Echolocation Process Research Articles

SonoNERFs: Neural Radiance Fields Applied to Biological Echolocation Systems Allow 3D Scene Reconstruction through Perceptual Prediction.

In this paper, we introduce SonoNERFs, a novel approach that adapts Neural Radiance Fields (NeRFs) to model and understand the echolocation process in bats, focusing on the challenges posed by acoustic data interpretation without phase information. Leveraging insights from the field of optical NeRFs, our model, termed SonoNERF, represents the acoustic environment through Neural Reflectivity Fields. This model allows us to reconstruct three-dimensional scenes from echolocation data, obtained by simulating how bats perceive their surroundings through sound. By integrating concepts from biological echolocation and modern computational models, we demonstrate the SonoNERF's ability to predict echo spectrograms for unseen echolocation poses and effectively reconstruct a mesh-based and energy-based representation of complex scenes. Our work bridges a gap in understanding biological echolocation and proposes a methodological framework that provides a first-order model of how scene understanding might arise in echolocating animals. We demonstrate the efficacy of the SonoNERF model on three scenes of increasing complexity, including some biologically relevant prey-predator interactions.

Cochlea development shapes bat sensory system evolution.

Sensory organs must develop alongside the skull within which they are largely encased, and this relationship can manifest as the skull constraining the organs, organs constraining the skull, or organs constraining one another in relative size. How this interplay between sensory organs and the developing skull plays out during the evolution of sensory diversity; however, remains unknown. Here, we examine the developmental sequence of the cochlea, the organ responsible for hearing and echolocation, in species with distinct diet and echolocation types within the ecologically diverse bat super-family Noctilionoidea. We found the size and shape of the cochlea largely correlates with skull size, with exceptions of Pteronotus parnellii, whose high duty cycle echolocation (nearly constant emission of sound pulses during their echolocation process allowing for detailed information gathering, also called constant frequency echolocation) corresponds to a larger cochlear and basal turn, and Monophyllus redmani, a small-bodied nectarivorous bat, for which interactions with other sensory organs restrict cochlea size. Our findings support the existence of developmental constraints, suggesting that both developmental and anatomical factors may act synergistically during the development of sensory systems in noctilionoid bats.

Paying attention to the man behind the curtain: Jim Simmons' contributions to bat echolocation

Echolocating big brown bats (Eptesicus fuscus) perceive their surroundings by broadcasting frequency-modulated (FM) ultrasonic pulses and processing returning echoes. These bats commonly navigate acoustically-cluttered environments, in which each broadcast is followed by multiple echoes at varying time delays and echo amplitudes. The bat must decode these echo cascades in order to create a coherent percept of its surroundings and adapt its flight and echolocation behavior in real time. Jim Simmons’ physiological and behavioral work—which continues to fuel research questions to this day—has significantly helped our understanding of how this decoding might be possible. In this talk, I will revisit some of Jim Simmons’ seminal work that contributed to our understanding of echolocation processing, and describe its influence on new generations of researchers who continue to build on Jim’s important work.

Echolocation as theory of digital sociality

Public attention on disconnection and digital detox focuses on the health and wellbeing associated with disconnecting without much attention on what happens to selfhood or identity when abruptly disconnected. In an age of ubiquitous internet and “always on” use practices, what does disconnection do? Focusing on what happens when we disconnect, at the micro level, reveals interesting echolocative communication patterns otherwise not noticed. Abruptly stopping the continuous call and response pattern of interaction among youth produces deep anxieties and feelings of existential vulnerability that are commonly brushed aside. The work in this article is part of a larger project related to echolocation as a theory of communication. In an era of constant connectivity and “always on” or more importantly, “always available” internet, the seemingly seamless and steady state of connectivity is, at the more granular level, a process of continual echolocation, in the way we might think of sonar, whereby certain animals like bats determine the shape and location of objects in space by sending steady streams of signals and attending closely to the quality of the echo. Echolocation challenges researchers and theorists to reconsider the core elements and processes in an era of continuous, machinic as well as human interaction in multiple and massive networks of information flow. This does not mean we no longer experience dyadic (two person) or intra interactions, of course, but echolocation, the process of moving, navigating, and positioning through radar-like call and response provides a promising model to apply to how humans make sense of who they are in the complexities of continuous and tangled data flows.

Visual Echolocation Concept for the Colorophone Sensory Substitution Device Using Virtual Reality.

