Synesthesia

How it works

Synesthesia is a condition in which input to one sense or concept automatically produces an experience in another¹. The most studied form is grapheme-colour synesthesia. A person with it sees or strongly associates a colour with each letter and number. The letter A might always be red and the number 7 always green. The pairings are fixed. Tested months apart, the person gives the same answers¹.

Other common forms link sounds to colours, words to tastes, or sequences such as months and numbers to positions in space. More than 60 forms have been described¹. Most people with synesthesia have more than one form.

A 2006 study of about 1,700 people found that 4.4% had some form of synesthesia¹. The most common type was coloured days of the week. About 1.4% had grapheme-colour synesthesia¹. Earlier estimates were much lower because they relied on people coming forward.

Synesthesia runs in families. About 40% of people with it report a close relative who also has it¹. Several genes have been linked to it, but there is no single synesthesia gene. The leading explanation is extra connections between neighbouring brain areas, for example between the area that recognises letters and the area next to it that handles colour¹. One idea is that these connections exist in all babies and are normally pruned away.

Synesthesia is not a disorder. Most people with it consider it normal or pleasant, and many do not realise until adulthood that other people do not share it¹.

History and culture

The novelist Vladimir Nabokov described his coloured alphabet in detail in his memoir. His mother and his son had it too³. The composers Franz Liszt and Olivier Messiaen and the painter Wassily Kandinsky are often described as synesthetes¹. Online communities such as r/Synesthesia let people compare their colour alphabets, which almost never match².