Several participants, including the synesthetes and others without synesthesia, observed patterns of rhythmic flashes similar to visual Morse code, and had to guess whether subsequent patterns were the same or different. When the flashes were accompanied by sound, like beeps, Saenz and Koch found no difference in the performance of those with synesthesia and those without.
But when the test was repeated without the audio track, the synesthetes outperformed the nonsynesthetes dramatically because they still "heard" the sounds. Two sensory pathways are better than one.
Although people with synesthesia are not handicapped, and do not suffer from their condition, they are fascinating to neuroscientists because of what their condition might tell about how the human brain functions.
"Very little is known about how the auditory and visual systems work together in the brain and communicate with each other," Saenz said. "We know that when we see and hear something at the same time, what we hear can influence what we see, and vice versa. But we don't really know why."
Lee Dye is a former science writer for the Los Angeles Times. He now lives in Juneau, Alaska.