Synaesthesia

What it is like

Someone with grapheme-colour synaesthesia might find that A is always red, 5 is always green and Tuesday is pale yellow. A grapheme is a written letter or digit. Some people see the colour on the page. More often they describe it as appearing in the mind's eye, firmly attached to the symbol. The pairings differ from person to person, and two synaesthetes will happily argue over the true colour of the letter E. In coloured hearing, sounds, voices or musical keys bring on colours, shapes and movement.

How it is tested

Because anyone can claim that Monday is blue, researchers use consistency as the test. A person is asked for the colour of each letter and digit, then asked again without warning weeks or months later. Synaesthetes give almost identical answers. Others, even when trying hard to remember, drift. A British study published in 2006 suggested that around four in a hundred have some form of synaesthesia. It runs in families and tends to appear in early childhood, and brain scans show colour areas responding when synaesthetes read or hear.

Synaesthesia and art

The novelist Vladimir Nabokov described his coloured alphabet in detail, and his mother and son had the trait too. Several composers and musicians have reported coloured hearing. Artists are often labelled synaesthetes after their deaths on thin evidence, and the painter Wassily Kandinsky is a much-debated case. It is worth keeping the trait apart from ordinary association. Most people will agree that a high note is brighter than a low one, or that some music feels red. Synaesthesia is narrower: specific, automatic and unchanging over decades.

Sources and further reading

• Synesthesia on Wikipedia
• American Psychological Association: Everyday fantasia, the world of synesthesia
• Cleveland Clinic: Synesthesia