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Suzanne P. McKee, Benoit R. Cottereau, Justin M. Ales, Anthony M. Norcia; Surface segmentation is more powerful in the fixation plane: evidence from EEG source imaging. Journal of Vision 2010;10(15):16. doi: https://doi.org/10.1167/10.15.16.
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Using high-density EEG source imaging, we have found that relative disparity enhances the population response to disparity modulation in extra-striate areas (Cottereau et al., 2010). In the current study, we used EEG imaging to explore how relative disparity produces this enhanced response. Our stimulus was a 5 deg disk surrounded by large annulus, both composed of sparse dynamic random dots. The central disk shifted repetitively between two disparities at 2Hz (disparity modulation), while the surround had a fixed disparity. The surround produced the largest effect when presented in the fixation plane, so that the disk was alternately breaking and making a planar surface; the effect was considerably smaller if the modulating disk straddled the fixation plane moving between equal and opposite signed disparities. This result suggests that surface segmentation is driving the enhanced activity associated with relative disparity. However, if disk and surround were shifted off the fixation plane together, so that the plane was still segmented by the modulation, the surround effect was greatly diminished. Therefore, surface segmentation is much more powerful for targets in the fixation plane than at other depths. Our findings show that areas near V3A are most sensitive to fixation plane segmentation, while the responses from the V1 area are not significantly altered by the location or presence of a surround.
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