Lateralized division of attention in the commissurotomized and intact brain

Abstract

The degree to which voluntary maintenance of independent attentional systems in left and right hemispheres during lateralized double simultaneous performances is possible for prolonged periods was assessed in five complete commissurotomy patients, two partial commissurotomy patients and eight normal subjects. Subjects performed a unimanual tactual sorting task as well as bimanual sorting tasks requiring (1) the same, (2) different or (3) opposite simultaneous decisions by left and right hemispheres. Normals were also given additional practice sessions with the same tasks in an effort to determine limitations in the capacity for dual processing. The results suggest that the cerebral commissures force the two hemispheres to work together and maintain attentional unity in the intact brain. Practice increases the capacity for simultaneous processing in normals, but this enhancement is most readily interpreted as the result of automation of performance decreasing the need for attentional supervision rather than as a division of the normal unity of focus in the intact attentional system.