Hearing Aid

Hearing Aid, electronic device that amplifies sounds for persons with hearing impairments (see Deafness). Hearing aids have the same basic components as any public-address system, but all the components are miniature and the amplified sound is delivered to the ear of only the hearing-aid user. The microphone, amplifier (consisting of transistors and integrated electronic circuits), miniature receiver, and battery of a hearing aid are enclosed either in a chassis or shell, which is worn behind or within the ear or in the stem or temple portion of eyeglasses. A small tube directs the amplified sound from the receiver into the ear canal of the wearer. A unit of this sort can fit into the ear canal with only a small protruding part. Individuals with more severe hearing impairments require a more powerful amplifier, usually encased in a chassis smaller than a deck of cards, which can be easily carried in a shirt pocket. A cord connects the amplifier to the receiver in the wearer’s ear. Most hearing aids have adjustable controls; some have directional microphones. If the hearing loss is caused by malformation of the ear canal or impaired function of the middle ear, a small vibrator may be clamped against the mastoid bone behind the ear with a headband; the sound is conducted by the vibrator through the bones of the head to the inner ear.

A more recently developed hearing aid called a cochlear implant is now available to some profoundly deaf persons whose auditory nerves remain functional. The device consists of electrodes that are embedded in the cochlea of the inner ear to stimulate the auditory nerve and are connected through the mastoid bone to a receiver surgically placed beneath the skin. A microphone near the ear relays sound signals to a microprocessor, which converts them into electric signals that are sent to a transmitter behind the ear and on to the receiver and cochlear electrodes. Although the cochlear implant does not reproduce the human voice, the device substantially improves sound perception for many users, particularly those children and adults who have postlingual deafness (deafness that occurred after a person learned to talk). For those with postlingual deafness, cochlear implants can significantly enhance the ability to understand speech, and some users are able to recognize environmental sounds and, in some cases, even music. Cochlear implants also help to a lesser degree many adults and children with prelingual deafness (deafness that occurred before a person learned to talk). For these people, cochlear implants can improve speech perception and talking, and these benefits improve with continued use of the device.