Detecting characteristics of 3D scenes is considered one of the biggest challenges for visually impaired people. This ability is nonetheless crucial for orientation and navigation in the natural environment. Although there are several Electronic Travel Aids aiming at enhancing orientation and mobility for the blind, only a few of them combine passing both 2D and 3D information, including colour. Moreover, existing devices either focus on a small part of an image or allow interpretation of a mere few points in the field of view. Here, we propose a concept of visual echolocation with integrated colour sonification as an extension of Colorophone—an assistive device for visually impaired people. The concept aims at mimicking the process of echolocation and thus provides 2D, 3D and additionally colour information of the whole scene. Even though the final implementation will be realised by a 3D camera, it is first simulated, as a proof of concept, by using VIRCO—a Virtual Reality training and evaluation system for Colorophone. The first experiments showed that it is possible to sonify colour and distance of the whole scene, which opens up a possibility to implement the developed algorithm on a hardware-based stereo camera platform. An introductory user evaluation of the system has been conducted in order to assess the effectiveness of the proposed solution for perceiving distance, position and colour of the objects placed in Virtual Reality.

Portfolio Optimization Using the Bat Algorithm

The bat algorithm is a meta-heuristic algorithm inspired by the bats behaviour characterized by using the echolocation process to localize their objective. In this work applied the bat algorithm has been used in order to solve the portfolio selection problem. This method has been adapted to the cardinality constrained efficient frontier model CCEF using four indexes Hang Seng in Hong Kong, DAX 100 in Germany FTSE 100 in USA and NIKKEI in Japan and the obtained results were compared to those of the unconstrained efficient frontier model (UEF). The bat method illustrates an optimal approximation between the constrained and the unconstrained models.

Extending the bat foraging metaphor for optimisation algorithm design

A particular feature of most species of bats is that they use echolocation, or 'active sensing', in which pulses of acoustic energy are emitted and the resulting echo is resolved into an 'image' of their surrounding environment. This is used to detect objects and to locate food resources such as flying insects. Previous work has taken inspiration from the process of echolocation to develop the 'bat algorithm' Yang, 2010 and this has demonstrated good results on a wide range of optimisation problems. In this paper we build on this work in order to stimulate further interest in exploration of a bat foraging metaphor as an inspiration for the design of optimisation algorithms. This study provides a review of some recent relevant literature on bat foraging and uncovers several aspects of the foraging process which have not been given explicit consideration in bat algorithm design thus far. We also outline a general framework of foraging behaviour which distinguishes between the role of 'perception', 'memory', and the use of the 'social' information available to a foraging bat. We demonstrate how some of these features can be integrated into an exemplar optimisation algorithm and test the performance of this algorithm on a series of benchmark problems. The study also provides several ideas for future work.

A beam based method for target localization: Inspiration from bats' directivity and binaural reception for ultrasonic sonar

The process of echolocation is accomplished by bats partly using the beam profiles associated with their ear shapes that allow for discrimination between different echo directions. Indeed, knowledge of the emitted signal characteristic and measurement of the echo travel time from a target make it possible to compensate for attenuation due to distance, and to focus on filtering through the receivers' beam profiles by comparing received echoes to the original signal at all frequencies in the spectrum of interest. From this basis, a beam profile method to localize a target in three-dimensional space for an ultrasonic sensor system equipped with an emitter and two receivers is presented. Simulations were conducted with different noise levels, and only the contribution of the receivers' beam profiles was considered to estimate the orientation of the target with respect to the receivers. The beam pattern of the Phyllostomus discolor's ear was adopted as that of a receiver. Analyses of beam resolution and frequency ranges were conducted to enhance the accuracy of orientation estimates. The choice of appropriate resolution and frequency ranges guarantee that error mean values for most of the orientations are within [0.5°, 1.5°], even in noisy situations: Signal-to-noise ratio values considered in this work are 35 and 50 dB.

Shape-specific activation of occipital cortex in an early blind echolocation expert

