PERCEPTION 



l6lg 



k •* ■ A 



fig. 17. Test for recognition of 

 solid forms. Subject palpates sample 

 form (front), and attempts to find the 

 identical form within the array (back). 

 A black curtain screens the test patterns 

 from subject's view. [From Teuber 

 (467), based on Ghent et al. (149).] 



level disturbance, independent of sensory status. 

 Neither of these possible interpretations seems to fit 

 the recent observations in man following brain injury. 

 On a variety of tests of object recognition (149, 417, 

 527), subjects palpate a given object with one hand, 

 and then try to find a replica of that object with the 

 other hand (see fig. 17). On a number of these tests, 

 men with sensory impairment of one hand show 

 impaired performance of object discrimination in 

 both hands, not only the one opposite their brain 

 injury, but also in the ipsilateral hand which had 

 seemed intact on all primary tests of sensory function 

 (see fig. 18). 



This unexpected finding shows that discrimination 

 deficits are associated with more basic sensory defects, 

 but transcend these basic delects by involving seem- 

 ingly unimpaired parts of the patient's body. These 

 observations are strikingly parallel to those made on 

 visual functions after lesions of the central visual 

 pathways; there, too, specific defects (scotoma) are 

 restricted to certain regions, while the more subtle 

 deficits, such as lowered flicker-fusion, go beyond 

 the area of primary defect and involve the entire 

 visual field. 



In addition, we must recall that .ill groups of 

 patients tend to show disturbances on the hidden- 

 figure tasks already discussed, so that somatosensory 

 changes are sufficient but not necessary for this 

 general perceptual deficit which is found after cerebral 

 lesion in man. The data available for infrahuman 

 forms with subtotal lesions within or beyond the 

 primary projection systems are analogous in certain 

 respects. 



EFFECTS OF SUBTOTAL LESIONS IN ANIMALS BELOW 



man. The most general consequence of subtotal 

 removal of primary projection fields in rodents, 

 carnivores or subhuman primates is again the re- 

 siliency of shape perception as such. Failure to find 

 some of the subtle associated changes in residual 

 function may be due to the absence of tasks that 

 would be sufficiently sensitive, rather than to an 

 absence of the deficits. The resiliency of form per- 

 ception has been shown, for instance, in rats with 



FORM 



C- contralateral hand 

 I -ipsilateral hand 



conlrol nonsens sensory 



no. i» Results of form recognition task (see lis;, 171. In the 

 control group (without brain injury), C and / hands are left 

 and iiulit, respectively. Note the reduction in score for both 

 hands in the group with sensory defect (as defined by ele- 

 ment. my sensory tests), even though the elementary defect is 

 restricted to one hand. The group with brain injury without 

 these elementary sensory defects (nonsensory) does not differ 

 from the controls. [From feuba \i<- I, based on Ghent el al. 

 (149) 



large striate cortex lesions, leaving only J ti0 of the 

 striate cortex intact (302). Similar observations on 

 rapid recovery of pattern vision after extensive but 

 subtotal ablations of striate cortex have been made 

 in monkeys [see Kliiver (260), Harlow (180) and 

 Settlage (420, 421)]. 



In Hebb's theory (188) of pattern vision, excitation 

 within the primary visual cortex (area 17) has to be 

 transmitted to surrounding prestriate regions for 

 perception to take place. The resiliency of pattern 

 vision in small islands of preserved cortex casts 

 doubts on these notions, unless one assumes that the 

 interaction between striate and prestriate systems 

 employs thalamic or other subcortical connections. 



Even more embarrassing to theory, however, are 

 the negative results after extensive removal of pre- 

 striate cortex in the monkey (115, 306). Traditional 

 doctrine has always assigned crucial functions to the 

 areas of cortex which surround primary projection 



