Relation between synesthetic grapheme-color associations and the sub-types of synesthesia

摘要

Grapheme-color synesthesia is a condition in which a visual letter or character induces a specific color sensation. By taking advantage of special characteristics of the Japanese language, we have revealed involvement of several linguistic properties of graphemes (e.g., phonology, orthographical shape, meaning or concepts) in determining grapheme-color synesthesia. For example, synesthetic colors for the Japanese phonetic scripts, Hiragana and Katakana, rely on sound quality, not visual shapes of graphemes. This is revealed by a remarkable consistency between synesthetic color choices for Hiragana characters and those for their Katakana counterparts that share phonemes but which are visually dissimilar graphemes (Asano & Yokosawa, 2011). Meaning and phonology both influence synesthetic colors for logographic Kanji characters (Asano & Yokosawa, 2012). To clarify the mechanisms underlying grapheme-color synesthesia the present study examined whether the sub-type of synesthetes (i.e. projector/associator) is related to processing grapheme-color associations. Projectors report experiencing synesthetic colors in external space, whereas associators report experiencing synesthetic colors a??in the mind's eye. Seventeen Japanese grapheme-color synesthetes participated in this study. According to the questionnaire by Skelton, Ludwig, & Mohr (2009), eight subjects were classified as projectors with the remainder classified as associators. Results revealed that the sub-type of grapheme-color synesthesia affected neither the degree of grapheme-color matching consistency over time nor the overall impact size of each linguistic factor (i.e., phonology, orthographic shape, and meaning or concepts) on grapheme-color associations. Nevertheless, the Hiraganaa??Katakana color consistency effect did show slightly greater, but statistically significant, strength for associators than for projectors. These findings suggest that although these sub-types differ in how they experience synesthetic colors, the process of determining grapheme-color associations is the same for both projectors and associators. Also we discussed implications of these results for a developmental model of grapheme-color association (Asano & Yokosawa, 2013).