Tongue Display Unit research. Functional magnetic resonance imaging (fMRI) scanner being used to view the brain functions of a person using 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 test subject has the TDU device in his mouth, and his head has been secured inside a head rest as he passes through the scanner (seen around him). The red beams indicate the focus of the scanning beams. TDUs can be used as pressure sensors for amputees and paraplegics, by surgeons carrying out operations, and by blind people. Photographed in France.