Vocal responses to left visual stimuli following forebrain commissurotomy.

Four forebrain commissurotomized patients, 12-15 yr post-surgery, along with one partially commissurotomized and three normal control subjects, were presented with a variety of stimuli to either the LVF (left visual field) or RVF. Three of four "split-brain" patients could name LVF numbers and two of four could name LVF letters. Irrespective of their accuracy, and unlike control subjects, all "split-brain" patients named LVF stimuli about twice as slowly as RVF stimuli. In addition, three of four patients could vocally categorize LVF stimuli into two classes (yes-no, odd-even, more or less than five). In this case, like the control subjects, they respond to LVG stimuli as quickly as to RVF stimuli. The results support an hypothesis that "split-brain" patients may transfer information from the right to the left cerebral hemisphere when making two-choice verbal categorizations of LVF stimuli, but are able to name some simple LVF stimuli directly from the right hemisphere. Combining categorization and naming tasks, however, can elicit interference, suggesting that the two tasks are not completely autonomous.