To understand how a cochlear implant works it is first necessary to understand how hearing ears hear and process sound. In hearing ears, sound waves cause changes in air pressure in the canal, which make the eardrum vibrate. These vibrations pass into the inner ear, or cochlear, which is filled with fluid.
The cochlear is like a snail in shape. If you imagine it rolled out, it resembles a piano keyboard in that it has low notes at one end and high notes at the other. All along the cochlear there are thousands of very sensitive cells called hair cells.
When a sound is made the fluid in the cochlear moves and stimulates these hair cells to send a small electrical charge to the auditory (hearing) nerve. This small electrical current passes along the nerve to the brain where it is understood as sound.
If the cochlear has damaged hair cells it will not be able to effectively change sound vibrations into an electrical current. A cochlear implant makes up for the lack of intact hair cells by placing an electrode array (with several electrode contacts) within the cochlear. This delivers sound and speech information directly to the auditory nerve by way of small electrical currents.
Unlike hearing aids, which make sound louder, a cochlear implant bypasses the non-functional parts of the ear and delivers small electrical signals directly to the auditory nerve.
The cochlear implant consists of two parts: the internal part and the external part. The internal part is implanted surgically under the skin behind the ear. The external part is worn on the outside of the body. The external part includes a microphone, speech processor and transmitter coil. The speech processor is worn on the body for small children because it is more robust and gives more information to alert the parent when it is not working. A smaller ear-worn processor can be used when the child is older.
- External speech processor captures sound and converts it to digital signals.
- Processor sends digital signals to internal implant.
- Internal implant turns signals into electrical energy, sending it to an array inside the cochlea.
- Electrodes stimulate hearing nerve, bypassing damaged hair cells, and the brain perceives signals; you hear sound.
The visible component of the cochlear implant is called the processor. It consists of a microphone, batteries and a mini computer that analyses incoming sounds and converts them into digital signals. These signals are then transmitted through the skin via a coil to the internal implant via radio waves.
The internal implant is designed to bypass damaged parts of the inner ear and send electrical stimulation directly to the auditory nerve which the brain interprets as sound.
A cochlear implant may benefit your child if:
- A severe to profound hearing loss has been diagnosed and hearing aids are not effective enough
- Your child has a significant hearing loss from recent meningitis
- Your child’s hearing is getting worse
- Your child has auditory neuropathy spectrum disorder and his/her speech and language development is not progressing as expected
It is important to note that just because your child fits the categories above it does not mean they will be a good candidate for an implant.
Advantages of a Cochlear Implant
- Most recipients can follow a normal conversation and participate more easily in the hearing community.
- Allows many children with profound hearing loss to achieve age-appropriate speech and language.
- May enable use of the telephone.
- Avoids problems with acoustic feedback and ear moulds.
- Can detect soft environmental sounds across the frequency range 250Hz-8KHz.
- Enables greater ease with high frequency consonant perception and production e.g. /s/ /sh/ /f/ /t/ /k/ /p/ /h/ /th/.
Disadvantages of a Cochlear Implant
- Requires significant time commitment to habilitation following surgery.
- Residual hearing in the implanted ear may be lost as a result of the surgery.
- The speech processor must be removed during water activities (such as swimming or showering) and the cochlear implant recipient will not be able to hear during this time.
An operation lasting for two to three hours is necessary to insert the implant. After surgery, patients stay overnight and go home the next day. The surgical process is explained in detail during each child’s assessment. A parent stays overnight with the child.
What do I do next?
If you have not been referred and you would like your child to be assessed for a cochlear implant, contact the following groups:
Northern Cochlear Implant Programme (Taupo North) Clinical Services Coordinator on 09 579 2333 or 0800 254 783 or firstname.lastname@example.org, or your local Ear Nose & Throat Specialist or Audiologist.