We investigated the effects of different types of smiles on the perception of uncooperative or untrustworthy behaviour. In five studies, participants assigned to one group played an economic game with a representative of another group. In an initial round, the representative acted uncooperatively by favouring their group and then displayed a dominance, reward, or affiliation smile. Participants rated the motives of the representative and played a second round of the game with a different member of the same outgroup. Following uncooperative or untrustworthy behaviour, affiliation smiles communicated less positivity and superiority, and a greater desire to both repair the relationship between groups and change the uncooperative decision than reward or dominance smiles. Perceptions of a desire to repair the relationship and to change the decision were associated with trust and cooperation in a subsequent round of the game. Together, these findings show that smiles that are subtly different in their morphology can convey different messages and highlight the importance of these expressions in influencing the perceptions of others' intentions.
Keywords: Smile; decision-making; facial expression; groups; trust.