Experimental task and conditions. (A) The payoff matrix for the prisoner’s dilemma. Participants engaged in 20 rounds of this task. (B) Counterpart strategies are defined by the probabilities of cooperation following a specific outcome10. We consider the extortion (starting with defection) and generosity (starting with cooperation) strategies. (C) The validated facial expressions for the counterpart’s virtual representation in the task. (D) Two emotion expression patterns were considered: cooperative (e.g., joy following mutual cooperation) and competitive (e.g., joy following participant exploitation).