Temporary changes of the auditory system due to exposure to noise for one or two days.

Abstract

A subject was exposed on two occasions to an octave band of thermal noise centered at 500 Hz. The first noise exposure was for 48 h at 81.5 dB SPL. Five weeks later, the second was for 29.5 h at 92.5 dB SPL. Auditory function was evaluated by several types of measurements made prior to an exposure, during periods of quiet interspersed within an exposure, and at various times after an exposure. Temporary threshold shift (TTS) measured after 4 min of quiet (TTS4) increased for the first 8–12 h of exposure and then remained constant as the exposure was continued. At 750 Hz, the value of TTS4 at asymptote was 10.5 dB for the 81.5-dB exposure, and 27.5 dB for the 92.5-dB exposure. Recovery from TTS required 3–6 days. While TTS was present: (1) the time constant of temporal integration was reduced at 750 Hz; (2) there was delayed recruitment of loudness; (3) the amplitudes of the Békésy tracings were reduced; (4) frequency discrimination was unaffected; and (5) threshold shifts measured by evoked-response audiometry approximated those measured behaviorally, but the slope of the input-output function of the evoked response (N1−P2) was unchanged.