Good overview of synaesthesia — sensory crossover — on K5.
Subjective reports and experimental evidence show that there is no imagination involved in the experiences of synaesthetes; they literally see letters or whole words as colours, or hear a symphony when someone familiar walks into the room. Moreover, the synaesthetic associations between the different sensory modalities involved are persistent, not random. As a result, any given stimulus will reliably induce the same effect in the `dependent' sense in an individual. This characteristic has formed the basis of a `gold standard' test for synaesthetes, discussed later.
(Thanks, Adrian!)
