Paranoid thinking and perceived competitive intention.

Paranoid thinking, that others are hostile, can be seen even in the general population. Paranoia is considered the expectation that others are competitors who aim to maximize the differences in payoffs rather than maximize their own payoffs. This study examined whether paranoia reflects the irrational belief that others have a competitive intention and is associated with avoiding perceived competition. We recruited 884 US residents via the Internet and conducted a modified Dictator Game, in which monetary allocation was carried out between the Dictator and the Recipient. The Dictator chooses either fair or competitive allocation while selecting the competitive allocation is irrelevant to increasing the Dictator's payoffs. The Recipient decides whether to accept the Dictator's decision or receive sure but low rewards. We found that Recipients with high-level paranoid thinking expected their opponent to select competitive allocation more than those with low levels, even when selecting it was costly for Dictators. Paranoid thinking was not associated with selecting sure rewards or competitive allocations. The results suggest that paranoia reflects the belief that others have a competitive intention but is not related to avoidance behavior against perceived threats and unilateral attacks.

Conjecturing Harmful Intent and Preemptive Strike in Paranoia.

Paranoia depicts a belief of others having harmful intent. Research using economic games has exhibited the correlation between paranoia and the propensity to characterize ambiguous intentions as harmful. Using a non-clinical sample recruited online from the United States (N=290), we examined whether paranoid thoughts influence aggressive behavior against the subjective perception of harmful intent. We conducted a preemptive strike game wherein aggressive behavior was assumed to be guided by the fear of an opponent. The outcomes indicate that (1) individuals with high paranoia assume harmful intent of an opponent more than those with low paranoia (2) conjecturing an opponent's harmful intent predicted an increase in the probability of a preemptive strike, and (3) paranoia did not have a statistically significant effect on encouraging a preemptive strike. Additionally, the exploratory analysis revealed that paranoia was related to participant's aggressiveness and with suppositions of other's self-interests and competitiveness. This study presents empirical evidence that paranoia is related to the perception of social threats in an uncertain situation. We discuss the possibility that paranoid ideation can promote or inhibit a preemptive strike.

Greater effects of mutual cooperation and defection on subsequent cooperation in direct reciprocity games than generalized reciprocity games: Behavioral experiments and analysis using multilevel models.

Reciprocity toward a partner's cooperation is a fundamental behavioral strategy underlying human cooperation not only in interactions with familiar persons but also with strangers. However, a strategy that takes into account not only one's partner's previous action but also one's own previous action-such as a win-stay lose-shift strategy or variants of reinforcement learning-has also been considered an advantageous strategy. This study investigated empirically how behavioral models can be used to explain the variances in cooperative behavior among people. To do this, we considered games involving either direct reciprocity (an iterated prisoner's dilemma) or generalized reciprocity (a gift-giving game). Multilevel models incorporating inter-individual behavioral differences were fitted to experimental data using Bayesian inference. The results indicate that for these two types of games, a model that considers both one's own and one's partner's previous actions fits the empirical data better than the other models. In the direct reciprocity game, mutual cooperation or defection-rather than relying solely on one's partner's previous actions-affected the increase or decrease, respectively, in subsequent cooperation. Whereas in the generalized reciprocity game, a weaker effect of mutual cooperation or defection on subsequent cooperation was observed.

Cultural Differences in Strength of Conformity Explained Through Pathogen Stress: A Statistical Test Using Hierarchical Bayesian Estimation.

The severity of the environment has been found to have played a selective pressure in the development of human behavior and psychology, and the historical prevalence of pathogens relate to cultural differences in group-oriented psychological mechanisms, such as collectivism and conformity to the in-group. However, previous studies have also proposed that the effectiveness of institutions, rather than pathogen stress, can account for regional variation in group-oriented psychological mechanisms. Moreover, previous studies using nations as units of analysis may have suffered from a problem of statistical non-independence, namely, Galton's problem. The present study tested whether or not regional variation in pathogen stress, rather than government effectiveness, affected collectivism and conformity to social norms by adjusting the effect of global regions using hierarchical Bayesian estimation. We found that the overall effect of pathogen stress remained significant in only one out of the four indices of the regional variability of conformity, and the effects of the government effectiveness also disappeared. Instead, we found that significant effects of both pathogen stress and government effectiveness in specific regions of the world, but these effects were not stable across the measurements. These results indicate that both the effects of pathogen stress and government effectiveness need further reevaluation.

