Dyschiria. An Attempt at its Systemic Explanation

Neurophysiological and Neuropsychological Aspects of Spatial Neglect, M.Jeannerod (editor) 0 Elsevier Science Publishers B.V. (North-Holland),1987

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DYSCHIRIA. AN ATTEMPT AT ITS SYSTEMIC EXPLANATION Edoardo R i s i a c h and Anna Berti

I t is argued, i n t h i s chapter, t h a t u n i l a t e r a l neglect i s s t i l l i n need of a s y s t e m i c e x p l a n a t i o n . The working h y p o t h e s i s i s t h e n s u g g e s t e d t h a t u n i l a t e r a l n e g l e c t h a s remained c o n c e p t u a l l y i s o l a t e d w i t h i n a syndrome of which i t may c o n s t i t u t e t h e most common, but n o t t h e e x c l u s i v e n o r even t h e n e c e s s a r y component. A t h e o r e t i c a l n e u r a l model of an a n a l o g s u b s e r v i n g b o t h s e n s o r y a n d mental r e p r e s e n t a t i o n i n t h e v i s u o - s p a t i a l domain i s o u t l i n e d . Depending on r e l a t i v e l y minor changes i n i t s l o c a t i o n w i t h i n t h e same f u n c t i o n a l u n i t , a c i r c u m s c r i b e d f a i l u r e of t h e a n a l o g may i n v o l v e n e g l e c t o r m i s r e p r e s e n t a t i o n of one s i d e of s p a c e , t h u s l e n d i n g t h e o r e t i c a l s u p p o r t t o o u r working h y p o t h e s i s . The t e r m hemispatial d y s c h i r i a is proposed f o r t h e syndrome of n e g l e c t - m i s r e p r e s e n t a t i o n a s a l a t e t r i b u t e t o H. Z i n g e r l e . who many y e a r s a g o , i n one of h i s p a p e r s which w a s a f o r e r u n n e r of t h i s s u b j e c t , e m p l o y e d t h i s term.

Introduction Looking back o v e r n e a r l y one c e n t u r y of i n q u i r y i n t o t h e complex c o n d i t i o n which u s u a l l y g o e s by t h e ( a r g u a b l y u n d e r i n c l u s i v e ) name of u n i l a t e r a l n e g l e c t of s p a c e , i t may be n o t i c e d t h a t -- a l m o s t w i t h o u t e x c e p t i o n -- t h i s c o n d i t i o n h a s o n l y been a d d r e s s e d under what might be c a l l e d a d e - i n t e r p r e t a t i v e approach. The t e r m d e - i n t e r p r e t a t i v e i s h e r e u s e d , i n h o p e f u l b u t uncommitted c o r r e s p o n d e n c e w i t h Haugeland (1978). t o d e n o t e t h e s h i f t i n scope which o c c u r s when a n o p e r a t i n g s y s t e m i s not e x p l a i n e d a s a whole but i n t e r m s of i t s s i n g l e components, under t h e assumption t h a t t h e g e n e r a l p a t t e r n b e i n g c a r r i e d o u t by t h e f o r m e r i s opaque t o t h e l a t t e r . S p a c e - r e l a t e d b e h a v i o u r may a c c o r d i n g l y be i n t e r p r e t e d i n t e r m s of s e p a r a t e s u b r o u t i n e s f o r s e n s o r y i n t e g r a t i o n , r e c e p t o r o r i e n t a t i o n , a t t e n t i o n a l s h i f t and s t e e r i n g of motor a c t i v i t y , w i t h l i t t l e o r no concern f o r t h e c o m p l e x i t y and meaning of t h e t o t a l program.Thus, l o c a l d i s f u n c t i o n s maybe h e l d r e s p o n s i b l e f o r f a i l u r e i n t h e e x e c u t i o n of t h e l a t t e r , w h i l e t h e s y s t e m i c d i s o r d e r i s l o s t t o view. Such h a v i n g been t h e p r e v a i l i n g a p p r o a c h t o u n i l a t e r a l n e g l e c t , t h e r e g r e t t a b l e consequences which have ensued a r e t h r e e f o l d : f i r s t , wrong i n t e r p r e t a t i o n s have been f o s t e r e d ; second, t h e c o g n i t i v e a s p e c t s of t h i s c o n d i t i o n have been o b s c u r e d and, t h i r d , t h e c o n t r i b u t i o n which t h e s t u d y of u n i l a t e r a l n e g l e c t can g i v e t o t h e r e a p p r a i s a l of t h e o r i e s a b o u t t h e a c t i v i t y of t h e b r a i n a s a whole h a s been d e l a y e d . S e n s o r y h y p o t h e s e s a s e x p l a n a t i o n s of u n i l a t e r a l n e g l e c t a r e well-known ( s e e Heilman 6 Watson, 1977, f o r a review) and do n o t r e q u i r e f u r t h e r a s s e s s m e n t , s i n c e t h e i r v a l i d i t y a g a i n s t which undermining arguments had a l r e a d y been a n t i c i p a t e d by Z i n g e r l e (1913), h a s been

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d e f i n i t i v e l y r e f u t e d by t h e d e m o n s t r a t i o n of n e g l e c t phenomena i n t h e r e p r e s e n t a t i o n a l domain. These phenomena w i l l p r e s e n t l y be reviewed. T h i s of c o u r s e , does n o t mean t h a t s e n s o r y d i s o r d e r s have no r o l e t o p l a y i n s h a p i n g t h e n e g l e c t syndrome. For example, i t h a s been found t h a t n e g l e c t p a t i e n t s w i t h c o n v e n t i o n a l l y diagnosed hemianopia show more s e v e r e n e g l e c t of t h e a f f e c t e d hemispace under v i s u a l c o n t r o l , t h a n i n a c o n d i t i o n i n which t h e l a t t e r i s p r e v e n t e d by a b l i n d f o l d (Chedru, 1976). C o n t r a r y t o t h e s e n s o r y h y p o t h e s e s , t h e r e h a s never beenanunambiguous f o r m u l a t i o n of an oculomotor h y p o t h e s i s . T h i s s o r t of e x p l a n a t i o n , i n d e e d , has been c r i t i c i z e d by some w r i t e r s a l t h o u g h i t h a s n e v e r been f a c t u a l l y upheld. The paper by S c h o t t , J e a n n e r o d and Zahin ( 1 9 6 6 ) , t o which s u c h a h y p o t h e s i s h a s been connected (e.g. D e Renzi, 1982, p. 1 0 6 ) , though l a y i n g s p e c i a l emphasis on oculomotor d i s o r d e r s i n t h e d e s c r i p t i o n of t h e syndrome, i s f a r from c l a i m i n g t h e i r unique r o l e i n t h e c a u s a t i o n of n e g l e c t ; t h e s e a u t h o r s , t o t h e c o n t r a r y , even s u g g e s t t h a t i t may be i n c o r r e c t t o t a l k of n e g l e c t o r i n a t t e n t i o n w i t h r e f e r e n c e t o a s p a c e which i s l o s t i n t h e s u b j e c t ' s r e p r e s e n t a t i o n , t h u s h i n t i n g a t t h e n e c e s s i t y of a much more s o p h i s t i c a t e d i n t e r p r e t a t i o n . I t i s , however, a w e l l e s t a b l i s h e d f a c t t h a t c l e a r m a n i f e s t a t i o n s of u n i l a t e r a l n e g l e c t can be f o u n d , d i s s o c i a t e d from c l i n i c a l l y d e t e c t a b l e oculomotor impairment (HCcaen, P e n f i e l d , B e r t r a n d & Malmo, 1956; Hbcaen, 1962; G a i n o t t i , 1968; B i s i a c h , L u z z a t t i & P e r a n i , 1979). Thus, t h e f r e q u e n t a s s o c i a t i o n of t h e two d i s o r d e r s s h o u l d e i t h e r depend on t h e a n a t o m i c a l c o n t i g u i t y of t h e l e s i o n s r e s p e c t i v e l y r e s p o n s i b l e f o r e a c h of them, o r on t h e d i s f u n c t i o n of a common l i n k , a disfunctionwhichmightexpress i t s e l f d i s p r o p o r t i o n a t e l y o n e i t h e r v e r s a n t . One p o i n t of i n t e r e s t , however, i s t h e f a c t -- t o which w e s h a l l r e t u r n l a t e r -- t h a t c o n j u g a t e gaze d e f e c t s t o w a r d t h e s i d e c o n t r a l a t e r a l t o t h e l e s i o n , o c c u r more f r e q u e n t l y a f t e r right-hemisphere i n j u r y (De R e n z i , Colombo, F a g l i o n i & G i b e r t o n i , 1 9 8 2 ) , which i s s u g g e s t i v e of a f u n c t i o n a l connectionbetween these d e f e c t s a n d u n i l a t e r a l neglect. A t t e n t i o n a l hypotheses a r e most prone t o b o i l away a s q u e s t i o n - b e g g i n g r e d e s c r i p t i o n s of n e g l e c t phenomena and r e s t a t e m e n t s of e x p e r i m e n t a l r e s u l t s . I n o r d e r f o r t h e e x p l a n a t i o n s t o be g e n u i n e , t h e y must s p e c i f y a n u n d e r l y i n g model of t h e mechanismwhich, under p a t h o l o g i c a l c o n d i t i o n s , may g i v e r i s e t o h e m i n e g l e c t . T h i s r e q u i s i t e i s met by t h e s u g g e s t i o n s of Kinsbourne (1970, 1977) and of Heilmanand h i s a s s o c i a t e s (Heilman&VanDen A b e l l , 1980; Heilman, Watson & V a l e n s t e i n , 1985). According t o K i n s b o u r n e , i n t h e nervous system t h e r e i s a c o m p e t i t i o n between two opposed v e c t o r s of l a t e r a l a t t e n t i o n , each p o i n t i n g t o t h e s i d e c o n t r a l a t e r a l t o t h e hemisphere of o r i g i n . R e l a t i v e h y p e r a c t i v a t i o n of one hemisphere, caused by s e l e c t i v e engagement i n p r o c e s s i n g i n f o r m a t i o n o r r e s u l t i n g from impairment of t h e o p p o s i t e hemisphere, enhances i t s o w n v e c t o r . The g r e a t e r i n c i d e n c e and s e v e r i t y of l e f t r a t h e r t h a n r i g h t n e g l e c t might be due t o t h e f a c t t h a t , c e t e r i s p a r i b u s , t h e l e f t-hemisphere v e c t o r i s p h y s i o l o g i c a l l y dominant i n r i g h t - h a n d e r s , and t h a t t e s t i n g p r o c e d u r e s o f t e n i n v o l v e l e f t-hemisphere a c t i v a t i o n . To a c c o u n t f o r h e m i s p h e r i c asymmetries i n t h e o c c u r r e n c e of n e g l e c t , Heilman and a s s o c i a t e s have i n s t e a d s u g g e s t e d t h a t t h e r i g h t hemisphere c o n t r o l s a t t e n t i o n o v e r t h e e n t i r e s p a c e , whereas t h e c o n t r o l of t h e l e f t i s l i m i t e d t o t h e r i g h t hemispace. W e w i l l n o t proceed t o e v a l u a t e t h e a t t e n t i o n a l i n t e r p r e t a t i o n per s e p r i o r t o c o n s i d e r i n g a f u r t h e r c o n c e p t i o n , w h i c h sees u n i l a t e r a l n e g l e c t a s a b a s i c a l l y representational disorder. This is not intended a s a t a c t i c t o c r e a t e s u s p e n s e ; w e w i s h t o a v o i d a r g u i n g pro and con t h e same i d e a s d e f i n e d w i t h d i f f e r i n g terms or metaphors. To p r e v e n t a m b i g u i t i e s , w e s h a l l h e r e a f t e r employ t h e t e r m s of "sensory" and "mental" r e p r e s e n t a t i o n t o r e f e r , r e s p e c t i v e l y and w i t h o u t any f u r t h e r i m p l i c a t i o n , t o t h e p a t t e r n of

