What is normal hearing?
For people with normal hearing, sound travels from the outer ear into the ear canal and causes the eardrum to vibrate. The eardrum is attached to three small bones in the middle ear that carry the vibration from the eardrum to a fluid-filled part of the inner ear called the cochlea. Movement in the fluid within the cochlea causes hair fibers (or hair cells) in the cochlea to move. The movement of these hair cells triggers a chemical reaction, which stimulates the hearing nerve. Then, the nerve sends the information to the brain, where it is recognized as sound.
What if I cannot benefit from a hearing aid? What is a cochlear implant?
A cochlear implant is a small electronic device that provides a sense of sound to children and adults who have severe to profound hearing loss and who cannot hear and/or understand speech with hearing aids. Unlike hearing aids, which amplify sound, cochlear implants bypass the outer, middle, and inner ear and directly stimulate auditory nerve fibers.
The cochlear implant system consists of two parts:
- an internal device that is surgically implanted into the inner ear and,
- an external component consisting of a headset and speech processor that is programmed individually to supply sound to a child.
How do cochlear implants work?
When a person has a hearing loss (whether due to a congenital impairment or to damage acquired later) that causes damage to the tiny hair cells in the inner ear, it is called a sensorineural hearing loss and is sometimes referred to as nerve deafness. This is because sound cannot stimulate the nerve normally. A cochlear implant bypasses the damage and directly stimulates the nerve to send information to the brain.
I don’t get it? How does it work specifically?
- Sounds are picked up by a microphone and turned into an electrical signal.
- The electrical signal is sent to a speech processor (worn either on the body or the ear) where it is “coded” or turned into a special pattern of electrical pulses.
- The electrical pulses are sent to the coil or headpiece, where they are transmitted across the skin by radio waves to the cochlear implant.
- The cochlear implant sends a pattern of electrical pulses to the electrodes, which are found on the electrode array, which has been implanted in the cochlea.
- The auditory nerve picks up the tiny electrical pulses and sends them to the brain.
- The brain recognizes these signals as sound.
What does the cochlear implant look like, and where is it placed?
A cochlear implant consists of three parts: receiver/stimulator, headpiece, and speech processor.
- Receiver/Stimulator. The receiver/stimulator is the part that is implanted. It looks like a magnetic disk about the size of a poker chip. It is placed under the skin behind one ear. A wire leads from the receiver/stimulator to an array of electrodes, which is fed into the cochlea in the inner ear. Surgery to implant the receiver may be done as an outpatient or may require a short hospital stay. The surgery usually takes between 2 and 3 hours to complete.
- Headpiece. A small headpiece is worn just behind the ear and contains the microphone and transmitter. The microphone picks up sound in the environment, and the transmitter sends the processed sound to the internal system. The transmitter is held in place over the implanted receiver/stimulator by small magnets in both the transmitter and the implanted device.
- Speech processor. The speech processor changes the acoustic sound into electrical information. The processor may be worn completely behind the ear or on the body in a harness or on a belt. It is attached to the transmitter and microphone by special cords.
What happens after the implant is in place?
Once in place, the implant system works as follows. Sound waves enter the microphone located in the headpiece. Sound is sent through a cord to the speech processor. The speech processor converts the sound into a special electrical signal that is sent up a cord to the transmitter. The transmitter then sends the information across the skin flap to the receiver/stimulator, which in turn sends the signal to the electrode array in the cochlea. The auditory or hearing nerve is stimulated and the information is sent to the brain and interpreted as sound.
What results are typical of a cochlear implant?
The cochlear implant will provide the ability to hear sound. The degree to which a person can understand speech varies greatly. Some individuals are unable to understand speech without visual cues, while others can easily use the telephone. We continue to conduct research focused on understanding why there is such great variability in performance after implantation.
General trends observed in the pediatric cochlear implant population:
- Children who use their cochlear implants on a full-time basis tend to understand more speech than those who do not
- Children born deaf who are implanted at a younger age tend to understand more speech after implantation
General trends observed in the speech and language development of pediatric cochlear implant users:
- Speech production skills mirror listening skills
- Speech production skills can continue to improve after an extended period
- Language skills seem to improve at a faster rate than in children with profound hearing loss who do not wear cochlear implants
- Reading skills of cochlear implant users appear to surpass what has been historically reported in deaf children in the sense that cochlear implant users tend to track more closely to their hearing peers than do their peers with profound hearing loss who use hearing aids
How do I know if I’m a candidate for a cochlear implant?
The current accepted criteria are as follows:
Young children: 12 months to 2 years
- Profound sensorineural hearing loss (nerve deafness) in both ears
- Lack of progress in development of auditory skill with a hearing aid or other amplification
- High motivation and realistic expectations from family
- Other medical conditions, if present, do not interfere with the cochlear implant procedure
Children: 2 to 17 years
- Severe-to-profound sensorineural hearing loss (nerve deafness) in both ears
- Little or no benefit received from hearing aids
- Lack of progress in the development of auditory skills
- High motivation and realistic expectations from family
Adults: 18 years and over
- Severe-to-profound sensorineural hearing loss in both ears
- Little or no useful benefit received from hearing aids
- Qualified candidates are those scoring, with a hearing aid, 50% or less on sentence-recognition tests in the ear to be implanted and 60% or less in the nonimplanted ear or bilaterally