smith, j. d., wilson, m., & reisberg, d. (1995). the role of subvocalization in auditory imagery....

7/29/2019 Smith, J. D., Wilson, M., & Reisberg, D. (1995). the Role of Subvocalization in Auditory Imagery. Neuropsychologia

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~ ) P e r g a m o nNeuropsychologia.Vol. 33, No. I1. pp . 1433-1454, 1995Colr~_'ght 1995~ Seicne= tdPrinted m Car.atBritain.All rights reserved0028-3932/95 $9.50+ 0.00

0 0 2 8 - 3 9 3 2 ( 9 5 ) 0 0 0 7 4 - 7

T H E R O L E O F S U B V O C A L IZ A T IO N I N A U D I T O R Y I M A G E R YJ . D A V I D S M I T H , * M A R G A R E T W lL S ON I" a n d D A N I E L R E I SB E R G:~

*De par tm en t o f Psycho logy and C en te r fo r C ogn i t ive Sc ience , Park H al l , S ta te Un iver s i ty o f New Y ork a tB uf fa lo , Am her s t , N Y 14260 , U .S .A . ; tThe Sa lk In s t i tu te fo r B io log ica l S tud ies , La Jo l la , C A 92037 , U .S .A . ;and :~Psycho logy Depa r tmen t , R eed C o l lege , Po r t land , OR 97202 , U .S .A .(Received 3 June 1994; accepted 16 February 1995)

Ab s t r ac tm Five exper imen ts exp lo red the u ti l i ty o f subvoca l r ehear sa l, and o f an inner - ear / inner -vo ice par tner sh ip , in task s o f aud i to ry imagery . I n th r ee task s ( r e in te rp re t ing amb iguous au d i to ryimages, pars ing meaningful let ter s tr ings , scanning familiar melodies) subjects rel ied on apar tner sh ip be tween the inner ea r and inner vo ice , one s imi la r to the phono log ica l loop sy s temdescr ibed in the sho r t - te rm memory l i t e r a tu re . Apparen t ly sub jec t s subvoea l ly r ehear sed theimagery mate r ia l , wh ich p laced the mate r ia l in a phono log ica l s to r e tha t a l lowed the imageryjudg em ent. In a fou r th task (d ist inguish ing voice d and u nvoice d cons onan ts in imag ery) , subjectss t i l l subvoea l ly r ehear sed , bu t seemed to need no add i t iona l phono log ica l s to r e to r espondco r r ec t ly . I n th i s ease they may have consu l ted a r t icu la to ry o r k ines the t ic cues in s tead . I n a f i f thexper im en t (mak ing h om opho ne judgemen ts ) , subject s hard ly even needed to subvoea l ly rehear se , ar esu l t sugges t ing tha t homophone judgemen ts r e ly on some d i r ec t r ou te f rom p r in t to phono logy .We cons ider the b read th o f the par tner sh ip be tween the inner ea r and inner vo ice , the leve l tha tsubvoea l r ehear sa l occup ies in the cogn i tive sy stem, and the func t iona l neu roan a tom y o f thephono log ica l loop sy stem.Key W ords : imagery ; aud i to ry imagery ; subvoca l iza t ion ; inner speech .

I N T R O D U C T I O NR e s e a r c h o n m e n t a l i m a g e r y h a s t y p i c a l l y f o c u s e d o n v i s u a l , n o t a u d i t o r y , i m a g e r y .F o r t u n a t e l y , t h i s g a p i s c l o s in g [ 5 0 ], f o r a u d i t o r y i m a g e r y i s i m p o r t a n t i n i ts o w n r i g h t ,o c c u p y i n g a n i n t r i g u i n g p o s i t i o n a m i d s t d i v e r s e p h e n o m e n a a n d r e s e a r c h d o m a i n s . F o re x a m p l e , i t m a y u n d e r l i e t h e r e h e a r s a l p r o ce s s es o f w o r k i n g m e m o r y [3 , 7 ] a n d t h ep h o n o l o g i c a l p r o c e s s e s s u b s e r v i n g s o m e a s p e c t s o f t e x t c o m p r e h e n s i o n [ 5 , 1 0 , 3 0 ] .L i k e w i s e , a u d i t o r y i m a g e r y m a y p l a y a r o l e i n m u s i c p e r c e p t i o n a n d c o g n i t i o n [ 19 , 2 1 , 36 ],t h e v e r b a l p r o c e s s e s o f s e l f - r e g u l a t o r y c o g n i t i o n a n d e v e n t h e a u d i t o r y h a l l u c i n a t i o n s o fs c h i z o p h r e n i a [ 60 ].I n e x p l o r i n g a u d i t o r y i m a g e r y , w e c a n n o t p r e s u m e t h a t i n s i g h ts a b o u t v i s u a l i m a g e r yw i l l s im p l y g e n e r a li z e , g i v e n t h e d i f f e r e n t s e n s o r y c h a r a c t e r is t i c s o f s o u n d a n d l i g h t, t h ed i f f e r e n t e v o l u t i o n a r y h i s t o r i e s o f h e a r i n g a n d v i s i o n , o r t h e d i f f e r e n t e n t a n g l e m e n t s o fh e a r i n g a n d v i s i o n w i t h s p e e c h a n d l a n g u a g e . F o r e x a m p l e , h u m a n s c o u l d w e l l r e l y o np r o c e s s e s o f s u b v o c a l r e h e a r s a l t o r e f r e s h o r e n l i v e n a u d i t o r y i m a g e s , a n d t h e a n a l o g s t ot h i s i n v i s u a l i m a g e r y r e m a i n u n c l e a r .

*Autho r to whom a l l co r r espondence shou ld be add ressed .1433


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1434 J. D. SMITH, M. WILSON and D. REISBERG

I n f ac t , r e s ea r ch on sho r t - t e rm memory con f i rms t ha t cove r t r ehea r sa l bene f i t s somecogn i t i ve func t i ons . Spec i fi c al ly , sho r t - t e rm m em ory fo r ve rba l m a t e r i a l s eems t o r e ly on aphono log i ca l l oop w i th two cons t i t uen t s - - a sho r t - l i ved s t o r e t ha t r ep r e sen t s ma t e r i a l i n aphon o log i ca l f o rm, a nd a p roces s o f r ehea r sa l t ha t r e - enac ts t h is ma t e r i a l, r e -p r e sen t s it t othe s t o r e , and t hus r e f r e shes and p r e se rves i t s con t en t s . I n tu i t i ve ly , t h i s concep t i on o fwork ing memory r e l i e s on a pa r t ne r sh ip be tween an ' i nne r e a r ' ( t he s t o r e ) and an ' i nne rvo i ce ' ( subvoca l r ehea r sa l ) . The i n t e rp l ay be tween t he se two r e sou rce s i n sho r t - t e rmmemory i s documen ted by expe r imen ta l and neu ropsycho log i ca l ev idence [3 , 4 , 9 , 30 , 59 ,62, 63, 73, 74].

Ou r r e sea r ch focuse s on o the r u se s the phono log i ca l l oop ha s f o r cogn i t i on . I np a r ti c u la r , m a n y i m a g e r y t a s k s r e qu i re t h a t s u b je c ts a n al y z e o r m a k e j u d g e m e n t s a b o u taud i t o ry s t imu l i t ha t a r e no t cu r r en t l y on t he s cene . We cons ide r t he pos s ib i l i t y t ha t t heinne r - ea r / i nne r -vo i ce pa r t ne r sh ip p rov ides a p l a t fo rm on wh ich t he se image ry p roces se sand j ud gem en t s t ake p l ace ( see a lso [7 ]) .Ev idence a l r eady ex i s ts t ha t cov e r t speech p l ays some ro l e i n aud i t o ry image ry . R e i sbe rge t a l . [ 53] exam ined t he im age ry ana logu e o f t he Ve rba l T ran s fo rm a t ion E f f ec t [ 66 -68 ] , ane f f ec t wh ich r e li es on t he f ac t t ha t c e r t a i n w ords an d ph ra se s , i f r epea t ed o ve r and ove r ,y i e l d a s o u n d s t r e a m c o m p a t i b l e w i t h m o r e t h a n o n e s e g m e n t a t i o n . F o r e x a m p l e , r a p i dr epe t i ti ons o f t he wo rd ' l if e ' p rod uce a so unds t r eam fu l ly com pa t ib l e w i th t he pe r cep t i ontha t e i t he r ' l i f e ' o r ' f l y ' i s be ing r epea t ed . These amb iguous sounds t r eams a r e u sua l l ype rce ived fi r st in one w ay t hen t he o the r , chang ing i n phen om ena l f o rm ju s t a s t he (v i sual )N e c k e r c u b e a n d d u c k / r a b b i t f ig u re s d o .

R e i s b e r g e t a l . asked whe the r imag ined r epe t i t i ons p roduce ve rba l t r ans fo rma t ions , j u s ta s hea rd r epe t i t ions do . Sub j ec t s imag ined t he s t imu lus wo rd ' s be ing r epea t ed b y a f ri end ' svo i ce , r a t he r t han ac tua l l y hea ri ng i t , and o f t en d id r epo r t t r ans fo rma t ions o f the i r image .Ho we ve r , t he se tr ans fo rm a t ions by image r s s eem to depend on su bvoca l i z a t i on , f o r t heya re e s sen t ia l ly e l imina t ed when suba r t i cu l a t i on i s b locked by hav ing sub j ec ts chew cand ydur ing t he t ri al . T he e f f ect s o f chewing cann o t be a t t r i bu t ed t o gene ra l d i st r ac t ion , becauseo the r concu r r en t a c t i v i t i e s , equa l l y d i s t r ac t i ng bu t no t i nvo lv ing t he a r t i cu l a to r s , c ausedno d i s rup t i on .M o r e o v e r , R e i s b e r g e t a l . f ound t ha t t he p robab i l i t y o f succes s i n t hi s t a sk g r ad ua l l ydec l ines as subvoca l iza t ion i s undercut . Spec i f ica l ly , subjec ts in a la te r exper iment werea l l owed d i f f e ri ng deg ree s o f voca l iz a t ion : Som e sub j ec t s a c tua l l y spoke t he am b iguo usph ra se ; o the r s wh i spe r ed i t; s til l o t he r s m ou the d i t w i th no m ovem en t o f a ir ; a f ou r thg roup imaged i t w i thou t mou th ing ; and a f i f t h g roup imaged i t w i th t he a r t i cu l a to r sc lam ped s ti ll . Acro ss these f ive grou ps , respec t ive ly , 80 , 65 , 55, 50 and 30% exper ien ced aphenomena l sh i f t i n t he t a rge t ph ra se ( a l l nonad j acen t pe r cen t ages a r e r e l i ab ly d i f f e r en tf rom one ano the r ) . As subvoca l i z a t i on waned , so waned t he capac i t y t o r e in t e rp r e t t heimage . Th ose f ami l i a r w i th t he sho r t - t e rm m em ory l i t e r a tu r e w i ll s ee t he c lo se ana logyb e t w e e n t h is r e s u lt a n d t h a t o f M u r r a y [4 2], w h o f o u n d t h a t m e m o r y t r a c es b e c o m e m o r erobus t a s t he i r r ehea r sa l becomes more exp l i c i t and ove r t ( i . e . mou th ing , wh i spe r ing ,saying) .These r e su l t s on a ud i t o ry im age ry f r ame t he is sue s f o r t he p r e sen t r e sea rch . F i r s t , we a ski f subvo ca l r ehea rsa l p rov ides sup por t t o au d i t o ry imag e ry in a b road e r r ange o f t a sks .Second , we a sk abou t t he p r ec i s e r o l e o f s u b v o c a li z a ti o n i n a u d i t o r y - i m a g e r y t a sk s . T h a tis , we w il l a sk w he the r t he i nne r vo i ce a lone p rov ides t he c r it ic a l i n fo rma t ion t ha t a l l owsimage ry j udgem en t s an d r econs t rua ls , o r whe the r t he i nne r e a r a l one does , o r whe the r t he


