Coding of spatial and temporal frequency in bat biosonar

Fledermäuse senden Ultraschallrufe aus und lauschen auf Echos um sich in ihrer Umgebung zu orientieren und Beute zu jagen. Dank dieser Fähigkeit zur Echoortung sowie zum aktiven Flug haben sich Fledermäuse eine überaus ergiebige ökologische Nische erschlossen, den nächtlichen Luftraum. Ihr "sechster Sinn" hat Fledermäusen also Unabhängigkeit vom Sonnenlicht beschert. Aber inwiefern kann Hören Sehen ersetzen? Die vorliegende Arbeit beschäftigt sich mit der Frage wie Echoortung bestimmte räumliche und zeitliche Parameter der Umgebung verarbeitet. Wenn es um die Wahrnehmung räumlicher Strukturen geht, stehen echoortende Tiere vor einer speziellen Herausforderung. Die Cochlea, das Sinnesepithel des Hör-systems, kann Rauminformation nicht direkt kodieren. Stattdessen muss Rauminformation errechnet werden, über den Vergleich der Signale an beiden Ohren. Im ersten Kapitel dieser Dissertation teste ich die Hypothese, dass Echoortung dennoch Raumfrequenzen heranzieht um ein Bild der Umgebung zu formen. Das Konzept der Raumfrequenz spielte eine entscheidende Rolle in unserem Verständnis von visueller Wahrnehmung. In der vorliegenden Arbeit zeige ich, dass trotz grundlegender mechanistischer Unterschiede zwischen Seh- und und Hörvermögen beide Sinnessysteme Zugang zu Raumfrequenzinformation haben. Sechs Fledermäuse (Phyllostomus discolor) wurden darauf andressiert, eine Oberfläche mit Wellen unter-schiedlicher Raumfrequenz und Tiefe von einer glatten Oberfläche zu unterscheiden. Meine Messungen zeigen dass Fledermäuse viel empfindlicher gegenüber hohen Raumfrequenzen sind als gegenüber niedrigen Raumfrequenzen, d.h. einen sensorischen Hochpassfilter für Raumfrequenz besitzen. Zusätzlich untersuchte ich welche sensorischen Reize den Fledermäusen zur Verfügung stehen um Raumfrequenz zu bewerten. Ich fand heraus, dass diese Reize sich grundlegend von solchen unterscheiden, welche die visuelle Wahrnehmung von Raumfrequenz vermitteln. Während visuelle Raumfrequenzwahrnehmung das Ergebnis feinabge¬stimmter räumlicher Empfindlichkeit der Retinazellen ist, wird Raumfrequenz¬wahrnehmung mit Echoortung durch objektspezifische Reflektionseigenschaften erreicht. Der Nachweis eines Hochpassfilters in der Echoortung von Fledermäusen offenbart funktionelle Gemeinsamkeiten zwischen Sehen und Echoortung, die beiden Systemen Zugang zum Raumprofil der Umgebung ermöglichen und damit der Figur-Grund-Wahrnehmung zugrunde liegen. Diese funktionellen Gemeinsamkeiten, aber mechanistischen Unterschiede machen deutlich, dass ein Sinnessystem-übergreifender Bedarf an räumlicher Umgebungsinformation besteht. Das Gehör brilliert in der Messung winziger Laufzeitunterschiede. Doch wenn es darum geht zeitlichen Änderungen von Echoparametern zu folgen, scheint das Echo-ortungssystem einer typischen Fledermaus im Nachteil. Der Ortungsruf einer frequenzmodulierenden Fledermaus ist zu kurz um einen kompletten Bewegungs¬zyklus abzubilden. Um Bewegung nachzuverfolgen müssen Fledermäuse die Laufzeit-unterschiede ganzer Sequenzen von Ruf-Echo-Paaren vergleichen. Im zweiten und dritten Kapitel der vorliegenden Arbeit quantifizierte ich die Empfindlichkeit von Fledermaus¬echoortung für zeitliche Modulationen verschiedener Echoparameter. Schlagende Insektenflügel erzeugen natürliche Echomodulationen, und zwar gleichzeitig Modulationen von Laufzeit und Lautstärke. Im zweiten Kapitel führe ich eine Methode ein, mit deren Hilfe sich Laufzeit und Lautstärke der Echos unabhängig voneinander manipulieren lassen. Eine akustische virtuelle Realität ermöglicht die separate Untersuchung der Effekte des jeweiligen Parameters auf die Wahrnehmung der Fledermaus. Ich zeige, dass bei der frequenz-modulierenden Fledermaus P. discolor die Empfindlichkeit für Modulationen der Echolaufzeit stark von der Modulationsrate abhängt. Am empfindlichsten waren die Tiere bei Modulationsraten unter 20 Hz und über 50 Hz. Ich zeige, dass Echoortung für Wechselwirkungen zwischen Modulationsrate und Rufrate anfällig ist, ein Phänomen, das ich als einen echoakustischen Wagenradeffekt bezeichne. Weiter zeige ich, dass bei hohen Modulationsraten Doppler-Verzerrungen zusätzliche spektrale und zeitliche Reize herbeiführen, was den Wiederanstieg der Empfindlichkeit bei hohen Modulationsraten erklären kann. Die bedeutet, dass für die weltweit hunderten Arten frequenzmodulierender Fledermäuse Doppler-Verzerrungen eine wichtige Rolle bei der Flügelschlagwahrnehmung spielen könnten. Im dritten Kapitel vertiefe ich meine Untersuchungen zum Thema Empfindlichkeit von Echoortung gegenüber Echomodulationen. Mit Hilfe der virtuellen Realität moduliere ich die Echolautstärke unabhängig von der Echolaufzeit. Ich kann zeigen, dass P. discolor diese Lautstärkemodulationen wahrnehmen kann und dass die Detektionsleistung der Tiere mit der Modulationsrate ansteigt. Ich führe an, dass sich die Wahrnehmung von Lautstärkemodulationen mit Echoortung grundlegend von der Wahrnehmung von Laufzeitmodulationen unterscheidet. Weiter spekuliere ich, dass der Wahrnehmung schneller Lautstärkemodulationen spektrale Reize zu Grunde liegen. In ihrer Gesamtheit liefert die vorliegende Arbeit experimentelle Nachweise zu wichtigen perzeptorischen Prozessen in der Echoortung frequenzmodulierender Fledermäuse. Meine Erkenntnisse zeigen eine Möglichkeit auf, wie Fledermäuse dem vermeintlich unumgänglichen Kompromiss zwischen räumlichem und zeitlichem Auflösungsvermögen entgehen könnten. Damit stelle ich eine Alternative zur