Abstract
Prosopagnosia is a deficit in recognizing familiar faces following brain damage whose study offers invaluable clues to understand the neural and functional aspects of normal face processing. Most studies of prosopagnosia have focused on processing of unfamiliar faces. As processing of personally familiar faces is substantially different from unfamiliar or famous face processing, these approaches lack ecological and thus informative value with reference to the underlying cause(s) of prosopagnosia. Here we present the first systematic investigation of familiar face processing in PS, a well-known case of acquired prosopagnosia with a deficit restricted to faces (Rossion et al., 2003; Schiltz et al., 2006). Due to largely preserved perceptual functions and an excellent memory, PS has been able to compensate for her deficits and has been pursuing her profession in a kindergarten. We conducted an exhaustive set of behavioral experiments with photographs of the 26 children of 3 to 4 years old that were in contact with PS and her 2 colleagues during the whole year. Tasks included familiar/unfamiliar face decisions (whole or half face, or face parts), and forced choice matching to improve the patient's performance. In striking contrast to controls, PS was most efficient in recognizing familiar faces by using the mouth relative to the eyes of the face, in line with our previous observation using the Bubbles methods (Caldara et al., 2005). Moreover, despite being able to perceive metric distances between features, several experiments (whole-part interference, face composite effect, assessment of ratio of face relations) showed that PS does not process individual faces holistically. These results suggest that the ability to integrate facial features into a holistic individual representation centered on the eyes of the face is a critical component of a normal face recognition system that can be selectively disrupted following brain damage.