Tongue Display Unit research. Functional magnetic resonance imaging (fMRI) scanner about to be 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 scanner is at left, with the researcher (Professor Christian Scheiber) at right. The TDU device is in the test subject's mouth, and the test subject will use the control device (in researcher's hand) to move himself through the scanner during the experiment. TDUs can be used as pressure sensors for amputees and paraplegics, by surgeons carrying out operations, and by blind people. Photographed in France.