Discrimination of motion direction in perimetrically blind fields.

Three patients with bilateral and two with unilateral striate cortex lesions have been tested for their ability to discriminate motion direction within their perimetrically blind field. No optokinetic nystagmus could be recorded in any of the three cases of cortical blindness, but all the patients could discriminate with a high level of success between two opposite directions of movement (at least along the horizontal plane) in a forced-choice indication task. In contrast, the two hemispherectomized patients remained at chance level in the same task. This indicates that the residual capacities observed in the patients with occipital lesions depend upon cortical structures. According to neurophysiological findings, the most likely substrate would be the homologue of area MT of the monkey.