Detecting Social Signals from the Face

This thesis investigates our sensitivity to social signals from the face, both in health and disease, and explores some of the methodologies employed to measure them. The first set of experiments used forced choice and free naIll1ng paradigms to investigate the interpretation of a set of facial expressions by Western and Japanese participants. Performance in the forced choice task exceeded that measured in the free naming task for both cultures, but the Japanese participants were found to be particularly poor at labelling expressions of fear and disgust. The difficulties experienced with translation and interpretation in these tasks led to the development of a psychophysical paradigm which was used to measure the signalling strength of facial expressions without the need for participants to interpret what they saw. Psychophysical tasks were also used to measure sensitivity to eye gaze direction. A 'live' and screen-based task produced comparable thresholds and revealed that our sensitivity to these ocular signals was at least as good as Snellen acuity. Manipulations of the facial surround in the screen-based task revealed that the detection of gaze direction was facilitated by the presence of the facial surround and as such it can be assumed that gaze discriminations are likely to be made in conjunction with other face processing analyses. The tasks developed in these chapters were used to test two patients with bilateral amygdala damage. Patients with this brain injury have been reported to experience difficulties in the interpretation of facial and auditory signals of fear. In this thesis, their performance was found to depend on the task used to measure it. However, neither patient was found to be impaired in their ability to label fearful expressions compared to control participants. Instead, patient SE demonstrated a consistently poor performance in his ability to interpret expressions of disgust.