Research at the University of Tennessee may be sweet music to the ears of millions of hearing-aid users.
Dissatisfaction and frustration with hearing aids lead many hearing impaired people to stop using, even discard, their expensive hearing devices. But Professor Anna Nabelek and a team of UT researchers have developed a 2- to 3–minute test that can be used to predict with 85-percent accuracy whether hearing aid users will succeed in using their hearing aids. Audiologists can use the test to determine whether patients are good candidates for traditional hearing aids or whether they might need higher-tech devices or additional help in adjusting to their hearing aids. The UT team also is looking at whether therapy or even medication might help patients become successful hearing-aid users.
Nabelek, who pioneered the work, and a number of researchers within UT’s Department of Audiology and Speech Pathology were the focus of the October issue of the Journal of American Academy of Audiology (volume 17, issue 9), a journal published for the world’s largest professional organization for audiologists.
The Noise Factor
Nabelek says only 35 percent of -hearing-aid users are happy with their hearing aids. “Many individuals—including manufacturers, audiologists, and -hearing-aid users–feel guilty and frustrated that people have difficulty wearing hearing aids,” she says. “But it’s nobody’s fault. It’s the nature of the beast.”
For years researchers thought they could remedy the problem by turning up the volume so hearing-aid users could better hear the words they were missing. The trouble was that the background noise got louder too. In 1991 Nabelek and her colleagues published the first study suggesting that successful hearing-aid use was related to a listener’s willingness to accept background noise. It was a simple but groundbreaking idea.
Samuel Burchfield, professor emeritus in audiology, saw the clinical potential of willingness to accept background noise, which seemed to be the key to answering an age-old question of why two people can look the same on paper, yet one loves his hearing aid and the other hates hers.
To predict hearing-aid success, UT researchers developed a simple test to measure a listener’s “acceptable noise level,” or ANL, in decibels (dB). First an individual listens to recorded speech and adjusts the volume to their “most comfortable listening level” (MCL). While the listener continues to follow the recording at the most comfortable volume, a separate recording of unintelligible multi-talker babble also begins to play, and the listener increases the volume of the babble to the loudest level he or she can put up with without becoming tense or tired while listening to and following the recorded speech. The level is the listener’s greatest acceptable background noise level, or BNL. The listener’s ANL is defined as the difference between the MCL for speech and the highest BNL that is acceptable.
For example, if a listener’s most comfortable listening level is 50 decibels (MCL=50), and she can still listen to and follow a story with as much as 47 dB of noise added (BNL=47), her ANL is 50 minus 47, or 3 dB. But if that same listener had become stressed trying to listen to the story with just 36 dB of added noise, her ANL would be 50 minus 36, or 14 dB. Thus those listeners who can accept the least background noise have the highest ANLs.
A listener’s ANL allows a researcher or practitioner to predict 85 times out of 100 whether the listener will wear a hearing aid successfully. People with high ANLs are less likely to be successful hearing-aid wearers. Those with low ANLs are more likely to be successful with their hearing aids.
ANL “Fingerprint”
With reliable predictions of success available, the focus now has shifted to “what we’re going to do with that information,” Nabelek says.
UT studies–funded by grants from the National Institutes of Health and the American Association of Retired Persons/Andrus Foundation–have established that ANL is not related to age, gender, hearing sensitivity, type of background noise, preference for background sounds, or understanding speech in noisy environ-ments. Physiological research by UT doctoral candidate Joanna Tampas and Associate Professor Ashley Harkrider shows that ANL seems to be a function of the brain, not the ear. Brain responses were different for people with low ANLs than for those with high ANLs.
The findings of this study indicate that acceptance of background noise might be innate. “It looks like you are born with your ANL and it stays with you for life,” Nabelek says. “I’ve tracked my ANL over a number of years, and it appears that my ANL has been stable.”
Tampas is continuing her research to help pinpoint where in the brain a person’s ANL is set, which could guide researchers toward effective therapies. And with the link between ANL and hearing-aid use established, UT researchers are trying to acquaint audiologists with the ANL measurement and how it could help them work with hearing-aid patients. Research published in the Journal of the American Academy of Audiology is expected to result in ANL’s wider clinical use.
Therapy, Meds, and More
Thanks to UT researchers, audiologists may one day be able to improve the chances that people with high ANLs can wear hearing aids successfully. Among the possibilities under study are advanced–technology hearing devices, therapy, and -medications. Assistant Professor Patrick Plyler says more sophisticated hearing aids, with such features as digital noise-reduction circuits and directional microphone technology, and assistive listening devices could help high-ANL users distinguish speech from noise. Research by Melinda Freyaldenhoven, who recently completed her doctorate at UT and accepted a position at Louisiana Tech University, indicates people accept more background noise with directional microphone hearing aids than with traditional ones.
“Most studies evaluating advanced technologies in hearing aids have been in intelligibility, or how well the user can understand speech,” Plyler says. But he and his colleagues want to study whether these devices influence a person’s ANL. If that’s the case, he says, audiologists working with patients with high ANLs may want to try hearing aids with advanced features from the outset.
“If a person starts wearing a hearing aid and they hate it, you can’t teach them to use it,” he says. If these advanced–technology devices make background noise more acceptable for people with high ANLs, “at least they’re willing to wear their hearing aid.”
Therapy might also help patients with high ANLs become more accepting of background noise, Nabelek says. Therapy is already being used to help patients with tinnitus, or ringing in the ears, tune out that constant distraction.
Most exciting, perhaps, is the possibility that medication may help patients with high ANLs. Freyaldenhoven has done a study that showed college students with attention deficit hyperactivity disorder were more accepting of background noise when they were taking their medicine. “This is one of the first studies to show you can change someone’s ANL with medication,” she says, noting that more research is needed to determine whether medication–and what medication–might help hearing-aid patients.
