Abstract
Past research has suggested that lateral motion and motion in depth are supported by different mechanisms. Here we present a series of steady-state VEP measurements, comparing responses to absolute and relative 2D and 3D motion in random dot displays, under conditions of vertical and horizontal binocular disparity. Displays consisted of test bars undergoing coherent lateral motion (2 Hz) that was either in phase between the two eyes or in anti-phase, alternating with reference bars without coherent motion. When motion was in anti-phase and bars were horizontal, the display produced horizontal binocular disparity consistent with 3D motion-in-depth. When the display was rotated 90ยบ, the vertical bars produced vertical disparity, which is not perceived as motion-in-depth. In-phase motion was perceived as 2D in-plane motion. Reference bars either contained static dots, producing relative motion/relative disparity between the test and reference bars, or incoherent motion, in which case only the absolute motion/absolute disparity modulation of the test bars remained. We measured motion-response functions by sweeping dot displacements from 0.5 to 16 arcmin. At the even harmonics, which reflect steady-state responses that are equivalent regardless of motion direction (left/right, up/down, towards/away), we saw a clear difference between 2D and 3D relative motion, where response thresholds were lower for 2D than 3D. This difference persisted for both the horizontal and vertical bars, suggesting that stereo-movement suppression (Tyler, 1971) may not solely be the result of perceived motion in depth. Absolute 3D motion produced weaker, but detectable responses for both display orientations, while responses to absolute 2D motion did not. A follow-up experiment using a blank reference bar for the absolute motion conditions replicated the previous results, except that absolute 2D motion now produced measurable responses. This result suggests that the motion system pools coherent and incoherent motion over space with a resulting reduction in sensitivity.
Meeting abstract presented at VSS 2017