[614 



II VNDHOOK OF I'HVSIOLOGV 



NEUROPHYSIOLOGY III 



choose the one with fewer contours. Some most un- 

 expected features of visual perception in bees, finally, 

 are implied in certain open-field experiments on the 

 'clustering' of bees at food sources [see Kalmus (246)]. 

 It is well known that bees congregate at flowers or 

 food dishes wherever there are other bees. This cluster- 

 ing can be enhanced by placing a mirror below the 

 food source, and even more by placing 'supernormal' 

 (i.e. outsi/ed) cardboard dummies of bees around the 

 food dish. Clearly, the analysis of pattern vision in 

 bees and in other invertebrates with compound eyes 

 is in need of much further study [see also Use (234)]. 



Changes in Perception of Shape After Cerebral Lesions 



In comparing perception across species one hopes 

 to find differences in function that might correspond 

 to known differences in structure. As we have seen, 

 the differences in perceptual repertoire of different 

 species are on the whole less marked than the simi- 

 larities. Studies of perception in the presence of defects 

 in neural structures aim at finding characteristic 

 changes as the result of ablation, injury or disease. 

 Yet, here too, lack of change or resiliency of percep- 

 tion is a major finding. Nevertheless, there are certain 

 alterations in perception after cerebral lesions that 

 may cast light on the normal bases of perception. As 

 in the phylogenctic studies, however, evidence for 

 these changes can be no better than the methods em- 

 ployed in analyzing their nature. In this respect, 

 methods developed in testing nonverbalizing organ- 

 isms turn out to be useful in assessing performance in 

 man with brain injury; conversely, studies of animals 

 with experimental ablations profit from tasks derived 

 in clinical settings (466). In die following, we shall 

 briefly consider effects ol total removal of primary 

 (cortical) projection s\ stems, then effects of subtotal 

 lesions within these s\ stems, and finally changes found 

 alter various lesions encroaching on neocortical struc- 

 tures outside the primary projection fields. 



EFFECTS OF To I \1 REMOVA1 OF 'PROJECTION SYSTEMS.' 



1 01 the visual system, it is generally agreed thai total 

 destruction of the geniculostriatc sector results in total 

 and irreversible loss oi pattern vision (see Chapter LX 

 by Neff in this volume). This is believed to take place, 



whether the lesions eliminate the lateral geniculate 



ies, or the optic radiation, or the visit. il cortex. It 

 is not clear whether in man some reactions to light 

 in.iv eventually return Nee, again, Chapter LX) In 

 the experimental monkey, bilateral occipital lobec- 



tomy abolishes pattern vision, but reactions to lumi- 

 nous flux are preserved (261). The question of re- 

 sidual vision in man after complete destruction of 

 striate cortex will remain unanswered until testing 

 methods such as Kluver's are applied in suitable clini- 

 cal cases 



Likewise, we may need to reinvestigate the tradi- 

 tional belief that effects of total striate cortex re- 

 moval on pattern vision are progressivelv less severe 

 as one moves down the phylogenctic scale (339). The 

 condition of rodents and carnivores following such an 

 operation may not be as different from that of pri- 

 mates as has been claimed. In still lower forms, dif- 

 ferences undoubtedly appear. Removal of the entire 

 forebrain in fish is said to have no effect on visual dis- 

 criminations whether established pre- or postopera- 

 tively [see the review by Herter (206)]. The status of 

 visual capacity in birds following forebrain removal is 

 puzzling and badly needs further examination. Visser 

 & Rademaker (491, 492) report that pigeons without 

 forebrains avoid vertical but not horizontal strings in 

 their path; they alight on the back of a cat while they 

 are in flight, but avoid cats while walking, etc. What 

 is needed is an extension of available testing tech- 

 niques to the study of decerebrate birds (and of birds 

 with lesions of the optic tectum). If there are phyletic 

 differences in visual organization, then homologous 

 removals of central nervous system tissue in different 

 species would not be expected to lead to homologous 

 changes in perception. 



The loss of shape perception in primates following 

 visual cortex resection may have parallels in the dis- 

 orders of auditory patterning, in primates and 

 carnivores, after certain bilateral removals of 'audi- 

 tory cortex' [sec Diamond & Neff (104) and Chapter 

 LX by Neff in this Handbook], Definition of the mini- 

 mal effective lesion in the auditory svstetn, however, 

 is difficult because ol the uncertainty regarding the 

 full extent of auditory projection fields in carnivores 

 and primates. This difficulty is even greater in the 

 somatosensory svsiem [cf. Cole & Clees (92)] where 

 total loss of reactions to tactile patterns .titer restricted 

 cortical removal has not yet been demonstrated ex- 

 perimentally, irrespective of whether the subjects were 

 primates, carnivores or rodents. 



effects 01 subtota] removai in vivs. Partial de- 

 struction of the visual cortex in man is followed by a 

 v.uietv of symptoms which may cast lighl on neural 

 correlates ol pattern v ision. There are two outstanding 



features of residual vision in such defective visit. il 



