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Youyang Hou, J. Devin McAuley, Molly Henry, Taosheng Liu; Patterns of neural activity associated with synesthetic color perception: a case study. Journal of Vision 2012;12(9):76. doi: https://doi.org/10.1167/12.9.76.
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Grapheme-color synesthesia is a rare perceptual phenomenon in which graphemes are perceived to be inherently colored. Previous research suggests that grapheme-color synesthesia is related to the cross-activation of the visual word from area (VWFA) and V4 (Nunn et al., 2002; Hubbard & Ramachandran, 2005), but the functional significance of the early visual activity for synesthetic experience is not known. We investigated neural patterns underpinning grapheme-color synesthesia using fMRI and multi-voxel pattern classification (MVPC). We tested one grapheme-color synesthete on a battery of behavioral tasks and found the synesthete’s performance consistent with a projector type. We then performed fMRI retinotopic mapping in the synesthete and four control subjects to localize early visual areas V1-V4. In a separate fMRI session, subjects viewed two color patches and two gray letters in separate blocks. The hue of the color patches matched the colors experienced by the synesthete for the selected letters. We used MVPC to decode different colors and letters (within category classification), and did not observe significant difference between the synesthete and controls. However, the synesthete showed significant higher classification accuracies in V1, V2, and V3 compared to controls in cross-category classification, (i.e., training a classifier on color data and decode letter data and vice versa). V4 showed an asymmetric effect: accuracy was higher in the synesthete than controls when the classifier was trained on letter data and tested on color data, but accuracy was similar for the synesthete and controls when the classifier was trained on color data and tested on letter data. Overall these results suggest that earlier visual areas like V1 may significantly contribute to the perceptual reality of synesthetic color perception in grapheme-color synesthesia.
Meeting abstract presented at VSS 2012
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