Use Of Acoustic Signals Research Articles

ECR Spotlight – Mathilde Martin

ECR Spotlight is a series of interviews with early-career authors from a selection of papers published in Journal of Experimental Biology and aims to promote not only the diversity of early-career researchers (ECRs) working in experimental biology but also the huge variety of animals and physiological systems that are essential for the ‘comparative’ approach. Mathilde Martin is an author on ‘ Use of acoustic signals in Cape fur seal mother–pup reunions: individual signature, signal propagation and pup home range’, published in JEB. Mathilde conducted the research described in this article while a PhD student in Dr Isabelle Charrier's lab at the Institute of Neurosciences Paris-Saclay (NeuroPSI), CNRS & Paris-Saclay University, France. She is now a postdoctoral researcher in the lab of Prof. Marta Manser at the University of Zurich, Switzerland, investigating acoustic communication to decipher how vocal signals modulate social interactions in group-living mammals, in relation to the species' ecological constraints.

Use of acoustic signals in Cape fur seal mother-pup reunions: individual signature, signal propagation and pup home range.

The Cape fur seal (Arctocephalus pusillus pusillus) is one of the most colonial mammals, with colonies of up to hundreds of thousands of individuals during the breeding season. During the lactation period, mothers and pups are regularly separated as females undertake multi-day foraging trips at sea. Mothers and pups use a mutual vocal recognition system to reunite after separation. Such communication is highly constrained by both high background noise and risk of individual confusion owing to the density of seals. This study aimed to experimentally assess the acoustic features relevant for mother-pup vocal identification and the propagation properties of their calls. Playback experiments revealed that mother and pup individual vocal signatures rely on both temporal and frequency parameters: amplitude and frequency modulations, timbre and fundamental frequency (f0). This is more parameters than in any colonial species studied so far. The combinational use of acoustic features reinforces the concept that both environmental and social constraints may have acted as selective pressures on the individual vocal recognition systems. Theoretical propagation distances of mother and pup vocalisations were estimated to be below the range of distances at which mother-pup reunions can occur. This suggests that Cape fur seals may have strong abilities to extract vocal signals from the background noise, as previously demonstrated in the highly colonial king penguin. Investigating the transmission of information throughout the propagation of the signal as well as the ability of the receiving individual to decipher vocal signatures is crucial to understanding vocal recognition systems in the wild.

A Scalogram-Based CNN Approach for Audio Classification in Construction Sites

The automatic monitoring of activities in construction sites through the proper use of acoustic signals is a recent field of research that is currently in continuous evolution. In particular, the use of techniques based on Convolutional Neural Networks (CNNs) working on the spectrogram of the signal or its mel-scale variants was demonstrated to be quite successful. Nevertheless, the spectrogram has some limitations, which are due to the intrinsic trade-off between temporal and spectral resolutions. In order to overcome these limitations, in this paper, we propose employing the scalogramas a proper time–frequency representation of the audio signal. The scalogram is defined as the square modulus of the Continuous Wavelet Transform (CWT) and is known as a powerful tool for analyzing real-world signals. Experimental results, obtained on real-world sounds recorded in construction sites, have demonstrated the effectiveness of the proposed approach, which is able to clearly outperform most state-of-the-art solutions.

Geographical variation in Cape fur seals' in‐air vocalizations across Southern Africa (Namibia and South Africa)

AbstractThe use of acoustic signals to communicate is widespread among marine mammals and vocalizations are involved in all their social interactions. Due to many factors, acoustic features of a species' vocalizations may differ among populations. The present study investigated both micro‐ and macro‐geographical variation in the vocalizations of Cape fur seal females, males, and pups. Acoustic measurements were performed on calls recorded at four South African and two Namibian sites (maximum range ~ 1,000 km). Comparisons among close sites in South Africa revealed no micro‐geographical variation (maximum range ~130 km) in females' and pups' vocalizations. Barks of subadult males had different features among sites, which may be explained mostly by the context of call production. At the macro‐geographical scale (South Africa vs. Namibia), all call types varied significantly among sites. Several extrinsic and intrinsic factors were suggested to drive such differences. For females' and pups' calls, differences might be explained by environmental factors, whereas for males' barks, behavioral differences are the most likely explanation for acoustic differences (breeding vs. resting sites). Such investigations help understand how acoustic communication in marine mammals is shaped by ecological drivers.