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SUBVOC ALIZATION IN AUDITORY IMAGERY 1435

i m a g e r y j u d g e m e n t s d e p e n d o n a p a r t n e r s h ip b e t w e e n t h e t w o r e s o u rc e s . O u r a t t e m p t t os pec i fy t h is f unc t i ona l r e l a t i ons h i p r eca l ls aga i n t he s ho r t - t e r m m em or y l i t e ra t u r e , i nw hich d i f fe rent e f fect s (e.g. pho nolo gica l s imi la r ity) a re l inked to the inp ut o r o utp utcom pon en t s o f t he l oop , an d i n w h i ch d i ff e r en t i n t e r fe r ence m an i pu l a t i ons ( e. g. co ncu r r en taud i t i on , con cu r r en t a r t icu l a t i on ) and ce r eb r a l a cc iden t s se l ec t ive ly t a r ge t on e o r t he o t he r[6, 62, 63, 71, 73].In d i scuss ing the da ta , we wi ll cons ider severa l fur the r is sues. F i r s t , we d escr ibe o theri n s t ances o f a r t i cu l a t o r y / phono l og i ca l in t e r ac t ions i n cogn i ti ve p roces s ing , t o em phas i zet he i r i m por t ance . Second , we cons i de r t he s pec i a l va l ue o f r e - p r e s en t a t i on by t he i nne rvo i ce when a t a s k r equ i r e s j udgem en t s abou t o r ana l ys e s o f i m age r y m a t e r ia l . Th i s i dea o fr e - p r e s en t a t i on exp l a i n s m or e f u l l y t he r e s t r i c t ed r o l e t he phono l og i ca l l oop p l ays i nl anguage p r oces si ng . Th i r d , we con s i de r the leve l i n t he cogn i ti ve s ys tem a t wh i ch t he i nn e rvo i ce and t he i nne r e a r r e s ou r ce s i n t e rac t . F i na l ly , we d is cuss t he f unc t i ona l neu r oa na t om yof t he i nn e r e a r an d i n ne r vo i ce , d r awi ng on r ecen t b r a i n - i m ag i ng s tud i es .

E X P E R I M E N T 1: V E R B A L T R A N S F O R M A T I O N SRe i s be r g e t a l . [ 53 ] s how ed t ha t t he r e i n t e r p r e t a t i on o f aud i t o r y i m ages depen ds onsubvoca l rehearsa l processes . But what ro le does th i s rehearsa l p lay? I s the k ines the t i c

s upp or t f r om a r t i cu l a ti on s u f f ic i en t f o r pe r f o r m a nce , o r i s som e a ud i t o r y / pho no l og i ca lrepresenta t ion involved as wel l? Exper iment 1 eva lua ted these two poss ib i l i t i es us ing thes tandard logic of se lec t ive in te r fe rence . Subvoca l rehearsa l ( the inner voice) , i s known tobe b l ock ed by co ncu r r en t a r t icu l a t i on (e .g . t ah - t ah r ep ea t ed a l oud b y t he s ub j ec t) , and t h isi n t e r f e r ence m a n i pu l a t i on t hus a l lows one t o a s k how pe r f o r m ance f a re s abs en t r ehea r sa l .The phono l og i ca l s t o r e ( t he i nne r e a r ) i s known t o be b l ocked by concur r en t aud i t o r yi npu t ( e. g. t ah - t ah r epe a t ed t h r oug h headp hones ) , and t h is i n t e r fe r ence m a n i pu l a t i on t husa l lows on e t o a s k ho w pe r f o r m ance fa r e s abs en t t he phono l og i ca l s t o re .W e a l r e a d y k n o w t h a t i m a g e r e c o n s tr u a ls s o m e h o w d e p e n d o n s u b v o c a l r e h ea r sa l . I fb l ock i ng t he i nne r e a r d i s r up t s pe r f o r m ance , t h is wi ll i nd i ca te t ha t i m age r y recons t r ua l sa l s o depend on t he phono l og i ca l s t o r e , and t ha t s ubvoca l r ehea r s a l and t he phono l og i ca ls t o r e wo r k i n pa r t ne r s h i p d u r i ng pe r f o r m a nce . I f b l ock i ng the phono l og i ca l s to r e does no td i s r up t pe r f o r m ance , t h i s wi l l i nd i ca t e t ha t s ubvoca l i za t i on p r ov i des m a i n l y k i ne s t he t i ci n f o r m a t i on f o r s ub j ec t s, and wi ll d i s con fi r m a pa r t ne r s h i p pa t t e r n f o r t ha t t a sk .M e t h o d

Subj ec t s . F o r t y - f iv e s u b j e c ts w e re a p p r o a c h e d i n v a r i o u s s c h o o l a n d p r o f e s s i o n a l s e tt i n g s a n d a s k e d t op a r t i c i p a t e i n a b r i e f (5 m i n ) p r o c e d u r e . F i f t e e n s u b je c t s w e r e a s s i g n e d a t r a n d o m t o e a c h o f t h e t h r e ee x p e r i m e n t a l c o n d i t i o n s - - n o i n t er f e re n c e , a r t i c u l a to r y s u p p r e s s i o n a n d i r r e le v a n t s p e e c h t h r o u g h h e a d p h o n e s .Su b je c t s r e c e iv e d $ 1 .0 0 fo r t h e i r p a r t i c ip a t i o n .Inter ference manipulat ions . Su b je c t s i n a l l c o n d i t i o n s im a g in e d a f r i e n d , o f t h e sa m e se x a s t h e m se lv e s ,r e p e a t i n g a t a r g e t w o r d . F o r t h e a r t i c u la t o r y - s u p p r e s s i o n g r o u p , s u b j e ct s w e re i n s t r u c t e d n o t t o s a y t h ere p e t i t i o n s a t a l l. To e n fo rc e t h i s i n ju n c t i o n , su b j e c t s w e re t o ld t o p re ss t h e i r l i p s t o g e th e r , c l e n c h t h e i r t e e th , a n dt o p r e s s t h e i r t o n g u e t o t h e r o o f o f t h e i r m o u t h w h i l e i m a g i n g t h e r e p e t it i o n s . T h i s s u p p r e s s i o n t e c h n i q u e s e e m e du n l ik e ly t o b e g e n e ra l l y d i s t r a c t i n g t o su b j e c t s , a n d u n l ik e ly to g e n e ra t e a d i s tu rb in g rh y th m in c o n f l i c t w i th t h er h y t h m o f t h e r e p e t it i o n s .O t h e r s u b j e c ts i m a g i n e d t h e r e p e t i t i o n s w h il e h e a r in g t a p e - r e c o r d e d p r o s e , r e a d b y a s p e a k e r o f t h e s a m e s e x a st h e s u b j e c t . D i s t r a c t i n g s p e e c h w a s c h o s e n t o i n c r e a s e t h e s i m i l a r i t y b e t w e e n t h e i n t e r f e r e n c e a n d i m a g e r ym a te r i a l s , fo l l o w in g s tu d i e s i n w o r k in g m e m o ry t h a t su g g e s t t h a t t h i s s im i l a r i t y i n c re a se s t h e i n t e r f e r i n g e f f ec t s o ft h e i r r e l e v a n t a u d i t o r y i n p u t s o n t h e p e r f o r m a n c e o f t h e f o c a l t a s k [ 3, 5 5] .P rocedure . T he e x p e r i m e n t e r, w h o w a s b l i n d t o t h e e x p e r i m e n t ' s h y p o th e s e s , e x p la i n e d t h a t s o m e w o r d s , w h e nr e p e a t ed , b e g i n t o s o u n d l i ke s o m e t h i n g el se . T h e n s h e r e p e a t e d t h e w o r d ' l if e ' f o r 1 m i n u t e , a t t w o r e p e t i t i o n s p e r


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1436 J .D . SMITH, M. WILSON and D. REISBERGs e c o n d , a n d t h e s u b j e c t l i s te n e d a n d r e p o r t e d a n y t r a n s f o r m a t i o n s . F o r t y o f 4 5 s u b je c t s h e a r d t h e t r a n s f o r m a t i o nto ' f l y ' and on ly the s e s ub jec t s ' da t a we re ana lyzed .N e x t s u b j e ct s w e r e g i v e n a n e w w o r d - - ' s t r e s s ' - - p r i n t e d o n a n i n d e x ca r d . T h e y w e r e t o i m a g i n e a f r i e n d ' s v o i c er e p e a t i n g i t w i t h n o g a p s a t t h e r a t e t h e e x p e r i m e n t e r h a d d e m o n s t r a t e d . T h e y w e r e i n s t r u c t e d n o t t o s a y t h e w o r dou t lo ud a t a l l , bu t ju s t t o im ag ine s i l en tly the f r i end ' s r epe t i t i ons . Sub jec t s imag ine d the repe t i t i ons fo r 1 min ,p a u s i n g o n l y t o r e p o r t t r a n s f o r m a t i o n s , b u t t h e n r e s u m i n g t h e im a g e r y .

T h e a r t i e u l at o r y - s u p p r e s s io n s u b j ec t s w e r e t o l d n o t t o " s a y t h e w o r d o u t l o u d a t a ll , d o n ' t w h i s p e r , d o n ' t e v e nm o v e y o u r t e e t h , t o n g u e , o r l i p s " . T o h e l p t h e m c o m p l y , t h e y w e re t o l d t o " p u t y o u r t e e t h t o g e t h e r , y o u r l i psf i rm l y t o g e t h e r, a n d p u t y o u r t o n g u e f i rm l y o n t h e r o o f o f y o u r m o u t h . T h i s w il l m a k e s u r e y o u u s e p u r ei m a g i n a t i o n f o r y o u r r e p e t i t i o n s ." I r r e l ev a n t - s p e e ch su b j e ct s w e r e t o l d t h a t t h e s p e e c h h e a r d t h r o u g h h e a d p h o n e sw o u l d b e o n l y b a c k g r o u n d s p e e c h, t h a t t h e y c o u l d c o m p l e te l y ig n o r e i t, a n d t h a t t h e y w o u l d n o t b e t e s t e d o n i t i na n y w a y .R e s u l t s

F o l l o w i n g R e i s b e rg e t a l . [ 53 ], we focused ou r da t a ana ly s is on t he t r ans fo rm a t ion o f' s tr e s s ' t o ' d r e s s ', t he t r ans fo rm a t ion t ha t w as hea rd b y 100% o f sub j ec t s i n the i rpe r cep tua l cond i t i ons , bu t was n o t e a s il y gues sed in t he i r gues s ing cond i t i on . I t i s t hus t het r ans fo rma t ion t ha t mos t c l ea r l y s i gna l s a b o n a f i d e pe rcep tua l d i s cove ry .

