Figure 1. Time course of shifts in the auditory brainstem response (ABR) threshold following exposure to 120-dB octave band noise (8.0–16.0kHz) for 2 h.

Significant elevation of the ABR threshold at 0 h (immediately after the noise exposure; 58.1±12.5 dB sound pressure level (SPL)), 12 h (73.6±14.4), and 24 h (48.6±15.7) exhibited a component of temporary threshold shift (TTS) during 0–24 h. The TTS was more severe at 12 h than at 0 h, and partial recovery was observed at 24 h. A significant permanent threshold shift was confirmed at 14 days (40.0±13.8), compared with the control level before the noise exposure (20.6±5.6 dB SPL).