Inducing synesthesia in non-synesthetes: Short-term visual deprivation facilitates auditory-evoked visual percepts.

After about five minutes of visual deprivation, sounds can evoke vivid colors and geometric patterns—hallucinations resembling synesthesia—in roughly half of people without synesthesia. This suggests that synesthesia may be a latent feature in all individuals, emerging when the sensory balance is altered, rather than requiring years to develop abnormal neural connections as the cross-activation model proposes.

Study at a glance

Abstract

Sounds can modulate activity in visual cortex, facilitating the detection of visual targets. However, these sound-driven modulations are not thought to evoke conscious visual percepts in the general population. In individuals with synesthesia, however, multisensory interactions do lead to qualitatively different experiences such as sounds evoking flashes of light. Why, if multisensory interactions are present in all individuals, do only synesthetes experience abnormal qualia? Competing models differ in the time required for synesthetic experiences to emerge. The cross-activation model suggests synesthesia arises over months or years from the development of abnormal neural connections. Here we demonstrate that after ∼5 min of visual deprivation, sounds can evoke synesthesia-like percepts (vivid colors and Klüver form-constants) in ∼50% of non-synesthetes. These results challenge aspects of the cross-activation model and suggest that synesthesia exists as a latent feature in all individuals, manifesting when the balance of activity across the senses has been altered.