Q: I recently purchased two hearing aids, and the one for the right side helps a lot, but I seem to get no extra clarity or help from that side; why do I need both hearing aids?
A: This is a question I am asked a lot, particularly from people who have been diagnosed with unilateral Meniere’s syndrome, (the disease attacks only one side, as opposed to both), although not limited to Meniere’s. The answer is complicated; in some cases the assistance of a hearing aid can be beneficial, in spite of the lack of understanding, in other cases it can have the opposite effect and will cause further trouble in the “good” ear. This can happen even when the pure tone test results indicate that both ears are measuring exactly the same.
For the answer to this we have to focus on a different area of the audiogram, an area that most people don’t even realize is there unless it is specifically explained to them. It used to be called the word discrimination score but is now more commonly referred to as the Speech or Word Recognition Score, (WRS). This score is generally measured at a level the patient has indicated as being their most comfortable level for speech in a quiet environment, (MCL) and consists of having 25-50 words read to them and repeated back to the tester. The number of words repeated correctly is calculated as a percentage; so if you correctly repeated 45 of 50 words, your score would be 90%. I just want to press home the fact that this does NOT mean that the person has lost 10% of their hearing, it is just a score for how well the patient hears common words at a level that is comfortable. That level is often raised for people with hearing loss.
In a person with normal hearing we would expect that score to be 90-100%, but as hearing loss sets in, the number can drop as well. It is not uncommon to see people with presbycutic hearing loss, (hearing loss due to the normal aging process), at anywhere from 80% and up. The difference is an indication that the missing high frequencies are causing some blurring of the words, particularly the consonant sounds, which tend to give words their clarity.
In some cases, Meniere’s disease being one of them, the damage is much more widespread, but occurs in the nerve endings that receive tones between the ones we test. Remember, we generally test 7 frequencies, the normal human cochlea can decipher several million more than that.
So why amplify an ear that will never fully understand speech? Well, sometimes it is not appropriate. For some people amplifying the “bad” ear can lead to interruption of the signal to the good ear, in which case, aided testing will show a lowering of the WRS when tested bilaterally. In those cases, the hearing aid simply acts to make the patient aware of sounds in his surroundings. Often a hearing aid will not be recommended for such a case. But when aided testing, (that is, testing done with the hearing aids in), indicates that there is an increase in WRS, then any added benefit is generally considered beneficial. Over time and with some aural rehabilitation, we can often improve the overall WRS, even if just slightly.
Even when we can’t, another consideration is the ability to pinpoint the origin and direction of a sound, something we need two ears to properly discriminate. Remember that hearing truly takes place in the brain; the ears are just the tools the brain uses to get the signal from outside to in. The time difference and amplitude difference, (what we generally refer to as “volume”), when a sound goes from one side to the other is something we can’t consciously notice, but the brain can calculate those very minute differences to determine where a sound comes from and have us turn our heads the right way. With only one ear, most people will assume that all sounds come from that side. But if you’re crossing a street and a bus is coming from your left, looking right won’t help you. I have seen this happen, and it very nearly killed the person. So the price of having the sound of the bus, and ONLY the sound of the bus, is that of a hearing aid, but that hearing aid saved your life; seems like a worthwhile thing to pursue. But again, there are exceptions. If you have any doubt, please don’t hesitate to ask.