Time-Varying Distortions of Binaural Information by Bilateral Hearing Aids: Effects of Nonlinear Frequency Compression.
Andrew D Brown, Francisco A Rodriguez, Cory D F Portnuff and 2 others
PMID 27698258WHAT IT FOUND
Hearing aid programs using wide dynamic range compression, with nonlinear frequency compression and bilateral beam-forming in some programs, distorted high-frequency timing and level cues in noise and speech.
This was measured in a manikin, not tested in patients.
Key findings
01All hearing aid programs tested, each of which included wide dynamic range compression, reduced level differences between the ears, especially at high frequencies and lateral angles.
02Both programs that included nonlinear frequency compression, in addition to wide dynamic range compression, distorted timing differences between the ears at 4 and 6 kHz.
03The hearing aid programs made level differences between the ears change over time for amplitude-modulated noise, and similar changes occurred for the word purse.
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
The measurements were made through a single hearing aid fitted to a single audiogram, so they do not show how all hearing aid users or all devices behave. Only one set of compression attack and release times was tested, and these settings reflect only some hearing aids on the market. The perceptual consequences of these distortions remain untested, so the study does not show that people wearing these programs localize or understand speech worse. The beam-forming program combined bilateral beam-forming with nonlinear frequency compression, so its result cannot be separated from the frequency compression effect. The hearing aids were programmed with manufacturer-recommended settings for a severe high-frequency sloping loss, so different losses or settings may behave differently.
The easy way to misread this
Do not read these acoustic distortions as proof that hearing aid users will localize or understand speech worse. The study measured a manikin, and the authors state that the perceptual consequences remain to be tested.