We have previously reported that an early-blind echolocating individual (EB) showed robust occipital activation when he identified distant, silent objects based on echoes from his tongue clicks (Thaler, Arnott, & Goodale, 2011). In the present study we investigated the extent to which echolocation activation in EB's occipital cortex reflected general echolocation processing per se versus feature-specific processing. In the first experiment, echolocation audio sessions were captured with in-ear microphones in an anechoic chamber or hallway alcove as EB produced tongue clicks in front of a concave or flat object covered in aluminum foil or a cotton towel. All eight echolocation sessions (2 shapes×2 surface materials×2 environments) were then randomly presented to him during a sparse-temporal scanning fMRI session. While fMRI contrasts of chamber versus alcove-recorded echolocation stimuli underscored the importance of auditory cortex for extracting echo information, main task comparisons demonstrated a prominent role of occipital cortex in shape-specific echo processing in a manner consistent with latent, multisensory cortical specialization. Specifically, relative to surface composition judgments, shape judgments elicited greater BOLD activity in ventrolateral occipital areas and bilateral occipital pole. A second echolocation experiment involving shape judgments of objects located 20° to the left or right of straight ahead activated more rostral areas of EB's calcarine cortex relative to location judgments of those same objects and, as we previously reported, such calcarine activity was largest when the object was located in contralateral hemispace. Interestingly, other echolocating experts (i.e., a congenitally blind individual in Experiment 1, and a late blind individual in Experiment 2) did not show the same pattern of feature-specific echo-processing calcarine activity as EB, suggesting the possible significance of early visual experience and early echolocation training. Together, our findings indicate that the echolocation activation in EB's occipital cortex is feature-specific, and that these object representations appear to be organized in a topographic manner.

Critical bandwidths in echolocating porpoises, dolphins and whales.

Odontocete cetaceans may differ from most mammals in their response to noise. A close look at the published data [Popov et al. (2006)] of the critical bandwidths of two species of porpoises, the harbor porpoise (Phocaena phocoena) and the finless porpoise (Neophocaena phocaenoides), shows constant bandwidth critical bands in the high frequency area where echolocation signals are processed. A further look at harbor porpoise critical band data [Kastelein et al. (2009)] can be interpreted to show a mixture of constant Q bandwidths at lower frequencies and constant bandwidth data at higher frequencies. Data from Lemonds et al. [1997] indicate that the bottlenosed dolphin shows typical mammalian constant Q filters in lower frequency whistle areas but shifts to constant bandwidths in the areas of high frequency where echolocation discrimination processing is assumed to occur. Recent work (Kloepper et al.) has shown substantial loss in echolocation discrimination performance in the false killer whale with the loss of high frequency hearing. General high frequency hearing loss due to noise in the environment may particularly affect the echolocation processing capabilities of odontocetes and thus the foraging capabilities and fitness of odontocete echolocators. [Work funded by the Office of Naval Research.]

Study of dolphin communicational behavior: procedure, motor and acoustic parameters

First results of the experiments on the acoustic communication of dolphins are reported. They are complemented with the demonstration of a motor reaction of the dolphin keeping watch on the respondent, which was the same for all participants of the dialogue, i. e. turn of the head or trunk towards each other during transmission/reception of the information. The procedure allows unequivocal comparison of the acoustic signals with the behavioral acts of the animals during the experience. All stages of the animal's learning as well as oscillograms of the acoustic signals during acoustic communication behavior and echolocation process connected with differentiation of targets are shown. The routine procedure of investigating formation of the learning set served as the basic model of the physiological experiment. The non-realized action with an increasing emotional load leading on its peak to, inevitable acoustic intervention in to the respondent's work played the role of stimulus of the communication reaction, thus supporting model of communication behavior.

HOW PORPOISES TRACK PREY WITH ECHOLOCATION

Humans have long been fascinated by animals that detect the world through sensory systems that we lack, such as dolphins and porpoises, which navigate by echolocation. However, many of these animals, which dwell in coastal waters, are at increasing risk from human activity. Ursula Verfuß from the University of Tübingen explains that many die entangled in fishermen's nets; `either they don't perceive the nets or they don't perceive them as a threat,' she says. Knowing that harbour porpoises residing in the German Baltic are particularly at risk, Verfuß and her colleagues Lee Miller, Peter Pilz and Hans-Ulrich Schnitzler were curious to know how the animals perceive the world around them. Having already discovered that the porpoises navigate by reducing the interval between echolocating clicks as they approach a landmark, the team decided to find out how the animals adjust their sonar as they close in on a tasty snack(p. 823).Verfuß travelled to the Fjord&Bælt centre in Kertminde,Denmark, to work with two young porpoises, Freja and Eigil. According to Verfuß, the porpoises were very cooperative and fun to work with, but working in the open was a challenge. `We couldn't film for days after a storm because the water was disturbed and another time the enclosure was full of jelly fish,' Verfuß recalls. However, when conditions were good, one of the porpoises' trainers threw a brook trout into the porpoises' enclosure while Verfuß filmed the animals and recorded their echolocation clicks as they homed in on the victim.According to Verfuß, the porpoises speeded up after hearing the splash and eventually rolled onto their backs in the final moments before sucking the fish down. And when Verfuß repeated the experiments with Freja's eyes covered, she slowed a little but still caught the fish. The porpoises could hunt successfully by echolocation alone, but how were they using echolocation to locate the hapless fish?Analysing the porpoises' click sequences, the team realised that the pursuit could be broken down into three phases: search, initial approach and final approach. During the search phase, the porpoises seemed to lock their navigation system onto a local landmark and gradually reduced the time intervals between clicks as they closed in. But as soon as the animals spotted the trout, the click pattern changed. The porpoises maintained a constant average click interval as they drew closer to the victim until they were close enough to pounce. Then they rapidly accelerated their click rate and reduced the click interval to a few milliseconds, just like echolocating bats, which produce a buzz of clicks in the moments before capturing an insect.Verfuß admits that she hadn't expected the porpoises to switch to an almost constant click interval during the initial approach phase. She had thought that the animals would continue shortening the click interval, sending clicks out as soon as the echo returned, speeding up the echolocation process as they approached the trout. However, Pilz suggested that maybe the porpoises switch to a constant click interval to confuse their targets. Verfußexplains that some fish have good hearing, and could be alerted to the porpoises' approach by the accelerating clicks. According to Verfuß, it is possible that by switching to a constant average click rate, the porpoises lull their prey into a false sense of security, making it easier to sneak up and gulp them down.

