Motion in depth from interocular velocity diVerences revealed by diVerential motion aftereVect

There are two possible binocular mechanisms for the detection of motion in depth. One is based on disparity changes over time and the other is based on interocular velocity diVerences. It has previously been shown that disparity changes over time can produce the perception of motion in depth. However, existing psychophysical and physiological data are inconclusive as to whether interocular velocity diVerences play a role in motion in depth perception. We studied this issue using the motion aftereVect, the illusory motion of static patterns that follows adaptation to real motion. We induced a diVerential motion aftereVect to the two eyes and then tested for motion in depth in a stationary random-dot pattern seen with both eyes. It has been shown previously that a diVerential translational motion aftereVect produces a strong perception of motion in depth. We show here that a rotational motion aftereVect inhibits this perception of motion in depth, even though a real rotation induces motion in depth. A non-horizontal translational motion aftereVect did not inhibit motion in depth. Together, our results strongly suggest that (1) pure interocular velocity diVerences can produce motion in depth, and (2) the illusory changes in position from the motion aftereVect are generated relatively late in the visual hierarchy, after binocular combination.  2005 Elsevier Ltd. All rights reserved.