To understand how the cochlear implant or a hearing aid helps those with hearing loss, it is important to understand how we hear. When there is a sound, say the ringing of a bell, the outer ear collects and sends it to the ear drum. The ear drum directs it at the three tiny bones in the middle ear: the hammer, anvil, and stirrup, which amplify the sound. Next, the inner ear, filled with fluid, receives the sound. The waves go through cochlea, where microscopic, tiny hair cells turn the sound vibration into electrical energy. The cochlea is a snail-shaped organ. Hair cells are arranged along the length from the base (large end) of the cochlea to the apex (small end). The hair cells near the base are stimulated by high frequency sounds and the ones closer to the apex are stimulated by low-frequency sounds. Then your brain, which receives the energy, interprets this energy as the “sound” of a doorbell.
Before deciding whether to use hearing aids or cochlear implants or a hybrid device, your hearing loss needs to be evaluated by an otolaryngologist. You will be referred to an audiologist to measure the degree of hearing loss, the particular sound frequencies that are impaired, the ability to understand speech and whether the hearing loss is sensorineural, conductive, or mixed. People with conductive hearing loss, who can distinguish words that sound similar, but at a higher volume will benefit by using hearing aids, which amplify the sound. For those whose inner ear is badly damaged, the hearing aid will be of no use. Hearing aids can only help you when you have significant numbers of working hair cells for each frequency being amplified. Most people with a hearing loss have relatively good low-frequency hearing and little or no high-frequency hearing. If such a person were to wear a hearing aid, the hearing aid would amplify the lower frequency sounds very well, but would not really help much, or at all, in the higher frequencies. The result is that no matter how much your hearing aid amplifies any high-frequency sounds, you still won’t be able to hear them.
This is where cochlear implants come in. They bypass these dead hair cells and “inject” the sound signal directly into the auditory nerve—thus your brain hears these sounds in spite of the dead hair cells. The cochlear implant is surgically implanted in the inner ear. Unlike a hearing aid, it does not make sound louder or clearer. Instead, the device bypasses damaged parts of the auditory system and directly stimulates the nerve of hearing, allowing the hearing impaired to receive sound.
A cochlear implant is a small, complex electronic device that compensate for damaged or non-working parts of the inner ear. When hearing is functioning normally, parts of the inner ear convert sound waves in the air into electrical impulses. These impulses are then sent to the brain, where a hearing person recognizes them as sound. A cochlear implant works in a similar manner. It electronically finds useful sounds and then sends them to the brain. Hearing through an implant may sound different from normal hearing, but it allows many people to communicate fully with oral communication in person and over the phone.
The cochlear implant is comprised of an array of electrodes, implanted into the cochlea of the inner ear, which transmit sounds to the auditory nerve and then to the brain, with the help of a signal-processing unit. More specifically, an implant has four basic parts:
1. An external microphone that picks up sound from the environment;
2. An external speech processor that selects and arranges sounds picked up by the microphone;
3. An external transmitter that receives signals from the speech processor and convert them into electric impulses;
4. Internal electrodes implanted into the cochlea of the inner ear, which sends the impulses to the brain.
An implant can give severely hard of hearing person a useful auditory understanding of the environment and facilitate lip reading ability. It can help deaf children with language acquisition, especially phonological development. The implant avoids problems with acoustic feedback and ear-mold issues associated with hearing aids. On the flip side, cochlear implants are very expensive, any surgery is potentially dangerous and cochlear implantation takes place very near to the facial nerves.
They are particularly suitable for those deafened children and adults who already have a memory for the spoken word. For them, the stimulus transmitted by the implant relates well to their previous knowledge of language and can be a useful aid. For others, the auditory information given via the implant may be insufficient and therefore the task of learning the spoken language may be enormous. Before deciding to go in for cochlear transplants, one has to consider that in case the implant is rejected by the body or doesn’t help as much as anticipated, the cochlea is possibly damaged and any natural residual hearing is completely destroyed.
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