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Daisuke Hamada, Hiroki Yamamoto, Jun Saiki; Multilevel analysis reveals individual differences and the regularity of grapheme-colors associations in synesthesia. Journal of Vision 2016;16(12):625. doi: 10.1167/16.12.625.
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Grapheme-color synesthesia is a condition in which visual perception of letters and numbers induces simultaneous perception of a given color. Previous studies have shown factors that affect synesthetic grapheme-color correspondence. Among them, some are systematically associated with grapheme properties: visual shape and ordinality (positions in a grapheme sequence). However, contributions of these factors differ across individuals. To understand the mechanisms underlying grapheme-color associations, we investigated whether factors determining grapheme-color associations are related to the 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." Twenty one Japanese grapheme-color synesthetes participated in this study. Using the questionnaire by Skelton, Ludwig, & Mohr (2009), we measured the type of subjective synesthetic experience on the projector-associator continuum. We measured the color coordinates (CIE L*a*b*) of synesthetic colors for the 26 alphabetical letters using a color-matching task. We obtained the data for visual shape similarity and ordinality from previous studies. Then we conducted a multilevel analysis with hue distance of synesthetic colors as dependent variables, visual shape similarity and ordinality as within-participant level independent variables, and synesthetic experience as inter-participant level independent variables. The results showed that individual differences in intercepts and slopes at the within-participant level could be explained by a parameter at the inter-participant level. Namely, the factor of the ordinality was expressed more strongly with associators than projectors. This finding suggests that grapheme-color associations are partly determined by the type of synesthetic experience spanning from projectors to associators.
Meeting abstract presented at VSS 2016
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