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Fang Fang, Huseyin Boyaci, Daniel Kersten; Border ownership representation in human early visual cortex and its modulation by attention. Journal of Vision 2008;8(6):393. doi: 10.1167/8.6.393.
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© 2015 Association for Research in Vision and Ophthalmology.
Natural images are usually cluttered because objects occlude one another. A critical step in visual object recognition is to identify the borders between image regions that belong to different objects. Single-unit studies have suggested that a representation of border ownership may form as early as V2. We used fMRI adaptation to investigate sensitivity to border ownership in human early visual cortex. Two stimuli were generated by modifying a black/white square-wave radial grating. In one stimulus, the white stripes were slightly longer than the black stripes in the radial direction. This provided contextual information that caused the borders between the white and the black stripes to appear to belong to the white stripes. In the other stimulus, the black stripes were slightly longer than the white stripes, which caused the borders to appear to belong to the black stripes. Subjects adapted to one of these two stimuli and were then tested with both stimuli. Their attention was directed either to a central fixation point or to the borders. Regions of interest in the early visual cortex were confined to areas corresponding to an annular interior part of the radial grating. This part was locally identical across the two stimuli, but as a consequence of the difference in the contextual information, the borders between the white and the black stripes were perceived to belong to either the white or the black stripes. When subjects attended to the border, we found a strong adaptation effect in V2 consistent across four subjects, but a weak effect in V1. However, when subjects attended to the fixation, the adaptation effect was largely abolished in both V1 and V2. Our data suggest that V2 is a critical area for the processing of border ownership and that this processing depends on feedback from higher-level visual areas.
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