Abstract
Noise-induced temporary threshold shift (NITTS) was observed by standard audiometric examinations and Békésy self-recording audiometry. The exposed noise was the intermittent traffic noise of the Shinkansen train (99 dB (A) at peak, 86 Leq dB (A) ), and the exposed duration time was 8 hours. The results obtained were as follows : 1) The hearing thresholds of the Békésy audiograms with normal hearing subjects, measured before, during and after noise exposure, were shifted significantly. And the amplitude of these audiograms by continuous test tone were decreased significantly. 2) After the noise exposure, there were no risen thresholds of the Békésy audiogram by interrapted test tones, but significantly decreased amplitude were noted. 3) The auditory acuity of the subjects exposed noise for 8 hours did not show a significant change in noise-less conditions for hours. 4) The auditory acuity of the workers in the noisy surroundings with normal auditory were measured in same noise exposed test. The results showed no decrease in the auditory thresholds of the Békésy audiograms by the continuous test tones. From th above-mentioned results it is assumed that by noise exposure, the amplitudes of the Békésy audiogram by continuous test tones firstly decrease, and secondly the shift of auditory threshold. Accordingly, if one wants to observe an influence of noise exposure on the auditory acuity, not only a shift in the auditory threshold but also a decrease in the amplitude of the Béekésy audiogram by continuous test tones should be investigated.
