Eye drift during fixation predicts visual acuity

Abstract

Visual acuity is essential for daily activities. It is believed that optics and anatomy alone determine the limits of visual resolution. However, in addition to these factors, eye movements greatly contribute to input dynamics, as the eyes jitter incessantly during fixation, displacing stimuli over many photoreceptors. Here we examined the relation between this motion (ocular drift) and differences in visual acuity in emmetropic observers. We show that: (a) large individual variability exists in the characteristics of ocular drifts; (b) these differences profoundly affect the structure of spatiotemporal signals to the retina; and (c) the spectral distribution of the resulting input signals strongly correlates with visual acuity. Building on these findings, we further show that individual acuity differences can be predicted from the motor behavior elicited by a simple fixation task, without directly measuring acuity. These results shed new light on how oculomotor behavior contributes to individual variability in acuity.

Sub-cone visual resolution by active, adaptive sampling in the human foveola

“…Smaller drifts induce luminance changes with higher spatial frequencies and models of retinal ganglion cell activity suggest a higher contrast sensitivity for high spatial frequency motion and less for low spatial frequencies compared to a static retina 24,55 . This is supported by other recent work which also showed that visual acuity thresholds can even be predicted from drift magnitudes measured in a sustained fixation task 32 .…”

“…3g), with a trend towards better visual acuity for small ocular drift motion. On a photoreceptor resolved scale, this confirms recent findings which showed individual acuity thresholds to be correlated with the drift motion during a non-AO acuity task, closely related to the drift measured in a sustained fixation task 32 .…”

“…Ocular drift has long been assumed to be a persistent jittery motion that follows random trajectories. Recent work showed that the amount of drift can vary and may be adapted to the task that has to be performed 26,32 . We here investigated if beyond this, humans are able to actively tune their ocular drift direction to exploit their prime spatial retinal processing properties.…”

“…Contrarily, recent studies on human psychophysics demonstrated fixational eye motion to be beneficial for fine spatial vision 26,29,30 . Especially drift motion has been increasingly argued to not just be randomly refreshing neural activity, but rather structuring it 26,31,32 and being under central control 33 .…”

“…Drift was shown to improve visual performance in resolution tasks 26,29,35 , and a recent model of early retinal signals suggests that if drift amplitude is tuned to object size, visual acuity would be enhanced 36 . Indeed, considerable differences in ocular drift between individuals exist 32,37 , and subjects exhibiting less drift were shown to have better acuity 32 . If such differences are a consequence of an active, adaptive mechanism, however, and how drift behavior is related to the photoreceptors that sample the retinal image is unknown.…”