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   Rehabilitation Engineering Research Center
   on Hearing Enhancement

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Dr. Ross on Hearing Loss

Is There a "Best" Hearing Aid?

by Mark Ross, Ph.D.
This article first appeared in
Hearing Loss (Sep/Oct 2006)

I recently received a letter asking me for hearing aid advice. It seems this woman had just purchased a single $1500 hearing aid on the advice of her ear doctor. The hearing aid itself a popular and well-known brand - was fit and sold by a professional audiologist. But then she learned that a friend had just purchased two hearing aids from Sears for $1100. She asked me if I knew whether one of the aids was better than the other. Insofar as one versus two aids is concerned, that was an easy question to answer: for most people with hearing loss, two hearing aids are better. But insofar as which one of the two electronic instruments was superior to the other, that's a question I couldn't answer. And yet we know it's one that people with hearing loss ask all the time. If she were to purchase two of the higher price instruments, the total cost would be $3000, or $1900 greater than the aids her friend bought. She understandably wondered whether or not she could have gotten the same or even greater hearing benefits at a much lesser cost. For most households, $1900 is a lot of money. So what kind of advice could I give her? Not very much I'm afraid.

If she could be assured that the difference in price was worth it, reflecting perhaps a more skilled and time-consuming fitting process as well as a superior hearing instrument, then the difference in cost would be easy to justify. But we can offer no such assurances. As of now, there is no ranking of hearing aids comparable to that which we see for automobiles and a host of other devices. It would be very helpful if she had an opportunity to try a set of each type of hearing aid, each being fit according to the manufacturer's suggestion, and then be permitted to make up her own mind whether a performance difference could justify the difference in prices. But then, what about the 100 or so other hearing aids out there on the market? How about comparisons that include listening in quiet as well as in different types of realistic noises? She couldn't try all this possibilities. And even if such a trial were possible, I know of no practical way that this can be accomplished. Clearly, the situation gets very complicated.

I've often likened the fitting of a hearing aid to an old fashioned marriage. There is the bride (the hearing loss), the groom (the hearing aid) and the matchmaker (the dispensing audiologist). It is the audiologist's job to ensure a good marriage, i.e. to join together the unique characteristics of each person's hearing loss to the right hearing aid. As we know, it takes a compatible bride and groom make for a happy marriage. So let's consider each of the three ingredients for nuptial bliss in this area.

The Hearing Loss

A major reason why it is not possible to identify a single "best" hearing aid for all is because of the large variety of hearing losses. These differences extend beyond a simple description of severity, which still remains a crucial factor. A person with a mild hearing loss would not be fit with the same hearing aid as someone with a severe to profound hearing loss. There are also differences in the audiometric "configuration" of the hearing loss, that is the degree of impairment at the different frequencies. Even with the flexibility incorporated in modern hearing aids, one would not necessarily recommend the same hearing aid for someone with much poorer high frequency hearing than for the person with a relatively equal hearing loss across frequencies. .

The degree and configuration of a hearing loss is only the most obvious consideration. There are often other auditory dimensions that must be considered, for example a person's tolerance of loud sounds. Even with the same audiogram, people will often differ on their ability to tolerate such sounds. These differences must be accommodated when choosing a specific type of hearing aid.

Beyond the hearing loss itself, each person also has unique communication needs and functional limitations. Some people, for example, will prefer hearing aids that adjust automatically to the loudness level of the input sounds. For one reason or another (perhaps arthritic hands), they'd rather that the hearing aid change the volume for them automatically. They want to hear soft sounds as well as they can, but at the same time require that loud sounds not be amplified to an uncomfortable level. (This requires a skilled fitting process.) Other people prefer to control their own loudness experiences and demand that their hearing aids include a volume control.

