Auditory-Threshold Recovery after Exposures to Pure Tones

Abstract

A modified Bekesy-type audiometer was used to obtain a continuous recording of the auditory threshold before and after monaural exposures to different durations and intensities of pure tones. Preliminary studies confirmed that the amount of temporary hearing loss at 1 kc following a 1-minute exposure to a 1-kc tone is greater when the stimulating tone is 20 db above threshold than when it is 80 db above threshold. Temporary hearing loss at higher frequencies, however, increases with exposure level. These preliminary results led to an investigation of the dependence of temporary hearing loss on the duration and the intensity of exposure tones. Recovery curves for the threshold at 1 kc following exposure by 1 kc indicate that exposure tones at or above 60 db sensation level yield a rapid recovery followed by either a slowing down of the recovery process or a second rise in the threshold. Following exposure to a 20-db tone, however, this rapid recovery is not so apparent, and therefore, when the temporary threshold shift is measured soon after exposure, the apparent loss after 20 db is greater than after higher intensities. The hearing loss two minutes after exposure does not change with increasing exposure level until the sensation level exceeds 80 db. Temporary hearing loss does not change significantly with exposure durations from 15 seconds to 1 minute, but increases as the durations increase to 2 and 4 minutes. These findings do not hold when the threshold for 1400 cps is measured following exposure to 1 kc. Here temporary hearing loss increases directly with duration for sensation levels at 80 db or above, and it increases directly with level for sensation levels greater than 60 db. Although these results are somewhat obscured by differences among individuals, the recovery curves, and their dependence on intensity and duration of exposure, point to more than one underlying recovery process.