Design and Implementation of Bio-inspired Underwater Electrosense

Underwater electrosense, manipulating underwater electric field for sensing purpose, is a growing technology bio-inspired by weakly electric fish that can navigate in dark or cluttered water. We studied its theoretical foundations and developed sophisticated sensing algorithms including some first-introduced techniques such as discrete dipole approximation (DDA) and convolutional neural networks (CNN), which were tested and validated by simulation and a planar sensor prototype. This work pave a solid way to applications on practical underwater robots

Estimation of relative position and coordination of mobile underwater robotic platforms through electric sensing.

International audienceIn the context of underwater robotics, positioning and coordination of mobile agents can prove a challenging problem. To address this issue, we propose the use of electric sensing, with a technique inspired by weakly electric fishes. In particular, the approach relies on one or several of the agents applying an electric field to their environment. Using electric measures, others agents are able to reconstruct their relative position with respect to the emitter, over a range that is function of the geometry of the emitting agent and of the power applied to the environment. Efficacy of the technique is illustrated using a number of numerical examples. The approach is shown to allow coordination of unmanned underwater vehicles, including that of bio-inspired swimming robotic platforms

Animal-Robot Interactions: Electrocommunication, Sensory Ecology, and Group Dynamics in a Mormyrid Weakly Electric Fish

