The effect of opponent’s emotional facial expressions on individuals’ cooperation and underlying mechanism in prisoner’s dilemma game

Previous research suggested that emotional facial expressions significantly influence perceivers’ behaviors in interactive decision-making. Although emotional facial expressions of opponents could bias participants’ behaviors, little was known about the reason for this effect. Based on the social functions of emotions and dual-process theories of decision-making, the present study aimed to explore the effect of three emotional facial expressions, i.e. happiness, neutral and anger, on individuals’ cooperative behaviors in prisoner's dilemma game and the underlying mechanism, i.e. the mediating role of expectations of others’ cooperation and the moderating role of individuals’ decision modes. Three experiments were designed to test the hypothesis. The emotional facial expressions were manipulated by grey-scale images of emotionally expressive faces (3 males and 3 females, 260 × 300 pixels) taken from a standard set of Chinese Affective Picture System (CAPS) in three experiments. Experiment 1 investigated the effects of emotional facial expressions (happiness/neutral/anger) on participants’ cooperation, as well as the mediating role of expectations of partner’ cooperation with a one-factor between-subjects design. A total of 180 adult participants were recruited for this experiment (109 females; mean age 22.36 ± 4.10 years) and were randomly assigned to happy, neutral or angry conditions. Experiment 2 adopted a 3(facial expressions: happiness/neutral/anger) × 2(decision modes: intuitive/deliberative) between-subjects design to examine moderating role of decision modes, as well as the mediating role of expectations of partner’ cooperation. A total of 185 adult participants were recruited for this experiment (130 females; mean age 21.48 ± 2.71 years). And the decision modes were manipulated by instructions. Experiment 3 adopted a 3(facial expressions: happiness/neutral/anger) × 2(time pressure: time constraint/time delay) between-subjects design to examine moderating role of time pressure, as well as the mediating role of expectations of partner’ cooperation. A total of 218 adult participants were recruited for this experiment (148 females; mean age 23.74 ± 3.11 years). And the time pressure were manipulated by imposing a time constraint. The results of the three experiments showed: (1) participants were found to be more cooperative towards happy partners compared to angry ones, and the expectations of partners’ cooperation mediated the relationship between emotional facial expressions and participants’ cooperative behaviors (Experiment 1); (2) only under the condition of intuitive decision mode, participants were found to be more cooperative towards happy and neutral partners compared to angry ones, and the expectations of partners’ cooperation mediated the relationship between emotional facial expressions and participants’ cooperative behaviors (Experiment 2); (3) only under the condition of time constraint, participants were found to be more cooperative towards happy partners compared to angry and neutral ones, and the expectations of partners’ cooperation mediated the relationship between emotional facial expressions and participants’ cooperative behaviors (Experiment 3). Our findings contribute to literature in two ways. Firstly, the study extends our understanding of the phenomenon that emotional facial expressions influence individuals’ cooperative behaviors. Secondly, our findings further enrich and extend the evidence and field of the interpersonal effect of emotional facial expressions in interactive decision-making. These findings thereby have important implications for understanding the mechanism underlying the effect of different emotional facial expressions on individuals’ cooperative decision-making.