Left hemisphere visual processes in a case of right hemisphere symptomatology. Implications for theories of cerebral lateralization.

A patient with a visuospatial disturbance characteristic of posterior right hemisphere disease was examined under different conditions of stimulus presentation. The visuospatial defect, which was shown by the failure to perceive abnormalities concerning the left side of objects and the misperception of spatial relations, was present under conditions of unrestricted visual exposure. However, when the stimulus material was briefly exposed in the right visual field, performance improved substantially. These data suggest that the visuospatial defect seen after right hemisphere disease is atributable to factors other than the incapacity of the left hemisphere to process visuospatial information. Our observations, together with other evidence, lead us to question those theories of cerebral lateralization based on the notion that visuospatial processing is special to the right hemisphere.