Synaesthesia

Synaesthesia is a perceptual phenomenon in which a stimulus in one sensory modality automatically and involuntarily triggers an additional experience in a different modality or sub-modality - for example, seeing specific colours when hearing musical notes (chromesthesia), tasting words (lexical-gustatory synaesthesia), or feeling touch on one's own body when observing another person being touched (mirror-touch synaesthesia). Over 75 types have been described; prevalence is roughly 4% of the adult population. Synaesthesia is highly individual, often congenital and familial, and typically stable over time. Synaesthetes frequently report social isolation and a lack of shared vocabulary for articulating their experiences, making it a relevant population for inclusive HCI and communication-support design.