a condition in which one type of sensory stimulation creates perception in another sense. The most common form of synesthesia is called “coloured hearing,” where a person experiences a visual sensation when receiving an auditory signal (for example, hearing the musical tone C and seeing the colour red). Although tone-colour relationships are not identical for all people, there are general uniformities: the deeper a musical note, the darker the colour. Similar colour perceptions, called photisms, may accompany sensations of taste, touch, pain, smell, or temperature. Synesthesia has been used as a literary device by poets as diverse as Edgar Allan Poe, Arthur Rimbaud, Hart Crane, and Dame Edith Sitwell.