The Best of 2008: Hearing Aids

Our Journal Club is back, doing our best to highlight some of our favorite articles from the previous year. We have our regular team members—Brad Stach, Linda Hood (both founding members), and David Wark (now a 5-year veteran). But we made a change this year that I think you will like. There is an increasing amount of research published each year related to cochlear implants. This category didn't fit conveniently into any of our four existing areas, so in past years we haven't been giving these articles the acknowledgement they deserve. This year, though, we've added a fifth category for articles devoted to cochlear implants. Our new team member for this area is Fan-Gang Zeng—David Kirkwood already has told you all about him. Welcome aboard, Fan-Gang! The year 2008 was pretty similar to past years regarding the number and quality of hearing aid articles. I tracked down around 200, split about 50/50 between 18 peer-reviewed and trade journals. Even if you only skim a few of these, that's still a lot of reading—maybe too much for a busy practitioner. I'll try to help. We had a couple unique topics last year, and sometimes hearing aid articles remind me of old songs. It was 30 years ago that Neil Young sang “It's better to burn out than it is to rust.” Wonder what that has to do with hearing aids? Check out the JAAA article by Mike Valente and associates. They reported on hearing aid battery rust for 320 batteries of different sizes from different manufacturers. A panel of audiologists also rated the rust. And you didn't think they had fun in St Louis! If rust isn't your thing, maybe cocktail parties are, and I know Jimmy Buffet was singing about that topic 30 years ago. Nicole Marrone and colleagues provide us with a 2008 article in Trends in Amplification titled “Evaluating the benefit of hearing aids in solving the cocktail party effect.” In case you're thinking this is related to guys dancing badly, the “effect” they're referring to actually has to do with speech understanding (and they tell us that the problem still exists). While they're both intriguing articles, neither quite made the cut. But 14 others did, and they are summarized in the following five categories. GREAT FOR THE CLINICIAN In this section, I mention publications that are easy to read and digest, and that just might give you a tip or two to use with your next patient. Some of 2008's best articles for the clinician are mentioned in my Not Ready For PubMed section, so if you're a clinician, check that out too. Here are a couple more good ones. I hear you're a big fan of open-canal (OC) fittings, and you frequently use models that include directional-microphone technology. We know that directional processing works quite well when the fitting is mostly “closed” (we've talked about that on these pages for many years). But given that with OC products we're providing little or no gain in the lower frequencies, which results in a smaller DI, is there still a significant directional advantage? Mike Valente and Karen Mispagel say “yes there is” in their IJA (International Journal of Audiology) publication. They found significant benefit for both laboratory speech testing and real-world listening in noise (as measured using the APHAB). A word of caution: We know from other research that OC directionality varies significantly among and within manufacturers, and also depends on the placement of the mini-BTE on the ear. I suspect these factors were controlled more in this study than they might be in your everyday clinical practice. Ten milliseconds, 100 milliseconds, 2 seconds, 5 seconds? Do you ever wonder if anyone really knows the best compression release times for hearing aids? If you believed someone did know, however, you'd probably put Brian Moore on the short list. He wrote a review article on this topic in Trends last year that provides a nice update for clinicians on what's been happening in this area. Just for fun, you might want to compare some of Brian's thoughts with the experiences you've had using different release times with various patients. If nothing else, thinking about “temporal dips” and “slow and fast releases” for slow and fast thinkers is certainly more interesting than computing compression ratios. NOT READY FOR PUBMED The trade journals are always filled with good hearing aid articles. Many are written by folks in the industry, as it's the most effective way for them to let you know about their new technology in a timely manner. I'll let you sort through these articles on your own—you'll notice that more and more these are not just marketing pieces, but include some evidence-based research support. Since you are critical consumers of literature, the first article I'd like to highlight in this section is precisely on that topic, written by Catherine Palmer (with help from staff and students) from the University of Pittsburgh and published in The Hearing Journal (HJ). This article provides some great guidelines on what to look for while you're reading (or even scanning) the literature. And it's not just for hearing aid articles; Linda Hood talks about