Research effect of duty cycle on composition of intermittent sound on hearing threshold shift in harbor porpoise
Kastelein, R.A., Van Acoleyen, L., Tuytens, K., Terhune, J.M., von Benda Beckmann, A.M., & Jansen, E. (2026). Effect of duty cycle composition of intermittent sound on temporary hearing threshold shift in a harbor porpoise (Phocoena phocoena). Aquatic Mammals, 52(4), 334-344. DOI
Abstract
Temporary hearing threshold shift (TTS) in mammals depends on aspects of the fatiguing sound causing the shift: frequency, sound pressure level (SPL), exposure duration, and duty cycle (DC). Intermittent fatiguing sounds consist of pulses alternating with inter-pulse intervals (IPIs). With ambient noise below “effective quiet thresholds” (Ward et al., 1976, p. 160) hearing can recover between pulses. Sounds with the same DC can have different combinations of exposure pulse and IPI durations, and it is unclear how DC composition affects TTS.
The effects of IPI on TTS and recovery was studied in a harbor porpoise (Phocoena phocoena) exposed to one-sixth-octave noise bands centered at 8 kHz with mean SPL of 144 dB re 1 μPa and DCs of 50% (cumulative sound exposure level: 177 dB re 1 μPa2s) and 100% (continuous; cumulative sound exposure level: 180 dB re 1 μPa2s). The 50% DCs were sounds with equal pulse and IPI durations of 10, 8, 6, 4, 2, 1, 0.5, 0.25, and 0.1 s. The TTS1-4 min elicited at 11.3 kHz was similar (~18 dB) for fatiguing sound IPIs between 10 and 4 s, higher (~20 dB) for 2 and 1 s IPIs, higher still (~22 dB) for 0.5 s IPI, and highest (~24 dB) for 0.25 and 0.1 s IPIs. The continuous sound caused 23.8 dB TTS.
Hearing recovered during IPIs of 10 to 4 s, less during IPIs of 2 to 0.5 s, and very little during IPIs of ≤ 0.25 s. Reverberations of the fatiguing sound in the pool may have added to the TTS caused when IPIs were short. As the effective quiet SPL for 8 kHz sounds in harbor porpoises is unknown, it is unclear which contributions reverberation energy and short recovery times played in causing the high TTS during exposures with IPIs < 4 s.
This study supports research indicating reduced TTS after exposure to intermittent sounds relative to exposures to continuous sounds, and it highlights the importance of quiet intervals between exposures for hearing recovery.