Similarity of actions depends on the functionality of previously observed actions

People have a tendency to imitate the behavior of others, sometimes even automatically. And yet, evidence suggests that many of our actions are controlled, mediated by current goals and careful considerations. Here, we investigated whether the observation and evaluation of previous actions of another person modulates the similarity of actions between people in present trials. We manipulated the functionality of a confederate's actions and the interactive context in 2 behavioral tasks, which consisted of games that participants played against a confederate or a virtual computer opponent. To measure effects of working memory load on imitation rates, participants additionally performed an easy or difficult auditory n-back task in parallel to the tasks. We show that participants occasionally produced rather bizarre and dysfunctional behavior when the confederate had done so as well. Even more importantly, results from both tasks show that participants most likely copied dysfunctional behavior in the present trial when the confederate performed functional actions in the previous trial. Thus, the positive evaluation of action consequences in previous trials increases the probability of similarity between the participant's and confederate's actions in present trials despite a chance to copy improper actions. Furthermore, we found a trend of increased action similarities when participants were under high working memory load in Experiment 1 but not in Experiment 2. These results suggest that copying an observed action is an efficient and effortless behavioral and social strategy to achieve similar goals as others, though with an increased risk of maladaptive behavior.