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Olga Shurygina, Arezoo Pooresmaeili, Martin Rolfs; Automatic pre-saccadic selection of stimuli perceptually grouped with saccade targets. Journal of Vision 2019;19(10):256. doi: https://doi.org/10.1167/19.10.256.
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Before the onset of a saccadic eye movement, visual performance increases at the saccade target. This pre-saccadic attention shift is obligatory and spatially confined. In natural vision, movement targets are often part of extended objects. Electrophysiological studies revealed an automatic spread of attention to objects grouped with an attended stimulus by Gestalt criteria (Wannig et al., 2011). Here, we assessed if this automatic spread of attention is reflected in enhanced visual sensitivity to perceptually-grouped stimuli before saccadic eye movements. We presented four gratings at the vertices of an imaginary diamond that was itself positioned in one of four locations of the screen. In each trial, the two stimuli closest to the central fixation point were potential saccade targets. A central cue indicated the current saccade target and provided the go-signal for the eye movement. Shortly after cue onset (25–225 ms), we probed sensitivity at one of the four stimuli by briefly changing the orientation of the grating at that location. Observers were required to report the direction of orientation change irrespective of its location. Performance in this task served as a direct measurement of attentional deployment. Crucially, in each trial, one of the two distant stimuli was grouped with the saccade target as they shared the same color and pattern of Brownian motion about their location (grouping by similarity and common fate). We observed a substantive pre-saccadic attention shift: performance was highest at the saccade target and steadily increased towards movement onset. Moreover, performance at the distant locations was better if that location was perceptually grouped with the saccade target. The time course for the involuntary selection of distant, grouped locations did not follow the pre-saccadic attention shift but remained constant across relative to movement onset. We conclude that grouping-based attentional selection occurs involuntarily and independently from movement execution.
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