Doctors do not explain much, or any of this actually. Nor do they explain that in every person, every individual, the case and instances are a variable, even if the individuals have the same congenital issues. When looking at a CT scan you should be able to notice thta the bony structures within the crainal cavity, especially around the vestibular bone region seem to vary widely.
Regarding persons that lose their hearing later in life or are born with normal hearing and incident structures -- the cochlear implant may work best for them, unless there are damages casused by disesae, such as ossifications. Sometimes these can be cleared away, but for the most part, those with normal inner ear structurs and vestibular bones, etc., will derive the most benefit from a cochlear implant. There are also the added advantages of auditory memory, meaning that the brain has already retained knowledge of sounds. Because of what is termed "plasticity," the brain can adjust much more easily to decode the "new" types of "sound" signals from a cochlear implant, whereas a congenitally deafened individual who may have not heard sounds, or may have not developed speech prior to losing hearing, may not have the benefit of stored "auditory memory."
... it should be incumbent upon the doctor(s) and surgeon(s) performing the procedure to educate, inform, advise and counsel the patient sufficiently so that there are (as they like to term) "no unreasonable expectations." It's just that from a direct experience (not my own -- I'm deaf and will stay that way!), the doctor(s) did NOT properly advise the patient regarding risks/benefits, and the surgery did NOT turn out well.
One category of cochlear implants that I am adamantly against is with infants and small children with congenital hearing loss. Such children have not had the opportunity to develop language (ASL) or a communication mode that can be used to express or convey to the parent(s) or doctor(s). A child with post-lingual deafness--- they have an established communication mode, and probably have normal structures. Their candidacy could be more ideal, they can also provide feedback, etc. and have auditory memory. As for children with congenital deafness, implanting them raises some issues with ethics, and these need to be critically examined. Parents are NOT the best spokespeople for the child because they are too emotionally involved in the decision and are blind to the possible consequences. So many congentially deafened children have been implanted and the results are dismal!
