ASA 124th Meeting New Orleans 1992 October

4aPP10. Hearing threshold shifts from repeated, 6-h daily exposures to impact noise.

Roger P. Hamernik

William A. Ahroon

Robert I. Davis

Sheau-Fang Lei

Auditory Res. Lab., SUNY--Plattsburgh, Plattsburgh, NY 12901

Recent results of research on the bidirectional transduction properties of the cochlea have opened new possibilities for understanding and explaining various phenomena associated with noise-induced threshold shifts. Several studies using animal models have shown that the cochlea is capable of developing a resistance to noise-induced threshold shift (TS) that is dependent upon previous exposure history and on the timing schedule of a repeated exposure. These results were obtained using continuous octave band stimuli. This paper will describe the developing resistance to TS from intermittent daily exposures to a broadband impact noise. The chinchilla was used as an animal model; the evoked auditory response as a measure of threshold; and the cochleogram used to quantify the sensory cell population. The animals (N=12) were exposed over a 20-day period to a 6-h daily exposure of 113- or 119-dB peak SPL impacts presented 1/s. Thresholds measured at the beginning and end of each exposure period showed that up to 30-dB resistance to TS could be developed over the first 5 days of exposure. The magnitude and time course of the resistance effect was frequency and intensity dependent. The audiometric and histological results of these intermittent exposures will be contrasted with equal-energy exposures using the same impacts but an exposure schedule without interruption. [Research sponsored by NIOSH Grant No. 2R010H02317.]