The neurological condition of synaesthesia, or so-called mixing of the senses, is to be discussed at a conference in Edinburgh.
Some synaesthetes see colours when they hear music or words, others experience tastes, smells or shapes in combination.
Scientists and synaesthetes will be meeting at Edinburgh University.
The keynote speaker is the Scots concert pianist, Joseph Long, a sound-colour synaesthete.
According to the UK Synaesthesia Association, each synaesthete has their own palette of colours and different types of trigger.
In the most common form of the condition people perceive words, letters or numbers as distinct colours.
The association said: "These sensations are automatic and cannot be turned on or off.
"Synaesthesia isn't a disease or illness and is not at all harmful, in fact, the vast majority of synaesthetes couldn't imagine life without it."
The conference takes place on Saturday and Sunday.