n s e s t o a t l e a s t 1 0 E n g l i s h w o r d s i n a c h i m p a n z e e t r a i n e d i n A S L . E a r l i e r s t u d i e s w i t h

c h i m p a n z e e s V i k i ( H a y e s , 1 9 5 1 ) a n d G u a ( K e l l o g g a n d K e l l o g g , 1 9 33 ) s u g g e s t e d t h a t s o m e

s p e e c h c o m p r e h e n s i o n m a y h a v e d e v e l o p e d i n ' h o m e - r e a r e d ' s u b j e ct s, b u t t h e se r e p o rt s w e r e

b a s e d o n d a t a c o l l e c t e d w i t h o u t c o n t e x t u a l c o n t r o l s a n d s o a r e in c o n c l u s i v e .

T h e s e c o n d d i f f e r e n c e b e t w e e n t h e L R C s t u d ie s i n v o l v i n g t h e c h i m p a n z e e s o n th e o n e h a n d

a n d t h e b o n o b o s o n th e o t h e r w a s t h e l a n g u a g e - l e a r n i n g e n v i r o n m e n t e x p e r i e n c e d b y t h e a p e s

a f t e r t h e i r in c l u s io n i n t h e p r o j e c t. T h e b o n o b o s l e a r n e d s y m b o l u s e o b s e r v a t i o n a l l y , w i t h a n

e m p h a s i s o n s y m b o l c o m p r e h e n s i o n . T h e c h i m p a n z e e s , o n t h e o t h e r h a n d , w e r e f i r s t t a u g h t

s y m b o l i c re q u e s t s k i ll s i n a s t ru c t u re d , t r i a l- b a s e d p a r a d i g m . A s S a v a g e - R u m b a u g h e t a l .

( 1 9 90 ) n o t ed , it ' m a y b e t h at a n e a r ly e m p h a s i s o n p r o d u c t iv e s y m b o l t r a i n i n g . . , m a y , in

i t s e l f , i n t e r f e r e w i th acqu i s i t i on p roces se s t ha t r e l y on obse rva t i on ' ( p . 250 ) .

I n o r d e r t o e v a l u a t e b o t h p r o d u c t i v e a n d r e c e p t i v e l a n g u a g e d i f f e r e n c e s i n t h e t w o s p e c i e s

o f P a n t h e n , t h e n e x t s t ep w a s t o r ai s e a m e m b e r o f e a c h s p e c i e s t o g e t h e r f r o m a n e a r l y a g e ,

p r o v i d i n g t h e m w i t h th e o p p o r t u n i t y t o l e a r n l a n g u a g e s k i l ls o b s e r v a t i o n a l l y a n d e m p h a s i z i n g

t h e c o m p r e h e n s i o n o f v e r b a l an d v i s u a l s y m b o l u s e in s t e a d o f r e q u i ri n g s y m b o l p r o d u c t i o n

f r o m t h e o u t s e t . ' T h i s i s t h e s a m e p a r a d i g m u s e d w i t h t h e o l d e r b o n o b o s , K a n z i a n d M u l i k a .

I f u n d e r s u c h c o n d i t i o n s t h e c h i m p a n z e e f a il s to d e v e l o p s p e e c h c o m p r e h e n s i o n s k il ls s i m i l a r

t o t h o s e t h a t b o n o b o s h a v e e x h i b i t e d , t h e n t h is s p e c i e s d i f f e r e n c e m a y r e p r e s e n t a k e y , a b r u p t

d e v e l o p m e n t i n t he p h y l o g e n y o f li n g u is t ic c o m p e t e n c e . I f a t th e o t h e r e x t r e m e , h o w e v e r , t h e

c h i m p a n z e e a n d b o n o b o p r o f i t e q u a l l y f r o m o b s e r v a t i o n a l l e a r n i n g , t h i s w o u l d t e s t i f y t o t h e

i m p o r t a n c e o f e a r l y e x p o s u r e t o a li n g u i st i c c u l tu r e i n f o s t e r i n g c o m p r e h e n s i o n s k il ls e v e n i n

s p e c i e s o t h e r t h a n o u r o w n .

T h i s c o m p a r i s o n h a s n o w b e e n e f f e c t e d w i th a s i n gl e b o n o b o a n d c h i m p a n z e e p a i r a n d t h e

r e s u lt s o f th e s t u d y r e l e v a n t t o c o m p r e h e n s i o n a r e r e p o r t e d h e r e in . T w o g e n e r a l a s p e c t s o f t h e

s u b j e c t s ' r e c e p t i v e l a n g u a g e d e v e l o p m e n t p r o v i d e d t h e f o c i o f t h e p r e s e n t s t u d y : th e i r in i ti a l

e n t r y i n t o t h e s y s t e m ( i. e. h o w t h e y f i rs t c a m e t o r e s p o n d a p p r o p r i a t e l y to u t t e r an c e s ) a n d t h e

e m e r g e n c e o f c o m p e t e n c e ( i. e. t h e g r o w t h o f th e i r s k il ls r e s p o n d i n g t o s i n g l e w o r d s a n d

c o m p l e x u t t er a n c e s ).


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e t h o d

Subjec ts

P a n b a n i sh a , t h e b o n o b o Pan pan i s cus ) , w a s b o r n a t t h e L a n g u a g e R e s e a r c h C e n t e r (L R C )

o n 1 7 N o v e m b e r 1 9 8 5 . S h e w a s r e a r e d b y h e r m o t h e r , M a t a t a , u n t i l s h e w a s 7 w e e k s o f a g e

w h e n h e r c a r e w a s t r a n s f e r r e d t o h u m a n c a r e g i v e r s . P a n p a n z e e , t h e c h i m p a n z e e P a n

troglody tes ) , w a s b o r n a t t h e m a i n s t a t io n o f th e Y e r k e s R e g i o n a l P r i m a t e R e s e a r c h C e n t e r o n

3 1 D e c e m b e r 1 98 5 ( th e f i rs t c h i m p a n z e e b o r n t h e r e a f t e r P a n b a n i s h a s b i r th ) a n d t r a n s f e r r e d

t o t h e L R C o n 8 J a n u a r y 1 98 6. F r o m t h a t d a y t h r o u g h t h e e n d o f th e s t u d y p e r i o d ( O c t o b e r

1 9 8 9) , P a n b a n i s h a a n d P a n p a n z e e w e r e n e a r l y a l w a y s t o g e t h e r a n d in t h e c o m p a n y o f a t l e a s t

o n e h u m a n c a r e g i v e r , e x c e p t f o r t h e l a s t m o n t h s o f th e s t u d y w h e n t h e s u b j e c ts s l e p t w i t h o l d e r

b o n o b o s a t n i g h t. T h e s u b j e c t s f o r m e d c l o s e a t t a c h m e n t b o n d s w i t h t h e c a r e g i v e r s w h o w o r k e d

w i t h t h e m c o n s i s te n t l y .

Rear ing and communica t i ve env i ronmen t

P a n b a n i s h a a n d P a n p a n z e e w e r e r e a r e d t o g e t h e r i n a n e n v i r o n m e n t s i m i l a r t o t h a t i n w h i c h

m a n y h u m a n c h i l d r e n a r e r a i s e d , b u t o n e t h a t t o o k i n t o a c c o u n t t h e a c t i v i t i e s a n d i n t e r e s t s

t o w h i c h y o u n g a p e s a r e p r o n e . E a t i n g , s l e e p i n g , b a t h i n g , c h a n g i n g d i a p e r s , t r a v e l i n g i n

t h e w o o d s a n d c l i m b i n g t r e e s , s o c i a l i n t e r a c t i o n w i t h o t h e r a p e s a n d h u m a n s , a n d q u i e t

w o r k s e s s i o n s ( d u r in g w h i c h v a r i o u s a s s e s s m e n t s m i g h t b e a d m i n i s te r e d ) f il le d th e y o u n g

a p e s d a y .

Th e d i f f e r en t r ou t i ne s o f the day , i n t e r spe r sed w i th occas ion a l tw i s t s o r su rp r i s e s , len t

s t ru c t u r e to th e y o u n g a p e s l i v e s a n d a l s o c r e a t e d a n o p t i m a l e n v i r o n m e n t f o r c o m m u n i c a t i o n

a b o u t o n g i n g a n d u p c o m i n g e v e n t s . S u c h a n e n v i r o n m e n t w a s c o n s i d e r e d c r u c i a l t o t h e

e m e r g i n g t h e o r y o f n o n - h u m a n l a n g u a g e a c q u i s i t i o n t h a t h a d b e e n e s t a b l i s h e d a f e w y e a r s

e a rl ie r w i t h th e b o n o b o s K a n z i a n d M u l i k a ( S a v a g e - R u m b a u g h , 1 99 1 ; S a v a g e - R u m b a u g h e t

al . , 1 9 8 6) . P a n p a n z e e a n d P a n b a n i s h a w e r e i n c l u d e d i n a ll a s p e c t s o f l a b o r a t o r y l if e , a n d e v e r y

e f f o r t w a s m a d e t o c o n v e y i n f o r m a t i o n t o th e m w i t h l e x i g r a m s a s w e l l a s w i th s p o k e n E n g l i sh .

