5 The Cornerstones of Current Synesthesia Research

It was not until 1975 that science again began to increasingly focus on synesthesia research. The pioneers were Lawrence E. Marks, Richard E. Cytowic, and Simon Baron-Cohen. In the 1970s, Marks was interested in the similarities shared by the senses, in particular seeing and hearing, as well as in synesthesia. He wrote On colored-hearing synesthesia: Cross-modal translations of sensory dimensions, a very comprehensive historical summary of sound-color synesthesia research. In contrast, Cytowic devoted himself primarily to synesthesia and in 1989 published the book Synesthesia: A Union of the Senses, in which he both described individual cases and developed a theory on the causes of the phenomenon. He assumed that the limbic system took on the role of a mediator between the senses and that it was hyperactive among synesthetes, whereby more sensory impressions were interconnected than normal. Finally, Simon Baron-Cohen successfully developed a test of genuineness, an objective measure of the temporal consistency of synesthetic perception and thus made synesthesia an object of scientific research again. In contrast to Cytowic, he regarded the neocortex as the locus of origin for synesthetic perceptions, and not the limbic system.