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Yuanhao Li, Michele A Cox, T Scott Murdison, Bin Yang, Janis Intoy, Zhetuo Zhao, Michele Rucci; Post-saccadic dynamics of visual sensitivity across the visual field. Journal of Vision 2021;21(9):1930. doi: https://doi.org/10.1167/jov.21.9.1930.
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© ARVO (1962-2015); The Authors (2016-present)
Humans continually move their eyes, alternating saccades with an otherwise incessant jitter known as ocular drift. Recent work has shown that this stereotypical alternation cyclically modulates the luminance flow impinging onto retinal receptors, yielding temporal signals that enhance high spatial frequency during eye drifts and enhance low spatial frequencies with saccades. Psychophysical experiments with foveal stimuli have provided support to these ideas. Here we examine whether similar principles apply outside the fovea, where photoreceptors are less dense. Following a saccade (6.6o amplitude), human observers (N=9) were asked to detect a circular grating (the stimulus; either 2 or 10 cycles/deg) embedded in a naturalistic noise field. Eye movements were continuously monitored at high resolution by means of Dual-Purkinje-Image eye-trackers, and the stimulus presented as soon as the saccade started (average delay: 11 ms) in 50% of the trials. Contrast sensitivity functions were measured at three eccentricities (0, 4 and 8) and with three durations of post-saccadic exposure (50, 150, or 500 ms). Only traces in which the saccade was followed by uninterrupted drifts were considered. Very similar dynamics were found at all considered eccentricities. Visual sensitivity to 2 cycles/deg was immediately high 50 ms following the saccade and did not improve with further post-saccadic exposure. In this low frequency range, sensitivity was surprising uniform across the visual field. In contrast, sensitivity to 10 cycles/deg continued to increase during post-saccadic fixation. As expected in this high frequency range, sensitivity decreased with increasing eccentricity, but the rate of improvement with post-saccadic exposure was similar across eccentricities. Most of the improvement occurred between 50 ms and 150 ms, but sensitivity continued to increase past 150 ms. These results suggest that the luminance modulations from the natural saccade-drift alternation contribute to a coarse-to-fine processing dynamics throughout the visual field.
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