Dolphins reduce hearing sensitivity in anticipation of repetitive impulsive noise exposures

The auditory steady-state response (ASSR) was continuously measured in two bottlenose dolphins during impulse noise exposures to determine whether observed head movements coincided with actual changes to auditory system sensitivity. Impulses were generated by a seismic air gun at a fixed inter-pulse interval of 10 s. ASSR amplitudes were extracted from the instantaneous electroencephalogram using coherent averaging within a sliding analysis window. A decline in ASSR amplitude was seen during the time interval between air gun impulses, followed by an elevation in ASSR amplitude immediately after each impulse. Similar patterns were not observed during control trials where air gun impulses were not generated. The results suggest that the dolphins learned the timing of the impulse noise sequences and lowered their hearing sensitivity before each impulse, presumably to lessen the auditory effects of the noise. The specific mechanisms responsible for the observed effects are at present unknown.

Automated summary

The study aimed to investigate whether observed head movements of dolphins during impulse noise exposures were correlated with changes in auditory system sensitivity. The results showed that the dolphins exhibited a decline in auditory steady-state response (ASSR) amplitude between air gun impulses, followed by an elevation in ASSR amplitude after each impulse. This pattern was not observed during control trials. The findings suggest that the dolphins learned the timing of the noise sequences and adjusted their hearing sensitivity to mitigate the auditory effects of the noise. The specific mechanisms behind these effects remain unknown.