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HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY III 



fields. The prestriate region was considered 'visuo- 

 psychic,' ilic midparietal •sensoripsychic,' and 

 certain temporal lobe structures (lateral and inferior 

 to primary auditory fields) were considered •audio- 

 psychic' In every instance the assumption was that 

 elementary sensory processes took place in the pro- 

 jection fields, and higher 'apperceptive' or 'associative' 

 perceptual processes, in the adjacent psychic field 

 (125, 362). Destruction of the latter was believed to 

 produce agnosia — a disorder of recognition of pat- 

 terns presented to a given sensory modality in the 

 absence of more elementary sensory disturbances 

 sufficient to account for the observed difficulties with 

 object recognition. This traditional view is difficult 

 to maintain in the case of the rat or the monkey, 

 although one might raise the question of whether 

 agnosia, in the classic sense (132, 362), should ever 

 be expected to occur in subhuman forms. As we have 

 seen, however, the evidence regarding agnosia in man 

 is far from clear. 



The data in lower forms, particularly the rat, 

 prompted Lashley (305) to propose that a primary 

 projection area, such as the visual cortex, might be 

 autonomous. No part of the cerebral hemisphere, 

 except the visual cortex itself, seemed to him essential 

 for establishing perceptual reactions, including those 

 of the most complex type of which the normal animal 

 was capable (304, 305). This view, however, is diffi- 

 cult to reconcile with the impression that any major 

 cortical region mediates both its own specific and 

 some more general activity, an impression that 

 derives just as much from Lashley's own maze- 

 running studies (300) in the rodent and from the 

 more recent work on reaction to complex perceptual 

 tasks in man (467). 



Observations which detract somewhat from the 

 concept of complete autonomy of the primary visual 

 area have been obtained by Sperr) (439) and Myers 

 III. observations are the mosi recent outcome 

 of a series of studies on effects in cats of combined 

 sagittal section of the optic chiasm and the corpus 

 callosum. Such 'split-brain' preparations (see fig. 19) 

 can be trained to make visual discriminations with 

 one eye, but they fail to transfer to the other (un- 

 trained) eye under most conditions of training and 

 testing." In such animals our hemisphere can be 



"It mjiixi l»- noted that this failure of transfei from hemi- 

 sphere to hemisphere is again a 1 tion of the 'level' of the 



task employed II the 'split-brain' animal is required to learn a 

 gimpli isual discrimination (vertical <*. horizontal stripes 

 in order to avoid .1 painful shock, the information does transfei 

 from 'Hi' thi other. 



left intact, while extensive lesions are made in the 

 other, instead of making the usual ablation in a 

 small area suspected to be critical, a large com- 

 plementary lesion can be made, leaving only the 

 critical area intact. If the visual cortex in one hemi- 

 sphere is isolated in this manner (see fig. igA), nearly- 

 all previously learned visual discriminations with the 

 eye on that side are lost. The simplest discriminations 

 (horizontal vs. vertical stripes), however, may be 

 occasionally preserved; if lost, they can be relcarncd. 

 Preoperatively learned discriminations between circle 

 and cross can also be relearned (though with deficit), 



fig. 19. Schematic views of experimental lesions in "split- 

 brain' cats /"/', complete s.mittal section of optic chiasm and 



of corpus callosum, combined with partial decortication of 

 lett hemisphere, leaving the visual cortex as an island of spared 



tissue Unit, mi, callosal section combined with another partial 

 hemidei in In .it 1. 111 . leaving an island of spared sensorimotor 



cortex From Sperr) (439); see also Myers (57).] 



