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Janneke Jehee, Devin Brady, Frank Tong; Attention improves decoding of stimulus orientation in early visual areas. Journal of Vision 2008;8(6):994. doi: https://doi.org/10.1167/8.6.994.
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Previous neuroimaging studies have shown that attending to a spatial location leads to enhanced BOLD responses in corresponding regions of the human visual cortex. However, it is unclear whether these enhanced cortical responses simply reflect the top-down selection of a spatial region or whether they might convey additional information about the attended features at that location. To address this issue, we used functional MRI in combination with multivariate pattern analyses to investigate the effects of attention on orientation-selective responses in early human visual areas. Subjects performed a near-threshold orientation discrimination task involving one of two laterally presented gratings. Gratings of independent orientation (base orientation of either 55 or 145 deg) were simultaneously presented to the left and right of a fixation point, twice in each trial. Attention was directed to either the left or right grating by a central cue. Small orientation changes were introduced between successive presentations of the gratings using an adaptive staircase procedure, and subjects had to report whether the second grating was rotated clockwise or counterclockwise relative to the first. Analyses of the amplitude of the BOLD response revealed much stronger responses for attended than unattended locations in early visual areas. To test whether this also resulted in additional information about the attended features at these locations, we used a pattern-based approach to decode the presented stimulus orientation from cortical activity found in these regions (Kamitani & Tong, Nat Neurosci, 2005). We found significantly better classification performance of the decoder in the attended condition as compared to the unattended condition in areas V1, V2 and V3. We conclude that attention not only enhances the strength of cortical responses in early visual areas, but also improves the feature selectivity of these responses when analyzed at a population level.
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