Abstract
During locomotion, optic flow provides important information for detection, estimation and navigation. On the other hand, binocular disparity, which carries compelling depth information, can potentially aid optic flow parsing. We explored the effect of binocular disparity on observers’ ability to detect object motion during simulated locomotion. Twelve participants were recruited and tested on our wide-field stereoscopic environment (WISE). The stimulus consisted of four spherical targets hovering in a pillar hallway, and it was presented in stereoscopic, synoptic (binocular but without disparity), and monocular viewing conditions. In each trial, one of the four targets moved either in depth (approaching or receding) or a direction parallel to the frontal plane (contracting or expanding). Participants detected the moving target during a simulated forward walking locomotion in a 4-alternative forced choice task. The locomotion speed was 1.4 m/s, and therefore the target motion was superimposed upon this optic flow. Adaptive staircases were adopted to obtain the thresholds of the target motion speed in each viewing condition. The results to date showed that participants’ thresholds in the stereoscopic condition were 20 - 40 % lower (better) than those in the synoptic condition when detecting approaching targets, t(7) = 3.85, p = .006, receding targets, t(7) = 2.83,p = .025, and contracting targets, t(7) = 2.57, p = .036. Furthermore, only when detecting expanding targets, threshold performance was significantly better in the synoptic condition than that in the monocular condition, t(7) = 2.67, p = .032. These results suggested that during locomotion, binocular disparity facilitates optic flow parsing.