Normas ambientales

What we are doing when we explore som ething ta c tu a lly i s to c r ea te a schema of i t . The fu n ctio n of th is i s tw o -fo ld , to guide fu rth er e x p lo ra tio n , and to aid a c tio n on or w ith the o b je c t. The q u estion i s , how fa r th is schema resem bles a v isu a l image, how fa r i t is a genuine s p a tia l r e p r e se n ta tio n . I f the theory argued for here is to have any v a lid it y , i t must be a genuine s p a tia l r e p r e se n ta tio n . I t might be thought th a t th is would be r e la t iv e ly easy to t e s t , by experim ents on ta ctu a l lea rn in g and v is u a l r eco g n itio n of form s, for in sta n c e . U n fo rtu n a tely , the issu e is com plicated by the fa c t th at the ta c tu a l exp loratory p ro cess, in sig h ted and in la t e blin ded p erson s, i s o fte n h elp ed , or at le a s t accompanied by, 'o p t i f ic a t io n ' , th at i s , by the c o n stru ctio n of a v is u a l image (R evesz, 1950). Hence the importance of evid en ce from the very e a r ly or c o n g e n ita lly b lin d . One view i s th at such people have no genuine s p a tia l sen se a t a l l . This i s the p o s itio n of von Senden (1 9 6 0 ), although i t i s co n trad icted both by the evidence he h im self c it e s , and by evid en ce from oth er sources (Gregory and W allace, 1963),

We have to ask what is s p e c if ic a lly v is u a l about the exp erien ce of sp a ce. O bviously, colour is one th in g , but a n o n -v isu a l r ep resen ta tio n of space would be more, or rath er l e s s , than a v isu a l scene drained of co lo u r.

I t would la ck , fo r in s ta n c e , the idea of a p e r sp e ctiv e tran sform ation. The sim p le st case of t h is i s a sim ple sc a le tran sform ation; we know th at a square sh e e p -fo ld on the other sid e o f the g len has something in common, v is u a lly , w ith the su rfa ce of a matchbox h eld in the hand, because the proxim al stim u li are s im ila r . But what is the s im ila r ity fo r a b lin d man? In one c a s e , the stim u li c o n s is t of a s e r ie s of hand grasp s, and in the other a s e r ie s of walks and tu rn s. In f a c t , i t i s known th at on recovery of s ig h t , e a r ly blinded persons fin d d if f ic u lt y w ith s c a le tran sform ation s, as in th e famous Chiselden case quoted by both von Senden and Gregory and W allace. Indeed, i t would seem th at th is is what lead s von Senden to h is c o n c lu sio n . Another source of evid en ce on th is p oin t i s work which has been done on the development of ta c tu a l maps as an aid to b lin d m o b ility . A ta c tu a l map i s more or l e s s a sc a le model of an area, or a plan view w ith r a ise d fe a tu r e s. The su b ject fa m ilia r ise s h im self w ith the map, and is then te s te d in fin d in g h is way about the a rea . I f sc a le tran sform ations are purely v is u a l, then th e c o n g e n ita lly b lin d should be te r r ib ly disadvantaged a t t h is , as indeed they a re. However, th is cannot be used as evidence th at they are unable to co n stru ct s p a t ia l r e p r ese n ta tio n s, sin c e i f they are given ex p erien ce in walking round the area, they are much l e s s disadvantaged compared to la te blinded and sig h ted given sim ila r ex p erien ce. They a re, of course, teste d on rou tes they have not walked b e fo r e . (Dodds, 1980).

There Is a d is tin c tio n between near and fa r sp a ce, and th is corresponds approxim ately to the d iffe r e n c e between an image and a p la n . I f I want to p resen t m yself w ith the p o s s ib il it i e s fo r a c tio n of a sm all o b ject in near sp a ce, I conjure up a v isu a l image of i t . I f , on the other hand, I want to p resen t the p o s s ib il it i e s of la rg e o b jects in fa r sp a ce, I most n a tu r a lly operate w ith a plan or map. This i s a h ig h ly schem atised o u tlin e image. A plan view , a r e a l concrete image from a p a r tic u la r p oin t of v iew , would do as w e ll, and indeed our a b ilit y to make and use maps i s p a r a s itic on our a b ilit y to make ordinary im ages. However, the r e la tio n sh ip between a map or a plan view and my a ctio n i s t o t a lly d iffe r e n t from th a t between an ordinary image and my a c tio n . There i s no reason at a l l to exp ect that b lin d people should be able to tra n sfe r from one to the o th er, because th is a b ilit y is p a r a s itic on th e a b ilit y to handle p e r sp e c tiv e . That i s , what i s la ck in g i s not s p a tia l awareness, but m erely one aspect of v isu a l awarenes s .

In v is io n , p e r sp e ctiv e transform ations are involved in , and to some ex ten t counteracted by, s iz e and d ista n ce constancy. The p ercep tion is some so r t of compromise between the proxim al stim ulus and the d is t a l. This i s presumably n ecessa ry in v isio n as a so rt of p la y -o ff between the fu n ctio n s of guiding exp loratory and instrum ental a c tio n , b u t, of course, t h is i s not n ecessary in touch. So, we would expect p e r fe c t constancy. The same would apply to o r ie n ta tio n

constancy, Indeed, th ere i s reason to b e lie v e th a t for the c o n g e n ita lly b lin d - those incapable of 'o p tif ic a t lo n ' - th ere i s no decrement in a r eco g n itio n task with change of o r ie n ta tio n of ta rg et (Dodds, 1980).

There i s an a sp ect of our v isu a l exp erien ce which