People are getting used to having an extra pair of arms – in virtual reality

What would you do with an extra pair of hands? The idea may seem unwieldy, like too much of a good thing. But a new study suggests that people can actually adapt to using additional robotic arms as if the limbs were their own body parts.

For decades, scientists have studied how the human brain acts when people manipulate tools. It is now believed that when you pick up a wrench or screwdriver, your brain interprets it as a substitute for your own hand. When wielding a long staff, your sense of personal space expands to accommodate the full length of the object so you don’t accidentally bump into someone with it when you turn around. But what happens to your perception of your own body when you add entirely new parts rather than simply changing the function, shape or size of existing ones?

This question could influence the design of new robotic devices and virtual reality spaces. Many roboticists are interested in building systems that would give humans the ability to use extra limbs and could potentially allow people to perform tasks that require an extra arm or leg, or even a tail. Virtual reality offers people the opportunity to try experiences not yet possible in the real world and to act as avatars that might look nothing like their controllers (or even humans at all). However, to be useful and usable, any additional real or virtual body parts must blend together as if they were always there. It is therefore essential to understand if and how this is possible to design both real cyborg parts and immersive video games.

A variety of experiments have attempted to determine how humans react to having an extra appendage. In these tests, researchers fitted participants with an extra rubber arm, hand, or finger, then touched the extra fake coin at the same time as they touched a real, sensitive one. These experiments showed that humans can feel that these extra or “supernumerary” limbs are part of their body. But the question of whether people can effectively use controllable sets of new members has not yet been widely studied.

That was the aim of a new study published last month in Scientific reports. The researchers immersed the participants in a virtual reality environment that included an avatar of themselves, with an additional pair of virtual robotic arms just below the real ones. The VR environment was crucial to understanding how humans might adapt to additional robotic body parts, says study co-author Ken Arai, a roboticist and cognitive scientist at the University of Tokyo. Experimenting with a pair of real-world robotic arms comes with the challenge of making them move without delay, as our brains would expect from our real body parts. But in virtual reality, the delay between the input of the sensors and the visible movement of the virtual arms is shorter, which makes the experience more realistic.

Participants controlled the simulated robotic arms using sensors attached to their feet and waist. Moving the lower leg in the physical world would trigger the extra arm on that side of the body to move in VR space. Flexing the toes told this virtual hand to make a grabbing motion. People manipulating the arms in virtual reality were also able to feel when the limbs interacted with virtual objects. For example, if the palm of a simulated robotic hand touched something in VR space, participants felt a vibration against the sole of the foot on the same side of the body.

Once hooked into the VR setup, participants engaged in a coordination task, using the extra arms to “touch” balls that appeared in random places. After each attempt, participants rated how much they agreed with statements such as “I felt like the limbs/arms of the virtual robot were my limbs/arms” and “I felt that the movements of the virtual robot’s arm were influencing my own movements.” When performing the touch the ball task multiple times, people’s responses became faster and they also reported feeling more ownership and autonomy over their new arms.

Another experiment tested how quickly people moved their robotic arms in response to virtual touches. Here, participants felt vibrations on their feet as they saw virtual objects touch their artificial limbs, and they were asked to move their robotic arms away from these objects. Sometimes the location of the physical vibration on the foot corresponded to where the virtual ball touched the limb – for example, a vibration on the top of the left foot would indicate contact on the back of the virtual left hand – as they have done so in the touchdown experience. But sometimes the feel didn’t match where the object seemed to be in VR. When the visible location of the VR object and the place where it appeared the robotic limb was being touched were aligned, participants moved their robotic arms away slightly faster than they did when the sensation did not match the feeling. position of the object. This pattern was also seen when the same experiment was performed on people’s real-world limbs. The researchers interpret this as a sign that the participants’ subconscious sense of personal space has expanded to include the area visible around their robotic arms in virtual reality.

Overall, the results suggest that participants felt like they had gained whole new body parts, not just as if they had extended their existing feet by adding a new tool. This potentially opens up a world of virtual and real possibilities.

“In virtual reality, we can have avatars of any shape or dimension,” says Andrea Stevenson Won, a human-computer interaction researcher who directs Cornell University’s Virtual Embodiment Lab and was not involved in the study. “You could give yourself wings and fly in virtual space and have this euphoric experience.” Knowing more about how people will feel about their avatars’ additional body parts will help researchers design this experiment. “How people might interpret the bodies of avatars, which don’t physically exist, and react to them as if they were real in some sense is an interesting question,” Won adds.

Arai, on the other hand, is very excited about the potential to expand what humans might be able to do in the physical world. Existing robotic systems could literally give people an extra pair of hands. “Perhaps this knowledge [from the VR system] can also be adapted to the real robotic system. This type of feedback loop will be very important in improving the design of supernumerary robotic limbs,” he says. “We want to allow things that are impossible for humans. If we want to add more members, it should be possible. Everything should be possible. »

Martin E. Berry