In t he no - in t e r fe r ence cond i t i on , 77% o f sub j ec t s r epo r t ed a t r ans fo rm a t ion o f ' s t r e s s ' t o' d r e s s ' du r ing t he 1 min o f imag ined r epe t it i ons . I n t he supp re s s ion and i r r e levan t - speechcond i t i ons , r e spec t ive ly , 25 and 13 % hea rd a t r ans fo rm a t ion t o ' d r e s s '. T hese pe r cen t agesd id no t d i f f e r f r om each o the r , bu t bo th we re r e l i ab ly l ower t han t he no - in t e r f e r enceg r o u p ' s r a t e o f t r a n s fo r m a t i o n , t ( 2 6 ) = 3 . 0 4 , P < 0 . 0 1 , f o r c o n t r o l v s s u p p r es s io n ;t ( 28 )= 4 .40 , P < 0 .01 , f o r con t ro l v s i rr e l evan t speech. B o th pe r cen t ages we re s imi l a r t ot h o s e f o u n d b y R e i s b e r g e t a l . f o r sub j ec ts who d id n o t engage i n image ry a t a ll, b u t on lyt r ied t o gues s t he t r ans fo rma t ions t ha t migh t oc cu r ( abou t 25% ) . These sub j ec t s we rein s t ruc t ed t o gues s wha t t he new wo rd cou ld change i n to i f i t we re r epea t ed ove r the w aythe expe r imen te r had r epea t ed ' l i f e ' . They we re cau t i oned no t t o s ay t he word a t a l l , andany v i s ib l e voca l i z a t i on w as imm ed ia t e ly co r r ec t ed . These sub j ec t s tended t o o f f er , a s t he i rrespon ses , var ious an agra m s of the s t imulus (e .g . tress , res t , and so for th) , bu t ra re ly gav ethe ' d r e s s ' r e sponse . Th i s p rov ides f u r t he r a s su r ance t ha t t h i s r e sponse does s i gna l agenu ine pe r cep tua l r eve rsa l .D i s c u s s i o n

The l a rge e f fec t o f a r t i cu l a to ry supp re s s ion obse rved he r e r ep l i c at e s t he ea r l i e r f i nd ingb y R e i s b e r g e t a l . : I n o rde r t o d i s ce rn t he se t r ans fo rma t ions , sub j ec t s need t o r ehea r sesubvo ca l l y t he image ry ma te r ia l . Bu t i n add i t ion , sub j ec ts a l so depend on t he i nne r e a r ( t hephono log i ca l s t o r e ) . I f t h i s a cce s s i s b locked (by i r r e l evan t speech ) , pe r fo rmance i s a l sodevas t a t ed . A ppa ren t l y , t hen , sub j ec t s f i nd r econs t rua l s o f am b iguo us au d i t o ry imagesu s i n g b o t h c o m p o n e n t s o f th e p h o n o l o g i c a l l o o p s y s te m .O f cou r se t h is in t e rp r e t a t i on r e s ts on the p r e sum pt ion t h a t a r t i cu l a to ry supp re s s ion andi r re levant speech have the i r e ffec t s by spec i f ical ly b lock ing sub voc a l rehearsa l a nd thephono log i ca l s t o r e , r e spec t i ve ly . Bu t one cou ld a rgue t ha t t he se man ipu l a t i ons d i s rup tpe r fo rm ance mere ly because t hey a r e gene ra ll y d i st r act ing . Fo r tu na t e ly , t h is i ssue ha s beenadd re s sed i n some de t a i l i n t he work ing -memory l i t e r a tu r e . Th i s ev idence i nd i ca t e s t ha tno t a l l conc u r r en t a c t iv i ti e s d i s rup t pe r fo rm ance i n t he way t ha t con cu r r en t a r t i cu l a t iondoe s [6] , and no t a l l i r re levant inp uts ha ve the im pac t o f t ask- i r re levant speech [55 , 56].These r e su l t s a r e pecu l i a r i f t he se ma n ipu l a t i ons a r e s imp ly gene ra ll y d i s tr ac t ing , and t hem os t na tu r a l i n t e rp r e t a t i on r ema ins t ha t t he se man ipu l a t i ons spec if ic a l ly d i s rup tphono log i ca l p roces s ing and t he phono log i ca l l oop [3 , 4 , 30 ] .


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SUBVOCALIZATION IN AUDITORY IMAGERY 1437

Thi s spec i f ic i ty app l i e s t o o u r im age ry t a sks , t oo . I n t he s t r e s s /d r es s t a sk , f o r exam ple ,pe r fo rm ance i s d i s rup t ed i f sub j ec t s m us t c l am p the i r a r t i cu la to r s i n p l ace. Ho we ve r , t he r ei s no i n t e r fe r ence w i th t h i s t a sk i f sub j ec t s hum wh i l e imag ing t he r epe t i t i ons [53 ] . I ncon t r a s t , sub j ec t s i n a f u r t he r expe r imen t w e re i n s truc t ed i n t he d i f f er ence be twe en vo i cedand unvo i ced consonan t s , and t hen r ece ived a p r i n t ed l i s t o f 36 one - sy l l ab l e words .S u b j e c t s w e r e a s k e d t o i m a g in e h o w e a c h w o r d w o u l d s o u n d i f p r o n o u n c e d a l o u d , a n d t oj u d g e w h e t h e r t h e i n i ti al c o n s o n a n t i n e a ch w o r d w o u l d b e v o i c e d o r u n v o i c e d . S u b j e c t swe re 7 6% co r r ec t i f th i s w as t he ir on ly t a sk . S ub j ec t s we re a l so succes s fu l i f t he i ra r t i cu l a to r s we re c l amped t i gh t l y shu t ( 68%, no t r e l i ab ly d i f f e r en t f r om 76%) . Howeve r ,p e r f o r m a n c e d r o p p e d a l m o s t t o c h a n c e le ve ls i f s u b je c ts w e re a s k e d t o h u m a l o u d w h i lem a k i n g t h e se j u d g e m e n t s ( 5 6 % , r e li a b ly d if f er e n t f r o m b o t h 7 6 a n d 6 8 % ) .Th i s pa t t e rn ma kes l i tt le s ense i f c l amp ing o r hum ming a r e mere ly d is t r ac ti ng i n som egenera l way. However , these resu l t s have a sens ib le se lec t ive- in te r fe rence in te rpre ta t ion .F o r t h e v o i c e d - u n v o i c e d t a s k , s u b je c t s n e e d i n f o rm a t i o n a b o u t t h ei r o w n v o c a l c h o r d s ( o rt he p l ann ing mech an i sms fo r t he voca l cho rds ) ; a cce s s t o t h i s i n fo rm a t ion i s d i s rup t ed byh u m m i n g b u t n o t b y c la m p i n g . V e r b a l t ra n s f o r m a t io n s , i n co n t r a s t, s e e m t o d e p e n d m o r eo n a r t i c u la t o r y i n f o r m a t i o n , a n d a c c es s t o t h is i n f o r m a t i o n i s b l o c k e d b y c l a m p i n g b u t n o tby humming . Th i s imp l i e s t ha t s t r e s s /d r e s s sub j ec t s a r e r e ly ing more on phono log i ca lr e p r e s e n ta t i o n s e n g e n d e r e d b y t h e m o v e m e n t a n d p o s i ti o n s o f te e t h, t o n g u e a n d l ip s ( o rt he i r p l ann ing o r con t ro l mechan i sms ) . The key po in t , t hough , i s t ha t t he se i n t e r f e r encema n ipu l a t i on s do w ha t t hey a r e mean t t o do . They spec if ic a ll y p r eem pt pa r t i cu l a renac tmen t p roces se s , r a t he r t han caus ing gene ra l d i s t r ac t i on .M oreo ve r , t he vo i ced /unvo i ced r e su l t d r aws a t t en t i on t o a f u r t he r po in t: Ap pa ren t l y ,t he i nne r v o i ce is no t a m ono l i t h i c en t it y ; i n st ead , cov e r t speech ha s m u l t i p le a sp ec t s ( ju s ta s ove r t speech does ), and a pa r t icu l a r t a sk migh t r equ i r e sup por t f r om some , bu t no t a l l,o f t he se a spec t s . I n add i t i on , i t seems pos s ib l e t o d i s rup t some a spec t s o f the i nne r vo i cewh i l e spa r i ng o the r s - -- e .g , t o d i s rup t vo i c ing bu t n o t a r t i cu l a ti on . Th i s f r ac t i ona t i on o f t heinner voice sugges ts tha t cover t rehearsa l se rves to c rea te a qui te spec i f ic s t imulus to bejudged o r i n t e rp r e t ed . Consequen t l y , f u r t he r r e sea r ch may be ab l e t o de t e rmine , f o r anyg iven aud i t o ry - im age ry t a sk , no t on ly whe the r subv oca l r ehea r sa l suppo r t s i t , bu t a l sowh a t f e a tu r e s o f subvoca l i z a t i on a r e c ri ti c al t o pe r fo rmance .

Tw o me thodo lo g i ca l po in t s f o l l ow f rom th i s d i s cus sion . F i r s t , f o r som e pu rpo se s onewi l l p re fer in te r fe rence mater ia l tha t i s qu i te s imi la r to the imagery mater ia l for the foca lt a sk , t hus i nc r ea s ing t he pow er o f t he in t e r fe r ence man ipu l a t i on . Second , f o r o the rp u r p o s e s , o n e m a y p r e f e r a b r o a d - b a n d i n t e r f e r e n c e m a n i p u l a t i o n , l i k e t h e c o m m o n l y -used r epe t i t ions o f 't ah - t ah ' , t ha t i nvo lve bo th t he a r t i cu l a to r s a nd vo i c ing . Th i s w ill a l l owone t o p rod uce r e li ab le i n t er f e r ence ef f ec t s w i tho u t hav ing t o kn ow in advance w h ichspec i f i c a spec t s o f subvoca l i z a t i on t he foca l t a sk r equ i r e s . Bo th o f t he se cons ide r a t i onshave g u ided o u r cho i ce o f p rocedu re s i n t he s t ud ie s r epo r t ed he r e .

In cont ras t , a fur ther methodologica l cons idera t ion car r ies l i t t l e weight . Tha t i s , i tappe a r s t o m ake l it tl e d if f e rence wh e the r one ch ooses a s il en t m ode o f a r t i cu l a to rysupp re s s ion ( a s we d id i n Expe r imen t 1 ), o r an o ve r t (a l oud ) m ode o f a r t i cu l a to rysupp re s s ion ( a s nea r l y a l l o the r r e sea r che r s have done ) . I n e i t he r c a se , supp re s s ionove r runs cov er t rehearsa l processes ; in ne i ther c ase is the e f fec t ive locus o f in te r fe rence theaud i t o ry i npu t f r om the concu r r en t t a sk . Th i s i s ev iden t i n ou r f i nd ing he r e t ha t s i l en tsupp re s s ion ha s t he s ame e f f ec t a s ove r t supp re s s ion ( see a lso R e i sbe rg e t a l . [53],Expe r im en t s 1 and 4 ). L ikewi se , i n m em ory r e sea r ch , Wi ld ing and W hi t e [ 74 ] f oun d i n


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1438 J.D. SMITH ,M. WILSONand D. REISBERGt h r e e e x p e r i m e n t s t h a t m o u t h e d a n d s p o k e n a r t i c u l a t o r y s u p p r e s s i o n w e r e e q u i v a l e n t i nt h e i r d i s r u p t i o n o f r h y m e j u d g e m e n t s . I r r e l e v a n t a u d i t o r y i n p u t h a d n e a r l y n o e f fe ct .I n d e e d , t h e l i t e r a t u r e s h o w s in g e n e r a l t h a t t h e e f f e ct s o f ir r e l e v a n t a u d i t o r y i n p u t a r e p a l ec o m p a r e d t o t h e ef fe c ts o f o v e r t a r t i c u l a t o r y s u p p r e s s i o n ( G a t h e r c o l e , p e r s o n a lc o m m u n i c a t i o n , J a n u a r y 1 99 5). T h i s is t r u e e v e n w h e n c o n c u r r e n t a u d i t i o n a n dc o n c u r r e n t a r t i c u l a t i o n h a v e t h e i d e n t i c a l c o n t e n t [ 1 6 ] .

T h i s p o i n t is e c h o e d b y G u p t a a n d M a c W h i n n e y [33], w h o c o m p a r e d m e m o r yp e r f o r m a n c e w h e n s u b j ec ts a r ti c u la t ed t h e w o r d T H E , w i th p e r f o r m a n c e w h e n s u b je c tst a p p e d t h e i r f i n g e r s a s a m o t o r i c d i s t r a c t o r w h i l e a t a p e l o o p p l a y e d T H E a s c o n c u r r e n ta u d i t i o n . A r t i c u l a t o r y s u p p r e s s i o n h a d s t r o n g e r e ff e ct s o n p e r f o r m a n c e t h a n d i d t h em o t o r - h e a r i n g d i s t r a c t io n . T h i s o b v i o u s l y f it s w e l l w i t h t h e c l a i m t h a t t h e e f f e c ts o fc o n c u r r e n t a r t i c u l a t i o n a r e t r u l y a r t i c u l a to r y i n n a t u r e ; t h e e f f ec ts s e e m n o t t o a r i s e f r o mt h e a c o u s t i c c o n s e q u e n c e s o f t h is a r t i c u l a t io n . *

E X P E R I M E N T 2: M E A N I N G F U L L E T T E R S T R I N G SE x p e r i m e n t 1 i n d i c at e s t h a t t h e i m a g i n e d v e r b a l - t r a n s f o r m a t i o n e f f e ct r e li es o n a

p a r t n e r s h i p b e t w e e n t h e in n e r v o i c e a n d i n n e r e a r. U n d e r a r t i c u l a t o r y s u p p r e s s i o n , c o v e r tr e h e a r s a l p r o c e ss e s a r e u n d e r m i n e d , a n d s o t h e o u t p u t f u n c t i o n t h a t r e p e a t s th e s t r in go p e r a t e s p o o r l y . U n d e r c o n c u r r e n t a u d i t i o n , t h e p h o n o l o g i c a l s t o r e i s o t h e r w i s e e n g a g e d ,a n d t h e in p u t p r o v i d e d b y c o v e r t r e h e a r s a l g o e s ' u n h e a r d ' . E i t h e r k i n d o f in t e r f e re n c em a k e s i m a g e r e c o n s t r u a l d if fi cu lt , b e c a u s e b o t h k i n d s o f p r o c e s s in g u n d e r li e t h e s u c c es s fu lr e c o n s t ru a l o f a n a u d i t o r y i m a g e.

