Hearing Aids

Editor: How well does your hearing aid provider fit your hearing aid? I don't mean the physical fit. I'm asking about the acoustic fit. It seems that at least one prominent audiologist believes that, in many cases, the answer is "not too well."

Here's an article from NVRC News. Please visit http://www.nvrc.org to learn more about these wonderful folks. If you share this article, please be sure to credit them.

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Audiologist Robert L. Martin, Ph.D., writes about fitting patients for hearing aids in his article Nuts & Bolts for the October 2004 issue of The Hearing Journal. Excerpts from his observations are divided into four categories: hearing, occlusion/fitting mechanics, feedback and word understanding in noise.

Hearing - Martin asserts that audiologists tend to focus on hearing thresholds in the mid-frequencies, overlooking the fact that patients often have a substantial hearing loss at 4000 Hz that needs to be corrected. There are almost twice as many speech cues in the octave band at 4000 Hz (23%) as in the band at 500 Hz (14%). If the hearing aid fitting provides inadequate amplification at the high frequencies, the patient is deprived of a lot of speech information.

Occlusion - When sound passes through an open unaided ear, it is amplified naturally by the pinna. A hearing aid obstructs the normal pathway of sound, so considerable amplification is needed just to get back to unaided hearing. Audiologists might be unaware of how serious occlusion is unless a measurement is taken of the hearing-aid-in-the-ear-turned-off curve, also known as the REOR (real-ear occluded response). Many hearing aid fittings have to produce over 30 dB of amplification just to get back to the open ear level.

Feedback - Audiologists strive to maximize venting so the patient is comfortable with his or her voice. In doing so, feedback problems can be created that are usually solved by reducing gain in the higher frequencies. But when the gain in the high frequencies is reduced, the speech cues in those zones are often eliminated.

Word Understanding in Noise - The problem of insufficient amplification in the band at 4000 Hz does not show up until patients wear their hearing aids in an adverse listening situation. Then, when noise reduces speech cues across all zones, patients need all the speech cues they can get. If the fitting is starved for speech information, word understanding deteriorates rapidly when listening conditions get worse. But if the fitting maximizes speech information, patients are still able to hear and recognize words even in substantial noise levels. Audiologists can be unaware that many hearing aid fittings fail to provide sufficient gain in the high frequencies because interaction with the patient is in a quiet office and fittings aren't verified with real-ear measurement.

A Solution - Martin maintains that completely open hearing aid fittings have a significant advantage over occluded fittings when it comes to delivering real-ear amplification in the high-frequency zone. Giving patients significant useful gain in the high frequencies markedly improves their ability to understand words in noise. When audiologists give patients as many speech cues as possible, the likelihood is strong that they will hear well in all listening situations.