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Definition of
"synesthesia"
Synesthesia is the
general name for a related set (a "complex") of various cognitive
states. Synesthesia may be divided into two general, somewhat
overlapping types. The first, which I sometimes call "synesthesia
proper", is as described above, in which stimuli to a sensory input
will also trigger sensations in one or more other sensory modes. The second
form of synesthesia, called "cognitive" or "category
synesthesia", involves synesthetic additions to culture-bound
cognitive categorizational systems. In simpler words, with this kind of
synesthesia, certain sets of things which our individual cultures teach us to
put together and categorize in some specific way – like letters, numbers,
or people's names – also get some kind of sensory addition, such as a
smell, color or flavor. The most common forms of cognitive
synesthesia involve such things as colored written letter characters
(graphemes), numbers, time units, and musical notes or keys. For
example, the synesthete might see, about a foot or two before her, different colors for different spoken
vowel and consonant sounds, or perceive numbers and letters, whether
conceptualized or before her in print, as colored. A friend of mine,
Deborah, always perceives the letter "a" as pink, "b"
as blue, and "c" as green, no matter what color of ink they are
printed with.
Synesthesia is additive;
that is, it adds to the initial (primary) sensory perception, rather than
replacing one perceptual mode for another. With my colored musical
timbres, I both hear and "see" the sounds; the visual images
don't replace the audial sensations. Both sensory perceptions may thus
become affected and altered in the ways they function and integrate with
other senses. Synesthesia is generally "one-way"; that is,
for example, for a given synesthete, tastes may produce synesthetic sounds,
but sounds will not produce synesthetic tastes. However, there have
been a few rare cases of synesthetes who have had "bi-directional"
synesthesia, in which, for example, music induces (synesthetic) colors and seeing
colors induces (synesthetic) sounds – the correspondences, however,
may not
be the same in both directions!
Regarding
synesthesia “proper”, stimuli to one sense, such as smell, are involuntarily
simultaneously perceived as if by one or more other senses, such as sight
or/and hearing. For example, I myself have three types of
synesthesiae: The sounds of
musical
instruments will sometimes make me see
certain colors, about a yard in front of me, each color specific and
consistent with the particular instrument playing; a piano, for example,
produces a sky-blue cloud in front of me, and a tenor saxophone produces an
image of electric purple neon lights. I also have had colored taste and smell sensations; for example, the taste of
espresso coffee can make me see a pool of dark green oily fluid about two
feet away from me.
The word
"synesthesia" comes directly from the Greek (syn-)
"union", and (aísthesis) "sensation", thus meaning
something akin to "a union of the senses".
"Synaesthesia" is the British English spelling of the word; in
American English, it is often spelled "synesthesia", without the
"a". The concept appears in other European languages, too:
In Danish it is synæstesi . The Dutch word is synesthesie .
In Finnish, synestesia. In French, it's synesthésie , one type of which is audition
colorée , "colored hearing". In German, it's Synästhesie
, and colored hearing is Farbenhören. In Italian, sinestetici ; in Polish, synestezja; in Russian, ( sinestezia );
in Swedish, it's synestesi.
Synesthesia has definite neurological
components and is apparently partially heritable, one component perhaps
passed down genetically on X-chromosomes. The percentage of the
general human population which has synesthesia varies with the
type involved; estimates run from 4 in 100 for basic types of
cognitive synesthesia (colored letters or musical pitches), to 1 in 3,000
for more common forms of synesthesia proper (colored musical sounds or
colored taste sensations), to 1 in 15,000 or more for people with rare
(such as one synesthete I know of who synesthetically tastes things she
touches) or multiple forms of synesthesia proper. Perhaps more than half of
all humans have a basic form of synesthesia in which they consider "higher"
sounds to be "brighter" and "lower" sounds to be
"darker".
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