Behold the wrath: Psychophysiological responses to facial stimuli

The complex musculature of the human face has been shaped by natural selection to produce gestures that communicate information about intentions and emotional states between senders and receivers. According to the preparedness hypothesis, different facial gestures are differentially prepared by evolution to become associated with different outcomes. As attested by psychophysiological responses in Pavlovian conditioning experiments, expressions of anger and fear more easily become signals for aversive stimuli than do expression of happiness. Consistent with the evolutionary perspective, the superior conditioning to angry faces is stronger for male than for female faces, for adult than for child faces, and for faces directed toward the receiver rather than directed away. Furthermore, it appears to be primarily located in the right cerebral hemisphere. The enhanced autonomic activity to angry faces signaling electric shock is not mediated by conscious cognitive activity, but is evident also when recognition of the facial stimulus is blocked by backward masking procedures. Similarly, conditioned responses can be established to masked angry, but not to masked happy faces. Electromyographic measurement of facial muscle activity reveals a tendency for emotional facial expression to rapidly and automatically elicit its mirror image in the face of the receiver, typically accompanied by the appropriate emotional experience. The research reviewed in this paper supports the proposition that humans have been evolutionarily tuned to respond automatically to facial stimuli, and it is suggested that such early automatic reactions shape the subsequent conscious emotional processing of the stimulus.The responsibility for this paper is shared equally between the authors. The research reviewed in the paper has been supported by separate grants to both authors from the Swedish Council for Research in the Humanities and Social Sciences, The Swedish Council for the Coordination and Planning of Research, and the Bank of Sweden Tercentennial Fund.