Differential hearing sensitivity in the adaptive background in a beluga whale

The ability of the auditory system to maintain high differential sensitivity in the adaptive background was investigated in a beluga whale (Delphinapterus leucas). Adaptive background was a train of tone pips following one another at a rate of 1 kHz. Each pip consisted of eight carrier cycles of 64 kHz. Every 128 ms, the train of pips was interrupted for 16 ms and replaced with a test signal (16-ms series of the same tone pips as in the adaptive background, but of another level). The level of the test signals varied from -15 to + 20 dB relative the level of adaptive background. Evoked potentials (the rate following response, RFR) produced by the test signals were recorded. Increasing of adaptive level led to RFR thresholds growth. The 10-dB rising of adaptive signals intensity level led to 7.8 dB rising of test signal threshold. The response amplitude dependence on the test stimulus level was almost independent of the level of the adaptive background. Thus, the beluga’s auditory system displayed high sensitivity to the change in acoustic signal level in the high-level background. [This study was supported by the Russian Foundation for Basic Research (Grant No. 18-04-00088).]