Concept driven color experiences in digit-color synesthesia

In digit-color synesthesia, black digits elicit conscious experiences of highly specific colors (photisms). This paper describes C, an undergraduate student who experiences digit-color synesthesia. We evaluated whether C's photisms could occur even in the absence of an externally presented digit. C was shown simple arithmetic problems (e.g., 5 + 2) followed by a color patch. C was significantly faster at naming the color of the patch when it was congruent with the photism associated with the answer to the problem than when the color patch was incongruent with the answer. These results replicate previous findings (Dixon, Smilek, Cudahy, & Merikle, 2000) and strongly suggest that for C, an externally presented inducing stimulus is not necessary to trigger a photism--activating the concept of a digit is sufficient.