Categorical perception of male and female faces depends on familiarity

The perception of face identity, race and also facial expressions has been shown to be categorical. For another characteristic of faces, sex, results have been conflicting so far. To resolve this controversy, we created male and female faces with similar perceived degrees of 'maleness' and 'femaleness', based on extensive ratings of faces and sex morphs from our face database. We then created sex continua using these controlled stimuli and tested categorical perception (CP) with classical discrimination and classification tasks. Participants were naïve (1), or had been familiarized with average faces of both sexes (2), or with the 'controlled' male and female faces (3). Our results confirm the lack of naturally occurring CP for sex in (1). Moreover, since only participants in (3) showed clear CP, our results suggest (as stated in the „single-route hypothesis‟) that the processing of sex and identity information in faces is not independent from each other. We found no evidence that familiarization with sex information (as given by average male and female faces) transfers to individual faces