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Alby Richard, Jan Churan, Daniel Guitton, Christopher Pack; Pre-saccadic changes in visual motion discrimination. Journal of Vision 2007;7(9):988. doi: 10.1167/7.9.988.
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© ARVO (1962-2015); The Authors (2016-present)
Changes in visual perception are known to accompany both the preparation and execution of saccadic eye movements. Specifically, saccades are associated with a decrease in visual sensitivity, as well as errors in visual spatial localization (Burr et al, 2002). Here we describe an enhancement of motion sensitivity that occurs in a period before the onset of saccades.
We tested subjects' ability to discriminate visual motion direction at different times before and during the execution of saccades. The stimulus was a two-frame motion pulse, constructed by shifting the phase of a Gabor patch on consecutive frames. The size and contrast of the Gabor stimulus varied randomly from trial to trial.
When the stimulus was presented a long time (70 – 150ms) before saccade onset, performance depended strongly on stimulus size and contrast. Discrimination was best for small stimuli at high contrast and for large stimuli at low contrast, presumably as a result of inhibitory spatial influences (Tadin et al, 2003).
When the stimulus was presented in a small time window (30 – 70ms) before saccade onset, the performance changed in a contrast dependent manner. In the majority of subjects tested, motion discrimination improved markedly for the high contrast gratings, but was impaired for low contrast stimuli.
These changes were not linked in any obvious way to the attentional shifts that are known to accompany saccades. Theories of attention based on contrast gain did not account for instances in which increased target saliency would be expected to decrease performance. Rather, the observed increase in performance may be linked to an eye movement signal or attentional mechanism that narrows the tuning curves of direction-selective neurons.
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