Longitudinal changes in auditory sensitivity in laboratory subjects

Abstract

Audiometric records of some 60 student subjects in our noise exposure experiments, who had been exposed twice a week, for periods of time ranging from 3 months to 3 yr, to noise doses severe enough to produce 10 to 30 dB of TTS2 (auditory fatigue measured 2 min after exposure), were examined for long‐term effects. The median of the first three daily pre‐exposure audiograms of each subject was compared to the last three and the differences analyzed. Although an apparent grand mean decrease in sensitivity of about 2 dB was found, all test frequencies (0.25–8 kHz in half‐octave steps) showed the same change, which indicates that the shift was a behavioral one rather than a real loss of auditory sensitivity; that is, there was no greater change at 2.8 or 4 kHz than at any other frequency. Examination of individual records showed an essentially random pattern of shifts. Thus under the conditions of our experiments, in which full audiometric recovery occurs between successive exposures, no cumulative effects seem to be occurring. Results do not support the microtrauma hypothesis. [Research supported by the National Institute for Occupational Safety and Health, Public Health Service.]