I t w a s i n th i s w a y , t h r o u g h o b s e r v a t i o n o f ad u l t m o d e l s a n d s u b s e q u e n t c o m p r e h e n s i o n o f

u t t e r an c e s , t h a t th e a p e s d e v e l o p e d l a n g u a g e s k il ls .

T h r o u g h o u t t h e s t u d y , c a r e g i v e r s s p o k e t o t h e s u b j e c t s i n E n g l i s h , m u c h a s t h e y w o u l d

s p e a k t o h u m a n i n fa n t s. N o s p e c i f ic p r o c e d u r e s w e r e f o l l o w e d i n s p e a k i n g w i t h t h e in f a n ts , b u t

s p e e c h c o u l d o ft e n b e c h a r a c t e r i z e d a s c h i l d - d i r e c t e d ( a l s o k n o w n a s m o t h e r e s e ) ( B e r k o -

G l e a s o n , 1 9 8 9 ), e s p e c i a l l y w h e n t h e s u b j e c ts w e r e v e r y s m a l l . I n f le c t io n , t o n e o f v o i c e , e y e

c o n t a c t , a n d g e s t u r e s w e r e a l l u s e d a s n e c e s s a r y t o c o m m u n i c a t e t h e d e s i r e d m e s s a g e d u r i n g

da i l y i n t e r ac t i on .

T h e p r in c i p al d i f f er e n c e b e t w e e n c o m m u n i c a t i o n w i t h t h e se a p e s a n d c o m m u n i c a t i o n w i t h

h u m a n i n fa n t s w a s t h at , w h e n e v e r p o s s ib l e , v is u o g r a p h i c s y m b o l s ( ca l le d l e x i g r a m s ) w e r e

u s e d t o s u p p l e m e n t o r c o m p l e m e n t t he E n g l i s h u t t er a n ce s . T h e s e s y m b o l s h a d b e e n c r e a t e d

a n d a s s i g n e d m e a n i n g s d u r i n g e a r l i e r s t u d y w i t h o t h e r a p e s ( R u m b a u g h , 1 9 7 7 ; S a v a g e -

R u m b a u g h e t aL, 1 9 8 6) . E a c h l e x i g r a m w a s g l o s s e d a s t h e e q u i v a l e n t o f a n E n g l i s h w o r d , s u c h

a s m i l k , d o g o r g o o d . A p p r o x i m a t e l y 2 5 6 l e x i g r a m s w e r e a v ai l a b le f o r u s e t h r o u g h o u t t h e

s t u d y p e r i o d . T h e s y m b o l s w e r e a r r a n g e d o n f a c e p l a t e s t h r o u g h o u t t h e l a b b u t t h e y

s o m e t i m e s a l so a p p e a r e d o n i n d i v i d u a l p h o t o g r a p h s o f t h e re f e r e n t s o r w e r e m o u n t e d

i n d i v i d u a l ly in a p p r o p r i a t e p l a c e s ( f o r e x a m p l e , t h e b e d r o o m l e x i g r a m w a s t a p e d t o t h e

b e d r o o m d o o r ) .


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1 26 K A R E N E . B R A K K E a nd E . S U E S A V A G E R U M B A U G H

Data collection procedures

Daily data T h r o u g h o u t t h e 4 y e a r s o f th e c o - r e a r i n g p r o je c t , th e c a r e g i v e r s w h o

a c c o m p a n i e d P a n b a n i s h a a n d P a n p a n z e e t h r o u g h o u t t h e d a y r e c o r d e d v i r t u a l ly a ll in s t a n c e s o f

s y m b o l p r o d u c t io n a n d s y m b o l a n d s p e e c h c o m p r e h e n s i o n b y e a c h s u b j ec t. : T h is w a s d o n e i n

o r d e r t o p r o v i d e a n e x h a u s t i v e r e c o r d o f a l l l a n g u a g e - r e l a t e d b e h a v i o r p r o d u c e d b y t h e a p e s

t h a t w o u l d b e a m e n a b l e t o s e v e r a l t y p e s o f a n a l y s e s r e l e v a n t t o d if f e r e n t a s p e c t s o f l a n g u a g e

a c q u i s it i o n . T h e A p p e n d i x p r o v i d e s e x a m p l e s o f n o t e s c o l l e c te d w i t h t h e s u b j e c ts d u r i n g t h e

s tudy pe r i od .

T h e d a i l y d a t a p r o v i d e d b y t h e a p e s a r e s i m i l a r t o t h o s e o f d i a r y s t u d i e s w i t h h u m a n

c h i l d r e n . E a c h e n t r y w a s h a n d w r i t t e n i n a n o t e b o o k a s s o o n a s p o s s i b l e a f t e r i t s o c c u r r e n c e

a l o n g w i t h c o d e s r e p r e s e n t i n g c o m m u n i c a t i v e f u n c t i o n a n d b e h a v i o r a l c o n c o r d a n c e o r

r e s p o n s e , a s w e l l a s c o n t e x t u a l n o t e s d e s c r i b i n g t h e c o n t e x t o f t h e u t t er a n c e o r r e c e p t i v e

b e h a v i o r . T h e e n t r i e s w e r e l a t e r e n t e r e d o n t o a c o m p u t e r d a t a b a s e , f r o m w h i c h t h e r e c e p t i v e

d a t a r e p o r t e d i n t h is m a n u s c r i p t w e r e e x t r a c te d .

T h e r e c e p t i v e e n t r i e s r e c o r d e d i n t h i s w a y r e p r e s e n t i n s t a n c e s d u r i n g d a i l y i n t e r a c t i o n i n

w h i c h a s u b j e c t s c o m p r e h e n s i o n o f c a r e g i v e r s u t t e r an c e s w a s e v i d e n t . T h e e x c h a n g e s

o c c u r r e d w i t h i n c o m m o n d a i l y r o u t i n e s a n d t h u s w e r e o f t e n c o n t e x t u a l l y a p p r o p r i a t e .

C a r e g i v e r s w e r e , h o w e v e r , i n s t r u c t e d t o r e c o r d o n l y i n s t a n c e s o f c o m p r e h e n s i o n t h a t d i d n o t

a p p e a r d e t e r m i n e d o r b o u n d b y e x t r a l i n g u i st i c c u e s i n c l u d i n g s e tt in g , g e s t u r e o r g l a n c e . T h u s ,

f o r e x a m p l e , a r e q u e s t o f g e t t he s o a p w o u l d n o t b e r e c o r d e d i f t h e u tt e r a n c e w a s

a c c o m p a n i e d b y t h e a d u l t s p o i n t i n g o r l o o k i n g t o w a r d t h e s o a p .

A l s o , b e c a u s e m o s t o f t h e a p e s c a r e g i v e r s h a d w o r k e d w i t h o t h e r a p e s i n s im i l a r c o n d i t io n s

a n d / o r h a d w o r k e d c o n s i s t e n t l y w i t h P a n b a n i s h a a n d P a n p a n z e e t h r o u g h o u t t h e s t u d y p e r i o d ,

t h e y w e r e a w a r e o f r e s p o n s e s t h a t w e r e m a d e f r e q u e n t l y a n d b e c a m e r o u ti n i z ed , a n d d i d n o t

r e c o r d t h e s e b e h a v i o r s a s e x a m p l e s o f c o m p r e h e n s i o n . I n f o r m a t i o n g u i d i n g t h e r e s p o n s e h a d

t o b e j u d g e d a s b e i n g g a i n e d f r o m t h e w o r d s p r e s e n t e d , o r f r o m t e x t u a l r a th e r t h a n c o n t e x t u a l

i n f o r m a t i o n . F o r e x a m p l e , an a p p r o p r i a t e r e s p o n s e t o U s e th e t o w e l a f t e r t a k i n g a b a t h

w o u l d n o t b e r e c o r d e d i f t h a t is e x a c t l y w h a t o c c u r r e d a t t h at s a m e t i m e e v e r y d a y a n y w a y .

H o w e v e r , t h e s a m e r e q u e s t a n d r e s p o n s e u s e d i n a n o v e l p la y s i tu a t io n , f o r e x a m p l e , w o u l d b e

r e c o r d e d .

