13, 2001- In
an earlier Frontiers segment ("Each
Sound is a Present"), Alan reads to a roomful of
deaf and hard of hearing children. How is it possible? Some
of the children, like six-year-old Timmy, use cochlear implants--
electronic devices that can restore hearing to the profoundly
deaf. Timmy's implant works so well, he is able to make the
very fine distinction among the consonant sounds "s," "f"
technology seems like a medical miracle to many hearing parents
and doctors who see the technology as a cure for deafness.
But the cochlear implant has long been the center of a stormy
debate. Some deaf advocates worry that the view of deafness
as an illness to be cured marginalizes the deaf and stigmatizes
those who can't --or don't wish to--use an implant.
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concept behind the cochlear implant is a relatively simple
one that scientists began considering in the 1950s. The cochlea
is a spiral-shaped structure in the inner ear thatin
hearing peopleconverts sound to nerve signals and sends
them to the brain. For the deaf and hard of hearing, the implanted
electrodes do the work of the damaged cochlea and stimulate
the auditory nerves directly.
have been refining the design since the '70s, when implants
used just one electrode to transmit sound to the brain. Even
these crude models provided enough auditory information to
aid in lip reading and alert the user to sounds such as a
door slamming or an object falling to the floor. Today's cochlear
implants use 22 electrodes and provide enough auditory information
for many users to converse orallyeven over the telephone
without the aid of lip reading. (See our audio feature "Tuning
"The inner ear is exquisitely complex and beautiful
and the thought of replacing it with a few wires at first
seemed absurd," says Dr. Robert Shannon
inner ear is exquisitely complex and beautiful and the thought
of replacing it with a few wires at first seemed absurd,"
says Dr. Robert Shannon of the Auditory Implants and Perception
Department at the House Ear Institute in Los Angeles. "We
lost sight of the fact that the ear is just the entry point
of sound into the brain."
Shannon, who has been working with implant patients since
1978, knows success when he hears it.
"The implant is an amazing thing to me," he says. "It still
gives me a thrill when a patient calls me on the phone. To
be able to restore hearing like that is a miraculous thing."
not every implant recipient experiences a miracle. There is
great variation in how much benefit patients get from the
implant. Some of the variation has to do with age at time
of implant, age at time of deafening, and other factors. But
most of the variation cannot be predicted at all.
Cochlea is embedded in the temporal bonethe
hardest bone in the human body
performance after implantation may have to do with how close
the electrodes are to a patient's nerve endings. Shannon compares
an ineffective implant to a pair of glasses with the wrong
prescription. Figuring out how to customize implants to individual
recipients, thereby improving success rates, will be an arduous
task. But the trouble some patients have with their implants
could be even more complicated.
It turns out that hearing, particularly when it comes to speech,
has less to do with the ear than most researchers assumed.
Without a more complete understanding of how the brain acquires
and processes language, who and when it's best to implant
remains up for debate in the scientific community.
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Alec N. Salt, Washington University