traditionellen Sichtweise, dass die sensorischen Einschränkungen des Gehörs automatisch zu geringerer Leistungsfähigkeit führen. Ich lege dar wie divers die Selektionsfaktoren sind, die auf das Echoortungssystem von Fledermäusen einwirken. Diese Dissertation nimmt daher Einfluss auf die Forschungsbereiche Neuroethologie, Verhaltensökologie, Tierphysiologie und Evolution, und kann zur Weiterentwicklung technischen Sonars beitragen.Bats emit ultrasonic cries and listen to the reflected sounds to orient and forage in their environment. The rich ecological niche of nocturnal air space became accessible through bats’ capability of sustained flight and echolocation. Their “sixth sense” gained them autonomy from sunlight, but to what extent can hearing replace vision? This thesis addresses the question how echolocation encodes certain spatial and temporal parameters of the environment. Echolocation poses a challenge to the perception of spatial layouts because the auditory sensory epithelium, the cochlea, does not explicitly encode space like the eye’s retina does; space must be computed by comparing echo cues at both ears. In the first chapter of this thesis, I test the hypothesis that despite this challenge, bat echolocation utilizes the concept of spatial frequency to form perceptual representations of bats’ habitat. Spatial frequency has been crucial to understand visual perception. I show that both sensory systems, echolocation and vision, have access to spatial frequency information despite their fundamental mechanistic differences. I trained six bats (Phyllostomus discolor) to discriminate ripples of different spatial frequencies from a smooth surface and measured echo-acoustic depth-contrast-sensitivity functions. I show that bats are much more sensitive to high spatial frequencies, exemplifying a spatial high-pass filter. Additionally, I evaluated the perceptual cues available to the bats to assess spatial frequency and found them fundamentally different from those in vision. While spatial frequency perception in vision is a result of spatial tuning, starting already in the retina, spatial frequency perception in echolocation is achieved by object-specific reflection properties that determine the perceived echo-acoustic object signature. The demonstration of a high-pass filter in bat echolocation reveals a functional similarity between vision and echolocation, which underlies figure-ground-separation and allows both systems access to the spatial contours in the environment. The functional similarities, yet mechanistic differences, highlight the need for spatial environmental information, independent of sensory system. The auditory system excels in measuring minute differences in echo arrival times. But when it comes to the tracking of changes of echo properties over time, the echolocation system of a typical bat seems to be at a disadvantage. The echolocation call of frequency-modulating bats is too short to track an entire movement cycle. In order to track movement, bats have to compare memorised sequences of call-echo pairs. In the second and third chapters, I quantified the sensitivity of bat echolocation to the temporal modulation of echo parameters. In nature, fluttering insect wings cause echo modulations; the echoes carry modulations in echo delay and in echo amplitude simultaneously. In the second chapter, I introduce an auditory virtual reality where I can manipulate delay independently from amplitude and tease apart the effects of both parameters on perception. I demonstrate that in the frequency-modulating bat Phyllostomus discolor the sensitivity for modulations in echo delay depends on the rate of the modulation, with bats being most sensitive at modulation rates below 20 Hz and above 50 Hz. I show that echolocation is susceptible to interference between call repetition rate and modulation rate. I propose that this phenomenon constitutes an echo-acoustic wagon-wheel effect. I further demonstrate how at high modulation rates sensitivity could be rescued by using spectral and temporal cues introduced by Doppler-distortions. Thus, I present evidence that Doppler distortions may play a crucial role in flutter sensitivity in the hundreds of frequency-modulating bat species worldwide. In the third chapter, I deepen my investigations into the sensitivity of bat echolocation to temporal echo modulations. I use the virtual reality approach to generate modulations in echo amplitude independent from echo delay. I show that Phyllostomus discolor successfully detected these modulations in echo amplitude and that their performance increased with the rate of the modulation. I suggest that amplitude-modulation detection with echolocation differs fundamentally from delay-modulation detection and speculate that the mechanism to detect fast amplitude modulations relies on spectral cues. In summary, this thesis provides experimental evidence on important perceptual processes in the echolocation of frequency-modulating bats. I give a proof-of-principle demonstration offering release from the supposed trade-off between temporal and spatial acuity and challenging the view that the auditory system’s sensory constraints inevitably lead to detrimental echo-acoustic performance. Thereby, my findings highlight the diversity of selective pressures working on the echolocation system of bats. This thesis therefore has implications on the fields of neuroethology, behavioural ecology, animal physiology and evolution, and may contribute to the further development of technical sonar