I n i ti a ll y , f r o m t h e s t a r t o f t h e s u b j e c t s p a r t ic i p a t io n i n e a r ly J a n u a r y t h r o u g h O c t o b e r 1 9 8 6,

c a r e g i v e r s r e c o r d e d o b s e r v a t i o n s o f t h e i n f a n t s b e h a v i o r s t h a t t h e y j u d g e d t o b e i n t e re s t in g o r

s i g n if ic a n t . T h e s e n o t e s w e r e n o t s y s t e m a t i c , b u t t h e r e w e r e s e v e r a l re f e r e n c e s t o t h e s u b j e c t s

c o m m u n i c a t i v e b e h a v i o r t h a t p r o v i d e d a g o o d p o r t r a y a l o f t h e i r e m e r g i n g c o m m u n i c a t i v e

c o m p e t e n c i e s . S t a r t i n g in l a t e O c t o b e r 1 98 6, d a i l y r e c e p t i v e d a t a w e r e c o l l e c t e d s y s t e m a t i c a l l y

f o r b o t h s u b j e c t s t h r o u g h O c t o b e r 1 9 8 9 . T h e d a t a s e t r e p o r t e d i n t h i s m a n u s c r i p t t h u s

r e p r e s e n t s, a s c o m p l e t e l y a s p o s s i b l e , th e c o m p l e t e c o r p u s o f d a i ly d a t a c o l l e c t e d d u r i n g t h i s

3 - y e a r p e r i o d , f r o m t h e f i r s t s y s t e m a t i c r e c o r d i n g o f c l e a r i n s t a n c e s o f c o m p r e h e n s i o n w h e n

t h e s u b j e c t s w e r e l e s s t h a n 1 y e a r o f a g e t h r o u g h t h e e n d o f t h e s t u d y w h e n t h e a p e s w e r e

n e a r l y 4 y e a r s o l d . A s u b s e t o f t h e s e d a t a w a s s e l e c t e d f o r t h e m o r e d e t a i l e d a n a l y s i s o f

s e n t e n c e t y p e s r e p o r t e d i n th i s m a n u s c r i p t ; t h e s e w e r e c o l l e c t e d f r o m J a n u a r y t h r o u g h O c t o b e r

1 9 89 . T h i s p e r i o d r e p r e s e n t s th e e n d o f t h e c o - r e a r in g p r o j e c t, t hu s t h e s u b j e c t s c o m p e t e n c i e s

w o u l d b e a s h i g h l y d e v e l o p e d a s p o s s i b le . T h e i n t e r v a l a l s o c o i n c i d e s w i t h t h e p e r i o d o f f o r m a l

t e s t i n g o f s p o k e n E n g l i s h a n d l e x i g r a m c o m p r e h e n s i o n r e p o r t e d b e l o w .


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P N

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U t t e r a n c e s d i r e c t e d t o t h e s u b j e c t s c o n s i s te d e i t h e r o f E n g l i s h o n l y , o r o f E n g l i s h w i t h

l e x i g r a m a c c o m p a n i m e n t . 3 A l l o f t h e u t t e r a n c e s e n t e r e d i n t h e d a t a b a s e w e r e i n c l u d e d i n t h e

i n it ia l , g e n e r a l a n a l y s i s f o r t h e t w o s u b j e c ts . F o r t h e m o r e d e t a i l e d a n a l y s i s o f s e n t e n c e t y p e s

( t h e 1 9 8 9 d a t a ), o n l y t h o s e e n t r ie s t h a t c o n s i s te d o f m u l t i w o r d u t t e r a n c e s a n d w e r e a m e n a b l e

t o s y n t a c t ic a n a l y s i s w e r e i n c l u d e d . T h e s e u t t e r a n c e s c o u l d b e c a t e g o r i z e d b y s e m a n t i c c o n t e n t

a n d w e r e c o d e d a c c o r d i n g ly ( e .g . A c t i o n - O b j e c t , O b j e c t - A c t i o n - L o c a t i o n , a n d s o o n ).

Single wo rd tes t data . I n a d d i ti o n t o t h e d a i l y re c o r d o f u t t e ra n c e c o m p r e h e n s i o n , a s e c o n d

t y p e o f e v a l u a t i o n w a s c o n d u c t e d d u r i n g t h e l a s t y e a r o f t h e s t u d y p e ri o d . T h i s c o n s i s t e d o f

c o n t r o l l e d t e s t s i t u a t i o n s i n w h i c h s u b j e c t s w e r e a s k e d t o i d e n t i f y a s p o k e n E n g l i s h w o r d b y

s e l e c t in g a m o n g t h r e e l e x i g r a m s p r e s e n t e d in u n i q u e a r r a y s .

T h e s e a s s e s s m e n t s p r o v i d e d a d e c o n t e x t u a l i z e d s i tu a t i o n t h a t c o u l d b e u s e d t o l i t e ra l ly t e s t

o r p r o b e l in k s b e t w e e n s p o k e n w o r d a n d g r a p h i c s y m b o l th a t th e s u b j e c t s h a d f o r m e d i n th e

n a t u r a l la n g u a g e - l e a r n i n g e n v i r o n m e n t d i s c u s s e d e a r l ie r . T h e a p e s w e r e r e q u i r e d t o g e n e r a l i z e

k n o w l e d g e g a i n e d i n d a i l y s o c i a l in t e r a c ti o n s t o v e r y d i f f e r e n t c ir c u m s t a n c e s .

T h e s e a s s e s s m e n t s c a n b e l i k e n e d t o a m u l t i p l e - c h o i c e v o c a b u l a r y t e st . T h e r e s p o n s e s t i m u l i

c o n s i s t e d o f t h e t a r g e t p l u s t w o r a n d o m l y s e l e c t e d a l t e r n a ti v e s . I n b o t h c o n d i t i o n s , a s t a n d a r d

p r o c e d u r e w a s f o l l o w e d ; t h e s u b j e c t s h a d b e c o m e f a m i l i a r w i t h t h i s t e s t s i t u a t i o n i n s i m i l a r

a s s e s s m e n t s o f s p o k e n E n g l i s h a n d p h o t o g r a p h i c s t i m u l i t h e p r e v i o u s y e a r . F o r e a c h t r i a l , E

g a i n e d t h e s u b j e c t ' s a t t e n t io n , t h e n p r e s e n t e d t h e s t i m u l u s w o r d e i t h e r v e r b a l l y o r b y p l a y i n g

a n a u d i o c a s s e t te . E t h e n o p e n e d a t e s t b o o k l e t h e l d b e t w e e n h e r s e l f a n d t h e s u b j e c t s o t h at o n l y

the sub j ec t cou ld s ee t he t h r ee a l t e rna t i ve s p l aced w i th in ( s ee F ig . 1 ) ; E was b l i nd t o t he

p o s i t i o n o f t h e t a r g e t a n d e a c h a l t e r n a ti v e . T h e s u b j e c t w a s t h e n a s k e d t o p o i n t t o o n e o f th e

t h r e e l e x i g r a m s i n t h e t e s t b o o k l e t .

A f t e r t h e s u b j e c t ' s r e s p o n s e , E l o o k e d t o s e e w h e r e S h a d p o i n t e d , j u d g e d w h e t h e r t h e

r e s p o n s e w a s c o r r e c t , a n d p r o v i d e d a p p r o p r i a t e v e r b a l f e e d b a c k ( e . g . ' T h a t ' s r i g h t ' o r ' N o ,

t h a t ' s n o t i t. S o r r y . ' ) p e r h a p s a c c o m p a n i e d b y a h u g . I f S p o i n t e d t o m u l t i p l e s y m b o l s , E a s k e d

' W h i c h o n e ? ' a n d a s k e d f o r a c l e a r , si n g l e r e s p o n s e b e f o r e l o o k i n g a n d j u d g i n g t h e re s p o n s e .

C o n t i n u e d m u l t ip l e r e s p o n s e s w e r e c o u n t e d a s i n c o r r e ct . S u b j e c t s w e r e u s u a l l y a l l o w e d t o e a t

o r p l a y q u i e t ly i n b e t w e e n t ri a ls r e g a r d l e s s o f p e r f o r m a n c e .

Videotaped records.

I n o rde r t o bu t t r e s s t he ea r l y no t e s o f i n i t i a l r e cep t i ve ep i sodes ( i . e .

b e f o r e n o t e s w e r e t a k e n s y s t e m a t i c a l l y ) a n d c o n f i r m t h e c o u r s e o f th e s u b j e c t s ' e a r l y

c o m m u n i c a t i v e d e v e lo p m e n t , v i d e o t a p e s f r o m t h e p e r i o d o f M a y t h r o u g h D e c e m b e r 1 9 86

w e r e r e v i e w e d . T h i r t y - s e v e n ta p e s , ty p i c a l l y r e c o r d e d w e e k l y o r b i w e e k l y a n d e a c h c o n t a i n i n g

1 - 2 h o u r s o f t h e s u b j e c t s' a c ti v it y , w e r e e x a m i n e d f o r e v id e n c e o f e m e r g i n g s p e e c h

c o m p r e h e n s i o n i n t h e y o u n g a p e s .

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Ear ly roo t s o f comprehens ion

T h e f i r s t r e c o r d e d i n s t a n c e s o f r e s p o n s e s t o l a n g u a g e i n e a c h s u b j e c t - - a l b e i t h e a v i l y

s u p p o r t ed b y c o n t e x t a n d t o n e o f v o i c e - - i n v o l v e d r e s p o n s e s t o tw o t y p e s o f re g u l a to r y

u t te r a n c es a t a p p r o x i m a t e l y 6 - 7 m o n t h s o f a ge . T h e s e u tt e ra n c e s w e r e ' n o ' a n d ' c o m e h e r e '.

B o t h w e r e i m p o r t a n t i n e s t a b l i s h i n g b e h a v i o r a l l i m i t s f o r t h e y o u n g a p e s a n d w e r e u s e d

f r e q u e n t l y t h r o u g h o u t t h e d a y . W i t h b o t h d e m a n d s , a c l e a r r e s p o n s e a c r o s s s i tu a t io n s w a s

e x p e c t e d b y t h e a d u l t , a n d i f th a t r e s p o n s e d i d n o t o c c u r t h e re w e r e d i r e c t b e h a v i o r a l

c o n s e q u e n c e s r e l e v a n t t o t h e s i tu a t i o n a t h a n d .