D o o t h e r a u d i t o r y i m a g e r y t a s k s a l s o i n v o l v e t h i s p a r t n e r s h i p ? I n o u r s e c o n dE x p e r i m e n t , s u b j e c t s im a g i n e d h e a r i n g a s t ri n g o f l e tt er s o r n u m b e r s b e i n g n a m e da l o u d , a n d h a d t o w r i t e d o w n t h e E n g l is h w o r d e a c h s t ri n g w o u l d s o u n d l ik e . F o r i n s t an c e ,t h e st ri n g N - M - E w o u l d s o u n d l ik e ' e n e m y ' i f s p o k e n a l o u d . L i k e i m a g e d v e r b a lt r a n s f o r m a t i o n s , t h i s t a s k , o n t h e f a c e o f it , r e q u i r e s a u d i t o r y i m a g e r y ; w il l i t a l s o r e q u i r et h e s u p p o r t o f i n n e r s p e e ch , a n d p e r h a p s t h e i n n e r e a r i n p a r t n e r s h i p ?M e t h o d

Subj ec t s . Twen ty-four mem bers of a university com mun ity were paid for their participation; six su bjects wereassigned at random to each o f four exp erimental conditions.Inter ference manipulat ions . Th is experiment adopted a standard 2 x 2 selective-interference design (betweensubjects). Articulatory suppression was provided by hav ing subjects repeat 'tah- tah' aloud--the mo st frequentblock to subvocalization n the literature. Aud itory interference was ag ain provided by irrelevant speech (in thiscase the poem J a b b e r w o c k y ) heard through headph ones. In all conditions, interference (when present) beganbefore each stimulus sheet was presented, and co ntinued until after the trial had end ed. No strict pace was set fo rrepetitions in the articulatory supp ression condition, but subjects who paused w ere reminded to continue.Ins t ruct ions to subjects . Subjects were told that they would be g iven strings of letters and num bers that, wh enpronounced out loud, so und l ike English words. For instance, the string M-T would be 'empty'. Subjects weretold to imagine hearing each string spoken aloud, and to w rite dow n the E nglish word it formed. Subjects werethen g iven a single sheet of pap er showing 10 strings. (Thus all strings were simultaneously visible o the sub ject.)

*We note that Gup ta and M acWh inney [34] ha ve rethough t their 1993 stud y [33], arguing that flaws in theprevious study block the conclusions hey had earlier endorsed--nam ely that the effectsof co ncurrent articulationare truly articulatory in natu re. How ever, and despite the ir argum ents, their current data do seem still toemph asize those articulatory effects. Even so, it rem ains an important go al to specify exactly how articulatorysuppression does reduce performance, and the research of G upta and M acWhinney is an innovative effort in thisregard.


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SUBVOCALIZATION N AUDITO RY IMAGE RY 1439Subjects were instructed hat they could skip items f theywished, and return to the m ater if they wished. Subjectshad 90 see to com plete he task.Results

W i t h n o i n t e r f e r e n c e , s u b je c t s i n t e r p r e t e d 7 2 % o f t h e s tr i n g s c o r r e c t ly . B u t , u n d e ra r t i c u l a t o r y s u p p r e s s i o n o r i r r e l e v a n t a u d i t o r y i n p u t , p e r f o r m a n c e d e c l i n e d t o 2 1 a n d4 0 % , r e s p e c t iv e l y , a n d t o 1 9 % w h e n s u b j e ct s w e r e u n d e r b o t h k i n d s o f i n t e r f e re n c es i m u l t a n e o u s l y ( se e F i g . 1 ). T h e s e d a t a w e r e a n a l y z e d u s i n g a tw o - w a y A N O V A w i t hS u p p r e s s i o n ( a b s e n t - p r e s e n t ) a n d I r r e l e v a n t S p e e c h ( a b s e n t - p r e s e n t ) a s b e t w e e n - s u b j e c t sf a c t o r s . T h e r e w a s a m a i n e f fe c t f o r b o t h k i n d s o f i n t e r f e r e n c e - - f o r A r t i c u l a t o r ySu pp ress ion [F (1 , 28) = 27 .4 , P < 0 .05 , MSe = 3 .8 3 ]; f o r I r r e l ev an t S p eech[F (1, 2 8 ) = 6 . 4 0 , P < 0 .0 5 , MSe= 3 . 8 3 ] . Im p o r t an t l y , t h e re w as a l so a r e l i ab l e i n t e r ac t i o nb e t w e e n S u p p r e s s i o n a n d I r r e l e v a n t S p e e c h [ F ( 1, 2 8 ) = 4 .7 0 , P < 0 .0 5 , MSe = 3.83]. Post-hoc t e s t s r e v e a l e d t h e c h a r a c t e r o f t h e i n t e r a c t i o n - - p e r f o r m a n c e w i t h n e i t h e r k i n d o fi n t e r f e re n c e o n t h e s c e n e w a s b e t t e r t h a n p e r f o r m a n c e i n a n y o t h e r c o n d i t i o n ; t h e r e w a s n od i f fe r e n c e a m o n g t h e o t h e r c o n d i t i o n s ( a r t i c u l a to r y s u p p r e s s i o n , i rr e l e v a n t s p ee c h , o r b o t hc o m b i n e d ) . ( N o t e : a l l post-hoc t e s t s i n t h i s p a p e r r e l i e d o n t h e L S m e a n s p r o c e d u r e f r o mt h e S A S p ack ag e . T o p re se rv e o v e ra l l p ro t ec t i o n l ev e l s fo r t h e se t e s t s a c ro s s t h e s e r i e s o fe x p e r i m e n t s , t h e r e q u i r e d l ev e l o f s i g n if i ca n c e f o r a c o n t r a s t b e t w e e n m e a n s w a s s e t a t0.02. )Discussion

A g a i n s u b j e c t s c l e a r l y n e e d e d t o s u b v o c a l i z e i n o r d e r t o p e r f o r m t h i s t a s k - - w i t hs u b v o c a l i z a t i o n b l o c k e d t h e y in t e r p r e t e d m a n y f e w e r s t r in g s c o r r e c tl y . B u t s u b v o c a lr e h e a r s a l a l o n e w a s n o t s u f f ic i e nt t o s u p p o r t i n t e r p r e t a t i o n . S u b j e c ts w e r e n o t j u s t u s i n gt h e f a c t th a t a r t i c u l a t i n g th e s t r in g N - M - E f e el s l ik e a r ti c u l a t in g ' e n e m y ' . G i v e n t h i sk i n e s t h e t i c s t r a t e g y , t h e i n n e r e a r w o u l d n o t b e n e e d e d a n d i r r e l e v a n t s p e e c h w o u l d n o ti m p a i r p e r f o r m a n c e . Y e t i t c l e a r l y d o e s , i n d i c a t i n g t h a t s u b j e c t s u s e a s t r a t e g y t h a tr e q u i r e s b o t h t h e i n n e r v o i c e a n d t h e i n n e r e a r . A p p a r e n t l y , s u b j e c t s p r o d u c e t h er e p e t i t io n s w i t h t h e i n n e r v o i c e, 'l i st e n ' w i t h t h e in n e r e a r , a n d t h e n i n t e r p r e t t h e a u d i t o r yo r p h o n o l o g i c a l s t r e a m . T h e s e r e s u l t s g e n e r a l i z e t h e p a t t e r n o b s e r v e d i n E x p e r i m e n t 1 -t h i s t a s k a l s o r e l i e s o n a p a r t n e r s h i p b e t w e e n s u b v o c a l i z a t i o n a n d t h e a u d i t o r y b u f f e r .

1 0 0 -9 0 -8 0 -

3 s o - n e r E a r

, . . . . . .~ 4 0 -~. 30-2 0 - B l o c k e d1 0 -

0 Inner Voice Inner VoiceAl lowed Blocked

Fig. 1. Perform ance percent correct) when subjects tried to interpre t letter strings pronounceableas English words. Subjects performed with the inner v oice available or blocked (by artieulatorysuppression) and w ith the inne r ear av ailable or blocked (by irrelevant aud itory input).


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1440 J.D . SMITH, M. WILSON and D. REISBERGE X P E R I M E N T 3 : F A M I L I A R T U N E S

B o t h o f th e t a s k s w e h a v e e x a m i n e d s o fa r h a v e r el ie d o n s u b v o c a l i z a t i o n , b u t b o t h h a v ea l s o f e a tu r e d j u d g e m e n t s a b o u t l a n g u a g e . I s th e u s e o f s u b v o c a l i z a t i o n r e s t r i c te d t oi m a g e r y f o r l i n g u i s t ic m a t e r i a l s , o r i s i t a l s o u s e d f o r a m o r e g e n e r a l r a n g e o fr e p r e s e n t a t i o n s ? T o a d d r e s s t h is q u e s t io n , w e t u r n t o a t a s k t h a t r e q u i r e s a j u d g e m e n ta b o u t p i t ch . W i l l s u b j e c t s s ti l l u s e s u b v o c a l i z a t i o n f o r t h i s t a s k ?Method

Subjects. Twenty mem bers of a university community were pai d for their par tic ipa tion.Interference manipulations. This experiment again ado pted a stand ard 2 x 2 selective- interference design(within-subjects) , with th e order of presen tation of the conditions counterbalanced across subjects. Subjects wereverbally instructed abo ut the interference at the beginning of each condition. A rticula tory suppression was ag ainprov ided by having subjects repeat ' tah - tah ' a loud, and au ditory interference was prov ided through headphones,with subjects hear ing " Tak e M e Out T o Th e Ball Ga me " being sung. Melodic mate r ia l was used as theinterference to m aximize the similarity between the interference ma teria l an d the ta sk mate rial. (Moreover, in thiscase a pilo t stud y had shown no interference effect from listening to prose.) Th e interference activity, wh enrequired fo r a con dition, began before the st imulus sheet was presented to the subject, and co ntinued un til the lasti tem was marked. No str ic t pace was set for repeating, but subjects who stopped repeating altogether werereminded by the experimenter's tappin g on the table .Stimuli. Stimuli were 32 familia r tunes (children's song s, showtunes, etc.), eigh t pe r condit ion . Stimuli alwaysapp eared in the same ord er for each subject, but, because the sequence of conditions was counterbalanced, theassignment of st imuli to the va r ious conditions was as well .Procedure. Subjects f irst heard the opening bars o f each tune being played on a p iano ( tape-recorded) , andwere asked to identify i t . This ensured that a ll stimuli had been heard recently by the subject, and also allowed usto exclude from analysis any stimuli unfamiliar to the subject. After subjects had heard all the tunes once, theywere then given the following instructions: "Y ou will be shown the names of familiar songs, and as ked to decidewhether th e me lody r ises or fa lls f rom the second o the thirdnote. Fo r example , 'Pop G oes The W ease l ' should b emarked ' r i ses ', whi le 'Take M e Out To The Ba l l Game ' should be m arked ' f a l l s ' . Do not ac tua l ly sing or hum thetunes. Instead, imaginehearing the tunes to help you decide." Th e song titles were then presented, wi th the songsfor tha t con dition l isted on a single sheet. All of the songs l isted did in fact change in pitch between the second a ndthird no tes-- i .e , the correct response was never 's tays the same' . The a ppro priate interference for each co ndition(if any) w as begun before the l ist of t i tles was presented.R e s u l t s

