Discrimination of ripple spectra in a bottlenose dolphin in quiet and after noise exposure

Abstract

The frequency resolving power (FRP) of hearing in quiet and after noise exposure was measured in a bottlenose dolphin using rippled-spectrum test stimuli and noninvasive recording of rhythmic evoked responses (the rate following response, RFR) to ripple phase reversals. Both the test signal and noise had band-limited spectra with the same central frequency; however, the noise had a non-rippled spectrum. The noise level was from -20 to 10 dB re test signal level. The baseline ripple density resolution depended on signal level and was the highest at levels from 80 to 100 dB re 1 μPa. At signal levels both above (up to 130 dB re 1 μPa) and below (down to 80 dB re 1 μPa) the optimal level, the ripple density resolution decreased. The impact of noise was different for different test signal levels. For low test signal levels (70 to 100 dB re 1 μPa), noise decreased RFR magnitude and resolution, whereas for high test signal levels (110 to 130 dB re 1μPa), low-level noise increased RFR magnitude and resolution. [Work supported by the Russian Science Foundation (Project 17-74-20107) awarded to E.V.S.]