Tuesday, February 22, 2011
Does your best friend's name taste like macaroni and cheese? Does your favourite song look like a blue bolt of lightning? Is four red? If so, you are most likely a synesthete - a person who experiences the rare neurological condition synesthesia. Synesthesia occurs when a stimulus induces not only the expected percept (perceived representation) but also an involuntary, automatically evoked percept, sometimes in another sensory modality. For example, the most common form of synesthesia is grapheme-colour - where seeing, hearing or thinking of a letter or digit evokes a colour. These associations are highly consistent (e.g. the letter A, will always evoke the colour green), and are present from childhood. For some synesthetes, the concurrent percept is projected into a specific location in space (i.e., right onto the grapheme) - these are called projectors. Associators, on the other hand, see the elicited percepts "in the mind's eye".
It is only in the past few decades that research involving synesthesia has flourished. Historically, the condition was regarded with much skepticism. At worst, synesthetes were condemned as mentally ill, and confined to asylums , at best they were considered to be overly imaginative, or liberally metaphorical. In the last two decades innovative, psychometric methods have also been used to empirically demonstrate and stud the existence of synesthesia. Tons of behavioral findings have demonstrated that synesthetic percepts behave like typical sensory percepts in attentional tasks, which established their perceptual reality.
In recent years, the focus has now shifted towards forming an explanatory framework for interpreting the various empirical findings. One difficulty in putting forward a complete framework is that there is a lack of knowledge concerning what is is about a synesthetes brain that is different from someone without synesthesia. For many years, synesthesia has been vaguely attributed to "crossed wires" in the brain. Despite sophisticated brain imaging methods (like fMRI and PET scannin), and substantial progress in neuroanatomy, the underlying mechanisms of synesthesia remain elusive. Several competing theories have emerged, with the main disagreement being whether the pathways implicated in synesthesia are unique to those with the disorder - indicating the presence of a structural brain difference - or if they are present in the normal population - indicating the presence of a functional brain difference. So, the question comes down to: extra wires or altered functioning?
If you're interested, check back for parts two and three, where I'll review some evidence for each of the sides of the debate!
For lots more information on synesthesia, including personal anecdotes, check out: http://www.mixsig.net/.
Hilary D. Duncan