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.
Observations on Disturbances of Equilibrium and Other Symptoms Induced by Jet-Engine Noise
Introduction IN a previous report (Dickson and Watson, 1949), mention was made of the occasional occurrence of the symptoms, unsteadiness, dizziness and lack of concentration in personnel working with turbo-jet aircraft. These disturbances were noticed chiefly in the vicinity of the impellor close to the, air intake at the fore end of the engines. The appearance of such subjective sensations seemed to be produced infrequently and erratically. Injudicious press reports of possible harmful effects resulting from exposure to ultrasonic frequencies generated by jet engines led to a number of purely psychological disturbances being experienced by jet personnel. At first sight therefore, the assumption that they were psychological in origin provided a reasonable, though not altogether satisfactory explanation. Reference to the literature on this subject has revealed no clear conclusions. A transient vestibular irritation induced by standing in close proximity to turbo-jet engines when run at certain speeds has been experienced by many observers, including the present writers. That this phenomenon is due solely to the presence of ultrasonic waves as was first suggested seems unlikely. It is well known that stimulation of the vestibule can be caused by sufficiently loud acoustic stimuli. Frequency analyses have shown that sounds within the normal range of audibility are generated by jet engines at sufficiently high intensities to provide an adequate stimulus to the labyrinth, even in normal individuals. Some reports, nevertheless, indicate that frequencies above the normal sound range can also produce similar effects. Ultrasonic spectra, however, reveal that during the test bed running of jet engines, frequencies above the range of audible sound are of so low an intensity as to be thought incapable of causing deleterious results.
Healing of experimental labyrinthine fistulas; further observations.
IN A PREVIOUS REPORT 1 it was pointed out that the closing of a labyrinthine fistula by new bone may occur from two sources, the periosteal surface and the endpsteal surface of the fistula. Factors which influence osteogenesis at these two surfaces were discussed. In addition to the problem of osteogenetic closure of the fistula, experience with human subjects 2 has focused attention on a further problem which may influence the functional result, the occurrence of a depression of hearing due apparently to an involvement of the sense organ of the cochlea which has been referred to as "postoperative labyrinthitis." The present report will be limited to the first of these problems, particularly to the prevention of the bony closure that originates from the periosteal surface. A number of observations relating to this problem were presented two years ago 1 and may be summarized: Meatal skin flap. In the monkey's ear bony