"Although medicine has known about synaesthesia for three centuries, it keeps forgetting that it knows."
--Richard Cytowic, in "Synaesthesia: Phenomenology and Neuropsychology-a Review of Current Knowledge"

The first reference to synaesthesia is believed to have been in John Locke's Essay Concerning Human Understanding. In his Essay, Locke recounted the story of a blind man who one day felt "betrayed" when he learned what scarlet signified. When the blind man's friend asked what he had thought scarlet was, the blind man answered that it was "like the sound of a trumpet." However, some authors place the first mention of synaesthesia much earlier: Pythagoras (6th century B.C.) and Aristotle (4th century B.C.) may have also written on the subject.

The two gurus of Calculus, Leibniz and Newton (and boy, don't we love them for inventing it!), both mentioned synaesthesia in 1704. Leibniz recounted another case of a blind man understanding scarlet by the sound of a trumpet, and Newton noticed a parallel between colors of the spectrum and the notes of a musical scale. This relationship was also noticed by Castel, and in 1735, he built what is assumed to be the world's first color organ.

There were a few other references to synaesthesia in the 1700s, and many more accounts were told in the 1800s, such as in 1883 when Galton noticed that synaesthesia seemed to be frequent in children. But this century has really seen an explosion in literature dedicated to understanding or recounting synaesthesia. In one of the more interesting events, Scriabin composed (1911) Prometheus, a work that was to incorporate music as well as light when performed (and therefore achieve a synaesthetic affect). Another interesting event occurred in 1944, when there was an attempt to teach colored hearing to those who did not naturally possess the skill.

Despite the numerous accounts of synaesthesia through the centuries, the scientific conception of the phenomenon has been rather fluid. The scientific community has, at various times, attributed synaesthesia to everything from "illusion" to a "crossing of the wires in the head" to genetics. At times, it was even thought that people who claimed synaesthetic experiences simply had schizophrenia. The definition of synaesthesia has been equally broad. In 1944, one article went so far as to claim that "Error in perception of disturbances when one first wears a new pair of glasses are probably a result of an influence which may be termed synesthetic....Ventriloquism is evidentially a synesthetic phenomenon too...." However, the definition has been narrowed considerably over time, and the general consensus is that synaesthesia only occurs when the stimulation of one sensory modality directly causes the perception of another modality. There are, however, several instances in which pseudosynaesthesia can occur.

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