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Joachim Bellet, Ziad Hafed; Phase-locking of behavioral fluctuations to microsaccade generation. Journal of Vision 2016;16(12):857. doi: https://doi.org/10.1167/16.12.857.
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© ARVO (1962-2015); The Authors (2016-present)
Our eyes are in constant motion even during periods of attempted gaze fixation. Among the types of fixational eye movements that are known to occur are microsaccades, which are tiny saccades (typically less than 1 of visual angle) occurring 1-3 times per second. Even though visual processing has already been shown to be modulated close to the time of microsaccades, it is not clear how microsaccade generation might influence longer-term fluctuations in brain activity and behavior. Here we show that visual processing is significantly affected even several hundreds of milliseconds after a microsaccade has occurred, and this happens because microsaccades reset the phase of ongoing brain oscillations. We conducted psychophysical experiments in which subjects had to make a targeting saccade, as fast as possible, towards a peripheral stimulus that was experimentally presented at different times after a microsaccade. Eight subjects were instructed fixate a circular white dot (0.1 diameter) in the middle of a gray screen. Fixation duration was randomized between 300 and 3000 ms. After this duration, the fixation dot disappeared and, simultaneously, a 1-diameter white target appeared 5 to the right or left of fixation. We investigated whether the relative time and direction of the microsaccade preceding target appearance could influence reaction time (RT) to the target. Mean RT varied in a rhythmic fashion depending on when the stimulus was presented relative to a microsaccade. The first 400 ms following a microsaccade revealed strong oscillations in RT (15 Hz), in the hemifield towards which the microsaccade was directed to; the next 400 ms presented similar (albeit lower-frequency) oscillations (10 Hz), but this time in the opposite hemifield. Our results suggest that visual processing is subject to oscillations that are phase-locked to the time of microsaccade generation, and that these oscillations are strongly dependent on microsaccades direction.
Meeting abstract presented at VSS 2016
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