Classification of Natural Textures in Echolocation

Through echolocation, a bat can perceive not only the position of an object in the dark; it can also recognize its 3D structure. A tree, however, is a very complex object; it has thousands of reflective surfaces that result in a chaotic acoustic image of the tree. Technically, the acoustic image of...

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Published inProceedings of the National Academy of Sciences - PNAS Vol. 101; no. 15; pp. 5670 - 5674
Main Authors Grunwald, Jan-Eric, Schörnich, Sven, Wiegrebe, Lutz, Suga, Nobuo
Format Journal Article
LanguageEnglish
Published United States National Academy of Sciences 13.04.2004
National Acad Sciences
Subjects
Acoustic echoes
Acoustics
Animals
Bats
Biological Sciences
Chiroptera - physiology
Computer Simulation
Echolocation - physiology
Experimental data
Female
Infrared radiation
Infrared reflection
Neurology
Nonlinear Dynamics
Phyllostomus discolor
Sensory perception
Simulation training
Sonar
Sound Spectrography - methods
Training
Ultrasonics
Waveforms
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Summary:Through echolocation, a bat can perceive not only the position of an object in the dark; it can also recognize its 3D structure. A tree, however, is a very complex object; it has thousands of reflective surfaces that result in a chaotic acoustic image of the tree. Technically, the acoustic image of an object is its impulse response (IR), i.e., the sum of the reflections recorded when the object is ensonified with an acoustic impulse. The extraction of the acoustic IR from the ultrasonic echo and the detailed IR analysis underlies the bats' extraordinary object-recognition capabilities. Here, a phantom-object playback experiment is developed to demonstrate that the bat Phyllostomus discolor can evaluate a statistical property of chaotic IRs, the IR roughness. The IRs of the phantom objects consisted of up to 4,000 stochastically distributed reflections. It is shown that P. discolor spontaneously classifies echoes generated with these IRs according to IR roughness. This capability enables the bats to evaluate complex natural textures, such as foliage types, in a meaningful manner. The present behavioral results and their simulations in a computer model of the bats' ascending auditory system indicate the involvement of modulation-sensitive neurons in echo analysis.
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Abbreviations: IR, impulse response; log10M4, base 10 logarithm of the waveform fourth moment.
This paper was submitted directly (Track II) to the PNAS office.
Edited by Nobuo Suga, Washington University, St. Louis, MO, and approved February 4, 2004
To whom correspondence should be addressed. E-mail: lutzw@lmu.de.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.0308029101