Game structure shapes individuals' norms in collective decision-making

Abstract

Collective decision-making often requires individuals to reconcile private benefits with collective benefits of cooperation. Norms can sustain the cooperation by shaping how individuals evaluate consequences of actions and respond to shared behavioral standard. However, whether different game structures give rise to different norms, and the specific mechanisms underlying such effects, remain unclear. Here, we compared linear and threshold public goods games (LPGGs and TPGGs) in repeated four-person interactions, combining model-free behavioral analysis, agent-based modelling and fNIRS hyperscanning. LPGG produced more dynamic contribution updating and was more influenced by others' recent behavior, whereas TPGG showed more stable consensus and stronger punishment enforcement. Agent-based modelling revealed a corresponding dissociation: LPGG placed greater weight on consequence-based social norms, whereas TPGG showed stronger conformity-based norms. These normative differences were accompanied by distinct neural characteristics. TPGG elicited stronger rTPJ activation, which was positively associated with contributions. dmPFC--rTPJ connectivity tracked distinct consequence-based social parameters, namely the baseline weight in TPGG and context-dependent modulation in LPGG. At the group level, interaction-specific dmPFC inter-brain neural synchrony emerged only in TPGG but not in LPGG. Together, these findings show that game structure does more than alter incentives: it reorganizes the behavioral, computational and neural mechanisms through which norms sustain collective cooperation.