Individual Variation in the Use of Acoustic Signals to Coordinate Group Movements among Tibetan Macaques (Macaca thibetana).

Simple SummaryVocal communication is widely used in most primate groups as one of the most effective ways to transmit information. However, the role of sound signals in group movements and their influencing factors are not well understood. In this study, we not only confirmed the recruitment function of vocalizations in group movements, but also found the effect of sex and social centrality on vocalizations. Social centrality indicates the degree of proximity relations between two individuals in a social network. Female Tibetan macaques and individuals with high social centrality were more likely to use vocalizations during collective movements. This study helps us understand the cooperative mechanisms of animal populations.To maintain group cohesion, social animals need to coordinate their actions during group movements. Several species use vocalizations to communicate with each other during coordination. However, the process of vocal communication and its influence in collective decision making is not clear. We studied a group of free-range Tibetan macaques (Macaca thibetana) at Huangshan, China, and recorded acoustic signals during their group movements. It was found that three kinds of sounds were used in their movements. Group movements with vocalizations recruited more participants than the movements without sound. Moreover, during group departures, individuals in the front emitted a higher frequency of vocalization than individuals in the rear. Sex and social centrality both had a significant influence on vocalizations. Social centrality indicates the degree of proximity relations between two individuals in a social network. Females and individuals with high social centrality emitted more sound in group movements. However, social rank and the number of relatives did not affect the emission of sound. These results suggest that the function of calls in collective movements relates to coordinating group movements. This study provides an insight into the association of acoustic communication with collective decision making.

Pressure Effects on Simultaneous Optical and Acoustics Data from Laser-Induced Plasmas in Air: Implications to the Differentiation of Geological Materials.

The shockwave generated alongside the plasma is an intimately linked, yet often neglected additional input for the characterization of solid samples by laser-induced breakdown spectroscopy (LIBS). The present work introduces a dual LIBS-acoustics sensor that takes advantage of the analysis of the acoustic spectrum yielded by shockwaves produced on different geological samples to enhance the discrimination power of LIBS in materials featuring similar optical emission spectra. Six iron-based minerals were tested at a distance of 2 m using 1064 nm laser light and under pressure values ranging from 7 to 1015 mbar. These experimental parameters were selected to assess the effects of pressure, one of the main factors conditioning the propagation of sound as well as a commonly investigated influence in LIBS experiments. Moreover, precise values for carrying out the analyses were set based on one of the most exciting scenarios in which LIBS data may be enhanced by laser-induced acoustics: space exploration. This is exemplified by the tasks performed by the Mars 2020 SuperCam instrument located onboard the Perseverance rover. Authors evaluated the use of acoustic signals both in the time-domain and frequency-domain in sensitive cases for the distinguishing of minerals exhibiting LIBS spectra featuring almost the same emission lines using PCA schemes for each pressure setting. Thus, we report herein the impact of the surrounding pressure level upon this diagnostic tool. Overall, this paper seeks to show how the analytical potential of simultaneous phenomena taking place during a laser-produced plasma event is subjected to the defined operational conditions.

The energetics of social signaling during roost location in Spix's disc-winged bats.

Long-term social aggregations are maintained by multiple mechanisms, including the use of acoustic signals, which may nonetheless entail significant energetic costs. To date, however, no studies have gauged whether there are significant energetic costs to social call production in bats, which heavily rely on acoustic communication for a diversity of social tasks. We measured energetic expenditure during acoustic signaling in Spix's disc-winged bats (Thyroptera tricolor), a species that commonly uses contact calls to locate the ephemeral furled leaves that they use for roosting. To determine the cost of sound production, we measured oxygen consumption using intermittent-flow respirometry methods, with and without social signaling. Our results show that the emission of contact calls significantly increases oxygen consumption; vocal individuals spent, on average, 12.42kJ more during social signaling trials than they spent during silent trials. We also found that as resting metabolic rate increased in males, there was a decreasing probability that they would emit response calls. These results provide support to the 'allocation model', which predicts that only individuals with lower self-maintenance costs can afford to spend energy in additional activities. Our results provide a step forward in our understanding of how physiology modulates behavior, specifically how the costs of call production and resting metabolic rate may explain the differences in vocal behavior among individuals.

