"Clearly, there is still no substitute for considering individual needs, capacities, and desires when fitting a hearing aid."
The research question in this study (published in the January 2003 issue of The Hearing Review) was whether people perform better with hearing aids that incorporate more advanced technology. While this may seem obvious, it is not. It still requires corroboration through clinical studies on human beings.
Three levels of technology were investigated. The first type was an analog, single channel, linear hearing aid (the Oticon Ergo). In this aid (the "classic" type), the amount of "gain" (amplification) is constant regardless of the sound level of the input sounds. It is up to the user to control the gain by manipulating a volume control.
The second type of aid was a multi-band digital hearing aid (the Oticon Digifocus). This aid employs "wide dynamic range compression" (WDRC) in which the gain automatically changes depending upon the loudness of the input sounds. A volume control is not necessary.
The third type of aid used in this study (the Adapto) is characterized as a "second generation" digital hearing aid. In addition to the features in the Digifocus, this aid includes several others of more recent vintage. One of these is a feedback control system (which, in addition to controlling acoustic squeal, also makes it possible to increase the size of the earmold vent).
Another one is termed the "voicefinder," a feature that is supposed to "know" the difference between speech and noise, even in the most difficult of listening situations.
One nice aspect of this study is that 13 different audiological practices agreed to participate, with all following the same procedures. This kind of experimental design does help foster confidence in the results. A total of 77 subjects were tested. All three hearing aids were fabricated to similar external dimensions, using the same ear impression to create the hearing shell. The subjects were informed only that three different types of hearing aids were being evaluated. This "blinded" procedure is intended to reduce an unconscious preference for more "advanced" hearing aids. (We know that people's preferences can be influenced by clever marketing terminology.)
After three weeks of use with each aid, both objective and subjective measures were made. For the objective measures, a speech perception test was administered under three conditions (in quiet, and two levels of competing noise).
Several different subjective measures were used. One, which is gaining popularity in professional circles, asks people to list specific situations in which they need the most listening help. Another subjective measure was comprised of more general listening situations and conditions, ones that apply to everybody. The subjects were asked to rate their listening performance in all of these situations. Finally, people were asked which hearing aid they preferred overall. The results of the objective measures show that the subjects obtained slightly higher word recognition scores as the technology advanced from the linear to the second-generation digital hearing aid. While the improvement was not dramatic, it was still apparent (and every little bit helps).
Subjectively, however, there were clear-cut preferences for the more advanced technologies, particularly the second-generation digital aid. The subjects preferred the advanced technologies both in the listening situations they personally selected as difficult for them as well as in the general situations.
In their ratings of overall preferences, 74 percent favored the second-generation digital aid, 16 percent the first generation digital aid, and the remaining 10 percent preferred the linear instrument.
These are very interesting results and I don't question their validitx. Interpreting them presents a bit of a challenge, however. We really don't know what specific acoustic features in the second-generation digital hearing aid were responsible for the higher subjective ratings (in particular compared to the prior generation digital hearing aidr
Is it the feedback cancellation circuit, the "voicefinder" circuit, the selection techniques that are used, or all of them operating synergistically? This study was not designed to answer this question by isolating particular features. Instead, it asked a perfectly reasonable question: which of these three hearing aids help people the most (regardless of the contribution of the numerous interacting features on any one of them). There is nothing wrong with this.
The reason I make this comment, however, is that I suspect that the main feature responsible for the improved subjective ratings is the feedback cancellation circuit. This circuit permits what the company calls "Open Ear" acoustics (basically a large vent through the earmold) because of its proven ability to reduce acoustic feedback. By controlling feedback electronically, the necessity for uncomfortably tight earmolds is precluded, while the large vent can enhance listening comfort through improved ear canal aeration.
But, and this is the point, this same feature is also found on a number of other commercially available hearing aids. Perhaps, therefore, similar results would be obtained with any hearing aid that incorporates this type feedback cancellation feature. We don't know the answer to this question, but it is one that would interest consumers.
There was another aspect of this study that I thought was particularly interesting. It was reasoned that perhaps the eight subjects who preferred the linear hearing aid were really expressing their desire for a volume control, which this aid contained and the other two did not. These eight subjects were later refitted with a newer model of the Adapto, one that permitted the inclusion of a volume control.
The authors' report that, after a further three-week trial, seven of these eight subjects then changed their preference to the more advanced digital hearing aid. In other words, these people may have made their initial judgment based on the availability of a volume control. Its presence could have been sufficiently positive, for them, to override any sound quality differences between the aids.
Actually, many of us can relate to this personal preference for a volume control. Indeed in this same issue of The Hearing Review, Sergei Kochkin analyzes a number of his previous survey studies in an attempt to isolate the impact of the volume control on customer satisfaction. According to him, about one-third of hearing users actively desire and can benefit from a volume control.
And, in an article in audiologyonIine.com, in which he details the specific advantages of a volume control, Dr. Max Chartrand believes that this percentage is most likely much higher.
There are good reasons for the preference of many hearing aid users for a volume control. It is simply not possible for an hearing aid dispenser to program an automatic volume control hearing aid so as to predict every type of listening situation a person would experience. I know there are times, even in the same situation, when I want to increase or decrease the degree of amplification. It may depend on how I'm feeling, who I'm listening to, the time of day, the nature of the background noise or the particular listening condition (like listening to the CD in my car).
In other words, many hearing aid users prefer to control their own listening experiences as much as possible. Of course other people feel differently or have different preferences. Clearly, there is still no substitute for considering individual needs, capacities, and desires when fitting a hearing aid. Still, in my judgment, volume controls should be included in all hearing aids unless contraindicated by personal and clinical considerations.
From Hearing Loss, May/June, 2003.
Acknowledgement: This column is supported, in part, by GRANT #133E980010 from the U.S. Department of Education, NIDRR, to the Lexington Center.
Mention of products or companies by the author does not Indicate SHHH endorsement, nor should exclusion suggest disapproval. Since everyone's communication problems and needs vary, SHHH suggests consulting with your hearing health professional.