What is synaesthesia?
Your brain usually interprets signals from the eyes as light, and those from the ears as sound. But a few people experience sounds as colours, smells as colours or even colours as smells. At least four in every hundred people have some form of this 'mixing of the senses' or synaesthesia. Almost any combination of two of the five senses is possible, although it is most common to see a certain colour when you hear a particular sound.