Broadband backscatter from individual Hawaiian mesopelagic boundary community animals with implications for spinner dolphin foraging

Broadband simulated dolphin echolocation signals were used to measure the ex situ backscatter properties of mesopelagic boundary community (MBC) in order to gain a better understanding of the echolocation process of spinner dolphins foraging on the MBC. Subjects were captured by trawling with a 2-m-opening Isaacs-Kidd Midwater Trawl. Backscatter measurements were conducted on the ship in a 2000 L seawater tank with the transducer placed on the bottom pointed upwards. Backscatter measurements were obtained in both the dorsal and lateral aspects for seven myctophids and only in the dorsal aspect for 16 more myctophids, six shrimps, and three squids. The echoes from the myctophids and shrimps usually had two highlights, one from the surface of the animal nearest the transducer and a second probably from the signal propagating through body of the subject and reflecting off the opposite surface of the animal. The squid echoes consisted mainly of a single highlight but sometimes had a low amplitude secondary highlight. The backscatter results were used to estimate the echolocation detection range for spinner dolphins foraging on the mesopelagic boundary community. The results were also compared with multi-frequency volume backscatter of the mesopelagic boundary community sound scattering layer.

Male sperm whale acoustic behavior observed from multipaths at a single hydrophone

Sperm whales generate transient sounds (clicks) when foraging. These clicks have been described as echolocation sounds, a result of having measured the source level and the directionality of these signals and having extrapolated results from biosonar tests made on some small odontocetes. The authors propose a passive acoustic technique requiring only one hydrophone to investigate the acoustic behavior of free-ranging sperm whales. They estimate whale pitch angles from the multipath distribution of click energy. They emphasize the close bond between the sperm whale's physical and acoustic activity, leading to the hypothesis that sperm whales might, like some small odontocetes, control click level and rhythm. An echolocation model estimating the range of the sperm whale's targets from the interclick interval is computed and tested during different stages of the whale's dive. Such a hypothesis on the echolocation process would indicate that sperm whales echolocate their prey layer when initiating their dives and follow a methodic technique when foraging.

Echolocation signals and pinnae movement in the fruitbat Rousettus aegyptiacus

The fruit bat Rousettus aegyptiacus has highly mobile pinnae. Little is known about the role that such movements play in sound localisation however and whether they interact with the process of echolocation in this species. Here we report the correspondence of echolocation signals in free flight with the downward wingbeat and forward movement of the pinnae, and demonstrate that the ears have a greater sensitivity to click stimuli in front of the animal when directed forwards than when back and to the side. The potential significance of the production of echolocation signals whilst the ears are moving from their least sensitive to their most sensitive position is discussed.

