Virtual hand illusion induced by visuomotor correlations.
BACKGROUND
Our 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.


RESULTS
To 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
We 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.
Sanchez-Vives
Maria V
MV
Institució Catalana de Recerca i Estudis Avançats, Barcelona, Spain. msanche3@clinic.ub.es
Spanlang
Bernhard
B
Frisoli
Antonio
A
Bergamasco
Massimo
M
Slater
Mel
M
D000293:Adolescent; D000328:Adult; D005385:Fingers; D006225:Hand; D006801:Humans; D008297:Male; D009903:Optical Illusions; D011434:Proprioception; D055698:Touch Perception; D014796:Visual Perception; D055815:Young Adult
Behav Brain Res. 2003 Jun 16;142(1-2):1-15
12798261
J Neurosci. 2005 Nov 9;25(45):10564-73
16280594
Conscious Cogn. 2006 Jun;15(2):423-32
16343947
Neuropsychologia. 1998 Nov;36(11):1133-40
9842759
Proc Natl Acad Sci U S A. 2008 Sep 2;105(35):13169-73
18725630
Perception. 2009;38(2):271-80
19400435
Cognition. 2002 Sep;85(2):177-87
12127698
Front Hum Neurosci. 2008 Aug 20;2:6
18958207
Behav Brain Res. 2008 Aug 5;191(1):1-10
18423906
J Cogn Neurosci. 2001 Apr 1;13(3):332-40
11371311
Nat Rev Neurosci. 2005 Apr;6(4):332-9
15803164
Perception. 2009;38(12):1804-20
20192130
Nature. 1998 Feb 19;391(6669):756
9486643
Proc Biol Sci. 2003 Jul 22;270(1523):1499-506
12965016