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Grapheme Frequency and Color Luminance in Grapheme-Color Synaesthesia

Individuals with grapheme-color synaesthesia experience vivid colors whenever they see, hear, or just think of ordinary letters and digits (Dixon, Smilek, Cudahy, & Merikle, 2000; Mattingley, Rich, Yelland, & Bradshaw, 2001). Currently, little is known about how specific colors become associated with specific letters and digits in synaesthesia. Beeli, Esslen, and Jancke (2007, this issue) report an interesting relation between grapheme frequency and the luminance and saturation of synaesthetic color experiences. They had 19 synaesthetes choose colors for spoken digits and letters from a digital color palette. The colors were quantified in terms of their hue, saturation, and luminance (the HSL color system). The results showed (a) that the luminance of synaesthetic colors increased with the frequency of digits in everyday language and (b) that the saturation of synaesthetic colors increased with increased letter and digit frequency. These findings indicate that there is a relation between how graphemes are encountered (and perhaps learned) in language and the basic qualities of synaesthetic color experiences. To assess the replicability of the findings reported by Beeli et al., we analyzed the grapheme-color pairings we have collected on-line over the past 5 years for large groups of synaesthetes and nonsynaesthetes.