Physiological and psychophysical measures from humans with temporary threshold shift.

Tuning curves and amplitude-intensity functions on wave I and wave V of the auditory-evoked brain stem response and psychophysical tuning curves were obtained from human subjects (N = 5) with noise-induced temporary threshold shift (TTS). All tuning curves were measured with the same stimuli. Maskers were pure tones presented simultaneously with the signal which was a 3.6-kHz tone pip. TTS was produced by a narrow-band noise centered at 2.6 kHz and presented at 86 dB SPL for 8 h. The maximum mean TTS was 28 dB and occurred at 3.5 kHz. Although intersubject variability of TTS was small, individual differences in other measurements were substantial. In some subjects, amplitudes of waves I and V decreased following the noise exposure with wave I typically being more affected, while in other subjects, little or no change in amplitude occurred. All tuning curves had wider response areas following noise exposure. In a given subject, changes in psychophysical and wave V tuning curves were similar and were less than changes measured for wave I. Recovery of tuning curves (low- and high-frequency side) to pre-exposure values required between 7 and 41 h depending upon the individual and preceded complete recovery of TTS.