Spatial Acuity and Prey Detection in Weakly Electric Fish

It is well-known that weakly electric fish can exhibit extreme temporal acuity at the behavioral level, discriminating time intervals in the submicrosecond range. However, relatively little is known about the spatial acuity of the electrosense. Here we use a recently developed model of the electric field generated by Apteronotus leptorhynchus to study spatial acuity and small signal extraction. We show that the quality of sensory information available on the lateral body surface is highest for objects close to the fish's midbody, suggesting that spatial acuity should be highest at this location. Overall, however, this information is relatively blurry and the electrosense exhibits relatively poor acuity. Despite this apparent limitation, weakly electric fish are able to extract the minute signals generated by small prey, even in the presence of large background signals. In fact, we show that the fish's poor spatial acuity may actually enhance prey detection under some conditions. This occurs because the electric image produced by a spatially dense background is relatively “blurred” or spatially uniform. Hence, the small spatially localized prey signal “pops out” when fish motion is simulated. This shows explicitly how the back-and-forth swimming, characteristic of these fish, can be used to generate motion cues that, as in other animals, assist in the extraction of sensory information when signal-to-noise ratios are low. Our study also reveals the importance of the structure of complex electrosensory backgrounds. Whereas large-object spacing is favorable for discriminating the individual elements of a scene, small spacing can increase the fish's ability to resolve a single target object against this background

Spatial processing of conspecific signals in weakly electric fish: from sensory image to neural population coding

In this dissertation, I examine how an animal’s nervous system encodes spatially realistic conspecific signals in their environment and how the encoding mechanisms support behavioral sensitivity. I begin by modeling changes in the electrosensory signals exchanged by weakly electric fish in a social context. During this behavior, I estimate how the spatial structure of conspecific stimuli influences sensory responses at the electroreceptive periphery. I then quantify how space is represented in the hindbrain, specifically in the primary sensory area called the electrosensory lateral line lobe. I show that behavioral sensitivity is influenced by the heterogeneous properties of the pyramidal cell population. I further demonstrate that this heterogeneity serves to start segregating spatial and temporal information early in the sensory pathway. Lastly, I characterize the accuracy of spatial coding in this network and predict the role of network elements, such as correlated noise and feedback, in shaping the spatial information. My research provides a comprehensive understanding of spatial coding in the first stages of sensory processing in this system and allows us to better understand how network dynamics shape coding accuracy

Processing Submillisecond Timing Differences in a Model Electrosensory System

Perception of sensory cues requires peripheral encoding followed by extraction of behaviorally relevant signal components by central neurons. Some sensory systems can detect temporal information with submillisecond accuracy, despite these signals occurring faster than the approximately 1 ms timescale of neuronal firing. In sound localization, the best studied example of this phenomenon, there are at least two distinct mechanisms for detecting submillisecond timing differences, indicating that multiple solutions to this fundamental problem exist. I investigated mechanisms for processing submillisecond timing differences by studying electrosensory processing in a time coding expert, mormyrid weakly electric fish, which can detect submillisecond differences in the duration of electric signals. First, I measured responses of peripheral receptors to stimuli of different durations. I found that each unit responded preferentially to longer stimuli, but with response thresholds that varied among units within the behaviorally relevant range of durations. This variability establishes a population code operating at near threshold intensities in which the number and identity of responding receptors represents duration. At higher stimulus intensities all units respond independent of duration, rendering the population code obsolete. Importantly, peripheral receptors respond either to the start or end of a signal. Thus, stimulus duration is also represented by a temporal code, as a difference in spike times between receptors. Next, I investigated the central mechanism for detection of submillisecond spike time differences by recording from time comparator neurons (Small Cells) in the midbrain. Recording from Small Cells is challenging because their somas are small and relatively inaccessible. I therefore designed a novel method using retrograde labeling to directly visualize and record from Small Cells in vivo. I showed that patterns of duration tuning vary among Small Cells due to a combination of blanking inhibition corresponding to one edge of a stimulus and variably delayed excitation corresponding to one or both edges of a stimulus. Other circuits that detect submillisecond timing differences rely either on precisely-timed inhibition or delay-line coincidence detection. I demonstrate a novel mechanism by which mormyrids combine delay-line coincidence detection with precisely-timed blanking inhibition to establish diverse patterns of duration tuning among a population of time comparators

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

Modern Telemetry

Telemetry is based on knowledge of various disciplines like Electronics, Measurement, Control and Communication along with their combination. This fact leads to a need of studying and understanding of these principles before the usage of Telemetry on selected problem solving. Spending time is however many times returned in form of obtained data or knowledge which telemetry system can provide. Usage of telemetry can be found in many areas from military through biomedical to real medical applications. Modern way to create a wireless sensors remotely connected to central system with artificial intelligence provide many new, sometimes unusual ways to get a knowledge about remote objects behaviour. This book is intended to present some new up to date accesses to telemetry problems solving by use of new sensors conceptions, new wireless transfer or communication techniques, data collection or processing techniques as well as several real use case scenarios describing model examples. Most of book chapters deals with many real cases of telemetry issues which can be used as a cookbooks for your own telemetry related problems

