Offer of a reward does not always promote trust in spatial games

TL;DR

This study investigates how different reward mechanisms influence trust in spatial trust games, revealing that excessive rewards can undermine trust, while moderate rewards can promote it under certain conditions.

Contribution

Introduces an inter-role reward mechanism in spatial trust games and demonstrates its complex effects on trust evolution through extensive simulations.

Findings

Moderate rewards can promote trust by breaking mistrust dominance.

Excessive rewards may lead to nonreturn strategies, suppressing trust.

Lower reward costs do not necessarily enhance trust, while moderate, costly rewards do.

Abstract

Trust is one of the cornerstones of human society. One of the evolutionary pressure mechanisms that may have led to its emergence is the presence of incentives for trustworthy behavior. However, this type of reward has received relatively little attention in the context of spatial trust games, which are often used to build models in evolutionary game theory. To fill this gap, we introduce an inter-role reward mechanism in the spatial trust game, so that an investing trustor can choose to pay an extra cost to reward a trustworthy trustee. With extensive numerical simulations, we find that this type of reward does not always promote trust. Rather, while moderate rewards break the dominance of mistrust, thereby favoring investment, excessive rewards eventually stimulate a nonreturn strategy, ultimately suppressing the evolution of trust. Additionally, lower reward costs do not necessarily promote trust. Instead, more costly, but not excessive, rewards enhance the advantage of the original investment, consolidating the clusters of rewarders and improving trust. Our model thus provides evidence about the counterintuitive nature of the relationship between trust and rewards in a complex society.