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Chaithanya Ramachandra, Bartlett Mel; Distance dependent contextual interactions in natural images. Journal of Vision 2010;10(7):1356. doi: 10.1167/10.7.1356.
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Long-range horizontal connections in V1 (Bosking et.al. 1997) are thought to mediate the facilitating effects of aligned contour elements in the extraclassical surrounds of V1 cells, and to contribute to contour integration at the perceptual level (Kapadia et.al. 1995). To better understand the nature of these nonlinear classical-extraclassical modulation effects, we have analyzed the statistics of object contours in natural images (from the Corel database) labeled by human subjects. We gathered joint statistics of multiple Gabor-like oriented edge detectors at varying spatial separations in natural images both on and off contours, and characterized the changes in the contour probability function P(contour | edge cues) as we varied the spatial separation and arrangement of the edge cues. We observed clear differences in the form of the contour probability function when the contributory edge elements were closely spaced within the classical receptive field, which led to symmetric AND-like interactions between edge cues, compared to the more asymmetric “contextual” interactions seen between flanker and central cues at greater spatial separations.
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