Synaesthesia: pitch-colour isomorphism in RGB-space?

A new experimental technique found coloured-hearing synaesthetes to possess localised isomorphism between pitch and colour. We found significantly more consistency in synaesthetes' pitch-colour matches than controls, with matches unaffected by musical experience, not facilitated by absolute pitch (AP) and responded to on the basis of pitch alone, without interference from note-name information. Synaesthetes also placed their colour responses to quartertones (notes falling between adjacent semitones) significantly closer to the RGB midpoint of their responses to the semitones lying either side. This is partial evidence for a direct, localised pitch-colour correspondence. Criteria for possible between-synaesthete similarities in patterning are also discussed, with limited evidence for localised patterning presented.