From unconscious to conscious perception: Emotionally expressive faces and visual awareness

The present thesis examines whether facial expression of emotion can be perceived without awareness and influence the selection process by which faces are brought into visual awareness. After reviewing existing literature on unconscious perception of facial expression, six experiments are reported in which participants searched for upright or inverted faces expressing positive and negative emotion among varying numbers of neutral face distractors. The slopes of the search functions for locating (Experiments 1a & 2a) and identifying (Experiment 3) the upright negative face were shallower than the slopes of the search functions for locating and identifying the upright positive face. It is unlikely that this observed slope difference was caused by the individual physical features of positive and negative faces because when the target faces were inverted to reduce holistic face perception, yet retain feature differences, the search function slopes for locating inverted positive and negative faces did not differ (Experiments 1b and 2b). Furthermore, it is unlikely that the observed search slope difference for upright positive and negative faces was the result of some global constellation of features rather than affect per se., because when emotion was varied independently of physical form the negative face was still associated with a shallower search slope (Experiment 4). Taken together, the present findings provide strong support for the claim that, when embedded in neutral face distractors, an unconsciously perceived negative face attracts attention to itself, and therefore is brought into visual awareness more efficiently than a face expressing positive emotion. By demonstrating such differential guidance of attention, support was found for the more general conclusion that the emotion expressed by a face that is outside of awareness can be perceived and bias the selection process by which emotionally expressive faces are brought into awareness. This conclusion is integrated with other investigations of how faces and facial expression influence the deployment of attention, neurological models of threat detection and ethological ideas regarding the social significance of facial expression.