How Gaze Direction and Dynamics Affect Visual Resolution
By Eric Craypo
Significance Statement
When humans hold their gaze on an object, their eyes are in constant motion, yet the consequent movement of the image on the retina is not perceived. Using advanced optical methods to measure the exact trajectory of fixated images on the photoreceptor mosaic and the consequent visual performance in a repeated acuity task we reveal a highly evolved oculomotor system. Humans exhibit machine-like control over their ocular fixation, using a combination of drifts and saccades (fast flicks of eye gaze) to maintain the image of fixated objects on a tiny retinal region called the preferred retinal locus (PRL). Only rarely does the gaze ever shift far enough away to compromise visual performance.
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Video Caption
Trials lasted 2 seconds with the stimulus appearing 1 sec after the beginning of each trial. The 2-sec trails are represented here at half speed. The yellow star represents the center of the fovea (where cone photoreceptors are most densely packed). The video shows the contours that contain 68% of points on the retina. Those points indicate the direction of the eye’s gaze over time; in other words, where on the retina the stimulus would have fallen if it were presented at different times during the 2-sec trials.. The dot in the middle of the contour represents the median of those point positions. The time of stimulus presentation is indicated by a change in the color of the contour. The area containing retinal positions becomes successively smaller as stimulus time approaches and remains small for a few hundred milliseconds afterward. The graph at the bottom plots the area of the contour over time, averaged across 2100 trials. The stimulus is presented at 0 sec (indicated on the horizontal axis).