In the latest experiment, vibrating pads with flashing lights were positioned on the subjects' backs. Virtual bodies were generated by a camera filming their backs and were viewed as though 2 metres in front of the subjects through a head-mounted display. Repeated stroking of their backs, and the sight of the doppelganger being stroked, created the feeling that they were outside of their bodies.

At the same time, the subjects saw flashes on their virtual bodies, and felt vibrations on their real bodies. Participants were asked to ignore the flashing lights and only report where the vibrations were by pressing a button as fast as possible. The extent to which the flashing light interfered with the reporting of the vibrations was an indicator of where subjects perceived the spatial location of the vibrations to be.

Some volunteers had out-of-body experiences and reported that the vibrations were felt in the location where the flash was seen on their virtual body.

'Promising future'

"This technology, although currently in basic research, seems to have a very promising future for clinical applications in restoring lost motor functions in paralysed people," says bioethicist Jens Clausen at the Institute for Ethics and the History of Medicine at the University of Tűbingen in Germany. "It's important to integrate prosthetics into one's self concept"

Because this work confirms that people can be made to feel that a touch on the real body is a touch on the virtual body, Jane Aspell of theLaboratory of Cognitive Neuroscience at the Swiss Federal Institute of Technology in Lausanne, who led the study, says: "This emerging field has interesting implications for virtual computer gaming, such as making avatars seem more real and increasing presence in the VR environment."

Aware animals?

Although full out-of-body experiences in the lab remain elusive, the group is now aiming to boost the illusion by inducing the subject to identify more strongly with the virtual body.

The advantage of this technique, in contrast to previous methods that only used questionnaires, is that sensory perception is measured during the test, and these behavioural measures are less biased as they require no higher-order reflection, says Aspell. This means that it might be appropriate to use the method in a clinical setting where some patients report neurological out-of-body experiences, for example.

Modified versions of these experiments could even be used in animals, the authors say – allowing scientists to look into whether self-consciousness is unique to humans or whether animals have some sense of self. Because the method doesn't require the filling in of a questionnaire, animals could possibly be trained to use the equipment.

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