A microtextured surface such as a homogeneously illuminated tracing-paper screen provides an excellent test surface for the movement aftereffect. When it is moved against the aftereffect at the appropriate velocity, a null occurs and the screen appears stationary. However, if patterned illumination is superimposed on the homogeneous field, the nulling breaks down. The pattern appears to move in one direction, driven by the aftereffect, and the screen can be clearly seen moving in the opposite direction. This breakdown begins to occur at luminances just above threshold for the detection of the pattern. The implication is that two populations of motion detectors are involved. Evidence in support of this postulate is presented.
Movement aftereffect of bi-vectorial transparent motion
