Body Ownership and the Motor System: Rapid Facilitation of Embodied Fake Hand Movement on Actual Movement Execution.

Body ownership-the perception that one's body belongs to oneself-has been explored using a rubber hand illusion, in which individuals misperceive a fake hand as their own (i.e., embodiment of the fake hand) when an unseen real hand and a visible fake hand are stroked synchronously. Thus, the movement of an embodied fake body may be represented in one's own sensorimotor system. Using a combination of the rubber hand illusion and a motor task, we investigated whether simple movement of the embodied fake hand influenced the subsequent movement of the participants' hand. The participants lifted their own index finger immediately upon observing the index finger lifting on the embodied (rubber hand illusion) or non-embodied (non-rubber hand illusion) fake hand (Experiment 1), and a light-emitting diode turning on near the fake hand (Experiment 2). The reaction times, peak velocities, and peak acceleration were extracted from the participants' finger-lifting movements. In Experiment 1, the reaction time was significantly shorter in the rubber hand illusion condition than in the non-rubber hand illusion condition, suggesting the rapid facilitation effect of embodied fake hand movement on actual movement. However, no such motor facilitation was observed in Experiment 2, confirming that the improved reaction time in Experiment 1 resulted from the visual movement of the fake hand rather than attention to the fake hand itself. In contrast to the reaction time, the peak velocity and acceleration did not differ significantly in either experiment. These findings reflect the similar sensorimotor representations of illusory and actual self-movement.