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Janis Intoy, Norick Bowers, Jonathan Victor, Martina Poletti, Michele Rucci; The impact of retinal image motion on extrafoveal sensitivity. Journal of Vision 2018;18(10):372. doi: 10.1167/18.10.372.
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Humans are not aware that their eyes are always moving, even during the inter-saccadic periods of "visual fixation" in which visual information is acquired and processed. In these periods, ocular drift continually shifts the image on the retina, converting spatial luminance patterns into temporal signals impinging onto retinal receptors. Previous work has shown that the visual system is sensitive to these modulations and uses them to enhance sensitivity to high spatial frequencies (Kuang et al, 2012; Boi et al, 2017). These effects likely play an important role in driving the responses of neurons in the foveola. However, it is commonly assumed that drift carries little impact outside of the foveola, where drift covers a smaller fraction of the larger receptive fields. Contrary to this widespread assumption, we show that drift improves sensitivity to high spatial frequencies even without foveal stimulation. We measured contrast sensitivity in seven observers as they reported the orientation (±45o) of 16 cpd gratings with controlled retinal image motion. We simulated the retinal effects of larger and smaller drifts by amplifying or attenuating retinal motion from normal drift by means of a real-time system for gaze-contingent display. An artificial scotoma (1o-diameter) was fully stabilized to the center of gaze to prevent foveal stimulation. We report several findings. First, we show that vision outside of the foveola benefits from ocular drift: discrimination is impaired when drift is eliminated. Second, normal retinal image motion optimizes performance: larger and smaller drifts reduce sensitivity. Third, models of retinal ganglion cells exposed to the same stimulation fully account for how sensitivity varies with the amount of retinal image motion. These findings indicate that the spatiotemporal input reformatting from eye drift exerts its action throughout the visual field. They suggest that individual deviations from normal drift may impair visual sensitivity.
Meeting abstract presented at VSS 2018
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