July 14, 2008 The sound of a noisy Chicago restaurant during the breakfast rush -- the clang of plates and silverware and the clamor of many voices -- was the crucial test of new hearing aid technology in a study conducted by researchers at Washington University School of Medicine in St. Louis.
The study showed that the hearing aids worked well in a noisy environment -- the most challenging test for a hearing aid. But the patients wearing the devices didn't need to fly from St. Louis to Chicago to participate in the test. Instead, the restaurant came to the clinic of Michael Valente, Ph.D., director of the Division of Adult Audiology in the Department of Otolaryngology at the School of Medicine. Or at least its sounds did.
"We have a sound room set up to be an exact duplication of being in a loud restaurant. It's real restaurant noise, and it allows us to realistically test hearing aids," Valente says. "One of the most common complaints I hear from people who wear hearing aids is that they have stopped going to restaurants because they can't communicate. So we are testing hearing aid technology that might better help people hear in noisy places."
The study, published in the International Journal of Audiology, was the first to use such a setting to test a new hearing aid technology -- open-fit hearing aids with directional microphones. Open-fit means the devices let ambient sounds into the ear canal, unlike more conventional hearing aids, which completely block off the canal. Canal blockage creates an occlusion effect that makes wearers' own voices sound a little like they are talking from the bottom of a barrel, so open-fit is an attractive new option.
Directional microphones actually aren't a new development. They have been available for many years on conventional hearing aids, but researchers have questioned whether open-fit aids with directional microphones will be effective. Directional microphones help users distinguish conversation from background noise by partially canceling out low frequency sounds coming from the sides and from behind. Because open-fit aids let sound pass directly to the eardrum, some believe this will lessen their ability to decrease background sounds.
"We found that the open-fit hearing aids with directional microphones on average gave wearers a 20 percent improvement in speech intelligibility in the restaurant setting compared to not having a hearing aid or wearing an open-fit aid without a directional microphone," Valente says. "We are the first to show that a directional microphone in open-fit can provide improved performance in noise."
In fact, the aids without directional microphones performed worse in the noisy situation than no aid at all. "That's not unusual," Valente says. "People often tell me that when they are in a noisy situation, they take out their hearing aids because they don't help and sometimes even make it harder to hear."
Open-fit hearing aids have been available for about three years. They are designed for people who have normal hearing in the low frequency range but have lost hearing in the upper range, where most conversational sounds are. This is a very common type of hearing loss that often comes with aging or prolonged noise exposure. Valente says the open-fit hearing aids are what most new patients are asking for because they are very light and almost invisible, but they are not the best choice for all hearing problems.
Studies such as this help clinicians counsel patients on choosing the type of hearing aid that will work best for them and also what to expect from any hearing device. "I tell patients that a hearing aid will definitely allow you to hear better in a quiet environment, but in a noisy place, it won't ever work as well as it does in quiet," Valente says. "I also emphasize that even normal-hearing people have trouble communicating in noise. I say, next time you go to a restaurant with someone, estimate how much of the conversation you hear. Then ask them how much of the conversation they heard. I'll bet the difference won't be as large as you think."
Next Valente will begin a project in collaboration with the National Association of Future Doctors of Audiology (NAFDA) of the Program in Audiology and Communication Sciences (PACS) at Washington University in which they will measure sound levels in restaurants in the St. Louis area. Very often patients when seen by an audiologist in the Audiology Department report they no longer frequent restaurants because communication is impossible. So Valente and his colleagues want to provide patients with a noise rating system that will help them determine whether they will find a restaurant's environment comfortable.
In this system, similar to programs currently in place in San Francisco and Washington, D.C., a rating of "one bell" would indicate a restaurant where the noise levels are soft enough to allow for easy communication, while a rating of "four bells" would indicate that communication would be very difficult. Valente and his colleagues will soon make this rating system available to the public via the restaurant review section of the St. Louis Post-Dispatch newspaper and Web site. In addition, it will be available on the Web site of the Division of Adult Audiology (audiology.wustl.edu).
Funding from Vivatone supported this research.
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- Valente et al. Unaided and aided performance with a directional open-fit hearing aid. International Journal of Audiology, 2008; 47 (6): 329 DOI: 10.1080/14992020801894832
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