Abstract
Big brown bats can discriminate between echoes that alternate in delay (jitter) by as little as 10–15 ns and echoes that are stationary in delay. This delay hyperacuity seems so extreme that it has been rejected in favor of an explanation in terms of artifacts in echoes, most likely spectral in nature, that presumably are correlated with delay. Using different combinations of digital, analog, and cable delays, we dissociated the overall delay of jittering echoes from the size of the analog component of delay, which alone is presumed to determine the strength of the apparatus artifact. The bats' performance remains invariant with respect to the overall delay of the jittering echoes, not with respect to the amount of analog delay. This result is not consistent with the possible use of delay-related artifacts produced by the analog delay devices. Moreover, both electronic and acoustic measurements disclose no spectral cues or impedance-mismatch reflections in delayed signals, just time-delays. The absence of artifacts from the apparatus and the failure of overlap and interference from reverberation to account for the 10-ns result means that closing the gap between the level of temporal accuracy plausibly explained from physiology and the level observed in behavior may require a better understanding of the physiology.
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Abbreviations
- FM:
-
frequency-modulated
- XCR:
-
cross-correlation function
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Acknowledgements
This research was supported by ONR Grant Nos. N00014-89-J-3055, N00014-95-L-1123, and N00014-99-l-0350, by NSF Grant Nos. BCS-9216718 and BES-9622297, by NIMH Grant No. MH00521 (RSDA) and NIMH Training Grant No. MH19118, by McDonnell-Pew Grant No. T89-01245-023, and by Deafness Research Foundation funds. A workshop was held at Sandbjerg, Denmark, in August 1994, to examine current problems in echolocation. Much of the discussion focused on issues surrounding observations of jitter hyperacuity by bats, and results from additional jitter experiments and control procedures were presented at that meeting. Pursuant to requests from several workshop participants, this paper gathers together findings relevant to whether echo delay or spectral differences can explain the bats' performance. We thank colleagues at the Sandbjerg workshop for their constructive suggestions about these experiments. Care and use of the animals was supervised by Brown University veterinarians and the Institutional Animal Care and Use Committee in accordance with Principles of Animal Care no. 86-23 (revised 1985) of the US National Institutes of Health Publication.
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Simmons, J.A., Ferragamo, M.J. & Sanderson, M.I. Echo delay versus spectral cues for temporal hyperacuity in the big brown bat, Eptesicus fuscus . J Comp Physiol A 189, 693–702 (2003). https://doi.org/10.1007/s00359-003-0444-9
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DOI: https://doi.org/10.1007/s00359-003-0444-9