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c o n s t r a i n t s imposed upon n e u r a l a c t i v i t i e s by c u r r e n t s e n s o r y s t i m u l a t i o n and t o p a t t e r n s of a c t i v i t y o r i g i n a t i n g from w i t h i n t h e nervous system i t s e l f , mimicking a s p e c t s of t h e f o r m e r i n any s e n s o r y domain and t h e r e b y r e c a l l i n g p a s t ( o r s i m u l a t i n g p o s s i b l e ) s t a t e s of a f f a i r s i n t h e world. Whenever a d j e c t i v a t i o n i s o m i t t e d , r e f e r e n c e w i l l be made t o something s h a r e d by b o t h k i n d s of r e p r e s e n t a t i o n .

ANeglectedClassiconNeglect The i d e a t h a t u n i l a t e r a l n e g l e c t i s a m a n i f e s t a t i o n of a more g e n e r a l r e p r e s e n t a t i o n a l d i s o r d e r i s l o n g s t a n d i n g . I t had been c l e a r l y e x p r e s s e d even b e f o r e t h e f u l l i n d i v i d u a t i o n of t h e syndrome had become, much t o B a b i n s k i ' s c r e d i t , an e s t a b l i s h e d f a c t i n c l i n i c a l n e u r o l o g y . I n 1914 and 1918, B a b i n s k i s u b m i t t e d a p a r t i a l o u t l i n e of t h e syndrome under c o n s i d e r a t i o n , which was d e s t i n e d t o remain famous, t o t h e French N e u r o l o g i c a l S o c i e t y . A t a d i s t a n c e of many y e a r s , two a s p e c t s of t h o s e e v e n t s may s t r i k e u s a s b e i n g s i n g u l a r . F i r s t , t h e b y s t a n d e r s (among whom were Souques, D e j e r i n e , P i e r r e - M a r i e , Meige & Claude) r e a c t e d somewhat t e p i d l y t o B a b i n s k i ' s p r e s e n t a t i o n of what was t o become one of t h e major i s s u e s i n neuropsychology. Second, n o t w i t h s t a n d i n g t h e a u r a of n o v e l t y i n t i m a t e d by t h e r e c o r d s of t h e two s e s s i o n s , t h e syndrome had i n f a c t a l r e a d y been d e l i n e a t e d . Even assuming t h a t t h e r e c e n t , n o t e w o r t h y c o n t r i b u t i o n of Z i n g e r l e , p u b l i s h e d i n t h e 1913 i s s u e of M o n a t s s c h r i f t f u r P s y c h i a t r i e und N e u r o l o g i e , could n o t have reached t h e French n e u r o l o g i c a l community owing t o t h e p o l i t i c o - m i l i t a r y v i c i s s i t u d e s of t h e moment, i t seems u n l i k e l y t h a t e a r l i e r s t u d i e s ( q u o t e d by Z i n g e r l e h i m s e l f ) had n o t enjoyed s u f f i c i e n t l y wide c i r c u l a t i o n i n F r a n c e . I n t h a t p a p e r , Z i n g e r l e d e s c r i b e d two p a t i e n t s (Cases 2 and 3) who had c o m p l e t e l y l o s t " t h e n o t i o n of one s i d e " . Both p a t i e n t s had a r i g h t - h e m i s p h e r e l e s i o n : Case 2 a s u s p e c t e d hemorrage i n t h e p o s t e r i o r limb of t h e i n t e r n a l c a p s u l e ; Case 3 a n a u t o p t i c a l l y a s c e r t a i n e d s m a l l a b s c e s s i n t h e f r o n t a l l o b e w i t h d i f f u s e meningeal p h l o g o s i s . Case 2 had a l e f t h e m i p l e g i a w i t h h e m i a n a e s t h e s i a and hemianopia. He would not t a l k about h i s p a r a l y s i s . Whenever h i s a t t e n t i o n was drawn t o h i s l e f t s i d e , a f t e r a momentary g l a n c e a t h i s l e f t l i m b s , he would pay no f u r t h e r a t t e n t i o n t o them and would s t a r t t o t a l k a b o u t a n o t h e r s u b j e c t . Although acknowledging t h a t a l l p e o p l e have a r i g h t and a l e f t s i d e , he d i d n o t seem t o a p p l y t h a t n o t i o n t o h i m s e l f . H e would a f f i r m t h a t a woman was l y i n g on h i s l e f t s i d e ; hewould u t t e r w i t t y r e m a r k s a b o u t t h i s and sometimes c a r e s s h i s l e f t arm. He would become p e r p l e x e d and s i l e n t whenever t h e c o n v e r s a t i o n touched upon t h e l e f t h a l f of h i s body; even a t t e m p t s t o evoke memories of i t were u n s u c c e s s f u l . No o t h e r i n t e l l e c t u a l d i s o r d e r s were found d u r i n g t h e c o u r s e of t h e i l l n e s s . About 1 4 days a f t e r t h e o n s e t , d e l u s i o n a l phenomena had d i s p e r s e d ; t h e p a t i e n t remembered t h e i m p r e s s i o n of a s t r a n g e woman a t h i s s i d e and wondered a t i t , b u t was o n l y a b l e t o g i v e a poor r e p o r t of h i s e a r l i e r s t a t e . Commenting o n t h i s c a s e , Z i n g e r l e acknowledged Anton's p r i o r c l a i m s t o h a v i n g drawn a t t e n t i o n t o t h i s p e c u l i a r syndrome and u n d e r l i n e d t h a t i t was f a r from b e i n g a f i x e d concomitance of somatosensory d i s o r d e r s due t o b r a i n l e s i o n , which could n o t , t h e r e f o r e , be a s c r i b e d any s u b s t a n t i a l c a u s a t i v e r o l e . On t h e o t h e r hand, Z i n g e r l e remarked t h a t t h i s p a t i e n t , though having l o s t somatosensory i n f o r m a t i o n from t h e l e f t s i d e of h i s body, could s t i l l p e r c e i v e i t t h r o u g h o t h e r s e n s e s ( s i g h t and t o u c h ) of t h e unimpaired s i d e ; t h e s e p e r c e p t s , however, had no b e a r i n g on h i s c o r p o r e a l Ego. Moreover, t h e p a t i e n t n o t o n l y l a c k e d s e n s a t i o n s from t h e l e f t s i d e of h i s body and a w a r e n e s s of h i s p a r a l y s i s : l i k e A n t o n ' s p a t i e n t he had a l s o l o s t t h e memory of t h i s s i d e . Case 3 never made u s e of h i s l e f t limbs though t h e y were n o t p a r a l y z e d .

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Figure 1

Hermann Z i n g e r l e (1870-1935)

He was a l e r t and co-operated i n n e u r o l o g i c e x a m i n a t i o n s e x c e p t when r e f e r e n c e was made t o h i s l e f t s i d e , i n w h i c h c a s e he seemed s u d d e n l y d e a f a n d would make no a t t e m p t t o u n d e r s t a n d t h e examiner, whose r e q u e s t seemed r a t h e r t o annoy him. About t h i s c a s e Z i n g e r l e remarked t h a t s i n c e t h e p a t i e n t was n o t p a r a l y z e d and h i s s e n s i b i l i t y was r e t a i n e d a t l e a s t in p a r t on t h e l e f t h a l f of h i s body, one had t o h y p o t h e s i z e a loss of r e p r e s e n t a t i o n of t h e l a t t e r o r a d i s o r d e r e d p r o c e s s i n g of s e n s o r y i n f o r m a t i o n needed f o r t h e s p a t i a l p e r c e p t i o n of t h e body. He a l s o a d m i t t e d t h a t i n t h i s c a s e t h e s e v e r e n e g l e c t of t h e l e f t s i d e might s u g g e s t a d i s o r d e r of a t t e n t i o n , a h y p o t h e s i s he had n o t e n v i s a g e d when d i s c u s s i n g Case 2, presumably on account of t h e f a c t t h a t p a t i e n t 2 c o u l d g i v e a t t e n t i o n t o h i s l e f t l i m b s , though m a n i f e s t i n g d e l u s i o n a l i d e a s about them.

