Synaesthesia: 4% of people hear colours and taste letters

Synaesthesia is a neurological phenomenon in which stimulation of one sense automatically triggers another — for example, music produces visions of colours and shapes, or individual letters evoke specific tastes. About 4% of the population experience it, including well-known figures such as Billie Eilish and Lady Gaga. Researchers continue to study the mechanisms behind the condition.