RESULTS FROM THE RETEST OF NOISE-INDUCED TEMPORARY THRESHOLD SHIFT (NI-TTS)
1967 Volume 70 Issue 8 Pages 1420-1429
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1967 Volume 70 Issue 8 Pages 1420-1429
An attempt was made in this paper to study the reliability of the retest of NI-TTS and to reaffirm that an abrupt and marked rise of the hearing threshold even following by slight difference of stimulous noise intensity can occur. That is, the amount and recovery process of a rise of hearing threshold induced by a 20-min exposure of intensities between 81 and 86 phon of white noise were measured using Bekesy audiometry at tone of 4000cps over a duration of 20min after noise stimulation.
All of the six subjects employed had normal hearing and were well trained with this testing method. They were repeatedly tested in the same way and conditions, above 3 times at intervals of 1 or 2 weeks.
The conculusions obtained from the present study were as follows:
1) The significant differences in a value of the hearing threshold shift obtained from retests were found in two of all subjects. The amount of one of three- to four-time measurements in them was decreased a half to a third as others.
2) The variations about recovery time from NI-TTS were relatively low.
But, at times, it was found to happen a remarkedly prolonged recovery.
3) The recovery pattern over a duration of 20 min after exposure termination, in general, tended to differ even in retest under the same condition. That the variation of the recovery pattern is high or low depends upon how to take a criteria of the characteristics.
Therefore, the estimate of this result should be more prudent, and further study will be demanded.
4) A diphasic recovery pattern (II type) like sensitization or bounce were not always appeared in the retests. The II type pattern was never found when tinnitus appeared not.
5) Concerning existence of small excursion of Bekesy tracings and tinnitus after noise exposure, it was found little significant difference in the remeasurements respectively. The change of tone colour of tinnitus was low, and, otherwise, duration of tinnitus seemed to vary easily in each retest.
