What is in a smile: The role of evaluation goal and response labels in facial muscle responses to prejudiced groups.

Based on the assumption that valence is permanently linked to facial responses, we expected that the corrugator muscle is contracted faster in response to overweight persons than to slim persons, whereas we expected faster contractions of the zygomaticus muscle in response to slim persons rather than to overweight persons. To detect such differences, we conducted experiments with different versions of a facial stimulus-response compatibility task that required participants to respond with the two facial muscles to photos of overweight or slim persons. Contrary to the assumption that valence is permanently linked to facial responses, in Experiments 1 and 2, social categories (overweight vs. slim persons) did not influence the response latencies assessed by electromyography. Whereas in Experiments 1 and 2, neutral labels were used for the muscle responses, in Experiment 3, affective response labels (smile vs. frown) were used. In Experiment 3, faster responses with the corrugator to overweight than to slim persons and with the zygomaticus to slim than to overweight persons were obtained. The influence of task and response label is consistent with the theory of event coding that suggests a more flexible link between valence and action.