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F i g . 1 . P a n b a n i s h a c o m p l e t e s a v o c a b u l a r y t r i a l b y a ) f i r st l i s t e n i n g t o t h e s p o k e n w o r d p r e s e n t e d v i a

h e a d p o h o n e s , a n d b ) p o i n t i n g to o n e o f t h e a v a i la b l e l e x i g r a m s a f t e r E l i ft s t h e s c re e n . P a n b a n i s h a

k e e p s h e r f i n g e r o n t h e l e x i g r a m u n t i l E c a n s e e a n d r e s p o n d t o h e r c h o i c e .


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COMPREHENSION IN PAN 29

B y A u g u s t 1 9 8 6 it w a s c l e a r th a t c a r e g i v e r s e x p e c t e d P a n b a n i s h a a n d P a n p a n z e e t o r e s p o n d

a p p r o p r i at e l y t o b o t h n o a n d c o m e h e r e , a n d th a t n o n - c o m p l i a n c e w a s c o n s id e r e d d ef ia n c e .

O b s e r v a t i o n s t h a t t h e a p e s l o o k e d a t t h e s p e a k e r a n d s o m e t i m e s v o c a l i z e d , m o v e d a w a y , o r

e n g a g e d i n d i s p l a y b e h a v i o r w h i l e d o i n g s o , s u p p o r t e d th e c a r e g i v e r s c o n c l u s io n s .

F r o m t h i s t i m e o n , P a n b a n i s h a a n d P a n p a n z e e s t a r t e d e m i t t i n g b e h a v i o r s r e l a t e d t o t h e

g r a p h i c s y m b o l s u s e d a r o u n d t h e m . T h e y o f t e n h e l d t h e i r f a c e s v e r y c l o s e a s t h e s y m b o l w a s

b e i n g t o u c h e d b y a n a d u l t. B e t w e e n 6 a n d 8 m o n t h s o f a g e , e a c h i n fa n t w e n t t h r o u g h a p e r i o d

d u r i n g w h i c h t h e y f r e q u e n t l y t o u c h e d a s y m b o l i m m e d i a t e l y a f t e r a c a r e g i v e r h a d t o u c h e d it.

S u c h b e h a v i o r s s u g g e s t e d t h a t t h e a p e s w e r e s t a rt i n g t o a t te n d v e r y c l o s e l y to c o m m u n i c a t i v e

u t t e rances , ev en i f t hey d id no t ye t demo ns t r a t e t ha t t hey un de r s tood exa c t l y wha t w as be ing s a id .

O c c a s i o n a l r e s p o n s e s t o n o n - r e g u l a t o r y w o r d s b e g a n t o a p p e a r w h e n t h e s u b j e c t s w e r e 8 - 9

m o n t h s o f a g e . O n s e v e r a l o c c a s i o n s d u r i n g t h i s p e ri o d , P a n b a n i s h a e m i t t e d a v o c a l ( e .g . f o o d -

b a r k ) o r b e h a v i o r a l r e s p o n s e t o m i l k o r g o , s o m e t i m e s r e s p o n d i n g to th e u se o f t h e l e x i g r a m

a n d s o m e t i m e s t o t h e s p o k e n E n g l i s h a l o n e .

P a n p a n z e e , s l i g h tl y y o u n g e r t h a n th e b o n o b o , c o n t in u e d t o a p p e a r m o r e d e p e n d e n t o n

c o n t e x t u a l s u p p o r t t h a n P a n b a n i s h a d u r i n g t h i s t i m e , s o m e t i m e s c h a n g i n g h e r b e h a v i o r i n

r e s p o n s e t o n e w i n f o r m a t i o n r e g a r d i n g f a m i l i a r r o u t in e s . T h e d a i l y n o t e s f r o m 6 A u g u s t 1 9 8 6

c o n t a i n t h e f o l l o w i n g d e s c r i p t io n : A s w e v i s i t [t he ] d o g s , P a n z e e s e e m s to a n t ic i p a t e w h e n I

t o u c h O P E N , o v e r a n d o v e r , t h a t w e a r e g o i n g t o l e t t h e m o u t a s w e h a v e t h e l a s t t w o d a y s .

H e r h a i r [ p i lo e r e c ts ] a n d s h e i m m e d i a t e l y [ r u ns ] a n d [ h o ld s ] t ig h t l y to K e l l y . ( P a n p a n z e e - -

k n o w n a s P a n z e e t o h e r c a r e g i v e r s - - w a s j u s t g e tt in g to k n o w t h e d o g s a t t h is t im e a n d w a s

appa ren t l y s t i l l a f r a id o f t hem. )

S y m b o l i c m a r k e r s w e r e r e g u l a r l y i n s e r t e d i n t o t h e o n g o i n g s t r e a m o f i n t e r a c t i o n w i t h

P a n b a n i s h a a n d P a n p a n z e e , s i g n a l i n g i m p o r t a n t t r a n s i t i o n p o i n t s i n t h e a c t i v i t y . T h e u s e o f

s y m b o l s a s m a r k e r s t o a n n o u n c e p a r t s o f ro u t i n e s h a d a p r e d i c t i v e v a l u e a n d l e t t h e i n fa n t a p e s

a n t i c i p a t e u p c o m i n g e v e n t s . T h i s a l l o w e d t h e i n d i v i d u a l t o m a k e a p p r o p r i a t e r e s p o n s e s ( s u c h

a s h o l d i n g a n a d u l t t i g h tl y ) a n d e x e r t s o m e c o n t r o l o v e r w h a t h a p p e n e d t o h er . C o n t e x t u a l

c u e s - - t h e t e m p o r a l a n d p h y s i c a l s e tt in g , t h e c a r e g i v e r s p o s t u re , g e s t u re s a n d v o c a l

i n t o n a t i o n - - m a y h a v e s u p p o r t ed t h e i n f a n t s i n te r p re t at io n o f th e m e s s a g e t o s o m e d e g r e e, b u t

c e r t a i n l y d i d n o t e t e rm i n e it. T h e c a r e g i v e r s t o p ic e a s i l y c o u l d h a v e b e e n a n o t h e r a c t i v it y o r

o b j e c t a p p r o p r i a t e t o t h e s a m e s e t t in g .

D u r i n g t h e l a s t f e w m o n t h s o f 1 9 8 6 c h a n g e s i n th e b e h a v i o r o f b o t h c a r e g i v e r s a n d t h e a p e s

t h e m s e l v e s b e c a m e a p p a re n t . P a n b a n i sh a a n d P a n p a n z e e n o w e n g a g e d i n n o t ic e a b l y im p r o v e d

v i s u a l a t te n t i o n t o t h e a d u l t s b e h a v i o r a s t h e c a r e g i v e r p r o c e e d e d t h r o u g h t h e s e q u e n t i a l s t e p s

i n v o l v e d i n t a l k i n g a b o u t a n d c a r r y i n g o u t r o u t i n e s . J o i n t a t t e n t i o n a l a c t i v i t i e s - - i n c l u d i n g

l o o k in g a t o b je c t s a n d e v e n p ic t u re b o o k s - - b e c a m e m o r e c o m m o n t h a n i n e a r li e r m o n t h s , w i t h

t h e i n f a n t a p e s o f t e n t a k i n g a n a c t i v e r o l l ( b y p o i n t i n g t o p h o t o s i n a b o o k o r m o v i n g a

c a r e g i v e r s h a n d t o w a r d a t o y , f o r e x a m p l e ) .

F o r t h e i r p a rt , c a r e g i v e r s b e c a m e m o r e d e m a n d i n g o f t h e s u b j e ct s , w a i t i n g u n ti l t h e y h a d t h e

s u b j e c t s f u ll a tt e n t io n b e f o r e p r o c e e d i n g w i t h c o m m u n i c a t i o n s o r a c ti v i ti e s o r a s k i n g th e

sub j ec t s t o f u l f il l pa r t s o f the rou t i ne s t hem se lves . I f t he sub j ec t s had d i f f i cu l t y do in g so ,

c a r e g i v e r s p r o v i d e d j u s t e n o u g h g u i d a n c e t o a c h i e v e t h e g o a l a t h a n d .

I t w a s a t t h is t i m e t h a t P a n b a n i s h a s a n d P a n p a n z e e s r e c e p t i v e s k il ls b e g a n t o b r o a d e n . B y

t h e e n d o f J a n u a r y 1 9 8 7, o n e o r b o t h i n f a n t s h a d a p p r o p r i a t e l y r e s p o n d e d a t l e a s t o n c e t o


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' c h a s e ' , ' b i t e ' , ' o r a n g s ' ( o r a n g u t a n s ) , ' t i c k l e ' , ' o p e n ' , ' b y e ' , ' b u g ' , ' g r a p e ' , ' K e l l y ' , ' t - r o o m ' ,

' r u b b e r b a n d ' , a n d ' w a t e r ' . T h e s e r e s p o n s e s a l l o c c u r r e d w i t h i n s o m e c o n t e x t , n a t u r a l l y , b u t

c a r e g i v e r s j u d g e d n o n e t o b e d e t e r m i n e d o r b o u n d b y t h e c o n t e x t i n w h i c h t h e y o c c u r r e d .

