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. Vll Experiments 2, 3, 4 and 5 of Chapter 3, have also been reported in Perception, 1995, Vol. 24, Supplement, pp. 14. The Face as a long distance transmitter. Jenkins, J., Craven, B. & Bruce, V. Experiments 1,2,3 and 4 of Chapter 3 were also reported in the Technical Report of the Institute of Electronics Information and Communication Engineers. HIP 96-39 (1997-03). Methods for detecting social signals from the face. Jenkins, J., Craven, B., Bruce, V., & Akamatsu, S. Experiments 2 and 5 of Chapter 3, and a selection of the patient studies from Chapter 6 were reported at the Experimental Psychology Society, Bristol meeting, 1996, and at the Applied Vision Association, Annual Meeting, April, 1996. Sensitivity to Expressive Signals from the Human Face: Psychophysical and Neuropsychological Investigations. Jenkins, J., Bruce, V., Calder, A., & Craven, B.

This thesis examines the way in which meaningful facial signals (i.e., eye gaze and emotional facial expressions) influence the allocation of visual attention. These signals convey information about the likely imminent behaviour of the sender and are, in turn, potentially relevant to the behaviour of the viewer. It is already well established that different signals influence the allocation of attention in different ways that are consistent with their meaning. For example, direct gaze (i.e., gaze directed at the viewer) is considered both to draw attention to its location and hold attention when it arrives, whereas observing averted gaze is known to create corresponding shifts in the observer’s attention. However, the circumstances under which these effects occur are not yet understood fully. The first two sets of experiments in this thesis tested directly whether direct gaze is particularly difficult to ignore when the task is to ignore it, and whether averted gaze will shift attention when it is not relevant to the task. Results suggest that direct gaze is no more difficult to ignore than closed eyes, and the shifts in attention associated with viewing averted gaze are not evident when the gaze cues are task-irrelevant. This challenges the existing understanding of these effects. The remaining set of experiments investigated the role of gaze direction in the allocation of attention to emotional facial expressions. Without exception, previous work looking at this issue has measured the allocation of attention to such expressions when gaze is directed at the viewer. Results suggest that while the type of emotional expression (i.e., angry or happy) does influence the allocation of attention, the associated gaze direction does not, even when the participants are divided in terms of anxiety level (a variable known to influence the allocation of attention to emotional expressions). These findings are discussed in terms of how the social meaning of the stimulus can influence preattentive processing. This work also serves to highlight the need for general theories of visual attention to incorporate such data. Not to do so fundamentally risks misrepresenting the nature of attention as it operates out-with the laboratory setting.