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B. M. Ramsden, C. P. Hung, A. W. Roe; Is there a substructure of functional organization for illusory contour processing in V2?. Journal of Vision 2001;1(3):206. doi: 10.1167/1.3.206.
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Electrophysiological and fMRI studies have suggested that V2 plays a role in illusory contour signaling in primates, although the precise organization and neural circuitry associated with this signaling is not known. Using high resolution optical imaging, we have previously reported that focal activations occur in V2 when oriented illusory contours are presented to anesthetized macaque monkeys. We showed that these submillimeter-sized activations (illusory domains) could coincide with orientation domains that arose in response to real contour stimuli of the same orientation. In V2, however, less than half of electrophysiologically sampled cells show real/illusory co-tuning. Is this because not all cells in orientation domains exhibit illusory tuning? Or, is this because there are two classes of orientation domain in V2, i.e. one that prefers illusory and real contours of a particular orientation, and another that prefers only a real contour orientation? To examine this potential for substructure in the V2 orientation map, we compared illusory and real response maps in five anesthetized macaques. Stimuli comprised drifting illusory contour gratings constructed from abutting lines, or drifting real line gratings. Stimuli were matched for spatial frequency, luminance and drift. Real and illusory response maps were derived using optical imaging methods. Map correspondence was examined by spatial correlation statistical techniques at a range of scales. Overall, we found a significant correlation between illusory and real maps in V2. However when we examined portions of imaged V2 in detail, we observed that illusory and real orientation domains did not always coincide. Rather we found spatial correlation patterns similar to that which we have consistently observed in V1. These finding suggest a sub-structure exists in the orientation map in V2: one portion that that co-signals real and illusory contours, and another that is V1-like and signals only real orientation.
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