Abstract

Tracking eye movements significantly alter the image motion statistics reaching the retina. To describe these motion statistics and the effect of tracking, we define a space dependent velocity distribution for the image, computed by sampling velocity through time at every spatial location in the image. The velocity distribution provides a measure of the average spatiotemporal variability of images rather than instantaneous velocity variations. The mean and variance of the velocity distribution are related to the bandwidth and variability of the spatiotemporal spectrum of images. We implemented several visual tracking strategies on digitized image sequences to investigate their effect on the velocity distribution. We find, as expected, that retinal motion statistics are markedly different from those of the external image. Smooth pursuit provides consistently small mean velocities in the center of the visual field (the point of tracking), but at the expense of increasing the mean velocity in the periphery. On the other hand, visual full field tracking (vestibulo-ocular and optokinetic eye movements) reduces velocity equally across the entire visual field.

© 1992 Optical Society of America