Action-Induced Rubber Hand Illusion

Abstract

In the rubber hand illusion (RHI), when a rubber hand is observed while the real hand is occluded from view, and the two are stroked synchronously, several illusions can be induced: proprioceptive drift toward the rubber hand, sensation of touch on the rubber hand, and ownership for the rubber hand. RHI has often been demonstrated for hands that are passive. We modified the basic protocol, such that action is required—the pressing of a button. Our device has two buttons, allowing real and rubber hands to press, either synchronously or asynchronously. Participants start a stopwatch when action begins or when stroking begins; they are instructed to stop the stopwatch, as soon as they begin to experience the illusion. Results reveal a significant difference between synchronous and asynchronous conditions for the act of pressing, as measured both by questionnaire and reaction time. Difference in proprioceptive drift, however, is only exhibited in the passive condition. This difference might be due to awareness that we are doing something, and due to what we call, the “silencing” of a subject of experience. We are the first to demonstrate that RHI can be induced not only when hands remain passive, but also when they act.