Component processes of human face perception in typical and atypical individuals

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Face perception is an essential component of human social interaction. It guides how we interact with others by enabling us to recognize individuals, identify their emotional state, and judge their attractiveness and trustworthiness. Because face perception operates so effortlessly and reliably, we rarely give it a second thought. But in fact, face perception and recognition are difficult achievements that are based on complex and poorly understood mechanisms. The real difficulty of face processing only becomes apparent when meeting people without any general perceptual or intellectual impairment, and without any history of neurological damage, who find it extremely hard to recognize family and friends from their faces. Behavioural tests of various aspects of face processing conducted by us and by other groups have shown that many of these people with developmental prosopagnosia (DP) have no comparable problems with object recognition, which indicates that faces and non-face objects are processed by different mechanisms. All DPs show severe deficits in the processing of identity, but other aspects of face processing, such as the perception of face parts and face configurations or the processing of emotional facial expression, can be intact or impaired, suggesting that DP is a heterogeneous condition. In our current ESRC-funded research project, we use a combination of behavioural and electrophysiological measures (event-related brain potentials, ERPs) to gain new insights into which aspects of face processing are damaged in DP. Our results so far point to early visual-perceptual stages of face processing as a major cause of the face recognition problems that affect individuals with DP. For example, people with intact face perception process upright faces and inverted faces very differently, which is interpreted as evidence that the perception of upright faces is "configural" or "holistic", whereas inverted faces are processed in a qualitatively different "part-based" fashion. We have found that people with DP do not show these typical processing differences between upright and inverted faces, indicating that their ability to process upright faces in a configural/holistic fashion did not develop properly. To find out more precisely how face perception differs between DPs and people with intact face processing, we will conduct a series of experiments with face and non-face stimuli that are specifically designed to engage different aspects of face processing (e.g., the perception of salient face parts such as the eyes, the processing of facial configurations, perceiving faces from different viewpoints, using face perception to remember individual faces), to find out which processes operate normally and which are impaired in people with DP. We will also study whether DPs and non-impaired people look at faces differently, and whether they use different parts of a face when trying to identify it. Finding out which aspects of face perception work well and which are impaired in DPs will have important implications for our understanding the mechanisms that underlie face perception in people with intact face processing abilities. It will also greatly expand our knowledge of why some people have severe deficits in face recognition. Such deficits can have an enormous impact on their social lives. Many have difficulty maintaining friendships due to perceived snubs and their recognition difficulties at work can be extremely troubling.