Synaesthesia

Synaesthesia is a joining together of sensations that are normally experienced separately. Studying synaesthesia may help us to understand how the brain segregates and integrates different sensations and thoughts. The Synaesthesia research group here at Sussex look at a wide variety of topics related to the phenomenon, encompassing the neurological and behavioural aspects as well as the potential application of synaesthesia research.

Synaesthesia has been a topic of interest to Psychologists ever since psychology emerged as a discipline in its own right in the late nineteenth century. It is an intriguing phenomenon because it challenges the tacit assumption that other people's perceptual experiences of the world are the same as our own. Philosophers may lose sleep over my experience of green is the same as your experience of green, but people on the street do not. This is because we can use language as a common currency to agree upon our experiences.

Synaesthesia is a complex experience and, being rare, it is difficult to study. Nevertheless, several interesting theories have been proposed and tested. The idea that synaesthesia is a mental illness is long gone, but that doesn't mean it's not "all in the head"! Positron Emission Tomography (PET) scans have shown that different areas of the brain are active for synaesthetes experiencing a cross-modal association than for non-synesthetes engaged in the same task. The synaesthetic experience depends exclusively on the left brain and is associated with a decreased blood supply to the neocortex. This results in enhanced limbic expression. Therefore, we can assume that the system responsible for synaesthesia is located or influenced by the limbic system more than the neocortex, which is not what most people would predict without the evidence from the PET scans. Additional support for this is that there is an emotional aspect associated with a synesthetic experience. In fact, in order to fulfill the diagnostic criteria for synaesthesia an emotional response must be present.