The past decade has seen tremendous technological improvements in hearing aids, from automatic adjustments to the wearer's environment, to bluetooth connectivity, to frequency lowering technology, to extended-wear devices. Many users who have worn aids for decades can appreciate some of these improvements. However, there is probably no one wearing hearing aids, no matter how successfully, who does not at least sometimes wish they could hear better. This is a common complaint that I, and any audiologist (no matter how good), will hear from patients. "I just need more clarity" -- if only it were so simple! Hearing aid users are understandably frustrated by what they perceive as a lack of speech clarity, especially when one considers the expense of today's advanced hearing aids, which is often an out-of-pocket cost.
There are several reasons why a person using hearing aids may not hear (or understand) speech as clearly as they would like to. First, the hearing aids may simply not be adjusted appropriately for the person's hearing loss. I have frequently seen patients who were fit with hearing aids elsewhere and found that the frequency response and amplification characteristics of the hearing aids were not giving them what they needed for their hearing loss. Sometimes some relatively simple programming adjustments can make a significant difference in the user's ability to hear and understand speech.
However, it is more common to find that despite numerous adjustments to the hearing aids settings the wearer still finds a "clarity gap" -- i.e., they feel they are simply not achieving the level of speech understanding that they desire. These situations can range from a simple awareness that "I know I won't hear perfectly in all environments," to a more difficult "I can't communicate effectively a majority of the time." This is one of the most frustrating and challenging situations that we encounter as audiologists.
There are a number of reasons why a hearing aid user may not understand speech well despite the use of advanced hearing aid technology. Most hearing aid users have what is called "sensorineural hearing loss," which is a hearing impairment that results from the degeneration of the sensory nerve cells of the inner ear, or cochlea. These sensory cells are called outer hair cells and are crucial to our ability to hear a wide range of sounds clearly. The extent of this cochlear damage can vary widely, but it generally causes at least some degree of "blurring" of speech sounds. The normal inner ear has a remarkable ability to make extremely fine distinctions among sounds. Unfortunately when a person has sensorineural hearing loss there is more than just a lack of loudness of sound; there is also a reduced ability of the inner ear to separate and sharply distinguish frequencies. This impaired "frequency resolution" can have significant deleterious effects on the person's ability to understand speech. In addition, some people with hearing loss (often, but not always, those with a more severe degree of loss) have impaired connections between the sensory receptor cells of the inner ear and the auditory nerve, or 8th nerve, responsible for carrying the electrical sound impulses to the brain.
Another reason that people with hearing loss may experience difficulty hearing speech clearly, even with hearing aids, is due to changes in how the auditory centers of the brain process speech. This can be especially true for listening to speech in complex environments, such as those with background noise. A large part of our ability to hear (and understand) speech in noise comes from the higher-level areas of the brain. It's not enough for sounds to reach the auditory cortex in a clear way (and this, as we have seen, is already compromised with sensorineural hearing loss); the brain must then assign meaning to what it has received and, in complex environments, sort out the signal of interest from the other unwanted noise. This is an extremely complex operation that requires rapid processing of signals and the use of various interconnections among different regions of the brain. There is good evidence that as we age, these "auditory processing" skills can decline significantly, adding another layer of difficulty in understanding speech for those with hearing loss.
All of this can certainly make the person with hearing loss (not to mention us audiologists) feel fairly pessimistic. However, despite all of the challenges we face in trying to provide help to those with impaired auditory systems, there is still reason to be hopeful. With the use of well-fit, appropriately adjusted hearing aid technology, the right counseling and setting of expectations, and the provision of other rehabilitative therapies (such as the LACE auditory training program -- see my post from 6/7/11), we can still significantly improve the quality of life for the majority of those with hearing loss. And that's why I love what I do.