it in her section too. Who better to talk about fast-acting multichannel compression than Ed Villchur, and he does just that in a Hearing Review article. Even if you're not a fan of fast-acting compression, you'll still find this an interesting review of the pros and cons of different compression time constants. If nothing else, you'll learn how Ed differentiates “phonemic compression” from “syllabic compression.” You'll find this an interesting companion to the Brian Moore review I mentioned earlier. An HJ Page Ten article I liked was about hearing aid selection, written by Marlene Bagatto from the University of Western Ontario. But my Journal Club colleague Brad Stach thinks this article fits better in diagnostics, so I'll let him tell you why it's a good read. But since we're talking about the folks at Canada's National Centre for Audiology, let me tell you about my favorite Not Ready for PubMed article of 2008, also from HJ, written by Richard Seewald and colleagues. Sadly, surveys indicate that as few as 20% of audiologists use probe-mic measures to verify hearing aid fittings for infants and children. One must assume, therefore, that the majority of audiologists rely on the default fitting provided by the software of their favorite manufacturer. Risky business? Seewald et al. examined these default fittings for nine different audiograms for a 6-month-old patient using the fitting algorithms from five major manufacturers. Their findings showed that for some fitting algorithms the prescribed maximum output substantially exceeded what would be considered appropriate, whereas for other algorithms the gain for soft speech inputs was considerably lower than what would be appropriate to facilitate speech and language learning. Overall, the different algorithms differed by 20 dB or more for some frequencies and input levels. This article should be a huge wake-up call to anyone fitting infants and children who believes that measuring the amplified signal delivered to the child's ear isn't necessary. BEST QUICK READ While most of us agree that bilateral hearing aid fittings are usually better than unilateral ones, there is not as much real-world evidence supporting this notion as you might think. In a multi-center study of over 200 participants, published in Ear and Hearing, Monique Boymans and colleagues examined this by conducting a battery of clinical tests (e.g., masking level difference, interaural timing) and using self-assessment questionnaires to assess real-world preferences. They found that clinical tests were poor predictors of bilateral benefit, but at the end of the trial period, 93% of the participants favored a bilateral fitting. You've probably had patients who said their tinnitus improved after using hearing aids, right? How often does that happen? Matthew Trotter and Ivor Donaldson discuss that in their brief article in the Journal of Laryngology and Otology. Their data are based on 25 years of experience: 2153 consecutive patients attending a tinnitus clinic. Of the 1440 patients fitted with hearing aids (43% bilaterally), about two-thirds reported some improvement in tinnitus following the use of hearing aids (no difference for bilateral vs. unilateral fittings). You might have guessed that outcome, but having an “n” of 1440 to support the notion helps! If you've been reading my review the past few years, you know that I've frequently mentioned the research by Kevin Munro related to unilateral hearing aid fittings and their cause of reorganization of the auditory system. It's interesting stuff. Well, last year Kevin wrote a review article in Trends, summarizing the research on this topic. He talks about evidence for both the perceptual and physiologic domains. If for no other reason, having all this information reviewed in one handy article makes it one of my favorites of 2008. And yes, it's a pretty quick read too. MOST THOUGHT PROVOKING By now you've probably all heard about the Acceptable Noise Level (ANL) test. We've talked about it on these pages before, most recently reporting that an individual's ANL has been found to be a good predictor of hearing aid use (e.g., one article suggests it predicts full-time hearing aid use with 85% accuracy). You might think, then, that people who have small ANLs (and use their hearing aids more) would also have improved benefit, and this would be reflected in a self-assessment scale such as the APHAB, right? Well, research by Melinda Freyaldenhoven, Anna Nabelek, and Joanna Tampas in JSLHR says it isn't so. In a sample of nearly 200 subjects they found no significant correlation between ANL scores and real-world benefit as measured by the APHAB. Mildly thought provoking, don't you think? So, have you been thinking much about trainable hearing aids? You know, the ones where the patient can adjust gain, compression, and/or the frequency response and then the hearing aid remembers what the patient likes for different inputs? And maybe the final result is a “better” fitting than if you had simply programmed the hearing aid to a prescriptive target? There was a series of articles in 2008 suggesting that the