Coding of spatial and temporal frequency in bat biosonar

Fledermäuse senden Ultraschallrufe aus und lauschen auf Echos um sich in ihrer Umgebung zu orientieren und Beute zu jagen. Dank dieser Fähigkeit zur Echoortung sowie zum aktiven Flug haben sich Fledermäuse eine überaus ergiebige ökologische Nische erschlossen, den nächtlichen Luftraum. Ihr "sechster Sinn" hat Fledermäusen also Unabhängigkeit vom Sonnenlicht beschert. Aber inwiefern kann Hören Sehen ersetzen? Die vorliegende Arbeit beschäftigt sich mit der Frage wie Echoortung bestimmte räumliche und zeitliche Parameter der Umgebung verarbeitet. Wenn es um die Wahrnehmung räumlicher Strukturen geht, stehen echoortende Tiere vor einer speziellen Herausforderung. Die Cochlea, das Sinnesepithel des Hör-systems, kann Rauminformation nicht direkt kodieren. Stattdessen muss Rauminformation errechnet werden, über den Vergleich der Signale an beiden Ohren. Im ersten Kapitel dieser Dissertation teste ich die Hypothese, dass Echoortung dennoch Raumfrequenzen heranzieht um ein Bild der Umgebung zu formen. Das Konzept der Raumfrequenz spielte eine entscheidende Rolle in unserem Verständnis von visueller Wahrnehmung. In der vorliegenden Arbeit zeige ich, dass trotz grundlegender mechanistischer Unterschiede zwischen Seh- und und Hörvermögen beide Sinnessysteme Zugang zu Raumfrequenzinformation haben. Sechs Fledermäuse (Phyllostomus discolor) wurden darauf andressiert, eine Oberfläche mit Wellen unter-schiedlicher Raumfrequenz und Tiefe von einer glatten Oberfläche zu unterscheiden. Meine Messungen zeigen dass Fledermäuse viel empfindlicher gegenüber hohen Raumfrequenzen sind als gegenüber niedrigen Raumfrequenzen, d.h. einen sensorischen Hochpassfilter für Raumfrequenz besitzen. Zusätzlich untersuchte ich welche sensorischen Reize den Fledermäusen zur Verfügung stehen um Raumfrequenz zu bewerten. Ich fand heraus, dass diese Reize sich grundlegend von solchen unterscheiden, welche die visuelle Wahrnehmung von Raumfrequenz vermitteln. Während visuelle Raumfrequenzwahrnehmung das Ergebnis feinabge¬stimmter räumlicher Empfindlichkeit der Retinazellen ist, wird Raumfrequenz¬wahrnehmung mit Echoortung durch objektspezifische Reflektionseigenschaften erreicht. Der Nachweis eines Hochpassfilters in der Echoortung von Fledermäusen offenbart funktionelle Gemeinsamkeiten zwischen Sehen und Echoortung, die beiden Systemen Zugang zum Raumprofil der Umgebung ermöglichen und damit der Figur-Grund-Wahrnehmung zugrunde liegen. Diese funktionellen Gemeinsamkeiten, aber mechanistischen Unterschiede machen deutlich, dass ein Sinnessystem-übergreifender Bedarf an räumlicher Umgebungsinformation besteht. Das Gehör brilliert in der Messung winziger Laufzeitunterschiede. Doch wenn es darum geht zeitlichen Änderungen von Echoparametern zu folgen, scheint das Echo-ortungssystem einer typischen Fledermaus im Nachteil. Der Ortungsruf einer frequenzmodulierenden Fledermaus ist zu kurz um einen kompletten Bewegungs¬zyklus abzubilden. Um Bewegung nachzuverfolgen müssen Fledermäuse die Laufzeit-unterschiede ganzer Sequenzen von Ruf-Echo-Paaren vergleichen. Im zweiten und dritten Kapitel der vorliegenden Arbeit quantifizierte ich die Empfindlichkeit von Fledermaus¬echoortung für zeitliche Modulationen verschiedener Echoparameter. Schlagende Insektenflügel erzeugen natürliche Echomodulationen, und zwar gleichzeitig Modulationen von Laufzeit und Lautstärke. Im zweiten Kapitel führe ich eine Methode ein, mit deren Hilfe sich Laufzeit und Lautstärke der Echos unabhängig voneinander manipulieren lassen. Eine akustische virtuelle Realität ermöglicht die separate Untersuchung der Effekte des jeweiligen Parameters auf die Wahrnehmung der