Bilateral visual cross-integration by human forebrain commissurotomy subjects.

Four forebrain commissurotomized patients were compared with one partially commissurotomized control subjects on their ability to cross-compare simultaneously flashed bilateral visual stimuli (colors, schematic faces, numbers, letters, patterns) as same or different, or to name the two stimuli. Two of the four patients were able to cross-compare some or all of the stimuli verbally, while another patient could name the two stimuli but not separately determine same-difference. It is hypothesized that (1) each cerebral hemisphere is capable of making separate verbal naming responses, and (2) brainstem interconnections between the 'disconnected' hemispheres allow some patients to integrate bilateral visual stimuli and make accurate same-different judgments.