The sound of change: visually-induced auditory synesthesia

Abstract

Summary Synesthesia is a benign neurological condition in humans characterized by involuntary cross-activation of the senses, and estimated to affect at least 1% of the population [1]. Multiple forms of synesthesia exist, including distinct visual, tactile or gustatory perceptions which are automatically triggered by a stimulus with different sensory properties [1–6], such as seeing colors when hearing music. Surprisingly, there has been no previous report of synesthetic sound perception. Here we report that auditory synesthesia does indeed exist with evidence from four healthy adults for whom seeing visual flashes or visual motion automatically causes the perception of sound. As an objective test, we show that ‘hearing-motion synesthetes' outperformed normal control subjects on an otherwise difficult visual task involving rhythmic temporal patterns similar to Morse code. Synesthetes had an advantage because they not could not only see, but also hear the rhythmic visual patterns. Hearing-motion synesthesia could be a useful tool for studying how the auditory and visual processing systems interact in the brain.