title: Assessment of the hemispheric lateralization of grapheme-color synesthesia with Stroop-type tests.
abstract: Grapheme-color synesthesia, the idiosyncratic, arbitrary association of colors to letters or numbers, develops in childhood once reading is mastered. Because language processing is strongly left-lateralized in most individuals, we hypothesized that grapheme-color synesthesia could be left-lateralized as well. We used synesthetic versions of the Stroop test with colored letters and numbers presented either in the right or the left visual field of thirty-four synesthetes. Interference by synesthetic colors was stronger for stimuli in the right hemifield (first experiment, color naming task). Synesthetes were also faster in the right hemifield when naming the synesthetic color of graphemes (second experiment). Overall, the lateralization effect was 7 ms (the 95% confidence interval was [1.5 12] ms), a delay compatible with an additional callosal transfer for stimuli presented in the left hemifield. Though weak, this effect suggests that the association of synesthetic colors to graphemes may be preferentially processed in the left hemisphere. We speculate that this left-lateralization could be a landmark of synesthetic grapheme-color associations, if not found for color associations learnt by non-synesthete adults.
authors: Grenoble Institut des Neurosciences, Institut National de la Santé et de la Recherche Médicale U836 & Université Grenoble Alpes, 38000 Grenoble, France; Centre de Recherche Cerveau et Cognition, Université de Toulouse & Centre National de la Recherche Scientifique, 31300 Toulouse, France.
authors: Mathieu J
authors: MJ
authors: Ruiz
authors: Centre de Recherche Cerveau et Cognition, Université de Toulouse & Centre National de la Recherche Scientifique, 31300 Toulouse, France.
authors: Jean-Michel
authors: JM
authors: Hupé
mesh_terms: D002648:Child; D003118:Color Perception; D007839:Functional Laterality; D006801:Humans; D010468:Perceptual Disorders / Q000175:diagnosis*; D010775:Photic Stimulation; D011930:Reaction Time; D057190:Stroop Test; D000080311:Synesthesia