The Studies “The Experimental Induction of Out-of-Body Experiences” by H. Henrik Ehrsson and “Video Ergo Sum: Manipulating Bodily Self-Consciousness” by Bigna Lenggenhager et al., both published in the August 24, 2007, issue of Science.
The Motive 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.
The Methods In his first experiment, Henrik Ehrsson of the Karolinska Institute in Stockholm, Sweden, tried to alter the subjects’ perception of their location in space. He seated 18 healthy individuals and filmed their backs with a pair of video cameras. While filming, he gave the subjects a stereoscopic view of their backs, using goggles that captured the video from both cameras. Ehrsson then 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.
In a second experiment, Ehrsson tested to see if the subjects would respond as if they were located in that “false” position. He outfitted subjects with sensors that monitor electrical conductance, then arranged the same setup and repeated the rod movements he had conducted in the first experiment. When he swung a hammer toward the two cameras at a point corresponding to the center of the face of the camera-generated illusory body, the subjects’ skin showed a spike in electrical conductance—a sign of increased sweating and emotional arousal—and they reported immediate anxiety.
Meanwhile, at the École Polytechnique Fédérale in Lausanne, Switzerland, Bigna Lenggenhager and her colleagues were conducting similar experiments. Team leader Olaf Blanke, a medical doctor who has treated epileptic and stroke patients who have had out-of-body experiences, placed a camera six and a half feet behind the back of each of 14 participants wearing 3-D video goggles. An experimenter then stroked their backs with a large pen so they could simultaneously see and feel their backs being caressed. Blanke guided the subjects backward and 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. He also filmed the back of a mannequin and projected the image into the subjects’ goggles. “They felt that the mannequin’s body was their body,” Blanke says.
The Meaning “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. Beyond helping us understand some fundamental elements of the out-of-body experience, this research could make for better game play. “We think this will enhance virtual reality applications in education, games, and therapy,” Ehrsson says. “People will feel that they are genuinely there in a virtual world.”