Hand Gesture Recognition Using Multiple Acoustic Measurements at Wrist

This article investigates the use of acoustic signals recorded at the human wrist for hand gesture recognition. The prototype consists of 40 microphones to be worn at the wrist. The gesture recognition performance is evaluated through the identification of 36 gestures in American sign language (ASL), including 26 ASL alphabetical characters and 10 ASL numbers. The optimal area for sensor band placement (distal/proximal) is examined to reveal the location of the highest discrimination accuracy. Ten subjects are recruited to perform over ten trials for each set of hand gestures. Using mutual information-based feature selection methods, two time-domain features: difference absolute mean value and log-energy entropy, is selected from 35 commonly used time-domain features for the hand gesture classification. As a proof-of-concept, two common classification methods, linear discriminant analysis and support vector machine, is used to classify hand gestures from the acoustic measurements recorded by each subject. Results show the intrasubject average classification accuracy above 90% using the two features with all 40 microphones, while the average classification accuracy exceeding 84% is obtained using ten microphones. These results indicate that acoustic signatures from the human wrist can be utilized for hand gesture recognition, while the use of few, simple features, with low computational requirements is sufficient to characterize some hand gestures. The proposed technique demonstrates a promising means for developing a low-cost wearable hand gesture recognition device using microphones.

An efficient acoustic-based diagnosis of inter-turn fault in interior mount LSPMSM

This paper investigates the use of acoustic signals in diagnosing stator inter-turn faults in Line Start Permanent Magnet Synchronous Motors (LSPMSMs). Singular spectrum analysis (SSA) is proposed to analyze the acoustic signal for fault detection. The proposed methodology involves collection of experimental acoustic data using a smartphone from an interior mount LSPMSM under different loading levels, healthy as well as faulty motor cases where different number of turns are shorted to emulate different fault levels. Acoustic signal for each case is analyzed using SSA, which results in decomposition of the signal into periodic components and noise. Fast Fourier Transform (FFT) of each component is carried out to find the unique frequency representative for each case. The results with the proposed methodology show that it is capable to detect the occurrence of inter-turn fault under different loading levels with the capability of distinguishing fault severity with readily available acoustic sensor of a smart phone. In addition, it is possible to differentiate between the load and no-load modes of operation.

Bioacoustics in cognitive research: Applications, considerations, and recommendations.

The multifaceted ability to produce, transmit, receive, and respond to acoustic signals is widespread in animals and forms the basis of the interdisciplinary science of bioacoustics. Bioacoustics research methods, including sound recording and playback experiments, are applicable in cognitive research that centers around the processing of information from the acoustic environment. We provide an overview of bioacoustics techniques in the context of cognitive studies and make the case for the importance of bioacoustics in the study of cognition by outlining some of the major cognitive processes in which acoustic signals are involved. We also describe key considerations associated with the recording of sound and its use in cognitive applications. Based on these considerations, we provide a set of recommendations for best practices in the recording and use of acoustic signals in cognitive studies. Our aim is to demonstrate that acoustic recordings and stimuli are valuable tools for cognitive researchers when used appropriately. In doing so, we hope to stimulate opportunities for innovative cognitive research that incorporates robust recording protocols. This article is categorized under: Neuroscience > Cognition Psychology > Theory and Methods Neuroscience > Behavior Neuroscience > Cognition.

Multimodal hand gesture recognition using single IMU and acoustic measurements at wrist.