A f t e r t h i s p o i n t , b o t h s u b j e c t s c o n t i n u e d t o r e s p o n d a p p r o p r i a t e l y t o a g r e a t e r v a r i e t y o f

u t t e r a n c e s , w i t h i n c r e a s i n g l y g r e a t e r d i s s o c i a t i o n f r o m c o n t e x t u a l s u p p o r t . H o w e v e r , a s w i l l

b e c o m e e v i d e n t in s u b s e q u e n t s e c t io n s o f t h is m a n u s c r i p t , t h e b o n o b o P a n b a n i s h a c o n s i s t e n t l y

d e m o n s t r a t e d g r e a t e r r e c e p t i v e u n d e r s ta n d i n g o f s y m b o l s a n d s p e e c h th a n d i d t h e c h i m p a n z e e

Panp anze e , bo th w i th in t he con t ex t o f da i l y ac t i v i t y and i n con t ro l l ed t e s t s i tua t i ons . The

c h i m p a n z e e n e v e r t h e l e s s d i d e v i d e n c e c o m p r e h e n s i o n o f s e v e r a l w o r d s a n d s e n t e n c e s u s i n g

t h e d i f fe r e n t m e a n s o f a s s e s s m e n t .

C o m p r e h e n s i o n o f c o m p l e x u t t e ra n c e s i n d a i l y i n te r a c t io n

D u r i n g t h e 3 - y e a r p e r i o d i n w h i c h u t t e r a n c e s w e r e r e c o r d e d , t h e b o n o b o P a n b a n i s h a

r e s p o n d e d a p p r o p r i a t e ly t o 2 6 16 o f 2 8 5 2 t o ta l r e c o r d e d u t te r a n c e s (9 2 ) w h i l e t h e c h i m p a n z e e

P a n p a n z e e r e s p o n d e d a p p r o p r i a t e l y t o 1 5 9 6 ( 8 1 ) o f t h e 1 8 25 u t t e r a n c e s t h a t w e r e d i r e c te d t o

h e r a n d r e c o r d e d . A s T a b l e 1 s h o w s , t h e a c c u r a c y r a t e f o r e a c h s u b j e c t r e m a i n e d c o n s i s t e n t

o v e r th e 3 - y e a r p e r io d . T h i s s u g g e s t s t h a t a t s o m e l e v e l t h e c a r e g i v e r s w e r e s e n s i t i v e to t h e

c h a n g i n g i n d i v id u a l c o m p e t e n c i e s o f t h e s u b j e c ts a n d m a d e r e q u e s t s o f th e m a c c o r d i n g l y .

P a n b a n i s h a r e c e i v e d a p p r o x i m a t e l y t w i ce a s m a n y s e n te n c e s a s P a n p a n z e e d u r i n g e a c h o f

t he f i rs t 2 yea r s o f t he s t udy ; th i s a lso sugges t s t ha t the ca r eg ive r s ' exp ec t e d ' m ore o f t he bono bo

t h a n o f th e c h i m p a n z e e . D e s p i t e th e i n c r e a s e d d e m a n d s , t h e b o n o b o c o n s i s t e n t l y r e s p o n d e d

wi th g r e a t e r a ccu racy t han d id he r ch im pan zee co un t e rp a r t ()~2 [1, 4655 ] = 121 .52 , p < 0 .01 ) . '

Table 1. Utterances presented to Panbanisha and Panpanzee 1986-1989

Number correct Total number given Percentage correct

Panbanisha

1986-1987 671 719 93

1988 1268 1406 90

1989 663 712 93

Total 2602 2852 92

Panpanzee

1986-1987 298 365 82

1988 593 718 83

1989 578 735 79

Total 1469 1818 81

B e c a u s e t h e d i f f e r e n c e b e t w e e n t h e s u b j e c t s ' c o m p e t e n c i e s w a s a p p a r e n t , a s u b s e t o f

s en t ences co l l e c t ed i n 1989 was ana lyzed i n f u r t he r de t a i l i n o rde r t o l oca t e pos s ib l e sou rce s

o f d i s s i m i l a r i t y . S e n t e n c e s w e r e c o d e d w i t h r e g a r d t o t h e n a t u r e a n d n u m b e r o f ' k e y t e r m s '

i nc luded . T hes e cons i s t ed o f a c t ion , agen t , ob j ec t , r e c ip i en t , and l oca t i on t e rm s tha t t he

s u b j e c t s w o u l d n e e d t o u n d e r s ta n d i n o r d e r to r e s p o n d a p p r o p r i a t e ly . A t o t al o f 7 1 3 u t t e r a n c es

w e r e r e c o r d e d f o r P a n b a n i s h a f r o m J a n u a r y 1 9 89 t h r o u g h O c t o b e r 1 98 9. O f t h e s e, 5 1 3 m e t th e

c r i t e r i a f o r i nc lu s ion i n t he cu r r en t ana ly s i s ( i . e . en t i r e u t t e r ance w i th mu l t i p l e ' k ey t e rms '

r e c o r d e d , s p e c i f i c a c t io n r e s p o n s e r e q u i r e d , s p e e c h a n d l e x i g r a m i n p u t o n l y ) . O f th e 7 3 8

u t t e r a n c e s p r e s e n t e d t o P a n p a n z e e d u r i n g t h e s a m e p e r i o d 4 7 7 m e t t h e c r i t e r i a a n d w e r e

s i m i l a r l y a n a l y z e d . M o s t o f t h e u t t e r a n c e s t h a t w e r e d r o p p e d w e r e r e c o r d e d a s s i n g l e - t e r m


11/28

OMPREHENSION INPAN 3

u t t e r an c e s s u c h a s ' t i c k l e ' o r ' b o w l ' . B e c a u s e m o r e o f t h e s e w e r e r e c o r d e d f o r P a n p a n z e e , h e r

d a t a s e t w a s i n f l u e n c e d s l i g h t ly m o r e t h a n P a n b a n i s h a ' s b y t h e i r e x c l u s i o n f r o m t h e a n a l y s is .

D u p l i c a t e ( in b o t h w o r d c o n t e n t a n d m o d a l i t y ) u t te r a n c e s w e r e a l s o d r o p p e d f r o m t h e a n a l y s is .

T h e r e m a i n i n g 4 8 3 u n i q u e s e n t e n c e s p r e s e n t e d to P a n b a n i s h a a n d t h e 3 81 u n i q u e s e n t e n c e s

p r e s e n t e d t o P a n p a n z e e w e r e t h e n a n a l y z e d b y i n p u t m o d a l i t y ( E n g l i s h o n l y v s E n g l i s h p l u s

l e x i g r a m ) a n d s e n t e n c e t y p e ( e . g . a c t i o n - o b j e c t , o b j e c t - a c t i o n - l o c a t i o n ) . T h i s w a s d o n e t o

d e t e r m i n e w h e t h e r w e c o u l d i d e n ti f y s o m e o f t h e d i ff e re n t c o m p o n e n t s o f l a n g u a g e

c o m p r e h e n s i o n t h a t a f f e c t e d th e p e r f o r m a n c e o f e a c h s u b j e c t.

Input modal i ty . O f t h e 4 8 3 u n i q u e u t t e r a n c e s p r e s e n t e d t o P a n b a n i s h a , 3 6 2 ( 7 5 ) u s e d

l e x i g r a m p l u s E n g l i s h i n p u t , w h i l e 1 21 w e r e i n s p o k e n E n g l i s h o n l y . T h r e e h u n d r e d a n d

e i g h t e e n ( 8 3 ) o f P a n p a n z e e ' s 38 1 s e n t e n c e s w e r e in E n g l i sh a n d le x i g r a m ; o n l y 6 2 w e r e

p r e s e n t e d i n E n g l i s h o n l y ) T h u s , t h e c a r e g i v e r s g a v e P a n p a n z e e a l o w e r p r o p o r t i o n o f

s e n t e n c e s i n E n g l i s h o n l y ( Z2 [ 1 , 8 6 3 ] = 9 . 7 2, p < 0 . 0 1 ). I n s o d o i n g t h e y p l a c e d f e w e r d e m a n d s

o n h e r s p e e c h c o m p r e h e n s i o n s k i l l s a n d p r o v i d e d r e l a t i v e l y m o r e l e x i c a l a s s i s t a n c e w i t h t h e

v i s u o g r ap h i c s y m b o l s .

N e v e r t h e l e s s , P a n b a n i s h a a g a i n a p p r o p r i a t e l y r e s p o n d e d t o r e q u e s t s f o r a c t i o n m o r e o f t e n

t h a n d i d P a n p a n z e e , r e g a r d l e s s o f w h e t h e r u t t e r a n c e s w e r e p r e s e n t e d i n E n g l i s h a l o n e o r

E n g l is h w i th l e x i g r a m a c c o m p a n i m e n t . R e s u l t s b y i n p u t m o d a l i ty a r e s u m m a r i z e d i n T a b l e 2 .

