Parallel processing streams in human visual cortex.

This study shows the existence in humans of independent neural processing streams in early visual cortex, which had previously been demonstrated in macaque monkeys. This evidence was obtained by controlled fixation testing of a subject who had suffered a small stroke in the right fusiform gyrus. The patient showed a severe disruption of color perception, shape discrimination and contrast sensitivity for stationary gratings in the upper left quadrant of his visual field. However, motion perception and contrast sensitivity for drifting gratings were relatively preserved. These results support the view that there are independent visual processing streams early in human visual cortex, and that these streams may subserve such functions as motion and color/form perception.