Visual processing in the split-brain cat: Analysis of the single-hemisphere deficit

Abstract

The self-sufficiency of the single hemisphere in the split-brain animal has been called into question in recent studies making direct comparisons of single- versus bihemispheric task mediation. Such comparisons seem to show that separation of the hemispheres reduces the cognitive capacity of the individual brain half significantly. When the brain is split with respect to the visual modality (as in the case of the subjects in this report) a sensory interpretation of unilateral behavioral loss offers itself, since sectioning the optic chiasm destroys crossed visual fibers, eliminating the temporal visual half-fields. Detailed analysis shows, however, that our subjects' unilateral performance is not consistent with a sensory interpretation of monocular loss. First, there is no unilateral loss preoperatively when vision is reduced 50% by eye occlusion; also there is no unilateral loss after optic chiasm section but before corpus callosum section; and finally, after both structures are sectioned there is a significant unilateral loss (as compared with binocular performance), but with asymptotic accuracy about the same for cue stimuli in nasal and temporal visual fields (i.e., for stimuli projecting to intact and denervated retina respectively). These data suggest, not a sensory loss, but the kind of single-hemisphere cognitive deficit obtained in studies in which task information (auditory or somesthetic cues) is experimentally confined to one brain half without any interference with receptor processes.