Auditory fatigue and induced loudness adaptation

Abstract

Measurements of induced loudness adaptation and temporary threshold shift (TTS) were made on 48 young subjects. Loudness adapatation of a continuous 60-dB test tone was induced in the right ear by an intermittent 1000-Hz inducer tone at 90 dB, presented every 30 s for 20 s. The loudness of a 1000-Hz or 1160-Hz test tone at 60 dB was measured after each occurrence of the inducer by the method of successive magnitude estimations. Induced adaptation caused the loudness of the continuous tone to decrease on the average by 38% (the equivalent of 14 dB) after 120 s. In a separate session, the subject's right ear was exposed for 45 min to a 1000-Hz tone at 90 dB SPL. One minute after exposure, thresholds were measured by Békésy tracking for 4 min. The maximum TTS, averaged across subjects, was 20.4 dB at a mean frequency of 1635 Hz. The correlation between maximum TTS and the amount of induced adaptation was 0.83. Thus ipsilaterally induced adaptation (IIA), which is akin to temporary loudness shift, may stem from cochlear mechanisms just as TTS does. Also, IIA could become the basis for an audiological test to identify those individuals most susceptible to auditory fatigue. [Work supported by Ministère de l'Environnement and NIH.]