Synesthesia. II. Psychophysical relations in the synesthesia of geometrically shaped taste and colored hearing.

The psychophysical function in two synesthetic subjects, one with geometrically shaped taste and the other with colored hearing, is investigated. Each synesthete is compared with three control subjects. Pilot studies are used to construct appropriate response domains. Compared to controls, synesthetes give a restricted set of responses that are also asymmetric with respect to the range of choices available in various subsets of the response domain. A combination of absolute and relative effects is also distinctive of synesthetic percepts. It is concluded that synesthesia is a distinct phenomenon unlike ordinary mediated associations, and occupies an intermediate position in the range of simple to complex brain mechanisms.