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Cochlear Implants: applying physics to improve hearing

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by Kate Williams AP Physics 1 Student

Most Americans who have the ability to hear cannot fathom the lifestyle changes that come with deafness or profound hearing loss. In the United States, twelve thousand babies are born partially or completely deaf every year. Conservative ways to support deafness are Sign Language, mouth reading, or just living life in complete silence. However, throughout the past few years, physics has allowed cochlear implants to become the first medical device used to replace a human sense.

Although cochlear implants have not been around for a very long time, physicists have been trying to invent a hearing device since the early 1800s. Physicist Alessandro Volta conducted an experiment in which he connected a battery to electrodes in his ear. Through this experiment, Volta heard “unpleasant noises” and started the phenomenon of artificial hearing. The first surgically implanted cochlea was designed by Williams House and passed by the Food and Drug Administration in 1984.

To fully understand the brain’s reaction to sound, scientists use physics and the study of sound waves. There are two different types of waves: longitudinal and transverse. Transverse waves move perpendicularly to the direction of motion (as shown in the bottom part of the diagram). Longitudinal waves are the opposite; their waves move parallel with the direction of motion (as shown in the top portion of the diagram). Before creating the cochlear implant, physicists had to fully understand that sound is a longitudinal wave. Mechanical longitudinal waves must have a medium in which to travel. This characteristic of longitudinal waves is an important principle of the implant that allows sound to always go through the skin and into the device.

A cochlear implant is very different from a hearing aid. Hearing aids simply use vibrations to reach the remaining hair follicles in the cochlea. However, profoundly deaf people may not have much, if any, hairs left in the cochlea which is why the cochlear implant is surgically placed and is constructed of an inner and outer part. The inner part of the implant has a small soft wire that is placed within the ear and wrapped around the inside of the cochlea. The outer part of the implant is constructed of a microphone and a speech processor. The processor must be with the user at all times for the device to work; although, it may be taken off to shower or sleep. This processor is important because it picks up the nearby noises and converts them using a transmitter that is attached to a magnet that connects the internal and external parts of the device. The transmitter sends the signals to the internal part of the implant and then on to the brain.

Even though this discovery has helped thousands of deaf people, it does not come without risks. One major risk of the surgery is that it just may not work. The human ear is a very sensitive area and sometimes the surgery is not successful for certain people. A common misconception about cochlear implants is that the effect on hearing is immediate; however, six weeks are required for the surgical site to heal and be ready for the external portion of the implant. When the audiologist first attaches the outer piece, the recipient may not hear anything at first. It is the doctor’s job to then adjust the frequency of the implant until sound is heard. Once sound is heard, deaf people do not automatically understand what they are hearing. Most of the recipients have spent the majority of their lives using Sign Language and staying completely mute to outside sounds. So, although they hear sounds, the recipient must then go through long months of speech therapy to learn how to speak and understand spoken words. Many deaf adults who get the implant end up never wearing it because their brain has gotten so used to hearing no sounds that tiny noises such as the sound of a dishwasher or the starting of a car cause them a great disturbance. There is also the concern in the deaf community that cochlear implants are taking away the use of Sign Language and a culture that has been around for a very long time. In the deaf community, the appropriateness of cochlear implants is still a controversial issue, but in the physics community, it is a discovery worth sharing.

Works Cited

Cochlear Implant. Digital image. Kids Health. Nemours, n.d. Web. 20 Apr. 2016.

“Cochlear Implants.” Cochlear Implants. NIH Publications, 18 Aug. 2014. Web. 19 Apr. 2016.

“How It Works.” Hearing with a Cochlear Implant. N.p., n.d. Web. 22 Apr. 2016.

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