It might be as little as a pair of hands and feet, researchers in Japan found after recording subjects who wore an Oculus Rift headset.
How connected are your body and your consciousness?
When Michiteru Kitazaki, a professor of engineering at Toyohashi University of Technology in Japan, recently posed this question in an email, he evoked an idea from Japanese culture known as tamashii, or the soul without a body.
Will it soon be possible, he wondered, to simulate the feeling of a spirit not attached to any particular physical form using virtual or augmented reality?
If so, a good place to start would be to figure out the minimal amount of body we need to feel a sense of self, especially in digital environments where more and more people may find themselves for work or play. It might be as little as a pair of hands and feet, report Dr. Kitazaki and a Ph.D. student, Ryota Kondo.
In a paper published Tuesday in Scientific Reports, they showed that animating virtual hands and feet alone is enough to make people feel their sense of body drift toward an invisible avatar.
Their work fits into a corpus of research on illusory body ownership, which has challenged understandings of perception and contributed to therapies like treating pain for amputees who experience phantom limb.
The original body ownership trick was the rubber-hand illusion. In the 1990s, researchers found that if they hid a person’s actual hand behind a partition, placed a rubber hand in view next to it and repeatedly tapped and stroked the real and fake hand in synchrony, the subject would soon eerily start to feel sensation in the rubber hand.
Today, technologists working on virtual reality are using modern-day riffs on the rubber-hand illusion to understand how users will adjust when presented with digital bodies that do not match their own. Some researchers have suggested that having users digitally swap bodies with people of other races, genders, ages or abilities could reduce implicit bias, though this work has its limits.
And taking ownership of an invisible body in cyberspace or otherwise could also have positive applications, like reducing social anxiety, Dr. Kitazaki said.
Using an Oculus Rift virtual reality headset and a motion sensor, Dr. Kitazaki’s team performed a series of experiments in which volunteers watched disembodied hands and feet move two meters in front of them in a virtual room. In one experiment, when the hands and feet mirrored the participants’ own movements, people reported feeling as if the space between the appendages were their own bodies.
This demonstrates the power of synchronized actions and our brain’s ability to fill in missing information, said V.S. Ramachandran, a professor at the University of California, San Diego and rubber-hand illusion pioneer who did not participate in the new study. The “improbability of synchrony occurring by chance” overrides all other information, he said, even knowledge that an invisible body cannot be yours.
In another experiment, the scientists induced illusory ownership of an invisible body, then blacked out the headset display, effectively blindfolding the subjects. The researchers then pulled them a random distance back and asked them to return to their original position, still virtually blindfolded. Consistently, the participants overshot their starting point, suggesting that their sense of body had drifted or “projected” forward, toward the transparent avatar.
Antonella Maselli, a researcher at the Santa Lucia Foundation, a neurological rehabilitation hospital in Italy, noted that the subjects in the study did not show significant conscious responses to seeing their invisible avatars being cut by a knife or colliding with a table.
Rather than an example of illusory body ownership, she said, the drifting effect may be more related to out-of-body experiences, in which people simply feel their bodies “displaced in space.” She added that the researchers might have found effects from the threats had they measured physiological responses, like changes in skin conductance or brain activity.
Dr. Kitazaki replied that the exact difference between out-of-body experiences and illusory body ownership is an open question, but agreed that future research should include such measurements.
Moving forward, he wants to investigate if it’s possible to get rid of even the virtual hands and feet in this study and see what it means, he said, to be totally “free from the current body.”