Abstract: Decision making is always involved in cooperation, reciprocity and fairness. Cooperation, reciprocity and fairness are not only the goals which our human beings is pursuing all the times, but also play a significant role in all kinds of subjects, such as psychology, social work and economics. Cooperation, reciprocity and fairness are the foundations of human existence and the pre-requisition for the economic and social development. They are so essential and crucial to us, we barely can survive without them. Decision making was affected by many factors such as emotion, intelligence. People make decision in social contexts. However, so far there are few studies attempting to investigate the effects of social exclusion on decision making. Social exclusion has drawn more and more attention as a pervasive and negative social experience in recent years in psychological area. The concept of social exclusion refers to the phenomenon that people’s need of belongingness and social relationships is thwarted because the one is excluded by a group or other people. Economic games are novel tools for us to study cooperation, reciprocity and fairness behaviors. In this study, we aim at investigating the effect of social exclusion on the behavioral responses of respondents in ultimatum games and dictator games. Meanwhile we also explore the factors that might modulate the effects of social exclusion on social decision making, such as fairness consideration and economic game types. In experiment 1, social inclusion and exclusion were manipulated using Cyberball (a virtual ball game). Participants were randomly assigned to excluded group or included group. Right after the Cyberball game there is a questionnaire contained several manipulation checks for inclusion/ostracism as well as their levels of four needs that they felt during the game. Cyberball was immediately followed by an ultimatum game. Firstly, participants were informed of the rules of UG, in which participants would play as a recipient and the allocator would be a novel player. Secondly, 51 participants played the ultimatum game with 6 different players, in which the recipients can either accept or reject the offer proposed by the allocator. The roles in the UG were determined by the computer. All the participants acted as recipient. In experiment 2, all the procedures were mostly the same as experiment 1. The only difference was the rules of the dictator game, in which the recipients can only accept the offer proposed by the allocator. All these 2 experiments investigated whether fairness consideration and economic game type would mediate the effect of social exclusion on social decision making. The whole study indicated：(1) Social exclusion had negative effects on social decision making. Specifically, social exclusion decreased cooperative behaviors in economic games. The excluded group was more likely to reject and felt less satisfied with the amount of money offered by the allocator compared to the controlled group. (2) The fairness consideration mediated the link between social exclusion and social decision making. With the severity of unfairness being enhanced, the excluded group was more likely to reject and felt less satisfied with the amount of money offered by the allocator. And they made more irrational decisions. (3) The economic game type had significant effect on social decision making of social excluded group. The excluded group in the dictator game was less satisfied with the amount of money offered by the allocator compared to the excluded group in the ultimatum games. These findings enhanced the ecological validity of research in social decision making as well as predictive validity of traditional decision making models, and shed light on the factors involved in social decision making.

Key words: social exclusion, social decision making, ultimatum game, dictator game

摘要： 本研究借助经典的最后通牒博弈范式（UG）和独裁者博弈范式（DG），将回应者/接受者作为研究对象，考察了不同公平条件、平等条件下社会排斥对社会决策的影响作用。实验结果发现：(1)在面对高不公平性的分配方案时，被排斥组比被接纳组更倾向于拒绝接受该分配方案；(2)被排斥组对高不公平性分配方案的满意度要显著低于被接纳组；(3)被排斥组在不平等的博弈（DG）条件下对分配方案的满意度显著低于平等博弈（UG）条件下对分配方案的满意度。本研究结果说明，社会排斥情境下的被试对公平与平等因素更加敏感：在高不公平条件下，被排斥的个体表现出更少的合作互惠行为，甚至不惜放弃自身经济利益，也要惩罚博弈对方的不公平行为；此外，在不平等的博弈条件下，被排斥的个体产生了更多的消极情绪体验。本文的研究结果提高了社会决策研究的生态效度和传统决策模型的预测效度，有利于更加完整透彻地了解社会决策的影响因素。

关键词: 社会排斥, 社会决策, 最后通牒博弈, 独裁者博弈