147th ASA Meeting, New York, NY

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Does A Little Noise Exposure Help Our Hearing?

Gerald Fleischer -
Reinhard Mueller
University of Giessen
Giessen, Germany

Popular version of papers 1aNS6 and 1aNS7
Presented Monday morning, May 26, 2004
147th ASA Meeting, New York, NY

According to prevailing concepts, sound is more or less detrimental to the ear. Loud noise can cause permanent auditory damage as well as rapid aging of hearing. Hence, it is generally assumed that persons not exposed to noise hear excellently and their hearing capability ages only slowly, if at all.

For more than a decade our group has been working on the relation between exposure to sound and auditory performance. We are only examining healthy persons, of all ages, and we are especially interested in studying and comparing entire groups of persons: office personnel, construction workers, high-school students, university students, airline pilots, dentists, orchestra musicians, fans of discotheques, avoiders of discotheques, etc. In order to determine the hearing capabilities of persons not exposed to noise, we conducted - in cooperation with FMM University in Xian - a field study in remote parts of China, examining Tibetian nomads, Tibetian monks, and peasants from the Qin-Ling mountain range. All told, we now have data on roughly ten thousand volunteers in our database.

Special analytical procedures permit direct comparisons between the various groups. We also separate, by program, persons with good hearing from those with auditory damage. This makes it possible to compare only the good-hearing persons of the various groups, or the persons with auditory damage. A ranking of the groups according to the quality of hearing leads to unexpected results. On top of the list--with the best hearing--are groups that live and work in an acoustic environment that is loud, but not excessively loud. At the bottom of the list are groups that are exposed to excessive noise but also those who are not exposed to noise at all. While excessive levels of noise undoubtedly damage the ear, hearing appears to suffer for those who grow up and live in a low-noise environment. We may call this "auditory deprivation," and it prevents the auditory system from fully developing its potential.

However, groups of persons living and working in a rich acoustic environment full of varying sounds, and many sound sources, hear better than normal. Apparently these acoustic conditions are training the auditory system to perform very well. What appears to be most effective is "interval training," in which hearers are subjected to periods of moderate noise, with relatively quiet conditions in between, over a long period of time. Aging is reduced in such trained ears. Looking at groups of good-hearing persons shows that they experience intervals of sound levels that are not excessively high. Working at a loud construction site, or at a ship yard, has no training effects on hearing; the sound level is too high, there are not enough periods of quiet and there are many powerful impulses.

Everyone knows that it is not healthy to sit on a chair for long periods. But it is good for a person's muscles, tendons, joints, etc. to walk, jog, dance, swim, etc. Tormenting methods of top athletes are not healthy. Apparently it is the same with the auditory system. A monotone no-noise environment prevents the hearing system from fully developing and maintaining its performance. Conditions with a variety of sound are apparently healthy even it is occasionally somewhat loud.

Excessive noise, however, undoubtedly damages the ear. Most dangerous for the ear are powerful shots and impulses.

Comparing men and women revealed a different vulnerability to auditory damage. Women have more damages at lower frequencies, compared to men, but less at higher frequencies, regardless whether the persons live in loud or quiet environments. This relatively strong effect could be observed in Central Europe as well as in East Asia.

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