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Wesley Chaney, Jason Fischer, Gerrit Maus, David Whitney; Spatial attention reduces correlated noise in the fMRI response. Journal of Vision 2014;14(10):620. doi: https://doi.org/10.1167/14.10.620.
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Spatial attention modulates sensory neural activity, enhancing the representation of relevant stimuli and leading to enhanced performance in a variety of tasks. However, the exact mechanisms by which attention modulates early sensory activity and how this impacts the fMRI BOLD response are not yet fully understood. Previous studies recording from single units in area V4 have demonstrated that attention reduces correlations in the noise of simultaneously observed neurons (Cohen and Maunsell, 2009; Mitchell et.al., 2009). We tested whether analogous reductions of correlated noise also occur at the population level using the fMRI BOLD signal. We examined the effects of attention on the representation of four Gabor stimuli presented simultaneously in each quadrant of the visual field at jittered eccentricities. Subjects attended for contrast decrements in the Gabors in one visual field (either upper or lower in alternating runs) while ignoring the Gabors in the other visual field. After regressing out stimulus driven activity in V1 and V2 in a General Linear Model analysis, we analyzed pairwise correlations of the residual timecourses in voxels representing either the attended or unattended visual fields. We found that attention to either the upper or lower visual field reduces both the correlation and coherence of these timecourses. This reduction is opposite to what would be predicted from reduced noise within individual voxels or an increase in stimulus driven activity due to attention and it cannot be explained by vasculature differences or local scanner artifact as each region is attended or ignored for an equal number of runs. This reduction in correlated noise within attended locations allows for more accurate signal estimation at the population level, and may facilitate readout by higher level processes that pool over information in early visual cortex.
Meeting abstract presented at VSS 2014
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