In 'colored-hearing' synesthesia, individuals report color experiences when they hear spoken words. If the synesthetic color experience resembles that of normal color perception, one would predict activation of parts of the visual system specialized for such perception, namely the human 'color center', referred to as either V4 or V8. Using functional magnetic resonance imaging (fMRI), we here locate the region activated by speech in synesthetes to area V4/V8 in the left hemisphere, and demonstrate overlap with V4/V8 activation in normal controls in response to color. No activity was detected in areas V1 or V2, suggesting that activity in primary visual cortex is not necessary for such experience. Control subjects showed no activity in V4/V8 when imagining colors in response to spoken words, despite overtraining on word–color associations similar to those spontaneously reported by synesthetes.
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This work was supported by the McDonnell–Pew Foundation and a Consciousness Studies Award from the University of Arizona. We thank John Harrison and Sue Chopping for assistance with various aspects of the research. J.A.G. is currently a fellow at the Center for Advanced Study in the Behavioral Sciences, Stanford University, with financial support from the John D. and Catherine T. Macarthur Foundation, Grant no.32005-0.
The authors declare no competing financial interests.
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Nunn, J., Gregory, L., Brammer, M. et al. Functional magnetic resonance imaging of synesthesia: activation of V4/V8 by spoken words. Nat Neurosci 5, 371–375 (2002). https://doi.org/10.1038/nn818
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