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The embodied self: Using virtual reality to study the foundations of bodily self-consciousness

August 24, 2007

A group of neuroscientists and a philosopher have devised a series of novel experiments using virtual reality that could shed light on decades of clinical data pointing to cognitive and perceptual mechanisms involved in humans' concept of self. Their results, published August 23 in Science Magazine, show that a person's sense of self can be manipulated using conflicting multisensory bodily input, indicating that spatial unity and bodily self-consciousness depend on brain mechanisms and can be explored experimentally.

The "I" one thinks of as "myself" is inextricably attached to one's bodily location. In patients with certain neurological conditions this sense of spatial unity can break down, causing disturbing sensations such as out-of-body experiences in which the global self is localized outside one's body limits (often called disembodiment).

Previous experiments have shown that people may attribute fake body parts to their own bodies. In the "Rubber Hand Illusion", a person's unseen hand is stroked synchronously with a visible fake hand, and then the person is asked to point to his own hand. Subjects invariably err in the direction of the fake hand, attributing it to their own bodies. Because the attribution does not involve the whole body, the sense of global bodily self-consciousness is not affected. EPFL Professor Olaf Blanke, graduate students Bigna Lenggenhager and Tej Tadi, and philosopher Thomas Metzinger hypothesized that the same approach could be used to study the concept of global bodily self consciousness by using a single, coherent body representation instead of just a body part.

Working with EPFL computer engineers, the researchers designed a series of simple virtual reality experiments in which a subject saw a projection of a three-dimensional representation of his own body, the body of a dummy, or a simple object directly in front of him. The subject then saw the back of the image being stroked with a paintbrush, either in or out of sync with someone stroking his own back. Immediately after, the subject was blindfolded and backed up, and then asked to return to his original position. Subjects whose backs were stroked synchronously with the virtual image of himself or the human dummy consistently overshot their position in the direction of the image; but subjects who saw no virtual image or a simple object did not. The synchronously stroked subjects went farther in the direction of the virtual image than those who were stroked out of sync.

According to the researchers, several subjects reported feeling "weird" but none actually reported the disembodiment classically described in an out-of-body experience. They knew the body image was not theirs. Despite this, the subjects still localized their selves to a position outside their own bodies, indicating that the brain is compiling a sense of spatial unity from an integration of visual, somatosensory and cognitive input, in which the visual appears to dominate.

In a departure from decades, if not centuries, of philosophical arguments that self-consciousness is a uniquely human trait related to language, memory and the capacity of self-referral, Blanke and colleagues' research indicates that humans' sense of the embodied self depends on brain mechanisms at the temporo-parietal junction. Experimentally creating illusions of the global self using virtual reality technology could open up avenues for investigating the neurobiological, functional and representational aspects of the embodied self, potentially in other primates as well as in humans.

Blanke's group plans future research using this approach to investigate a spectrum of disturbed body perceptions ranging from body-related hallucinations to full-blown out-of-body experiences in patients with brain damage or psychiatric illnesses.

Ecole Polytechnique Fédérale de Lausanne