Principle component analyses of questionnaires measuringindividual differences in synaesthetic phenomenology

Questionnaires have been developed for categorising grapheme-colour synaesthetes intotwo sub-types based on phenomenology: associators and projectors. The general approachhas been to assume a priori the existence of two sub-types on a single dimension (withendpoints as projector and associator) rather than explore, in a data-driven fashion, otherpossible models. We collected responses from 175 grapheme-colour synaesthetes on twoquestionnaires, the Illustrated Synaesthetic Experience Questionnaire (Skelton, Ludwig, & Mohr, 2009) and Rouw and Scholte’s (2007) Projector–Associator Questionnaire. AfterPrinciple Component Analysis both questionnaires were comprised of two factors whichcoincide with the projector/associator distinction. This suggests that projectors and associ-ators are not opposites of each other, but separate dimensions of experience (e.g. some syn-aesthetes claim to be both, others claim to be neither). The revised questionnaires providea useful tool for researchers and insights into the phenomenology of synaesthesia.