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Z i n g e r l e ' s m e r i t i s n o t c o n f i n e d t o t h e k e e n n e s s of h i s c l i n i c a l r e c o r d s . He o f f e r e d a n i n t e r p r e t a t i o n of t h e d i s o r d e r which is s t i l l up-to-date and a f f o r d e d a glimpse of t h e r e l e v a n c e i t would have f o r t h e neurologyof cognition. The l o s s of s e n s o r y i n f o r m a t i o n may be placed a l o n g s i d e t h e i m p o s s i b i l i t y of r e p r o d u c t i o n of e a r l i e r memories (from a l l s e n s o r y m o d a l i t i e s ) i n t h e framework of a d i s o r d e r e d a w a r e n e s s of t h e l a t e r a l i t y of o n e ' s own body, It is p a r t i c u l a r l y important, not o n l y t h a t t h e m a n i f e s t r e c a l l cannot be awakened by c o r r e s p o n d i n g sensoryinformation,butalsothatthedefectcannotbeamendedthrough s i g h t and t o u c h and t h e p a t i e n t does n o t r e c o g n i z e t h e l e f t h a l f of h i s body, he does n o t s e e i t a s h i s p r o p e r t y I n h i s awareness, the body's r e p r e s e n t a t i o n i s a p. .p e a r e n t l y c o n f i n e d t o t h e r i g- h t h a l f (Zingerle's i t a l i c s ) .

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Thus, a c c o r d i n g t o Z i n g e r l e , t h e b a s i c e x p l a n a t i o n o f t h e s y n d r o m e l i e s i n d i s o r d e r e d r e p r e s e n t a t i o n . He added t h a t t h i s e x p l a n a t i o n must be s u f f i c i e n t l y f l e x i b l e i n o r d e r t o a c c o u n t f o r t h e v a r i a b i l i t y of t h e syndrome. I n d e e d , whereas some patientsaretotallyobliviousof o n e s i d e o f t h e s p a c e , o t h e r s , though unaware of t h e i r p a r a l y s i s , do n o t i g n o r e t h e l e f t h a l f of t h e i r body. A s a l r e a d y remarked by Anton, s e n s o r y i n f o r m a t i o n i n t h e s e p a t i e n t s c o u l d undergo f a u l t y c e n t r a l p r o c e s s i n g , so t h a t i n s t e a d of n e g l e c t , t h e y d i s p l a y d e l u s i o n a l b e l i e f s c o n c e r n i n g t h e l e f t h a l f of t h e i r body. I t is not easy t o f i n d a s a t i s f a c t o r y e x p l a n a t i o n f o r t h e s i n g u l a r s t a t e of o b l i v i o n which f o r so many y e a r s h a s d e p r i v e d neuropsychology of such a n i m p o r t a n t c o n t r i b u t i o n and h a s l e f t u n c h a l l e n g e d t h e t e n d e n c y whereby ( s t r i c t 0 s e n s u c o n s i d e r e d ) u n i l a t e r a l n e g l e c t has remained c o n c e p t u a l l y i s o l a t e d w i t h i n a syndrome of which i t may indeed c o n s t i t u t e t h e most common, but n o t t h e e x c l u s i v e n o r even t h e n e c e s s a r y component. I n d e e d , l e s i o n s which i n v o l v e ( i n most instances) the r i g h t temporoparieto-occipital carrefour or functionally related brain structures (see V a l l a r & P e r a n i , t h i s volume) do not always r e s u l t i n mere n e g l e c t : sometimes t h e p a t i e n t s do a t t e n d t o t h e l e f t h a l f of s p a c e , though t h i s r e v e a l s a p a t h o l o g i c a l s t a t e of a g e n e r i c a l l y n e g a t i v e kind. They maymourn o v e r t h e i r p a r a l y z e d limbs w h i l e a b s u r d l y d e c l a r i n g t h e m s e l v e s r e a d y t o engage i n a c t i v i t i e s from which t h e y a r e now o b v i o u s l y p r e c l u d e d . Well-known are t h e s o - c a l l e d somato-paraphrenic phenomena (Gerstmann, 1942), whereby a p a t i e n t c o n t e n d s , e . g . , t h a t h i s l e f t arm b e l o n g s t o a n o t h e r p e r s o n i n s p i t e of t h e f a c t t h a t he can l o o k a t i t , t o u c h i t and sometimes even move i t d e l i b e r a t e l y , o r can r e c o g n i z e a r i n g on one of t h e f i n g e r s of h i s l e f t hand a s h i s . S t i l l more, t h e p a t i e n t s ' a t t e n t i o n a p p e a r s i n some i n s t a n c e s i n v i n c i b l y a t t r a c t e d towards t h e a l i e n l i m b s , f o r which t h e y may show a s p i r i t e d d i s l i k e and even p e r s e c u t o r y i m p u l s e s ( C r t i c h l e y , 1953). The pleomorphism of t h e s e m a n i f e s t a t i o n s could e x p l a i n t h e d e l a y , t h e slow c o u r s e and t h e r e s i d u a l u n c e r t a i n t y of t h e i r f r a m i n g i n t o a u n i t a r y complex. I n d e e d , t h e l a c k i n c u r r e n t l i t e r a t u r e of a t e r m s u i t a b l e f o r comprehensive d e n o t a t i o n makes a n e n d u r i n g abeyance i n t h e s e t t l e m e n t of t h e d i s o r d e r s under c o n s i d e r a t i o n i n t o a u n i t a r y syndrome e v i d e n t . Y e t , i f under t h e working a s s u m p t i o n of a s i n g l e Grundstoerung i t makes s e n s e t o c o l l e c t t h e d i v e r s e phenomena a t i s s u e (whether d e f e c t i v e -- n e g l e c t -- o r p r o d u c t i v e -- somato-paraphrenia and a n a l o g o u s d i s o r d e r s r e l a t e d t o e x t r a p e r s o n a l s p a c e ) i n t o a u n i t a r y c l u s t e r , i t is a l s o c o n v e n i e n t t o d e s i g n a t e them c o l l e c t i v e l y w i t h a s i n g l e term, which ought t o be b o t h

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c o n s i s t e n t a t t h e d e s c r i p t i v e l e v e l and uncommitted a t t h e i n t e r p r e t a t i v e l e v e l . There is indeed no need t o c o i n a new word, s i n c e t h e term ' d y s c h i r i a ' (Greek c h e i r , c h e i r o s : 'hand' a n d , by e x t e n s i o n , ' s i d e ' ) , employed by Z i n g e r l e (Note l ) , meets b o t h r e q u i r e m e n t s and p e r f e c t l y c a p t u r e s t h e concept of a l i e n a t i o n of one s i d e of space which, however m a n i f e s t e d , i s t h e e s s e n t i a l f e a t u r e o f t h e syndrome. I t may be t h a t on account of t h e heavy i d e o l o g i c a l c o n d i t i o n i n g due t o Behaviourism, and more p r e c i s e l y due t o t h e a v e r s i o n f o r p o s t u l a t e d e n t i t i e s such a s r e p r e s e n t a t i o n s , an even b e t t e r c i r c u l a t i o n of Z i n g e r l e ' s paper would n o t have e x e r t e d s t r o n g t h e o r e t i c a l i n f l u e n c e o v e r s e v e r a l decades. I t is a f a c t (and p e r h a p s a s i g n i f i c a n t one) t h a t t h e s t u d y of d y s c h i r i a went through a l o n g p e r i o d of r e l a t i v e s t a g n a t i o n , u n t i l Geschwind ( 1 9 6 5 ) . K i n s b o u r n e (1970) a n d H e i l m a n a n d a s s o c i a t e s ( s e e H e i l m a n e t a l . , 1985) reawakened i n t e r e s t i n t h i s a r e a by d e m o n s t r a t i n g t h a t i t could r e p a y f r e s h a n d v e r s a t i l e i n q u i r y .

NeglectPhenomenaintheRepresentationalDomain In r e c e n t y e a r s anumber of e x p e r i m e n t a l c o n t r i b u t i o n s h a v e r e s u m e d t h e

r e p r e s e n t a t i o n a l t h e o r y of d y s c h i r i a . P a t i e n t s w i t h n e g l e c t f o r t h e l e f t s i d e of s p a c e can make c o r r e c t s a m e - d i f f e r e n t judgments of p a i r s of v i s u a l s t i m u l i w h e n e v e r t h e d i f f e r e n c e (e.g. i n shape) l i e s i n t h e u n a f f e c t e d r i g h t hemispace, whereas t h e y commit e r r o r s when t h e d i f f e r e n c e , a s i n F i g u r e Za, l i e s i n t h e n e g l e c t e d l e f t hemispace. T h i s i s obvious enough. However t h e same outcome was o b t a i n e d ( B i s i a c h e t a l . , 1979) i n a c o n d i t i o n i n which t h e p a t t e r n s , i n s t e a d of b e i n g s t a t i o n a r y and exposed t o f u l l v i s i o n , were moved from l e f t t o r i g h t o r i n t h e o p p o s i t e d i r e c t i o n behind a c e n t r a l v e r t i c a l s l i t ( F i g u r e 2b) so t h a t

a

b

Figure 2 Patterns employedtodemonstrate representational neglect.

