Attenuation of Perceived Motion Smear During the Vestibulo-ocular Reflex

Abstract

Abstract: : Purpose: The image of a physically stationary target moves across the retina during eye movements, leading potentially to the perception of motion smear. Previous studies indicated that perceived motion smear is less when a physically stationary target is presented during voluntary saccades, pursuit, or vergence than when similar retinal-image motion occurs during steady fixation. The goal of this study was to assess whether the perception of motion smear is attenuated also during the involuntary vestibulo-ocular reflex (VOR). Methods: Four observers matched the length of perceived smear in two experimental conditions, designed to produce similar trajectories of retinal image motion. In the fixation condition, a target was presented in rightward or leftward motion (5 - 20 deg/s) while the stationary observer attempted to maintain straight-ahead fixation in darkness. In the VOR condition, the target moved with the observer, who underwent full-body rotation around a vertical axis in darkness. Horizontal eye movement recordings during VOR trials allowed us to calculate the eye velocity (5-36 deg/s) and the extent of the target's retinal image motion. In both conditions, the target was a green laser spot, 2.5 log units above its detection threshold, presented to one eye for a duration of 50 - 200 ms. Results: Perceived motion smear was significantly less during the VOR than fixation for target durations longer than 100 ms (mean ratio = 0.58; p = 0.037). Further, the extent of perceived smear in the VOR trials decreased with the velocity of eye movement up to approximately 10 deg/s. A control experiment indicated that the extent of perceived motion smear during fixation did not vary systematically with the horizontal eccentricity of the target (10 deg). Conclusions: As during voluntary eye movements, perceived motion smear is reduced substantially if retinal image motion is produced by the involuntary VOR, rather than physical target motion during fixation. Our results implicate extra-retinal signals in the attenuation of perceived motion smear and suggest that extra-retinal signals for other involuntary eye movements, such as congenital nystagmus, can contribute to the reduction of perceived smear during eye motion.

Keywords: 618 vestibulo-ocular reflex • 477 motion-2D • 585 space perception