Seeing Sounds

Synaesthesia is a relatively rare, but intriguing condition in which single sensory events produce spontaneous associated experiences in other sensory modalities. It is an anomaly of sensory processing where the synaesthete experiences multi and poly-sensory experiences of perceptual events. Examples include the experience of letters or numbers as colours; graphemic-colour synaesthesia, another is to experience sound as colour. An example of a poly-sensory combinations may include the experience of a sound as both a colour and a taste, or a taste as a shape and colour. One of the more intriguing qualities of synaesthesia is that although the experience is highly stable within an individual, the pattern of anomalous percepts over the synaesthetic population is highly idiosyncratic. As such, few synaesthetes have exactly the same perceptual response to the same stimulus. Indeed, even in grapheme-colour synaesthesia (the most common manifestation of synaesthesia), it is very rare for any two synaesthetes to share exactly the same grapheme/colour combination.

Synaesthesia is a fascinating condition about which we know relatively little. Current theories regarding the cause of synaesthesia describe it as a sensory phenomenon that may arise from cross-wiring between adjacent brain maps that are responsible for perception and form. Alternatively (or possibly even in addition to), it is suggested that synaesthesia might occur as a result of the sprouting of additional neural connections between otherwise independent parts of the brain. Others propose that it is due to a failure of pruning of unnecessary neural connections that normally takes place during maturation. Dr Kristen Pammer currently has a grant supported by the Australian Academy of Science to investigate the neurological correlates of synaesthesia.