Because the extent and type of hair cell damage, electrical signal patterns, and sensitivity of the hearing nerve are different for each person, a specialist must fine-tune the sound and speech processor for every patient.
By measuring the lowest and highest current for each electrode, the clinician finds the softest and loudest sounds that will be heard (each electrode produces a different sound with different pitch). The sound and speech processor matches sounds on different electrodes with different volumes and attempts to create an accurate version of the original sound. However, because a limited number of electrodes are taking over the function of the thousands of hair cells in a normal ear, sounds won't be totally "natural."
After the first few programming sessions, the user begins to pick up sounds with the implant, but giving the implant full power is a gradual process that takes several months. In children who are born deaf, the stimulation from the implant will allow them to develop the brain pathways necessary to hear sounds. This is an extended process with programming and intensive therapy that often lasts for several years.
During the programming process, the user attends speech and language therapy sessions to help identify and interpret the new sounds he or she is hearing. In addition, an important part of the therapy includes parent education and training.
Therapy will help a child develop and understand spoken language through detecting, imitating, and associating meanings of sounds. These sessions last at least a year, along with parent education and training programs. In many cases, therapy has helped kids with cochlear implants develop speech and language on par with their peers and attend mainstream schools.
Some families choose to have implants in both ears. This can help with speech detection when there is background noise and in localizing the source of sounds.From: http://kidshealth.org