Acquired prosopagnosia abolishes the face inversion effect

Individual faces are notoriously difficult to recognize when they are presented upside-down. Since acquired prosopagnosia (AP) has been associated with an impairment of expert face processes, a reduced or abolished face inversion effect (FIE) is expected in AP. However, previous studies have incongruently reported apparent normal effects of inversion, a decreased or abolished FIE, but also a surprisingly better performance for inverted faces for some patients. While these discrepant observations may be due to the variability of high-level processes impaired, a careful look at the literature rather suggests that the pattern of FIE in prosopagnosia has been obscured by a selection of patients with associated low-level defects and general visual recognition impairments, as well as trade-offs between accuracy and correct RT measures. Here we conducted an extensive investigation of upright and inverted face processing in a well-characterized case of face-selective AP, PS (Rossion et al., 2003). In 4 individual face discrimination experiments, PS did not present any inversion effect at all, taking into account all dependent measures of performance. However, she showed a small inversion cost for individualizing members of a category of non-face objects (cars), just like normal observers. A fifth experiment with personally familiar faces to recognize confirmed the lack of inversion effect for PS. Following the present report and a survey of the literature, we conclude that the FIE is generally absent, or at least clearly reduced following AP. We also suggest that the paradoxical superior performance for inverted faces observed in rare cases may be due to additional upper visual field defects rather than to high-level competing visual processes. These observations are entirely compatible with the view that AP is associated with a disruption of a process that is also abolished following inversion: the holistic representation of individual exemplars of the face class.