Perception of optical flow in cortical blindness: a case report.

Motion perception was studied in a subject with bilateral lesion of the visual cortex, involving severe damage to cortical areas V1 and V4, but with no apparent damage to visual associative areas situated in occipito-parietal and lateral occipito-temporal (presumably V5) zones. He was able to perceive optical flow motions simulating motion in depth in "blind" parts of his visual field, provided that the stimulus-onset was temporally dissociated from its motion. Moreover, he was able to discriminate between different velocities and directions of motion. The results suggest that perimetrically "blind" parts of the visual field in this patient have true capacities to process visual motion. They are discussed in reference to the subject's ability to move freely in his environment and in reference to the role of extrastriate visual pathways in visual motion processing.