To facilitate hand gesture recognition, we investigated the use of acoustic signals with an accelerometer and gyroscope at the human wrist. As a proof-of-concept, the prototype consisted of 10 microphone units in contact with the skin placed around the wrist along with an inertial measurement unit (IMU). The gesture recognition performance was evaluated through the identification of 13 gestures used in daily life. The optimal area for acoustic sensor placement at the wrist was examined using the minimum redundancy and maximum relevance feature selection algorithm. We recruited 10 subjects to perform over 10 trials for each set of hand gestures. The accuracy was 75% for a general model with the top 25 features selected, and the intra-subject average classification accuracy was over 80% with the same features using one microphone unit at the mid-anterior wrist and an IMU. These results indicate that acoustic signatures from the human wrist can aid IMU sensing for hand gesture recognition, and the selection of a few common features for all subjects could help with building a general model. The proposed multimodal framework helps address the single IMU sensing bottleneck for hand gestures during arm movement and/or locomotion.

First evidence of underwater vocalisations in hunting penguins.

Seabirds are highly vocal on land where acoustic communication plays a crucial role in reproduction. Yet, seabirds spend most of their life at sea. They have developed a number of morphological, physiological and behavioural adaptations to forage in the marine environment. The use of acoustic signals at sea could potentially enhance seabirds’ foraging success, but remains largely unexplored. Penguins emit vocalisations from the sea surface when commuting, a behaviour possibly associated with group formation at sea. Still, they are unique in their exceptional diving abilities and feed entirely underwater. Other air-breathing marine predators that feed under water, like cetaceans, pinnipeds and marine turtles, are known to emit sound underwater, but such behaviour has not yet been described in seabirds. We aimed to assess the potential prevalence and diversity of vocalisations emitted underwater by penguins. We chose three study species from three different genera, and equipped foraging adults with video cameras with built-in microphones. We recorded a total of 203 underwater vocalisation from all three species during 4 h 43 min of underwater footage. Vocalisations were very short in duration (0.06 s on average), with a frequency of maximum amplitude averaging 998 Hz, 1097 Hz and 680 Hz for King, Gentoo and Macaroni penguins, respectively. All vocalisations were emitted during feeding dives and more than 50% of them were directly associated with hunting behaviour, preceeded by an acceleration (by 2.2 s on average) and/or followed by a prey capture attempt (after 0.12 s on average). The function of these vocalisations remain speculative. Although it seems to be related to hunting behaviour, these novel observations warrant further investigation.

Energy-efficient scheme for target recognition and localization in wireless acoustic sensor networks

The development of wireless acoustic sensor networks has driven the use of acoustic signals for target monitoring. Most monitoring applications require continuous network connectivity and data transfers, which can rapidly exhaust nodes’ energy. Consequently, sensors must collaborate in an adequate architecture to perform target recognition and localization tasks and then to send the results to a remote server with a reduced data volume. The design of an energy-efficient scheme that achieves acoustic target recognition and localization remains an open research problem. Accordingly, this article proposes a low-energy acoustic-based sensing scheme for target recognition and localization to be implemented in a cluster-based sensing approach designed to appropriately balance energy consumption and local processing performed by sensor nodes. A reduced set of low-complexity feature extraction methods in the time domain signal are used in the recognition process. The scheme uses the received energy of the acoustic signals for the target localization. This article details the network architecture, the scheme specification, and its implementation. The results show that the scheme can classify targets with 81.34% accuracy. It requires 3.2 mJ of energy when executed in MICAz, achieving 99% energy savings compared to streaming 3 s of an acoustic signal to a remote server.

Minimization of Energy Hole in Under Water Sensor Networks (UWSNs)

The major difference between underwater sensor networks (UWSNs) and terrestrial sensor networks is the use of acoustic signals as a communication medium rather than radio signals. The main reason behind this is the poor performance of radio signals in water. UWSNs have some distinct characteristics which makes them more research-oriented which is the large propagation delay, high error rate, low bandwidth, and limited energy. UWSNs have their application in the field of oceanographic, data collection, pollution monitoring, off-shore exploration, disaster prevention, assisted navigation, tactical surveillance, etc. In UWSNs the main advantages of protocol design are to a reliable and effective data transmission from source to destination. Among those, energy efficiency plays an important role in underwater communication. The main energy sources of UWSNs are batteries which are very difficult to replace frequently. There are two popular underwater protocols that are DBR and EEDBR. DBR is one of the popular routing techniques which don't use the full dimensional location information. In this article the authors use an efficient area localization scheme for UWSNs to minimize the energy hole created. Rather than finding the exact sensor position, this technique will estimate the position of every sensor node within certain area. In addition to that the authors introduced a RF based location finding and multilevel power transmission scheme. Simulation results shows that the proposed scheme produces better result than its counter parts.

