Investigating categorical perception of gender with 3-D morphs of familiar faces

We could find no evidence for categorical perception of face gender using unfamiliar human faces (I Bülthoff et al, 1998 Perception 27 Supplement, 127a). Therefore we have investigated whether familiarising participants with the stimuli prior to testing might favour categorical perception. We created artificial gender continua using 3-D morphs between laser-scanned heads. The observers had to classify all faces according to their gender in a classification task. If perception of face gender is categorical, we would expect participants to classify the morphs into two distinct gender categories. Furthermore, they should differentiate pairs of morphs that straddle the gender boundary more accurately than other pairs in a discrimination task. The participants were familiarised before testing with half of the faces used for creating the morphs. They could categorise most familiar and unfamiliar faces into distinctive gender categories. Thus, they could extract the gender information and use it to classify the images. On the other hand, we found no evidence of increased discriminability for the morph pairs that straddle the gender boundary. Apparently, observers did not perceive the gender of a face categorically, even when these faces were familiar to them