Face processing in congenital prosopagnosia

Face recognition is one of the most important abilities for everyday social interactions. Congenital prosopagnosia, also referred to as ``face blindness'', describes the innate, lifelong impairment to recognize other people by their face. About 2 % of the population is affected. This thesis aimed to investigate different aspects of face processing in prosopagnosia in order to gain a clearer picture and a better understanding of this heterogeneous impairment. In a first study, various aspects of face recognition and perception were investigated to allow for a better understanding of the nature of prosopagnosia. The results replicated previous findings and helped to resolve discrepancies between former studies. In addition, it was found that prosopagnosics show an irregular response behavior in tests for holistic face recognition. We propose that prosopagnosics either switch between strategies or respond randomly when performing these tests. In a second study, the general face recognition deficit observed in prosopagnosia was compared to face recognition deficits occurring when dealing with other-race faces. Most humans find it hard to recognize faces of an unfamiliar race, a phenomenon called the "other-race effect". The study served to investigate if there is a possible common mechanism underlying prosopagnosia and the other-race effect, as both are characterized by problems in recognizing faces. The results allowed to reject this hypothesis, and yielded new insights about similarities and dissimilarities between prosopagnosia and the other-race effect. In the last study, a possible treatment of prosopagnosia was investigated. This was based on a single case in which a prosopagnosic reported a sudden improvement of her face recognition abilities after she started a special diet. The different studies cover diverse aspects of prosopagnosia: the nature of prosopagnosia and measurement of its characteristics, comparison to other face recognition impairments, and treatment options. The results serve to broaden the knowledge about prosopagnosia and to gain a more detailed picture of this impairment.