When 2 is orange and two is blue
UPI Science News
Published 3/18/2002 5:03 PM

WASHINGTON, March 18 (UPI) -- The rare and puzzling phenomenon of synesthesia -- a linking of the senses that produces such things as colored letters and numbers -- probably is caused by cross-wiring in the higher centers of the brain, scientists said Monday.

A study of W. O., a medical professor in Tennessee, shows the phenomenon is not an illusion produced in the early stages of visual processing, according to Vanderbilt University psychologist Thomas Palmeri. The study appears in the March 19 Proceedings of the National Academy of Sciences.

W. O., whose name is kept confidential, has the most common form of synesthesia -- he sees letters, words and numbers in color. When the letter or number is itself colored, Palmeri said, W. O. sees both colors.

W.O. underwent a range of tests, but the one that demolished the "illusion" theory came when he was shown numbers and letters, in such a way that neither eye saw the whole image. If the illusion were produced by a flaw in what's called the primary visual cortex, the synesthetic color should not occur, Palmeri said.

"He had the normal synesthesia," Palmeri said, "so it's not happening in the primary visual cortex."

In another test, the researchers created figure fives and figure twos that were mirror images of each other and printed a sheet of black fives, with a single black two hidden among them.

For most people, finding the two would be a difficult task, Palmeri said, but for W.O., "it just popped right out" because the man sees "2" as orange and "5" as green.

When the numbers were 6 and 8, W.O. had no advantage, Palmeri said, because he sees those figures as nearly the same shade of dark blue.

The coloring does not appear to be linked to meaning: the figure "2" is orange for W.O., but the word "two" is blue, Palmeri says.
A 2000 study in the journal Nature, though, showed the mere concept of a number can trigger the color response.

Psychologist Mike Dixon of the University of Waterloo in Canada, author of the Nature study, said his lab shortly will publish experiments that used the same "scoreboard 5" as the Palmeri group -- a figure that's identical to what Dixon called a "scoreboard S."

In those experiments, he said, the subject saw different colors depending on which meaning -- "5" or "S" -- was associated with the image.

"Form definitely plays a role," Dixon said, "but ultimately it's the meaning the determines the color."

Dixon added, however, Palmeri and his colleagues performed "very creative experiments to narrow down when in the visual system this occurs."

The phenomenon has been known for about 300 years, although researchers are only now beginning pin it down. Many famous artists have been synesthetes, including author Vladimir Nabokov and musician Alexander Scriabin.

The condition appears to run in families: Nabokov, as a toddler, complained to his mother the numbers and letters on his blocks were the "wrong" colors. His mother, also a synesthete, understood perfectly.

(Reported by Michael Smith in Toronto)
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