Dyschiriu

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t h e p a t i e n t s had t h e o p p o r t u n i t y of f o c u s s i n g a t t e n t i o n on a l l d e t a i l s i n s u c c e s s i o n but t h e a p p r e h e n s i o n of t h e whole s h a p e r e q u i r e d , a s i n e x p e r i m e n t s s u c h a s t h o s e of P a r k s (1965) and Hochberg ( 1 9 6 8 ) , a p r o c e s s of m e n t a l , r e p r e s e n t a t i o n a l r e c o n s t r u c t i o n . T h u s , t h e mental s p a c e i n which t h e s e v i s u a l r e p r e s e n t a t i o n s were u n f o l d e d t u r n e d o u t i t s e l f t o be n e g l e c t e d i n i t s l e f t half e x a c t l y a s t h e o u t e r space. A s i m i l a r experiment w i t h somewhat d i f f e r e n t p a t t e r n s (Ogden, 1985) has r e c e n t l y confirmed t h e s e results. The same phenomenon was e n c o u n t e r e d w i t h mental r e p r e s e n t a t i o n s drawn from long-term memory. P a t i e n t s w i t h l e f t n e g l e c t were a s k e d t o g i v e a d e s c r i p t i o n of t h e c a t h e d r a l s q u a r e i n M i l a n , w i t h which t h e y were q u i t e f a m i l i a r , w h i l e imagining t h e c a t h e d r a l t o be i n f r o n t of them ( B i s i a c h 6 L u z z a t t i , 1978; B i s i a c h , C a p i t a n i , L u z z a t t i 6 P e r a n i , 1981). A v a r i a b l e number of d e t a i l s , some of which f a i r l y s a l i e n t , were o m i t t e d from t h e l e f t h a l f of t h e v i e w . When a d e s c r i p t i o n o f t h e sameviewwas r e q u e s t e d , b u t from t h e o p p o s i t e v a n t a g e p o i n t , p r e v i o u s l y o m i t t e d l e f t - s i d e d e t a i l s were r e p o r t e d once t r a n s p o s e d t o t h e r i g h t , whereas r i g h t - s i d e d e t a i l s w h i c h t h e p a t i e n t had r e p o r t e d a moment b e f o r e , were o m i t t e d once t r a n s p o s e d t o t h e l e f t . Q u i t e comparable r e c o r d s had p r e v i o u s l y been made by Messerli ( p e r s o n a l communication, F e b r u a r y 1984) by a s k i n g n e g l e c t p a t i e n t s t o g i v e a mental d e s c r i p t i o n of t h e P l a c e Neuve i n Geneva, d u r i n g r o u t i n e c l i n i c a l t e s t i n g . A r e l a t e d and e v e n m o r e t e l l i n g o b s e r v a t i o n h a s m o r e r e c e n t l y b e e n reported (Raxter & Warrington, 1983), r e l a t i v e t o a p a t i e n t w i t h l e f t n e g l e c t who m i s s p e l l e d t h e l e f t h a l f of words, b o t h f o r w a r d s and backwards, a s i f r e a d i n g l e t t e r a f t e r l e t t e r from words w r i t t e n on a n imaginary d i s p l a y , of which t h e l e f t h a l f was h i d d e n t o t h e m i n d ' s eye. I t i s e s p e c i a l l y s i g n i f i c a n t ( a s i t w i l l be a r g u e d l a t e r ) t h a t t h i s p a t i e n t was q u i t e aware of h i s d i s o r d e r and t h a t he himself " d e s c r i b e d a t t e m p t i n g t o s p e l l l i k e r e a d i n g o f f an image i n which t h e l e t t e r s on t h e r i g h t s i d e were c l e a r e r t h a n t h o s e on t h e l e f t " ! T h i s s i n g u l a r phenomenon might i n f a c t be f a r from e x c e p t i o n a l , s i n c e i t has s u b s e q u e n t l y been o b s e r v e d i n a n o t h e r n e g l e c t p a t i e n t (Gazzaniga & B a r b u t , p e r s o n a l communication, J u n e 1985).

Implications Relative to the Structure and Levels of Neural Representation

of Space

T h e r e seem t o be two r a d i c a l l y d i s t i n c t ways i n which t h e b r a i n may a c c o m p l i s h t h e t a s k of p r e s e r v i n g s p a t i a l p r o p e r t i e s o f i n f o r m a t i o n t h r o u g h o u t p e r c e p t i o n , t h o u g h t and a c t i o n ; t h a t i s p e r f o r m i n g t h e f u n c t i o n w e c o n s i d e r when w e t a l k of space r e p r e s e n t a t i o n . One way i s t h a t of some mechanism o p e r a t i n g a s a s p a t i a l a n a l o g ; t h e o t h e r is based upon a p r o p o s i t i o n a l encoding of s p a t i a l r e l a t i o n s . I t would exceed t h e s c o p e of t h i s c h a p t e r t o d w e l l o n a n d a t t e m p t a f u l l e l u c i d a t i o n o f t h e s e two c o n c e p t s s i n c e t h e work of Shepard e t a l . ( e . g . S h e p a r d , 1 9 7 5 ) , Kosslyn e t a l . (e.g. K o s s l y n , 1980) and P y l y s h i n (e.g. Pylyshyn, 1980, 1 9 8 1 ) , a l o n g w i t h a w e a l t h of c o r o l l a r y w r i t i n g s a r g u i n g pro and c o n t r a i m a g i n a l and i m a g e l e s s t h o u g h t -- o r a g n o s t i c (e.g. Anderson, 1978) -- p r o v i d e s v a s t pabulum t o whomever were tempted by t h e e n t e r p r i s e . What seems p l a i n , anyhow, i s t h a t bothmodes e x i s t and i n t e r p l a y i n t h e nervous system. T h i s i s obvious i f , a t one extreme of t h e dichotomy, one t h i n k s of t h e mapping of v i s u a l space on t h e s u r f a c e of t h e r e t i n a and of t h e more o r l e s s r e a d j u s t e d r e t i n o t o p i c arrangement of n e u r a l s t r u c t u r e s more and more remote from t h e p e r i p h e r y up t o t h e s o - c a l l e d a s s o c i a t i o n c o r t e x , and g r a n t s t h a t a n a t o m i c a l c o n t i g u i t y c o r r e s p o n d s , i n t h e s e s t r u c t u r e s , t o f u n c t i o n a l c o n t i g u i t y . Consider f o r i n s t a n c e t h e p r o j e c t i o n o f a chess-board o n t h e r e t i n a : s p a t i a l r e l a t i o n s among d i f f e r e n t l o c i of t h e chess-board a r e r e p r e s e n t e d i n a p i c t u r e - l i k e f a s h i o n by c o r r e s p o n d i n g

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r e l a t i o n s among d i f f e r e n t l o c i of t h e r e t i n a ; n o t , of c o u r s e , by v i r t u e of t h e a c t u a l s p a t i a l p o s i t i o n of t h e l a t t e r b u t t h r o u g h a p p r o p r i a t e c o n n e c t i v i t y which might p r e s e r v e i t s f u n c t i o n -- a t t h e c o s t of c o n s i d e r a b l e w i r i n g entanglement -- even i f , owing t o a whim of n a t u r e , d i o p t r i c media were such as t o s c a t t e r t h e images of e x t e r n a l o b j e c t s i n a d i s o r d e r l y way o v e r t h e whole r e c e p t o r s u r f a c e . T h i s not b e i n g t h e c a s e , a s p a t i a l l y c i r c u m s c r i b e d d e s t r u c t i o n of t h e r e t i n a o r of a r e t i n o t o p i c a l l y o r g a n i z e d s t r u c t u r e such a s primary v i s u a l c o r t e x , e n t a i l s a s p a t i a l l y circumscribed sensory scotoma which demonstrates that neural r e p r e s e n t a t i o n of t h e e x t e r n a l w o r l d , a t t h e s e l e v e l s , depends on a n a n a l o g d e v i c e , l i k e a s u n - d i a l ( a n exemplary a n a l o g ) which i f d e s t r o y e d i n one q u a d r a n t can no l o n g e r r e p r e s e n t t h e c o r r e s p o n d i n g a r c of t i m e , w h i l e r e g u l a r l y f u n c t i o n i n g f o r t h e remainder. A t t h e o t h e r extreme, however, t h e s p a t i a l l o c a t i o n s of i n d i v i d u a l s q u a r e s of t h e chess-board may be r e p r e s e n t e d i n a much more a b s t r a c t way by means of symbols made up by one l e t t e r and one d i g i t ; and t h e o p e r a t i o n s performed on such symbols r e l y upon a n e u r a l mechanism, t h e p r o p e r t i e s of which a r e remote from t h o s e of t h e above c o n s i d e r e d a n a l o g and more and more a k i n t o t h e s y s t e m s u b s e r v i n g t h e r e p r e s e n t a t i o n of s p a t i a l r e l a t i o n s i n any n a t u r a l l a n g u a g e , t h a t i s t o t h e p r o p o s i t i o n a l mode of r e p r e s e n t a t i o n p a r e x c e l l e n c e . Any t r a c e of a n a l o g p r o c e s s i n g h a s h e r e d i s a p p e a r e d and no s e l e c t i v e d i s o r d e r -of language would e n t a i l a d i s o r d e r e d r e p r e s e n t a t i o n o f a c i r c u m s c r i b e d a r e a of space. Now, i f b o t h modes of r e D r e s e n t a t i o n o D e r a t e and c o - o n e r a t e i n t h e nervous system, why s h o u l d t h e r e be any d e b a t e about them ? The c o n t r o v e r s y seems t o r e l a t e t o t h e i r comparative a c c e s s i b i l i t y t o t h e i l l - d e f i n e d c a t e g o r y of c o g n i t i o n . N e e d l e s s t o s a y t h a t i f s u c h a c a t e g o r y i s s i m p l y d e f i n e d a c c o r d i n g t o t h e p r o p o s i t i o n a l q u a l i t y of r e p r e s e n t a t i o n s a c t i v e a t i t s l e v e l , t h e n analogue p r o c e s s i n g i s ope l e g i s r e l e g a t e d t o a n o t h e r (more o r l e s s t a c i t l y u n d e r r a t e d ) domain of nervous a c t i v i t y . What K o s s l y n h a s endeavoured t o a r g u e f o r a l o n g time and what w e o u r s e l v e s have r e p e a t e d l y claimed ( B i s i a c h e t a l . , 1979; B i s i a c h , B e r t i & V a l l a r , 1985a; B i s i a c h , 1985; B i s i a c h , M e r e g a l l i & B e r t i , 1985c; Bisiach,Perani,Papagno,Vallar& Berti, f o r t h c o m i n g ) is t h a t n o n - p r o p o s i t i o n a l modes of r e p r e s e n t a t i o n p l a y a c e n t r a l r o l e i n c r u c i a l a s p e c t s of c o g n i t i o n s u c h a s b e l i e f - f i x a t i o n and t h e complex of s e l f - m o n i t o r i n g a c t i v i t i e s which c o n s t i t u t e what we o r d i n a r i l y d e s i g n a t e by t h e term ' a w a r e n e s s ' . F u r t h e r s c r u t i n y o f e v i d e n c e from i n v e s t i g a t i o n of u n i l a t e r a l n e g l e c t and r e l a t e d d i s o r d e r s and of argumentsadvanced on i t s b a s i s w i l l e l u c i d a t e t h e p o i n t . F i r s t of a l l . it needs be observed t h a t t h e a n a l o g mode of p r o c e s s i n g of s p a t i a l r e l a t i o n s is not c o n f i n e d t o p e r c e p t u a l a c t i v i t y : a s s t a t e d i n t h e f o r e g o i n g s e c t i o n , i n d e e d , i t i s s h a r e d by r e p r e s e n t a t i o n a l a c t i v i t i e s s u c h a s t h o s e i n v o l v e d i n r e c o n s t i t u t i n g t h e shape of a n o b j e c t moving behind a s l i t , i n imagining and d e s c r i b i n g a view and e v e n , a t l e a s t i n some o c c a s i o n s , i n word-spelling. In f a c t , s p a t i a l l y c i r c u m s c r i b e d d e s t r u c t i o n of b r a i n s t r u c t u r e s may n o t o n l y produce s p a t i a l l y c i r c u m s c r i b e d s e n s o r y losses but also spatially circumscribed scotomata in mental r e p r e s e n t a t i o n s . T h i s s u g g e s t s t h a t t h e same a n a l o g may a t a c e r t a i n s t a g e s u b s e r v e p e r c e p t i o n as w e l l a s m e n t a l r e p r e s e n t a t i o n ; which f i t s w i t h t h e a n a t o m i c a l argument s u g g e s t i n g t h a t t o p o l o g i c a l l y o r g a n i z e d c o r t e x beyond primary a r e a s , g i v e n i t s c o n s i d e r a b l e e x t e n t , is much more l i k e l y t o be implied b o t h i n p e r c e p t i o n and i n m e n t a l r e p r e s e n t a t i o n (Merzenich & Kaas, 1980). To c o u n t e r one of t h e arguments advanced a g a i n s t t h e t h e s i s of imaginal ( i . e . a n a l o g ) v i s u o s p a t i a l mental r e p r e s e n t a t i o n (Pylyshyn, 1981), i t is w o r t h r e a f f i r m i n g ( c f B i s i a c h e t a l . , 1985a) t h a t t h e appearance of a m e n t a l scotoma i n n e g l e c t p a t i e n t s cannot be i n t e r p r e t e d a s c o n s t r u e d by t h e p a t i e n t s t h e m s e l v e s i n t h e a c t of i m a g i n i n g how t h e y would