Reinforcement learning accounts for moody conditional cooperation behavior: experimental results.

In social dilemma games, human participants often show conditional cooperation (CC) behavior or its variant called moody conditional cooperation (MCC), with which they basically tend to cooperate when many other peers have previously cooperated. Recent computational studies showed that CC and MCC behavioral patterns could be explained by reinforcement learning. In the present study, we use a repeated multiplayer prisoner's dilemma game and the repeated public goods game played by human participants to examine whether MCC is observed across different types of game and the possibility that reinforcement learning explains observed behavior. We observed MCC behavior in both games, but the MCC that we observed was different from that observed in the past experiments. In the present study, whether or not a focal participant cooperated previously affected the overall level of cooperation, instead of changing the tendency of cooperation in response to cooperation of other participants in the previous time step. We found that, across different conditions, reinforcement learning models were approximately as accurate as a MCC model in describing the experimental results. Consistent with the previous computational studies, the present results suggest that reinforcement learning may be a major proximate mechanism governing MCC behavior.

Reinforcement Learning Explains Conditional Cooperation and Its Moody Cousin.

Direct reciprocity, or repeated interaction, is a main mechanism to sustain cooperation under social dilemmas involving two individuals. For larger groups and networks, which are probably more relevant to understanding and engineering our society, experiments employing repeated multiplayer social dilemma games have suggested that humans often show conditional cooperation behavior and its moody variant. Mechanisms underlying these behaviors largely remain unclear. Here we provide a proximate account for this behavior by showing that individuals adopting a type of reinforcement learning, called aspiration learning, phenomenologically behave as conditional cooperator. By definition, individuals are satisfied if and only if the obtained payoff is larger than a fixed aspiration level. They reinforce actions that have resulted in satisfactory outcomes and anti-reinforce those yielding unsatisfactory outcomes. The results obtained in the present study are general in that they explain extant experimental results obtained for both so-called moody and non-moody conditional cooperation, prisoner's dilemma and public goods games, and well-mixed groups and networks. Different from the previous theory, individuals are assumed to have no access to information about what other individuals are doing such that they cannot explicitly use conditional cooperation rules. In this sense, myopic aspiration learning in which the unconditional propensity of cooperation is modulated in every discrete time step explains conditional behavior of humans. Aspiration learners showing (moody) conditional cooperation obeyed a noisy GRIM-like strategy. This is different from the Pavlov, a reinforcement learning strategy promoting mutual cooperation in two-player situations.

Transient nature of cooperation by pay-it-forward reciprocity.

Humans often forward kindness received from others to strangers, a phenomenon called the upstream or pay-it-forward indirect reciprocity. Some field observations and laboratory experiments found evidence of pay-it-forward reciprocity in which chains of cooperative acts persist in social dilemma situations. Theoretically, however, cooperation based on pay-it-forward reciprocity is not sustainable. We carried out laboratory experiments of a pay-it-forward indirect reciprocity game (i.e., chained gift-giving game) on a large scale in terms of group size and time. We found that cooperation consistent with pay-it-forward reciprocity occurred only in a first few decisions per participant and that cooperation originated from inherent pro-sociality of individuals. In contrast, the same groups of participants showed persisting chains of cooperation in a different indirect reciprocity game in which participants earned reputation by cooperating. Our experimental results suggest that pay-it-forward reciprocity is transient and disappears when a person makes decisions repeatedly, whereas the reputation-based reciprocity is stable in the same situation.

[Effect of consensus on punitive behavior].