W i t h n o i n t e rf e r en c e , s u b j ec t s j u d g e d p i t c h c o n t o u r s s u c c es s fu l ly 8 3 % o f t h e t im e( c h a n ce p e r f o r m a n c e w o u l d b e 5 0 % ) . B u t , u n d e r s u p p r e s s i o n o r i r r e le v a n t a u d i t o r y i n p u t ,p e r f o r m a n c e d e c l i n e d t o 6 5 a n d 68,/0, r e s p e c t iv e l y , a n d s t a y e d a t 6 8 % w h e n s u b j e c t s w e r eu n d e r b o t h k i n d s o f i n te r f e re n c e s i m u l t a n e o u s l y . ( P e r fo r m a n c e i n a l l c o n d i t i o n s w a sr e l i a b l y a b o v e c h a n c e - l e v e l s . ) T h i s p a t t e r n s u g g e s t s t h a t a l l i n t e r f e r e n c e c o n d i t i o n s h u r tp e r f o r m a n c e a b o u t e q u i v a l e n t ly . T h is p a t t e r n w a s c o n f i r m e d b y a n a l y z i n g t h e d a t a u s i n g at w o - w a y A N O V A w i t h S u p p r e s s i o n ( a b s e n t - p r e s e n t ) a n d I r r e l e v a n t S p ee c h ( a b s e n t -p r e s e n t ) a s w i t h i n - s u b j e c t f a c t o rs . T h e r e w a s a s i g n i f ic a n t i n t e r a c t i o n b e t w e e n S u p p r e s s i o na n d I r r e l e v a n t S p e e ch [ F (1 , 1 9 ) = 4 . 7 0 , P < 0 . 0 5 , M S e = 3 0 1 . 1 ] . M o r e o v e r , p o s t - h o c t e s t sc o n f i r m e d t h a t a l l t h r e e i n t e r fe r e n c e c o n d i t i o n s ( s u p p r e s s i o n , i r r e l e v a n t s p e e c h , o r b o t h )p r o d u c e d e q u i v a l e n t p e r f o r m a n c e , a n d a ll p r o d u c e d w o r s e p e r f o r m a n c e t h a n w h e n n oi n t e r f e r e n c e w a s p r e s e n t .Discuss ion

T h i s r e s u lt r e ve a l s t h e p a r t n e r s h i p p a t t e r n o n c e a g a i n . W e k n o w t h a t s u b j e c t s m u s ts u b v o c a l i z e t o p e r f o r m w e l l i n th i s t a s k b e c a u s e b l o c k i n g s u b v o c a l i z a t i o n i m p a i r sp e r f o r m a n c e . B u t t h e y a l s o n e e d a c c e s s t o t h e in n e r e a r , g i v e n th e i m p a c t o f i r r e l e v a n ta u d i t o r y i n p u t s o n p e r f o r m a n c e . W e t h e r e f o r e co n c l u d e t h a t s u b j e c t s s i ng th e s e tu n e s a n d


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l i s t e n t o t h e m s e l v e s w i t h t h e i n n e r e a r , j u d g i n g t h e p i t c h c h a n g e s f r o m t h e s e a u d i t o r yrepresentat ions .

Whi le th i s resu l t p la in ly does ex tend the partnersh ip pat t ern to a musica l judgement ,further research w ou ld be use fu l for judg in g ho w lyr ics f igure in the present resu lt s . O urt a s k , r e q u i r i n g s u b j e c t s t o j u d g e a p i t c h c h a n g e f r o m t h e s e c o n d t o t h e t h i r d n o t e , c a ns u r e l y b e d o n e w i t h o u t r e f e r e n c e t o l y ri cs , b u t , a t t h e s a m e t im e , w e k n o w t h a t s o n g l yr ic sare a pow erfu l ret r ieva l cue for melod ies [22 , 35 , 36 ]. Thus , subjects m ight re ly on the lyr icst o h e l p s c a n t h r o u g h t h e t a r g e t m e l o d i e s . T h i s w o u l d i n t r o d u c e a l i n g u i s t i c e l e m e n t i n t oo u r t a s k , a n d t h i s c o u l d e n c o u r a g e u s e o f t h e p h o n o l o g i c a l l o o p . T h u s , a v a l u a b lee x p e r i m e n t i n t h is a r e a w o u l d b e o n e t h a t t a u g h t s u b je c ts w o r d l e s s t u n e s , a n d t h e n s t u d i e dt h e e f f e c t s o f i n t e r f er e n c e .

E X P E R I M E N T 4: P L U R A L A N D P A S T - T E N S E M O R P H E M E SO u r fi r st t h r e e e x p e r i m e n t s h a v e d o c u m e n t e d a c o n s i s te n t p a t te r n . W e h a v e c h o s e n t a s k st h a t s e e m e d l i k e l y t o d r a w o n a u d i t o r y i m a g e r y a n d , i n e a c h c a s e , i m a g e r y p e r f o r m a n c e

has re l ied on an inner-ear / inner-vo ice partnersh ip . Exp er imen t 4 , how ever , dem onstr atesthat there are except ions to th i s partnersh ip pat t ern . In i t s f oca l t ask , subject s madej u d g e m e n t s a b o u t t h e p r o n u n c i a t i o n o f w o r d - f i n a l p h o n e m e s . I n p a rt ic u la r , w e u s e d t h ei n f le c t i o n a l m o r p h e m e s f o r p a s t te n s e a n d f o r p l ur a ls , t a k i n g a d v a n t a g e o f t h e f a c t t h a t t h ep r o n u n c i a t i o n o f t h e s e m o r p h e m e s i s a l te r e d b y th e v o i c in g o f th e p r e c e d in g s e g m e n t . F o re x a m p l e , ' c a t s ' e n d s i n a n u n v o i c e d / s / s o u n d b u t ' d o g s ' e n d s i n a v o i c e d / z / s o u n d .S im i la rl y, ' w a l k e d ' e nd s in a n u n v o i c e d / t / s o u n d b u t ' j og g e d ' en d s i n a v o i c e d / d / s o u n d .M e t h o d

Subjects. T w e n t y - f o u r m e m b e r s o f a u n i v e r si t y c o m m u n i t y w e r e p a i d p a r t i c i p a n t s i n t h e b r i e f ex p e r i m e n t .( T h e s e s a m e s u b j e c t s h a d a l s o s e r v e d i n E x p e r i m e n t 2 . ) S u b j e c t s w e r e a s s i g n e d a t r a n d o m t o o n e o f f o u rexpe r im en ta l cond i t ion s - - -no in t e rfe rence , a r t ieu la to ry s u ppre s s ion a lone , i r r e l evan t s peech a lone , o r bo th .Stimuli. Two s t imu lus l i s t s we re p repa red , w i th 10 s t imu l i on each l i s t . One o f the l i s t s con ta ined words a l le n d i n g i n t h e l e t t e r ' s ' ; s o m e o f t h e w o r d s w e r e p l u r a l n o u n s ; o t h e r s w e r e p r e s e n t - t e n s e v e r b s ; o t h e r s w e r ep o s se s si v es . E a c h o f t h e w o r d s o n t h e l i st h a d a d i f f e r en t p e n u l t i m a t e p h o n e m e ( i. e. t h e p h o n e m e d e t e r m i n i n gw h e t h e r t h e f i n a l 's ' w i l l b e v o i c e d o r n o t ) ; i n o t h e r w o r d s , e a c h p e n u l t i m a t e p h o n e m e a p p e a r e d o n l y o n c e i n t h es er ie s. G i v e n t h e v a r i e t y o f p e n u l t i m a t e p h o n e m e s , h a f t o f t h e w o r d s o n t h e l i s t w o u l d b e p r o n o u n c e d w i t h t h ew o r d - f i n a l p h o n e m e v o i c e d , a n d o t h e r h a l f u n v o i c e d . T h e s e c o n d l i st c o n t a i n e d p a s t - te n s e v e r b s , e a c h s p el le d w i t ht h e r e g u l a r ' e d ' e n d i n g . A g a i n , e a c h w o r d o n t h e l i st h a d a u n i q u e p e n u l t i m a t e p h o n e m e , s u c h t h a t h a l f o f t h ew o r d s w o u l d b e p r o n o u n c e d w i t h a t e r m i n a l / e d / , a n d h a l f w i t h a t e r m i n a l / t / . N o w o r d s w e r e in c l u d ed in e i t h erl i s t fo r w h ich the in f l e c t ion wou ld a dd a s y ll ab le -- -i .e , we exc luded words l ike ' ba t ' (pa s t t ens e 'ba t t ed ' ) and' h o u s e ' ( p l u r a l ' h o u s e s ') .P r e s u m a b l y , s u b j e ct s d o n o t k n o w e x p li c it ly w h i c h w o r d - f i n a l p h o n e m e s m u s t b e v o i c e d a n d w h i c h a r eu n v o i c e d . B u t s u b j e ct s s u r el y c a n d i s c r i m i n a te u p o n h e a r i n g w h i c h a r e w h i c h . T h e q u e s t i o n i n E x p e r i m e n t 4 i sw h e t h e r s u b j e c t s c a n m a k e t h i s j u d g e m e n t f r o m i m a g e d s o u n d s .Interference manipulations. Th is expe r im en t ag a in em ployed a 2 x 2 s e l ec t ive - in te r fe rence de s ign (be tweens u b j ec t s) . A r t i c u l a t o r y s u p p r e s s i o n w a s p r o v i d e d b y h a v i n g s u b j e c t s r e p e a t ' S u z ie - S u z ie ' a l o u d w h i l e m a k i n g a l lt h e S v s Z ju d g e m e n t s , a n d ' t e d d y - t e d d y ' f o r a l l o f t h e T v s D j u d g e m e n t s . I n t h i s w a y w e p r o v i d e d s u b a r t i c u l a t e dm a t e r i a l t h a t w a s p h o n o l o g i c a l l y s i m i la r t o t h e t o - b e - ju d g e d m a t e r i a l. I r r e l e v a n t sp e e c h i n p u t t o o k t h e f o r m o fr e p e t i t i o n s o f e i t h e r ' S u z i e ' o r ' t e d d y ' t h r o u g h h e a d p h o n e s , c o r r e s p o n d i n g t o t h e t o - b e - j u d g e d m a t e r i a l , o n c ea g a i n t o p r o v i d e d i s r u p t iv e p h o n o l o g i c a l m a t e r i a l . I n t e r f e re n c e b e g a n b e f o r e t h e s t im u l u s s h e e t w a s p r e s e n t e d ,a n d c o n t i n u e d u n t i l a f t e r t h e l i s t w a s c o m p l e te d . A g a i n , n o s t ri c t p a c e w a s s e t f o r r e p e a t i n g , b u t s u b j ec t s w h op a u s e d w e r e r e m i n d e d t o c o n t i n u e .Procedure. S - Z s u b j e ct s w e r e t o l d t h a t t h e y w o u l d s e e w o r d s e n d i n g i n S t h a t w o u l d e i t h e r s o u n d a s t h o u g ht h e y e n d e d i n ' s ' o r e n d e d i n ' z ' . T h e y w e r e t o i m a g i n e h e a r i n g e a c h w o r d s p o k e n a l o u d , a n d m a r k t h e o n e s t h a ts o u n d l i k e t h e y e n d i n ' z ' . T - D s u b j e ct s w e r e t o l d t h a t s o m e p a s t - t en s e v e rb s t h a t e n d i n ' e d ' c a n b e p r o n o u n c e d a si f t h e y e n d w i t h ' t ' i n s t e ad . T h e y w e r e t o l d t o i m a g i n e e a c h w o r d o n t h e i r li s t s p o k e n a l o u d , a n d t o m a r k t h e o n e st h a t s o u n d l i k e th e y e n d w i t h a ' t ' s o u n d . T h e w o r d i n g f o r t h e T - D i n s t r u c t i o n w a s m o r e c a r e f u l t h a n f o r t h e S - Z


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1442 J.D. SMITH ,M. WILSONand D. REISBERGinstruction because som e pilot subjects refused to believe that an y of the stimu li co uld end in a 't ' sound.Following these instructions, subjects received instructions app ropriate to their interference condition.Results

T a b l e 1 s h o w s t h e l ev e ls o f p e r f o r m a n c e i n al l e i g h t c o n d i t i o n s o f t h e e x p e r i m e n t . W h e nt h e p l u r al d a t a w e r e a n a ly z e d u s in g a t w o - w a y A N O V A w i t h S u p p r e s si o n ( a b s e n t -p r e s e n t ) a n d I r r e l e v a n t S p e e c h ( a b s e n t - p r e s e n t ) a s b e t w e e n - s u b j e c t f a c t o r s , t h e r e w a s am a i n e f f e c t f o r S u p p r e s s i o n [ F (1 , 2 8 ) = 5 . 76 , P < 0 .0 5 , MSe = 1 . 9 6 ] ; b u t n o t f o r I r r e l e v a n tS p e e c h [ F ( 1 , 2 8 ) = 0 . 78 , MSe = 1 . 9 6 ] , a n d t h e r e w a s n o i n t e r a c t i o n b e t w e e n S u p p r e s s i o na n d I r r e l e v a n t S p e e c h [ F ( 1 , 2 8 ) = 0 .0 2 , MSe = 1 . 9 6 ] . I n a l l c o n d i t i o n s , p e r f o r m a n c e w a sr e l i a b l y a b o v e c h a n c e - l e v e l s .