Mormyrid weakly electric fish possess a specialized electrosensory system. During the process of active electrolocation, these animals perceive self-generated electric organ dis-charges (EOD) and are thereby able to detect objects in their nearby environment. The EOD is a short, biphasic pulse, which is simultaneously used to communicate with conspe-cifics. There are two principles according to which information exchange occurs during electrocommunication. The waveform of the EOD constitutes a relatively stable identity marker that signals species, gender, and status of an individual. In contrast, the temporal sequence of inter-discharge intervals (IDI) is highly variable and encodes context-specific information. Modifications of IDI-duration not only alter the instantaneous discharge fre-quency but also enable the generation of specific signaling patterns and interactive dis-charge sequences. One such interactive discharge behavior is the so-called echo response, during which a fish responds with a constant latency of only a few milliseconds to the EOD of a conspecific. Animals can synchronize their signaling sequences by mutually generating echoes to each other's signals over a coherent period. Although active electrolocation and electrocommunication are mediated by different types of electroreceptor organs and neural pathways, an unambiguous assignment of electromotor behavior to only one of the two functions is often problematic. In this thesis, the significance of IDI-based signaling sequences during motor and electro-motor interactions of the mormyrid fish Mormyrus rume proboscirostris were investigated. To this end, different electrical playback sequences of species-specific EODs were generated via mobile fish dummies, and the motor and electromotor responses of live fish were analyzed. In Part One of this thesis, electrocommunication strategies of the fish were analyzed, and particularly the functions of double pulses, discharge regularizations, and echo responses were examined in an adaptive context. Double pulses were classified as an aggressive mo-tivation signal, whereas regularizations may have a communicative function during the early stages of the sequential assessment of a potential opponent. In this context, discharge synchronization by means of echo responses may enable a mutual assessment for the net benefit of both contestants. Because echo responses occur in various behavioral contexts, and artificial echoes of the dummy evoked increased echoing by the fish, it was hypothesized that the echo response serves a more general purpose by enabling mutual allocation of social attention between two fish. In Part Two of this thesis, a biomimetic robotic fish was designed to investigate the senso-ry basis on which fish followed the dummy. It was shown that electrical playback signals induced following-behavior in live fish, whereas biomimetic motility patterns had no ef-fect. By subsequently reducing the mobile dummy to only the electric signaling sequence from the perspective of the fish, it could be shown that passive perception of electrical communication signals is also involved in mediating the spatial coordination of social in-teractions. This passive perception is likely mediated by the same electroreceptor organs that are used during electrocommunication. The EOD can therefore be considered to be an essential social stimulus that makes it possible to integrate a dummy into a group of weak-ly electric fish as an artificial conspecific. The influence of an interactively signaling mobile dummy fish on small groups of up to four individuals was investigated in Part Three of this thesis. Typical schooling behavior was a rare occurrence in this context. However, EOD-synchronizations through mutual echo responses between two fish, or between a fish and the interactive dummy, were fre-quently observed during social interactions in small groups. Motor interactions during synchronization episodes supported the hypothesis that mormyrids may use discharge synchronizations between individuals to allocate social attention, and the echo response may thus adopt a particularly useful function during communication in groups.Schwach elektrische Fisch aus der Familie der Mormyriden verfügen über ein spezialisier-tes elektrosensorisches Sinnessystem. In einem Prozess, der als aktive Elektroortung be-zeichnet wird, sind diese Tiere in der Lage, selbstgenerierte elektrische Organentladungen (EOD) wahrzunehmen, und dadurch Objekte in ihrer unmittelbaren Nähe zu detektieren. Das EOD ist ein kurzer bipolarer Puls, der gleichzeitig auch zur Kommunikation mit Artge-nossen dient. Informationsaustausch während der Elektrokommunikation basiert auf zwei verschiedenen Prinzipien: Die Wellenform des EOD stellt einen relativ konstanten Identi-tätsmarker dar, der beispielsweise Art, Geschlecht und Status eines Individuums signali-siert. Die zeitliche Abfolge der Intervalle zwischen den EODs ist hingegen höchst variabel und kodiert kontextspezifische Information. Durch Modifikation der Intervalldauer ändert sich nicht nur die Entladungsfrequenz, sondern es können auch spezifische Signalmuster und interaktive Entladungssequenzen generiert werden. Ein interaktives Entladungsver-halten stellt beispielsweise die Echoantwort dar, bei der ein Fisch mit einer konstanten Latenz von wenigen Millisekunden auf das EOD eines Artgenossen reagiert. Zwei Tiere können ihre Entladungssequenzen synchronisieren, indem sie ihre Signale über einen kohärenten Zeitraum gegenseitig mit Echos beantworten. Obwohl aktive Elektroortung und Elektrokommunikation über unterschiedliche Rezeptororgansysteme und neuronale Pfade vermittelt werden, ist eine eindeutige Zuordnung der elektromotorischen Verhal-tensäußerungen der Fische zu nur einer der beiden Funktionen oft problematisch. In der vorliegenden Arbeit wurde die Bedeutung intervallbasierter EOD-Sequenzen für motorische und elektromotorische Interaktionen des Mormyriden Mormyrus rume proboscirostris erforscht. Hierzu wurden verschiedene elektrische Playbacksequenzen artspezifischer EODs generiert und durch mobile Fischattrappen wiedergegeben. Die mo-torischen und elektromotorischen Verhaltensreaktionen der Fische wurden analysiert. Im ersten Teil der Arbeit wurden Elektrokommunikationsstrategien der Fische analysiert und die adaptive Funktion insbesondere von Doppelpulsen, Entladungsregularisierungen und Echoantworten untersucht. Doppelpulse wurden als aggressives Motivationssignal kategorisiert, wohingegen die Kommunikationsfunktion von Regularisierungen im gegen-seitigen Einschätzen zu Beginn einer kompetitiven Begegnung zu liegen scheint. Entla-dungssynchronisation durch gegenseitige Echoantworten kann dabei eine Einschätzung des Gegenübers zum Vorteil beider Parteien erleichtern. Da Echoantworten in verschiede-nen Verhaltenssituationen auftreten und artifizielle Echoantworten der Attrappe vermehrt zu Echos vonseiten der Fische führten, wurde postuliert, dass die Echoantwort eine generellere Funktion bei der Fokussierung gegenseitiger sozialer Aufmerksamkeit über-nehmen kann. Im zweiten Teil der Arbeit wurde ein biomimetischer Fischroboter konstruiert, um zu untersuchen, auf welcher sensorischen Grundlage die Fische der Attrappe folgen. Es konnte gezeigt werden, dass elektrische Playbacksignale, nicht aber biomimetische Bewe-gungsmuster, Folgeverhalten der Fische induzieren. In einem weiteren Schritt konnte durch die Reduktion der Attrappe auf die elektrischen Signalsequenzen aus der Perspektive der Versuchsfische gezeigt werden, dass passive Wahrnehmung elektrischer Kommu-nikationssignale auch bei der räumlichen Koordination sozialer Interaktionen von Bedeu-tung ist. Dies wird mutmaßlich über die gleichen Rezeptororgane vermittelt, die auch für die Elektrokommunikation verantwortlich sind. Das EOD kann daher als ein soziales Signal betrachtet werden, das es ermöglicht, eine Attrappe als künstlichen Artgenossen in eine Gruppe schwach elektrischer Fische zu integrieren. Der Einfluss einer elektrisch interaktiven mobilen Fischattrappe auf kleine Gruppen von bis zu vier Individuen wurde im dritten Teil der Arbeit getestet. Typisches Schwarmver-halten konnte in diesem Zusammenhang nur selten beobachtet werden. In kleinen Gruppen kam es während sozialer Interaktionen jedoch häufig zu EOD-Synchronisationen durch Echoantworten zwischen zwei Fischen, oder zwischen einem Fisch und der interaktiven Attrappe. Motorische Verhaltensinteraktionen im Zeitraum dieser Synchronisationen stützen die Hypothese, dass Mormyriden durch elektrische Entladungssynchronisation soziale Aufmerksamkeit zwischen Individuen herstellen können, und die Echoantwort somit besonders in Gruppen eine nützliche Kommunikationsfunktion übernehmen kann

