Synesthesia

Synesthesia is a neurological condition, often described as an involuntary joining, in which the real information of one sense is accompanied by a perception in another sense. This additional perception is regarded by the person experiencing it, the 'synesthete', as real, rather than a facet of a lively imagination.

So, for example, people with synesthesia are able to 'see' sounds as a particular colour or to 'hear' colours or geometric shapes. One of the commoner manifestations is the ability of a synesthete to 'see' music. It may be that she (most synesthete's are female) perceives violins as a rich, shiny burgundy, whereas cellos are mellow golden yellow, like melted honey. A piano could be royal purple, while the screeching of a car's brakes is a jagged lightening bolt, the sickening green-yellow of a bruise.

In another example, a person who sees a sequence of numbers such as: 1345287, who may view it as: 1345287.

There is an association in the UK run by and for people with synesthesia, as well as others in other countries.