Paraplegic with Tongue Display Unit. Researcher (right) handing a Tongue Display Unit (TDU) to a paraplegic (left). 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. This wireless TDU will be placed in the patient's mouth to stimulate the tongue with information received from pressure sensors on the paralysed areas of his body (here, the lower body and legs). This sensory input (seen on the screen) helps the paraplegic to avoid prolonged pressure in one area, and so prevent pressure sores and ulcers developing. TDUs can also be used by amputees, surgeons and the blind. Photographed in the TIMC-IMAG Laboratory in La Tronche, France.