HOW do you find your way around when it鈥檚 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 鈥渢ongue display unit鈥濃�攁 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. 鈥淚t
was just amazing,鈥� she says. 鈥淛ust by feeling it on my tongue, my brain got the
message where to go.鈥�
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The human tongue is highly sensitive to touch because it contains a high
density of nerve fibres and mechanosensors. 鈥淚t also presents an electrical
resistance that鈥檚 consistent over time,鈥� says Kaczmarek. A large part of the
brain鈥檚 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鈥攗nlike 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鈥檚 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 鈥渇izzy鈥� sensation, that some people may
dislike. 鈥淚t鈥檚 kind of like when you stick your tongue on a 9-volt battery,鈥� she
says. 鈥淏ut not as scary.鈥