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Michele Rucci, Naghmeh Mostofi; Visual suppression within the foveola during microsaccades. Journal of Vision 2017;17(10):921. doi: 10.1167/17.10.921.
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© ARVO (1962-2015); The Authors (2016-present)
Much research has focused on the transient reduction in visual sensitivity that occurs around the time of saccades, a phenomenon known as saccadic suppression. While it is well established that visual thresholds increase before and during a saccade, it remains unclear whether this phenomenon extends to microsaccades, the very small saccades that keep the retinal projection of the attended stimulus within the high-acuity foveola. Previous studies focused on how microsaccades affect the visibility of peripheral stimuli during sustained fixation. However, it is now clear that humans use microsaccades to explore fine detail (Ko et al, 2010), and a critical question is how microsaccades affect the visibility of stimuli within the foveola. Here we measured sensitivity to contrast changes in a search task designed to model primate's social grooming, a task that naturally led to frequent microsaccades. Observers searched for fleas (the targets) in a naturalistic noise field that also contained dust particles (the distractors). Both targets and distractors were 5' dots, but targets transiently revealed themselves by changing contrast (a flea jump; a 10 ms pulse), which the observer reported by pressing a button on a joypad. A high-resolution gaze localization technique (Poletti et al, 2013) and synchronization of contrast pulses with microsaccades enabled precise spatiotemporal stimulation of selected regions within the foveola. We show that a strong suppression in foveal sensitivity occurs at the time of microsaccades. At all tested eccentricities within the foveola, suppression starts ~50 ms before microsaccade onset and is followed by an enhancement in visual sensitivity immediately after microsaccade end. Contrast sensitivity also decreases rapidly within eccentricity within the foveola, so that a considerable increment in threshold can already be observed at only 15' eccentricity. These results show that microsaccades profoundly affect visibility at the very center of gaze.
Meeting abstract presented at VSS 2017
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