Dartmouth psychology professor Megan Steven spoke about a neurological phenomenon known as synesthesia at Wednesday’s neuroscience lecture sponsored by the College Student Interest Group in Neuroscience (Co-Sign). Synesthesia is an involuntary mixing of the senses that can cross visual, auditory, pain, and even taste boundaries. This blend of input causes an altered sense of perception, in which ordinary sensory data such as graphemes, certain words, or even entire people become inextricably linked to other sensory data such as colors or tastes.

Official estimates place the frequency of synesthetes in the population at around 1 in 2000; however anecdotal evidence would suggest that this is closer to 1 in 20.

Steven presented three examples of people with synesthesia in order to illustrate varying degrees and types of sensory association. The first was Heather Birt, who, upon exposure to certain stimuli saw three-dimensional colored blocks of numbers ranging from zero to infinity and categorized in rows of ten.

The second example was one of the few cases described as negative. James Wannerton, a pub owner, experienced distinct tastes for every word that he was presented with. Steven’s first name, for instance, was linked to the taste of cold macaroni.

Wannerton’s synesthesia created a constantly changing spectrum of tastes for each conversation and thus could be not only distracting, but also unpleasant based on the taste association of certain words. For example, the name Derrick tasted strongly of ear wax.

The final synesthete holds significant promise for advancing synesthesia’s role in the cognitive sciences. John Fullwood perceives distinct colors for words that can be placed in a sequence, such as the days of the week. However, Fullwood has been blind for over ten years and thus receives no visual data from his eyes.

This indicates that the visual cortex can process vision not only immediately after onset of blindness, but also after long periods without visual data.

Synesthesia offers many opportunities to understand the multi-sensory experience that categorizes everyday human life. For instance, through an experiment that isolated first the tactile centers of the brain, then the visual and finally utilized a combination of the two, an entirely new structure was found. The Superior Temporal Sulcus (STS) was seen via MRI to be activated during moments of multi-sensory perception along with the specialized sensory regions of the brain.

When synesthetes were monitored alongside non-synesthete control subjects, brain imaging revealed that only the STS of synesthetes was activated during perception of  achromatic letters. The fact that the STS was activated during an activity that should require the use of only one sense may relate to synesthesia’s sensory blending.

This could shed more light on the role of the STS in regulating sensory input in non-synesthetes. Steven emphasized that more research is needed not only to understand synesthesia itself, but also to unlock its potential for uncovering some of the mysteries of sensory experiences. From perfect pitch to the neurological basis of an abstract ability such as human creativity, Steven asserts that synesthesia may play an important role in the future of the cognitive sciences.