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Helena X Wang, Shlomit Yuval-Greenberg, David J Heeger; Suppressive interactions underlying visually evoked miniature saccades. Journal of Vision 2013;13(9):1338. doi: 10.1167/13.9.1338.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose. To constrain computational models of underlying neural activity by characterizing how saccades during intended fixation depend on the spatial locations and contrasts of pairs of visual stimuli. Methods. Observers were instructed to maintain fixation on a small central marker, while parafoveal and peripheral spots were each flashed briefly (80 ms) and regularly at each of four cardinal locations (above, below, left, or right of fixation). A parafoveal stimulus (0.8º eccentricity) was presented either alone or simultaneously with one of the peripheral stimuli (5º eccentricity). We systematically varied the contrast of the parafoveal stimuli, while holding the contrast of the peripheral stimuli (when present) constant. Eye movements were recorded with a video-based eye tracker (Eyelink 2000, SR Research) to detect miniature saccades (<1º) following each stimulus presentation. Results. A large proportion of miniature saccades were biased toward the parafoveal stimuli ("congruent saccades"). Congruent saccades typically occurred 100-200 ms following stimulus onset. A later increase in overall miniature saccade rate was also evident, as documented in the literature, but it did not exhibit congruency toward the parafoveal stimuli. The rate of congruent saccades increased with parafoveal stimulus contrast and saturated at high contrasts when the parafoveal stimuli were presented alone. Congruent saccade rate was suppressed by the peripheral stimuli. The effect of the peripheral stimuli could best be characterized as subtractive, i.e., leading to a constant decrease in miniature saccade rate at all parafoveal contrasts. Conclusion. We interpret these results in the context of computational models of neural activity in the visuomotor map of the superior colliculus. Visual stimulation near fixation biases the vector mean of activity toward the representation of the stimulus. Distant stimuli interact with nearby stimuli, suppressing activity and reducing the rate of miniature saccades evoked by nearby stimuli.
Meeting abstract presented at VSS 2013
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