Observations on visual processes after posterior callosal section

T h e neurologic and psychologic consequences of cerebral conin i i ssuro toniy ' -~ have been the sub.ject o f a number of reports in recent years. These studies generally emphasize the profound breakdown in the communication that occurs between the two cerebral hemispheres after total midline cornniissural section. Visual, tactual, olfactory, propriocept ive, a n d a variety of other discriminatory tasks trained to one half brain are not available for processing i n the opposite halt' brain. Similarly, sensory events occurring in the left language hemisphere are usually described while those presented to the disconnected right hemisphere are not. T he se re in a r ka b I e sp I i t br a i n f i n d i ngs are not apparent in patients who have had the anterior one-half to two-thirds o f the corpus callosuin sectioned." In the present paper we report on two patients with posterior section o f the corpus callosuni. One showed all the disconnection effects seen i n visual testing o f the original series o f split-brain patients. The other patient, who had a similar operation at the age of 10 some nine years before testing, showed no disconnection effect. The results in the first case suggest that interhemispheric coininunication involving visual information nor ma I I y courses through the posterior t h i rd