Event-related potential and behavioural evidence of goal-based expectations for consistent actions among group members

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People expect group members to act consistently. However, because actions are organized hierarchically, incorporating deep-level goals and shallow-level movements, it remains unclear what level of action is expected to be consistent among group members. We determined that these two levels of action representations can be dissociated in object-directed actions and measured the late positive potential (LPP), which indicates expectation. We found that participants identified a new agent's actions more quickly when this agent pursued a consistent goal while moving in a manner inconsistent with group members than when this agent pursued an inconsistent goal while moving in the same manner as group members. Moreover, this facilitation effect disappeared when the new agent was from a different group, revealing goal-based expectations for consistent actions among group members. The LPP amplitude during the action-expectation phase was greater for agents from the same group than for agents from a different group, suggesting that people implicitly generate clearer action expectations for group members than for other individuals. Additionally, the behavioural facilitation effect was observed when the goal of actions was clearly identifiable (i.e. performing rational actions to reach an external target) rather than when there was no clear association between actions and external targets (i.e. performing irrational actions). The LPP amplitude during the action-expectation phase was greater after observing rational actions than after observing irrational actions performed by two agents from the same group, and the expectation-related increase in LPP predicted the behavioural measurements of the facilitation effect. Hence, the behavioural and event-related potential evidence suggest that people implicitly expect group members to behave consistently according to goals rather than movements per se.