Abstract
Purpose :
Blurred images moving in stereoscopic depth are neurally sharpened more than laterally moving equally blurred binocular images having the same retinal image velocities. We examined whether asymmetric motion sharpening – a retinal process that sharpens the trailing edges of moving ocular images but not the leading edges – caused the difference between stereoscopic and lateral motion sharpening.
Methods :
10 normally binocular young adults viewed images on an Asus 3D display. The test images were 1°w x 2°h bars of 50% contrast on a dark gray background, with 42’ edge blurs. The bars moved at velocities of 0.5°/s or 2.0°/s. Experiment 1: Monocular test bars appeared for 0.5 sec above or below a fixation cross, at random. To measure asymmetric motion sharpening, the leading edge of a test bar was matched to its 42’ trailing edge by a PEST staircase technique. Matches were obtained for all combinations of eye, motion direction, and velocity. Experiment 2: Binocular images, moving laterally or in stereoscopic depth, were constructed from the perceptually edge-matched ocular images derived from experiment 1, thus removing asymmetric sharpening. Moving test bar blur was then measured by matching its blur, via PEST, to an adjustable-blur static comparison bar on the opposite side of fixation. Experiment 3: Performed like experiment 2, but with test bars constructed from ocular images having physically equal 42’ left and right edge blurs.
Results :
Mixed ANOVAs evaluated the effects of motion direction, subject, eye, and velocity on match blur. Experiment 1: Leading edge blurs had to be reduced by 19.6% at 2°/s to match trailing edge blurs (F=92.5, p≤0.0001). Experiment 2: Stereoscopic motion sharpening was stronger than conjugate lateral motion sharpening at 2°/s (F=6.68, p=0.036). Experiment 3: Stereoscopic motion sharpening was again stronger than lateral motion sharpening at 2°/s (F=7.11, p=0.032). The relative strength of stereoscopic motion sharpening did not differ between experiments 2 & 3. (F=1.2, p=0.37).
Conclusions :
(1) Asymmetric motion sharpening does occur with the type of stimuli we used. (2) Motion sharpening is stronger in stereoscopic motion-in-depth than in conjugate lateral motion, with or without edge-matched ocular images. (3) Stronger stereoscopic motion sharpening must be a property of a symmetric sharpening process in cortical stereoscopic motion-in-depth cells.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.