is orange but "two" is blue
David F. Salisbury
March 19, 2002
appears to be a natural form of virtual reality
For nearly 300
years, people who claimed to hear colors, feel sounds or taste shapes
risked being dismissed as having overactive imaginations.
Last year, however,
several scientific studies of this rare condition produced compelling
evidence that it is a genuine perceptual phenomenon. Now, a Vanderbilt
study of the most common form of synesthesia - the perception that
numbers, letters and words have distinct colors - has confirmed
these earlier findings and provided additional evidence that synesthetic
experiences originate during the central stages of visual processing
in the brain.
study, reported in the March 19th issue of the journal Proceedings
of the National Academy of Sciences, consisted of administering
a battery of perceptual tests to an adult male known as WO who experiences
synesthesia. The tests go far beyond the tests of individuals with
synesthesia that have previously been reported.
Little is known
about synesthesia's causes or its prevalence. Estimates range from
one in 2,000 to one in 25,000 and there is also some evidence that
the condition is more common in women than in men. Nevertheless,
a number of famous people - including the poets Baudelaire and Rimbaud,
the painters Kandinsky and Klee, the composers Lizst and Scriabin
- have been linked to synesthesia. In an attempt to describe what
synesthesia is like, novelist and synesthete Vladimir Nabokov wrote
that he saw the letter "c" as light blue; associated "a" with the
look of "weathered wood," and got a feeling like "a sooty rag being
ripped" from the letter "r."
who served as the subject of the new study is a middle-aged man
who reports that he has had the condition since early childhood.
"WO sees letters, numbers and individual words printed in black-and-white
in vivid color. If the characters are printed in different colored
ink, he can see that color as well," says Thomas J. Palmeri, assistant
professor of psychology, who headed up the study. His collaborators
are Centennial Professor of Psychology Randolph Blake, Assistant
Professor of Psychology René Marois, graduate student Marci A. Flanery
and Professor of Pathology and Psychiatry William Whetsell, Jr.
Synesthetic colors are repeatable and reliable
that WO had normal eyesight and color vision, the researchers began
by documenting the consistency of his synesthetic color associations.
To do so, they drew up a list of 100 common words of one syllable.
In two sessions, separated by more than a month, they asked him
to name the synesthetic color associated with the words in the list.
They found that his color associations were remarkably consistent.
In the two sessions, he associated the same color with 97 of the
words. His only mismatches occurred in confusing beige, off-white
and light brown. He also consistently matched the synesthetic colors
of 12 words with colors from a Pantone palette containing more than
1,000 shades. "These associations are highly reliable. WO says that
the colors have stayed the same all of his life and our observations
lend credence to his claim," says Blake.
form during visual processing
of tests were designed to explore the range of conditions that invoke
synesthetic colors. In one test, the researchers created large characters
made out of small characters, such as a large five made out of a
large number of small twos. They found that, when WO's attention
was directed to the large five, it took on the dark green color
that he associates with five. But when his attention was directed
to the small twos, the color suddenly switched to orange.
also created figures in which different parts of the letters or
numbers were presented separately to WO's right and left eyes. So
his brain had to fuse the right and left views together before he
could see the entire figures. He reported having no trouble seeing
the colored figures.
suggests that his synesthetic associations take place at a central
level of vision processing after information from the two eyes has
been combined," Palmeri notes.
colors act like real colors
Next the researchers
administered a series of tests to determine the extent to which
WO's synesthetic colors act like real colors. There are standard
perceptual tests where color is a disadvantage and another set of
tests where it is an advantage. The researchers adapted these tests
for WO's synesthesia.
test is a classic example of how color can interfere with a simple
identification task. When subjects are asked to name the color of
ink in which color words are printed, they can do so faster when
the ink color and color name are same ("red" printed in red ink)
than they can when the two are different ("green" printed in red
ink). The researchers adapted this test by printing words in colors
that either agreed or conflicted with their synesthetic color and
then recording how long it took WO to identify them. For example,
WO sees the word "moose" as pink, so they printed it in pink letters
and he sees the word "charge" in green, so they printed it in blue.
They found that it took him longer to name the words where the synesthetic
color conflicted with the ink color than it did when they were the
same. The researchers also found that he was slower at naming the
synthetic colors associated with words when they matched the ink
color than he was when they conflicted.
A standard test
where color confers a real advantage is a search test where the
target is a different color than the distracters surrounding it.
Subjects report that the colored target "pops out" of the page.
As a result, the time it takes them to pick out the target is about
same regardless of the number of distracters in the scene. WO sees
"2" as orange and "5" as green but he sees both "6" and "8" as nearly
the same shade of dark blue. Using a special font so that the "2"
and "5" are mirror images, the researchers made up two sets of computer
displays. One set had single white "2s" hidden among varying numbers
of white "5s." The other set had single white "8" hidden among varying
numbers of white "6s."
who took these tests found the 2-among-5 search slightly harder
than the 8-among-6 search. But WO found the 2-among-5 search much
easier and was able to find the target significantly faster than
non-synesthetes because the figures appeared as different colors,
while his performance on the 8-among-6 search, which look the same
to him, was comparable to that of the non-synesthetes.
are some subtle differences, these tests showed that synesthetic
colors act in a way that is very like real colors,"
for synesthesia model
support a model of synesthesia recently advanced by Vilayanur Ramachandran
and Edward Hubbard
from the University of California, San Diego that is based on an
idea that has been around for decades: that synesthesia is caused
by a subtle cross-wiring in the brain. Specific regions in the brain
process information about different aspects of the visual scene,
such as color, shape and motion. Recent brain mapping studies have
found that a primary color area is adjacent to an area that handles
numbers and letters. Another color area lies next to a primary auditory
area. If the neurons in these regions were more densely wired or
strongly connected than normal, it could explain why some people
see words, numbers and sounds in color.
Palmeri's home page
Blake's home page
Marois' home page
Whetsell Jr. online information
Synesthesia Experience - a website with firsthand accounts from
selected synesthetes; demos and examples of phenomena like synesthesia
Online: Extensive bibliography of synesthesia in art and science
Hoover Bartlett; An Ear For Color: Exploring the Curious World of
Synesthesia, Where Senses Merge in Mysterious Ways; Washington Post;
January 22, 2002
Carpenter, American Psychological Association Monitor, "Everyday
fantasia: The world of synesthesia;" March 2001