Image Segmentation based on Relative Motion and Relative Disparity Cues in Topographically Organized Areas of Human Visual Cortex

The borders between objects and their backgrounds create discontinuities in image feature maps that can be used to recover object shape. Here we used functional magnetic resonance imaging (fMRI) to study the sensitivity of visual cortex to two of the most important image segmentation cues: relative motion and relative disparity. Relative motion and disparity cues were isolated using random-dot kinematograms and stereograms, respectively. For motion-defined boundaries, we found a strong retinotopically organized representation of a 2-degree radius motion-defined disk, starting in V1 and extending though V2 and V3. In the surrounding region, we observed phase-inverted activations indicative of suppression, extending out to at least 6 degrees of retinal eccentricity. For relative disparity, figure responses were only robust in V3, while suppression was observed in all early visual areas. When attention was captured at fixation, figure responses persisted while suppression did not, suggesting that suppression is generated by attentional feedback from higher-order visual areas. Outside of the early visual areas, several areas were sensitive to both types of cues, most notably hV4, LO1 and V3B, making them additional candidate areas for motion- and disparity-cue combination. The overall pattern of extra-striate activations is consistent with recent three-stream models of cortical organization.