At suprathreshold sound levels, interactions between masking noise and sound signals are liable to compressive nonlinearity in the auditory system. The compressive nonlinearity is a property of the “active” cochlear mechanism. It is not known whether this mechanism is capable to function at frequencies close to or above 100 kHz that are available to odontocetes (toothed whales, dolphins, and porpoises). This question may be answered by the use of the frequency-specific masking. Auditory evoked potentials to sound stimuli in a bottlenose dolphin, Tursiops truncatus, were recorded in the presence of simultaneous maskers. Stimulus frequencies were 45, 64, or 90 kHz. Maskers were on-frequency bandlimited noise or low-frequency noise of frequencies 0.25–1 oct below the stimulus frequency. The stimuli provoked responses as a series of brain-potential waves following the pip-train rate. For the on-frequency masker, the masker level at threshold dependence on the signal level was 1.1 dB/dB. For maskers of 1 oct below the stimulus, the dependence was 0.53–0.57 dB/dB. The data considered evidence for the compressive nonlinearity of responses to stimuli, and therefore, are indicative of the functioning of the active mechanism at frequencies up to 90 kHz.
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All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. The study was supported by the Russian Science Foundation (Grant # 17-74-20107 to EVS).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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