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perceive t h e represented o b j e c t given t h e i r sensory loss. Indeed, u n i l a t e r a l n e g l e c t may be p r e s e n t i n p a t i e n t s w i t h f r o n t a l l e s i o n s which do not i n v o l v e v i s u a l pathways, and when i t i s a s s o c i a t e d w i t h t r u e hemianopia t h e p a t i e n t s , as a r u l e , a r e q u i t e unaware of t h e l a t t e r . T h u s , b o t h p e r c e p t i o n and m e n t a l r e p r e s e n t a t i o n seem t o r e q u i r e a common s u b s t r a t u m on which i n f o r m a t i o n o r i g i n a t i n g e i t h e r from w i t h o u t ( p e r c e p t i o n ) of from w i t h i n t h e n e r v o u s s y s t e m i t s e l f (mental r e p r e s e n t a t i o n ) is l a i d down by means of an a n a l o g p r o c e d u r e r e i n s t a t i n g t h e s p a t i a l p r o p e r t i e s of s e n s o r y a r r a y s . An o v e r s i m p l i f i e d , two-dimensional model of t h i s p r o c e s s i n g s t a g e i s p r e s e n t e d i n F i g u r e 3 ( s e e B i s i a c h e t a l . , 1985c, f o r f u r t h e r d e t a i l s ) . I n w h a t f o l l o w s , t h e t e r m s ' c e l l assembly' w i l l r e f e r t o long-term f u n c t i o n a l g r o u p i n g s of cross-connectedneuronswithina l a r g e r n e t (Hebb, 1949) a s w e l l a s t o v e r y s h o r t - t e r m g r o u p i n g s (Goddard, 1980; von d e r Malsburg, 1981; C r i c k , 1984) such a s t h o s e which r a p i d l y form and d e c a y i n consequence of c u r r e n t s e n s o r y s t i m u l a t i o n .

Figure 3 Model of 2-dimensionalvisuo-spatial processing. P e r c e p t i o n of t h e h o r i z o n t a l l y e l o n g a t e d p a t t e r n MN r e q u i r e s , i n O U K model, t r a n s f e r of i n f o r m a t i o n from a s e n s o r y t r a n s d u c e r ( l a y e r I) t o a s p a t i a l p r o c e s s o r c o n s i s t i n g of a n e u r a l n e t in which a p p r 0 p r i a t . e c e l l s u b a s s e m b l i e s ( l a y e r 11) a r e d i r e c t l y r e c r u i t e d by s i n g l e s u b p a t t e r n s (M,

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N) and i n d i r e c t l y r e c r u i t e d by a c t i v e s u b a s s e m b l i e s a t t h e same l e v e l .

I n d i r e c t r e c r u i t m e n t may c o n t r i b u t e t o t h e p e r c e p t i o n of a p a r t i a l l y occluded s t i m u l u s . C e l l s u b a s s e m b l i e s u n r e l a t e d t o a c t u a l p o r t i o n s of t h e incoming s t i m u l a t i o n ( l a y e r 111) b u t s p a t i a l l y c o r r e s p o n d i n g t o t h e " v e r i d i c a l " s u b a s s e m b l i e s of l a y e r I1 may a l s o be r e c r u i t e d by t h e l a t t e r and, through pathways o m i t t e d i n t h e f i g u r e , by a u t o c h t h o n o u s , s e l f - o r g a n i z i n g a c t i v i t y of t h e system. I n normal p e r c e p t i o n c r o s s - t a l k i s prevented by i n h i b i t i o n of p a r a s i t i c l a y e r 111 s u b a s s e m b l i e s from s p a t i a l l y matching s u b a s s e m b l i e s of l a y e r 11, so t h a t t h e o u t p u t of t h e p r o c e s s o r ( l a y e r IV) c o n s t i t u t e s t h e a d e q u a t e c o d i f i c a t i o n of t h e p e r c e i v e d o b j e c t , ready f o r whatever f u r t h e r p r o c e s s i n g through h i g h e r o r d e r c e l l a s s e m b l i e s and whatever mode of r e p r e s e n t a t i o n ( a n a l o g o r p r o p o s i t i o n a l ) might be r e q u i r e d . L a y e r 111, on t h e o t h e r hand, s u b s e r v e s m e n t a l r e p r e s e n t a t i o n a l a c t i v i t i e s s u c h a s v i s u a l imagery, t o which -- i n normal c o n d i t i o n s and by v i r t u e of t h e damping a c t i o n from l a y e r 11 -- no b e l i e f of r e a l i t y i s f i x e d . Complete i n a c t i v a t i o n o f one h a l f of t h e a n a l o g ( F i g u r e 4 ) e n t a i l s

IV

Figure 4 Disorder underlying u n i l a t e r a l neglect. u n i l a t e r a l n e g l e c t of t h e c o r r e s p o n d i n g h a l f of s p a c e . I n a c t i v a t i o n l i m i t e d t o one h a l f of l a y e r I1 would u n i n h i b i t t h e a c t i v i t y i n t h e c o r r e s p o n d i n g h a l f of l a y e r 111 ( F i g u r e 5 ) a n d r e l e a s e n o n - v e r i d i c a l r e p r e s e n t a t i o n o f one h a l f of s p a c e r e s u l t i n g i n phenomena of p a t h o l o g i c a l c o m p l e t i o n a n d / o r i n e r r o n e o u s b e l i e f s such a s t h o s e e x e m p l i f i e d by a n o s o g n o s i c and somato-paraphrenic phenomena o r by a n a l o g o u s d e l u s i o n s r e l a t i v e t o one h a l f of e x t r a p e r s o n a l space.

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IV

111

II

Figure 5 D i s o r d e r u n d e r l y i n g p a t h o l o g i c a l completion. ~t i s i m p o r t a n t t o n o t e t h a t l a y e r I1 i s not d i r e c t l y a c c e s s e d by t h e s e n s o r y t r a n s d u c e r ; t a k i n g v i s u a l m o d a l i t y as t h e most f a m i l i a r paradigm, i n f o r m a t i o n c a r r i e d by t h e s e n s o r y t r a n s d u c e r i s i n f a c t assumed t o undergo d i s j u n c t p r o c e s s i n g of s e p a r a t e f e a t u r e s such a s c o l o u r , s h a p e and movement, c a r r i e d o u t i n p a r a l l e l by s p e c i a l i z e d c o r t i c a l a r e a s b e f o r e r e a c h i n g l a y e r 11. F u r t h e r m o r e , t h e network of t h i s l a y e r a c t s as a r e t i n o i d (Trehub, 1 9 7 7 ) on which o v e r w r i t t e n images from t e m p o r o - s p a t i a l l y s e p a r a t e e y e - f i x a t i o n s a r e d i s e n t a n g l e d and reassembled conforming t o c o r o l l a r y i n f o r m a t i o n r e l a t i v e t o e x p l o r a t o r y eye- and head-movements. The same is t r u e f o r t h e u n f o l d i n g of images s u c h as t h o s e g e n e r a t e d by moving o b j e c t s behind a s t a t i o n a r y s l i t , which might imply c o m p u t a t i o n s o v e r ( n o t n e c e s s a r i l y e x e c u t e d ) oculomotor programs. A c o r r e s p o n d i n g r e t i n o i d c o n s t i t u t e d by endogenously r e c r u i t e d c e l l a s s e m b l i e s , s u c h a s t h o s e a r t i f i c a l l y diagrammed as a s e p a r a t e l a y e r of t h e same f u n c t i o n a l u n i t i n o u r model ( l a y e r 111) might a c h i e v e t h e s y n t h e s i s of a c o m p o s i t e m e n t a l r e p r e s e n t a t i o n . To what e x t e n t programs f o r eye- and head-moements a r e i n v o l v e d h e r e i s f a r from c l e a r . The f a c t t h a t , even i n p a t i e n t s w i t h s e v e r e l y d e p r e s s e d v i g i l a n c e , i p s i l e s i o n a l eye d e v i a t i o n i s more marked a f t e r r i g h t t h a n a f t e r l e f t a c u t e b r a i n damage (De RenzI e t a l . , 1982) i s s u g g e s t i v e of some i m p l i c a t i o n o f t h e oculomotor f u n c t i o n , a t i t s h i g h e s t l e v e l s of o r g a n i z a t i o n , i n t h e b u i l d i n g of complex m e n t a l images which may

