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| Cochlear Implants - How Do They Work |
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| Extracted from www.helpkidshear.org |
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| Speech and other sounds are picked up
by the microphone and sent to the speech processor. The processor
codes the sounds into an electrical signal which is sent via
a cable to the transmitting coil. The coil passes the signal
through the skin to the implant which transforms the signal
to electrical pulses. The pulses pass from the electrode array
and stimulate hearing nerve fibres within the cochlea. |
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| The speech processor does not just
make sounds louder as does a hearing aid. Instead, it selects
out some of the important information in the speech signal
and then produces a pattern of electrical pulses in the patient's
ear. This pattern is selected to sound as close as possible
to the original speech sound. It is not possible to make sounds
completely natural, because there are only 22 electrodes that
are replacing the function of tens of thousands of hair cells
in a normally hearing ear. |
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| The electrical patterns are different
for each person and need to be programmed into the speech processor
by a trained Audiologist. The differences arise because the
electrodes are not always in the same position relative to
the surviving nerves and the nerves vary in sensitivity to
electrical currents. The clinician must measure the lowest
and greatest current for every electrode to determine the softest(T
level) and loudest sounds(C level) that will be heard. The
different electrodes produce sounds with different pitch. The
speech processor combines sounds on different electrodes with
different loudness, to build up something as close to the original
sound as possible. |
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| The hearing process using a cochlear
implant can be summarized as follows: |
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| This image is extracted with courtesy
of www.helpkidshear.org. |
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| a. Sounds and speech are detected by
the microphone. |
| b. The information from the microphone
is sent to the speech processor. |
| c. The speech processor analyses
the information and converts it into an electrical
code. |
| d. The coded signal travels via a
cable to the transmitting coil in the headset. Radio waves
from the transmitter coil carry the coded signal through the
skin
to the implant inside. |
| e. The implant package decodes the
signal. The signal contains information that determines how
much electrical current will be sent to the different electrodes. |
| f. The appropriate amount of electrical
current passes down the appropriate lead wires to the chosen
electrodes. |
| g. The position of the stimulating
electrodes within the cochlea will determine the frequency
or pitch of the sounds. The amount of electrical current will
determine
the loudness of the sounds. |
| h. Once the nerve endings in the
cochlea are stimulated, the message is sent up to the brain
along the hearing nerve. The brain can then try to interpret
the stimulation as a meaningful sound. |
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