Dissociating semantic and perceptual components of synaesthesia: behavioural and functional neuroanatomical investigations.

Colour digit synaesthetes experience atypical dual perceptions wherein achromatic digits are perceived along with coloured photisms. Recent studies have employed Stroop or priming tasks and exhibited interference or facilitation in synaesthesia [Nature 410 (2001) 580-582; Perception 28 (1999) 651-664]. We compared a synaesthete to a semantic control with arbitrary colour-number associations and demonstrated that these tasks do not elicit effects unique to synaesthesia. In contrast, we present functional neuroimaging data that clearly differentiates between these two conditions.