Tongue Display Unit sensory data. Screenshot showing the sensory data from the external buttock pressure sensors (left) and the sensory input (right) provided by a Tongue Display Unit (TDU). 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. The red area (left) and the green dots (right) show excessive pressure is being placed on the patient's right-hand buttock. As the patient is a paraplegic (paralysed in the lower body), they will not realise this and are in danger of developing a pressure sore. TDUs can also be used by amputees, surgeons and the blind. Photographed in the TIMC-IMAG Laboratory in La Tronche, France.