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Ashley Clark, Janis Intoy, Martina Poletti; Linking individual differences in fixational eye movements and visual acuity. Journal of Vision 2021;21(9):2763. doi: https://doi.org/10.1167/jov.21.9.2763.
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© ARVO (1962-2015); The Authors (2016-present)
During fixation, ocular drift continually shifts the retinal projection of objects across the foveola, where visual acuity is highest. Previous research showed that the spatiotemporal modulations introduced by ocular drift enhance high spatial frequencies in a way that depends on drift characteristics; the smaller the drift, the higher the spatial frequencies enhanced. Based on these findings, we hypothesized that differences in high acuity thresholds across observers are linked to individual variations of ocular drift. To investigate this issue, we measured visual acuity thresholds of 10 observers while monitoring ocular drift with a high-precision eye-tracker. Subjects performed a 4AFC discrimination task. Stimuli consisted of single digits, which size was adjusted using an adaptive procedure (width ranging from 0.4' to 4.5'). To quantify the amount of retinal motion generated by ocular drift, we calculated its diffusion coefficient, which defines how rapidly the line of sight moves away from its current location. Ocular drift diffusion coefficient varied by a factor of four across the tested observers (average; 14 ± 5 arcmin2/second). As a result, the range of spatial frequencies being enhanced by drift varied between 10 cpd to 60 cpd across individuals. Consistent with our prediction, we found a significant correlation (r = 0.73, p = 0.02) between acuity thresholds and drift diffusion coefficients across subjects: the higher the visual acuity, the lower the drift diffusion coefficient. The same correlation was observed when drift was measured independently from the task, during fixation on a marker. Importantly, the spatial frequencies enhanced by drift matched with the most informative frequencies for discriminating among digits in the task. These findings show that differences in ocular drifts are related to individual variability in acuity. They support the idea that drift luminance modulations impact acuity and suggest that acuity could be inferred by the characteristics of eye drifts.
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