Fledermaus. Ich zeige, dass bei der frequenz-modulierenden Fledermaus P. discolor die Empfindlichkeit für Modulationen der Echolaufzeit stark von der Modulationsrate abhängt. Am empfindlichsten waren die Tiere bei Modulationsraten unter 20 Hz und über 50 Hz. Ich zeige, dass Echoortung für Wechselwirkungen zwischen Modulationsrate und Rufrate anfällig ist, ein Phänomen, das ich als einen echoakustischen Wagenradeffekt bezeichne. Weiter zeige ich, dass bei hohen Modulationsraten Doppler-Verzerrungen zusätzliche spektrale und zeitliche Reize herbeiführen, was den Wiederanstieg der Empfindlichkeit bei hohen Modulationsraten erklären kann. Die bedeutet, dass für die weltweit hunderten Arten frequenzmodulierender Fledermäuse Doppler-Verzerrungen eine wichtige Rolle bei der Flügelschlagwahrnehmung spielen könnten. Im dritten Kapitel vertiefe ich meine Untersuchungen zum Thema Empfindlichkeit von Echoortung gegenüber Echomodulationen. Mit Hilfe der virtuellen Realität moduliere ich die Echolautstärke unabhängig von der Echolaufzeit. Ich kann zeigen, dass P. discolor diese Lautstärkemodulationen wahrnehmen kann und dass die Detektionsleistung der Tiere mit der Modulationsrate ansteigt. Ich führe an, dass sich die Wahrnehmung von Lautstärkemodulationen mit Echoortung grundlegend von der Wahrnehmung von Laufzeitmodulationen unterscheidet. Weiter spekuliere ich, dass der Wahrnehmung schneller Lautstärkemodulationen spektrale Reize zu Grunde liegen. In ihrer Gesamtheit liefert die vorliegende Arbeit experimentelle Nachweise zu wichtigen perzeptorischen Prozessen in der Echoortung frequenzmodulierender Fledermäuse. Meine Erkenntnisse zeigen eine Möglichkeit auf, wie Fledermäuse dem vermeintlich unumgänglichen Kompromiss zwischen räumlichem und zeitlichem Auflösungsvermögen entgehen könnten. Damit stelle ich eine Alternative zur traditionellen Sichtweise, dass die sensorischen Einschränkungen des Gehörs automatisch zu geringerer Leistungsfähigkeit führen. Ich lege dar wie divers die Selektionsfaktoren sind, die auf das Echoortungssystem von Fledermäusen einwirken. Diese Dissertation nimmt daher Einfluss auf die Forschungsbereiche Neuroethologie, Verhaltensökologie, Tierphysiologie und Evolution, und kann zur Weiterentwicklung technischen Sonars beitragen.Bats emit ultrasonic cries and listen to the reflected sounds to orient and forage in their environment. The rich ecological niche of nocturnal air space became accessible through bats’ capability of sustained flight and echolocation. Their “sixth sense” gained them autonomy from sunlight, but to what extent can hearing replace vision? This thesis addresses the question how echolocation encodes certain spatial and temporal parameters of the environment. Echolocation poses a challenge to the perception of spatial layouts because the auditory sensory epithelium, the cochlea, does not explicitly encode space like the eye’s retina does; space must be computed by comparing echo cues at both ears. In the first chapter of this thesis, I test the hypothesis that despite this challenge, bat echolocation utilizes the concept of spatial frequency to form perceptual representations of bats’ habitat. Spatial frequency has been crucial to understand visual perception. I show that both sensory systems, echolocation and vision, have access to spatial frequency information despite their fundamental mechanistic differences. I trained six bats (Phyllostomus discolor) to discriminate ripples of different spatial frequencies from a smooth surface and measured echo-acoustic depth-contrast-sensitivity functions. I show that bats are much more sensitive to high spatial frequencies, exemplifying a spatial high-pass filter. Additionally, I