Motion direction discrimination in blind hemifields.

Abstract

We tested motion direction discrimination with random dot cinematograms (RDCs) projected into the contralateral homonymous visual field defects of 10 patients with unilateral cerebral hemispheric lesions. Five patients had medial occipital lesions that spared the putative motion area in lateral occipitotemporal cortex and the optic radiations and other white matter tracts proximal to this site. The other 5 had lesions involving this area or the proximal optic radiations. Eye position was monitored to ensure fixation. No patient in either group discriminated motion direction in signal/noise RDCs at a level better than chance, and the performance of those with lesions restricted to medial occipital lobe did not differ from those with lateral occipital or optic radiation lesions. A subgroup of patients with medial occipital lesions also performed a "frequency of discrimination" experiment, using 100% coherent dot motion with stimulus velocities ranging as high as 79.4 degrees/sec. Their results on these tests were also no better than chance. Sparing of the putative motion area in lateral occipitotemporal cortex and its input fibers is not a sufficient condition for residual direction discrimination (blindsight) with RDCs in homonymous visual field defects.