Temporary threshold shift in hearing induced by an octave band of continuous noise in the bottlenose dolphin

Abstract

Temporary threshold shift in hearing at 7.5 kHz was studied with an Atlantic bottlenose dolphin. Immediately following a threshold measurement, the animal was required to station in a hoop and be exposed to an octave band of continuous noise from 5 to 10 kHz. Noise exposure sessions lasted about 50 min, with the requirement that the animal spend a total of 30 min in the hoop. The dolphin also had two preferred locations both about a meter to the side of the hoop, one at the surface, and the other at the hoop depth. The noise levels at the hoop and to the side were about the same but with different spectra. The noise at the surface was about 3-dB lower. After exposure to the fatiguing stimulus, the animal’s hearing sensitivity was immediately measured. The animal’s hearing was not affected when the noise was 171 dB at 1 μPa with a total energy flux density of 205 dB at 1 μPa2<th>s. Temporary threshold shifts of 12–18 dB were obtained when the noise increased to 179 dB with an energy flux density of 213 dB or 1330 J/m2. The fatiguing stimulus was about 96 dB above the animal’s pure tone threshold of 84 dB. [Work supported by ONR.]