Seeing sounds: Researchers uncover molecular clues for synesthesia. One in 25 people have synesthesia, perceiving the world in unusual ways. An experience with one sense automatically leads to perception in another sense: for example, seeing colors when listening to music. Now researchers report clues into biological origins of such variations in human perception. They studied families with synesthesia, and describe genetic changes that might contribute to their differences in sensory experience. Source 3y.