What are cochlear implants, how do they work, and who typically gets them?

DO-IT Factsheet #395
http://www.washington.edu/doit/Stem/articles?395

A cochlear implant is a small, complex electronic device that can help to provide a sense of sound to a person who is profoundly deaf or severely hard-of-hearing. The implant consists of an external portion that sits behind the ear and an internal portion that is surgically placed under the skin. An implant includes the following components:

An implant does not restore normal hearing. Instead, it can give a person who is deaf a useful representation of sounds in the environment and help him or her to understand speech.

A cochlear implant is very different from a hearing aid, which amplifies sounds so they may be detected by an ear. Cochlear implants directly stimulate the auditory nerve. Signals generated by the implant are sent by way of the auditory nerve to the brain, which can learn to recognize the signals as "sound." Since the signals from a cochlear implant are different from normal sounds it takes time to learn to interpret the meaning of the impulses. However, it allows many people to recognize warning signals, understand other sounds in the environment, and enjoy a conversation in person or by telephone.

Adults who have lost all or most of their hearing later in life can often benefit from cochlear implants. They learn to associate the signal provided by an implant with sounds they remember. This often provides recipients with the ability to understand speech solely by listening through the implant, without additional visual cues such as those provided by lip reading or sign language.

Cochlear implants, coupled with intensive postimplantation therapy, can help young children acquire speech, language, and social skills. Most children who receive implants are between two and six years old. Early implantation provides exposure to sounds that can be helpful during the critical period when children learn speech and language skills. In 2000, the FDA lowered the age of eligibility to 12 months for one type of cochlear implant.