The Effects of High Intensity Noise on Human Equilibrium
Abstract : Five experiments were conducted on the effects of broadband, high intensity noise on human equilibrium. The ability of subject to balance on narrow rails was measured during exposure to the noise; and immediately after termination of the noise. Four different noise conditions were used in each experiment: control, 120, 130, and 140 dB (re. 0.0002 dyne/sq cm). In the first experiment subjects wore earmuffs and earplugs; in the second, only earplugs were worn; and in the third experiment, subjects wore earplugs and one earmuff to produce an asymmetrical exposure. At an ambient level of 140 dB, a detrimental effect was obtained in all three experiments. At lower intensities of noise, there were performance decrements only for the asymmetrical exposure. In the remaining two experiments, conducted after termination of the noise, detrimental effects were obtained for asymmetrical auditory exposure but not for equal auditory exposure. The results of these experiments are interpreted as a possible quantitative demonstration of the direct effect of high intensity noise on the vestibular system.
Rail test to evaluate equilibrium in low-level wideband noise. AMRL-TR-66-85.
Abstract : Psychomotor performance on a rail test was measured during free-field exposure to wideband noise at an overall level of 120 dB re 0.0002 dyne per square centimeter. Subjects wore various combinations of ear protectors to obtain experimental conditions of: (1) sound pressure levels equal in both ear canals (balanced condition) and (2) sound pressure level greater in one ear canal than in the other (unbalanced condition). Man's ability to maintain his equilibrium was adversely affected by the unbalanced noise condition. The rail test may be a useful measure of psychomotor performance in intense noise. Future research will be directed to rail test performance in exposure conditions higher than those employed in this study. (Author)
Some Biological Effects of Intense High Frequency Airborne Sound
Some experiments have been conducted to determine the effect of intense high frequency airborne sound on mice and a variety of insects. The sound source was a high frequency siren. The frequency used was about 20 kc and its acoustic level, in the region where the subjects were placed, was between 160 and 165 db (relative to 10−16 watts/cm2). With sufficient exposure—from 10 seconds for flies and mosquitoes to 3 or 4 minutes for roaches and caterpillars—the sound proved lethal in all cases. More detailed work was performed on mice and the roach, Periplaneta americana. In both cases it was definitely established that the heating produced by sound absorption was sufficient to cause death. In addition to the heating there are other effects, notably tissue rupture, as evidenced by the almost complete destruction of the wings on flies and mosquitoes and the rapid deterioration and final disappearance of the external pinna of a mouse which had received a sub‐lethal dose. During observations it has been impossibl...