Duke Ellington saw musical notes as individual colors and textures. Vladimir Nabokov heard letters in varying shades. And physicist Richard Feynman calculated the letters and numbers in equations in different hues.
They all had synesthesia, a neurological blending of the senses. This ability, which can combine sound, sight, touch, taste and smell in surprising ways, is largely unknown to the general public, but may actually be fairly common. Estimates vary, but according to psychologist Alicia Callejas, PhD, of the University of Granada in Spain, current research indicates that up to 4 percent of people may have some form of the ability.
Her work focuses on the most common form of synesthesia in which color is linked to letters, words and numbers, and how that can influence people's perceptions. For instance, seeing a number in blue, when you have always pictured it in red, makes synesthetes uncomfortable.
This dissonance may extend beyond the numbers themselves. Callejas and her graduate adviser, psychologist Juan Lupiáñez, PhD, conducted a study in which neutral stimuli-in this case a cartoon-were presented in grids identified by colored numbers. If the numbers were in the "wrong" color for a particular participant, he or she was more likely to feel negative about the corresponding cartoon. That finding suggests synesthesia may influence people's perceptions of memories and events, says Callejas.
Callejas's work has implications for nonsynesthetes as well.
"Synesthesia can provide us with information about how the brain is organized and how different areas are connected," she notes. Of particular interest is whether synesthetes have new and different connections between different areas of the brain, or whether these connections are present, albeit dormant, in everyone, Callejas concludes.
Perhaps someday any of us may not only listen to the blues, but see them, too.