starting point of the training (e.g., the initial programmed gain and output settings) can influence the trained outcome. Such were the findings of Gitte Keidser, Harvey Dillon, and Elizabeth Convery, in their article in JASA. They used two baseline responses, “flat” and “steep,” which were implemented for each listener by applying tilts of −4.8 and +4.8 dB/octave to the individual's prescribed NAL-RP responses. After five rounds of training, substantial differences existed for preferred gain across frequencies, clearly biased by the starting baseline (individuals with steeply sloping, high-frequency losses were less biased). The authors suggest that future studies of hearing aid training should include real-life performances (theirs was in laboratory conditions only) and possibly include measures of the participants' cognitive processing abilities. They conclude by stating that training should begin from an appropriate starting response. So now we're at the thought-provoking part. When today's patients are fitted with this technology, their “starting response” may vary by 10-15 dB depending on who does the fitting. So what's “appropriate?” ALL-AROUND FAVORITES Two of my favorite articles from the past year relate to amplification for children. One was published in IJA by Teresa Ching, Mandy Hill, and Harvey Dillon. While most experts agree that children should be fitted using an evidence-based prescriptive approach verified with probe-mic measures, this is not common clinical practice. Naysayers suggest that there just isn't much real-world evidence to support the use of these fitting procedures, and that “getting close” to a good fitting is good enough. Ching and colleagues addressed this very issue by using a cross-over design in a double-blind comparison of three frequency responses (the NAL-RP and two modifications—one a “boost” and one a “cut” of the higher frequencies) for 30 children with severe to profound hearing loss. The children wore their hearing aids set to each of these three different responses in their everyday life, and three different questionnaires were used to assess their real-world performance: the PEACH, the TEACH, and the SELF. Guess what they found? Group real-world performance was significantly better when the children were fitted with the NAL-RP rather than one of its modifications. A second paper that I liked, also related to children, was by Andrea Pittman in JSLHR. It examined word learning and how it relates to extended high-frequency bandwidth. We've talked about the work of Pat Stelmachowicz in this area in previous years. A line in the opening paragraph of this article caught my eye: By the time a child graduates from high school he or she has learned over 60,000 words. Hmm. Assuming the kid starts working on this little project when he is really young, that's about 9 words a day—hardly time for a bathroom break! The major problem of course is that hearing loss can seriously slow down this process. In this study, a dynamic word-learning paradigm was used to determine the number of exposures required to learn a new word in a short time (15 minutes). The purpose was to determine the rate of word learning for children (both normal-hearing and hearing-impaired) for words that were processed to have either frequency bandwidths that approximated typical hearing aids or an extended bandwidth more typical of that of normal hearing. As you would predict, children with normal hearing required fewer trials for learning. But more importantly, the children with hearing loss required nearly three times as many trials (27 versus 10) to learn the words for the limited bandwidth condition than for the extended bandwidth. So we'll say again, extended bandwidth is a good thing for many children! When picking my favorite article of the year, I usually look for research that is well-designed and addresses an important clinical question. An interesting finding is good too, but not mandatory. An article that met those criteria was by Ruth Bentler, Yu-Hsiang Wu, Jerrica Kettel, and Richard Hurtig, published in IJA. As you know, digital noise reduction (DNR) has been around for over a decade and is standard in nearly all hearing aids. But does research evidence show any truly real-world benefit? Unfortunately, not much. In their comprehensive examination of DNR benefit, these Iowa researchers conducted a double-blind study that examined DNR off versus DNR on and also variations of the onset time of the DNR. Data collection included personality testing (it was Iowa after all), electroacoustic analysis, laboratory speech tests, lip-reading interactions, and self-report of benefit from real-world use. So what did we learn about the true benefit of DNR? It's all there in IJA's August issue! IN CLOSING There it is for another year. You'll have to work on the other 180 or more hearing aid articles on your own! I'll close with a somewhat altered quote from Sir Francis Bacon: “Some journal articles are to be tasted, others to be swallowed. Some are to be chewed and digested.” I hope I've whetted your appetite.

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