Metacontrol of hemispheric function in human split-brain patients.

Four commissurotomy patients were tested for ability to match tachistoscopically presented stimuli with pictures in free vision, according to either structural appearance or functional/conceptual category. Patients were given ambiguous, structural, or functional instructions on any given run to trials with simultaneous double stimulus input to the two cerebral hemispheres. With ambiguous instructions, appearance and function matches were performed by the right and left hemispheres, respectively. When instructions were specific, appearance instructions tended to elicit appearance matches and right-hemisphere control. When function instructions were given, left-hemisphere control and function matches tended to be elicited. In three of the four patients, however, there was a significant number of dissociations between controlling hemisphere and strategy of matching.