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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.

Virtual reality

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.

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.