Abstract
The rubber hand illusion (RHI) is a phenomenon in which hidden human touches to a hand are perceived as arising from a fake hand. The RHI is known to reflect the role of multisensory interaction in coherent body representation. While RHI has mainly been studied using tactile stimuli provided by an experimenter, sensory consequences from self-produced stimulation have been shown to elicit percepts that differ from those given by identical, but externally produced, stimulation. Here we investigated whether an externally-produced stimulus is essential for eliciting the RHI. To address this issue, a 3D haptic device was used. This device allows participants to touch their own real, but hidden, hand while simultaneously viewing a virtual fake hand. Two conditions involved self-produced-touch and externally-produced-touch. In the self-produced-touch condition, participants moved their right hand with the haptic device to repeatedly touch their invisible real left hand. In this condition, a virtual left hand was visible and the pointer of the haptic device touched this hand in perfect synchrony with a participant's right hand motions. In the externally-produced-touch condition, an experimenter repeatedly touches a participant's real hidden (left) hand, again using the haptic device. Results indicated that RHI emerged in both conditions. Participants' reports of proprioceptive drifts from real hand position showed RHI in the self-produced-touch condition although amplitudes of the drifts were smaller than in the externally-produced-touch condition. Average ratings on the RHI questionnaire provided converging data. These findings lead to the conclusions that self-produced stimulation can elicit an RHI illusion that conveys a feeling of ownership of a visible fake hand, and externally-produced tactile stimulation appears unnecessary for RHI. Causes of reduced RHI with self-produced tactile stimulation are discussed.