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Scott Watamaniuk, Jeremy Badler, Stephen Heinen; Fixating an imaginary foveal stimulus increases microsaccades. Journal of Vision 2018;18(10):1011. doi: 10.1167/18.10.1011.
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© ARVO (1962-2015); The Authors (2016-present)
Microsaccades point to an attended object, and we previously showed an attended object in the fovea elicits more microsaccades than one in the periphery. Here we ask if the microsccade increase was mediated by the position error to a foveal target, or if attention at the fovea alone is sufficient to modulate the saccadic mechanism. Observers fixated a 9-dot stimulus composed of a 6° circular array of eight dots, and a central one. In separate blocks of trials, they detected near-threshold luminance increases at either the central dot, or at a randomly selected peripheral dot, that occurred an average of 6 times within a 20 sec trial. An EyeLink 1000 recorded eye movements at 1000 Hz. Saccade rate was higher when the luminance-detection task was on the central spot than when it was on a peripheral one, suggesting that attention at the central spot was evoking microsaccades. We then tested if attention directed to the fovea alone, without a stimulus, is sufficient to evoke microsaccades. Observers viewed the center of the 8-dot peripheral array with no central element. In one condition, the attention task (luminance change detection) was imposed on the peripheral dots as before. In another condition, observers detected a near-threshold stimulus that appeared in the center with the same frequency as the peripheral luminance change. We found that microsaccade rate was higher when observers attended the center even during epochs when no stimulus was present. Thus, foveating an imaginary stimulus still engaged the saccadic system. Analyzing microsaccade direction, more saccades were directed toward the center when the imaginary stimulus was attended, indicating that physical position error is not necessary for the generation of "corrective" microsaccades. The results suggest that the frequency of spontaneous microsaccades in the absence of a stimulus can reveal if attention is at the fovea.
Meeting abstract presented at VSS 2018
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