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Bryan Alvarez, Lynn Robertson; Differences in feature vs object binding across depth: Evidence from grapheme-color synesthesia. Journal of Vision 2008;8(6):745. doi: 10.1167/8.6.745.
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© ARVO (1962-2015); The Authors (2016-present)
Grapheme-color synesthesia is a human phenomenon in which a letter or number (grapheme) evokes the visual perception of color. The color is most often described as existing in the mind's eye (non-projector synesthetes) and less commonly as existing in the same spatial location as the printed text (projector synesthetes). Data have been collected from 12 grapheme-color synesthetes and matched non-synesthetic controls from a novel psychophysical experiment we developed looking at the effect of depth as it relates to synesthetic color priming. Our findings replicate previous studies showing synesthetes, and not non-synesthetes, are faster to name the color of a target patch that is congruent to the synesthetic color evoked by an achromatic letter that precedes the target patch. Critically, projector synesthetes show an interaction between spatial depth (as produced by stereoscopic goggles) and reaction time that resembles a pattern for non-synesthetes viewing colored letters followed by color patches. The combined data from these two experiments suggest that the mechanism underlying form-induced color is similar to that which induces wavelength color in non-synesthetes. It further supports previous claims that synesthesia exists at one end of a spectrum of physiological and perceptual experience ranging from non-synesthetic to complete awareness of synesthetically induced percepts. We are following up this imaging data with structural MRI to look for correlations between behavioral performance, perceptual descriptions, and neuroanatomical differences.
Funding for this work was provided by a grant from the National Eye Institute.
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