Processing Difficulties Following Commissurotomy in the Monkey

Split-brain, partial-split, and normal monkeys were trained to perform a nested match-to-sample task. Results showed that split-brain monkeys with visual information limited to one hemisphere performed more poorly than partial-split and normal animals. At the same time, when the split-brain animals used both hemispheres their performances were the same as controls. These groups were then compared on a color discrimination reversal task and similar results were found. Taken together, these findings suggest that the processing difficulties seen in one half of a split-brain animal are frequently more apparent than real. These studies rule out earlier interpretations that such defects are due to mass action effects. Rather, the poor performance by one-half brain is due to the interfering response made by the opposite hemisphere.