MOTION DIRECTION DISCRIMINATION IN BLIND HEMIFIELDS

We tested motion direction discrimination with random dot cinematogram s (RDCs) projected into the contralateral homonymous visual field defe cts 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 o ther white matter tracts proximal to this site. The other 5 had lesion s involving this area or the proximal optic radiations. Eye position w as monitored to ensure fixation. No patient in either group discrimina ted motion direction in signal/noise RDCs at a level better than chanc e, and the performance of those with lesions restricted to medial occi pital lobe did not differ from those with lateral occipital or optic r adiation lesions. A subgroup of patients with medial occipital lesions also performed a ''frequency of discrimination'' experiment, using 10 0% coherent dot motion with stimulus velocities ranging as high as 73. 4 degrees/sec. Their results on these tests were also no better than c hance. Sparing of the putative motion area in lateral occipitotemporal cortex and its input fibers is not a sufficient condition for residua l direction discrimination (blindsight) with RDCs in homonymous visual field defects.