P a n b a n i s h a r e s p o n d e d a p p r o p r i a t e l y o n 9 0 o f E n g l i s h o n l y s e n t e n c e s a n d o n 9 5 o f E n g l i s h

p l u s l e x i g r a m s e n t e n c e s . P a n p a n z e e r e s p o n d e d a p p r o p r i a t e l y o n 7 8 o f E n g l i s h o n l y

s e n t e n c e s a n d 7 3 o f E n g l i s h p lu s l e x i g r a m s en t e n c e s. T h u s , g i v e n th a t c a r e g i v e r s w e r e

sens i t i ve t o t he capab i l i t i e s o f t he sub j ec t s and ad ju s t ed t he i r i npu t a pr ior i e a c h s u b j e c t

r e s p o n d e d e q u a l l y w e l l t o E n g l i s h s e n t e n c e s w i t h o r w i t h o u t l e x i g r a m s u p p l e m e n t s . T h e

b o n o b o , h o w e v e r , h a d o n l y a f e w i n a p p r o p r i a t e r e s p o n s e s w h i l e t h e c h i m p a n z e e h a d d i f fi c u l ty

w i t h a b o u t o n e o u t o f e v e r y f o u r r e q u e s t s m a d e o f h e r .

Tab le 2. Comprehensionof different input m odalities

N um ber c o r r e c t N u m b e recorded Percentageorrect

Panbanisha

Eng lish on ly 109 121 90

English + lexigram 342 362 94

Panpanzee

English only 49 62 79

English + lexigram 229 318 72

Note: one utterance directed to Panpanzee was presented via lexigram only, with no speech

(she w as partially correct; see text).

R e c e p t i v e l a n g u a g e c o m p e t e n c y r e f le c t s th e i n t e r p l a y o f s e v e r a l s e n s o r y , c o g n i t i v e , a n d

m o t o r s y s t e m s . T h e d i f f e r e n t i a l r a t e s o f a p p r o p r i a t e r e s p o n s e s b e t w e e n s u b j e c t s c o u l d a r i s e

f r o m s e v e r a l fa c to r s. F o r e x a m p l e , P a n p a n z e e m a y s i m p l y n o t h a v e u n d e rs t o o d a s m a n y w o r d s

a s t h e b o n o b o , h e r re s p o n s e s m a y h a v e b e e n m o r e c o n t e x tu a l ly b o u n d t h an P a n b a n i s h a ' s , s h e

m a y h a v e h a d t r o u b l e w i t h e x t r a c t i n g i m p o r t a n t i n f o r m a t i o n f r o m l o n g c o m p l e x s t r i n g s o f

w o r d s , o r s h e m a y h a v e b e c o m e d i s t r a c t e d m o r e e a s i l y a n d t h u s w o u l d n o t a t t e n d c l o s e l y t o

the u t t e r ances d i r ec t ed t o he r .

A l t h o u g h h e r c a r e g i v e r s d i d c o n s i d e r P a n p a n z e e t h e m o r e d i s t r a c ti b l e o f th e t w o s u b j e c t s ,

t h i s t ype o f a t t en t i ona l d i f f e r en ce d id no t l end i t s e l f t o d i r ec t ana ly s i s w i th t h i s da t a ba se . O the r


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1 32 K A R E N E . B R A K K E a nd E . S U E S A V A G E R U M B A U G H

factors, however, were exa min ed by analyz ing this group of sentences from 1989 as well as

more structured vocabulary tests administered throughout the study period.

Sentence type and complexity

In order to determine whether sentence type or complexity

affected Panpanzee's responses, caregiver utterances were categorized according to

grammatical form. The sentence types along with correct, incorrect, and partially correct

responses for each subject are presented in Table 3. Percentage of sentences given in each

syntactic category is depicted in Fig. 2; the percentage correct r esponse for each sentence type

is sho wn in Fig. 3.

Table 3. Sentencecomprehensionby grammatical form January 1989-October 1989

Panbanisha Panpanzee

Sentence type* Ct I PC NR C I PC NR

Two-term

AO 221 13 3 136 33 6 5

OA 4 5

OL 19 1 19 1 2

AL 42 1 21 2 2

AR 13 1 8

Three-term

AOL 77 4 2 2 37 16 9 3

OAL 7 10 6

ALO 14 9 2 1

AOR 10 1 1 5 1 1

ARO 12 1 12 6 1 1

ARL 6 2 1

Other 2__6 2 1__33

Totals 451 23 7 2 278 69 25 9

483 Total sentences 384 Total sentences

* 'Key term' codes: A = Action, O = Object, L = Location, R = Recipient.

t Responsecodes: C = Correct response, I = Incorrect response, PC = Partially correct response,

NR = No response/ignore.

The distribution of sentence types was similar for the two subjects. Approximately half of

all sentences given were in Act ion- Obje ct form, such as ' GIV E BOW L' or 'Slap the ball'

(lexigrams are indicated by all-caps). Another 17 for each subject were Act ion -Ob jec t-

Location, for example, ' Take the orange to the group room.' Most other sentences comprised

two- or three-term combina tions of action, object, location, and recipient. Sente nce types that

were presented only rarely, such as 'O bje ct- Loc ati on- Act ion ' or four-term utterances such as

'Action-Recipient-Object-Location ' , are represented in the 'Other' category.

Panbani sha responded appropriately to at least 92 of each sentence type (or group of

related sentence types): her performance did not appear affected by the grammatical form or

lengt h of the utterance. In fact, the low num ber of totally inappropri ate responses made by the

bonob o precluded any log -li near analysis of the effect of sentence type because expected cell

values could not be raised to appropriate levels, even when different sentence types were

combined.


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C O M P R E H E N S I O N I N

P N

33

26

2 0 0

1 8 0

1 0 0

6 0

0

m

b

e

r

R

e

o

o

r

d

e

d

A O O L A L A R A O L O A L A L O A R O A O R

O t h e r

t t e r ance

Type

P a n b a n l e h a ~ P a n p a n z e e

Fig. 2. Total number of sentences that were presented to Panbanisha and Panpanzee that fit the criteria

for inclusion see text). These sentences comprised the 1989 subset of utterances. The proportional

distribution of the different sentence types was very similar for the two subjects.

P

e

r

o

@

n

t

C

o

r

r

e

O

t

1 0 0

8 0

6 0

4 0

2 0

0

A O O L A L A R A O L O A L A L O A R O A O R T o ta l

t t e r ance Type

P a n b a n l a h a ~ P a n p a n z e e

Fig. 3. Percentage of appropriate responses made to the different sentence types by the two subjects.

Panbanisha responded well to all grammatical categories, but Panpanzee had significantly more

difficulty with three-term sentences and Action-Object utterances than with the other two-term

categories.


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134 KAREN E. BRAKKE and E. SUE SAVAGE-RUMBAUGH

Panpanzee, on the other hand, performed extremely well in response to some sentence types

but had many errors with others. Her percentage correct ranged from 57

(Action-Object-Location) to 90 (Action-Recipient). In order to determine the significance

of differences between sentence types, Panpanzee' s data were submitted to log- linear analysis.

Because of the low number of sentences included in some categories, some sentence types

were grouped together in order to facilitate this analysis. By reducing the number of

categories, expected values for the remaining cells were raised to levels considered acceptable

for such analysis (Tabachnick and Fidell, 1989). The groupings were made based on types and

number of key terms included and are presented in Table 4. The 'other' category was dropped

from this analysis because it contained a disjoint group of sentences and its inclusion as a

category was meaningless.

Table 4. Pan panzee s performance by sentence type: log-li near analysis results

Sentence Observed Expected Adjusted

types frequency frequency residual

Correct responses

AO + OA 141.00 134,55 1.522

OL 19.00 16,00 1.482

AL + AR 29.00 24,00 2.050

OAL + ALO 19.00 20,36 -0.6 02

AOR + ARO 17.00 19,64 -1. 184

AOL + ARL 39.00 49.45 -3.1 58

Other responses

AO + OA 44.00 50.45 -1.5 22

OL 3.00 6,00 -1.4 82

AL + AR 4.00 9.00 -2.050

OAL + ALO 9.00 7,64 0.602

AOR + ARO 10.00 7,36 1.184

ARL + AOL 29.00 18,55 3.158

Likel ihood ratio chi-square = 16.97638, df = 5, p = 0.005.

Log- linear analysis supports the conclusion that the chimpanzee' s performance varied as a

function of sentence type (G2 [5, 381] = 16.98, p < 0.01). Review of adjusted residuals

indicates that she responded relatively well to Action-Location and Action-Recipient

utterances (e.g. 'GO SCRUBBY-PINE-NOOK' or 'WASH KAREN') and had particular

difficulty with the cluster of Action-Object-Location and Action-Recipient-Location

utterances (almost wholly attributable to AOL errors, e.g. 'CARRY the STRING to the

GROUP ROOM') No other adjusted residuals were significant, although the direction of the

residuals for correct responses to all two-term sentence types were positive while the residuals

for all three-term categories were negative.

