Answer: To perceive their prosthetic limbs.
Researchers at Ecole polytechnique fédérale de Lausanne (EPFL) have found a way to change how amputees perceive their prosthetic limbs using virtual reality (VR) technology. The issue at stake here is that the “phantom limb” that amputees feel in place of their missing limb is much smaller, and they expect to see what they feel when they look at an attached prosthetic limb. And since prosthetic limbs are still a long way away from providing full touch sensation, their users have to look at them often.
In their method of combating this, the EPFL team creates tactile sensation on a specific point of the phantom limb, in this case the tip of the index finger. At the same time, the same spot is illuminated in an image of the prosthesis in the VR headset. Over time, the user’s brain is able to match the phantom limb that they feel to the prosthesis they see. Additionally, they reported that this perception lasted for about 10 minutes after the simulation concluded.