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Jacqueline C. Snow, Lars Strother, Alexandra C. Coros, Jody C. Culham; How independent are form and color in the ventral visual pathway?. Journal of Vision 2012;12(9):510. doi: 10.1167/12.9.510.
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The human ventral visual pathway represents object shape, color and category, but the degree to which shape and color are dissociable in occipito-temporal cortex is unknown. We examined color sensitivity in shape-sensitive visual cortex and shape-sensitivity in color-sensitive visual cortex. Shape-sensitivity was measured via fMRI-adaptation (fMR-A) using objects that varied or repeated within blocks. Object images were either color photographs (shape and color) or monochrome silhouettes (shape only). Color sensitivity was measured by comparing fMRI responses to scrambled color photographs and scrambled monochrome silhouettes. Object-, face-, body- and scene-selective areas in ventro-lateral occipito-temporal cortex were functionally localized in a separate experiment, which in combination with our main experiment, enabled us to delineate a lateral ‘shape stream’ from a more medial ‘color stream’. The streams were distinctly separable in posterior occipito-temporal cortex but overlapped in anterior ventro-temporal cortex. We found that areas of maximal overlap between these two streams did not correspond to any single category-selective cortical area. We also examined the relative sensitivity to object shape in the absence of color, to color in the absence of shape, and to the combination of shape and color. The shape stream showed consistent fMR-A to object shape throughout, but fMR-A to colored objects was highest anterior and ventral to object-selective lateral occipital cortex. The shape pathway showed a similar posterior-to-anterior trend in color sensitivity for scrambled objects, suggesting that fMR-A for colored objects was at least partly due to color adaptation in the absence of form. The color stream showed a posterior-to-anterior increase in fMR-A responses to object shape and colored photographs that was maximal where the shape and color streams overlapped. Our results demonstrate clear posterior-to-anterior changes in the relative sensitivity to shape and color, which may exhibit different degrees of neural independence at progressive stages of visual processing.
Meeting abstract presented at VSS 2012
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