The corpus callosum contains more than 200 million fibers connecting the two hemispheres of the brain, and plays a role in many aspects of interhemispheric integration. In patients who have undergone complete callosotomy, this integrative pathway is severed and yet these patients are remarkably unaffected in daily living. In the past, split-brain research has elucidated many of the lateralized and specialized functions of the two hemispheres of the brain. The current proposal is aimed at expanding this focus to study not only hemispheric specialization but also interhemispheric integration. Proposed experiments investigate the extent to which perceptual and cognitive functions are coordinated callosally. We hypothesize that there is duplication of function between the hemispheres in basic visual and attentional processes and therefore these processes do not rely on callosal integration. In contrast, we hypothesize that higher level perceptual and cognitive functions involve hemispheric specialization and therefore depend on callosal pathways for integration. Remarkably, in more than twenty years of research on callosal function, these fundamental hypotheses have not been rigorously tested. Specifically, we will investigate possible non-callosal pathways for the integration of form and location information across the hemispheres, the updating of each hemisphere's map of visual space when eye motions occur, and the ways in which attention is allocated. Possible callosal interactions for perceptual and memory processes will be investigated by studying the binding of contour fragments by the visual system in the synthesis of object percepts, and the binding of elements of events in memory encoding.