Three of the four sentence types that Panpanzee had the most difficulty with (as indexed by

percentage correct) were three-term sentences. Even if the action term of such an utterance is

relatively simple, such as 'get' or 'give', there still remain at least two additional terms that

must be remembered and integrated as the action is carried out. Panpanzee's response patterns

indicate that she may have had difficulty with one or more of the steps required to remember

and/or coordinate the multiple terms in her responses. A review of the contextual notes

accompanying the entries reveals that Panpanzee often acted on the appropriate object but took

it to the wrong location or performed an inappropriate but familiar action on that object. For


15/28


e x a m p l e , a f t e r re t r i e v in g a s w e e t p o t a t o f r o m t h e r e f r i g e r a t o r P a n p a n z e e c a r r ie d i t to t h e s i n k

a n d w a s h e d i t ( a s is o f t e n d o n e ) i n s t e a d o f p u tt i n g i t i n th e m i c r o w a v e o v e n a s r e q u e s te d . T h i s

p a t t e r n u s u a l l y d i d n o t o c c u r i f P a n p a n z e e a l r e a d y p o s s e s s e d t h e o b j e c t i n q u e s t io n o r i f i t w a s

i m m e d i a t e l y a v a i l a b l e ; s h e t h e n c o m p l e t e d t h e r e q u e s t a p p r o p r i a t e l y . H e r b e h a v i o r s u g g e s t e d

d i f f ic u l t y in r e m e m b e r i n g o r r e l a ti n g a l l o f th e c o m p o n e n t s o f th e u t t e ra n c e . I t s e e m e d t h a t i f

t h e l i n g u i s t i c i n f o r m a t i o n b e c a m e t o o c o m p l i c a t e d , P a n p a n z e e f e l l b a c k o n h e r e x t a n t

k n o w l e d g e o f ty p i c a l r o u ti n e s t o c o m p l e t e w h a t s h e t h o u g h t w a s a n a p p r o p r i a t e a c ti o n . In o t h e r

w o r d s , w h e n c h a l l e n g e d , c o n t e x t u a l i n f o r m a t i o n o v e r r o d e v e r b a l o r t e x t u a l i n f o r m a t i o n f o r

P a n p a n z e e .

T h e s e d i f f i c u l t i e s d o n o t a p p e a r t o b e r e s p o n s i b l e f o r t h e c h i m p a n z e e ' s e r r o r s i n t h e

A c t i o n - O b j e c t c a t e g o r y . M o s t o f t h e s e r e q u e s t s w e r e s y n t a c t i c a l l y r e l a t i v e l y s i m p l e . I n s t e a d ,

t h e h i g h n u m b e r a n d v a r i e t y o f s u c h s e n t e n c e s p r e s e n t e d i n d i c a te s t h a t s o m e o t h e r f a c t o r s u c h

a s v o c a b u l a r y s i z e m a y h a v e c o n t r i b u t e d t o h e r e r r o r s . D a t a f r o m c o n t r o l l e d t e s t s o f s i n g l e -

w o r d c o m p r e h e n s i o n , r e p o r t e d b e l o w , a r e c o n s i s te n t w i t h t h e r e su l t s o f t h e s e n t e n c e a n a l y s i s

a n d i n d i c a t e t h a t v o c a b u l a r y s i z e m a y i n d e e d h a v e c o n t r i b u t e d t o h e r l o w e r l e v e l o f a c c u r a c y

i n r e s p o n d i n g t o u t t e ra n c e s m a d e d u r i n g r e g u l a r d a i l y i n te r a c ti o n .

Table 5. Single-word test results

Number of words meeting Number of trials

Total 75 criterion correct

words

Condition tested Panban Panzee Panban Panzee

English to lexigram 217 179 79 603/733 365/795

(82 ) (36 ) (82 ) (46 )

Audiotaped English 76 71 39 224/247 171/277

to lexigram (93 ) (51 ) (91 ) (62 )

English to lexigram 8 (Pb) 7 18 22125 61/78

(retest) 23 (Pz) (88 ) (78 ) (88 ) (78 )

Tests of single w ord comprehension

A s s h e d i d w i t h t h e u t t e r a n c e s p r o v i d e d i n n a t u r a l s e t t i n g s , t h e b o n o b o P a n b a n i s h a

p e r f o r m e d c o n s i s t e n t l y w e l l o n t h e b l i n d r e c e p t i v e v o c a b u l a r y t e s t . P a n p a n z e e h a d m o r e

d i ff ic u l ty a l t h o u g h s h e p e r f o r m e d w e l l a b o v e c h a n c e l e v e l s a n d h e r v o c a b u l a r y a p p e a r e d t o b e

i n c r e a s i n g i n s i z e t h r o u g h o u t t h e s t u d y . T h e r e s u l t s o f th e t w o t e s t c o n d i t i o n s a n d t h e a g e s o f

t h e s u b j e c ts d u r i n g e a c h a r e p r e s e n t e d in T a b l e 5 a n d a r e s u m m a r i z e d b e l o w .

English to lexigram.

E n g l i s h t o l e x i g r a m t e s t i n g b e g a n i n J a n u a r y 1 9 8 9 . A t o t a l o f 2 1 7

s y m b o l s w e r e t es t ed w i t h P a n b a n i s h a a n d P a n p a n z e e . T h e b o n o b o P a n b a n i s h a w a s c o r r e c t o n

8 2 o f t h e t ri a ls p r e s e n t e d t o h e r a n d m e t t h e 7 5 c r i te r i o n ( a t l e a s t t h r e e o u t o f f o u r c o r r e c t )

o n 1 7 9 o f t h e w o r d s ; s h e w a s 1 0 0 c o r r e c t ( a t l e a s t t h r e e o f th r e e c o r re c t ) o n 1 4 0 o f t h e se .

P a n p a n z e e , t h e c h i m p a n z e e , s e l e c te d t h e c o r r e c t l e x i g r a m o n o n l y 4 6 o f t h e t ri a ls , m e e t i n g

c r i te r i o n o n 7 9 o f t h e s y m b o l s . S h e w a s 1 0 0 c o r r e c t o n 3 3 o f t h e s e. T a b l e 6 l is ts th e w o r d s

i n e a c h s u b j e c t ' s r e c e p t i v e v o c a b u l a r y a s d e t e r m i n e d b y t h i s m e a n s .


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KAREN E. BRAKKEand E. SUE SAVAGE-RUMBAUGH

Table 6. English --~ lexigram receptive vocabularies, 1989

Panbanisha

Apple Groom Nail

Austin Group Room No

Backpack Gully Gushers Noise

Bad Hamburger Noodles

Ball Hammer Observation Room

Balloon Happy Oil

Banana Hat Onion

Bedroom Hide Open

Bite Hilltop Orange

Blackberries Honeysuckle Orange drink

Blanket Hot Orange juice

Blueberries Hotdog Orangutan

Book Hug Outdoors

Bowl Hurt Paint

Bubble Ice Panbanisha

Bug In Panzee

Bunny Jello Paper

Butt Jelly Peaches

Butter Juice Peanut

Cabinet Kanzi Peas

Camper Cabin Karen Perrier

Can opener Keepaway Phone

Car Kelly Pillow

Carrot Key Pineapple

Carry Kiwi Plastic bag

Cereal Knife Play

Chase Koolaid Popsicle

Cheese Krista Potato

Cherry Lana Privet berry

Chow Lemon Quiet

Clay Lemonade Rain

Clover Lever Raisin

Coffee Light Refrigerator

Coke Lighter River

Cold Liz Rubber band

Collar Log Cabin Salt

Colony Room Lookout Point Sandpile

Crisscross Comers Mary Ann Scare

Dog Matata Scrubby Pine Nook

Egg Melon Sherman

Fire Middle Test Room Shirt

Flatrock Midway Shop

Go Milk Shot

Good Money Slap

Goodbye Monster Sleep

Gorilla Mouth Snake

Grab Mushroom Soap

Grapes Mushroom Trail Sour cream

Spin Surprise Treehouse

Spoon Sweet potato Turtle

Staff Office T-room TV

Stethoscope Throw Umbrella

Stick Tickle Vacuum

Straw Tomato Velvet plant

Strawberries Toolroom Vitamin

String Toothbrush Wash

Sue Toothpaste Water

Sue s Gate Towel Wipes


17/28

CO MPREH EN SIO N IN P N

137

S u e s O f f i c e T o y Y e s

Sugar Tr as h Y ogu r t

Sugarcane Tree

P a n p a n z e e

A p p l e I c e R a i s i n

A us t i n Je anni ne R o c k

B a d K i w i S a l t

B a l l o o n K o o l - a i d S c a r e

Banana Lana Shirt

Bi t e L i ght e r S n a k e

Blackberries M M ' s S o a p

Blueberries M elon Sparkler

B o o k M i d d l e T e s t R o o m S t ic k

B u g M i d w a y S tr aw

Bu nny Mus hr oom St r aw ber r y

C h a s e N o S t r i n g

C h ow O bs e r vati on R oo m Sugar

C l ove r O i l Sugar c ane

C o f f e e O n i o n S w e e t p o ta to

C o k e O p e n T i c k l e

C r i s s c r os s C om e r s O r ange Tom at o

D o g O r ange j u i c e Toot hbr ush

Fire Perrier W ater

Fo ot Pineapple Yogurt

G o o d b y e P l a y

G r o o m P o p s i c l e

H i d e P o t a t o

H o n e y s u c k l e P r i v e t b e r r y

H ur t Q ui e t

T h i s t e s t p r o v i d e d t h e c l e a r es t d e m o n s t r a t i o n th a t P a n b a n i s h a ' s r e c e p t i v e v o c a b u l a r y w a s

m o r e e x t e n s i v e t h a n P a n p a n z e e ' s . I t is e q u a l l y i m p o r ta n t , th o u g h , t o n o t e t h at t h e 3 - y e a r - o l d

c h i m p a n z e e e x h i b i te d c o m p r e h e n s i o n o f n e a r ly 8 0 s p o k e n w o r d s u n d e r c o n t r ol le d ,

d e c o n t e x t u a l i z e d t e st c o n d i t i o n s , a p e r f o r m a n c e t h a t f a r e x c e e d s t h at o f o t h e r Pan trogl odytes

s i m i l a r ly t es t e d ( S a v a g e - R u m b a u g h , 1 9 8 6 ). T e s t s w i t h S h e r m a n a n d A u s t in , e v e n a s a d u l ts ,

y i e l d e d o n l y c h a n c e p e r f o r m a n c e i n r e s p o n s e t o a n y s p o k e n w o r d s ( C e r u t t i e t aL 1 9 9 3 ) .

