The interaction of synesthetic and print color and the role of visual imagery

Abstract

Synesthesia is understood to be an automatic perceptual phenomenon paralleling print color in some ways but also differing in others. We examined this juxtaposition in a group of 13 grapheme-color synesthetes using a color priming paradigm where one of four prime types appeared for 750 msec on each trial followed immediately by a colored patch (probe). Primes induced either no color, print color only, synesthetic color only, or both forms of color simultaneously (e.g., a letter “A” printed in red that also triggers synesthetic red). Synesthetes named the probe color out loud as quickly and accurately as possible. All stimuli appeared foveally and probes were printed in the same or different color (where relevant) as that induced by primes. Replicating previous work, subjects were faster to name a probe color that was congruent with the prime color than if it was incongruent. Importantly, we found that synesthetes primed with a grapheme that induced the same print and synesthetic color showed significantly larger priming effects than when primed with either individual forms of color, suggesting an additive interaction of the two color types. Additionally, synesthetes exhibited a strong positive correlation between color priming effects (synesthetic and combination color only) and the vividness of self reported imagery as assessed with the Vividness of Visual Imagery Questionnaire (Marks, 1973). Yoked non-synesthete controls run on the same paradigm showed significant color priming effects only for primes printed in color and showed no correlations with VVIQ. These results suggest that synesthetic and print colors operate through separate but overlapping networks of color perception, with grapheme-color synesthetes possessing an extra dimension of visual space that can be bound like “normal” color but remains perceptually independent to normal color. This additional synesthetic color space may operate through a unique mechanism tied to visual mental imagery.