Motion-in-Depth Sharpening: No Evidence for a Vergence Corollary Discharge Component

Abstract

Purpose : Motion sharpening causes blurred images to appear sharper when moving than when stationary. Sharpening is stimulated by retinal image motion, but it is unclear whether vergence corollary discharge contributes to the sharpening of a pursued motion-in-depth stimulus. Previous findings in motion smear perception suggest that motor signals for convergence and divergence may provide additional sharpening of fine detail viewed in darkness. This study tested the hypothesis that corollary discharge from vergence eye movements contribute to motion sharpening.

Methods : 14 naive, normally binocular, young adults viewed a 3D display at 1.069m. Subjects binocularly followed a fixation target moving in depth (crossed or uncrossed) at 1 or 3°/s. A 0.5°W x 2°H luminous test bar with 24' blurred edges was presented for 250ms 70' above or below fixation. The test bar moved with the fixation target (Exp 1) or at fixed stereoscopic depth (Exp 2). A comparison bar of variable blur determined by a PEST protocol was then presented for 250ms during steady fixation and the subject reported which bar was sharper. Eye movements were monitored by a ViewPoint^TM eye tracker to calculate the velocity of any retinal image motion during the experimental trials. Subjects also performed control trials by fixating a stationary target while a blurred test bar moved in stereoscopic depth at the retinal image velocities measured during the experimental trials. Control trials revealed motion sharpening due to retinal image motion during the experimental trials. Experimental match values were then adjusted by the corresponding control values to correct for retinal image slippage.

Results : Within-subjects ANOVAs measured the effect of velocity (1 or 3°/s) on match blur in experiments 1 and 2. No velocity effect was found in experiment 1 (F=1.1,p=0.32) which is consistent with the null hypothesis. As expected, experiment 2 showed significant sharpening (F=17,=0.001), but the effect disappeared when control retinal image motion was subtracted (F=2.8,p=0.12).

Conclusions : Our results suggest that the perceived sharpness of neither a fixated target moving in depth, nor a non-fixated background target, is affected by vergence corollary discharge. Motion sharpening during motion-in-depth is caused by retinal image motion.

This is a 2020 ARVO Annual Meeting abstract.

 

Effect of vergence velocity on match blur values in Exp 1 and 2 uncorrected (A,B) and corrected for retinal image motion (C,D).