Strategies of the Hearing System Against Noise and Auditory Damage

The auditory system is extremely sensitive. In order to survive it developed impressive strategies to avoid, or reduce, damages caused by noise. This article, based on a contribution to the Norwegian University of Science and Technology (NTNU, Trondheim) attempts to present some aspects of this fascinating topic.

Introduction
Life is full of manifold activities and events, some pleasant and others
repelling. Hearing is important for everyone, and thus the auditory
system has to be able to adapt to extremely different conditions. Some
people lead a nomadic life in remote areas, sitting in the grass with a
few animals, and are practically not exposed to any technical noise.
Others are visiting discotheques regularly, for decades, and race with
motorbikes, while a classmate works in a library and collects stamps.
Looking into books on ear and hearing the authors invariably
point out how extremely sensitive our sense of hearing is, and this is
certainly correct. However, keeping in mind how many people pay lots
of money to be at the side of the road at automobile races, at the
airport during air shows and stunts, or near the stage in open-air
concerts, it is apparent that the hearing system must have protective
mechanisms to avoid – or minimize – noise-induced auditory damage.
The ear has to be able to hear and follow the bumble-bee, flying from
flower to flower, Fig. 1, but it must also withstand the acoustic
emission from cut-off grinders, hammer-drills and other popular tools.
To get an understanding of the plasticity and bio-technical finesse of
the functional components involved in hearing, it is useful to see what
solutions some other mammals with a highly effective auditory system
have come up with. Of course, not everything will be presented and
discussed here, but the topics covered may help to understand that our
hearing system is highly regulated and devoted to avoid damages of
various kinds. As a result of its long evolutionary efforts [12], it
appears to be amazingly farsighted and intelligent.

You can download this article here: Fleischer-2008-NTNU-paper-3MB.pdf

The Intelligent Ear

In 2002 an article was published on auditory performance of persons living in remote parts of the PR China. The study was performed in cooperation with the ENT Department of FMM university in Xian. Most of the persons examined were not exposed to technical noise, but a few of them had to endure extreme levels of noise, over a long time. Contrary to common assumptions, it could not be confirmed that persons not exposed to technical noise are hearing better than persons living in loud cities. Furthermore, it was apparent that acute acoustic trauma was wide spread, caused by fire crackers and other devices resulting in powerful impulses. The equal-energy-concept that is the basis for auditory protection does not explain these findings.

You can download the full article here: Fleischer-2002-TheIntelligentEar.pdf (2.2 MB)