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Neurobiological signatures of natural and trained synaesthesia

Tuesday, February 7, 2017 - 5:00pm

Cohen Hall, Room 402

Anil Seth
Sackler Centre for Consciousness Science
University of Sussex

Synaesthesia offers a unique window into the neurocognitive mechanisms underlying conscious perception, and has frequently been associated with creativity in especially the visual arts. Intriguingly, recent evidence suggests that extensive training can induce synesthesia-like experiences in non-synaesthetic adult volunteers. On the other hand, classical neuroimaging findings of colour-selective responses during natural (grapheme-colour) synaesthesia remain inconsistently reported. Focusing on the specific case of grapheme-colour synaesthesia, I will describe a series of studies linking neural responses to phenomenology in both natural and ‘trained’ synaesthesia. For natural synaesthetes, our results show that colour-specific specific brain responses can be predicted by individual differences in synaesthetic phenomenology captured by ‘localisation’ and ‘automaticity’.  For trained non-synaesthetes, we find coordinated phenomenological, behavioural and neurophysiological changes following training, revealing an unexpectedly powerful capability for perceptual plasticity even in adults. Finally, I will highlight an overlooked property of synaesthesia, which is that synaesthetic concurrents usually lack perceptual ‘presence’; that is, they are not experienced as being part of the external world. A new theory based on counterfactual predictive processing suggests why this might be so.