Forty years ago, it was first demonstrated that direct electrical stimulation of the cochlea could restore auditory sensations in people with profound sensorineural hearing loss. In recent years, the effectiveness of cochlear implants has increased enormously, through a better understanding of the principles of auditory coding and technological improvements in implant design.
Cochlear implants (CIs) are prescribed only for people with severe to profound hearing impairments who cannot benefit at all from conventional hearing aids. A CI involves surgical implantation of electrodes in the cochlear to provide electrical stimulation of the auditory nerve through an externally worn speech processor. Approximately four weeks after surgery, the intensity of neural stimulation for each electrode is tailored or "mapped" based on each person's audibility and uncomfortable loudness levels. For many, the transformation is nothing short of remarkable. Following implantation, successful CI users experience a change from total deafness to a level of restored hearing that allows them to talk on the telephone, attend movies and music concerts, and participate in community meetings and social gatherings. .
In spite of the enormous benefits, the initial adjustment to a CI can be difficult and quite lengthy. Immediately after implantation, listeners often report that the sound delivered by the implant has a strange and unnatural quality. Their difficulties are exacerbated by the presence of noise and reverberation. It is only after a period of time, even as long as 30 months, that they grow accustomed to the device so that they are able to interpret the sound and combine it with visual cues for effective communication.