Brain oscillations during perceptual closure in grapheme-colour synaesthetes T van Leeuwen1, M Wibral2, W Singer3, L Melloni4 |
|---|
1Department of Neurophysiology, Max Planck Institute for Brain Research, Germany |
| In grapheme-colour synaesthetes, letters and numbers evoke colour. Synaesthesia may involve hyperbinding of colour and graphemes; we investigated whether this alters the threshold of conscious perception. At the neural level, binding processes are associated with increased synchronization between different features. Using magnetoencephalography and a visual closure task we investigated the impact of synaesthesia on the threshold of awareness. Twenty synaesthetes and 20 controls were presented with synaesthesia-inducing (letters and numbers) and non-inducing stimuli (symbols). Stimuli were embedded in a coloured noise background, which was congruent with the synaesthetic colour or neutral (symbols). The amount of noise was parametrically varied and the visibility threshold of the embedded grapheme was determined by subjective visibility ratings. Both groups showed similar visibility thresholds in the symbols condition, but synaesthetes perceived more synaesthesia-inducing stimuli than controls . Synaesthetic hyperbinding may aid synaesthetes during closure. Magnetoencephalography data showed induced gamma band activity (50-70 Hz and 80-100 Hz) over occipital sensors; for letters, synaesthetes showed increased gamma power compared to controls. Source localisation (50-70 Hz) of successfully identified graphemes revealed activity in early visual areas (V2) as well as area V4 and parietal cortex. We suggest that altered gamma activity reflects hyperbinding. |
| Up Home |
|---|