Biosonar performance of foraging beaked whales (Mesoplodon densirostris)

Toothed whales (Cetacea, odontoceti) emit sound pulses to probe their surroundings by active echolocation. Non-invasive, acoustic Dtags were placed on deep-diving Blainville's beaked whales (Mesoplodon densirostris) to record their ultrasonic clicks and the returning echoes from prey items, providing a unique view on how a whale operates its biosonar during foraging in the wild. The process of echolocation during prey capture in this species can be divided into search, approach and terminal phases, as in echolocating bats. The approach phase, defined by the onset of detectable echoes recorded on the tag for click sequences terminated by a buzz, has interclick intervals (ICI) of 300-400 ms. These ICIs are more than a magnitude longer than the decreasing two-way travel time to the targets, showing that ICIs are not given by the two-way-travel times plus a fixed, short lag time. During the approach phase, the received echo energy increases by 10.4(+/-2) dB when the target range is halved, demonstrating that the whales do not employ range-compensating gain control of the transmitter, as has been implicated for some bats and dolphins. The terminal/buzz phase with ICIs of around 10 ms is initiated when one or more targets are within approximately a body length of the whale (2-5 m), so that strong echo returns in the approach phase are traded for rapid updates in the terminal phase. It is suggested that stable ICIs in the search and approach phases facilitate auditory scene analysis in a complex multi-target environment, and that a concomitant low click rate allows the whales to maintain high sound pressure outputs for prey detection and discrimination with a pneumatically driven, bi-modal sound generator.

A model of echolocation of multiple targets in 3D space from a single emission.

Bats, using frequency-modulated echolocation sounds, can capture a moving target in real 3D space. The process by which they are able to accomplish this, however, is not completely understood. This work offers and analyzes a model for description of one mechanism that may play a role in the echolocation process of real bats. This mechanism allows for the localization of targets in 3D space from the echoes produced by a single emission. It is impossible to locate multiple targets in 3D space by using only the delay time between an emission and the resulting echoes received at two points (i.e., two ears). To locate multiple targets in 3D space requires directional information for each target. The frequency of the spectral notch, which is the frequency corresponding to the minimum of the external ear's transfer function, provides a crucial cue for directional localization. The spectrum of the echoes from nearly equidistant targets includes spectral components of both the interference between the echoes and the interference resulting from the physical process of reception at the external ear. Thus, in order to extract the spectral component associated with the external ear, this component must first be distinguished from the spectral components associated with the interference of echoes from nearly equidistant targets. In the model presented, a computation that consists of the deconvolution of the spectrum is used to extract the external-ear-dependent component in the time domain. This model describes one mechanism that can be used to locate multiple targets in 3D space.

Human echolocation: The ECOTEST system

The ECOTEST (EChOlocation TEST) is one of the modules of a PC based system — Rousettus — developed in order to study the human echolocation process, i.e. the ability for auditive perception of obstacles without the use of vision. The ECOTEST allows, rapidly and in a flexible way, the construction and management of specially designed auditive perception tests in order to analyse the psychoacoustic aspects of echolocation. Efficient construction of the tests, using real or artificial echolocation signals as sound stimuli, was achieved through the implementation of a specific computational language. The results, which are based on an experiment carried out with 30 sighted subjects and one blind person, indicated that the ECOTEST is a potentially valuable tool for the evaluation, prediction and training of the echolocation ability by the visually handicapped person through auditive perception tests.

The use of CF/FM sounds in bats

The manner in which bats process their echolocation calls involves two main components: (1) producing and transmitting the signals; and (2) receiving and analyzing them [Fenton and Brock, Bats, Facts On File (1992)]. The high-frequency signals constituting these calls consist of constant frequency (CF) sounds and frequency modulated (FM) sounds. CF components were found to be used for prey detection and identification; FM components were found to be utilized to update distance information. The Doppler shift also helps in detection of targets and gauging the speed of moving targets. Thus, combining the pulses and the resultant echoes enables the bat to determine object distances, sizes, and shapes. Bats were found to have their own call frequencies and are insensitive to a wide range of potential jamming sounds, which allows them to clearly distinguish their own calls amidst environmental cacophony. Experiments have shown that only when entire CF/FM simulations were used did the bats perform discrimination tests badly [J. D. Altringham, Bats: Biology and Behavior (Oxford U.P., New York, 1996)]. This indicates that the echolocation process may be essentially a series processing of CF/FM signals rather than parallel processing of both types.

Energy spectrum analysis: a model of echolocation processing.

Previous analyses of echolocation have suggested that correlation-equivalent processing might be used in certain cases. A frequency domain approach based on energy spectrum analysis of the signal and its echoes combined is proposed as the processing mechanism for echolocation. It is a generalized wide-band mechanism and can account for the large diversity of wide-band signals known to be used for orientation. Neurobiological investigations neither confirm nor deny any specific kind of correlation equivalent processing, but this proposal offers the first frequency domain correlation-equivalent possibility. A review of time separation pitch reveals that an identical analysis has been used to explain that phenomenon. Extensions of the model can explain many of the phenomena observed in echoloction. Subject Classification: [43]80.50, [43]80.60; [43]60.40; [43]65.62, [43]65.68.