23 August 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).
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.
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.