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Biosonar navigation above water I: estimating flight height

J Neurophysiol 113: 1135-45. doi: 10.1152/jn.00263.2014. Epub 2014 Nov 19.

Authors/Editors: Hoffmann S
Genzel D
Prosch S
Baier L
Weser S
Wiegrebe L
Firzlaff U
Publication Date: 2015
Type of Publication: Journal Articles 2001 - 2017

Abstract

Locomotion and foraging on the wing require precise navigation not only in the horizontal plane. Navigation in three dimensions and specifically, precise adjustment of flight height is essential for flying animals. Echolocating bats drink from water surfaces in flight, which requires an exceptionally precise vertical navigation. Here we exploit this behavior in the bat, Phyllostomus discolor, to understand the biophysical and neural mechanisms which allow for sonar-guided navigation in the vertical plane. In a set of behavioral experiments, we show that for echolocating bats, adjustment of flight height depends on the tragus in their outer ears: Specifically, the tragus imposes elevation-specific spectral interference patterns on the echoes of the bats' sonar emissions. Head-related transfer functions of our bats show that these interference patterns are most conspicuous in the frequency range around 55 kHz. This conspicuousness is faithfully preserved in the frequency tuning and spatial receptive fields of cortical single- and multi-units recorded from anaesthetized animals. In addition, we recorded vertical spatio-temporal response maps, which describe neural tuning in elevation over time. One class of units, which were very sharply tuned to frequencies around 55 kHz, showed unusual spatio-temporal response characteristics with a preference for paired echoes where especially the first echo originates from very low elevations. These behavioral and neural data provide the first insight into biosonar based processing and perception of acoustic elevation cues that are essential for bats to navigate in three-dimensional space.

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