A left hemisphere contribution to visuospatial processing.

Men with chronic, focal, unilateral missile injures of the brain--twenty-five with left hemisphere lesions (LH group) and twenty with right hemisphere lesions (RH groups)--and twenty-two control subjects were given two visuoperceptual and two visuospatial tests. The LH group was significantly impaired in relation to the control group on both the spatial tasks. A different pattern of dissociable perceptual and spatial deficits was found in the experimental groups: better preserved perceptual than spatial performance was observed more frequently in the LH group whereas the converse--relatively better spatial than perceptual performance--was more evident in the RH group. Double dissociations in performance on the two spatial tasks were found predominantly in the LH group. These findings suggest an important left hemisphere contribution to visuospatial processing and the possibility of a more focal representation of spatial abilities in the left hemisphere than in the right.