Action-Perception Trade-Offs for Anguilliform Swimming Robotic Platforms with an Electric Sense

International audienceThe work presented addresses the combination of anguilliform swimming-based propulsion with the use of an electric sensing modality for a class of unmanned underwater vehicles, and in particular investigates the relative influence of adjustments to the swimming gait on the platform's displacement speed and on sensing performance. This influence is quantified, for a relevant range of swimming gaits, using experimental data recordings of displacement speeds, and a boundary element method-based numerical simulation tool allowing to reconstruct electric measures. Results show that swimming gaits providing greater movement speeds tend to degrade sensing performance. Conversely, gaits yielding accurate sensing tend to prove slower. To reconcile opposing tendencies, a simple action-perception cost function is designed, with the purpose of adjusting an anguilliform swimmer's gait shape, in accordance with respective importance afforded to action (i.e. movement speed) and perception

Mathematical models of depth perception in weakly electric fish

Weakly electric fish use electrolocation - the detection of electric fields - to sense their environment. The task of electrolocation involves the decoding of the third dimension - depth - from a two-dimensional electric image. In this work we present three advances in the area of depth-perception. First, we develop a model for electrolocation based on a single parameter, namely the width of the electric image. In contrast to previous suggested algorithms, our algorithm would only require a single narrow tuned topographic map to accurately estimate distance. This model is used to study the effects of electromagnetic noise and the presence of stochastic resonance. Second, considering the problem of depth perception from the perspective of information constraints, we ask how much information is necessary for location disambiguation? That is, what is the minimum amount of information that fish would need to localize an object? This inverse problem approach gives us insight into biological electrolocation and provides a guide for future experimental work. Our final contribution is to provide a mathematical foundation for two of the most accepted depth perception models currently in use

