That is the question that Vanderbilt's Palmeri wanted to confront. He was in his office a couple of years ago, talking with colleagues and fellow psychologists Randolph Blake and Rene Marois, about a short item in a recent issue of the journal Nature. The item described some headway in the study of synesthesia, and it piqued their interest as students of the cognitive process.
Blake told his colleagues that another colleague, subsequently identified as WO, had the condition.
"We were really intrigued and started testing him," Palmeri says.
They wanted to learn two things: whether WO really saw what he thought he saw, and what part of the brain allowed him to do it. The first part of that question is the easier part. An answer to the second is still up for debate.
Since WO claimed that plain black letters and words appeared to him in vivid colors, the researchers devised a number of experiments to see if the perception claimed by WO was real.
They drew up a list of 100 common, one-syllable words, and asked WO to tell them the color of each word.
A month later they repeated the experiment. He got it right 97 percent of the time. The only time he missed was with the easily confused colors of off-white, beige and light brown. Other researchers have done the same experiment with similar results.
The Vanderbilt team then showed WO pages of black numbers. In one test, a few 5s were interspersed among 2s and he was asked to pick out the 5s. Since they stood out as a different color, he completed the task in a fraction of the time required for people without the condition.
Those and other tests led the researches to conclude that the condition was real.
Wires Crossed in the Brain?
Next, parts of the numbers were presented separately to each eye. WO didn't see the color with just part of the number. It took both parts to produce the color. So the color came only after his brain reassembled the parts.
"This strongly suggests," Palmeri says, "that his synesthetic associations take place at a central level of vision processing after information from the two eyes has been combined." Others have postulated that the condition occurs much earlier in the visual process.
Other researchers, including Vilayanur Ramachandran, director of the Brain and Perception Laboratory at the University of California, San Diego, believe the condition may result from "cross wiring" of the brain. Ramachandran, a pioneer in the field of phantom limbs, in which persons claim to experience pain and other sensations in missing limbs, notes that the area of the brain that detects colors is adjacent to the area that handles letters and numbers.
Perhaps, he suggests, people like WO simply pick up information from one mental data stream and blend it into another. But whatever the cause, Ramachandran and graduate student Edward Hubbard have carried out studies similar to those at Vanderbilt and they have collected convincing evidence that the perceptions claimed by people with synesthesia are real.
Which brings us to this question: What, after all, is real? Green numbers are green because they occupy that specific region of the color spectrum. If someone sees a number that is painted in green, and perceives it as blue, is he seeing the real world?
To a physicist, maybe not. To a cognitive scientist, maybe so.
It doesn't really matter anymore to WO. He says parts of medical school were a breeze, thanks to his synesthesia. All those long words in biology and anatomy that are so hard to remember came easier to him, because if he forgot the letters, he could at least remember the colors.
Lee Dye’s column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.