If you are looking for a simple, bare-bones definition of audiology, here it is: Audiology is the profession that figures out and fixes difficult hearing problems.
People come to us and say, “I can’t hear…” and complete their sentence with phrases like “…my wife, the TV, my grandchildren, what people are saying when I’m in a group.” The remediation of their hearing problems is at the very heart of our profession.
Hearing loss comes in different degrees. In this article I will discuss people with what I will call “poor” hearing. These are people with severe-to-profound hearing loss who often describe their condition like this: “I am deaf. I only hear if someone is talking to me from directly in front. I hear a little, but I don’t understand what people are saying.”
To help people with severe hearing loss, the audiologist needs to know the science of speech intelligibility: how the information of speech is distributed across the frequency spectrum, how changes in intensity affect word understanding, and, most importantly, how to find the point where the “upward spread of masking” kicks in and degrades word understanding as intensity increases.
Conventional hearing tests include the SRT (Speech Reception Threshold) and the Word Understanding test. Neither of these tests predicts how well a patient will hear when there is noise in the environment. Also, the Word Understanding Testing, as it is usually administered, does not tell you what the patient’s functional dynamic range of hearing is, so you are not sure what happens to word understanding if you increase or decrease the volume on the hearing aid.
TEST WORD UNDERSTANDING
If the patient has poor hearing, it is very helpful to conduct word-understanding tests at multiple presentation levels and record the results on a graph. This graph goes by different names, including the articulation index. It helps the practitioner “see” the zone (on the intensity scale) where the patient is able to understand words and the zone where the patient is unable to understand words.
I want to stress the words able and unable because we need a clear idea of where the boundaries between hearing and not hearing lie. We need to see (on a chart or graph) the zone where a patient can “hear well” (understand words) and “not hear well” (hear speech, but not understand it).
When you graph a speech articulation function for a patient with poor hearing, you find large zones of “deafness” (areas where the person is unable to understand the words). This is discouraging. However, you also see a small zone of functional hearing. This “precious zone” is the zone you work with when you fit hearing aids.
USING THE WINDOW OF HEARING
I call this narrow zone of good hearing the “window.” Like light coming through the window of your house, only the sounds that come through the window of hearing are productive. All other sounds miss the window and result in the patient being “unplugged” or “frustrated.”
When you increase the volume of words but they are still below the patient’s zone of good hearing, the patient is “unplugged,” i.e., unable to hear the words or carry on a conversation. Increasing the volume above this window frustrates patients because, even though they are receiving a lot of speech sound, they are unable to understand it.
Now there is good news and bad news about this situation. Many people with poor hearing are fitted with hearing aids that make it difficult or impossible for them to get into the functional zone of their hearing. The good news is that there are a great many tools available that can help us (as communication experts) adjust the hearing aid settings so the patient is able to hear well in specific listening situations.
If the hearing aids are fitted properly they keep the output from exceeding the upper limit of the hearing zone where speech understanding deteriorates. Well-fitted hearing aids can be switched into a setting that is effective for listening in a noisy environment. That allows patients to go to their favorite restaurant and enjoy a conversation over dinner with friends or family.
For people who cannot be made to hear well with hearing aids, audiologists would do well to refer them for a cochlear implant evaluation. Cochlear implants provide auditory access when hearing aids no longer can. With current technology, people with severe and profound hearing losses can be expected to have better speech understanding with cochlear implants then they can with hearing aids.
Carrying forward what Dr Madell writes about CI’s, in fact they have become so good, Med-El’s devices now have regulatory approval for treating single-sided deafness (CE marque); and it was the Hot Topic at the CI Conference last week.
I think it is important to stress that poor hearing is not simply hearing loss that is severe in quantity, but also hearing loss that is severe in QUALITY. I think a good audiologist spends time evaluating this aspect of hearing, as this knowledge empowers us to assist effectively with the consequences of the hearing loss, AND provide counselling an support in managing expectations.