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undergo t h e abovementionedlocaldisarrangement i n a s y n d r o m e - - d y s c h i r i a -- which i s i t s e l f mainly r e l a t e d t o r i g h t hemishpere l e s i o n . However, t h i s i m p l i c a t i o n does n o t seem t o be v e r y c l o s e , s i n c e -- a p a r t from t h e a l r e a d y mentioned p o s s i b i l i t y of d i s s o c i a t i o n between n e g l e c t and oculomotor d i s o r d e r s -- i t h a s been argued t h a t s h i f t i n g s of a t t e n t i o n may be q u i t e independent of eye-movements(Posner,Pea h V o l p e , 1982). I t is a l s o w o r t h o b s e r v i n g t h a t t h e v e r y c o n c e p t of c e l l assembly i m p l i e s t h a t t h e n e u r a l n e t of l a y e r s I1 and 111 i s f a r from b e i n g a n a i v e s t r u c t u r e . Even e x c l u s i v e l y s e n s o r y - d r i v e n a c t i v i t y d e v e l o p s h e r e t h r o u g h s y n a p s e s tuned by p r i o r e x p o s u r e t o t h e environment. S o , t h i s n e u r a l n e t i s n o t a p a s s i v e s t r u c t u r e on which s e n s o r y and m e n t a l r e p r e s e n t a t i o n s a r e t e m p o r a r i l y laid-down from a s e n s o r y b u f f e r o r from a s e p a r a t e long-term s t o r e ; i t i s s u g g e s t e d t o c o n t a i n , b e s i d e s t h e " s u r f a c e " image c u r r e n t l y e n t e r t a i n e d and i n t h e form of p o s s i b l e p a t t e r n s of n e u r a l a c t i v i t y a p t t o be t r i g g e r e d by a p p r o p r i a t e i n p u t , a l l k i n d s of "deep" o r " q u i e s c e n t " r e p r e s e n t a t i o n s a v a i l a b l e t o a n i n d i v i d u a l nervous s y s t e m d e p e n d i n g o n p a s t and p r e s e n t c o n t i n g e n c i e s ( s e e van d e r M a l s b u r g , 1981, f o r a d e t a i l e d model of dynamic network s t r u c t u r e s s u c h a s t h e one e n v i s a g e d h e r e ) . The c o m b i n a t o r i a l expanse of s y n a p t i c a c t i v i t y i n t h i s network i s h e l d t o be such a s t o make r e a s o n a b l e i t s s u g g e s t e d a b i l i t y t o s u b s e r v e a n a l o g r e p r e s e n t a t i o n a l p r o c e s s e s i n a l l t h e i r complexity. Two o t h e r i s s u e s c o n c e r n i n g t h e s p a t i a l p r o c e s s o r o u t l i n e d i n o u r m o d e l remain t o be c o n s i d e r e d . The dynamics of t h e l a t t e r , i n d e e d , must be s u c h as t o account f o r two i m p o r t a n t d a t a . One i s t h e f a c t t h a t i n n e g l e c t p a t i e n t s a l e f t / r i g h t s p a t i a l a n i s o t r o p y may a l s o be o b s e r v e d i n t h e hemispace i p s i l a t e r a l t o t h e l e s i o n . T h i s phenomenon i s known t o c l i n i c a l n e u r o l o g i s t s i n t h e g u i s e of p a r a d o x i c a l e x t i n c t i o n of t h e l e f t m o s t ( n e a r e r t o t h e f o v e a ) of two s i m u l t a n e o u s v i s u a l s t i m u l i d e l i v e r e d i n t h e r i g h t f i e l d of r i g h t - p a r i e t a l p a t i e n t s and has been d e m o n s t r a t e d by v a r i o u s e x p e r i m e n t a l p r o c e d u r e s b o t h i n a n i m a l s (La M o t t e & Acuna, 1978) and i n man ( C o r i n & Bender, 1972; Kinsbourne, 1977; Altman, Balonov h D e g l i n , 1979; B i s i a c h , C o r n a c c h i a , S t e r z i 6 V a l l a r , 1984; Gazzaniga 6. L a d a v a s , t h i s volume). The o t h e r is t h e f a c t t h a t h e m i n e g l e c t seems t o r e l a t e t o a t l e a s t two d i s t i n c t f r a m e s of s p a t i a l r e f e r e n c e : one r e t i n o t o p i c and one p o s s i b l y connected w i t h t h e m i d - s a g i t t a l p l a n e of t h e p a t i e n t l s body (Heilman h V a l e n s t e i n , 1979; B i s i a c h , C a p i t a n i & P o r t a , 1985b; Gazzaniga h Ladavas, t h i s volume). P e r h a p s , t h e b e s t d e m o n s t r a t i o n t h a t t h e d i s o r d e r i s n o t o n l y framed i n terms of r e t i n o t o p i c c o o r d i n a t e s is t h e f a c t t h a t i n t a s k s r e q u i r i n g t h e s c a n n i n g of a v i s u a l a r r a y , e.g. i n a c a n c e l l a t i o n t a s k , p a t i e n t s w i t h l e f t n e g l e c t a l m o s t always s t a r t from t h e r i g h t m o s t i t e m and proceed l e f t w a r d s u n t i l t h e y s t o p , t h u s n e g l e c t i n g i t e m s l o c a t e d i n t h e same r e t i n a l p o s i t i o n w h i c h , d u r i n g f o v e a t i o n o f t h e e a r l i e r s c a n n e d i t e m s , was occupied by non-neglected items ( a f a c t , i n c i d e n t a l l y , which seems t o p r o v i d e t h e most e l e m e n t a r y c o n f u t a t i o n of s e n s o r y e x p l a n a t i o n s of unilateral neglect). An i n t e r p r e t a t i o n of t h e f i r s t phenomenon may be advanced i n t e r m s of r e c e p t i v e f i e l d s of c e l l s c o n t r i b u t i n g t o t h e c o n s t i t u t i o n of n e u r a l n e t s implementing a n a l o g s p a t i a l p r o c e s s o r s . I n d e e d , i t h a s been found t h a t i n t h e p o s t a r c u a t e c o r t e x of monkeys, where one s u c h a n a l o g might be l o c a t e d , 20% of t h e n e u r o n s have e x c l u s i v e l y c o n t r a l a t e r a l , 2% i p s i l a t e r a l and 69% b i l a t e r a l f i e l d s ( R i z z o l a t t i , S c a n d o l a r a , M a t e l l i 6 G e n t i l u c c i , 1981). B i l a t e r a l f i e l d s a r e always a s t r i d e t h e m i d l i n e , and v a r y i n h o r i z o n t a l e x t e n s i o n , so t h a t i n i t s most l a t e r a l a r e a s s p a c e r e p r e s e n t a t i o n r e l i e s a l m o s t e x c l u s i v e l y on t h e c o n t r a l a t e r a l c o r t e x , w h i l e p r o c e e d i n g towards t h e m i d l i n e i t shows a p r o g r e s s i v e t r e n d towards b e i n g e q u a l l y s h a r e d between t h e two hemispheres. " I n t h e c a s e of l e s i o n of one hemisphere t h e

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whole v i s u a l f i e l d w i l l be a f f e c t e d b u t w i t h a g r a d i e n t of s e v e r i t y g o i n g from a maximum i n t h e extreme c o n t r a l a t e r a l h e m i f i e l d t o a minimum i n t h e extreme i p s i l a t e r a l hemif i e l d " ( R i z z o l a t t i , G e n t i l u c c i & M a t e l l i , 1985). I n man, an a s y m m e t r i c a l i p s i l a t e r a l c o n t r i b u t i o n t o s p a c e r e p r e s e n t a t i o n i n a n a l o g p r o c e s s o r s might c a u s e t h e d i s p r o p o r t i o n a t e i n c i d e n c e of hemineglect f o l l o w i n g l e f t and r i g h t hemisphere l e s i o n . An a l t e r n a t i v e e x p l a n a t i o n o f t h e same phenomenonmight assume t h a t s e n s o r y r e p r e s e n t a t i o n of a p a t t e r n of e c c e n t r i c s t i m u l a t i o n i n t h e v i s u a l f i e l d , does not remain anchored t o t h e r e t i n a l c o o r d i n a t e s of t h e proximal s t i m u l u s , b u t i t s c e n t r o i d , a s i t were, i s f o v e a t e d f o r f u r t h e r p r o c e s s i n g by t h e m i n d ' s eye t h r o u g h a t r a n s l a t i o n o v e r t h e s u r f a c e of a r e t i n o i d s t r u c t u r e ; f o r m a l model of t h i s p r o c e s s h a s been provided by Trehub (1977). I n p a t i e n t s w i t h l e f t h e m i n e g l e c t , t h e l e f t h a l f of s t i m u l u s c o n f i g u r a t i o n , wherever l o c a t e d i n t h e o u t e r s p a c e , would t h u s f a l l i n t o t h e d i s o r d e r e d h a l f of a s t r u c t u r e s u p p o r t i n g e g o c e n t r t c space r e p r e s e n t a t i o n so t h a t i t s p r o c e s s i n g r e l a t i v e t o t h a t of t h e r i g h t h a l f i s t o a v a r i a b l e e x t e n t impaired. A s f o r t h e second i s s u e , i t seems n e c e s s a r y t o i n f e r t h a t e a c h p o i n t of t h e a n a l o g f o r s p a c e r e p r e s e n t a t i o n -- whatever t h e r e l a t i v e c o n t r i b u t i o n of e a c h hemisphere t o i t s i m p l e m e n t a t i o n -- i s double-indexed i n t e r m s of r e t i n a l and body c o o r d i n a t e s , o r t h a t s p a c e r e p r e s e n t a t i o n a r t i c u l a t e s i n a m a n i f o l d of a n a l o g s w i t h d i f f e r e n t frames of r e f e r e n c e . I t i s w o r t h n o t i n g h e r e t h a t t h e a c t u a l e x i s t e n c e of more t h a n one s p a t i a l a n a l o g i s s u g g e s t e d by i n d i c a t i o n s of d o u b l e d i s s o c i a t i o n between n e g l e c t f o r p e r s o n a l o r p e r i p e r s o n a l space and n e g l e c t f o r e x t r a p e r s o n a l s p a c e found i n monkeys ( R i z z o l a t t i e t a l . , 1985) a s w e l l a s i n m a n ( B i s i a c h , P e r a n i , V a l l a r & B e r t i , forthcoming).

