Spatial and temporal tuning of motion in depth.

We used the Pulfrich effect to investigate perception of motion in depth. Independent manipulation of spatial and temporal frequency content in stereoscopic motion stimuli revealed the tuning characteristics of motion-in-depth perception. Sensitivity to interocular phase difference between sinusoidally oscillating sine-wave gratings was measured in four observers who judged direction of motion in depth. Discrimination thresholds in terms of interocular phase difference were determined to investigate spatial and temporal tuning characteristics of a system that is based on interocular phase difference, interocular delay, binocular disparity and velocity difference. Temporal frequency tuning of interocular phase difference thresholds was band pass and relatively dependent on spatial frequency variation. These results together with evidence from two control experiments support the idea that sensitivity to direction of motion in depth is limited by a stereo-motion system that monitors binocular horizontal disparity and motion rather than interocular phase difference, interocular delay, or interocular velocity difference.