A group of University scientists recently developed a new hearing aid device which will allow users to hear a higher-quality sound than existing technology permits. The device is called a cochlear implant – a type of hearing aid implanted in a spiraled, snail-like structure in the ear called the cochlea.
Led by Kensall Wise, professor of electrical engineering and computer science, the group developed the cochlear implant to improve the hearing of profoundly deaf patients and help surgeons minimize damage when inserting the device.
“Currently, people (with cochlear implants) have trouble with tonal languages,” Wise said, referring to languages like Mandarin that rely heavily on tonal accents.
To improve this, the group devised a way to use high-density electrodes in the implant so that more tones are audible independently.
“The hope is that we will improve cochlear implants in order to understand the limits of what cochlear implants can do,” Wise said.
Wise said current technology allows an implant to use about 22 stimulating sites. However, the new implant could have 128 stimulating sites, which would provide a much higher resolution of sound.
But problems with current cochlear implants are not only limited to the quality of sound.
“If the implant is not inserted far enough, everyone sounds like Mickey Mouse,” Wise said.
Wise said his team wants to insert the electrode more deeply in order to cover a greater range of frequencies, especially low frequencies or bass sounds can only be stimulated in the deepest part of the cochlea.
The danger when inserting the implant is causing damage to fragile structures in the cochlea. Currently, to insert an implant, surgeons have to push a small, wire-like structure into the cochlea. This causes the wire to take on the spiral shape of the cochlea as it is implanted.
“We are making the implant like an inchworm, so that we can articulate its movement and allow it to crawl into position. It will be like a party favor that unrolls; only it will unroll to lightly grip the interior wall (where it can stimulate the auditory nerve).”
A device with this capability would further reduce the risk of damaging vital structures as the cochlear implant is inserted.
“The idea is to have the implant hug the inner wall as tightly as possible,” Wise said.
“Because the new electrode arrays are smaller than previous ones, sensors can be added to the implant to ensure a higher level of safety. For example, position sensors could be added as well as sensors that tell when an implant contacts a wall,” Wise said.
This process would ensure that fragile structures are not ruptured or broken when the cochlear implant is inserted, allowing the electrodes to move deeper into the ear.
“The cochlear implant (pictured) is actually sized for guinea pigs,” Wise said.
“The human electrode array is four times as long, but has the same high density of electrode sites (as the pictured device).”
Cochlear implants work with an external microphone – this is usually a small device which wraps around the user’s ear – that converts different sounds into electrical signals.
To give users an actual sense of hearing, the implants stimulate the remaining functional auditory nerves with short pulses of electrical current.
Cochlear implants are generally used by patients with impaired hearing but do not restore full hearing to a patient. They can restore hearing over a small set of pitches, depending on which auditory nerves are still functioning.
Nonetheless, implant users who had profound hearing loss can talk on the phone, meaning that users do not have to lip read to understand sounds. All auditory information comes from the implant.
After more testing, Wise said that the group hopes to begin working with a company to manufacture at least a few pieces of the device, but it is unlikely that they will be manufactured for another four or five years.
These newer cochlear implant technologies will then be available for profoundly deaf patients – if they want to use them.
Despite the success of the device, cochlear implants are controversial. Several profoundly deaf patients in the signing deaf community have been against use of the device in children born with hearing loss. Members from this community feel that the devices detract from the deaf community.
An article published in Nature magazine in 2004 suggested that people opposed to cochlear implants experience, “a level of social intimacy that is rare among the hearing.”
Carol Padden, a linguist at the University of California, San Diego, contributed to the article. In it, Padden explained some of the opposition to the technology.
“I will meet another deaf person for the first time and in five or ten minutes, it’s not uncommon to know a great deal about their family and personal life,” she said.
The paper explained the argument of those opposed to cochlear implants by addressing the even more controversial issue of genetic testing, “Employing a genetic diagnosis to avoid having a baby with a disability is controversial enough,” Padden wrote. But interestingly, Padden wrote that a small number of deaf people would consider testing to ensure that they had a deaf baby.
Only a minority of potential cochlear implant users are opposed to the devices. In fact, most parents are encouraging doctors to test their children for hearing loss as early possible.