evaluated the perceptual cues available to the bats to assess spatial frequency and found them fundamentally different from those in vision. While spatial frequency perception in vision is a result of spatial tuning, starting already in the retina, spatial frequency perception in echolocation is achieved by object-specific reflection properties that determine the perceived echo-acoustic object signature. The demonstration of a high-pass filter in bat echolocation reveals a functional similarity between vision and echolocation, which underlies figure-ground-separation and allows both systems access to the spatial contours in the environment. The functional similarities, yet mechanistic differences, highlight the need for spatial environmental information, independent of sensory system. The auditory system excels in measuring minute differences in echo arrival times. But when it comes to the tracking of changes of echo properties over time, the echolocation system of a typical bat seems to be at a disadvantage. The echolocation call of frequency-modulating bats is too short to track an entire movement cycle. In order to track movement, bats have to compare memorised sequences of call-echo pairs. In the second and third chapters, I quantified the sensitivity of bat echolocation to the temporal modulation of echo parameters. In nature, fluttering insect wings cause echo modulations; the echoes carry modulations in echo delay and in echo amplitude simultaneously. In the second chapter, I introduce an auditory virtual reality where I can manipulate delay independently from amplitude and tease apart the effects of both parameters on perception. I demonstrate that in the frequency-modulating bat Phyllostomus discolor the sensitivity for modulations in echo delay depends on the rate of the modulation, with bats being most sensitive at modulation rates below 20 Hz and above 50 Hz. I show that echolocation is susceptible to interference between call repetition rate and modulation rate. I propose that this phenomenon constitutes an echo-acoustic wagon-wheel effect. I further demonstrate how at high modulation rates sensitivity could be rescued by using spectral and temporal cues introduced by Doppler-distortions. Thus, I present evidence that Doppler distortions may play a crucial role in flutter sensitivity in the hundreds of frequency-modulating bat species worldwide. In the third chapter, I deepen my investigations into the sensitivity of bat echolocation to temporal echo modulations. I use the virtual reality approach to generate modulations in echo amplitude independent from echo delay. I show that Phyllostomus discolor successfully detected these modulations in echo amplitude and that their performance increased with the rate of the modulation. I suggest that amplitude-modulation detection with echolocation differs fundamentally from delay-modulation detection and speculate that the mechanism to detect fast amplitude modulations relies on spectral cues. In summary, this thesis provides experimental evidence on important perceptual processes in the echolocation of frequency-modulating bats. I give a proof-of-principle demonstration offering release from the supposed trade-off between temporal and spatial acuity and challenging the view that the auditory system’s sensory constraints inevitably lead to detrimental echo-acoustic performance. Thereby, my findings highlight the diversity of selective pressures working on the echolocation system of bats. This thesis therefore has implications on the fields of neuroethology, behavioural ecology, animal physiology and evolution, and may contribute to the further development of technical sonar

