Amputee with Tongue Display Unit. Researcher (right) monitoring the use of a Tongue Display Unit (TDU) by an amputee (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. A wireless TDU in the patient's mouth is stimulating the tongue with information received from the pressure sensors on the ends of the amputated limbs (here, the feet). This sensory input (seen on the screen) helps the amputee to keep his balance and avoid falling over. TDUs can also be used by paraplegics and surgeons carrying out operations, and by blind people. Photographed in the TIMC-IMAG Laboratory in La Tronche, France.