Target shape perception and clutter rejection use the same mechanism in bat sonar

http://crossmark.crossref.org/dialog/?doi=10.1007/s00359-016-1085-0&domain=pdf

Web End = J Comp Physiol A (2016) 202:371379 DOI 10.1007/s00359-016-1085-0

ORIGINAL PAPER

http://crossmark.crossref.org/dialog/?doi=10.1007/s00359-016-1085-0&domain=pdf

Web End = http://crossmark.crossref.org/dialog/?doi=10.1007/s00359-016-1085-0&domain=pdf

Web End = http://crossmark.crossref.org/dialog/?doi=10.1007/s00359-016-1085-0&domain=pdf

Web End = http://crossmark.crossref.org/dialog/?doi=10.1007/s00359-016-1085-0&domain=pdf

Web End = http://crossmark.crossref.org/dialog/?doi=10.1007/s00359-016-1085-0&domain=pdf

Web End = http://crossmark.crossref.org/dialog/?doi=10.1007/s00359-016-1085-0&domain=pdf

Web End = http://crossmark.crossref.org/dialog/?doi=10.1007/s00359-016-1085-0&domain=pdf

Web End = http://crossmark.crossref.org/dialog/?doi=10.1007/s00359-016-1085-0&domain=pdf

Web End = Target shape perception and clutter rejection use the same mechanism in bat sonar

Michaela Warnecke1http://orcid.org/0000-0001-5774-4578

Web End = James A. Simmons2

Abstract Big brown bats (Eptesicus fuscus) emit frequency-modulated (FM) biosonar sounds containing two or more harmonic sweeps. Echoes from frontally located targets arrive with rst and second harmonics intact, leading to focused delay images. Echoes from offside or distant objects arrive with the second harmonic relatively weaker (lowpass-ltered), leading to defocused images, which prevents their clutter interference effects (Bates et al. J Exp Biol 214:394401, 2011). Realistic targets contain several glints at slightly different distances and reect several echoes at correspondingly different delays. The bat registers the delay of the nearest glints echoes in the time domain. The delays of echoes from the farther glints are registered in the frequency domain, from interference nulls in the spectrum. Lowpass-ltering of echoes directly affects the image of the nearest glint by defocusing the delay image. However, lowpass-ltering also is superimposed on the interference spectrum used to register the farther glints, which distorts the pattern of interference nulls, defocusing the farther glints inversely, in the spectral domain, before they are perceived as delays. Differences in blurring between time-domain and frequency-domain parts of images identies separate computational paths to perceptually reconstruct objects and prevent interference from off-side or distant clutter.

Received: 21 July 2015 / Revised: 12 March 2016 / Accepted: 15 March 2016 / Published online: 4 April 2016 Springer-Verlag Berlin Heidelberg 2016

Keywords Bat echolocation Echo delay Clutter interference Image defocusing

Abbreviations

ALT Amplitude-latency trading FM Frequency-modulated FM1 First harmonicFM2 Second harmonicIC

Inferior colliculus S+ Positive stimulus

S Negative stimulus

SD

Standard deviation

Introduction

Echolocating big brown bats (Eptesicus fuscus) emit ultrasonic frequency-modulated (FM) biosonar sounds containing two prominent downward-sweeping harmonics, FM1 (sweeping from ~55 to 22 kHz) and FM2 (sweeping from ~110 to 44 kHz) (Grifn 1958; Neuweiler 2000). They perceive objects from echoes that return to their ears (Grifn 1958; Moss and Surlykke 2010; Simmons 2012) and estimate...