RETINOTOPIC AND DIRECTIONAL DEFECTS IN MOTION DISCRIMINATION IN HUMANS WITH CEREBRAL-LESIONS

We investigated the discrimination of motion direction in peripheral a nd central vision in 23 patients with unilateral cerebral hemispheric lesions on computed tomography or magnetic resonance imaging. We used random dot cinematograms that determined a percent coherence motion th reshold for 16 points in the peripheral field and for four directions separately in central vision. We measured asymmetry of right- versus l eft-field peripheral discrimination (retinotopic defects) and asymmetr y of central discrimination for rightward versus leftward motion (dire ctional defects), compared with normal subjects. Five patients had dir ectional asymmetries of foveal motion perception, all worse for motion toward the side of their lesions. One patient had a bidirectional def ect for the perception of horizontal motion. For 3 of these 6, the ave rage of all horizontal and vertical motion discrimination thresholds w as also elevated. Two had contralateral retinotopic defects. One of th ese also had an ipsidirectional foveal defect, but the other did not. The remaining 5 patients with ipsidirectional foveal defects had hemia nopias that precluded testing for coexistent retinotopic defects. The lesions of the 6 patients with ipsidirectional defects overlapped in w hite matter underlying the lateral temporo-occipital cortex, at the ju nction of Brodmann areas 19 and 37. In contrast, lesions of patients w ithout directional defects spared this region.