Perceived differences in partner extraversion and agreeableness modulate task co-representation in joint action

In everyday interactions, our perceptions of a partner's personality traits, such as extraversion and agreeableness, significantly influence how we engage with them. However, joint action research has largely overlooked the impact of these perceived partner traits on the co-representation of partners' task performance in a joint action setup. To address this, we conducted three experiments where participants first learned about their partner's personality through a trait learning task and then performed a joint Simon task with their perceived (not real) partner. Experiment 1 showed that perceived differences in partner extraversion and agreeableness significantly modulated the joint Simon effect (JSE), with a significantly larger JSE observed for partners perceived as extraverted or agreeable compared to those perceived as introverted or disagreeable. In contrast, perceived differences in partner conscientiousness did not exhibit such a modulation effect. Experiment 2 revealed that this modulation effect disappeared when these traits were perceived as peripheral to the partner's personality. Experiment 3 demonstrated similar modulation effects on the JSE as those observed in Experiment 1, while controlling for potential influences of valence. Overall, these results suggest that perceived partner traits, particularly extraversion and agreeableness, can modulate task co-representation. However, this effect occurs only when these traits are central to the partner. These findings highlight the influence of perceived socially relevant traits on shaping task co-representation in a joint action setup.