Investigating face-specificity through congenital prosopagnosia: studies on perceptual phenomena and eye movement patterns

Congenital prosopagnosia consists of the failure to develop normal face recognition ability despite intact low-level perceptual and intellectual functioning, and in the context of normal exposure to faces throughout the individual’s life. Typically, these individuals are able to perceive facial stimuli as faces but fail to identify a face as familiar or unfamiliar and to identify it. Despite the large amount of studies that have investigated face recognition in individuals with typical development and in congenital prosopagnosics over the last twenty years, we are still far from a complete understanding of the mechanisms underlying typical and atypical face recognition, and some research questions are still open. For this reason, the present dissertation investigates some perceptual effects in individuals with a selective deficit in face recognition processing in order to reach a better understanding of what happens during a successful and unsuccessful face recognition process. In particular, by using a combination of behavioural and eye-tracking methods, I investigated whether the left perceptual bias and the self-face advantage are shown by individuals with congenital prosopagnosia and are truly face-specific or not. My results demonstrate that, whereas the left perceptual bias seems to characterize the recognition of unfamiliar faces in good recognizers, individuals with congenital prosopagnosia seem to show an opposite bias (i.e., a right perceptual bias) during the recognition of the self-face. Moreover, despite their face recognition impairment, congenital prosopagnosics consistently show high accuracy in recognizing their own face (i.e., a self-face advantage). Furthermore, some of the studies I conducted on the visual scanning strategies of this population demonstrated that the self-face advantage phenomenon is not associated with a different exploration of the face stimuli, suggesting that it could reflect a more general self-advantage and not be face-specific. Finally, the evidence presented in this dissertation also highlights that individuals with face impairment from birth show some difficulties in recognizing stimuli with high degree of similarity (such as objects belonging to the same class), and that these difficulties are associated with a different pattern of visual exploration. Overall, the evidence illustrated in the present thesis helps to shed light on the mechanisms characterizing face recognition and to expand our knowledge on the impairment affecting individuals with congenital prosopagnosia.