Abstract
Acquired prosopagnosia - the inability to recognize individual faces despite preserved low-level visual and intellectual abilities - can inform normal face recognition theories. Here, we present the extensive investigation of a new case of prosopagnosia, GG (66 years old), who sustained a stroke to the right posterior cerebral artery, damaging the occipital lobe, lateral fusiform and parahippocampal gyri, unilaterally in the right hemisphere. GG presents a massive prosopagnosia, being unable to recognize from their face both famous and familiar people.
Our behavioural testing of GG (25 experiments) and age-matched controls aimed at addressing three major issues in the literature: (1) can the impairment be restricted to faces; (2) is it a matter of detection or individualization of faces; (3) what is the nature of the deficit. First, GG failed all experiments involving face retrograde/anterograde memory and perception. Contrariwise, he was normal at mnesic and perceptual tests with several other object categories (chairs, boats, cars, birds, dogs, famous places). Moreover, he showed normal basic visual integrative processes (Navon effect, 3D figures matching, dots configurations perception). Second, a set of face detection tasks (faces in visual scenes, Mooney and Arcimboldo faces) revealed preserved facial detection abilities, even when face detection is based on global information rather than detailed features. Third, we tested GG with classical paradigms measuring holistic face processing (face inversion effect, composite effect, whole-part advantage). Strikingly, GG did not show any of the three effects. Finally, two face matching experiments showed a reduced sensitivity to the eyes region, and a processing bias to the mouth.
Altogether, these observations are in line with different previous studies of prosopagnosia, indicating that lesions to different localizations in the right cortical face network can lead to an inability to extract a holistic representation of the individual face, a fundamental process for normal face recognition.