Vocal fold vibratory and acoustic features in fatigued Karaoke singers

Session 3aMU - Musical Acoustics and Speech Communication: Singing Voice in Asian CulturesKaraoke is a popular singing entertainment particularly in Asia and is gaining more popularity in the rest of world. In Karaoke, an amateur singer sings with the background music and video (usually guided by the lyric captions on the video screen) played by Karaoke machine, using a microphone and an amplification system. As the Karaoke singers usually have no formal training, they may be more vulnerable to vocal fatigue as they may overuse and/or misuse their voices in the intensive and extensive singing activities. It is unclear whether vocal fatigue is accompanied by any vibration pattern or physiological changes of vocal folds. In this study, 20 participants aged from 18 to 23 years with normal voice were recruited to participate in an prolonged singing task, which induced vocal fatigue. High speed laryngscopic imaging and acoustic signals were recorded before and after the singing task. Images of /i/ phonation were quantitatively analyzed using the High Speed Video Processing (HSVP) program (Yiu, et al. 2010). It was found that the glottis became relatively narrower following fatigue, while the acoustic signals were not sensitive to measure change following fatigue. © 2012 Acoustical Society of Americapublished_or_final_versio

Use of Pattern Classification Algorithms to Interpret Passive and Active Data Streams from a Walking-Speed Robotic Sensor Platform

In order to perform useful tasks for us, robots must have the ability to notice, recognize, and respond to objects and events in their environment. This requires the acquisition and synthesis of information from a variety of sensors. Here we investigate the performance of a number of sensor modalities in an unstructured outdoor environment, including the Microsoft Kinect, thermal infrared camera, and coffee can radar. Special attention is given to acoustic echolocation measurements of approaching vehicles, where an acoustic parametric array propagates an audible signal to the oncoming target and the Kinect microphone array records the reflected backscattered signal. Although useful information about the target is hidden inside the noisy time domain measurements, the Dynamic Wavelet Fingerprint process (DWFP) is used to create a time-frequency representation of the data. A small-dimensional feature vector is created for each measurement using an intelligent feature selection process for use in statistical pattern classification routines. Using our experimentally measured data from real vehicles at 50 m, this process is able to correctly classify vehicles into one of five classes with 94% accuracy. Fully three-dimensional simulations allow us to study the nonlinear beam propagation and interaction with real-world targets to improve classification results

