Developing auditory weighting functions in a bottlenose dolphin (Tursiops truncatus).

Abstract

The variation in susceptibility to noise as a function of frequency is handled by “weighting” sound exposures to emphasize frequencies where auditory sensitivity is highest. This technique allows the use of single, weighted numeric values for impact or damage‐risk criteria, regardless of the sound frequency. Human weighting schemes were derived from measurements of equal loudness curves obtained from subjective experiments where listeners directly compare the loudness of sounds at different frequencies. Response times to acoustic detection tasks provide an indirect method to construct equal‐latency contours in terrestrial mammals that are analogous to equal‐loudness contours. The need for empirical measures of loudness contours or auditory weighting functions in marine mammals became especially apparent following experiments of temporary threshold shift (TTS) in dolphins that revealed frequency‐dependent effects for onset‐TTS levels. The objective of this effort was to develop auditory weighting functions for Tursiops truncatus by directly measuring subjective loudness as a function of the sound frequency. The resulting equal‐loudness contours emphasize frequencies at which auditory sensitivity is highest and lessen the importance of other frequencies, similar to human A‐ and C‐weighting networks. [Work supported by the ONR.]