Impulsive or non-impulsive: Determining hearing loss thresholds for marine mammals (PDF)

Zeddies, D.G., S.L. Denes, K. Lucke, S. B. Martin, and M.A. Ainslie

The Effects of Noise on Aquatic Life (2023)

DOI: 10.1007/978-3-031-10417-6_188-1

It is well known that short loud sounds and longer quieter sounds can produce hearing loss. The idea that equivalent sound energy results in equivalent hearing loss founds our thinking about hearing loss, including regulations to protect hearing (e.g., NIOSH 1998). But it is also recognized that similar level sounds with different temporal characteristics may result in different amounts of hearing loss. This is codified for regulatory purposes (e.g., NMFS 2018) as lower thresholds for predicting hearing loss in marine mammals exposed to impulsive sounds compared to non-impulsive sounds. Currently, a qualitative approach is used to classify sound sources, which is problematic because sources can produce various sounds, some sources do not neatly fit into either category, and sound characteristics change with propagation.

Kurtosis is a measure of the probability distribution of received sound levels. For hearing, kurtosis appears to better predict hearing loss from exposure to some sounds with differing amounts of transients. The kurtosis of a signal can be used to adjust the received level, allowing for a smooth transition between impulsive and non-impulsive sounds. The adjustment focuses on sounds instead of sources, allows for the consideration of propagation effects, and includes the animals’ hearing frequency sensitivity.