History of synesthesia research

Synesthesia is a neurological condition in which two or more bodily senses are coupled. For example, in a form of synesthesia known as grapheme-color synesthesia, letters or numbers may be perceived as inherently colored. Historically, the most commonly described form of synesthesia (or synesthesia-like mappings) has been between sound and vision.

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Early historical mentions

The earliest mentions of synesthesia are debated. Although it is well established that Pythagoras referred to the music of the spheres, whether this early mention refers to synesthesia or rather to a metaphorical/mystical interpretation of mathematical harmonies is unclear.

John Locke in An Essay Concerning Human Understanding (1689) reports:

A studious blind man, who had mightily beat his head about visible objects, and made use of the explication of his books and friends, to understand those names of light and colours which often came in his way, bragged one day, That he now understood what scarlet signified. Upon which, his friend demanding what scarlet was? The blind man answered, It was like the sound of a trumpet.

– Locke, An Essay Concerning Human Understanding, Book III, Chapter IV, section 11

Again, whether this is an actual instance of synesthesia, or simply reflects metaphorical speech, is debated. A similar example appears in Leibniz's New Essays on Human Understanding (written in 1704, but not published until 1764); indeed given that the New Essays is intended as a rebuttal to Locke, it may even have been the same individual. Although it is mainly speculation, there is reason to believe that the person Locke referred to was the mathematician and scientist Nicholas Saunderson, who held the Lucasian professor chair at Cambridge University, and whose general prominence would have made his statements noticeable. In Letters on the blind, Denis Diderot, one of Locke's followers, mentions Saunderson by name in related philosophical reflections.

In 1710, Thomas Woodhouse reported the case of another blind man who perceived colors in response to sounds (see Marks 1975). The first agreed upon account of synesthesia comes from Sachs in 1812, who reports on his colored vowels as part of his PhD dissertation (on his albinism), although its importance has only become apparent restrospectively.

Numerous other philosophers and scientists, including Isaac Newton (1704), Erasmus Darwin (1790) and Wilhelm Wundt (1874) may have referred to synesthesia, or at least synesthesia-like mappings between colors and musical notes. Indeed, the father of psychophysics, Gustav Fechner reported a case of colored vowels in 1876 (see Marks 1975).

Turn of the century investigations

These early investigations aroused little interest, and the phenomenon was first brought to the attention of the scientific community in the 1880s by Francis Galton (Galton 1880a; Galton 1880b; Galton 1883). Following these initial observations, research into synesthesia proceeded briskly, with researchers from England, Germany, France and the United States all investigating the phenomenon. These early research years corresponded with the founding of psychology as a scientific field (see history of psychology). By 1926, Mahling cites 533 published papers dealing with colored hearing (or hearing → color synesthesia) alone (Marks 1975).

Although there is still debate as to when the first international academic conference to seriously look at synesthesia took place, a likely candidate is the following: From March 2nd through 5th of 1927, Georg Anschütz (who was once a student of Alfred Binet) presided over the convening of the first Kongresse zur Farbe-Ton-Forschung (Congress for Color-Tone Research), in Hamburg, Germany. A 2nd congress took place 1 – 5 October, in Hamburg, Germany; a 3rd October 2 – 7, 1933; and the 4th and final conference in this series took place October 4 – 10, 1936 (Jewanski 1999).

In addition to drawing concerted scientific interest, the phenomenon of synesthesia started arousing interest in the salons of fin de siecle Europe. The French Romantic poets Arthur Rimbaud and Charles Baudelaire wrote poems which focused on synesthetic experience. Baudelaire's Correspondances (1857) (full text available here) introduced the Romantic notion that the senses can and should intermingle. Kevin Dann (Dann 1998) argues that Beudelaire probably learned of synesthesia from reading medical textbooks that were available in his home, and it is generally agreed that neither Baudelaire, nor Rimbaud were true synesthetes. Rimbaud, following Baudeliare, wrote Voyelles (1871) (full text available here) which was perhaps more important than Correspondances in popularizing synesthesia. Numerous other composers, artists and writers followed suit, making synesthesia well-known among the artistic community of the day.

Due to the difficulties in assessing and measuring subjective internal experiences, and the rise of behaviorism in psychology, which banished any mention of internal experiences, the study of synesthesia gradually waned during the 1930s. Marks (1975) lists 44 papers discussing colored hearing from 1900 to 1940, while in the following 35 years from 1940 to 1975, only 12 papers were published on this topic.

The modern renaissance

In the 1980s, as the cognitive revolution had begun to make discussion of internal states and even the study of consciousness respectable again, scientists began to once again examine this fascinating phenomenon. Led by Lawrence E. Marks (Marks 1975) and Richard Cytowic (Cytowic 2002 first ed. 1989 Cytowic 2003 first ed. 1993) in the United States, and by Simon Baron-Cohen and Jeffrey Gray (see Baron-Cohen & Harrison 1997) in England, research into synesthesia began by exploring the reality, consistency and frequency of synesthetic experiences. In the late 1990s, researchers began to turn their attention towards grapheme-color synesthesia, one of the most common (Day 2005; Rich, Bradshaw & Mattingley 2005) and easily studied forms of synesthesia. In 2006, the journal Cortex published a special issue on synesthesia, composed of 26 articles from individual case reports to functional neuroimaging studies of the neural basis of synesthesia. Synesthesia has been the topic of several recent scientific books and novels and a recent short film has even included characters who experience synesthesia (for more information, see the main synesthesia page).

Mirroring these developments in the professional community, synesthetes and synesthesia researchers have come together to found several societies dedicated to research and education about synesthesia, its consequences and uses. In 1995, the American Synesthesia Association was founded, and has been having annual meetings since 2001. In England, the UK Synaesthesia Association, arose out of a similar desire to bring together synesthetes and the people who study them, and has held two conferences (in 2005 and 2006). Similarly, since its inception in 1993, Sean A. Day has administered the "synesthesia list", an e-mail list for synesthetes and researchers around the world. With increased scientific knowledge and public outreach, awareness of this condition is growing world-wide.

See also

• American Synesthesia Association
• UK Synaesthesia Association

References