Virtual reality: the day I had six-fingered hands

OCULUS. We never thought that having six fingers on each hand would seem so natural. Yet here we are, waving them in complete relaxation while five minutes earlier, we had indeed five … Yes, but that was before entering this demonstration room of an Inria laboratory, along the tracks of the Gare de Lyon in Paris, and wearing an Oculus Rift. Last week, the Hybrid and MimeTIC teams at Inria Rennes presented a confounding experiment: generating an illusion of polydactyly (having extra fingers) via a virtual reality headset. This project is part of their research on incarnation within simulated universes. “In a virtual reality headset, not seeing your own body is a problem,” explains Anatole Lecuyer, research director and head of the Hybrid team. The question of virtual incarnation has recently appeared in the scientific community : how to appropriate one’s body ? What facilitates, or breaks, this appropriation ? Are social interactions affected ? »

HOUND DOG TAYLOR. The use of avatars serves this appropriation (many projects seek to integrate into virtual worlds even the hands) but, suddenly, Inria wanted to know what happens when we modify the structure of the virtual body. Hence this simulation of polydactyly. That we tested, as a good amateur of the bluesman Hound Dog Taylor (who had six fingers on his left hand). But this is not an imperative.

An extra finger between the little finger and ring finger

Once equipped with the head-mounted display, and after a phase of adaptation to the virtual environment, our 3D-modeled hands quickly count six fingers. Their movements are synchronized with those of real hands followed by a Leap Motion sensor. The extra finger is between the little finger and ring finger. “It is a blurred area of perception, worse than for the thumb, forefinger and middle finger. When you move the ring finger, you usually train the little finger with”, notes Anatole Lecuyer.

ANNULAR. Then, appears a virtual brush. The bristles begin to brush each finger, in random order, including the sixth. Simultaneously, in reality, an Inria researcher passes a real brush on our real fingers. The utensil is also equipped with a motion sensor that synchronizes the virtual and the real. And surprise: when the brush comes to tickle, in the Oculus Rift, this famous sixth finger, we feel it for real ! It is very sharp, even if this finger, we know very well, we do not have it…

In reality, the brush is passed over the ring finger. But the brain is deceived by what it sees in the Oculus and makes vision and sensation match. The most striking thing is that there is no need for any acclimatization to the situation, no phase of adaptation : this sensation of an extra finger is immediately necessary. So much so that when researchers modify virtual reality to return to five-fingered hands (normal, therefore, with us anyway), it is the shock : the unpleasant impression that something is missing, of an amputation.

ARTICLE. Inria conducted this experiment with twenty-four people, obviously not aware of what was going to happen. It was the subject of an article published last Thursday in Frontiers and robotics in AI (here in open access). “Overall, people had a good appropriation of the six-fingered hand. They felt no discomfort, comments Anatole Lecuyer. In 96% of cases, they lifted the ring finger when asked to lift the sixth finger. “The platform is now available to other researchers, whether it is working on other structural changes in the body or on the perception of avatars. In the meantime, the story does not say whether an extra finger, even a virtual one, would have helped to type this article faster.

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