Abstract
The cognitive process of categorizing perceptually similar stimuli into qualitatively different categories is fundamental to any systematic acting upon the world, as it helps to
reduce the immense number of entities to more manageable fragments and spares us from
learning anew each time we encounter an unknown individual. Categories are evident
in all sensory modalities and range from relatively simple (e. g., color perception) to the
most abstract human concepts, as for example faces. Categorical perception (CP) has
been shown for face identity (e. g., Beale Keil 1995), ethnicity (Levin Beale, 2000),
and facial expression (Calder et al., 1996). Astonishingly, for sex, a natural facial characteristic
consisting of only two biologically relevant categories, con
icting results have
been reported so far. CP for sex has been shown (Campanella et al., 2001) when sex
information was varied linearly (by morphing) between male and female face identities,
thus intermixing identity and sex information. When sex continua were created based on
single face identities (Bultho and Newell, 2004), no CP for sex was found in nave participants.
So the question remained open whether or not there is CP for the perception of
sex as a facial dimension or if processing of the sex of a face is directly linked to processing
of the face's identity, as proposed by the "`single-route hypothesis"' (e. g., by Rossion,
2002, Ganel Goshen Gottstein, 2002; Bultho Newell, 2004). To overcome one potential
constraint of earlier studies, i. e., 'asymmetric' sex morph continua, we performed
extensive ratings of faces and sex morphs from our face database, to create 'controlled'
male and female faces with similar perceived degrees of 'maleness' and 'femaleness'. We
then examined CP of sex for these faces with classical discrimination and classication
experiments. Critically, we manipulated the degree of familiarization of the faces prior to
testing, as follows. Observers were either nave, or familiarized with the average male and
female face of all faces, or the endpoint identities of the morph continua, or with other
male and female faces with the same perceived degree of maleness and femaleness than
the test faces. Our results conrm the lack of naturally occurring CP for sex and provide
more evidence for the linked processing of sex and identity, as participants showed clear
CP only after familiarization with the test face identities.
