This paper introduces the Hierarchical Mindreading Model (HMM), a new model of mindreading in two-person, mixed-motive games such as the Prisoners’ Dilemma. The HMM proposes that the strategies available to decision makers in these games can be classified on a hierarchy according to the type of mindreading involved. At Level 0 of the HMM, there is no attempt to infer the intentions of the other player from any of the context-specific information (i.e., signals, payoffs, or partner reliability). At Level 1, decision makers rely on signals to infer the other’s intention, without considering the possibility that those signals might not reflect the other’s true intention. Finally, in Level 2 strategies, decision makers infer the other player’s intended choice by integrating information contained in their signals with the apparent reliability of the other participant and/or the game’s payoffs. The implications of the HMM were tested across four studies involving 962 participants, with results consistently indicating the presence of strategies from all three levels of the HMM’s hierarchy.

In social interactions, people frequently encounter gain (i.e., all outcomes aregains from the status-quo) or loss (all outcomes are losses from the status-quo)social dilemmas, where their personal interests conflict with social interests.We ask whether there are any behavioral differences in social interactions whenit comes to gains and losses. Using the Prisoner’s Dilemma games, inthree studies we observed that participants were less cooperative in the lossdomain than in the gain domain. This effect was robust, not moderated by payoffamount (Study 1), cooperation index (Study 1), domain comparison (Studies 1 and2), and personal loss aversion (Study 3). Social motive and belief explainedthis effect: compared to the gain domain, participants in the loss domainaroused more pro-self motive and less prosocial motive, and showed strongerbeliefs that their partner would defect, which led them to cooperate less. Thesefindings suggest that gain and loss domains affect individual motivation andbelief, subsequently affecting strategic choices in social dilemmas.

Rational trust decisions depend on potential outcomes and expectations of reciprocity. In the trust game, outcomes and expectations correspond to the structural factors of risk and temptation. Two experiments investigated how risk and temptation influenced information search and final decisions in the trust game. The central finding was that trustors underemphasized temptation relative to its effects on the expected value of trust. Instead, trustors made decisions egocentrically, focusing on potential outcomes. In Experiment 1, information search data revealed that trustors often made decisions without learning about the payoffs related to temptation. Experiment 2 investigated whether trustors were able to use temptation to form accurate expectations of reciprocity. Trustors understood, but underestimated, the relationship between temptation and the probability of reciprocity. Moreover, they did not fully consider expectations in their final trust decisions. Changes in potential outcomes had larger effects on trust than comparable changes in expectations. These results suggest that levels of trust are too high when the probability of reciprocity is low and too low when that probability is high.

Interventions to increase cooperation in social dilemmas depend on understanding decision makers’ motivations for cooperation or defection. We examined these in five real-world social dilemmas: situations where private interests are at odds with collective ones. An online survey (N = 929) asked respondents whether or not they cooperated in each social dilemma and then elicited both open-ended reports of reasons for their choices and endorsements of a provided list of reasons. The dilemmas chosen were ones that permit individual action rather than voting or advocacy: (1) conserving energy, (2) donating blood, (3) getting a flu vaccination, (4) donating to National Public Radio (NPR), and (5) buying green electricity. Self-reported cooperation is weakly but positively correlated across these dilemmas. Cooperation in each dilemma correlates fairly strongly with self-reported altruism and with punitive attitudes toward defectors. Some strong domain-specific behaviors and beliefs also correlate with cooperation. The strongest example is frequency of listening to NPR, which predicts donation. Socio-demographic variables relate only weakly to cooperation. Respondents who self-report cooperation usually cite social reasons (including reciprocity) for their choice. Defectors often give self-interest reasons but there are also some domain-specific reasons—some report that they are not eligible to donate blood; some cannot buy green electricity because they do not pay their own electric bills. Cooperators generally report that several of the provided reasons match their actual reasons fairly well, but most defectors endorse none or at most one of the provided reasons for defection. In particular, defectors often view cooperation as costly but do not endorse free riding as a reason for defection. We tentatively conclude that cooperation in these settings is based mostly on pro-social norms and defection on a mixture of self-interest and the possibly motivated perception that situational circumstances prevent cooperation in the given situation.

Online experiments have become a valuable research tool for researchers interested in the processes underlying cooperation. Typically, online experiments are asynchronous, participants complete an experiment individually and are matched with partners after data collection has been completed. We conducted a registered report to compare asynchronous and synchronous designs, where participants interact and receive feedback in real-time. We investigated how two features of synchronous designs, pre-decision matching and immediate feedback, influence cooperation in the prisoners dilemma. We hypothesized that 1) pre-decision matching (assigning participants to specific interaction partners before they make decisions) would lead to decreased social distance and increased cooperation; 2) immediate feedback would reduce feelings of aversive uncertainty and lead to increased cooperation; and 3) individuals with prosocial Social Value Orientations would be more sensitive to the differences between synchronous and asynchronous designs. We found no support for these hypotheses. In our study (N = 1,238), pre-decision matching and immediate feedback had no significant effects on cooperative behavior or perceptions of the interaction; and their effects on cooperation were not significantly moderated by Social Value Orientation. The present results suggest that synchronous designs have little effect on cooperation in online social dilemma experiments.

Social dilemmas occur when the pursuit of self-interest by individuals in a group leads to less than optimal collective outcomes for everyone in the group. A critical assumption in the human sciences is that people's choices in such dilemmas are individualistic, selfish, and rational. Hence, cooperation in the support of group welfare will only occur if there are selfish incentives that convert the social dilemma into a nondilemma. In recent years, inclusive fitness theories have lent weight to such traditional views of rational selfishness on Darwinian grounds. To show that cooperation is based on selfish incentives, however, one must provide evidence that people do not cooperate without such incentives. In a series of experimental social dilemmas, subjects were instructed to make single, anonymous choices about whether or not to contribute money for a shared “bonus” that would be provided only if enough other people in the group also contributed their money. Noncontributors cited selfish reasons for their choices; contributors did not. If people are allowed to engage in discussion, they will contribute resources at high rates, frequently on irrational grounds, to promote group welfare. These findings are consistent with previous research on ingroup biasing effects that cannot be explained by “economic man” or “selfish gene” theories. An alternative explanation is that sociality was a primary factor shaping the evolution of Homo sapiens. The cognitive and affective mechanisms underlying such choices evolved under selection pressures on small groups for developing and maintaining group membership and for predicting and controlling the behavior of other group members. This sociality hypothesis organizes previously inexplicable and disparate phenomena in a Darwinian framework and makes novel predictions about human choice.