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Cochlear Implants

Cochlear implants are hearing devices that transmit sound signals directly to the brain. This transmission to the brain helps people with a damaged inner ear be able to interpret sounds. They are different from hearing aids, which only amplify sound, not transmit it to the brain.

How they work

A cochlear implant has external and internal pieces

A cochlear implant consists of five main parts: the microphone, speech processor, transmitter, stimulator, and electrode array. The microphone, speech processor, and transmitter are worn on the outside while the stimulator and electrode array are under the skin and inside the ear. The microphone picks up sounds from the environment, those sounds are then processed by the speech processor and turned into signals for the transmitter. The transmitter is connected to the stimulator by a magnet. The stimulator receives the signals from the transmitter and converts them into electric impulses. Those impulses are sent to the electrode array which stimulates different sensory cells that in turn activate the auditory nerve.

Technologies of cochlear implants

Speech Processors

Implanted Speech Processors

From the Department of Otolaryngology at the University of Melbourne in Australia, a completely implanted speech processor was implanted in three patients. This new speech processor has all the traditionally external pieces under the skin. This new implant is referred to as TIKI. All patients benefited from the implant. However, with the microphone being completely under the skin, according to Beiter and Nel from Macquarie University, it "has limited sensitivity such that speech intelligibility is somewhat degraded" and "body noise interference is bothersome" to the users. The patients were also given an external speech processor called ESPrit 3G, which could be worn with the TIKI. All patients reported better hearing with the ESPrit 3G than with the TIKI alone. However, the patients "continue to use the invisible hearing mode on a limited daily basis," as reported by the original research group. Research to improve the microphone and signals for the implanted speech processor are still continuing.

Waterproof Speech Processors

A previous challenge for speech processors was water. Speech processors could not be worn at the pool or in the shower. However, new technologies have been developed to remedy that problem. A few speech processors have actually been designed to be worn in water, such as Neptune by Advanced Bionics. The Neptune design differs from the traditional speech processor that hangs on the ear, and instead is clipped to a headband, armband, or article of clothing. Other companies, such as Med El and Cochlear, have created waterproof sleeves designed to fit the traditional speech processor. These sleeves are not permanent and much be replaced after a certain number of uses. The number of uses differ from company to company as all have their own design. In every case, these waterproof designs allow wearers to be around any type of water, be it salt water, chlorinated water, or soapy water from the shower.

Single Unit Speech Processors

Instead of a traditional speech processor that sits behind the ear and has a coil that leads to the transmitter, there is an option of a single unit speech processor. A single unit speech processor has the microphone, speech processor, and transmitter as a single unit that sits traditionally where the transmitter would sit. According to an article from the Otology and Neurotology journal, these single unit speech processors showed no difference in performance from the traditional behind the ear speech processors. In most cases, single sided deaf users preferred the single unit speech processor over the behind the ear processor.

Electrode Array

Electrode arrays are the most significant pieces of technology related to the cochlear implant as they are the pieces inserted into the cochlea itself. Different electrode arrays have been designed by different companies, but according to Finley and Skinner from UNC School of Medicine, the speech scores for the different electrode arrays are all similar. The electrode itself does not seem to make a difference. What does make a difference according to their research is the placement of the electrode in the inner ear. This can be complicated as the inner ear is sensitive to trauma. A study mentioned in The National Center for Biotechnology Information concluded that electrode arrays with volume dimensions greater than the inner ear caused the most damage, while electrode arrays with "greater stiffness in the vertical plane" seemed to have done the least damage. New design models are continually improving in order to reduce trauma to the inner ear during insertion as well as improving its placement.