"Many people who lose a limb experience the sensation that it is still attached to their body. This is also often accompanied by a feeling of pain in the missing appendage. Amputees who experience "phantom limb pain" could find relief with a 3D virtual reality system that creates the illusion that they can once again control their missing limb. The person using the system wears a head-mounted display and operates a controller with their remaining limb. The system lets them control a virtual arm or a leg, which is shown in 3D in place of their missing limb."