Self-Organizing and Scalable Routing Protocol (SOSRP) for Underwater Acoustic Sensor Networks.

Underwater Acoustic Sensor Networks (UASN) have two important limitations: a very aggressive (marine) environment, and the use of acoustic signals. This means that the techniques for terrestrial wireless sensor networks (WSN) are not applicable. This paper proposes a routing protocol called “Self-Organizing and Scalable Routing Protocol” (SOSRP) which is decentralized and based on tables residing in each node. A combination of the hop value to the collector node and the distance is used as a criterion to create routes leading to the sink node. The expected functions of the protocol include self-organization of the routes, tolerance to failures and detection of isolated nodes. Through the implementation of SOSRP in Matlab and a model of propagation and energy being appropriate for marine environment, performance results are obtained in different scenarios (varying both nodes and transmission range) that include parameters such as end-to-end packet delay, consumption of energy or length of the created routes (with and without failure). The results obtained show a stable, reliable and suitable operation for the deployment and operation of nodes in UASN networks.

A year-long record of low-frequency, long-range, ducted sound propagation from the Canada Basin to the Chukchi Shelf

The Pacific Arctic Region, has experienced decadal changes in atmospheric conditions, seasonal sea-ice coverage, and seawater temperature. From the October 2016 to September 2017, the Canada Basin Acoustic Propagation Experiment (CANAPE) was conducted to understand the changing soundscape and to explore the use of acoustic signals as a remote sensing tool in the modern Arctic. During the experiment, low-frequency signals from five tomographic sources located in the Canada Basin were recorded by an array of hydrophones with both horizontal and vertical apertures located on the Chukchi Shelf at the 150 m isobath. The propagation distances ranged from 240 km to 520 km, and the propagation conditions changed from persistently ducted in the basin to seasonally upward refracting on the continental shelf. The water column properties and ice draft were measured by oceanographic sensors on the basin tomography moorings and by an array of oceanographic moorings on the continental shelf and slope to characterize the temporal and spatial variability of the environment. This talk examines the range-dependent measurements and explains the observed variability in the received signals through propagation modeling using the oceanographic measurements. [Work sponsored by ONR.]

Acoustic propagation from the Canadian Basin to the Chukchi Shelf

The Pacific Arctic Region, encompassing the Bering, Chukchi, Western Beaufort, and Eastern Siberian shelves and seas, has experienced decadal changes in atmospheric conditions, seasonal sea-ice coverage, and seawater temperature. In the summer of 2016, the Canada Basin Acoustic Propagation Experiment (CANAPE) was conducted to understand the changing soundscape and to explore the use of acoustic signals as a remote sensing tool in the modern Arctic. During the experiment, low-frequency signals from five tomographic sources located in the Canada Basin were recorded by a short vertical line array of hydrophones deployed from a research vessel. The recordings were made at seven stations located in the Canada Basin, on the continental rise, and on the Chukchi Shelf. The propagation distances ranged from 50 km to 500 km, and the propagation conditions changed from ducted by the Beaufort Lens in the basin to upward refracting on the continental shelf. Multiple measurements of the sound speed profile were acquire...

The acoustic repertoire of the Atlantic Forest Rocket Frog and its consequences for taxonomy and conservation (Allobates, Aromobatidae).

