The Noise Induced Temporal Threshold Shift (NITTS)

Abstract

It is well known that noises are the cause of hearing impairment. However, various protective methods have advanced whose fruits are coming up these days.Many studies are done in regard to the influence of occupational noises on hearing ability and most of these reports are clear in contents. Compared with this, reports and estimation methods of the influence of social or environmental noises still do not go over the stage of hypothetical and dissatisfactory contents.We tried experiments on five healthy persons by changing the level and duration of sound field ambient noise to find out its level and duration in which NITTS was produced. In these experiments, various noises including occupational noises were considered to be sources of sound field ambient noises. Five kinds of noises, noise of the passing bullet trains of the Japan National Railways, noise of Boeing B-747 jet planes, the traffic noise on main roads, the metal spray noise within factories, and noise of riveters were chosen.The survey results showed that industrial noises produced an obvious TTS while the train passing noise did not. It was also observed that TTS might be produced slightly by a certain type of noises but might not clearly be produced by another type of noises of higher level.