4aAB4 – Analysis of bats’ gaze and flight control based on the estimation of their echolocated points with time-domain acoustic simulation

Taito Banda – dmq1001@mail4.doshiha.ac.jp
Miwa Sumiya – miwa1804@gmail.com
Yuya Yamamoto – dmq1050@mail4.doshisha.ac.jp
Yasufumi Yamada – yasufumi.yamada@gmail.com
Faculty of Life and Medical Sciences, Doshisha UniversityKyotanabe, Kyoto, Japan

Yoshiki Nagatani – nagatani@ultrasonics.jp
Department of Electronics, Kobe City College of Technology, Kobe, Japan.

Hiroshi Araki – Araki.Hiroshi@ak.MitsubishiElectric.co.jp
Advanced Technology R&D Center, Mitsubishi Electric Corporation, Amagaski, Japan

Kohta I. Kobayasi – kkobayas@mail.doshisha.ac.jp
Shizuko Hiryu – shiryu@mail.doshisha.ac.jp
Faculty of Life and Medical Sciences, Doshisha University, Kyotanabe, Kyoto, Japan

Popular version of paper 4aAB4 “Analysis of bats’ gaze and flight control based on the estimation of their echolocated points with time-domain acoustic simulation.”
Presented Friday morning, December 7, 2017, 8:45-9:00 AM, Salon F/G/H
174th ASA in New Orleans

Bats broadcast ultrasound and listen to the echoes to understand surrounding information. It is called echolocation. By analyzing those echoes, i.e., arrival time of echoes, bats can detect the position of objects, shape or texture [1-3]. Contrary to the way people use visual information, bats use the sound for sensing the world. How is the world different between the two by sensing? Because both senses are completely different, we cannot imagine how bats see the world.

To address this question, we simulated the echoes arriving at the bats during obstacle-avoiding flight based on the behavioral data so that we could investigate how the surrounding objects were described acoustically.

First, we arranged microphone arrays (24 microphones) and two high-speed cameras in an experimental flight chamber (Figure 1) [4]. The timing, positions and directions of emitted ultrasound as well as the flight paths were measured. A small telemetry-microphone was attached on the back of the bat so that the intensity of emitted ultrasound could be recorded accurately [5]. The bat was forced to follow a S-shaped flight pattern to avoid the obstacle acrylic boards.

Based on those behavioral data, we simulated propagation of sounds with the measured strength and direction emitted at the position of the bat in the experiment, and we could obtain echoes reaching both left and right ears from the obstacles. By using interaural time difference of echoes, we could acoustically identify the echolocated points in the space for all emissions (square plots in Fig.2). We also investigated how the bats show spatial and temporal changes in the echolocated points in the space as they became familiar with the space (top and bottom panels).

We analyzed changes in the echolocated points by using this acoustic simulation, corresponding to which part of objects the bats intended to gaze at. In a comparison between before and after the habituation in the same obstacle layout, there are differences in the wideness of echolocated points on the objects. By flying the same layout repeatedly, false detection of objects was reduced, and their echolocating fields became narrower.

It is natural for animals to pay their attention toward objects adequately and adapt both flight and sensing controls cooperatively as they became familiar with the space. These finding suggests that our approach in this paper, i.e., acoustic simulation based on behavioral experiment is one of effective ways to visualize how the object groups are acoustically structured and represented in the space for bats by echolocation during flight. We believe that it might serve a tip to the question; “What is it like to see as a bat?”

ehcolocation
Figure 1 Diagram of bat flight experiment. Blue and red circles indicate microphones on the wall and the acrylic boards, respectively. Two high-speed video cameras are attached at the two corners of the room. Three acrylic boards are arranged to make bats follow S-shaped flight pattern to avoid the obstacles.

echolocation
Figure 2 Comparison of echolocated points between before and after space habituation. The measured positions where the bat emitted the sound are shown with circle plots meanwhile the calculated echolocated points are shown with square plots. Color variation from blue to red for both circle and square plots corresponds to temporal sequence of the flight. Sizes of circle and square plots correspond to the strength of emissions and their echoes from the obstacles at the bat, respectively.

References:
[1] Griffim D. R., Listning in the dark, Yle University, New Haven, CT, 1958

[2] Simmons J.A., Echolocation in bats: signal processing of echoes for target range, Science, vol. 171, pp.925-928., 1971

[3] Kick S. A., Target-Detection by the Echolocating Bat, Eptesicus fuscus, J Comp Physiol, A., vol. 145, pp.431-435, 1982

[4] Matsuta N, Hiryu S, Fujioka E, Yamada Y, Riquimaroux H, Watanabe Y., Adaptive beam-width control of echolocation sounds by CF-FM bats, Rhinolophus ferrumequinum nippon, during prey-capture flight, J Exp Biol., vol. 206, pp.1210-1218, 2013

[5] Hiryu S, Shiori Y, Hosokawa T, Riquimaroux H, Watanabe Y., On-board telemetry of emitted sounds from free-flying bats: compensation for velocity and distance stabilizes echo frequency and amplitude, J Comp Physiol A., vol. 194, pp.841-851, 2008

Robotic Sonar System Inspired by Bats

Robotic Sonar System Inspired by Bats

Team at Virginia Tech hopes to create small, efficient sonar systems that use less power than current arrays

WASHINGTON, D.C., May 20, 2015 — Engineers at Virginia Tech have taken the first steps toward building a novel dynamic sonar system inspired by horseshoe bats that could be more efficient and take up less space than current man-made sonar arrays. They are presenting a prototype of their “dynamic biomimetic sonar” at the 169th Meeting of the Acoustical Society of America in Pittsburg, Penn.

