November 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" and "th."

The 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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The Bionic Ear

The 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 that—in hearing people—converts 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.

Researchers 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 orally—even over the telephone without the aid of lip reading. (See our audio feature "Tuning In")

"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 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."

And 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."

But 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.

The Cochlea is embedded in the temporal bone—the hardest bone in the human body

Poor 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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Photos: Alec N. Salt, Washington University