Masked hearing thresholds and critical bandwidths for dolphins and a white whale at 20 and 30 kHz

Abstract

Critical bandwidth is an important measure of the frequency selectivity within the auditory filters of the ear. In studies of masked hearing thresholds, the bandwidth of the masking noise must be greater than the subject’s critical bandwidth for the frequency of interest. There have been few direct measurements of critical bandwidths for dolphins and none exist for white whales. Underwater pure-tone hearing thresholds were estimated for three dolphins, Tursiops truncatus, and one white whale, Delphinapterus leucas, at 20 and 30 kHz. Band-limited Gaussian masking noise projected at 80 and 90 dB re: 1 μPa2/Hz was centered around the test frequencies. Six different noise bandwidths were used in threshold estimation and were presented in a quasi-random order. Bandwidths had Q values of 0.8, 1, 1.3, 2, 4 and 10, where Q is the ratio of the center frequency to bandwidth. Thresholds were estimated using the method of free response paradigm and an up–down staircase psychophysical procedure for stimulus presentation. Results of the present study add to the existing knowledge of critical bandwidths for dolphins and provide the first data on critical bandwidths for white whales. [Work supported by the Office of Naval Research.]