Electrophysiological investigation of temporal resolution in three pinniped species: Adaptive implications

Abstract

Electrophysiological studies of auditory temporal processing in marine mammals have traditionally focused on the role of highly refined temporal resolution in dolphin echolocation. Studies in manatees, however, have found their temporal resolution to be better than expected, leading to speculation that such capabilities are an adaptation for underwater sound localization. This study measured the ability of auditory brainstem responses to follow rhythmic click stimuli in California sea lions (Zalophus californianus), harbor seals (Phoca vitulina), and northern elephant seals (Mirounga angustirostris). Trains of 640-s clicks were presented in air at repetition rates of 125–1500 per second and averaged rate-following responses were recorded. Rate-following responses were detected in both the harbor seal and the sea lion at rates up to 1000 clicks per second, indicating that pinnipeds, like manatees, possess temporal resolution greater than humans but inferior to dolphins. While this finding might support an underwater sound localization hypothesis, comparable results were obtained in preliminary testing of a dog (Canis familiaris), suggesting that increased temporal resolution in pinnipeds may not be the result of the evolutionary pressure of an aquatic environment, but rather a result of increased high-frequency hearing essential to mammalian sound localization. [Work supported by NOPP, ONR, and NMFS.]