Q: (D. M., Hamilton) I have a hearing loss in my left ear, but the hearing aid is being recommended for the right ear, which is normal. Does this sound like a reasonable way of fitting someone in my circumstances?
A: This is another great question, because there are so many ways to answer it. Without knowing for sure which system was specifically recommended, I would take an educated guess that the dispenser is referring to a C.R.O.S. or Bi-C.R.O.S. system, both of which would be perfectly reasonable in this case, depending on what the results were like for the “bad” ear, and how it compared to the “good” ear.
Most people look at the audiogram, (the written report containing the graph of the pure tone results, as well as a lot of other information), and see ONLY the graph of the hearing loss. But that will only tell half the story. The graph represents the minimum so und pressure levels you require in order to just barely hear the sound at the specific frequencies tested. We generally cover octaves between 250 Hz and 8000 Hz, and sometimes some of the half octaves. Speech sounds, on the other hand, can fall anywhere from 10 Hz to 10,000 Hz and beyond. Aside from this there is also another box in which is recorded the results of the speech testing. A minimal hearing test will cover two speech tests: The first is the SRT or speech recognition threshold. The second is the WRS or word recognition score.
In a previous article I made mention of the speech results, which can predict how well a person will do with a hearing aid. In short, we are not always able to completely fix what has broken; at least not yet. The best correlation I can think of is a prosthetic leg. If a person has the misfortune of losing one of their legs, and is fitted with a prosthetic leg, it is never going to fully replicate the real leg. It is a good replacement, that is, it keeps them mobile, allows them to do things that a person with only one leg couldn’t do, but it won’t, for example, have any feeling. The nerve endings will never allow feeling in a prosthesis, so the ability to traverse rough terrain will require using other senses, and the feedback from the other leg.
When person loses clarity, not just hearing, but clarity, they may not ever get any use from that ear again. If all sound drawn to the brain from that ear is distorted, then amplifying it will only amplify that distortion. In some cases proper rehabilitation will help that, but in many cases, like that of severe Meniere’s disease, that clarity is lost forever. So in those cases, like that of the prosthetic leg, we rely on the good ear to do all of the hearing. To accomplish this, we use a C.R.O.S., or a hearing aid that is enabled with Contralateral, (opposite side), Routing of Sound. Using a microphone on the bad ear, we send all sound from that side, (in the above case it would be the left ear), and transfer it over to the right, which, hopefully, has less issues of clarity. What generally confuses people is that they have to wear hearing aids in both ears, since the microphone on the left is housed the same way as any other hearing aid, even though it doesn’t actually help that side. This way, all sound, from either side is processed through the better ear. Over time the brain will come to recognize the amplified sound over the natural sound, and at that point people are often able to lateralize the sound, (tell where it’s coming from). But this is a long process and requires counseling and rehabilitation.
The “Bi” comes into play when the person has one very bad or dead ear, but the “good” ear also has some hearing loss, (good word recognition, but lower than normal hearing levels). The same principles apply; send all the sound to the ear with better understanding so the patient can understand more speech.
The fact is, however, many patients either can’t, or don’t have the patience to acclimatize themselves to this. People have an expectation that, like glasses, hearing aids will provide an instant fix to their problem, which is a misconception. Most people, whether they have loss in one ear or both, good understanding or bad, need time to acclimatize to wearing hearing aids. As the technology gets better and better the time it takes for this to change is decreasing, and sometimes it is as instantaneous as we all want it to be, but for the most part it takes some time. But once they have taken that time, the rehabilitative portion of using hearing aids can really begin.
If you would like further explanation, please feel free to call either of the offices and we would be glad to go into more detail.