The size and visibility of a hearing aid is often a major consideration when a hearing aid is pre-selected for someone. As much as I personally deplore a primary focus on any other factor but hearing, for some people the appearance (or lack of it) of a hearing aid is extremely important. It is necessary, therefore, to consider personal preferences. In these instances both the hearing aid user and the dispenser must weigh the pros and cons of different hearing aids to determine which one best fills the bill. For some people the tiniest hearing aid, inserted way down into the ear canal, is not practical for one reason or another (degree of hearing loss, size and shape of ear canal, etc.). On the other hand, other people may be able to achieve both their listening and cosmetic goals with the tiniest and most invisible of hearing aids.

Even with similar audiograms, human beings differ in many other ways besides their hearing loss. Hearing aids incorporate certain features and each hearing aid user requires that the features included in a hearing aid reflect his or her personal situation. This may necessitate the inclusion of a telephone coil (as it usually should), direct audio input capability (to use a personal FM system), directional microphones, an effective acoustic feedback control system, etc. No single hearing aid possesses all the features included in all the hearing aids now on the market. Specific decisions do have to be made.

The point I'm making here is that the entire fitting process must be individualized. Hearing aids are not just fit to a pair of ears, but to a human being with a unique life style, communication needs, and personal capabilities and limitations (including financial). Testimonials, whether provided by manufacturers in their marketing efforts or through personal knowledge, cannot predict how a different person will perform with the same hearing aid. A hearing aid may well be providing the marvelous results that are claimed, but generalizing these claims to different people is chancy at best. This same logic also applies when some friend or family member reports an absolutely horrendous listening experience with a specific hearing aid. This same hearing aid may well be just right for someone else..

The Hearing Aid

Modern hearing aids share two general characteristics. First, there are a wide variety of styles out there, with different speech processing characteristics, sizes, shapes, and special features. Second, in spite of these differences, a large number of them can be electroacoustically programmed in similar ways. For example, the manufacturers' computer-fitting algorithms all provide some sort of "target" acoustic output for people with diverse types of hearing loss. It is possible to reach the same target with a number of hearing aids from different manufacturers, since current models permit an enormous variety of optional responses. But if different hearing aids can be programmed to produce a similar pattern of amplification would one be better than the other? Or would they perform similarly? The answer is possibly yes and possibly no. We just don't know.

Hearing aids do more than simply provide sound amplification. Just because two aids can amplify speech sounds to a similar output target, does not mean that they are similar in other respects as well. For example, many hearing aids incorporate some sort of automatic volume control (AVC) during the amplification process. This takes a measurable bit of time to accomplish (the so-called "time constants"). Because of contrasting fitting philosophies, manufacturers utilize different time constants in their AVC operation. This dimension does not appear when one examines the basic amplification pattern of a hearing aid; in addition to this, there are also other subtle electroacoustic differences between hearing aids. These types of variations can affect how well people understand speech through hearing aids, though we really don't know if or how much. One reason a hearing aid trial period is recommended is because of the often unpredictable performance of hearing aids; the only way to really determine how well a hearing aid operates on a specific person is to try it in real-life.

Of course, consumers would like to know which hearing aid would perform best for them in direct comparisons, such as was implicit in the question with which I began this article. Years ago, such "head-to-head" comparisons were a routine practice, mainly in non-profit centers (the classic "Carhart technique") but at the time hearing aids were capable of delivering basically only one electroacoustic option. So comparisons were relatively easy. Even so, obtaining valid results required a time-consuming battery of speech tests lots of speech tests - a requirement that few audiologists at the time could honor and then only in non-profit centers (in the days before professional audiologists dispensed hearing aids). Nevertheless, major questions kept being raised regarding the reliability of the technique and it was eventually superseded. Currently, this type of procedure is simply impractical. There are just too many hearing aids and variations, and the results obtained with one type of hearing loss would not necessarily apply to someone with a different type of hearing problem.

The many choices we now have, compared to years ago, means that somehow the full range of available hearing aids and adjustments have to be winnowed down to a practical few. It is impossible to try them all. However, it is at this point that, at least for two hearing aid specific features, it is possible to choose an objectively "better" performing hearing aid.

