Face processing in typical and congenitally prosopagnosic adults: behavioural and neuroimaging investigations

Faces are crucial for human social interaction. For most people, recognizing familiar faces is seemingly effortless. However, people who suffer from congenital prosopagnosia (CP) never develop this skill. The current thesis consists of a series of five studies investigating the cognitive as well as neural aspects of both atypical (CP) and typical face processing. In the first study, I adopted "covert" (implicit) face recognition tasks to characterize the exact nature of the cognitive impairment of a participant with CP, showing that "covert tasks" can represent a more sensitive assessment tool for this purpose than traditional "overt tasks". In the second study, I demonstrated that covert recognition is a general feature of CP by assessing a group of eleven CPs with three behavioural tasks. Importantly, I showed that different behavioural tasks vary in the sensitivity of detecting covert recognition. In a third study, by coupling Magnetoencephalography (MEG) with structural brain images (MRIs), I demonstrated that CPs show typical face-selective neuromagnetic activity within the right lateral occipital cortex (rLO) and fusiform gyrus (rFG). Crucially, I characterized the link between brain activity and behaviour, by examining the correlation between MEG activity and the performance on a series of face processing tasks. In a fourth study, using functional Magnetic Resonance Imaging (fMRI), I demonstrated that the pattern of fMRI activity within the right anterior temporal lobe (rAT) differs between CPs and people with normal face processing skills. Finally, in a fifth study, I investigated the spatio-temporal dynamics of typical face perception by coupling MEG recording with MRIs. I demonstrated that the human visual system can categorize places just as rapidly as it categorizes faces, suggesting that early categorization of visual stimuli may be a more general phenomenon than so far assumed. Altogether, these five studies make a significant contribution to our current understanding of the cognitive as well as neural mechanisms underlying face processing difficulties in CP. In addition, they provide crucial insights into the temporal dynamics of typical visual processing.