Impaired grating discrimination following right hemisphere damage.

We investigated the effect of unilateral brain lesions on visual discrimination of low-, middle- and high-frequency gratings. The performance of patients with right hemisphere lesions was significantly impaired compared with that of both controls and patients with left hemisphere lesions. This impairment was largely limited to patients with right posterior hemispheric lesions and was present with all spatial frequencies. These findings run counter to the hypothesis that high and low spatial frequencies are preferentially processed by different hemispheres.