Dependence of stereomotion on the orientation of spatial-frequency components

It is known that sensitivity to stereoscopic motion in depth is not based upon the fine analysis of static disparities but instead is based on the binocular combination of motion-sensitive mechanisms. We show in this paper that an 'aperture problem' arises for the analysis of motion in depth, just as it does for monocular motion sensitivity. We extend Adelson and Movshon's solution to the aperture problem by intersection of perpendicular constraints to the three-dimensional case, and show that it predicts velocity matches for oblique gratings moving in depth, for orientations close to vertical. We show that binocular plaids give rise to motion in depth when the component orientations match in each eye, and the monocular motions are horizontal. The match velocities are consistent with intersection of perpendicular constraints. In three dimensions intersection of perpendicular constraints may be necessary, but is not a sufficient condition for the perception of coherent stereoscopic motion in depth.