MACKAY has made use of the phenomenon of simultaneous contrast to provide evidence for the existence in the human visual system of neural channels that are sensitive to the density of visual texture. Using the same phenomenon, we have provided comparable evidence for the existence of lateral interaction between channels sensitive to velocity. That such channels do exist is suggested by the preliminary psychophysical observations of Pantle and Sekuler, who demonstrated a luminance threshold elevation for moving contours that is limited to a range of values around the velocity of the adapting contour.