Stimulus-induced drift inhibition revealed by retinal eye-tracking

Abstract

Abstract It is now well established that the movement of the eyes, which occurs constantly even during fixation, tends to “freeze” in response to perceptual events, with a magnitude and time course that depends on the stimulus properties, attention, and anticipation. This “freeze” or oculomotor inhibition (OMI) was found for microsaccades, blinks, smooth-pursuit, and catch-up saccades; yet remains unclear whether it also applies to ocular drift. Since video-based eye-trackers are known to produce positional artifacts, we used here data from a high-speed and precision retinal imaging eye-tracker (FreezEye Tracker, FET). The observers (n = 15) watched a series of flashed Gabor patches, with different spatial frequency and contrast while their eyes were tracked. We analyzed the data by removing the saccades, aligning the traces, and computing four drift measures relative to the stimulus onset: (1) velocity, (2) area, (3) diffusion, and (4) heat map. We found that all measures produced a highly significant modulation over time. The overall drift velocity, area, and diffusion followed the microsaccade inhibition pattern, whereas the heat map peaks showed the opposite pattern. The drift inhibition was also stimulus dependent, showing shorter onset and prolonged release estimates for more salient stimuli, matching the microsaccade OMI for the onset but showing the opposite for the release. Overall, the results confirm that the oculomotor inhibition effect can be generalized for ocular drift, but its opposite stimulus dependency for inhibition release and the shifted time course may suggest a complex interdependency between drift and saccades.