A device that relays a person's body movements to an array of electrodes on their tongue could help people with balance problems recover their poise, or wheelchair users avoid pressure sores.
The wireless "tongue display" being used by French researchers is worn in the mouth like an orthodontic retainer. A matrix of 36 electrodes on the underside transmits electrical impulses to the tongue.
"The sensation is a kind of 'ticklish' feeling," says Yohan Payan, a researcher at the TIMC lab near Grenoble, France.
"The idea is that if one of your senses is lacking, you try to use another sense to convey information", he says, adding that it initially takes around 10 minutes for people to learn to use the information from the display.
Payan and colleagues are instead interested in helping people with conditions that affect their perception of body movements and balance. Output from movement sensors on a person's body is sent to the tongue display to help the brain detect and correct stability and posture.
Trials have included using the device to display head position, and pressure on the soles of the feet and have had promising results.
In one experiment volunteers became worse at balancing when their backs were tired, but could compensate when they felt foot pressure on their tongue too. Another study projected data from the ankles onto the tongue. Volunteers found they were better able to compensate for difficulties in sensing the joints when their muscles were tired.
Payan's team is now using the tongue display to help people in wheelchairs stay healthy. "Paraplegic patients suffer from pressure sore problems due to the absence of perception of the point of pressure on the buttock area," he explains.
Pressure sensors on the wheelchair's seat connect to the tongue display to make a person aware of pressure they would otherwise not feel, so they can shift position to avoid sores. The same technique can be used for amputees who have balance problems or pressure sores from their prosthesis.
The tongue display design used by Payan's team was developed by Kurt Kaczmarek and colleagues at University of Wisconsin, Madison, US, as an alternative to vision.
The French team made the device smaller and wireless – improvements that Kaczmarek is enthusiastic about. "It will enable not only practical, wide-scale deployment of rehabilitation applications for balance or vision disorders, but also a new era in human-machine interfaces."
Maurice Ptito of the McGill University, Montreal, Canada, agrees. He is currently using a tongue display to help blind people navigate around obstacles.
Ptito says that studying how the brain uses balance information from the tongue display could help reveal the way balance is usually regulated.
Tongue displays could also be a help in situations where people are overloaded with information, such as when flying aircraft, driving racing cars, taking space walks or new communication devices, Kaczmarek adds.