The interaction of synesthetic and print color and its relation to visual imagery.

Synesthetic color induced by graphemes is well understood to be an automatic perceptual phenomenon paralleling print color in some ways, but also differing in others. We addressed this juxtaposition by asking how synesthetes are affected by synesthetic and print colors that are the same. We tested two groups of grapheme-color synesthetes using a basic color-priming method in which a grapheme prime was presented, followed by a color patch (probe), the color of which was to be named as quickly and accurately as possible. The primes induced either no color, print color only, synesthetic color only, or both forms of color (e.g., a letter "A" printed in red that also triggered synesthetic red). As expected, responses to name the probe color were faster if it was congruent with the prime color than if it was incongruent. The new finding (Exp. 1) was that a prime that induced the same print and synesthetic colors led to substantially larger priming effects than did either type of color individually, an effect that could not be attributed to semantic priming (Exp. 2). In addition, the synesthesia effects correlated with a standard measure of visual imagery. These findings are discussed as being consistent with the hypothesis that print and synesthetic color converge on similar color mechanisms.