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.
[7] 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.
Henry David Thoreau remarked in a letter to Ralph Waldo Emerson in 1848 that a child he knew had asked him "if I did not use ‘colored words.'
"[8] The first agreed upon account of synesthesia comes from German physician Georg Tobias Ludwig Sachs in 1812, who reports on his colored vowels as part of his PhD dissertation (on his albinism),[5][9] although its importance has only become apparent retrospectively.
[10][6] The father of psychophysics, Gustav Fechner reported on a first empirical survey of colored letter photisms among 73 synesthetes in 1871,[11][12] followed in the 1880s by Francis Galton.
[7] 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 2 – 5 March 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.
[19] 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[7] and Richard Cytowic[20][21] in the United States, and by Simon Baron-Cohen and Jeffrey Gray[22] in England, research into synesthesia began by exploring the reality, consistency and frequency of synesthetic experiences.
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).