T h e p a s t - t e n s e d a t a s h o w e d t h e s a m e p a tt e r n : a m a i n e f fe c t f o r S u p p r e s s i o n[ F ( 1 , 2 8 ) = 7 . 1 5 , P < 0 . 0 5 , MSe=l.26]; b u t n o t f o r I r re l e v a n t S p e e c h [ F ( 1 , 2 8 ) = 1 . 2 1 ,MSe = 1 .2 6 ], a n d n o i n t e r a c t i o n [ F ( 1 , 2 8 ) = 0 . 6 2 , MSe = 1 . 2 6 ] . A g a i n , p e r f o r m a n c e i n a l lc o n d i t i o n s w a s a b o v e c h a n c e le v el s.Discussion

L i k e t h e t a s k s o f E x p e r i m e n t s 1 - 3 , su b j e ct s p e r f o r m e d b e s t w h e n t h e y w e r e a b l e t os u b v o c a l iz e . A r t i c u l a t o r y s u p p r e s s i o n h u r t t h e i r c a p a c i t y to ju d g e t h e s o u n d o f p l u r a l a n dp a s t - t e n s e m o r p h e m e s . H o w e v e r , t h e r e t h e r e s e m b l a n c e w i t h p r e v i o u s r e s u l t s e n d s : I nE x p e r i m e n t 4 , th i s c o v e r t a r ti c u l a t io n a l o n e w a s s u f fi ci en t t o s u p p o r t o p t i m a l p e r f o r m a n c e .S u b j e c ts m a y h a v e b e e n j u s t a r t i cu l a t in g ' d o g s ' a n d ' w a l k e d ' a n d f e el in g th e k i n e s t h e ti cc u e s p r o v i d e d b y t h a t e n a c t m e n t . T h e r e i s n o e v i d e n c e , a s t h e r e w a s i n p r e v i o u se x p e r i m e n t s , t h a t t h e i n n e r e a r w a s n e e d e d f o r t h i s t a s k , o r t h a t t h i s t a s k r e v e a l s a n yp a r t n e r s h i p b e t w e e n t h e i n n e r e a r a n d i n n e r v o i c e .

O n e m i g h t w o r r y , o f c o u r s e , t h a t t h e m o r p h e m e t a s k i s j u s t t o o e a s y to b e a f f e c te d b yi n t e rf e r e n c e in t h e i n n e r e a r . O r p e r h a p s t h e i n n e r - e a r i n t e rf e r e n c e u s ed w a s t o o w e a k . B u tt h e m o r p h e m e t a s k w a s n o t a t c e i l i n g , a n d w a s s u b j e c t t o i n t e r f e r e n c e ( i n t h e i n n e r v o i c e ) .A n d t h e i n n e r - e a r m a n i p u l a t i o n w a s v e r y s i m i la r t o t h o s e th a t i m p a i r e d p e r f o r m a n c e i nE x p e r i m e n t s 1 a n d 2 , a n d m o r e o v e r r e li ed o n p h o n o l o g i c a l m a t e r i a l h i g h ly s i m i l a r t o t h em a t e r i a l i n t h e f o c a l t a s k , m a k i n g i t p o t e n t i a l l y e s p e c ia l l y d i s r u p t i v e i n t h i s p a r t i c u l a r

Tab le 1. Perform ance und er selective-interferenceconditions when theinner v oice was available or blocked (by articulatory suppression) andwhen the inner ear w as available or blocked (by irrelevant auditoryinput). (A) Percen t correct when subjects udg ed w hether wo rds spelledwith 'S' are pronounced with 'S' o r 'Z ' . (B) Percent correct whensubjects judged w hether words spelled with 'E D ' are pro nounced with'D ' o r 'T '

Inner voiceAvailable Blocked

(B) T/D judgem entsInner earAv ailable 84 70Blocked 85 77

(A) S/Z judgementsInner earAv ailable 90 78Blocked 94 85


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SUBVOCALIZATION N AUDITORY MAG ERY 1443i n s t a n c e . Y e t t h e r e w a s n o d i s r u p t i o n . T h e r e s e e m s t o b e s o m e t h i n g d i f f e r e n t a b o u t t h em o r p h e m e t a s k t h a t n e e d s e x p l a i n i n g . I n p a r t i c u l a r , i t i s i n t r i g u i n g t h a t t h e i n n e r v o i c er e m a i n s r e l e v a n t f o r t h is t a s k e v e n w h e n t h e i n n e r e a r d r o p s o u t e n t i re ly . T h i s s u g g e s t s t h a tt h e i n n e r v o i c e c a n p r o v i d e d i f f e r e n t s o r ts o f c u e s a n d s i g n a l s t o t h e c o g n i t i v e s y s t e m .P o s s i b l y s u b v o c a l r e h e a r s a l i s u s e d m o r e k i n e s t h e t i c a l ly i n th i s c as e , s o t h a t t h e r e s t o f t h ep h o n o l o g i c a l l o o p s y s t e m d o e s n o t c o m e in t o p l a y f o r th e s / z o r t / d t a sk s . I n d e e d , g i v e nt h is r e s u lt , o n e m i g h t a r g u e t h a t t h e s /z a n d t / d t a s k s a r e ' k i n e s t h e ti c j u d g e m e n t s , ' a n d n o tt a s k s o f a u d i t o r y i m a g e r y p r o p e r . W e w o u l d s u g g e s t, h o w e v e r , t h a t l i tt le h a n g s o n t h i sc l as s if i ca t io n , a n d , o n a n y a c c o u n t , t h e se t a s k s a r e c le a r ly p e r t in e n t t o o u r u n d e r s t a n d i n go f t h e f u n c t i o n o f t h e i n n e r - e a r/ i n n e r - v o i c e p a r t n e r s h i p .

E X P E R I M E N T 5: H O M O P H O N E ST h u s f a r a ll f o u r a u d i t o r y - i m a g e r y t a sk s h a v e b e n ef it ed f r o m s u b v o c a l r e h ea r sa l , a n d

t h r e e o f t h e m h a v e r e v e a l e d t h e in n e r e a r a n d i n n e r v o i c e i n p a r t n e r s h i p . I t a p p e a r s t h a tj u d g e m e n t s a b o u t i m a g i n e d s o u n d s o f t e n r el y o n t h e c o m p o n e n t s o f , o r e v e n h a v e t h ep r e c i se a r c h i t e c tu r e o f , t h e p h o n o l o g i c a l l o o p s y s t e m p r o p o s e d b y B a d d e l e y a n d o t h e r s .

H o w e v e r , t h i s r e l ia n c e m a y n o t e x t e n d t o a l l t a s k s o f a u d i t o r y i m a g e r y , a n d j u d g e m e n t sa b o u t p s e u d o - h o m o p h o n e s s e e m a c a n d i d a te f o r s u ch a ta s k . W o u l d ' p h y t e ' s o u n d l i ke a nE n g l i sh w o r d i f p r o n o u n c e d a l o u d ? W o u l d ' c a y o s s '? A n s w e r i n g t h e s e q u e s ti o n s s e e m s t or e q u ir e a ju d g e m e n t a b o u t s o u n d , y e t t he s e j u d g e m e n t s s h o w s u b s t an t ia l i n d e p e n d e n c ef r o m t h e p h o n o l o g i c a l s t o re a n d f r o m s u b a r ti c u la t io n . F o r e x a m p l e , B a d d e le y a n d S a l a m e[8] f o u n d t h a t i r r e le v a n t s p e e ch i n p u t l e a ve s h o m o p h o n e j u d g e m e n t s u n i m p a i r e d ,s u g g e s t i n g t h e i r i n d e p e n d e n c e f r o m t h e i n n e r e a r . S i m i l a r l y , a r t i c u l a t o r y s u p p r e s s i o nl e av e s h o m o p h o n e j u d g e m e n t s e s s en t ia l ly i n t a c t [5 , 12 ].

H o w e v e r , n o t e a n i m p o r t a n t l im i t a ti o n o f th e se s e p a r a t e i n t e r f e r e n c e s t u d i e s . P e r h a p ss u b j e c t s c a n u s e e i t h e r a k i n e s t h e t i c o r a p h o n o l o g i ca l s t r a te g y in m a k i n g h o m o p h o n ej u d g e m e n t s . I n t h is c as e , t h e re p r e s e n t a t i o n s u s e d t o p e r f o r m t h e t a s k m i g h t ' m o v ea r o u n d ' , a s s u b j ec t s s im p l y s w it c h m o d e s d e p e n d i n g o n w h i c h v a r i e t y o f i n te r f e r e n c e is o nt h e sc e n e. O n t h is v ie w , t h e n , h o m o p h o n e t a s k s w o u l d b e i m m u n e t o d i s r u p t i o n f r o me i t h e r t h e i n n e r v o i c e o r i n n e r e a r a l o n e . O b v i o u s l y t h e c r u c ia l c o n d i t i o n f o r d e t e c t in g t h iss w i t c h in g s t r a t e g y is t o r u n s u b j ec t s w i th b o t h k i n d s o f i n te r f e r e n c e p r e s e n ts i m u l t a n e o u s l y . T o o u r k n o w l e d g e , s u b je c ts h a d n e v e r b e e n r u n u n d e r t h is d o u b l ep h o n o l o g i c a l j e o p a r d y , a n d s o E x p e r i m e n t 5 a t t e m p t e d t o c la r if y t h is s it u a t io n .

M e t h o dSub jec t s . Twelvemem bers of a u niversity comm unity were paid for their participation in the experimen t. Eachsubject made hom ophon e judgem ents under all four experim ental conditions--no interference, articulatorysuppression alone, irrelevant speech alone, or both, and were given these experimen tal treatments in counter-balanced fashion.Inter ference manipulat ions . Th is experim ent's 2 x 2 selective-interferencedesign was carried out within subjects.Articulatory su ppression was pro vided by hav ing subjects count from one to six repetitively, a suppressionmanipulation adopted b y Besner et a l . [12]. Subjects were coached toward s the repetition rate used in Besner e tal. 's Experim ent 6 (metronom e 170). As previously,auditory interference was provided by irrelevant speech heardthrough headpho nes (the reading of prose material).S t imu l i . The stimuli were nonsense words, both pseudo-h omo phon es and otherwise, which were constructedfollowing B esner et a l . [12]. The stimuli were drawn from a set of 48 carefullymatched pairs. One m ember of eachpair was a pseudo-homophone (aynjel or raynbo); the other a nonsense wo rd (ayntel or raunbo). Usin g thesepairs, four 24-w ord lists were constructed. Eac h list contained 12 pseudo-hom ophon es and 12 nonsense word s,but never contained both memb ers of a pair.


