Institute for Sensory Research
Syracuse University
621 Skytop Road
Syracuse, NY 13244-5290
Phone: 315.443.9714 (lab)
Fax: 315.443.1184

 

Julian Martin Fernandez

 

Motion in Depth

 

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 inter-ocular velocity differences. 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 inter-ocular velocity differences play a role in motion in depth perception. We studied this issue in two different ways. 

In the first study, we used frontoparallel motion adaptation. If inter-ocular velocity differences contribute to motion in depth, we would expect that discriminability of direction of motion in depth should be improved after adaptation to frontoparallel motion. This is because an inter-ocular velocity difference is a comparison between two monocular frontoparallel motion signals, and because frontoparallel speed discrimination improves after motion adaptation. We found that adapting to frontoparallel motion does improve both frontoparallel speed discrimination and motion-in-depth direction discrimination. No improvement would be expected if only disparity change over time contributes to motion in depth. For details see Fernandez & Farell (2005b).

In the second study, we used the motion aftereffect, the illusory motion of static patterns that follows adaptation to real motion. We induced a differential motion aftereffect to the two eyes (i.e., we adapted only one eye) and then tested for motion in depth in a stationary random-dot pattern seen with both eyes. This differential translational motion aftereffect produced a strong perception of motion in depth. Details can be found in Fernandez & Farell (2005c).

Together, our results strongly suggest that (1) pure inter-ocular velocity differences can produce motion in depth, and (2) the illusory changes in position from the motion aftereffect are generated relatively late in the visual hierarchy, after binocular combination.