SpatialAnalogsandCognitiveProcesses In o u r model, r e p r e s e n t a t i o n by s p a t i a l a n a l o g i s f a r from b e i n g a stupid picture-in-the-head c r i t i c a l l y s u r v e y e d and i n t e r p r e t e d by a n i n t e l l i g e n t mind's e y e . The f i r i n g of c e l l a s s e m b l i e s of l a y e r s I1 and I11 must be r e g a r d e d a s a n i n t r i n s e c a l l y c o g n i t i v e a c t i v i t y , s i n c e no h i e r a r c h i c a l l y h i g h e r form of s e n s o r y and mental r e p r e s e n t a t i o n seems t o e x i s t and, a s w i l l p r e s e n t l y be a r g u e d , i t shows d i r e c t involvement i n c o n s c i o u s n e s s . Whatever r e s i d u e s of a n c e s t r a l a v e r s i o n might be r a i s e d a g a i n s t t h e n o t i o n of an e n t i t y where c o g n i t i v e p r o p e r t i e s merge w i t h e x t e n s i o n a l p r o p e r t i e s , t h i s is t h e c r u c i a l a s p e c t of O U T model. Both l a c k of r e p r e s e n t a t i o n and c o n t e n t f u l m i s r e p r e s e n t a t i o n of one h a l f of s p a c e such a s c o n j o i n t l y o r s e p a r a t e l y o b s e r v a b l e i n d y s c h i r i a a r i s e from i n t r i n s i c changes i n t h e s p a t i a l a n a l o g , not from f a i l u r e of a superimposed s c a n n i n g d e v i c e which we have no f a c t u a l r e a s o n t o h y p o t h e s i z e ( B i s i a c h e t a l . , 1985c; B i s i a c h & B e r t i , 1985) and whichwould i m p l y a n i n f i n i t e r e g r e s s of s p a c e r e p r e s e n t a t i o n s . I t is worth s t r e s s i n g t h i s point i n order t o d i s p e l t h e b e l i e f t h a t a n a l o g t h e o r i e s u n a v o i d a b l y s h a r e t h e "assumption t h a t images a r e e s s e n t i a l l y i n n e r o b j e c t s a t which t h e homunculus can look" ( N e i s s e r , 1978). Due t o o u r n a t u r a l d i s i n c l i n a t i o n t o l o o k c r i t i c a l l y beyond t h e i r f a c e v a l u e , metaphors a r e o f t e n q u i t e m i s l e a d i n g and i t i s admonishing t h a t under t h e v e r y t e r m s of " a t t e n t i o n a l s e a r c h l i g h t " C r i c k (1984) h a s p r o v i d e d a n e u r a l model which n i c e l y f i t s w i t h o u r h y p o t h e s i s i d e n t i f y i n g t h e m i n d ' s l a y e r s I1 and 111. eye w i t h t h e p a t t e r n of a c t i v i t i e s o c c u r r i n g i n , not I n C r i c k ' s model, " i n t e n s i f i c a t i o n " of p a r t of a r e p r e s e n t a t i o n C u r r e n t l y e n t e r t a i n e d Ln t h e b r a i n may be s e l f - o p e r a t e d by two p o s i t i v e f e e d b a c k loops: one i n t r a t h a l a m i c , i n v o l v i n g r e l a y and r e t i c u l a r n e u r o n s and b a s i c a l l y sensory-driven; t h e o t h e r cortico-thalamic, g r a f t e d i n t o t h e f o r m e r and a c c e p t i n g top-down i n f l u e n c e s . Such a k i n d of a u t o g e n o u s ,

over,

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s e l e c t i v e m o d u l a t i o n of i n f o r m a t i o n i n an a n a l o g r e p r e s e n t a t i o n a l network might c o n s t i t u t e t h e n e u r a l i m p l e m e n t a t i o n of n o n - p r o p o s i t i o n a l t h o u g h t processes. In o u r model, s h i f t s of f o c u s i n mental s p a c e r e f l e c t m i g r a t i o n of a c t i v i t y o v e r t h e s u r f a c e of s p a t i a l a n a l o g s ; t h u s , t o some e x t e n t , i n t e r p r e t a t i o n s of d y s c h i r i a may c o n v e n i e n t l y be p h r a s e d i n terms of a t t e n t i o n a s l o n g a s n e g l e c t phenomena a r e c o n s i d e r e d , even i n t h e domain of mental r e p r e s e n t a t i o n . T h i s is however no l o n g e r t r u e w i t h r e f e r e n c e t o m i s r e p r e s e n t a t i o n s which may sometimes be i n v o l v e d i n f o r e g r o u n d c o g n i t i v e a c t i v i t y . F u r t h e r m o r e , i n t e r p r e t a t i o n s i n t e r m s of a t t e n t i o n f a i l t o a c c o u n t f o r phenomena s u c h a s t h e i n t r o s p e c t i v e r e p o r t of B a x t e r and W a r r i n g t o n ' s p a t i e n t and might miss t h e s u b t l e r p o i n t t h a t what a p p e a r s a s a s h i f t of a t t e n t i o n m i g h t m e a n a r e c o i l f r o m d a u n t i n g r e p r e s e n t a t i o n s . C o g n i t i v e p r o c e s s e s e n t e r i n g a way of p r o p o s i t i o n a l r a t h e r t h a n of a n a l o g p r o c e s s i n g , and t h e r e f o r e n o t p r i m a r i l y a f f e c t e d by t h e d i s o r d e r u n d e r l y i n g d y s c h i r i a , may not o n l y be t o t a l l y u n a b l e t o compensate t h e l a t t e r b u t may themselves be e n t r a p p e d and m i s l e a d , a s we have a r g u e d on t h e ground of c l i n i c a l and of e x p e r i m e n t a l e v i d e n c e ( B i s i a c h , B e r t i & V a l l a r , 1985; B i s i a c h , M e r e g a l l i S B e r t i , 1985); which i s f a r from b e i n g a n i n d i c a t i o n o f c o g n i t i v e supremacy. By f a r t h e most c r i t i c a l , t h e r e remain t h e i m p l i c a t i o n s of d y s c h i r i a f o r t h e o r i e s of c o n s c i o u s n e s s , meant a s s e l f - m o n i t o r i n g and t h e h i g h e s t form of s e l f - c o n t r o l of nervous a c t i v i t i e s . In s p i t e of i t s i m p o r t a n c e , o r r a t h e r because of i t , t h i s a s p e c t w i l l o n l y be i n t r o d u c e d h e r e s u c c i n t l y ( s e e B i s i a c h , 1985, f o r amplerdiscussionandatentativeelucidationof t h e t e r m o f consciousnessasemployedinthis c h a p t e r ) . C l i n i c a l and e x p e r i m e n t a l e v i d e n c e ( e . g . B i s i a c h e t a l . , 1985a. c ; B i s i a c h , P e r a n i , Papagno, V a l l a r 6 B e r t i , f o r t h c o m i n g ) shows t h a t t h e r e p r e s e n t a t i o n a l scotoma m a n i f e s t i n g i t s e l f i n t h e m a n i f o l d t r a i t s of u n i l a t e r a l n e g l e c t and t h e f a l s e b e l i e f s which a r e f i x e d t o r e p r e s e n t a t i o n s i s s u e d , i n o u r model, from t h e d i s o r d e r e d h a l f of t h e s p a t i a l a n a l o g as a consequence o f some c i r c u m s c r i b e d b r a i n l e s i o n s e n c r o a c h u n c o n t r o l l e d o n c o g n i t i v e p r o c e s s e s . In s e v e r e c a s e s , any e f f o r t t o b e s e t t h e p a t i e n t and f o r c e him t o admit and c r i t i c a l l y e v a l u a t e h i s p a t h o l o g i c a l c o n d i t i o n is doomed t o f a i l u r e : e i t h e r t h e p a t i e n t e l u d e s t h e problem a l t o g e t h e r , o r he c u t s s h o r t and s h e l t e r s h i s c o g n i t i v e d i s o r d e r by arguments of which a c o n f u t a t i o n would be i n v a i n . An i l l u s t r a t i v e i n s t a n c e of a n u n s u c c e s s f u l i n t e r v i e w c a r r i e d o n l o n g e r t h a n u s u a l w i t h a p a t i e n t who had l e f t n e g l e c t a n d a n o s o g n o s i a f o r l e f t h e m i p l e g i a , maybe found i n B i s i a c h e t a 1 . ( 1 9 8 5 ~ ) . The consequences of t h i s p e r t u r b a t i o n a r e however local and c o g n i t i v e a c t i v i t y o u t s i d e t h e c o r r u p t e d v e i n may remain t o t a l l y u n a f f e c t e d . T h e s e f a c t s s u g g e s t that r e l a t i v e l y p e r i p h e r a l l e v e l s of nervous a c t i v i t y s u c h a s t h o s e of a n a l o g mechanisms of r e p r e s e n t a t i o n may p l a y a c r u c i a l r o l e i n t h e g e n e r a t i o n of t h o s e e v e n t s whereby s e n s o r y and m e n t a l r e p r e s e n t a t i o n s a c q u i r e t h e p r o p e r t y of b e i n g c o n s c i o u s . We know from b l i n d - s i g h t (Weiskrantz, W a r r i n g t o n , S a n d e r s S M a r s h a l l , 1974) t h a t c o n s i d e r a b l e p r o c e s s i n g of i n f o r m a t i o n d e l i v e r e d by s e n s o r y t r a n s d u c e r s can t a k e p l a c e w i t h o u t any c o n s c i o u s c o r r e l a t e . We a l s o know t h a t i n t e r r u p t i o n of t h e f l o w of s e n s o r y i n f o r m a t i o n up t o a c e r t a i n s t a g e beyond p r i m a r y s e n s o r y a r e a s is monitored by t h e b r a i n . On t h e o t h e r hand, w e know ( a t l e a s t s i n c e A n t o n ' s 1899 c e l e b r a t e d p a p e r ) t h a t f a i l u r e of a more c e n t r a l s t r u c t u r e ( t o which t h e s p a t i a l a n a l o g of our model r e f e r s ) n o t o n l y c u t s a d e f i n i t e amount of i n f o r m a t i o n o u t of c o n s c i o u s n e s s , b u t r e n d e r s , a s a r u l e , t h e d e f e c t i t s e l f unconscious and may r e l e a s e u n c r i t i c i z e d p a t h o l o g i c a l r e p r e s e n t a t i o n s . T h i s seems t o e n t a i l t h a t c o n s c i o u s n e s s is i n h e r e n t i n t h e r e p r e s e n t a t i o n a l a c t i v i t y of t h e s e a n a l o g s t r u c t u r e s , b o t h as r e f e r r i n g t o t h e m o n i t o r i n g of

