Vibrating pads placed on people鈥檚 arms can make the illusion of holding light or heavy objects in virtual reality more convincing by making us disregard some inputs from our senses.
Some virtual reality systems create a perception of mass by slowing down the movement of a virtual object relative to how much our limbs move. For example, if a person picks up a heavy metal sphere, the system can cause a 鈥渓ag鈥� by only moving a fraction of the distance that their hand moves in reality, giving the impression of heaviness. If they pick up a virtual sphere made of light plastic, the system can allow it to move slightly faster than the user鈥檚 arm moves in reality, giving the impression of lightness.
But if that trick is used too heavily then the illusion breaks, says at the University of Tokyo. 鈥淎t some point the user starts to feel weird,鈥� he says. 鈥淭he user notices that the physical portion and visual portion is different. And then the user starts to feel like 鈥榦h, it鈥檚 not my body anymore鈥�.鈥�
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Hirao鈥檚 solution is to trick the user鈥檚 brain into relying more on the visual information they are receiving than the sensation of the position of their limbs, which comes from sensors called proprioceptors in our muscles, tendons and joints.
His team placed small vibrating motors above tendons in the arm to add noise to the signals from proprioceptors, making the signal less useful and causing the brain to lean more heavily on visual information 鈥� which in this case comes from the virtual world.
In an experiment with 20 participants in virtual reality, the researchers simulated different weights by changing the difference between the movement of users鈥� hands and the virtual objects they were handling.
They recorded the point at which the discrepancy became noticeable and found that adding tendon vibration made the illusion more persistent.
Hirao says the technique essentially 鈥渉acks鈥� the way that the brain compiles sensory information into a coherent scene. 鈥淭he brain starts to feel like 鈥榦h, the haptic information is now useless, so let鈥檚 rely more on visual information to make the final decision to define our perception鈥�,鈥� he says.
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