Cochlear implant is an electronic device. The speech processor in vitro converts the sound into an electrical signal with a certain coding form, and directly stimulates the auditory nerve through the implanted electrode system to restore, improve and rebuild the hearing function of the deaf. Cochlear implant is a kind of sound signal processor, which can convert sound signals into electrical signals that can be recognized by auditory nerves. Cochlear implant can convert sound into electrical signal after receiving it by directional microphone, and transmit it to speech processor, amplify and filter the sound, and then transmit it from transmitter to receiver, and the generated electrical pulse is sent to corresponding electrodes, thus arousing the excitement of auditory nerve fibers, and then transmit the sound information to the brain to produce hearing.

Hearing aid, as its name implies, is to amplify the sound and help the deaf to hear it. It realizes the function of amplifier. However, due to the severe hearing loss of some patients with severe or extremely severe deafness, the average hearing threshold in speech frequency region often exceeds 90 decibels, and even the amplified sound is difficult to hear, and the effect is still poor after wearing hearing AIDS. This is because the sensory cells in the inner ear are damaged due to inner ear diseases, drug poisoning or other reasons, which seriously hinders the transmission of auditory information. Although the external amplified sound is naturally clear, the patient's central auditory system cannot feel enough information.

No matter how well your hearing aid or cochlear implant system is debugged, these sound waves (current pulses) are meaningless until they are recognized by the auditory cortex of the brain and become understandable sounds, words or music. This is why you can still hear the sound of drumming and clapping after turning on your mobile phone or wearing a hearing aid, but you are indifferent to calling his name behind your back. We should know that our brain has a lot of room for growth and change, which means that the consequences of cochlear implant and hearing aid are largely determined by the plasticity of the brain.