THE RELATION BETWEEN SLIGHT DIFFERENCE OF NOISE INTENSITY AND AUDITORY FATIGUE

Abstract

This paper was attempted to study on the temporary threshold shift (TTS) at 4000cps by a 20-min noise exposure through a earphone to each of a subdivided tone, approximately 2db step, within the range of 79 to 88 phon of white noise. The change of auditory sensitivity was observed by means of Bekesy-type audiometer. Nine subjects tested were adult men with normal hearing who had well experienced the Bekesy audiometry. These results were as follows:
1) Although the intensities of stimuli of tones were slightly different respectively, a noise intensity which produced a remarked rise of TTS and a prolonged recovery from it was found in all the subjects.
2) A noise intensity level producing of such an elevated threshold was significantly defferent each other:
No. 1 and No. 7 were found at 81db; No. 2 at 82db; No. 3, No. 5, No. 6 and No. 9 at 84db; No. 4 and No. 8 at 86db.
3) Observing the recovery process over a duration of 20 min, the following was noted, that the elevated threshold after stimuli, being recovered to normal threshold, still showed the elevation in 7-9 min after stimuli were ceased. This was classified to class IV & V. These recovery types were more frequently found on 1 grade less intensity of tone than the fatiguing tone intensity producing the remarked threshold shift and prolonged recovery of it. And these recovery pattern dissappeared on the interruped threshold tone at a frequency of 4000cps.