Imagine that when you see a city's skyline, you taste blackberries.
Or maybe when you hear a violin, you feel a tickle on your left knee.
Perhaps you are completely convinced that Wednesdays are light red. If
you have experiences like these, you might have synesthesia.
What is synesthesia?
Synesthesia is a condition in which one sense (for example, hearing) is
simultaneously perceived as if by one or more additional senses such as
sight. Another form of synesthesia joins objects such as letters, shapes,
numbers or people's names with a sensory perception such as smell, color
or flavor. The word synesthesia comes from two Greek words, syn
(together) and aisthesis (perception). Therefore, synesthesia
literally means "joined perception."
Synesthesia can involve
any of the senses. The most common form, colored letters and
numbers, occurs when someone always sees a certain color in
response to a certain letter of the alphabet or number. For example, a
synesthete (a person with synesthesia) might see the word "plane" as mint green or the number "4" as dark brown. There are also synesthetes who
hear sounds in response to smell, who smell in response to touch, or who
feel something in response to sight. Just about any combination of the
senses is possible. There are some people who possess synesthesia
involving three or even more senses, but this is extremely rare.
Synesthetic perceptions are specific to each person. Different people
with synesthesia almost always disagree on their perceptions. In other
words, if one synesthete thinks that the letter "q" is colored blue, another synesthete might see
"q" as orange.
Although there is no officially established method of diagnosing
synesthesia, some guidelines have been developed by Richard Cytowic, MD, a
leading synesthesia researcher. Not everyone agrees on these standards,
but they provide a starting point for diagnosis. According to Cytowic,
synesthetic perceptions are:
Involuntary:
synesthetes do not actively think
about their perceptions; they just happen.
Projected:
rather than experiencing something in the "mind's eye," as might happen
when you are asked to imagine a color, a synesthete often actually sees a
color projected outside of the body.
Durable and
generic: the perception must be the same every time; for example,
if you taste chocolate when you hear Beethoven's Violin Concerto, you must
always taste chocolate when you hear it; also, the perception must be
generic -- that is, you may see colors or lines or shapes in response to a
certain smell, but you would not see something complex such as a room with
people and furniture and pictures on the wall.
Memorable: often, the
secondary synesthetic
perception is remembered better than the primary perception; for example,
a synesthete who always associates the color purple with the name "Laura" will often remember that a woman's name is
purple rather than actually remembering "Laura."
Emotional: the
perceptions may cause emotional reactions such as pleasurable feelings.
Who has it?
Estimates for the number of people with synesthesia range from 1 in 200
to 1 in 100,000. There are probably many people who have the condition
but do not realize what it is.
Synesthetes tend to be:
Women: in the U.S.,
studies show that three times as many women as men have synesthesia; in
the U.K., eight times as many women have been reported to have it. The
reason for this difference is not known.
Left-handed:
synesthetes are more likely to be left-handed than the general
population.
Neurologically normal:
synesthetes are of normal (or
possibly above average) intelligence, and standard neurological exams are
normal.
In the same family:
synesthesia appears to be inherited in some fashion; it seems to be a
dominant trait and it may be on the X-chromosome.
Some celebrated people who may have had synesthesia include:
Vasily Kandinsky (painter, 1866-1944)
Amy Beach (pianist and composer, 1867-1944)
Olivier Messiaen (composer, 1908-1992)
Charles Baudelaire (poet, 1821-1867)
Franz Liszt (composer, 1811-1886)
Arthur Rimbaud (poet, 1854-1891)
Richard Phillips Feynman (physicist,
1918-1988)
Mary J. Blige (singer, songwriter, 1971-)
It is possible that some of these people merely expressed synesthetic
ideas in their arts, although some of them undoubtedly did have
synesthesia.
The Biological Basis of Synesthesia
Some scientists believe that synesthesia results from "crossed-wiring" in
the brain. They hypothesize that in synesthetes, neurons and synapses that
are "supposed" to be contained within one sensory system cross to another
sensory system. It is unclear why this might happen but some researchers
believe that these crossed connections are present in everyone at birth,
and only later are the connections refined. In some studies, infants
respond to sensory stimuli in a way that researchers think may involve
synesthetic perceptions. It is hypothesized by these researchers that
many children have crossed connections and later lose them. Adult
synesthetes may have simply retained these crossed connections.
It is unclear which parts of the brain are involved in synesthesia.
Richard Cytowic's research has led him to believe that the limbic system is primarily responsible for
synesthetic experiences. The limbic system includes
several brain structures primarily responsible for regulating our
emotional responses. Other research, however, has shown significant
activity in the cerebral cortex during synesthetic
experiences. In fact, studies have shown a particularly interesting
effect in the cortex: colored-hearing synesthetes have been shown to
display activity in several areas of the visual cortex when they
hear certain words. In particular, areas of the visual cortex
associated with processing color are activated when the synesthetes hear
words. Non-synesthetes do not show activity in these areas, even when
asked to imagine colors or to associate certain colors with certain words.
Synesthesia and the Study of Consciousness
Many researchers are interested in synesthesia because it may reveal
something about human consciousness. One of the biggest mysteries in the
study of consciousness is what is called the "binding problem." No one
knows how we bind all of our perceptions together into one complete whole.
For example, when you hold a flower, you see the colors, you see its
shape, you smell its scent, and you feel its texture. Your brain manages
to bind all of these perceptions together into one concept of a flower.
Synesthetes might have additional perceptions that add to their concept of
a flower. Studying these perceptions may someday help us understand how
we perceive our world. |