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Julian K. Ghloum, Laura C. Gibson, Marcus Watson, Kathleen Akins, Lawrence Chen, James T. Enns, Janet F. Werker, Daphne Maurer; Reduced Perceptual Narrowing in Synaesthesia: Discrimination of Native and Non-native Stimuli. . Journal of Vision 2014;14(10):237. doi: 10.1167/14.10.237.
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Synaesthesia is a neurological condition in which input to one sense causes an automatic and consistent extra percept, often in another sense (e.g., C sharp elicits a pale yellow). Synaesthesia is hypothesized to arise, at least in part, from less-than-normal neural pruning of the exuberant connections in sensory cortical areas during infancy (reviewed in Maurer, Gibson, & Spector, 2013). Perceptual narrowing describes an infants' increasing skill at differentiating among stimuli within native categories (e.g., upright own-race human faces) and the simultaneous loss of a more general ability to discriminate stimuli from non-native categories (e.g., other-race, other-species, inverted faces) (reviewed in Maurer & Werker, in press). Perceptual narrowing is thought to reflect experience-dependent pruning of initially exuberant neural connections and typically occurs by 9 months of age. Here we tested the hypothesis that adult synaesthetes show evidence of less perceptual narrowing, i.e., whether adult synaesthetes are better than non-synaesthetic adults in discriminating items from non-native categories. Participants performed a speeded simultaneous matching-to-sample task on upright human and chimp faces that differed only in spacing of the internal features. The task involved matching one of the two faces at the bottom of the screen with the face at the top of the screen. A subset of participants performed the same task with inverted human faces. Planned comparisons revealed synaesthetes (n=41) were more accurate than non-synaesthetes (n=40) in discriminating among chimp faces (t(79)=2.7, p=.004), with no difference for upright human faces (t(79)=1.108, p=.135). In addition, synaesthetes (n=19) were more accurate than non-synaesthetes (n=28) in discriminating among inverted human faces (t(45)=2.726, p=.005). The results suggest that synaesthetes undergo less perceptual narrowing during development, providing behavioral evidence for a developmental mechanism underlying synaesthesia.
Meeting abstract presented at VSS 2014
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