Coloured Speech Perception: Is Synaesthesia what Happens when Modularity Breaks Down?

Evidence was reported earlier from a single case that chromatic–lexical (CL) synaesthesia was a genuine phenomenon. A study is presented in which nine subjects were tested who also reported having coloured hearing. The following questions were addressed: (a) were these cases also genuine (ie consistent over time), (b) were they truly lexical, or rather variants of this condition, such as chromatic–graphemic (CG) or chromatic–phonemic (CP) synaesthesia, (c) did the experimental subjects show any commonalities between them, and (d) were they able to give information on a standard questionnaire about the phenomenology and ontogenesis of the condition? Subjects were asked to describe the colour sensation experienced on hearing items from a list of 130 words, phrases, and letters. The experimental group were not informed of any retest, but were retested more than one year later. A control group (n = 9), matched for IQ, memory, age, and gender, were read the same list and asked to associate a colour with each list item. They were informed at the time of testing that they would be retested on a sample of items from the list a week later. 92.3% of the responses of the experimental group when retested one year later were identical to those given in the original test, compared with only 37.6% of the control subjects' responses (retested one week later). This confirmed the genuineness of these nine cases. All nine experimental subjects showed CG synaesthesia, none showing either CL or CP synaesthesia. Among the experimental group, some consistency was found in the colours evoked by hearing specific letters, suggesting the condition has a neurological basis. There was also evidence of a genetic sex-linked familial pattern underlying the condition. The importance of these distinct forms of synaesthesia for our understanding of the modularity of speech perception and colour vision is discussed.