A form of synaesthesia in which people experience letters or numbers in colour may be trainable. The discovery could shed new light on how such traits develop.

Synaesthesia is thought to have a genetic component, but some people have reported synaesthetic experiences following hypnosis, so Olympia Colizoli at the University of Amsterdam in the Netherlands, and colleagues, wondered if it might also be possible to acquire synaesthesia through training.

To test the idea, they gave seven volunteers a novel to read in which certain letters were always written in red, green, blue or orange (see picture). Before and after reading the book, the volunteers took a “synaesthetic crowding” test, in which they identified the middle letter of a grid of black letters which were quickly flashed onto a screen. Synaesthetes perform better on the test when a letter they experience in colour is the target letter.


The volunteers performed significantly better on this test after training compared with people who read the novel in black and white.

The findings suggest that natural synaesthesia may develop as a result of childhood experiences as well as genetics, says Colizoli, who presented the findings at the Forum of European Neuroscience in Amsterdam last week.