Is human motion detection subserved by a single or multiple channel mechanism?

Two recent versions of a single channel model of motion perception have had impressive success in explaining direction discrimination by human observers for spatially filtered noise images in two-flash apparent motion. It has been argued that the dramatic breakdown in motion perception which occurs when one image in the two-flash sequence is low-pass filtered can be explained only by a single channel model. We show that neither version of the single channel model which has been proposed can explain performance for noise images chosen to provide comparable stimulation in the spatial channels known to subserve human vision. A multi-channel model of motion perception has little difficulty in explaining these results.