The More Common the Digit, the More Luminous the Color in Grapheme Color Synaesthesia

A psychological phenomenon known as “grapheme-color synaesthesia” describes individuals who experience vivid colors whenever they see, hear, or think of ordinary letters and digits.

A hallmark of synaesthesia is that individuals tend to be idiosyncratic in their experiences, though these experiences are consistent for synaesthetes throughout their lifetime.

But new research appearing in the September issue of Psychological Science, a journal of the Association for Psychological Science, adds to a growing body of evidence suggesting that a particular commonality exists across synaesthetes, who otherwise have very  distinctive experiences.

Psychologist Daniel Smilek and his colleagues at the University of Waterloo have found that a relationship exists between how frequently a synaesthete uses a given digit and the brightness of synaesthetic color experiences  That is, the more often letters or digits are used in everyday life, the more luminous the synaesthetic colours.

Interestingly, the researchers also found that this relationship is not limited to synaesthetic colour experiences. When non-synaesthetes were asked to select a colour to associate with each letter of the alphabet and the digits 0-9, the non-synaesthetes also selected more luminous colours for digits and letters used more frequently.

The relationship between letter and digit frequency, and color luminance was much weaker for non-synaesthetes than synaesthetes, however. Smilek writes “the evidence suggests the possibility that the unusually strong grapheme-colour associations made naturally in synaesthesia may more closely reflect normal cognitive processes than previously thought.”