If it is determined that the person can benefit from a hearing aid that incorporates directional microphones, then it makes sense to compare directionally indexes (DI) on different aids. The DI is an overall metric of the effectiveness of directional microphones. It indicates the degree to which sounds arriving from the rear and sides of the microphone are weakened relative to those coming from the front. While even a 2 dB difference can be advantageous when speech perception scores are tested under controlled research conditions, it takes about 4 to 6 dB for a user to really notice any significant benefit. Information about the directional characteristics of a hearing aid should be available in the hearing aid specifications provided to the audiologist by the manufacturer. The larger this number, the better, other considerations being relatively equal.

The other hearing aid feature that can be objectively assessed is the effectiveness of an acoustic feedback management system. Some current aids include a circuit that permit a user to additionally increase the degree of amplification of a hearing aid without causing an acoustic squeal. Furthermore, unlike previous methods to control feedback, these systems accomplish this task without modifying the frequency response of the hearing aid. According to a recent article that examined the extent of increased gain possible in six different hearing aids, the increase varied from about 6 to 15 dB among them. This may be enough for someone to reach a desired loudness level without being disturbed by an acoustic squeal. Furthermore, the recent popularity of "open-fit" hearing aids where the ear canal is not occluded by an earmold - is only possible because feedback can now be more effectively controlled than with previous generation instruments. The higher the volume can be increased before the onset of feedback, the greater the likelihood of a successful hearing aid fitting. Unfortunately, this metric is not yet routinely included in the published hearing aid specifications. It is, however, the kind of information that an audiologist should know, or should acquire from hearing aid manufacturer.

How about trying to acquire the "best" hearing aid by purchasing a "top of the line" model and paying premium prices? Surely that will guarantee the best possible performance! In our society we are conditioned to believe that "you get what you pay for," i.e. that lower price items, of any kind, implies shoddy workmanship or faulty design and are simply not as good as similar items that cost more. Therefore, this reasoning goes, by buying the most costly hearing aid one can obtain the maximum possible benefit. In some ways, insofar as a higher cost may permit the inclusion of a few desirable features (as the two above) there is some merit to this argument. However, when the results of large-scale surveys that compare benefit and satisfaction to cost are examined, the results are far from clear-cut.

In an article published several years ago, Sergei Kochkin reported on the results of 36 customer satisfaction surveys that he and colleagues conducted over the years. Among the factors he looked at was the relationship between the cost of a hearing aid and a user's satisfaction with its performance. In general, the price that one paid for a hearing aid was only "slightly" correlated to the measured benefit that one actually obtained from the aid. As I examine his results, it appears that benefit pretty much remains the same regardless of price beyond the mid-range cost of the hearing aids. It is below the mid-range that benefit increases slightly and I emphasize "slightly" - as the price of a hearing aid increases. Higher prices, therefore, do not guarantee greater satisfaction. Furthermore, and not surprisingly, as one pays more for a hearing aid, one's expectations also increase. People who pay more expect more, but evidently this doesn't happen, at least not enough to meet their higher expectations. Rather, it seems, the more people pay for a hearing aid, the less they are likely to be satisfied with the benefits that they do receive. According to the results reported by Kochkin, the perceived value of the hearing aid declines as the price of the hearing aid increases. One cannot, evidently, buy better hearing (or happiness?) with money.

The Audiologist

In actuality, I do not believe that there is a single "best" performing hearing aid for an individual. Rather, there is likely to be a relatively large number of hearing aids that produce virtually similar speech recognition skills. But hearing aids with similar speech recognition scores can and do differ on a number of other dimensions, e.g. size, special features, and cost. And this is where the "matchmaker" - the audiologist - comes in. It is this person's job to make the best possible match between the consumer and a specific hearing aid. It is the hearing aid dispenser who has to select a specific hearing aid, one that meets all the known requirements (an appropriate amplified signal, all the desirable features, cosmetic preference and cost considerations). It follows that there is no more important factor in a hearing aid fitting than the competency and dedication of the hearing aid dispenser.

