Abstract
BackgroundOur body schema gives the subjective impression of being highly stable. However, a number of easily-evoked illusions illustrate its remarkable malleability. In the rubber-hand illusion, illusory ownership of a rubber-hand is evoked by synchronous visual and tactile stimulation on a visible rubber arm and on the hidden real arm. Ownership is concurrent with a proprioceptive illusion of displacement of the arm position towards the fake arm. We have previously shown that this illusion of ownership plus the proprioceptive displacement also occurs towards a virtual 3D projection of an arm when the appropriate synchronous visuotactile stimulation is provided. Our objective here was to explore whether these illusions (ownership and proprioceptive displacement) can be induced by only synchronous visuomotor stimulation, in the absence of tactile stimulation.Methodology/Principal FindingsTo achieve this we used a data-glove that uses sensors transmitting the positions of fingers to a virtually projected hand in the synchronous but not in the asynchronous condition. The illusion of ownership was measured by means of questionnaires. Questions related to ownership gave significantly larger values for the synchronous than for the asynchronous condition. Proprioceptive displacement provided an objective measure of the illusion and had a median value of 3.5 cm difference between the synchronous and asynchronous conditions. In addition, the correlation between the feeling of ownership of the virtual arm and the size of the drift was significant.Conclusions/SignificanceWe conclude that synchrony between visual and proprioceptive information along with motor activity is able to induce an illusion of ownership over a virtual arm. This has implications regarding the brain mechanisms underlying body ownership as well as the use of virtual bodies in therapies and rehabilitation.
Highlights
The problem of self-recognition is concerned with how the central nervous system distinguishes what is part of the body and what is not
In this paper we extend these results by exploiting a virtual reality system, and hand tracking with a data glove, showing that the illusion of ownership of the virtually presented hand occurs on the basis of visuomotor synchrony between movements of the real hand and the virtual hand
The results we obtain with visuomotor synchrony are very similar to those of both the visuotactile synchrony based rubber hand [2] and virtual hand illusions [3]
Summary
The problem of self-recognition is concerned with how the central nervous system distinguishes what is part of the body and what is not. A demonstration that the problem of self-recognition is not straightforward is the fact that it is easy to generate illusions that involve misattribution of a rubber hand [2] or even a hand displayed in virtual reality [3] to the self. This is achieved through tactile stimulation of the hidden real hand and corresponding and synchronous visual stimulation on the visible fake hand. In the rubber-hand illusion, illusory ownership of a rubber-hand is evoked by synchronous visual and tactile stimulation on a visible rubber arm and on the hidden real arm. Our objective here was to explore whether these illusions (ownership and proprioceptive displacement) can be induced by only synchronous visuomotor stimulation, in the absence of tactile stimulation
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