Swedish scientist H. Henrik Ehrsson devised a way to convince people's brains that what they were looking at, an image of their bodies projected in front of them, were in fact occupied BY them. He proved that the brains responded to the illusion "as if" it were real; he provoked measurable autonomic distress output by threatening to hit the "virtual" body with a hammer.
His study “The Experimental Induction of Out-of-Body Experiences” was published in Science, Aug. 24, 2007.
(See here for list of 30 of his articles.)
Swiss scientist Bigna Lenggenhager induced virtual body illusions in her subjects, then had them move themselves out of position, then back into positions where they thought they had previously been, but which were in fact where their "virtual" bodies had been.
Her paper “Video Ergo Sum: Manipulating Bodily Self-Consciousness” was also published in the August 24, 2007, issue of Science.
How is this possible?
The Discover article says,
"While we navigate the world, our brains are constantly integrating sensory information gathered by sight, touch, and hearing. But sometimes the system goes haywire, and people experience the illusion that they are outside their physical bodies, floating above them and peering back from a distance of about 6 to 10 feet. These “out of body” experiences typically occur when people suffer strokes, epileptic fits, or migraines or are taking drugs. Two cognitive neuroscientists explored the boundaries of body perception by reproducing an out-of-body experience in the lab."
Henrik Ehrsson, Karolinska Institute in Stockholm, Sweden
- 18 healthy individuals were seated. Their backs were filmed with a pair of video cameras while they wore goggles that
a)gave them a stereoscopic view of their backs
b)captured the video from both cameras.
- Ehrsson induced the illusion; he "repeatedly touched each person’s actual chest with one rod while, with another rod, he jabbed toward a point below and in front of the two cameras that corresponded to the “virtual chest” of the image projected into the goggles. With the shift in perspective through the goggles, subjects reported that they felt as though they were physically embodying a space six and a half feet behind where they actually were."
Ehrsson wanted to find out if the subjects would respond "as if" they were located in the illusory position.
- Sensors that monitor electrical conductance were applied to the subjects.
- The first experiment was duplicated.
- This time, "he swung a hammer toward the two cameras at a point corresponding to the center of the face of the camera-generated illusory body"...and, "the subjects’ skin showed a spike in electrical conductance—a sign of increased sweating and emotional arousal—and they reported immediate anxiety."
Bigna Lenggenhager et al., École Polytechnique Fédérale in Lausanne, Switzerland
- A camera was placed six and a half feet behind the back of each of 14 participants wearing 3-D video goggles.
- Their backs were stroked with a large pen; they could simultaneously see and feel their backs being caressed.
- The subjects were guided backward, then asked them to return to their previous position.
- "Participants overshot the distance by an average of 10 inches, moving closer to the position of their “virtual” bodies."
- The back of a mannequin's body was stroked, and the image projected into the subjects’ goggles. Subjects felt that the mannequin’s body was their body.
“We now understand how the brain combines information from the eyes and from the skin to compute or determine where the self is located in space,” Ehrsson says. Both experiments show how easily the brain can be tricked or how it “cheats,” he says, using memory and prior experiences to fill in data gaps."
Here is a youtube video about this. (Olaf Blanke, shown in the video, was Lenggenhager's team leader.)
Here is a link to Sandra Blakeslee's new book, The Body Has a Mind of its Own, which discusses these kinds of phenomena and attendant research in greater detail.
Just one additional thought for now.. why wouldn't this setup work for treating back pain? Someone could find 20 or so subjects with back pain, any old kind of back pain at all, acute, chronic, what have you, any age, any sort of work, any socioeconomic group... put the goggles on them, induce the illusion. Instead of getting the subjects to move forward and back or instead of eliciting threat responses from their autonomics, instead, the "virtual" backs, could be "treated". Or a film clip of the "virtual" back could be shown to move freely. I wonder if this illusion would be sufficient to get the subjects' brains to stop producing the pain output?
Dec. 29th '07: Back in to add a link to a youtube video on goggle-induced virtual reality games for phantom limb pain.