A cochlear implant is a surgically implanted electronic device that provides a sense of sound to a person who is profoundly deaf or severely hard of hearing. The cochlear implant is often referred to as a bionic ear.
The implant consists of an external portion that sits behind the ear and a second portion that is surgically placed under the skin. An implant has the following parts: a microphone, which picks up sound from the environment; a speech processor, which selects and arranges sounds picked up by the microphone; a transmitter and receiver/stimulator, which receive signals from the speech processor and convert them into electric impulses; an electrode array, which is a group of electrodes that collects the impulses from the stimulator and sends them to different regions of the auditory nerve.
An implant does not restore normal hearing. Instead, it can give a deaf person 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. Hearing aids amplify sounds so they may be detected by damaged ears. Cochlear implants bypass damaged portions of the ear and directly stimulate the auditory nerve. Signals generated by the implant are sent by way of the auditory nerve to the brain, which recognizes the signals as sound. Hearing through a cochlear implant is different from normal hearing and takes time to learn or relearn. However, it allows many people to recognize warning signals, understand other sounds in the environment, and enjoy a conversation in person or by telephone.
Children and adults who are deaf or severely hard-of-hearing can be fitted for cochlear implants. According to the Food and Drug Administration (FDA), as of April 2009, approximately 188,000 people worldwide have received implants. In the United States, roughly 41,500 adults and 25,500 children have received them.
Adults who have lost all or most of their hearing later in life often can 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 requiring any visual cues such as those provided by lipreading or sign language.
People with mild or moderate sensorineural hearing loss are generally not candidates for cochlear implantation. After the implant is put into place, sound no longer travels via the ear canal and middle ear but will be picked up by a microphone and sent through the device's speech processor to the implant's electrodes inside the cochlea. Thus, most candidates have been diagnosed with profound sensorineural hearing loss.
The presence of auditory nerve fibres is essential to the functioning of the device: if these are damaged to such an extent that they cannot receive electrical stimuli, the implant will not work. A small number of individuals with severe auditory neuropathy may also benefit from cochlear implants.
Cochlear implant surgery, coupled with intensive postimplantation therapy, can help young children to 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.
Use of a cochlear implant requires both a surgical procedure and significant therapy to learn or relearn the sense of hearing. Not everyone performs at the same level with this device. The decision to receive an implant should involve discussions with medical specialists, including an experienced cochlear-implant surgeon. The process can be expensive. For example, a person’s health insurance may cover the expense, but not always. Some individuals may choose not to have a cochlear implant for a variety of personal reasons.
Surgical implantations are almost always safe, although complications are a risk factor, just as with any kind of surgery. An additional consideration is learning to interpret the sounds created by an implant. This process takes time and practice. Speech-language pathologists and audiologists are frequently involved in this learning process. Prior to implantation, all of these factors need to be considered.
Individuals who have acquired deafblindness (loss of hearing and vision combined) may find cochlear implants a radical improvement in their daily life. It may provide them with more information for safety, communication, balance, orientation and mobility and promote interaction within their environment and with other people, reducing isolation. Having more auditory information that they may be familiar with may provide them with sensory information that will help them become more independent.
Some effects of implantation are irreversible; while the device promises to provide new sound information for a recipient, the implantation process inevitably results in damage to nerve cells within the cochlea, which often results in a permanent loss of most residual natural hearing. While recent improvements in implant technology, and implantation techniques, promise to minimize such damage, the risk and extent of damage still varies.
In addition, while the device can help the recipient better hear and understand sounds in their environment, it is not as good as the quality of sound processed by a natural cochlea. The main problem is with the age of recipient. While cochlear implants restore physical ability to hear, this does not mean the brain can learn to process and distinguish speech if the recipient has passed the critical period of adolescence. As a result, those born deaf who receive an implant as an adult can only distinguish simple sounds, such as a ringing phone vs a doorbell, while others who receive implant early can clearly understand speech. The success rate depends on a variety of factors, most critically the age of recipient but also the technology used and the condition of the recipient's cochlea.