In this study, we investigated the cognitive processes and nonverbal cues used to detect altruism in three experiments based on a zero-acquaintance video presentation paradigm. Cognitive mechanisms of altruism detection are thought to have evolved in humans to prevent subtle cheating. Several studies have demonstrated that people can correctly estimate levels of altruism in others. In this study, we asked participants to distinguish altruists from non-altruists in video clips using the Faith game. Participants decided whether they could trust allocation of money to the targets who were videotaped while talking to the experimenter. In our first experiment, we asked the participants to play the Faith game under cognitive load. The accuracy of altruism detection was not reduced when participants simultaneously performed a cognitive task, suggesting that altruist detection is rapid and effortless. In the second experiment, we investigated the effects of affective status on the accuracy of altruism detection. Compared with participants in a positive mood, those in a negative mood were more hesitant to trust videotaped targets. However, the accuracy with which altruism levels were detected did not change when we manipulated participants’ moods. In the third experiment, we investigated the facial cues by which participants detected altruists. Participants could not detect altruists when the upper half of the target’s face was hidden, suggesting that judgment cues exist around the eyes. We also conducted a meta-analysis on the effect size in each experimental condition to verify the robustness of altruism detection ability.
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