Abstract
Synesthesia is well understood to be an automatic perceptual phenomenon paralleling print color in some ways but also differing in others. Following a study presented previously, we address this juxtaposition by asking whether synesthetic color binds to the location of an invoking grapheme in the same way as print color. We tested 17 grapheme-color synesthetes using stereo glasses to produce the perception of two planes in 3D depth. On each trial, an achromatic letter (prime) appeared for 750 msec on the near or far plane of space and participants named the immediately following color patch (probe) quickly and accurately. The prime and probe appeared in the same line of sight and either on the same or different spatial planes. The probe color was either the same or different to the synesthetic color induced by the prime. Supporting previous work, we found faster responses to name the probe colors congruent with synesthetic colors than incongruent, but synesthetes as a group did not show effects of spatial priming, unlike non-synesthetes who exhibited faster RTs when prime and probe locations were different. However, individual synesthetes showed dramatically different spatial priming effects, exhibiting a positive correlation between their spatial priming scores and mental imagery measures (Marks, 1973). Specifically, synesthetes with more vivid visual imagery were faster to name a color when the prime and probe were on the same plane while those with weaker visual imagery showed the opposite pattern. Results from 17 non-synesthetes primed with colored letters but the same probe task showed that under the current conditions, negative spatial priming is the norm. Thus, synesthetes with strong visual imagery appear to overcome the typical prime/probe conflict, suggesting that synesthetic color may operate through a cortical network that interacts with printed color but exists as a separate feature representation.
National Eye institute NIH#EY16975.