Synaesthesia: mechanisms and broader traits

Synaesthesia is a condition in which perceptual or conceptual stimulation in one modality leads to additional experiences within the same or different modality. In grapheme-colour synaesthesia achromatic letters or numbers elicit secondary synaesthetic colour experiences while in mirror-touch synaesthesia observing touch to another person results in tactile sensations on a synaesthete’s own body. This thesis examines broader differences in personality and social perception associated with synaesthesia and investigates neural mechanisms underlying social perception in typical adults. Firstly, an association between grapheme-colour synaesthesia and personality traits was examined which revealed an altered personality profile in this group. Additionally grapheme-colour synaesthesia showed typical and (in some cases) superior social perception abilities relative to typical adults which most likely reflects wider perceptual differences related to sensitivity to high spatial frequency information previously found in this group. Secondly, an investigation into the wider consequences of mirror-touch synaesthesia revealed that the presence of this form of synaesthesia is linked with lower levels of alexithymia relative to typical adults and lower interoceptive sensitivity relative to grapheme-colour synaesthetes and controls. This thesis also explored the neural mechanisms underlying social perception in typical adults using non-invasive transcranial alternating current stimulation. This revealed that enhancing occipital gamma oscillations facilitates facial anger perception offering a new avenue to examine the neural mechanisms underlying social perception advantage in synaesthesia. Current findings are discussed in the context of existing literature on synaesthesia and social perception.