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Daisuke Hamada, Hiroki Yamamoto, Jun Saiki; Correspondence between synesthetic colors and ordinal colors in grapheme-color synesthesia. Journal of Vision 2017;17(10):1360. doi: https://doi.org/10.1167/17.10.1360.
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Grapheme-color synesthesia is a condition in which visual perception of letters induces simultaneous perception of a given color, often developed in childhood. Hamada, Yamamoto, & Saiki (2016) showed that synesthetic colors are concentrated in multiple regions in the color space, that is, they form "synesthetic color clusters". Why did these synesthetic color clusters emerge? Given that ordinal colors induced by physical stimuli is a basis of synesthetic colors, we assumed that high-sensitive ordinal colors become synesthetic colors for each synesthete in childhood. If the assumption is correct, synesthetic color clusters correspond to the high-sensitive ordinal colors. In the present study, we investigated whether color sensitivities corresponding synesthetic color clusters (clustered colors) is higher than color sensitivities not corresponding synesthetic color clusters (non-clustered colors). In addition, we investigated whether a difference of sensitivities between clustered colors and non-clustered colors are related to a difference in subjective experiences perceiving synesthetic colors. Some synesthetes termed "projectors," perceived their associated colors visually in external space." Others, termed "associators," perceived their colors in internal space, characterizing them as existing "in my mind's eye" or "in my head." Twelve synesthetes were measured thresholds of the color discrimination for clustered colors and non-clustered colors, respectively, by the Cambridge colour test. We used a regression analysis to assess the impact of the subjective experiences perceiving synesthetic colors on the difference of color thresholds between clustered colors and non-clustered colors. The analysis showed that associators were more sensitive to clustered colors than non-clustered colors. In contrast, projectors were more sensitive to non-clustered colors than clustered colors. This finding suggests the possibility that high-sensitive ordinal colors become synesthetic colors, but in projectors, the visual experience of synesthetic colors in everyday life from childhood leads to decrease the color sensitivity of clustered colors, as "adaptation" decreases sensitivities of stimuli.
Meeting abstract presented at VSS 2017
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