The Rubber Hand Illusion Depends on the Tactile Congruency of the Observed and Felt Touch

The rubber hand illusion (RHI) occurs when the participants' own unseen hand is stroked in synchrony with an observed rubber hand. It manifests itself in terms of a tendency to misreport the position of one's own hand as nearer to the rubber hand (proprioceptive drift) and in terms of feelings of ownership of the rubber hand. Many studies have examined whether the illusion depends on characteristics of the hand (e.g., orientation, skin color), but very few have examined the importance of the tool that delivers the tactile sensation. We demonstrate that the RHI depends on the congruency of the tool used to stroke the real/rubber hands. The RHI is diminished when using tools that are incongruent with respect to their visual appearance and predicted tactile consequences (e.g., touching the dummy with a pencil and the real hand with a paintbrush) relative to when they are congruent. Theoretical models of visuotactile integration used to explain the RHI need to be extended to incorporate the qualitative nature of the observed and felt touch and not just its synchrony and location.