In addition to the cost of punishment, the fear that others would evaluate punishers negatively can be a major obstacle for resolving the second-order social dilemma or failure of providing sanctions useful for solving a social dilemma problem. In an experiment with 81 participants, we tested whether providing information that other participants were in favor of punishing non-cooperators in a social dilemma situation would enhance cooperation in the second-order dilemma (i.e., punishment of non-cooperators). Participants received feedback of three bogus "participants" choices in a four-person social dilemma, in which one bogus participant defected and two others cooperated, and then received a chance to punish the sole non-cooperator. The hypothesis was supported among those who were motivated to punish the non-cooperator. They punished the non-cooperator when they were informed that the other participants also wanted to punish the non-cooperator. The feedback information that the other participants wanted to punish the non-cooperator induced the participants who were not motivated to punish the non-cooperator to punish less.

Rejection of unfair offers in the ultimatum game is no evidence of strong reciprocity.

The strong reciprocity model of the evolution of human cooperation has gained some acceptance, partly on the basis of support from experimental findings. The observation that unfair offers in the ultimatum game are frequently rejected constitutes an important piece of the experimental evidence for strong reciprocity. In the present study, we have challenged the idea that the rejection response in the ultimatum game provides evidence of the assumption held by strong reciprocity theorists that negative reciprocity observed in the ultimatum game is inseparably related to positive reciprocity as the two sides of a preference for fairness. The prediction of an inseparable relationship between positive and negative reciprocity was rejected on the basis of the results of a series of experiments that we conducted using the ultimatum game, the dictator game, the trust game, and the prisoner's dilemma game. We did not find any correlation between the participants' tendencies to reject unfair offers in the ultimatum game and their tendencies to exhibit various prosocial behaviors in the other games, including their inclinations to positively reciprocate in the trust game. The participants' responses to postexperimental questions add support to the view that the rejection of unfair offers in the ultimatum game is a tacit strategy for avoiding the imposition of an inferior status.

Stress hormones predict hyperbolic time-discount rates six months later in adults.

OBJECTIVES: Stress hormones have been associated with temporal discounting. Although time-discount rate is shown to be stable over a long term, no study to date examines whether individual differences in stress hormones could predict individuals' time-discount rates in the relatively distant future (e.g., six month later), which is of interest in neuroeconomics of stress-addiction association. METHODS: We assessed 87 participants' salivary stress hormone (cortisol, cortisone, and alpha-amylase) levels and hyperbolic discounting of delayed rewards consisting of three magnitudes, at the time-interval of six months. For salivary steroid assays, we employed a liquid chromatography/ mass spectroscopy (LC/MS) method. The correlations between the stress hormone levels and time-discount rates were examined. RESULTS: We observed that salivary alpha-amylase (sAA) levels were negatively associated with time-discount rates in never-smokers. Notably, salivary levels of stress steroids (i.e., cortisol and cortisone) negatively and positively related to time-discount rates in men and women, respectively, in never-smokers. Ever-smokers' discount rates were not predicted from these stress hormone levels. CONCLUSIONS: Individual differences in stress hormone levels predict impulsivity in temporal discounting in the future. There are sex differences in the effect of stress steroids on temporal discounting; while there was no sex defference in the relationship between sAA and temporal discounting.

[Adaptive foundation of group-based reciprocity].

A one-shot sequential prisoner's dilemma game with an in-group and an out-group member was conducted to test the group heuristic hypothesis for the in-group bias in minimal groups. Eighty-nine participants played the role of a second player and faced a fully cooperative first player. The results showed that in-group bias occurred only in the common knowledge condition in which the first player and the second player mutually knew each other's group membership, but not in the private knowledge condition in which the first player did not know the second player's group membership. These results provide support for the group heuristic hypothesis that in-group bias is an adaptive strategy in an assumed generalized exchange system to avoid a bad reputation as a defector.

[Accuracy of judgment about others' cooperative behavior: effects of attractiveness and facial expressiveness].

