Abstract

Although several studies have investigated the cognitive nature of the synaesthetic experience, very little is known about the stage in information processing at which the synaesthetic response arises. Specifically, we are still unclear about how much perceptual processing of an inducing stimulus is required before synaesthesia is experienced. Is synaesthesia induced by particular featural properties of a stimulus or might it be driven by a more abstract representation determined by lexical meaning? Or perhaps synaesthesia is triggered by some combination of bottom-up and top-down processing of a representation which is invariant to specific perceptual properties of the stimulus but dependent on it cognitive category. Recent studies on grapheme-colour synaesthesia provide some insight into this issue. In the following chapter, I begin with an overview on how letters and words may be represented in both the neurotypical and synaesthete brain. I then extend the discussion to evidence suggesting that synaesthetic colours may not be triggered by low-level, pattern-specific properties of these stimuli but by a more multisensory representation. Moreover, results from a large number of multi-lingual synaesthetes do not concur with the idea that synaesthesia is consistently linked to a lexical semantic representation. Instead, our studies suggest that colours are induced by the concept of the inducing stimulus, which involves an intermediate, multisensory representation that may be more heavily weighted by visual than auditory perceptual information. The extent to which this cognitive process holds true for all grapheme-colour synaesthetes, or indeed other types of synaesthesia, has yet to be determined.