Single-shot Prisoner's Dilemma Research Articles

Sequential interactions—in which one player plays first and another responds—promote cooperation in evolutionary-dynamical simulations of single-shot Prisoner's Dilemma and Snowdrift games

Cooperation is a central topic in evolutionary biology because (a) it is difficult to reconcile why individuals would act in a way that benefits others if such action is costly to themselves, and (b) it underpins many of the ‘major transitions of evolution’, making it essential for explaining the origins of successively higher levels of biological organization. Within evolutionary game theory, the Prisoner's Dilemma and Snowdrift games are the main theoretical constructs used to study the evolution of cooperation in dyadic interactions. In single-shot versions of these games, wherein individuals play each other only once, players typically act simultaneously rather than sequentially. Allowing one player to respond to the actions of its co-player—in the absence of any possibility of the responder being rewarded for cooperation or punished for defection, as in simultaneous or sequential iterated games—may seem to invite more incentive for exploitation and retaliation in single-shot games, compared to when interactions occur simultaneously, thereby reducing the likelihood that cooperative strategies can thrive. To the contrary, I use lattice-based, evolutionary-dynamical simulation models of single-shot games to demonstrate that under many conditions, sequential interactions have the potential to enhance unilaterally or mutually cooperative outcomes and increase the average payoff of populations, relative to simultaneous interactions—benefits that are especially prevalent in a spatially explicit context. This surprising result is attributable to the presence of conditional strategies that emerge in sequential games that can't occur in the corresponding simultaneous versions.

Parallel versus Sequential Update and the Evolution of Cooperation with the Assistance of Emotional Strategies

Our study contributes to the debate on the evolution of cooperation in the single-shot Prisoner's Dilemma (PD) played on networks. We construct a model in which individuals are connected with positive and negative ties. Some agents play sign-dependent strategies that use the sign of the relation as a shorthand for determining appropriate action toward the opponent. In the context of our model in which network topology, agent strategic types and relational signs coevolve, the presence of sign-dependent strategies catalyzes the evolution of cooperation. We highlight how the success of cooperation depends on a crucial aspect of implementation: whether we apply parallel or sequential strategy update. Parallel updating, with averaging of payoffs across interactions in the social neighborhood, supports cooperation in a much wider set of parameter values than sequential updating. Our results cast doubts about the realism and generalizability of models that claim to explain the evolution of cooperation but implicitly assume parallel updating.

Opposing BOLD responses to reciprocated and unreciprocated altruism in putative reward pathways

Mesencephalic dopamine neurons are believed to facilitate reward-dependent learning by computing errors in reward predictions. We used fMRI to test whether this system was activated as expected in response to errors in predictions about whether a social partner would reciprocate an act of altruism. Nineteen subjects received fMRI scans as they played a series of single-shot Prisoner's Dilemma games with partners who were outside the scanner. In both ventromedial prefrontal cortex and ventral striatum, reciprocated and unreciprocated cooperation were associated with positive and negative BOLD responses, respectively. Our results are consistent with the hypothesis that mesencephalic dopamine projection sites carry information about errors in reward prediction that allow us to learn who can and cannot be trusted to reciprocate favors.

Biased face recognition in the Prisoner's Dilemma Game

Students were asked to participate in a series of single-shot Prisoner's Dilemma games. Each subject chose a strategy before the experiment began and was required to play the same strategy with each opponent. These “opponents” were photographic reproductions of young women and men, accompanied by labels indicating whether they were cooperators or defectors. Subjects also rated the attractiveness of the opponents. One week later, subjects again rated the photographs without descriptions. Half of the photographs had been seen previously and half were new. Subjects were asked to report which of the photographs they remembered from the previous week. Effects of the four factors (strategy and sex of opponents, and strategy and sex of subjects) on the number of photographs recognized were investigated. The strategy and sex of subjects had no apparent effects, whereas strategy and sex of opponents had a significant interactive influence: Males who had been portrayed as defectors and both groups of females were recognized at higher rates than males who had been portrayed as cooperators. The present study indicates that the biased face recognition of potential cheaters is too robust to be affected by the strategy and sex of subjects, whereas a difference results from the sex of faces presented to subjects.

Effective choice in the single-shot Prisoner's Dilemma tournament

This paper discusses the results of a single-shot Prisoner's Dilemma computer tournament. In the single-shot Prisoner's Dilemma tournament each pair of players interacts only once. But players can establish and detect reputations because they know how their current opponent has behaved in previous games with other players. The results show that cooperation is worthwhile, even in single-shot games, provided the outcomes of previous games are common knowledge.

The social implications of nonzero-sum games

It is argued that a reorientation of the theory and application of nonzero-sum (NZS) games is needed in order for that discipline to have a beneficial impact on societal problems such as war. Accordingly, a general strategy of cooperation with minimum sanctions (CMS) is developed and applied to prisoner's dilemma (PD) and dollar auction games. It is shown that tit-for-tat-like strategies are appropriate for all PD games, not just iterated PD, and that, contrary to previous consensus, it is rational to cooperate in the single-shot PD. In evaluating NZS strategies in human or computerized tournaments, special NZS scoring rules should be used. A water-division bargaining example is included to illustrate the superiority of the maximum-welfare approach to the Nash bargaining solution.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>