Cooperation in interdependent relationships is based on reciprocity in repeated interactions. However, cooperation in one-shot relationships cannot be explained by reciprocity. Frank, Gilovich, & Regan (1993) argued that cooperative behavior in one-shot interactions can be adaptive if cooperators displayed particular signals and people were able to distinguish cooperators from non-cooperators by decoding these signals. We argue that attractiveness and facial expressiveness are signals of cooperators. We conducted an experiment to examine if these signals influence the detection accuracy of cooperative behavior. Our participants (blind to the target's behavior in a Trust Game) viewed 30-seconds video-clips. Each video-clip was comprised of a cooperator and a non-cooperator in a Trust Game. The participants judged which one of the pair gave more money to the other participant. We found that participants were able to detect cooperators with a higher accuracy than chance. Furthermore, participants rated male non-cooperators as more attractive than male cooperators, and rated cooperators more expressive than non-cooperators. Further analyses showed that attractiveness inhibited detection accuracy while facial expressiveness fostered it.

Salivary testosterone levels and autism-spectrum quotient in adults.

OBJECTIVES: The purpose of this study is to examine the relationship between salivary testosterone levels and autistic traits in adults. METHODS: A total of 92 male and female adults participated in the present study. Their salivary testosterone level (T) and score of Japanese version of Autism-spectrum Quotient (AQ) were assessed to examine the relationship between salivary testosterone level and autistic traits in adults. RESULTS: We observed a positive correlation between T and AQ in a group of both sexes. The correlation disappeared when we conducted correlation analysis by sex. However, although there was no sex difference in the score of the subscale of attention switching, attention switching was related to T. CONCLUSIONS: Although the relationship between T and AQ may mainly result from sex differences, the subscale of attention switching may be modulated by testosterone.

Salivary alpha-amylase levels and big five personality factors in adults.

OBJECTIVES: Salivary alpha-amylase (sAA) has been utilized as a non-invasive measure of sympathoadrenal medullary (SAM) activation. Little is known regarding the relationship between personality inventories and baseline sAA. This study was designed to examine the relationships between the scores of big five inventory (BFI) factors, age, and sAA in adults (aged twenty to seventy years old). METHODS: We assessed 97 participants' BFI scores and sAA. The correlations between the BFI factor scores and sAA were examined. RESULTS: We observed (1) a positive correlation between Neuroticism and sAA, and a negative correlation between Agreeableness and sAA and (2) a positive correlation between age and sAA. These correlations between BFI scores and sAA remained significant after controlling for age. After controlling for age, all BFI factors except Conscientiousness were related to sAA. CONCLUSIONS: Subjects with high Neuroticism and low Extraversion, Agreeableness and Openness may have high sAA. sAA has been demonstrated to be useful for examining the relationship between adrenergic activity and personality, in a non-invasive manner.

The private rejection of unfair offers and emotional commitment.

In a series of experiments, we demonstrate that certain players of an economic game reject unfair offers even when this behavior increases rather than decreases inequity. A substantial proportion (30-40%, compared with 60-70% in the standard ultimatum game) of those who responded rejected unfair offers even when rejection reduced only their own earnings to 0, while not affecting the earnings of the person who proposed the unfair split (in an impunity game). Furthermore, even when the responders were not able to communicate their anger to the proposers by rejecting unfair offers in a private impunity game, a similar rate of rejection was observed. The rejection of unfair offers that increases inequity cannot be explained by the social preference for inequity aversion or reciprocity; however, it does provide support for the model of emotion as a commitment device. In this view, emotions such as anger or moral disgust lead people to disregard the immediate consequences of their behavior, committing them to behave consistently to preserve integrity and maintain a reputation over time as someone who is reliably committed to this behavior.

[Reciprocity and identity protection: reasons for rejection in the ultimatum game].

An ultimatum game and two impunity games, in which rejection by the Responder had no impact on the Proposer's earnings, were conducted with 228 participants. The impunity game was run in two conditions: with feedback information, where the Responder's choice was disclosed to the Proposer, and without feedback information, where the Responder's choice was not disclosed to the Proposer. These two conditions were used to determine whether the motivation for rejection in the impunity game was social punishment or identity protection. The three game conditions and the Responder or Proposer roles were manipulated between participants. The rejection rates in the two impunity games were about half the rate in the ultimatum game: there was no difference in the rejection rates between the two feedback conditions of the impunity game. These results indicate that rejection in the ultimatum game is largely based on identity protection. The adaptive role of maintaining self-image as a commitment device was discussed.