In Spanish | In the United States alone, more than 2.1 million adults have lost enough hearing to be candidates for a cochlear implant, a surgically implanted hearing aid that works differently from a hearing aid. Yet less than 6% of people eligible for a cochlear implant have actually received one. Some of them might not even realize that they are eligible.
Older people with particularly delicate hearing loss where only certain tones are missing are often unaware that they are candidates, says RenÃ© Gifford, professor of hearing and speech sciences and director of the cochlear implant program at the Vanderbilt University. High-pitched sounds like birdsong are difficult to hear with this type of loss, although low-pitched sounds like dog barking may sound normal, she says. This means that these people will often be able to hear the voices of others but will not always understand them.
Now, âall-in-oneâ devices specially designed for these hearing impaired people are available, incorporating the best of hearing aids and cochlear implants.
A different path for sound
How hearing normally works. When a bird outside your window begins to sing, its twittering enters your ear canal as sound waves. These waves travel through the bones of your middle ear, are converted into vibrations, and end up in the snail-shaped cochlea of ââyour inner ear. The cochlea encodes these loud chirps as tiny electrical impulses. The impulses then follow each other along neighboring auditory nerves to the brain. The result: you recognize the pattern as a sparrow’s trill.
How hearing works for people with hearing loss. For people with the type of acute hearing loss described by Gifford, the vibrations of a chirping bird song always reach the inner ear. But inside the cochlea, the structures that would normally turn those high-pitched sounds into electrical impulses are missing or damaged. Thus, the bird’s high notes never reach the brain, although low notes such as that of a dog’s growl can still pass.
How hearing works with a cochlear implant. To bypass damaged parts of the inner ear and let sounds follow a different path, a surgeon inserts a small titanium device – the âimplant,â 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 almost as soft – which are implanted in the inner ear alongside the auditory nerves. Then, when a sparrow begins to sing, the song is picked up by a microphone on an external device (called a âsound processorâ and worn behind the ear like a hearing aid) and relayed to the internal device. Here, the chirps are encoded as tiny electrical impulses, which are then sent directly to the auditory nerves and to the brain. This way, even a person with severe hearing loss can still “hear” the sparrow’s trill.
Mix the ups and downs
“The reason why high frequencies are so important for understanding speech is that most consonant sounds are found in the high frequency region,” Gifford explains. âConsonants are what make speech crisp, clear, and linguistically meaningful. For example, without treble, a phrase like “The chef’s specialty is four cheese pizza” would sound like this: “_uh __eh___ __eh__al i_ _uh _or __ee_ _ee__ah. Understanding would be even worse in a noisy environment, as background noise muffles the low frequencies of speech, leaving people with low frequency loss nothing to cling to.