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1444 J. D. SMITH, M. WILSON and D. REISBERGProcedure. Subjects were told that they would see strings of letters arranged in lists, and that some of thestrings would sound like actual English words. They were to put a checkmark by the ones that do. It was stressedthat they would be timed, and that they should work as fast as they could without making errors. Subjects Brstworked through a practice list of 12 words structured as described above. When an interference manipulation wasapplied, it was initiated tirst, and then at the experimenters Go the subject turned the page and began the list.In preparation for articulatory suppression, subjects were told that they would also perform a repetitive

counting task, counting from one to six at a rate that they then practiced. In preparation for irrelevant speech,subjects were told they would perform while hearing someone reading over headphones. They were told that theywould not be quizzed on this auditory material and could just ignore it as they worked through the list. Inpreparation for receiving both interference manipulations simultaneously, subjects received both sets ofinstructions.Results

Table 2 shows decision time (latency to complete the 24-item lists) and percent accuracyunder the four conditions. When the latency data were analyzed using a two-way ANOVAwith Suppression (absent-present) and Irrelevant Speech (absent-present) as within-subject factors, there were no main effects and no interaction.

When the error data were similarly analyzed, there was a main effect for suppression[F(l, ll)= 5.32, P< 0.05, h4Se =4.79]; but no main effect for irrelevant speech[F (1, 11) -C1 O, MSe = 1.431; and no interaction [F (1, 11) < 1 O, A4Se = 4.191.Discussion

The latency result replicates others showing that homophone judgements are slowed byneither articulatory suppression nor irrelevant auditory input. The error result shows thathomophone judgements are made only slightly less accurate by articulatory suppression,and are not affected by auditory input. These two results reflect accurately the combinedfindings from several other experiments [5, 8, 121. The key result, though, lies in thecondition with both forms of interference simultaneously present, and both components ofthe phonological loop simultaneously blocked. Subjects make homophone judgementsfluently even then, when they have nowhere to hide.

Thus, the pseudo-homophone task represents a second case in which judgements ofimagined sounds seem not to depend on the partnership between the inner ear and innervoice. We do find a reliable effect of concurrent articulation. As in Experiment 4, thissuggests that if either component of the phonological loop is the more essential element, itis the inner voice. However, Experiment 5 joins others in confirming that homophone

Table 2. Performance under selective-interference conditions when the innervoice was available or blocked (by articulatory suppression) and when theinner ear was available or blocked (by irrelevant auditory input). (A) Averagetime (set) to complete 24 homophone judgements. (B) Percent correct inmaking 24 homophone judgements

Inner voiceAvailable Blocked(A) Time to completionInner earAvailableBlocked(B) Percent correctInner earAvailableBlocked

30.5 31.730.8 29.8

89 8289 83


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S U B V O C A L I Z A T I O N I N A U D I T O R Y I M A G E R Y 1445

pe r f o r m ance i s s ubs t an t i a l l y s pa r ed even wi t h t he i nne r vo i ce den i ed . Seve r a l f a c t o r sp r o b a b l y c o n t r i b u t e t o t h i s p a t t e r n : O u r p s e u d o - h o m o p h o n e t a s k r e q u i r e s a j u d g e m e n tabo u t a s ing le r ep r e s en t a t i on , r a t he r t han a com par i s on am ong m ul t ip l e r ep r e s en t a ti ons ;t he t a s k r e li es on an eno r m ous l y we l l -p r ac ti c ed t r ans l a ti on ( f r om p r i n t t o phono l ogy) ; t het a s k a l s o r equ i r e s no ana l ys is o r d i s s ect ion o f t he r ep r e s en t ed s ound . W hi ch o f t he s ef ac t o r s a r e c r uc i al , t hough , r em a i ns a t op i c f o r f u t u r e r e s ea r ch . C l ea r ly , t hough , p s eudo-ho m op ho ne pe r f o r m ance r ai se s in t e r e s ti ng ques t i ons abou t w hen a t a s k wi ll s how t hepa r t ne r s h i p pa t t e r n , and wh en no t . W e cons i de r th i s is s ue be low.

G E N E R A L D I S C U S S I O NI n t h r ee t a s ks we obs e r ved a pa r t ne r s h i p be t ween t he i nne r e a r and i nn e r vo ice . Tha t is ,s ub j ec ts s ubvoca l l y r ehea r s ed t he r equ i r ed i m ag e r y m a t e r ia l , t he r eby r ep r e s en t i ng i t i n apho no l og i ca l s to r e ( the i nne r e a r ) , and t h i s enab l ed t hem t o m ake a j udg em en t abou t t he

i m age ' s s ound p r ope r t ie s . Ev i dence f r om o t he r dom a i ns em phas i ze s bo t h t he b r ead t h andthe the ore t i ca l s igni f icance of th i s par tnersh ip p a t t e rn .F i r s t, a s we have m en t i oned , s ho r t - t e r m m em or y r ehea r s a l r elie s on a pho no l og i ca l l oops ys t em t ha t a l s o f ea t u r e s an i n t e r ac t i on be t ween s ubvoca l r ehea r s a l and a phono l og i ca l

s tore [3 , 4 , 30 ] . In fa c t , the s imi la r i ti es tha t l ed us to b or ro w h eavi ly f ro m the w orkin g-m em or y m o de l i n r e s ea r ch i ng aud i t o r y i m age r y l ed Badde l ey and Log i e [7 ] t o a s k i f t hep h o n o l o g i c a l m e m o r y s y s t e m m i g h t e v e n b e t h e s e at o f a u d i t o r y i m a g e ry .As ano t he r exam pl e o f t he pa r t ne r s h i p , s i l en t m ou t h i ng o f v i s ua l l y - p r e s en t ed l i s t sc rea tes m em or y e ffec ts tha t w ere long a t t r ibute d to acou s t i c cod ing (e.g. the su tt ix e f fec t) ,and s om e o f t he se e f fec ts do no t occu r i f l ip m ovem en t s a r e d i s cou r aged [ 43 ] ( f u r t he rd i s cuss i on o f aud i t o r y - m oda l i t y ef fects c an be f o und i n [ 18 , 20, 23 , 44 ] ). Th e pa r t ne r s h i pm ode l exp l a i n s t h i s pa t t e r n : s ubvoca l i zed ( m ou t hed ) s peech i m ages cou l d we l l l oad t hei nne r ea r , and p r od uce pho no l og i ca l ( 'aud i t o r y ' ) e f fec ts i n a wa y t ha t i m ages den i eds ubvoca l i za t i on do no t .

Th e r e i s a l so ev i dence t ha t w h i s pe r ed and m ou t h ed r epe t i ti ons o f s y l lab le s caus e V O Tbo un da ry sh i f ts in the ide nt i f i ca t ion of speech s t imul i [17]. Thi s resu l t is prob lem at ic i fhab i t ua t i on e f fec ts a r e v i ewed a s pu r e l y aud i t o r y ; bu t n o t i f we a s s um e t ha t s ub voca lr ehea r s a l l oads t he i nn e r e a r , and t ha t s om e hab i t ua t i on e f f ect s r e s ide wi t h in t ha t quas i -p e r c e p t u a l m e d i u m .F i na l l y , t he i nne r - ea r /i nne r - vo i ce pa r t ne r s h i p a l so ho l ds p r om i s e f o r exp l a i n ing t heha l l uc i na t i ons o f s ch i zophr en i a [ 60 ] . Sens o r y t heo r i e s o f h a l l uc ina t i ons hav e f a il ed t o

exp l a i n why aud i t o r y ha l l uc i na t i ons ( i . e . vo i ce s ) s o dom i na t e t he s ch i zophr en i c ' sexper ience , and why the voices seem poor ly exte rna l i zed ( i . e . they seem to res ide in thepa t i en t ' s t h r oa t and head ) . As one s ch i zophr en i c s a i d , " I 'm hea r i ng t he vo i ce s aga i n - -t h e y ' r e c o m i n g r i g h t th r o u g h t h e v o ic e b o x . " A n o t h e r s ai d, " s o m e b o d y is a t t a c k in g m ean d m y l ips m ov e" (G ou ld [31] , p . 424; see a l so Go uld [32]) . The se observa t ion s a reea s i l y exp l a i ned , t hough , on t he v i ew t ha t s ch i zophr en i c s s ubvoca l i ze and t hen "hea r "t he ha l l uc i na t o r y s peech i m ages t ha t r e s u l t . Cons i s t en t wi t h t h i s , e l e c t r om yogr aphys om e t i m es r evea l s a r t i cu l a t o r y ac t i v i t y co r r e l a t ed wi t h ha l l uc i na t i ons . Mor eove r , s om et he r apeu t i c i n t e r ven t i ons ( and s om e con t r o l l ed s t ud i e s ) have r educed ha l l uc i na t i ons byhav i ng s ch i zophr en i c s c l am p t he i r a r t i cu l a t o r s , m uch a s we do i n ou r expe r i m en t s t ob l ock us e o f t he i nne r vo i ce . Thus , s ch i zophr en i c vo i ce s m ay r ep r e s en t ye t ano t he r


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1446 J.D. SMITH, M. WILSON and D. REISBERG

(a lbe i t b izar re ) ins tanc e of the inner -ear / inner -vo ice par tnersh ip . ( Fo r de ta i l eddiscuss ion, see [13 , 29, 60] . )Thus s peech pe r cep t i on and s peech p r oduc t i on i n t e r ac t i n a va r i e t y o f t a s ks anddom a i ns . I n o t he r con t ex t s , s i m i la r i n t e r ac t i ons have been exp l a ined by t he M ot o r T heo r yo f Sp eech Pe r cep t i on [ 38 ], o r by l i nk i ng s peech pe r cep t ion c l o s e ly to t he pe r cep t i on o fa r t i cu l a t o r y ge s t u re s [ 28 ]. W i t hou t endor s i ng e i t he r a ccoun t , we do endor s e a conce r t ede f f o r t t o de s c r ibe m or e f u ll y t he p r oces si ng i n te r ac t ions l ink i ng aud i t o r y pe r cep t i on an dpr odu c t i on . T r ac i ng t he connec t i ons j o i n i ng s peech , im age r y , and m em or y r e s ea r ch m ayenc our age a c loser ana lys i s of th i s in te rac t ive u t i li ty .

