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Chai-Youn Kim, Randolph Blake; Are real and synesthetic colors mediated by shared neural mechanisms?. Journal of Vision 2006;6(6):1073. doi: 10.1167/6.6.1073.
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Background: Individuals with color-graphemic synesthesia experience colors when viewing achromatic alphanumeric characters, and accompanying synesthesia is activation of color-responsive brain areas. Whether real and synesthetic colors arise from activation of the same population of neurons remains unknown, however, so we used rapid, event-related fMRI to address this question. Methods: fMRI BOLD signals were measured while synesthetic observers saw two alphanumeric characters presented in rapid succession. RC condition: a colored, non-alphanumeric character was followed by another non-alphanumeric character either the same or different in color; none of the RC characters evoked synesthesia. SC condition: an achromatic letter evoking a given synesthetic color was followed by another achromatic letter evoking either the same or a different synesthetic color. To control attention, observers were required to categorize each character based on shape. BOLD signal time series were analyzed from individual, functionally defined, color-selective voxels. Results & Conclusions: Same color pairs evoked BOLD responses that differed in amplitude from responses evoked by different color pairs, and this differential activation was equivalent for RC and SC conditions. Results suggest that perception of real and synesthetic colors is mediated by shared neural mechanisms.
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