The researchers said their findings lend support to the hypothesis that the condition is due to cross-activation between adjacent brain areas involved in perceiving shapes and colors. Some synesthetes report seeing colors when listening to music, or feeling tactile shapes while tasting food. This cross-activation might develop, they theorize, by a failure of the "pruning" of neural connections between the areas in the developing brain.
The rare condition called synesthesia--in which people's sensory perceptual circuitry seems to be miswired--was long dismissed as an oddity not worthy of scientific study. Now, however, researchers such as Hubbard and his colleagues are using the condition to gain insights into the neural basis of perception.
In their experiments with synesthetes who report seeing colors when they view numbers or letters, the researchers first sought to determine whether synesthetes really see the colors.
In one such experiment, they presented six synesthetes with patterns of black letters or numbers--known as "graphemes"--on a white background. They chose those graphemes that the synesthetes reported elicited specific colors. They designed the experiment so that if the synesthetes really were seeing the colors, that color perception would help them distinguish shapes such as triangles or squares formed by the graphemes. In another experiment, the researchers found that synesthetic color helped the synesthetes pick out specific numbers or letters in a crowded display.
The researchers found that the synesthetic colors really did help the synesthetes distinguish the shapes or gra