Of cou r s e , ques t i ons do r em a i n abou t t he na t u r e o f t he i nne r - ea r / i nne r - vo i cepa r t ne r s h i p , and we cons i de r t h r ee now. F i r s t, w e cons i de r t he r o l e o f t he pa r t ne r s h i pin cogni t ive process ing , wi th an emphas i s on when i t i s used , and when i t i s not . Second,we cons i de r t he l evel o f abs t r ac t i on a t wh i ch t he pa r t ne r s h i p o pe r a t e s. T h i r d , w e cons i de rt h e f u n c t i o n a l n e u r o a n a t o m y o f th e i n n e r e a r a n d i n n e r v oi ce .T h e fu n c t io n o f t h e p a r tn e r s h ip i n c og n it iv e p r o c e s s in gAc cor d i ng t o an em er g i ng cons ens us , t he phono l og i ca l l oop s ys t em appea r s no t t o beneede d f o r a va r i e t y o f l anguage f unc t i ons . It i s no t needed , f o r exam pl e , a s a bu f f e r o ra s s em bl y p l a t f o r m f o r no r m a l s peech p r oduc t i on . N or is i t nece ss a r y f o r no r m a l l anguagecom pr ehen s i on , o r f o r r ead i ng ( e i t he r s i ng le - wor d ta s ks, o r even eve r yday r ead i ngc o m p r e h e n s i o n ) .Reg a r d i ng s peech p r oduc t i on , even pa t ien t s wi t h p r o f ou nd l y i m pa i r ed s ho r t - t e r mm em or y s ys tem s can have r ea s onab l y no r m a l conve r s a t i ona l s peech : Va l l a r and Badde l ey[ 62 , 63 ], f o r exam pl e , s t ud ied a pa t i en t ( P . V. ) who was i m pa i r ed on a va r i e t y o f s t anda r dwo r k i ng - m e m o r y m eas u r e s . None t he l e s s , t h is pa t i en t s howed r ap i d v o l un t a r y a r t i cu l a t i onand no rm al co nve rsa t iona l speech ( see a lso [47 , 58]) . Ga therc ole and Bad deley ([30], p . 89)conc l ude t ha t " t he we i gh t o f neu r ops ycho l og i ca l ev i dence f avour s t he v i ew t ha t no r m a lphono l og i ca l wor k i ng m e m or y sk ills a r e no t neces s a r y f o r t he p lann i ng a nd p r o duc t i on o fs pon t ane ous s peech" . Rega r d i ng s peech pe r cep ti on , s eve re defi cits o f t he phono l og i ca ll oop s ys t em can s till s pa r e l anguage com pr ehens i on . Al l t h r ee o f War r i ng t on et al . ' s [69]s ho r t - t e r m m em or y pa t ien t s had r ea s onab l e l anguage com pr ehens i on , a s d i d P .V. ( see a l so[65]).Rea d i ng a l s o p r oceeds wi t hou t u s i ng t he phono l og i ca l loop a s a p r i n t - t o - s ound bu f fe r .The pho no l o gy o f s ing le wor ds can be f l uen tl y de r i ved f r om p r i n t even wh i l e a rt i cu l a ti on i ss uppr e s s ed ( e. g. t he s peed a nd accu r acy o f p s eudo- h om oph one ve r i f ic a t ion is p r e s e rved ;s ee [5 , 12 ] ) , and even wh i le bo t h com pone n t s o f t he l oop a r e b l ocked s i m u l t aneous l y( Expe r i m en t 5 ) . Thes e p s eudo- hom ophones a l s o caus e f r equen t e r r o r s by expe r i m en t a l' p r oo f r ead e r s ' ( e. g. t hey ove r l ook t he e r r o r i n " i d l e and boa r d" [ 24 ]); and ps eudo - wo r dsa l so l odge m or e s ecu r e ly i n m em or y t han do o t he r n onw or ds [ 11 ]. Bo t h o f t he s e e ff ect spers i s t even when ar t i cu la t ion i s suppressed .Ar t i cu l a t o r y s uppr e s s ion does no t even a f fec t t he s peed o r a ccu r acy wi t h w h i ch s ub j ect sver i fy s imple sentences [2] or subjec t s ' m em ory for prose passages [72]. A ppa rent ly , then ,t he phono l og i ca l l oop p l ays on l y a m i no r r o l e in no r m a l r ead i ng , e it he r a t t he s i ng l e -wor dleve l or in bas ic reading comprehens ion .Thus , t h r ee s epa r a t e s t r eam s o f on - l i ne l anguage com pr ehens i on - - s peak i ng , l i s t en i ng ,r ead i n g - - f l ow f l uen t l y even when t he i nne r - ea r / inne r - vo i ce pa r t ne r s h i p is den i ed t ocogn i t ive p r oces s ing . So wh a t i s t he pa r t ne r s h i p go od f o r , t hen?


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The p r e s en t r e s u l t s s how t ha t s ubvoca l r ehea r s a l and t he i nne r - ea r / i nne r - vo i cepa r t ne r s h i p is va l uab l e i n f ind i ng new cons t r ua l s f o r i m age r y m a t e r i a l ( Expe r i m en t 1 i n[53]) ; assem bl ing v i sua lly presented ph ono logica l ma ter ia l in to a poss ib le l angua ge s t ream( Exp e r i m en t 2) ; ana l yz i ng a f am i l i a r m e l ody t o c om par e t he p i tches o f d i f f e r en t no t e s( Exp e r i m en t 3 ); and s o f o r t h . Thus , even t hou gh t he pa r t ne r s h i p i s unneces s a r y f o r ' on -l ine ' l angu age p r oces s ing , i t does ap pea r neces s a r y whe neve r a t a s k r equ i r e s s ub jec t s to r e -p r e s en t aud i t o r y m a t e r i a l o r r e - s can i t , i n o r de r t o ana l yze t he m a t e r i a l , m akecom par i s ons , o r f o r m i n t e r p r e t a t i ons o f i t.Seve r a l o t he r r e s u l t s a r e cons i s t en t wi t h t h i s gene r a l v i ew. Fo r exam pl e , r hym ej udge m e n t s wi t h v i s ua l s t im u l i (e .g . do ' ph r a i gm ' and ' s t am e ' r hym e? ) requ i r e t hei ns pec t i on o f m en t a l l y - rep r e s en t ed phono l og i ca l m a t e r i a l , i ts s egm en t a l anal ysi s , and t hent h e c o m p a r i s o n o f t w o s e p a ra t e r e p r es e n ta t io n s . R h y m e j u d g e m e n t s s h o u l d t h e r e fo r e u s et he phon o l og i ca l l oop , and s hou l d be i m pa i r ed by a r t i cu l a t o r y s uppr e ss i on . The y a r e [12,37 , 74 ]. J udg i ng w he t he r t wo wo r ds have t he s am e s t re s s pa t t e r n a l so r equ i r e s r ep l ay i ng thewo r ds com par a t i ve l y , and a l s o bo r r ow s t he phono l og i ca l loop [ 16 ]; s ee a l s o [ 15 ].

O ne m i gh t a l s o expec t tha t p r oces s ing o f pa r ti cu l a r ly com pl ex l anguage wo u l d ove r - t axt he on - l i ne pa r s ing r ou t i ne s , c r ea ti ng a need t o r e ly on s om e s o r t o f ' back - up ' s y s tem , inwh ich input s a re prese rved an d re - inspec ted , off -l ine . In su ch cases l i st eners m ight sw i tchi n t o ' l oop m o de ' , u s i ng t he obv i ous bu f f e r ing u t il it y o f the r ehea r s a l l oop i n o r d e r t o ge tby . G a t he r co l e an d Badde l ey [ 30] d i scus s t he ev i dence s uppor t i ng t h is v i ew.Th ou gh m us i c r em a i ns t h i n l y r e s ea r ched i n r e l evan t ways , we wou l d expec t t he s am epa t t e r n . Recep t i ve m us i c ( l is ten ing ) and p r oduc t i ve m us i c ( si ng ing ) m i gh t we l l no t bo r r o wt he ph ono l og i ca l l oop s ys t em , and m i gh t s u r v i ve d i s r up t ions o f th i s l oop ( e .g . t he r e l evan tneu r ops y cho l og i ca l d i s o rde r s ). H owev e r , wh en t he t a s k r equ i r es t he com p ar i s on o f nove lm e l od i c f r agm en t s [40 ] , o r w hen ana l y t i c j udgem en t s o f m us i ca l m a t e r i a l a r e r equ i r ed( Expe r i m en t 3 i n [ 36 ] ) , we w ou l d p r ed i c t a r e li ance on t he phon o l og i ca l l oop , a ndpe r f o r m anc e de fi c it s unde r a r t i cu l a t o r y s uppr e s si on .Th us t he ph ono l og i ca l l oop s eem s t o be r eq u i r ed whenev e r t he cogn i ti ve sys t em pauses ,and s t eps back f r om i t s f lu i d i npu t a nd o u t pu t m odes , ne i t he r o f wh i ch bo r r ows t he l oop .The l oop p r ov i des a d i s t i nc t i ve i n t e r m es h i ng o f t he i npu t and ou t pu t u t i l i t i e s f o r t hepur po s e o f r e - p r e s en t a t i on , i n s pec t ion , o f f- li ne j udgem en t s an d i n t e r p r e ta t i ons .Th e level o f the partnership in the cognitive sy stem

Can we be m or e p r ec i s e , t hough , abou t how t h i s r e - p r e s en t a t i on occu r s , o r abou t howthe ' inner v oice ' is r ea li zed? Th e neu ropsy cholo gica l ev idence has c r i t ica l ly shap ed ideas o nt h is po i n t . I t i s c l ea r, f o r exam pl e , t ha t s ubv oca l r ehea r s a l does no t dep end o n pe r i phe r a la r t i cu l a t o r y m echan i s m s . Dem ons t r a t i ng t h i s po i n t , Badde l ey and Wi l s on [ 9 ] s t ud i ed ag r ou p o f dys a r t h r i c s , whos e l anguage w as ( cen t ra l ly ) i n t ac t, bu t w ho had l o s t the ab i li ty t ocon t r o l t he a r t i cu l a t o r y m us c u l a t u r e and s peak . Subvoca l r ehea r s a l was c l ea rl y i n t ac t int h e se p a t ie n t s, f o r t h e y s h o w e d n o r m a l m e m o r y s p an s ; a n d s h o w e d t h e u s u a l w o r d - l e n g t hand phon o l og i ca l s i m i l a r it y e f fec ts f o r v i s ua ll y p r e s en t ed m em or y m a t e r i a l . B adde l ey andWi l s on conc l uded t ha t phono l og i ca l cod i ng and s ubvoca l r ehea r s a l c an ope r a t e cen t r a l l yw i tho ut th e ac tua l rea l i za t ion of speech ( see a l so [45 , 64]) .Badde l ey and Wi l s on s ugges t , t he r e f o r e , t ha t s ubvoca l r ehea r s a l i nvo l ves t he cen t r a lm e c h a n i s m s a n d m o t o r s e q u e n ci n g r o u t in e s o f s p ee c hplanning. T h e s e c o n t r o l m e c h a n i s m swer e p r e s um ab l y i n t ac t in t he i r pa t i en ts wh o ha d l ong s pok en no r m a l l y , be f o r e s udden l yf o r f e i ti ng t he s u r f ace and ou t w ar d r ea l iz a t ion o f s peech ac ts . Log i e et al. [39] end orse th i s


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1448 J. D. SMITH, M. WILSON and D. REISBERG

speech -p l ann ing v i ew o f r ehea rsa l , bu t a l so add a cau t i ona ry no t e : Hav ing ov e r t speech ,a n d n o t j u s t c o v e r t, m a y i n c re a s e s p a n s o m e w h a t , j u s t a s M u r r a y [ 42 ] s h o w e d t h a t o v e r tr ehea r sa l by no rm a l i nd iv idua l s i ncr ea se s span . Pos s ib ly , t oo , som e judge me n t s a bo u tspeech sounds may r ea l l y need some more k ine s the t i c s i gna l p rov ided by t he a r t i cu l a to r s(e.g. the s -z an d t --d jud gem ents of Exper im ent 4) . In cases l ike th i s , m ore sur fac er ea l i z a t i ons fo r speech cou ld be r equ i r ed , and we wou ld expec t dysa r t h r i c i nd iv idua l s t of a il in m ak ing t he se j udgem en t s .

Unde r t h i s speech -con t ro l p roposa l , ap r ax i c pa t i en t s - - spec i f i c a l l y t hose w i th ad i s t u rban ce o f speech p l an n ing - - sho u ld show de f ic i ts i n the func t i on ing o f t hephono log i ca l l oop , and t hey do . These pa t i en t s , ope r a t i ng w i thou t a r t i cu l a to rys u p p r e ss i o n , p e r f o r m a v a r i e ty o f t a s k s j u s t a s n o r m a l s d o w h e n o p e r a t in g w i t ha r t i cu l a to ry supp re s s ion [73 ] .

W e wou ld u rge one cau t i on , t hough , i n i n t e rp r e t ing t h is ' s peech -p l ann ing ' v i ew o fsubvoca l i z a t i on . A s we have s een , subvoca l i z a t i on i s d i s rup t ed by concu r r en t ch ewing [53] ,and a l so by t he r equ i r emen t t ha t sub j ec t s ' c l amp ' t he i r a r t i cu l a to r s i n a f r ozen pos i t i on(Expe r im en t 1 , o r [ 53 ]) . These r e su l ts a r e e a s i ly accom m oda t ed i f we a s sume tha t ' s peech -p l ann ing ' i nc ludes bo th t he s e lec t ion o f sounds t o b e u t t e r ed , and a l so some ea r l y s tepstoward p l ann ing t he ac tua

smith, j. d., wilson, m., & reisberg, d. (1995). the role of subvocalization in auditory imagery....

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