Фізика з основами біофізики

The text-book "Physics with Fundamentals of Biophysics" published in English is intended for the students who attend the English-speaking lectures in educational institutions of Ukraine; it can be useful for the foreign students and post-graduate students, translators and everybody who is interested in English terminology in the field of physics and biophysics. The main objectives of the course “Physics with Fundamentals of Biophysics” is to expose principal laws and theses of physics which make it possible to study general regularities of natural phenomena; to apply the principles and methods of the physical sciences to biological problems; to consider the biophysical problems which are concerned with the viability of living objects (plants, animals, microorganisms) and their interaction with the environment; to elucidate possible application of physical instrumentation to agricultural, biological, ecological, and medical practice. The text-book is supplied with the examples of solutions of practical biophysical problems, control questions pertaining to those problems that require clarification. Rating system of estimation of students´ level of knowledge is offered also. Each text modulus contains the vocabulary of physical and biophysical terms. The informative material is given in appendix.Даний підручник виданий англійською мовою, призначений саме для підготовки студентів, що слухають лекції англійською мовою в навчальних закладах ІІІ-IV рівнів акредитації України. Він може бути корисним для іноземних студентів та аспірантів, перекладачів та всіх, хто цікавиться англомовною термінологією в галузі фізики та біофізики. Основна мета підручника - навести основні положення, закони та теорії з курсу загальної фізики; розглянути фізичні процеси та механізми, що складають основу життєдіяльності живих організмів – рослин, тварин, мікроорганізмів; викласти проблеми впливу зовнішніх фізичних факторів на живі організми та їх здатності реагувати на ці фактори; висвітлити принципи дії та можливі застосування сучасних фізичних методів та приладів у сільськогосподарській, біологічній, екологічній та медичній практиці. Підручник містить приклади розв’язання практичних біофізичних проблем, контрольні завдання для перевірки засвоєння матеріалу студентами та запитання, відповіді на які студенти зможуть дати у разі ознайомлення із відповідними розділами підручника. Для оцінки знань студентів пропонується рейтингова система. Кожний змістовний модуль має словник фізичних та біофізичних термінів. Інформативний матеріал представлений у додатку

Defense Technical Information Center thesaurus

This DTIC Thesaurus provides a basic multidisciplinary subject term vocabulary used by DTIC to index and retrieve scientific and technical information from its various data bases and to aid DTIC`s users in their information storage and retrieval operations. It includes an alphabetical posting term display, a hierarchy display, and a Keywork Out of Context (KWOC) display

Proton-Ion Medical Machine Study (PIMMS), 1

The Proton-Ion Medical Machine Study (PIMMS) group was formed following an agreement between the Med-AUSTRON (Austria) and the TERA Foundation (Italy) to combine their efforts in the design of a cancer therapy synchrotron. CERN agreed to host this study in its PS Division and a close collaboration was set up with GSI (Germany). The study group was later joined by Onkologie-2000 (Czech Republic). Effort was first focused on the theoretical understanding of slow extraction and the techniques required to produce a smooth beam spill for the conformal treatment of complex-shaped tumours with a sub-millimetre accuracy by active scanning with proton and carbon ion beams. Considerations for passive scanning were also included. The more general and theoretical aspects of the study are recorded in Part I and the more specific technical design considerations are presented in a second volume Part II. The PIMMS team started their work in January 1996 in the PS Division and continued for a period of three years

Investigating the build-up of precedence effect using reflection masking

The auditory processing level involved in the build‐up of precedence [Freyman et al., J. Acoust. Soc. Am. 90, 874–884 (1991)] has been investigated here by employing reflection masked threshold (RMT) techniques. Given that RMT techniques are generally assumed to address lower levels of the auditory signal processing, such an approach represents a bottom‐up approach to the buildup of precedence. Three conditioner configurations measuring a possible buildup of reflection suppression were compared to the baseline RMT for four reflection delays ranging from 2.5–15 ms. No buildup of reflection suppression was observed for any of the conditioner configurations. Buildup of template (decrease in RMT for two of the conditioners), on the other hand, was found to be delay dependent. For five of six listeners, with reflection delay=2.5 and 15 ms, RMT decreased relative to the baseline. For 5‐ and 10‐ms delay, no change in threshold was observed. It is concluded that the low‐level auditory processing involved in RMT is not sufficient to realize a buildup of reflection suppression. This confirms suggestions that higher level processing is involved in PE buildup. The observed enhancement of reflection detection (RMT) may contribute to active suppression at higher processing levels