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Kiyohiro Maeda, Hiroki Yamamoto, Toyomi Matsuno, Masaki Fukunaga, Asuka Nakagoshi; Color selective response suppression under metacontrast masking in the human visual cortex. Journal of Vision 2005;5(12):29. doi: https://doi.org/10.1167/5.12.29.
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© ARVO (1962-2015); The Authors (2016-present)
In metacontrast masking, the visibility of a target flash is reduced by a subsequent mask surrounding the target. For a colored target, the maximum visibility reduction occurs when a mask has the same color as the target (von der Heydt et al., 1998; Beer et al., 2002). We used fMRI to investigate the color pathway underlying this color selective masking in the human visual cortex. Visual stimulus consisted of an annular target and two masks surrounding the target. The target and masks were equi-luminant red or green on a gray background. In a block paradigm, we compared brain activity evoked by the isochromatic target and masks with that evoked by the heterochromatic pairs. In parallel with perceptual masking, brain activity was attenuated for the isochromatic pairs. Although this color selective suppression was widespread from V1 to higher visual areas including hMT+ and LO, remarkable response reduction occurred equally in V2 and V3, and maximally in VO/V8/hV4. This two-step response suppression along the presumed cortical hierarchy suggests that V2 and VO/V8/hV4 play special roles for the color selective masking. It is likely that in these two regions there exist narrowly-tuned color selective neurons and that their spatiotemporal interaction influences color visibility.
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