Do echolocating toothed whales direct their acoustic gaze on- or off-target in a static detection task?

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Echolocating mammals produce directional sound beams with high source levels to improve echo-to-noise ratios and reduce clutter. Recent studies have suggested that the differential spectral gradients of such narrow beams are exploited to facilitate target localization by pointing the beam slightly off targets to maximize the precision of angular position estimates [maximizing bearing Fisher information (FI)]. Here, we test the hypothesis that echolocating toothed whales focus their acoustic gaze askew during target detection to maximize spectral cues by investigating the acoustic gaze direction of two trained delphinids (Tursiops truncatus and Pseudorca crassidens) echolocating to detect an aluminum cylinder behind a hydrophone array in a go/no-go paradigm. The animals rarely placed their beam axis directly on the target, nor within the narrow range around the off-axis angle that maximizes FI. However, the target was, for each trial, ensonified within the swath of the half-power beam width, and hence we conclude that the animals solved the detection task using a strategy that seeks to render high echo-to-noise ratios rather than maximizing bearing FI. We posit that biosonar beam adjustment and acoustic gaze strategies are likely task-dependent and that maximizing bearing FI by pointing off-axis does not improve target detection performance.

OriginalsprogEngelsk
TidsskriftJournal of the Acoustical Society of America
Vol/bind149
Nummer1
Sider (fra-til)581-590
Antal sider10
ISSN0001-4966
DOI
StatusUdgivet - jan. 2021

Bibliografisk note

Funding Information:
We are indebted to Stephanie Vlachos, Christopher Quintos, Marlee Breese, and Paul Nachtigall for their hospitality, dedicated collaboration, and highly skilled training of the animals. We also thank Danuta Wisniewska, Aude Pacini, Nina K. Iversen, Jessica Chen, Laura Kloepper, Aliza Milette, Sanami Nakayma, and Adam Smith for their assistance during data collection. We thank Paul Nachtigall and John R. Buck for constructive discussions and two anonymous reviewers for helpful comments on an earlier version of this manuscript. Experiments were conducted under University of Hawai’i Institutional Animal Care and Use Committee Protocol 09-712 and United States Marine Mammal Permit No. 978-1567 issued to Paul Nachtigall. This work was supported by Frame grants from the National Danish Research foundation (FNU) to P.T.M. (6108-00355B) and by funding from ONR to P. L. Tyack. We dedicate this paper to the late Professor Whitlow Au, the founding father of quantitative studies of toothed whale echolocation.

Publisher Copyright:
© 2021 Acoustical Society of America.

Copyright:
Copyright 2021 Elsevier B.V., All rights reserved.

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