DOI: 10.5176/2251-1865_CBP13.94
Authors: Bryan D. Alvarez, Lynn C. Robertson,
Abstract:
Synesthesia is well understood to be an automatic perceptual phenomenon paralleling print color in some ways but also differing in others. 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 a group of 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 plane or the far plane followed immediately by a color patch (probe). Participants were asked to name the probe color as quickly and accurately as possible. The prime and probe appeared in the same line of sight and were either on the same or different spatial planes. The probe was also either the same or different color as the synesthetically induced color. In line with previous work, we found faster responses to name the probe color if it was congruent with the synesthetic color than if it was 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. This suggests that synesthetic color is not bound to the same location as the inducing letter. However, closer examination showed that synesthetes differed dramatically in terms of spatial priming effects, exhibiting a positive correlation between their spatial priming scores and mental imagery measures (Marks, 1973). This correlation showed that synesthetes with more vivid visual imagery produced positive spatial priming (faster response to name the color when the prime and probe were on the same plane) while those with weaker visual imagery produced negative spatial priming. Results with a group of 17 non-synesthetes using colored letter primes but the same probe task showed that under the current conditions, negative spatial priming is the norm. These results are discussed in terms of conflicts between prime and probe when both are in the same line of sight and on the same plane. Synesthetes with strong visual imagery appear to overcome this conflict, suggesting that synesthetic color may operate through a cortical network that interacts with printed color but exists as a separate feature representation.
Keywords: synesthesia; grapheme-color; priming; binding; visual imagery
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