Seeing with your tongue

HOW do you find your way around when it's pitch dark? You could try sucking on an electrode that transmits visual cues to your brain via your tongue. Its developers hope that some day the system could help blind people get about easier.

Paul Bach-y-Rita and Kurt Kaczmarek of the University of Wisconsin in Madison have developed a device they call a "tongue display unit"-a grid of 144 gold-plated electrodes covering an area a little larger than a postage stamp. In one prototype, a video camera feeds signals to the TDU via a small box of electronics.

Cheryl Schiltz tested the tongue display by using it to navigate a computer maze. With her eyes closed, she pushed buttons to move through the maze as directed by the computer. To signal her to turn left, the leftmost electrodes tingled her tongue. To go straight, the tingling pulsed from back to front. "It was just amazing," she says. "Just by feeling it on my tongue, my brain got the message where to go."

The human tongue is highly sensitive to touch because it contains a high density of nerve fibres and mechanosensors. "It also presents an electrical resistance that's consistent over time," says Kaczmarek. A large part of the brain's cortex is devoted to the sensory perception of the tongue. And because the tongue is awash with conductive saliva, it is an efficient surface for delivering electrical impulses-unlike exposed skin, which is covered with a layer of dead skin cells and can go from sweaty to dry in minutes.

It takes 50 hours of practice to become familiar with the unit, says Bach-y-Rita. Quite quickly, people stop noticing the weird sensation and learn how to interpret it, similar to the way people learn Braille.

So far the unit has been used to convey very simple information, such as computer-generated graphics. But within five years, the researchers expect to condense the system into an inconspicuous unit that fits in the user's mouth, with a wireless link from a spectacle-mounted video or infrared camera. For underwater use, it could be linked to a sonar sensor. US Navy diving teams have already tested a system in murky waters.

An orientation feedback system to assist people who have lost their sense of balance may also be on the horizon. Head-mounted accelerometers would sense roll and pitch so that when the user wobbles, the system signals to correct left or right.

Schiltz says the TDU produces a "fizzy" sensation, that some people may dislike. "It's kind of like when you stick your tongue on a 9-volt battery," she says. "But not as scary."

Author: Caroline Seydel

New Scientist issue: 17th March 2001

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