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t h e s e a c t i v i t i e s and a s r e f e r r i n g t o t h e i r c o n t r o l . Without t a k i n g i n t o c o n s i d e r a t i o n t h e d i s o r d e r e d a p p a r a t u s which i s r e s p o n s i b l e f o r anosognosia r e l a t i v e t o some forms of d y s p h a s i a , and which i s s t i l l t o o o b s c u r e t o be d i s c u s s e d h e r e , no f u r t h e r mechanisms f o r c o n s c i o u s n e s s seem t o e x i s t , e i t h e r i n t h e form of a u n i t i z e d , h i e r a r c h i c a l l y superimposed component of t h e c o g n i t i v e machinery o r emerging from t h e whole of c o g n i t i v e a c t i v i t i e s of t h e b r a i n . A s f o r t h e l a t t e r , what we have s o f a r l e a r n t from d y s c h i r i a c h a l l e n g e s t h e h y p o t h e s i s of an i s o t r o p i c s t r u c t u r e of t h o u g h t , whereby a t t h i s l e v e l each p r o c e s s has f r e e a c c e s s t o any o t h e r p r o c e s s , b o t h i n t h e s e n s e of an u n l i m i t e d range of i n f o r m a t i o n a n d i n t h a t of a n u n l i m i t e d f i e l d of c o n t r o l ( F o d o r , 1983). T h i s h y p o t h e s i s i s undermined by phenomena such a s t h o s e a l r e a d y p o i n t e d o u t by Z i n g e r l e w i t h r e f e r e n c e t o h i s Case 2 , who w h i l e knowing t h a t a l l human b o d i e s have a l e f t and a r i g h t s i d e , could n o t a p p l y t h a t n o t i o n t o h i m s e l f . Phenomena of t h i s kind s u g g e s t t h a t t h o u g h t i t s e l f may have a t e x t u r e imposed by p r o c e s s o r s o r g a n i z e d i n t h e form of a n a l o g s and may b r e a k a l o n g t h e l i n e s of t h i s t e x t u r e , w i t h consequences which c a n n o t be amended by any kind of p r o p o s i t i o n a l a c t i v i t y .

Conclusions

We have t r i e d t o s k e t c h a s y s t e m i c a n a l y s i s of d i s o r d e r s which have s o f a r been r e l a t i v e l y n e g l e c t e d n o t w i t h s t a n d i n g t h e w e i g h t t h e y may have i n t h e advancement of o u r i n s i g h t i n t o c o g n i t i o n . We a r e s t i l l f a r from having a n e n t i r e l y connected s t o r y , however, and o u r r e p r e s e n t a t i o n a l e x p l a n a t i o n of t h e s e d i s o r d e r s , a s w e l l a s o u r i n f e r e n c e s about c o g n i t i v e a c t i v i t i e s , l a r g e l y r e s t on t h e a s s u m p t i o n t h a t n e g l e c t and m i s r e p r e s e n t a t i o n of one s i d e of s p a c e e x p r e s s d i s f u n c t i o n of t h e same f u n c t i o n a l u n i t . We have o u t l i n e d a model of a u n i t of t h i s k i n d , where a c i r c u m s c r i b e d f a i l u r e of t h e mechanism can indeed g e n e r a t e , a c c o r d i n g t o r e l a t i v e l y m i n o r changes i n i t s l o c a t i o n , n e g l e c t o r m i s r e p r e s e n t a t i o n ; y e t , however p l a u s i b l e , t h i s o f f e r s no proof t h a t what r e a l l y happens i n t h e nervous system f o l l o w s t h e s e lines. Our s u g g e s t i o n h a s a n o t a b l e a n t e c e d e n t i n Z i n g e r l e ' s paper. To-day, a r e p r e s e n t a t i o n a l e x p l a n a t i o n of t h e d i s o r d e r s c o n s i d e r e d i n t h i s c h a p t e r a l s o b e n e f i t s from t h e f a c t t h a t , u n l i k e i n Z i n g e r l e ' s t i m e s , 'representation' i s no l o n g e r a m e r e l y p s y c h o l o g i c a l c o n s t r u c t . N e u r o p h y s i o l o g i s t s have g i v e n t h i s c o n c e p t a p h y s i c a l f o u n d a t i o n t h r o u g h d i s c o v e r i e s c o n c e r n i n g t h e a c t i v i t y of networks which a r e s u g g e s t e d t o p r o v i d e a n e u r a l model of e g o c e n t r i c s p a c e (e.g. M o u n t c a s t l e , 1981). Indeed, it i s i n t h e l i g h t of recent neurophysiological and n e u r o p s y c h o l o g i c a l advances t h a t Z i n g e r l e ' s c o n t r i b u t i o n shows i t s f u l l s i g n i f i c a n c e . S e n t t o p r e s s i n t h e t w i l i g h t of an epoch (whose d i s s o l u t i o n , due t o a c u r i o u s c o i n c i d e n c e , was d e l i m i t e d t o time by t h e two s p e e c h e s made by B a b i n s k i i n F r a n c e ) t h e paper of t h e Graz n e u r o l o g i s t would seem t o have s h a r e d t h e d e s t i n y of t h e Austro-Hungarian empire. I t s i m p o r t a n t t h e o r e t i c a l message had no r e v e r b e r a t i o n . I n t h e p r e s e n t c h a p t e r , t h e r e s t o r a t i o n of t h e t e r m ' d y s c h i r i a ' h a s been proposed on two grounds. I t s a b i l i t y t o c o v e r t h e f u l l range of phenomena of a l t e r e d c o g n i t i o n of a h a l f - s p a c e seems, a t t h e v e r y l e a s t , h e u r i s t i c a l l y h e l p u l i n d e f i n i n g a f i e l d which s t i l l l a c k s t h e a p p r o p r i a t e u n i t y t o be f u l l y r e c o g n i z e d as a c r u c i a l node i n t h e i n v e s t i g a t i o n of c o g n i t i v e b r a i n - a c t i v i t i e s . F u r t h e r m o r e , r e a d o p t i o n of t h i s term would be a w e l l - d e s e r v e d t r i b u t e t o t h e A u s t r i a n n e u r o l o g i s t and would compensate f o r so many y e a r s of n e g l e c t . Although t h i s p r o p o s a l may e n c o u n t e r r e s i s t a n c e r a n g i n g from p e r s o n a l t h e o r e t i c a l s t a n c e s t o s i m p l e i n d i f f e r e n c e , i t i s t o be hoped t h a t i t w i l l a t l e a s t e n j o y t h e s e r i o u s c o n s i d e r a t i o n of t h o s e who a t t r i b u t e a c e r t a i n v a l u e t o our c u l t u r a l i n h e r i t a n c e .

198

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A c k n w l e d g e i e o t s : The p r e p a r a t i o n of t h i s c h a p t e r was s u p p o r t e d by a g r a n t from t h e M i n i s t e r 0 d e l l a P u b b l i c a I s t r u z i o n e t o t h e f i r s t a u t h o r . We g r a t e f u l l y acknowledge t h e h e l p of F r a n c e s A n o l e r s o n , who c a r e f u l l y reviewed t h e E n g l i s h . Footnote 1. The term ' d y s c h i r i a ' was t a k e n from J o n e s , who i s l i k e l y t o have coined i t . I n 1910, under t h e t i t l e of "Die P a t h o l o g i e d e r D y s c h i r i e " , E. J o n e s , a T o r o n t o U n i v e r s i t y p r o f e s s o r , had d e s c r i b e d t w o p a t i e n t s s u f f e r i n g from " h y s t e r i a " and " h y s t e r o n e u r a s t h e n y " r e s p e c t i v e l y . T h e i r symptoms were v e r y complex b u t not w i t h o u t s i m i l a r i t y t o Z i n g e r l e ' s o r g a n i c c a s e s . The n e u r o t i c n a t u r e of s u c h symptoms might however be q u e s t i o n e d , s i n c e t h e f i r s t p a t i e n t had developed them f o l l o w i n g a r a i l w a y a c c i d e n t , p o s s i b l y involving head trauma, whereas the second suffered from "hystero-epylept ic'lseizures.