A ud i o taped En g l i sh to lex ig ram. I n o r d e r t o f u r t h e r e n s u r e t h a t t h e p e r f o r m a n c e o f t h e s e

s u b j e c ts w a s n o t d e p e n d e n t o n f e a t u r e s o f t h e s it u a t io n s u c h a s h o w t h e ex p e r i m e n t e r w a s

s a y i n g t h e t ar g et w o r d , s e v e r a l w o r d s w e r e s u b s e q u e n t l y e v a l u a t e d u s i n g a u d i o t a p e d E n g l i s h

p r e s e n t e d o v e r h e a d p h o n e s . A g a i n , P a n b a n i s h a ' s p e r f o r m a n c e w a s c o n s i s t e n t w i t h e a rl ie r

t e s ts . S h e s e l e c t e d t h e c o r r e c t l e x i g r a m o n 9 1 o f th e t r ia l s a n d m e t c r i t e r io n o n 7 1 o f th e 7 6

w o r d s . P a n p a n z e e w a s c o r r e c t o n 6 1 o f t h e t ri al s, m e e t i n g c r it e ri o n o n 3 9 o f th e w o r d s i n t h e

t a p e d s t i m u l u s s e t .

B e c a u s e P a n p a n z e e ' s p e r f o r m a n c e i m p r o v e d i n t h e h e a d p h o n e c o n d i t i o n r e l a t i v e t o t h e

s p o k e n E n g l i s h t a s k , th e w o r d s t h a t e a c h a p e h a d f a i le d i n o n e c o n d i t io n a n d p a s s e d i n th e

o t h e r w e r e r e t es t e d w i t h o u t t h e h e a d p h o n e s i n S e p t e m b e r 1 9 8 9 ( i. e . th i s te s t w a s c o n d u c t e d

u n d e r t h e s a m e c o n d i t i o n s a s t h e la r g er E n g l i s h t o l e x i g r a m t e st s e t t h at b e g a n 9 m o n t h s

e a r li er ) . T h i s w a s d o n e i n o r d er t o d e t e r m i n e w h e t h e r P a n p a n z e e ' s i m p r o v e m e n t c o u l d b e

a t tr ib u t ed t o m a t u r a ti o n o r w h e t h e r t h e h e a d p h o n e p r e s e n t a ti o n a c t u a ll y g a v e P a n p a n z e e s o m e

a d v a n t a g e o v e r t h e ' l i v e - s p e e c h ' c o n d i t i o n b y f o c u s i n g h e r at te n t io n o n t h e t a s k m o r e

e f f e c t i v e l y .


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138 KAREN E. BRAKKE and E. SUE SAVA GE RUMB AUGH

I n t h is f i na l s ubs e t, Panb an i s ha was t e s t ed on e i gh t wor ds ( t h r ee o r f ou r tr ia l s pe r wo r d ) and

was co r r ec t on 22 o f 25 tr ia l s. Th e on l y s y m b o l on w h i ch s he f a i l ed to m e e t c r it e r i on was

f oo d . Panb an i s ha had a l s o m i s s ed t h is w or d i n t he i den t ica l cond i t i on ea r li e r bu t had p a s s ed

i t in t he au d i o t aped cond i t i on .

Pan panz ee was r e t e s t ed on 23 w or ds ; s he was c o r r ec t on 61 o f 78 t r ia l s and m e t c r i t e r ion on

18 o f t he wor ds . Four o f t he f i ve wor ds t ha t t he ch i m panzee f a i l ed t o i den t i f y a t t h i s t i m e

( b l a n k e t , g o o d , m u s h r o o m - t r a il , t u r t le ; t h e f if th w a s r a i n ) w e r e o n e s t h a t sh e h a d

m i s s ed i n t he f i rs t l i ve - s pe ech cond i t i on and had pa s s ed whe n l i s ten i ng t o headpho nes . The

da t a s ugges t t ha t bo t h s ub j ec t s we r e s t i l l expe r i enc i ng s om e vocabu l a r y g r owt h du r i ng t h i s

pe r i od , becaus e i n t h i s f i na l t e s t t hey each pe r f o r m ed be t t e r on m os t o f t he s ym bo l s t hey had

f a i l ed m o n t hs ea r l i e r und e r i den t i ca l cond i t i ons . How eve r , a f ew w or ds ( s uch a s r a i n ) m ay

h a v e b e e n o n t h e c u s p o f c o m p r e h e n s i o n a t t h is t im e , a n d m a y h a v e b e e n s u b j e c t t o

f l u c tu a t in g p e r f o r m a n c e a s e v i d e n c e d b y h e r m a s t e r y o n o n e o c c a s i o n a n d f a i lu r e a t a l a te r

date.

i s c u s s i o n

F o r t h e f i r s t t i m e , m e m b e r s o f t w o n o n - h u m a n s p e c i e s h a v e b e e n r a i s e d t o g e t h e r f r o m

i n f a n c y a n d p r o v i d e d w i th a n e n v i r o n m e n t th a t f o s te r s d e v e l o p m e n t o f n o n - s p e e c h l a n g u a g e

c o m p e t e n c y . T h i s a l lo w s d i r e c t c o m p a r i s o n s t o b e m a d e b e t w e e n m e m b e r s o f t h e s e s p ec i es

and s ugges t s a r ea s o f inqu i r y t ha t m ay p r ove f r u i t f u l f o r i nves t i ga t ion o f the l anguag e - l ea r n i ng

p r o c e s s i n h u m a n s .

The da t a s e t s r epo r t ed above , a l t hough co l l ec t ed i ndependen t l y u s i ng d i f f e r en t t e chn i ques ,

d e m o n s t r a t e r e m a r k a b l e c o n v e r g e n c e o f r e s u l t s . U n d o u b t e d l y , t h e b o n o b o h a d t h e g r e a t e r

r e c e p t i v e c o m p e t e n c y o f t h e t w o s u b j e c t s t h r o u g h o u t t h i s p e r i o d o f d e v e l o p m e n t . H e r

p e r f o r m a n c e w a s n o t a f f e c t e d b y r e m o v i n g p o t e n t ia l c o n t e x t u a l s u p p o r t o r b y c o m b i n i n g t h e

w o r d s s h e k n e w i n to c o m p l e x s e n t e n c e s. P a n b a n i s h a s p a t te r n o f r e c e p t i v e d e v e l o p m e n t ,

t o g e t h e r w i th t h a t re p o r t e d f o r M u l i k a ( S e v c i k an d S a v a g e - R u m b a u g h , 1 9 9 4) a n d f o r K a n z i a t

o l d e r a g e s ( S a v a g e - R u m b a u g h e t a l . 1986) , pa i n t s a po r t r a i t o f bon obo l anguage acqu i s i t ion

t ha t, i n cha r ac t e r , i s n o t un l i ke t ha t o f ch i l d r en p r i o r t o 21/~ yea r s o f age . A l t hough t he a pe s

v o c a b u l a r y s iz e a p p e a r s t o i n c r e a se m o r e s l o w l y t h an t h a t o f h u m a n c h i ld r e n , b o t h l e a rn b y

p a r t i c i p a t i n g i n r o u t i n e s w i t h l e x i c a l m a r k e r s u s e d b y a n a d u l t , a n d b o t h u n d e r g o

d e c o n t e x t u a l iz a t i o n o f s y m b o l c o m p r e h e n s i o n a s t h e y m a t u r e .

M o r e s u r p ri si n g t h a n t h e b o n o b o s h i g h l e v e l o f p e r f o r m a n c e w a s t h e c h i m p a n z e e s

d e m o n s t r a ti o n o f s p e e c h c o m p r e h e n s i o n . A l t h o u g h h e r l e v e l o f a c c u r a c y r e m a i n e d l o w e r th a n

P a n b a n i s h a s t h r o u g h o u t t h e s t u d y p e r i o d , P a n p a n z e e n e v e r th e l e s s d e m o n s t r a t e d s p e e c h

c

the development of language in bonobos and chimpanzees

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