Object Localization in Fluids based on a Bioinspired Electroreceptor System

Wolf-Homeyer S. Object Localization in Fluids based on a Bioinspired Electroreceptor System. Bielefeld: Universität Bielefeld; 2019.Weakly electric fish use self-generated electric fields for communication, active electrolocation and navigation. Additionally to visual sense, this ability enables them to detect objects and food even in dark or turbid waters. Specialized muscle cells in the tail region actively generate an electric field in the surrounding fluid, shaped like a dipole between tail and head. This dipole field may be distorted depending on environmental parameters such as the presence of objects of different geometry or material properties in the animal's vicinity. Electroreceptors, distributed all over the fish' skin allow to perceive distortions of the field, caused by objects. Furthermore, fish execute stereotyped scanning behaviors to obtain additional sensory information of detected objects. The development of innovative sensor systems for short-range exploration in fluids is still in its infancy. Also, the use of electric fields in bio-inspired technologies is still at an early stage. Based on the biological model of weakly electric fish, the question has already been examined if an array of electrodes can be used for a contactless object detection and localization and finally for navigation in fluids (Solberg et al. 2008). This examination is performed by analyses of electric field modulations, based on so-called EEVs. An EEV (Ensemble of Electrosensory Viewpoints) is a scalar field representation of the influence of an object on the electric field in the form of potential differences measured between two electrodes for every possible object location. The first part of this thesis explores the characteristics of the electric dipole field and the resulting EEV by means of numerical simulations to determine the influence of an object placed in the emitted field. It will also be investigated how many receptors are required and which arrangement is to be preferred to uniquely identify the positions of spherical objects in the vicinity of the sensor system. For this, a receptor system composed of a simple biomimetic abstraction of an emitter dipole and an orthogonally arranged pair of sensor electrodes is used. Inspired by the scanning movements of the fish, a fixed, minimal scanning strategy, composed of active receptor system movements is developed. The active electrolocation strategy introduced here is based on the superposition of extracted EEV contour-rings in order to find intersections of these contours. The second part of this work focuses on the development of an *application* for active electrolocation which is based on a minimal set of scanning movements as a precursor for the partitioning of the later search area in which sensor-emitter movements take place. In this application, EEVs are also used as major components of two localization algorithms. In order to find points within the search space which are part of several contour-rings, intersection points have to found. Due to numerical inaccuracies intersection points may degrade to contour-segments which lie very close to each other but do not touch. For this case, a nearness metric is used to identify such points. However, in this part of the work the EEVs are based on a simplified analytical representation, which renders the corresponding algorithms suitable for embedded computer systems. In the third part of this thesis, a fitted histogram representation of EEVs is used to compare a large number of different movement sequences to select the optimal composition from this variety. For this, the general shape of an EEV has to be considered, which plays a major role in estimating the best sequence

ELECTROLOCATION-BASED OBSTACLE AVOIDANCE AND AUTONOMOUS NAVIGATION IN UNDERWATER ENVIRONMENTS

Weakly electric fish are capable of performing obstacle avoidance in dark and complex aquatic environments efficiently using a navigation technique known as \emph{electrolocation}. That is, electric fish infer relevant information about surrounding obstacles from the perturbations that these obstacles impart to their self-generated electric field. This dissertation draws inspiration from electrolocation to demonstrate unmapped reflexive obstacle avoidance in underwater environments. The perturbation signal, called the \emph{electric image}, contains the spatial information of the perturbing objects regarding their location, size, conductivity etc. Electrostatic equations elucidate the concept of electrolocation and the mechanism of obstacle detection using electric field perturbations. Spatial decomposition of an electric image using Wide-Field Integration processing extracts relative proximity information about the obstacles. The electric field source is changed to an oscillatory one and a quasistatic approach is taken. Simulations were performed in straight tunnel, cluttered corridor and an obstacle field. Experimental validation was conducted with a setup comprising a tank, a computer-controlled gantry system and an electro-sensor. Consistency between the simulations and the experiments was maintained by recreating similar environments. Simulations using both the electrostatic and the quasistatic approach demonstrate that the algorithm is capable of performing various maneuvers like tunnel centering, wall following and clutter navigation. The experimental results agree with the simulation results and validate the efficacy of the approach in performing obstacle avoidance. The presented approach is computationally lightweight and readily implementable, making underwater autonomous navigation in real-time feasible