Alas, not all "matchmakers" are equally caring or equally competent. True, all must meet certain minimum standards in order to be certified or licensed as hearing aid dispensers. But hearing aid users would like some assurance that the person they're working with operates with more than just "minimum" requirements. As it happens, a "best practices" protocol is available. The profession of audiology has recently developed "Guidelines for the Audiological Management of Adult Hearing Impairment." These guidelines reflect the current state of knowledge regarding the entire process of hearing aid selection for adults, from the initial comprehensive audiological evaluation, the inclusion other types of hearing assistive technologies, to the provision of an appropriate follow-up program. This is a very impressive document (in 44 pages), one that sets a high standard for practicing audiologists. (There is another one for children.) It outlines and recommends what should be done, which begs the question of what is actually being done. There have been a few recent surveys that have examined the nature of the clinical procedures when hearing aids are being fit. The results of the most recent such survey (abbreviated in scope) was published in the May/June 2006 issue of Audiology Today. It does not present the most encouraging of pictures.

What these results indicate is that only a minority of the respondents appeared to be adhering to the letter and spirit of the guidelines developed by the American Academy of Audiology (AAA). Relatively few audiologists performed such tests as measuring speech perception in noise (with and without a recommended hearing aid) or determining loudness tolerances across frequencies. Few include real-ear, probe-microphone measurements in their procedures. This test examines the sound levels existing in the ear canal while the hearing aid is in place. It is the only and, in my opinion, the most important objective measure that can be made while a hearing aid is being worn.

The survey results suggest that the entire hearing aid selection process is being truncated because insufficient time is being devoted to all three of the necessary stages in the dispensing process (pre-fitting, fitting, and post-fitting). Indeed, in my opinion the current price structure of hearing aids purchased through private dispensers, as opposed to the internet or discount houses, can only be justified by the fact that it supports the additional professional time and expertise to ensure that maximum benefit is being achieved. We know that this extra time can pay off; there is good evidence to indicate that a person's satisfaction with hearing aids is directly related to the time spent working with the dispensing professional. In short, it is the professional recommending and fitting the hearing aid, one who follows as closely as realistic possible the recommended guidelines developed by the AAA, who can best ensure that a hearing aid is selected that can be placed in the "best" category for that person.

Let us define in a little more detail what it means for a hearing aid to be in the "best" category. What this really means is that while there may be a number of aids that would perform similarly for that person, with the recommended one at least the user is not obtaining less benefit than is currently possible. Presumably, with an aid in the "best" category, the amplified sounds being delivered by the hearing aid permit a person to approach the listening limitations imposed by his/her damaged auditory system. This is an important concept. No matter how excellent the hearing aid, no matter how well fit it is, an impaired auditory system will impose functional limits that cannot be exceeded. Basically, it is our ears that set the upper limits of what is possible, and not the hearing aids. In short, the "best" hearing aid is one in which the residual capabilities of an impaired auditory system are fully exploited.

The problem with this concept is that predicting the speech perception capabilities of a pathological auditory system is a chancy matter. One cannot administer, in any practical way that I know of, a battery of the most refined psychoacoustic tests and thereby precisely predict the upper limits of a subject's speech perception, in quiet and in noise. We do know, however, that certain audiological information can be very helpful in this regard. This would include aided audibility measures (how much of the actual amplified speech sounds exceed the impaired thresholds), or the latest tests for measuring speech perception in noise. Unfortunately, however, less than 50% of the audiologists surveyed actually administer these kind of tests. It's not that they don't know how, but it seems that they are constrained by real or perceived time limitations. And, yes indeed, being an effective "matchmaker" does take time. But time well spent.

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