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, Olaf 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.
Olaf 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.
At the Karolinska Institutet in Sweden, Dr. Henrik Ehrsson who also works as a research scientist at the University College London in the United Kingdom, has performed similar experiments. His study titled "The experimental induction of out-of-body-experiences" has also been published in the journal Science.
"The idea for the study came to me several years ago", stated Dr. Henrik Ehrsson, research leader in the Department of Clinical Neuroscience. "I wondered what would happen if you moved a person's eyes to somewhere else in the room. It has been found that the visual perspective is crucial in determining how the ego is experienced."
The experiments involve the scientists connecting two video cameras placed side by side - like robot eyes - to a display on the volunteer's head, one camera for each eye. The cameras are positioned behind the volunteers and aimed at them. The volunteers then see themselves from outside, as if they were someone else looking at them.
But to be able to induce an out-of-body experience it is also necessary for the volunteers to sense their self outside their physical body. The scientist can induce such a sensation by standing in front of the cameras and poking a point just below them, that is to say the chest of the "phantom body" - the illusory body the volunteers perceive outside their physical body - while the actual chest is touched without the volunteers seeing that this is being done.
"The brain then responds to the hand that touches the illusory body, whereupon the volunteer has a powerful experience of being several metres outside their actual body", stated Dr. Ehrsson. "The self has thus moved two metres in space and left the actual body, which instead feels like an empty shell, a doll."
To prove the illusion scientifically, Dr. Ehrsson hit the phantom body of the twelve volunteers with a hammer, and measured a degree of skin sweating in response to the provocation. It was found that the volunteers exhibited the same physiological stress response as when someone's real body is threatened, but only during the periods when the volunteers were actually experiencing the out-of-body illusion.
The new tool in the laboratory environment means that it is possible for the first time to undertake scientific research on what we call the self, both fundamental research and applied research, for example in computer science. "In the future it may be possible not just to control a person in a virtual environment but to become the virtual person, that is to say one's self will be able to move to virtual persons", stated Dr. Ehrsson.
Karolinska Institutet is one of the leading medical universities in Europe. Through research, education and information, Karolinska Institutet contributes to improving human health. Each year, the Nobel Assembly at Karolinska Institutet awards the Nobel Prize in Physiology or Medicine.