Spatial echo suppression and echo-acoustic object normalization in echolocating bats

The processing of acoustic cues is critical for all animals in a wide range of behaviours including orientation, predator-prey interactions and social communication. The auditory system can process these sound information with amazing precision. Echolocating bats have developed an extraordinary ability to deal with acoustic cues. Their echo-imaging system has enabled them to detect, pursue and capture tiny prey like insects, to avoid obstacles and to interact with their environment, often in total darkness. Bats heavily rely on the evaluation of echoes for orientation and hunting. The evaluation of external, echolocation- independent sounds also plays an important role for bats, e.g. while localizing prey via prey-generated noise or for social purposes. The current thesis addresses two different aspects of the very complex echo-acoustic situation these extraordinary animals are confronted with in their daily life. The first approach of this thesis is concerned with the question how bats deal with misleading spatial information of echoes. Acoustic orientation most often takes place in echoic environments. Accurate sound localization in natural, echoic environments is a vital task of the auditory system. Many behavioral studies have shown that for accurate sound localization, the auditory system relies only on the spatial information provided by the first wave front and that spatial information of the (delayed) echoes is suppressed (‘precedence effect’). For a bat, this approach is also useful when localizing external, echolocation-independent sound sources, but it is in conflict with the processing of the echoes of self-generated sounds in an echolocation context. In a two-alternative, forced choice paradigm, it is investigated whether and to what extend the echolocating bats Megaderma lyra and Phyllostomus discolor spontaneously suppress the spatial information of either a second echo of their sonar emission or echoes of different external, echolocation-independent sounds. In general, M. lyra and P. discolor did not suppress the spatial information of a second echo independent of the delay. Only one M. lyra showed significant echo suppression. However, this suppression could not be confirmed in an exact repetition of the experiment. Furthermore, it is shown that in the bat M. lyra, spatial echo suppression is restricted to an external sound which carries semantic meaning for the bat, in this case, a typal contact call. Abstract sounds like an acoustic impulse, a time-inverted contact call, or only the first syllable of the contact call do not induce spontaneous echo suppression. The current data indicate that while bats may be able to suppress the spatial information of echoes, this is not their default mode of auditory processing. The reason for this exceptional absence of spatial echo suppression may lie in the shorter time constants of cochlear processing in the ultrasonic frequency range and the strong influence of cognitive components associated with the precedence effect. This study emphasises the contribution of high-level semantic auditory processing to echo suppression. The aim of the second approach was to characterize how echolocating Phyllostomus discolor deals with size-induced variations in echoes due to different-sized ensonified objects. Echolocating bats can identify three-dimensional objects exclusively through the analysis of acoustic echoes of their ultrasonic emissions. However, objects of the same structure can differ in size and the auditory system must achieve a size-invariant, normalized object representation for reliable object recognition. This study describes the behavioral classification of echoes of complex virtual objects that vary in object size. In a phantom-target playback experiment, it is shown that the bat P. discolor spontaneously classified most scaled versions of objects according to trained standards. This psychophysical performance is reflected in electrophysiological responses of a population of cortical units received from a cooperated study, which showed an object-size invariant response. The current results indicate that echolocating bats have indeed a concept of auditory object normalization

Habitat use by \u3cem\u3eMyotis yumanensis\u3c/em\u3e and \u3cem\u3eTadarida brasiliensis mexicana\u3c/em\u3e in South San Francisco Bay wetlands: An Acoustic Study

