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

Components for Protecting and Optimizing Good Hearing

In November 2010 I had the pleasure to give a lecture at the International Convention of Sound Designers on the marvelous capabilities of the human ear. The meeting took place at the Congress Center in Leipzig, Germany. One of the reasons for this topic is the fact that the EU-standards for protecting the ear at the workplace create much trouble for sound designers. The acoustic conditions at their work places are declared harmful, but sound designers hear much better than the normal population. This discrepancy is caused by wrong assumptions of the standard.

Here is the abstract.

Studies on the auditory performance of entire groups of persons reveal that people ex-
posed to low sound levels do not generally hear better than those living and working in
loud acoustic conditions. Hence, the basis for world-wide standards to protect the ear
are incorrect and insufficient. Reason for this are powerful neural mechanisms of the
auditory system that is working hard to prevent noise-induced auditory damage and to
optimize various aspects of hearing. Studying special conditions at the workplace, as
well as at places related to hobbies and other activities, indicates the existence of several
such functional components. Overall sensitivity of hearing can apparently be reduced in
loud environments. Anticipating exposure to short loud events the auditory system can
rapidly reduce the sensitivity. Masking effects of low frequencies can be scaled down in
order to focus on high frequencies. Strong low-frequency components protect against si-
multaneous high-frequency noise. Very short impulses are more harmful than longer ones.
Most dangerous are rarely occurring unexpected powerful impulses. Auditory threshold
and threshold of pain are both subject to training. Damage caused by impulses result in
characteristic forms of audiograms. — The auditory neural system can be damaged or
reprogrammed by a single powerful impulse.

The article is published under the CC BY-NC-SA 3.0 license.

You can download the original file, which is about 49 MB, or a compressed version of about 12 MB, lacking clickable links.