Self-motion path discrimination: effects of image stabilization

Abstract

Path-deviation thresholds were measured as the effects of eye movements in the retinal flow were minimized through image stabilization. Thresholds obtained with image stabilization were compared to those obtained with unstabilized viewing to determine whether the elimination of eye movements from the retinal flow improves self-motion judgments. The results showed that, at slow forward speeds, eliminating the retinal effects of eye movements did not improve path-discrimination performance; subjects required more of an angular deviation to discriminate a circular from a straight motion path with image stabilization than with unstabilized viewing. In an effort to understand the results, eye movements were measured in unstabilized viewing conditions, and the measured eye velocities were used to estimate the retinal-image motion. The results showed that, for slow forward speeds, eye movements increased the average retinal speed, independent of the circular flow direction. At fast forward speeds, there was no significant increase in the average retinal-image speed due to eye movements. A parsimonious explanation for the decreased performance with image stabilization at the slow forward speed is that retinal-image motion was too slow to optimally stimulate the visual motion sensors.