Wired for sound: How cochlear implants work

Wired for sound: How cochlear implants work

Thursday, September 28, 2000

By MACAULAY CAMPBELL
SEATTLE POST-INTELLIGENCER

Hearing loss and deafness affects 28 million people worldwide. Some regain hearing with the help of a cochlear implant, a device that converts sound into electric pulses for deaf people with a functioning auditory nerve. The internal and external components of the device fulfill the role of a damaged inner ear by transmitting signals directly to the brain through the cochlea. (See story.)

How the ear works
1. Sound waves funnel into the outer ear and travel down the ear canal to the eardrum.
2. The sound waves cause the eardrum to vibrate, which sets three tiny bones (the malleus, incu and the stapes) in the middle ear into motion.

3. The movement of these bones causes fluid in the cochlea to vibrate creating a ripple effect within the chambers of the cochlea.
4. The ripples make tiny hairs (more than 15,000) in the cochlea bend, sending electrical impulses to the auditory nerve where they are interpreted as sound in the brain.

How the cochlear implant works
1. Sound is picked up by a small microphone that cradles the ear.
2. A thin cord carries the sound to a miniature computer that filters, analyzes and digitizes the sound into coded signals.
3. The signals are sent to the transmitter coil, which rests on top of the skin and is held in place by magnets (one inside transmitter coil and another inside implant).

4. The device transmits signals to the cochlear implant under the skin that delivers electrical impulses to the array coiled around the cochlea.
5. Electrodes along the array stimulate the auditory nerve fibers in the cochlea.
6. The resulting electrical sound information is carried along the auditory nerve to the brain for interpretation.

The array
Inserted approximately an inch into the cochlea, the array consists of 22 electrodes that are individually programmed to decipher sounds. Every cochlear implant is customized for the user.

Sources: Cochlear Corp., University of Washington Medical Center, World Book Encyclopedia

The information on this page is adapted from a detailed illustration that appeared in the Post-Intelligencer. The original is available for download as an 11-by-14-inch Acrobat PDF file.

To view it, you will need the Acrobat 4.x Reader.