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Biosonar navigation above water II: exploiting mirror images

J Neurophysiol 113: 1146-55. doi: 10.1152/jn.00264.2014. Epub 2014 Nov 19.

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

Abstract

As in vision acoustic signals can be reflected by a smooth surface creating an acoustic mirror image. Water bodies represent the only naturally occurring horizontal and acoustically smooth surfaces. Echolocating bats flying over smooth water bodies encounter echo-acoustic mirror images of objects above the surface. Here, we combined an electrophysiological approach with a behavioral experimental paradigm to investigate whether bats can exploit echo-acoustic mirror images for navigation and how these mirror-like echo-acoustic cues are encoded in their auditory cortex (AC). In an obstacle-avoidance task where the obstacles could only be detected via their echo-acoustic mirror images, most bats spontaneously exploited these cues for navigation. Sonar ensonifications along the bats' flight path revealed conspicuous changes of the reflection patterns, with slightly increased target-strengths at relatively long echo delays corresponding to the longer acoustic paths from the mirrored obstacles. Recordings of cortical spatio-temporal response maps (STRMs) describe the tuning of a unit across the dimensions of elevation and time. The majority of cortical neuronssingle- and multi-units showed a special spatio-temporal pattern of excitatory areas in their STRM indicating a preference for echoes with (relative to the setup dimensions) long delays and, interestingly, from low elevations. This neural preference could effectively encode a reflection pattern as it would be perceived by an echolocating bat detecting an object mirrored from below. The current study provides both behavioral and neurophysiological evidence that echo-acoustic mirror images can be exploited by bats for obstacle avoidance. This capability effectively supports echo-acoustic navigation in highly cluttered natural habitats.

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