Visual perception of line direction in patients with unilateral brain disease.

The accuracy of identifying the slope of briefly exposed lines was assessed in patients with lesions of the left or right hemisphere and in a group of control patients without history or evidence of brain disease. The frequency of impaired performance was remarkably high in the patients with right hemisphere lesions. In contrast, the patients with left hemisphere lesions did not perform differently from the control group. Visual field defect, aphasic disorder, and age were not related to performance level. The striking interhemispheric difference in performance on this visuospatial task suggests its further development for clinicodiagnostic purposes.