The use of acoustic signals is a common characteristic of most anuran species to mediate intraspecific communication. Besides many social purposes, one of the main functions of these signals is species recognition. For this reason, this phenotypic trait is normally applied to taxonomy or to construct evolutionary relationship hypotheses. Here the acoustic repertoire of five populations of the genus Allobates from the Brazilian Atlantic Forest are presented for the first time, on a vulnerable to extinction Neotropical taxon. The description of males’ advertisement and aggressive calls and a female call emitted in a courtship context are presented. In addition, the advertisement calls of individuals from distinct geographical regions were compared. Differences in frequency range and note duration may imply in taxonomic rearrangements of these populations, once considered distinct species, and more recently, proposed as a single species, Allobates olfersioides. Calls of the male from the state of Rio de Janeiro do not overlap spectrally with calls of males from northern populations, while the shorter notes emitted by males from Alagoas also distinguishes this population from the remaining southern populations. Therefore, it is likely that at least two of the junior synonyms should be revalidated. Similarities among male advertisement and female calls are generally reported in other anuran species; these calls may have evolved from a preexisting vocalization common to both sexes. Male aggressive calls were different from both the male advertisement and female calls, since it was composed by a longer and multi-pulsed note. Aggressive and advertisement calls generally have similar dominant frequencies, but they have temporal distinctions. Such patterns were corroborated with the Atlantic Forest Rocket Frogs. These findings may support future research addressing the taxonomy of the group, behavioral evolution, and amphibian conservation.

The acoustic repertoire of Cavia intermedia as a contribution to the understanding of the Caviidae communication system

Wild cavies from the taxon Cavia aperea–Cavia porcellus are known for their extensive use of acoustic signals for communication including a courtship call that is a rarity in Mammalia. The genus Cavia includes an insular species (Cavia intermedia) derived from a continental “asocial” Cavia magna. We hypothesized that the courtship call and all the other 12 acoustic signals previously described for C. aperea–C. porcellus were synapomorphies of the genus and took the opportunity of recording the critically endangered C. intermedia. Four field trips lasting 10 days were conducted in 2008 and 2009. After collecting and analysing nearly 350 sound files of 38 individuals, we found all the 12 calls of wild and domestic cavies previously described, including the courtship call, and a new call, a peep. Despite the presence of the peep, our description of C. intermedia acoustic repertoire showed the evolutionary stability of the acoustic repertoire of this rodent genus of 6 species, even after domestication of C. porcellus and 8000 years under insular selective forces in C. intermedia. We present a discussion about the communicative function of Cavia calls in a comparative context and its repertoire size in accordance with the complexity level of sociality of this caviomorph rodent.

Contextual flexibility in the vocal repertoire of an Amazon parrot

BackgroundUnderstanding the role of avian vocal communication in social organisation requires knowledge of the vocal repertoire used to convey information. Parrots use acoustic signals in a variety of social contexts, but no studies have evaluated cross-functional use of acoustic signals by parrots, or whether these conform to signal design rules for different behavioural contexts. We statistically characterised the vocal repertoire of 61 free-living Lilac-crowned Amazons (Amazona finschi) in nine behavioural contexts (nesting, threat, alarm, foraging, perched, take-off, flight, landing, and food soliciting). We aimed to determine whether parrots demonstrated contextual flexibility in their vocal repertoire, and whether these acoustic signals follow design rules that could maximise communication.ResultsThe Lilac-crowned Amazon had a diverse vocal repertoire of 101 note-types emitted at least twice, 58 of which were emitted ≥5 times. Threat and nesting contexts had the greatest variety and proportion of exclusive note-types, although the most common note-types were emitted in all behavioural contexts but with differing proportional contribution. Behavioural context significantly explained variation in acoustic features, where threat and nesting contexts had the highest mean frequencies and broad bandwidths, and alarm signals had a high emission rate of 3.6 notes/s. Three Principal Components explained 72.03 % of the variation in temporal and spectral characteristics of notes. Permutated Discriminant Function Analysis using these Principal Components demonstrated that 28 note-types (emitted by >1 individual) could be correctly classified and significantly discriminated from a random model.ConclusionsAcoustic features of Lilac-crowned Amazon vocalisations in specific behavioural contexts conformed to signal design rules. Lilac-crowned Amazons modified the emission rate and proportional contribution of note-types used in each context, suggesting the use of graded and combinatorial variation to encode information. We propose that evaluation of vocal repertoires based on note-types would reflect the true extent of a species’ vocal flexibility, and the potential for combinatorial structures in parrot acoustic signals.Electronic supplementary materialThe online version of this article (doi:10.1186/s12983-016-0169-6) contains supplementary material, which is available to authorized users.