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 (upper left) has the TDU device in his mouth, and has been passed through the scanner behind him. He is using a non-magnetic TDU due to the strong magnetic fields used by the MRI scanner. The researcher (lower right) is looking at a sagittal (vertical sideways slice) brain scan obtained by the scanner. TDUs can be used as pressure sensors for amputees and paraplegics, by surgeons carrying out operations, and by blind people. Photographed in France.