Same critical features are used for identification of familiarized and unfamiliar faces

Many studies have shown better recognition for faces we have greater experience with, relative to unfamiliar faces. However, it is still not clear if and how the representation of faces changes during the process of familiarization. In a previous study, we discovered a subset of facial features, for which we have high perceptual sensitivity (PS), that were critical for determining the identity of unfamiliar faces. This was done by assigning values to 20 different facial features based on perceptual rating, converting faces into feature-vectors, and measuring the correlations between face similarity ratings and distances between feature-vectors. In the current study, we examined the contribution of high and low-PS features to face identity after familiarization. To familiarize participants with unfamiliar faces, we used an individuation training protocol that was found to be effective in previous studies, in which different names are assigned to different faces and participants are asked to learn the face-name association. Our findings show that even after repeated exposure to the same image of each identity, which allows close examination of all facial features, only high-PS features contributed to face identity, while low-PS features did not. This subset of high-PS features includes both internal and external features and part and configuration features. We therefore conclude that identification of familiarized and unfamiliar faces may rely on the same subset of critical features. These findings further support a new categorization of facial features according to their perceptual sensitivity.