Sound frequency predicts the bodily location of auditory-induced tactile sensations in synesthetic and ordinary perception.

Abstract

For individuals with sound-touch synesthesia, sounds consistently evoke strong, localized sensations on the body. We systematically investigated the relationship between sound frequency and the characteristics of induced tactile experiences in synesthetes (n = 19) and controls (n = 23). Sound frequency strongly predicted the location of tactile sensations in synesthetes and controls. Synesthetes experienced touch more frequently and tended to report sensations in more spatially focused regions of the body, reflecting a sharper mapping between sound frequency and somatotopy. This spatial distribution of touch according to sound frequency reflects a behavioral mapping between tonotopy and somatotopy suggesting the involvement of early, tonotopically- and somatotopically-organized brain areas. These findings highlight a strong similarity between auditory-tactile mappings in synesthetic and ordinary perception, suggesting that synesthesia only differs in the strength of the mappings and therefore may be on a spectrum with ordinary perception. Furthermore, these findings offer insights into the neural mechanisms of sound-touch mappings, suggesting they rely on cross-modal neural pathways utilized in ordinary perception.