Minimum audible angles for aerial pure tones in a northern elephant seal (Mirounga angustirostris)

Abstract

Recent work has shown that several pinniped species localize aerial broadband signals as accurately as some terrestrial carnivores. Additionally, both harbor seals and California sea lions can better localize both the lower and higher frequencies of their hearing range compared to performance at intermediate frequencies. These results are congruent with the duplex theory of sound localization which states that low frequencies are localized by interaural time differences while high frequencies are localized by interaural intensity differences. Northern elephant seals are land breeding pinnipeds whose range of best hearing sensitivity is shifted toward lower frequencies compared to other pinnipeds tested thus far. In this study, we tested a female northern elephant seal in a hemi-anechoic chamber at six frequencies ranging between 0.8 and 16 kHz that were presented at levels approximately 25 dB above threshold. A left/right behavioral procedure was used to measure minimum audible angles (MAAs) at 75 percent correct discrimination. MAAs ranged from approximately three to fifteen degrees. Best performance occurred at the lower frequencies while worse performance occurred at the two highest test frequencies. Unlike sea lions and harbor seals, this subject showed a decreased ability to utilize interaural intensity differences above 4 kHz.