中文摘要：

第三方惩罚对合作行为的影响有两面性,可能与其激活的社会规范有关。通过有/无第三方的独裁者博弈范式,研究发现合作行为在有第三方时主要受命令性规范影响;在无第三方时,主要受描述性规范影响。第三方惩罚频率越高,个体在有第三方时的合作行为也越高,撤去第三方后个体合作行为的下降也越大。这可能因为第三方惩罚不仅能有效提示群体中的命令性规范（应该如何做）,还能暗示出该情境下的描述性规范（大多数人如何做）。

英文摘要：

Third-party punishment （TPP） plays an important role in both improving cooperation and maintaining social norms. However, Cognitive Evaluation Theory suggests that TPP may also negatively affect cooperation, because TPP reduces the internal motivation of cooperative behaviors. Therefore, the influence of TPP on cooperation may have two different manifestations depending on the specific kind of activated social norms -- descriptive norms （what most people actually do） or injunctive norms （what people should do）. This study used two experiments to examine the influence of TPP on cooperation. Experiment 1 analyzed the effects of the two different social norms on cooperation without TPP. The subjects （120 university students） participated in a two-round Dictator Game, which used a 2 （high/low descriptive norms） by 2 （high/low injunctive norms） between-subjects design. Experiment 2 （with 300 university students） examined the influence of different TPP frequencies on cooperation. The subjects participated in a four-round Dictator Game with a third-party member who could punish both the dictator and the receiver in Round 2 and 3. In Round 3, the subjects were informed the frequency of TPP （a between-subjects factor）, which were controlled by the experimenter on 10 levels ranging from 0% to 90%. The result showed that descriptive norms had a more significant influence in comparison to injunctive norms, and there was a significant interaction between the two types of norms. Descriptive norms played a more important role on cooperation when there was no punisher, whereas injunctive norms＇ effect on cooperation was stronger when there was a punisher. The results also implied that a low frequency of TPP could successfully increase the level of cooperation, even when the punishment sanction was removed. We also found that higher frequency of TPP reduced the internal motivation on cooperation. An explanation of these effects was that TPP could not only remind subjects of the injunctive norm