En español | In the U.S. alone, more than 2.1 million adults have lost enough hearing to be a candidate for a cochlear implant, a surgically implanted hearing device that works differently than a hearing aid. Yet fewer than 6 percent of those eligible for a cochlear implant have actually received one. Some of them might not even realize they're eligible.
Older adults with a particularly tricky kind of hearing loss where only certain tones are missing are often unaware that they are candidates, says René Gifford, a professor of hearing and speech sciences and director of the cochlear implant program at Vanderbilt University. High-pitched sounds like birdsong are hard to hear with this type of loss, though low-pitched ones like dog barks can sound normal, she says. That means these people will often be able to hear others’ voices but not always understand them.
Now “all-in-one” devices specially designed for these hearing-impaired individuals are available, incorporating the best of both hearing aids and cochlear implants.
A different path for sound
How hearing works normally. When a bird outside your window starts to sing, its twittering enters your ear canal as sound waves. These waves travel through the bones of your middle ear, get converted into vibrations, and wind up in the snail-shaped cochlea in your inner ear. The cochlea encodes those noisy chirps as tiny electrical pulses. The pulses then zip along the nearby hearing nerves up to the brain. The result: You recognize the pattern as a sparrow's trill.
How hearing works for people with hearing loss. For those with the type of high-pitched hearing loss that Gifford describes, vibrations from a twittering birdsong still arrive at the inner ear. But inside the cochlea, the structures that would normally turn those high-pitched sounds into electrical pulses are missing or damaged. So the bird's high notes never reach the brain, even though low notes such as those in a dog's growl can still get through.
How hearing works with a cochlear implant. To bypass damaged parts in the inner ear and let sounds follow a different path, a surgeon inserts a small titanium device — the “implant,” which contains a tiny computer chip — under the skin behind the ear. Signals are sent from this device to electrodes — as thick as a few hairs and nearly as soft —that are implanted in the inner ear alongside the hearing nerves. Then, when a sparrow starts to sing, the song is picked up by a microphone on an external device (called a “sound processor” and worn behind the ear like a hearing aid) and relayed to the internal device. Here the chirps get encoded as tiny electrical pulses, which are then sent directly to the hearing nerves and on up to the brain. This way, even a person with serious hearing loss can still “hear” the trill of the sparrow.
Blending highs and lows
“The reason that high frequencies are so important for speech understanding is that most consonant sounds are in the high-frequency region,” Gifford says. “Consonants are what make speech crisp, clear and linguistically meaningful.” For example, without high pitches, a sentence like “The chef's special is the four-cheese pizza” would be heard something like this: “_uh __eh___ __eh__al i_ _uh _or __ee_ _ee__ah.” Comprehension would be even worse in a noisy environment, because background noise drowns out low pitches in speech, leaving nothing left for people with a high-frequency loss to grab onto.
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When these types of losses are mild, special approaches aren't needed. Regular hearing aids can just boost the missing tones by making them louder. But when people lose too much high-pitched hearing over time — whether from noise exposure, medications, genetics or just natural aging — even the best hearing aids often can't compensate, Gifford says.
To help, cochlear implant companies have developed systems that combine a cochlear implant with a hearing aid. These all-in-one devices deliver what is known as “electric-acoustic stimulation” for those who can hear only low tones.
How electric-acoustic stimulation works
To replace a person's missing high tones, a cochlear implant bypasses the damaged inner ear and sends high-pitched electrical signals directly to the hearing nerves. For the rest of the sounds, the person's natural hearing fills in with the help of a hearing aid.
These two types of hearing together span the full range of highs and lows. “The brain is astoundingly plastic, and it will adapt to blend both sounds even though they're very different,” says Jason Galster, an audiologist and director of clinical research at Advanced Bionics. “The sum of the parts for some people can be better than each.”
This “allows people to use the natural hearing they have and get back what sounds they were missing,” says Patricia Trautwein, an audiologist and vice president of market access and reimbursement at Cochlear Americas. The difference can be especially noticeable during conversations in noisy environments.
The key to these combo electric-acoustic systems — available from cochlear implant companies including Advanced Bionics, Cochlear and MED-EL — lies in protecting the intact parts of the inner ear during surgery. Advances in both implant design and surgical techniques over the past several years have made this easier than ever before.
Demand for these all-in-one systems is likely to grow, especially among older adults. “Many people do not realize how much they are struggling with hearing loss, because it tends to progress slowly over time,” Gifford says. Her center has recently seen a jump in people asking about cochlear implants. For those with hearing loss, she says, struggles to carry on conversations during the pandemic — with lips hidden and voices muffled by masks — were likely a wake-up call to just how bad their hearing had become.
Is it time for more than a simple hearing aid?
"We counsel individuals to consider pursuing [an] evaluation if they answer ‘no’ to at least two of these questions,” says René Gifford.
- Are you able to talk on the phone without visual cues (such as video calls or caption calling)?
- Are you able to understand television programs without closed-captioning?
- Are you able to effectively engage in conversations at large group gatherings such as dinner parties?
- Do you feel that you obtain significant communication benefit from your current hearing aids?
Regina Nuzzo writes about science, health and medicine. Her work has appeared in Reader's Digest, Prevention, Scientific American, the Los Angeles Times, and The New York Times, among others. She is a professor of mathematics at Gallaudet University in Washington, D.C., and uses a hearing aid and cochlear implant herself.