Cooperative Interaction between Change in Disparity and Size for the Perception of Motion in Depth

Abstract

While an object is moving in depth, its retinal disparity and size are cooperatively changing along the viewing distance. We examined the effect of a cooperative relation between the two cues for the perception of motion in depth—changes in disparity and size—with the Wheatstone stereoscopic display. In experiment 1, we used a stereoscopic stimulus whose disparity and size were independently modulated with sine-wave form, but at different frequencies (0.7 Hz vs 0.8 Hz, and vice versa). So, the cooperative and the uncooperative phases between the two cues repeatedly followed each other. The subjects continuously pushed a response key when the stimulus was clearly perceived to be moving in depth. In general, the impression of motion in depth was clear when the two cues were simultaneously modulated in similar phase, but not in different phase. In experiment 2, we measured the perceived distance of a stimulus that is moving in depth, when the two cues were moderated in the same phase and in counterphases. The perceived distance was increased when the two cues moved in the same phase. We found that not only the effect of each cue, but also the effect of the cooperative change of the two cues was affecting the perception of motion in depth. These results suggest that the cooperative interaction of two cues, that is their relative phase, is important for the perception of motion in depth.