Research on bat habitat use within coastal estuaries is limited. The purposes of my study were to determine whether Yuma myotis (Myotis yumanensis) and Mexican free-tailed bats (Tadarida brasiliensis mexicana) differentiate between open water and marsh within saline and brackish habitats and to examine whether climatic factors are correlated with general activity and tidal height with foraging of the two species. I recorded echolocation sequences over 30 survey nights in Alviso, California. Two Anabat II® detectors were randomly deployed each survey night in open salt water and salt marsh or open brackish water and brackish marsh. I identified M. yumanensis and T. b. mexicana sequences within each of the four habitats and feeding buzzes in open brackish water and brackish marsh. Additionally, I logged air temperature and wind speed per hour, percent moonlight visibility per survey night, and tidal height at 15-min intervals. I recorded 1,896 sequences, 845 from M. yumanensis and 983 from T. b. mexicana. For both species, there was a significant difference in frequency of occurrence and mean number of echolocation sequences per survey night in open water versus marsh for saline but not for brackish habitats. Furthermore, T. b. mexicana demonstrated greater preference than M. yumanensis for open salt water. Although the call frequency of T. b. mexicana increased with higher air temperature and lower moonlight visibility, the presence/absence of echolocation calls from the two species could not be predicted from the three climatic variables. Mean tidal height did not differ between M. yumanensis and T. b. mexicana sequences with feeding buzzes and sequences without buzzes in open brackish water and brackish marsh. The results increase our knowledge about bat habitat use in estuaries and provide important information to enhance bat conservation in coastal wetlands

Exploring Animal Behavior Through Sound: Volume 1

This open-access book empowers its readers to explore the acoustic world of animals. By listening to the sounds of nature, we can study animal behavior, distribution, and demographics; their habitat characteristics and needs; and the effects of noise. Sound recording is an efficient and affordable tool, independent of daylight and weather; and recorders may be left in place for many months at a time, continuously collecting data on animals and their environment. This book builds the skills and knowledge necessary to collect and interpret acoustic data from terrestrial and marine environments. Beginning with a history of sound recording, the chapters provide an overview of off-the-shelf recording equipment and analysis tools (including automated signal detectors and statistical methods); audiometric methods; acoustic terminology, quantities, and units; sound propagation in air and under water; soundscapes of terrestrial and marine habitats; animal acoustic and vibrational communication; echolocation; and the effects of noise. This book will be useful to students and researchers of animal ecology who wish to add acoustics to their toolbox, as well as to environmental managers in industry and government

The interaction of bats (Microchiroptera) with wind turbines : bioacoustic and other investigations

The phenomenon of bat mortality at wind turbine installations has been generating increasing concern, both for the continued development of the wind industry and for local ecology. Bat-turbine interactions appear to be globally widespread, but are not well understood. The work outlined in this thesis primarily addresses the acoustic properties of moving turbine blades and the way in which bat-like pulses interact with them. In addition, possible factors for bat attraction to wind turbine installations are assessed. The main contributions of this thesis are (1) the formulation and application of a novel equation to rate turbine rotors in terms of bat detectability, identifying that features such as rotor angular velocity, number of blades, blade width and bat species all influence the likelihood of rotor detection; (2) passive and active ultrasonic measurements from turbine rotors in order to assess the nature of acoustic bat interaction with turning blades, showing that frequency and amplitude information in returned echoes can vary significantly, echoes may be attractive to bats as mimicry of echoes returned from flying insects, and that some turbines do not emit ultrasonic noise detectable to all bat species; (3) assessment of the Doppler shift profiles generated by moving blades in order to investigate the changing nature of frequency information returned to an echolocating bat, concluding that blades turning under low wind speed conditions may not be detectable by some bat species; (4) Monte Carlo simulation of bat-like rotor sampling to account for the temporally short nature of reflected echoes, with the result that some bat species may not be able to achieve enough echoes to accurately interpret blade movement in the short approach time-window; (5) the creation and utilisation of artificial bat-like pulses for lab-based experimental work and (6) the investigation of insect attraction to turbine paint colours to determine the potential abundance of bat prey around turbine installations, finding that existing turbine colours are significantly attractive to insect species. By applying the conclusions of this work suggestions for the mitigation of the problem are detailed, the implementation of which may help to reduce the issue of bat mortality for both the wind industry and bat species in the future.EThOS - Electronic Theses Online ServiceGBUnited Kingdo