Bats use biological sonar, called echolocation, to navigate and hunt, and horseshoe bats are especially skilled at using sounds to sense their environment. “Not all bats are equal when it comes to biosonar,” said Rolf Müller, a mechanical engineer at Virginia Tech. “Horseshoe bats hunt in very dense forests, and they are able to navigate and capture prey without bumping into anything. In general, they are able to cope with difficult sonar sensing environments much better than we currently can.”

To uncover the secrets behind the animal’s abilities, Müller and his team studied the ears and noses of bats in the laboratory. Using the same motion-capture technology used in Hollywood films, the team revealed that the bats rapidly deform their outer ear shapes to filter sounds according to frequency and direction and to suit different sensing tasks.

“They can switch between different ear configurations in only a tenth of a second – three times faster than a person can blink their eyes,” said Philip Caspers, a graduate student in Müller’s lab.

Unlike bat species that employ a less sophisticated sonar system, horseshoe bats emit ultrasound squeaks through their noses rather than their mouths. Using laser-Doppler measurements that detect velocity, the team showed that the noses of horseshoe bats also deform during echolocation–much like a megaphone whose walls are moving as the sound comes out.

The team has now applied the insights they’ve gathered about horseshoe bat echolocation to develop a robotic sonar system. The team’s sonar system incorporates two receiving channels and one emitting channel that are able to replicate some of the key motions in the bat’s ears and nose. For comparison, modern naval sonar arrays can have receivers that measure several meters across and many hundreds of separate receiving elements for detecting incoming signals.

By reducing the number of elements in their prototype, the team hopes to create small, efficient sonar systems that use less power and computing resources than current arrays. “Instead of getting one huge signal and letting a supercomputer churn away at it, we want to focus on getting the right signal,” Müller said.

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1aAB11 – A New Dimension to Bat Biosonar

Rolf Müller – rolf.mueller@vt.edu
Anupam K. Gupta – anupamkg@vt.edu
Yanqing Fu – fyq@vt.edu
Uzair Gillani – uzair@vt.edu
Hongxiao Zhu – hongxiao@vt.edu

Virginia Tech
1075 Life Science Circle
Blacksburg, VA 24061

Popular version of paper 1aAB11
Presented Monday morning, October 27, 2014
168th ASA Meeting, Indianapolis

Sonar is a sensing modality that is found in engineering as well as in nature. Man-made sonar systems can be found in places that include the bows of nuclear submarines and the bumpers of passenger cars. Likewise, natural sonar systems can be found in toothed whales that can weigh over 50 tons as well as in tiny bats that weigh just a few grams. All these systems have in common that they emit ultrasonic waves and listen to the returning echoes for clues as to what may be going on in their environments.

Beyond these basic commonalities, man-made and biological sonar systems differ radically in their approach to emitting and receiving the ultrasonic waves. Human sonar engineers tend to favor large numbers of simple elements distributed over a wide area. For example, sonar engineers fit hundreds of emitting and receiving elements into the bow of a nuclear submarine and even automotive engineers often arrange a handful of elements along the bumper of a car. As small flying mammals, bats did not have the option of distributing a large number of sonar elements over wide areas. Instead, they were forced to take a radically different approach. This biological approach has led to sonar systems that are based on a small number of highly complex emitting and receiving elements. At the same time, they have achieved levels of performance that remain unmatched by their man-made peers.

Bat biosonar has only one emitting element, in some bat species this is the mouth and in other, nasally emitting species, the nose. In all bat species, the echoes are received through two receiving elements, i.e., the two ears. But where is the complexity that allows these three elements to vastly outperform naval sonars with hundreds of emitting and receiving elements?

Over the past few years, research on two groups (families) of bats with particularly sophisticated sonar systems has yielded clues to the existence of a new functional dimension in bat biosonar that could be a key factor behind the remaining performance gap between engineered sonar and biosonar. Horseshoe bats (Rhinolophidae) and Old World leaf-nosed bats (Hipposideridae) emit their biosonar pulses nasally and have elaborate baffle shapes (so-called “noseleaves”) that surround the nostrils and can be seen to act as miniature megaphones.
Old World leaf-nosed bat
Figure 1. Noseleaves (“miniature megaphones”) and outer ears of Old World leaf-nosed bats.

Close-up studies of live bats have shown that the noseleaves and the outer ears of these species are both highly dynamic structures. The noseleaves of these bats, for example, have not only much greater geometric complexity than man-made megaphones, but most intriguingly their walls are dynamic: Each time the bat emits an ultrasonic wave packet through its nostrils, it can set the walls of its noseleaf in motion. Hence, the outgoing ultrasonic wave interacts with a changing surface geometry. On the reception side, certain horseshoe bats, for example, have been shown to change the shape of their outer ears within one tenth of second. This is about three times as fast as the proverbial blink of an eye. As for the noseleaf, these changes in shape can take place as the bat receives the ultrasonic echoes.

Figure 2 (video). Motions of the outer ear in an Old World leaf-nosed bats (landmarks added for tracking purposes).

While it is still not certain whether these dynamic features in the sonar system of bats have a function and help the animals to improve their sensory abilities, there is a growing body of evidence that suggests that these fast changes are more than just an oddity. The shape changes in the noseleaves and outer ears are the results of a highly specialized muscular machinery that is unlikely to have evolved without a significant functional advantage acting as a driving force. The resulting changes in shape are big enough to have an impact on the interaction between surface geometry and the passing ultrasonic waves and indeed acoustic impacts have been demonstrated using numerical as well as experimental methods. Finally, dynamic effects are wide-spread among bats with sophisticated sonar systems and are even found in unrelated species that are most likely to have acquired them in response to parallel evolutionary pressures.