Implants - How Do They Work?
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.
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.
The electrical patterns are different for each person and need to be programmed into the speech processor by a trained clinician. 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 and loudest sounds 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.
process using a cochlear implant can be summarized as follows:
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