Distinct Motor Contagions During and After Observation of Actions by a Humanoid Co-Worker

Multiple studies have shown that the mere observation of movements by a robot can affect an observing human's movement; effects referred to as motor contagions. However, previous studies have either analyzed motor contagions induced during (which we call on-line contagions), or induced after (off-line contagions) observation of the robot, but never both together. It thus remains unclear whether and how these two contagions differ from each other. Here, in an empirical industrial co-worker setting, we examine the differences in the off-line and on-line contagions induced in participants by the observation of the same movements performed by a human, or a humanoid robot co-worker. We observed that while the off-line contagions predominantly affect the participant's movement velocity, the on-line contagions affect their movement frequency. Furthermore, the off-line contagions were prominent after observing another human, while the on-line contagions were equally strong with either a human or a humanoid coworker. These results suggest that actions by a humanoid robot can induce distinct effects on human behaviors, during and after observation.