Dynamics of sensorimotor behavior in electrolocation and electrocommunication

Pedraja F. Dynamics of sensorimotor behavior in electrolocation and electrocommunication. Bielefeld: Universität Bielefeld; 2019.How are external sensory stimuli perceived, integrated and represented within the central nervous system? How does the nervous system generate appropriate behavioral responses based on this input and how does this behavior affect perception? The above questions have in common that they view sensory input and motor control as two sides of the sensorimotor loop. In this closed-loop system, actions inevitably generate sensory flow that can serve to organize behavior. To look, to smell, to touch, etc. are perceptual acts that depend on the interaction, coordination and interpretation of motor and sensory information through neural mechanisms. Active sensory systems are particularly amenable to the study of the reciprocal relations of motor and sensory components, as parts of closed loop control structures. A notable advantage of these sensory systems is the experimental accessibility of their sensory input, both in terms of its measurement and in terms of detailed modeling reconstructions of the input. In the case of weakly electric fish studied in this thesis, the animals sense and process environmental perturbations of a self-generated electric field. The fact that this field serves as the carrier of sensory information and at the same time is controlled by the animal, enables to precisely determine aspects of sensing that are often hard to obtain or quantify in sensory systems that do not actively generate the carrier: where, when and what an animal samples. Drawing on these benefits, my thesis focuses on the role of motor and electromotor behavior in sensorimotor integration. For this, a biophysical model for the active and passive electroreception was combined with physiological recordings and behavioral approaches. The central topics addressed are: (i) Object detection and sensorimotor learning. The sensory information obtained by the African species Gnathonemus petersii while learning a detection task was computationally reconstructed using boundary element methods (BEM). This revealed that the improved task performance was paralleled by an enhancement of the quality of the sensory information, which was mediated by changes of the electromotor patterns. The versatile manner in which the fish changed the spatial and temporal allocation of otherwise stable motor components not only improved the quality of the sensory input, but also resulted in shifts of the animals' attention towards the object. (ii) Dynamic choice of optimal behavior. Extending on the above results, I next explored how changing the distance of an object to be detected by the fish influenced the electromotor behavior. With increasing complexity (distance), the fish resorted to a new motor strategy. This consisted in first approaching a salient element in the arena, from where the fish then made a perceptually-guided decision. This interpretation is backed up by analyzing the trajectories in the context of attractors, revealing that the focus of attention was altered in a task-dependent manner. (iii) Distance estimation using a non-visual form of motion parallax. In the above experiments it is implicitly assumed that electric fish acquire spatial information like the position and distance of a target. How this is achieved dynamically has been addressed recently. Based on the properties of the electric field geometry, theoretical considerations indicated that relative movements might provide depth information. In a behavioral assay, I show that this novel form of electric parallax exists and is used across phylogenetically distant taxa of weakly electric fish (Apteronotus albifrons, Eigenmania virescens and Gnathonemus petersii). Notably, these species electrically sample the environment in temporally distinct ways (using discrete pulses or quasi-sinusoidal waves), suggesting an ubiquitous role for parallax in electric sensing. (iv) The role of multi-modal integration in socially relevant agonistic behaviour. Extending on the above results, I next addressed if passive as well as active electric sensory information can be used to evaluate more complex features of the environment. For this I turned to social interactions of the South American species Gymnotus omarorum to study if an electrical assessment of a competitor is possible. Based on modeling the sensory consequences of dyadic encounters, I showed that passive as well as active sensory information can drive agonistic interactions. This suggests that aggressive interactions may be triggered by information about contenders obtained through the active and passive electrosensory system. (v) Hierarchy as a social consequence of electric interactions. The above analysis indicated that active as well as passive electrolocation may contribute in a non-reciprocal manner to social interactions. Gymnotus omarorum then was tested in intra- and intersexual dyads in small plain arenas. A sex-independent dominant-subordinate status emerged after highly aggressive contests. Subordinates signaled their submission by retreating and emitting specific (submissive) electric signals. The emergence of a dominant-subordinate status was also observed in a larger arena after longer but milder contests with rare electric signaling of submission with a unique consequence: the persistence of dominance over time with no outcome reversion