Synaesthesia. Some of you might recognise the word from high school English classes. It is a poetic device that combines senses, such as ‘cold music’ or ‘loud shirt’. But it also refers to a neurological condition in which one concept is involuntarily associated with another.
A common form of this is associating numbers with colours. For example, a lot of synesthetes see the number five as inherently red. So when it is another colour, it seems weird.
Another type of synaesthesia connects visual movement with sound. These people here certain sounds when they see visual motion or flicker.
Other types include seeing colours when hearing sound (particularly music) and personification in which letters and numbers are associated with personalities. Another quite interesting form is tasting words, wherein words leave a taste in the mouth of the synethete.
Apparently, five per cent of the population will see red when seeing a five or hear a C-sharp when seeing blue. But the number is higher among artists, ranging at about 25%.
Is synaesthesia a trait of a creative? Not necessarily, but there does seem to be quite a number of creative with it. Me, I just see a 5 when I see a 5.