Interactions between cortical and subcortical visual areas: evidence from human commissurotomy patients.

Two commissurotomy patients performed an oculomotor task that required integrating visual information from the two hemifields. In marked contrast to previous "split-brain" findings, visual information from both hemifields was available for oculomotor control and perceptual function, provided that accurate performance depended on relatively crude visual discrimination. When finer spatial resolution was required, interfield performance declined to chance levels. The failure of a subject with occipital damage to accurately localize comparable stimuli in her blind field implies that cross-integration of the visual fields in commissurotomy patients requires interactions between cortical and subcortical visual areas.