Research press release


Nature Biomedical Engineering

Biomedical engineering: Sound compression in hearing aids may make them worse

補聴器で用いられる音処理アルゴリズムは、似た音を聞き分ける装着者の能力を低下させる可能性があることが、動物実験から明らかになった。このことを報告する論文が、Nature Biomedical Engineering に掲載される。この知見は、短期的にはもっと単純な装置の方がヒトには有効と考えられることを示すとともに、将来的には補聴器を改良するための新たな方法を示唆している。


今回、Nicholas Lesicaたちは、聴覚障害のあるスナネズミにヒトの発話の音を聞かせ、下丘(脳の聴覚中枢の1つ)のニューロン活動を調べた。彼らは、この脳領域のニューロンが、未処理の音、線形増幅処理を行った音、増幅・圧縮処理を行った音に対してどのように応答するかを記録した。その結果、増幅・圧縮処理を行うとニューロンの応答がゆがみ、このゆがみは圧縮の除去によって部分的には修正されるが、全てが修正されるわけではないことが明らかになった。さらに、難聴でない場合でも、増幅処理のみでニューロンの応答がゆがむことも見いだされた。これは、補聴器の使用者が経験する知覚上の問題の多くが、実際には正常なものであることを示唆している。


Algorithms for sound processing used in hearing aids can diminish the wearer’s ability to distinguish between similar sounds, reports an animal study published in Nature Biomedical Engineering. The findings indicate that simpler devices may be more effective for people in the short term, and suggest a new approach for improving hearing aids in the future.

Hearing aids are the main treatment for mild-to-moderate hearing loss. However, many people who could benefit from hearing aids do not wear them. This is partly because hearing aids do not adequately restore hearing in real-world settings. Basic hearing aids are designed with linear amplification, which provides a constant level of amplification regardless of the incoming sound level. Many hearing aids are also built with compression algorithms designed to selectively amplify soft sounds.

Nicholas Lesica and colleagues investigated the activity of neurons in the inferior colliculus — one of the brain’s hearing centres — of hearing-impaired gerbils while they were exposed to sounds from human speech. The authors recorded how neurons in this region of the brain responded to sounds that were unprocessed, processed by linear amplification, or processed with amplification and compression. They found that the responses of neurons with amplification and compression were distorted, and that removing compression corrected some, but not all, of the distortions. They also found, however, that amplification alone distorted neural responses even in the absence of hearing loss. This suggests that many of the perceptual problems experienced by hearing aid users are, in fact, normal.

The authors conclude that uptake of hearing aids could be improved rapidly without loss of benefit by making simple devices with linear amplification widely accessible, but that improving hearing aids will ultimately require new sound processing algorithms that compensate for the negative effects of amplification.

doi: 10.1038/s41551-021-00707-y


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