Surgeon with Tongue Display Unit. The TDU, first developed in 1999, stimulates the tongue with input from an external sensor, and is an example of a tactile vision subsitution device. TDUs can be used as pressure sensors for amputees and paraplegics, by surgeons carrying out operations, and by blind people. This model, unlike the early ones, is wireless and ergonomically designed to fit inside the mouth. The square of tactile stimulators (gold) stimulate the tongue with information from the surgical tools. The surgeon's moves are monitored and if he strays, even slightly, from the planned trajectory the electrodes on his tongue produce impulses that direct him in the right direction. Photographed in France.