Improvements of Sound Localization Abilities by the Facial Ruff of the Barn Owl (Tyto alba) as Demonstrated by Virtual Ruff Removal

BACKGROUND:When sound arrives at the eardrum it has already been filtered by the body, head, and outer ear. This process is mathematically described by the head-related transfer functions (HRTFs), which are characteristic for the spatial position of a sound source and for the individual ear. HRTFs in the barn owl (Tyto alba) are also shaped by the facial ruff, a specialization that alters interaural time differences (ITD), interaural intensity differences (ILD), and the frequency spectrum of the incoming sound to improve sound localization. Here we created novel stimuli to simulate the removal of the barn owl's ruff in a virtual acoustic environment, thus creating a situation similar to passive listening in other animals, and used these stimuli in behavioral tests. METHODOLOGY/PRINCIPAL FINDINGS:HRTFs were recorded from an owl before and after removal of the ruff feathers. Normal and ruff-removed conditions were created by filtering broadband noise with the HRTFs. Under normal virtual conditions, no differences in azimuthal head-turning behavior between individualized and non-individualized HRTFs were observed. The owls were able to respond differently to stimuli from the back than to stimuli from the front having the same ITD. By contrast, such a discrimination was not possible after the virtual removal of the ruff. Elevational head-turn angles were (slightly) smaller with non-individualized than with individualized HRTFs. The removal of the ruff resulted in a large decrease in elevational head-turning amplitudes. CONCLUSIONS/SIGNIFICANCE:The facial ruff a) improves azimuthal sound localization by increasing the ITD range and b) improves elevational sound localization in the frontal field by introducing a shift of iso-ILD lines out of the midsagittal plane, which causes ILDs to increase with increasing stimulus elevation. The changes at the behavioral level could be related to the changes in the binaural physical parameters that occurred after the virtual removal of the ruff. These data provide new insights into the function of external hearing structures and open up the possibility to apply the results on autonomous agents, creation of virtual auditory environments for humans, or in hearing aids

Информационная система заказа, обслуживания и мониторинга доставки продукции в пределах городской черты

В работе рассматриваются программные компоненты информационной системы доставки: заказ продукции широкого потребительского профиля в магазинах города с возможностью определения магазина по требуемой клиентом продукции, обслуживание доставки продавцом и курьером, а также мониторинг процесса доставки заказа клиентом. Система состоит из серверной (программный интерфейс приложения, база данных, сервис кэширования) и клиентской части (мобильное и веб-приложение).The study considers the software components of the delivery information system: ordering products of a wide consumer profile in city stores with the ability to determine the store for the products required by the client, delivery service by the seller and courier, as well as monitoring the process of order delivery by the client. The system consists of a server (application programming interface, database, caching service) and a client (mobile and web application)

Исследование динамических режимов бортового авиационного выпрямителя

Объектом исследования является бортовой авиационный выпрямитель на основе преобразователя с высокочастотным звеном. Цель работы – разработать имитационную модель бортового авиационного выпрямителя, провести проверку на адекватность полученной системы и исследовать динамические режимы выпрямителя.The object of research is an on-board aircraft rectifier based on a high-frequency converter. The purpose of the work is to develop a simulation model of an on-board aviation rectifier, to check the adequacy of the resulting system and explore the dynamic modes of the rectifier

Coding of auditory signals in narrowband neurons in the inferior colliculus of the barn owl

The barn owl (Tyto alba) is a well-known model system for auditory processing and sound localization. Several morphological and neuronal adaptations enable these birds to catch prey even in total darkness solely by using acoustic information such as the rustling of a mouse moving on the ground. Performing this task requires many complex computational processes as to discriminate time differences between both ears in the range of a few microseconds or exploiting level differences of only a few decibels. One of the nuclei involved in auditory processing is located in the midbrain and is called inferior colliculus. This nucleus can be roughly subdivided into a central nucleus (ICC) and an external nucleus (ICX) both with separate functions in neuronal processing of auditory information. Two major goals were pursued in this doctoral thesis. First, an alternative model of sound localization in reference to the Jeffress model was tested. Second, the response properties of ICC neurons to double-stimulation that mimics snapshots of complex signals varying either in temporal or level-dependent manner were recorded. Both approaches served to shed light on the complex processing in the auditory midbrain and to contribute to the long lasting debate on the different competing models of auditory processing. The first part of this thesis tackles the question of whether an alternative model to the Jeffress model for sound localization could be involved in the encoding of extremely large interaural time differences (ITDs). While the animal’s head size limits the range of naturally experienced ITDs to the so-called physiological range, a neuronal response to ITDs far exceeding this range can be recorded in the IC of barn owls. Although the Jeffress model of sound localization is well established in the auditory system of the barn owl, the model is insufficient to explain the recorded responses to large ITDs. As an alternative to the Jeffress model, the stereausis model was tested for its ability to explain the described responses to large ITDs. This model assumes a systematic mismatch of frequencies between both ears that vary as a function of ITD. For the barn owl, neither the data recorded in ICC nor a comparison of the recorded data with the predictions of a cross-correlation model for sound localization could support the stereausis model. The second part of the thesis investigated the effect of adaptation in the ICC. When tested with tonal double-stimulation, the response of recorded units to the second stimulus (probe) was generally reduced compared to the response to the first stimulus (masker). This effect is known as response adaptation. Subsequently, it was tested how response adaptation could be compensated for by changing the stimulus paradigm. Two different paradigms were applied: first, the stimulus level of the probe was varied to investigate how much increase in stimulus level was necessary to overcome response adaptation. Second, the interval between masker offset and probe onset was increased from 25 ms to 1600 ms to test for the recovery periods. It turned out that ICC neurons were very sensitive to faint changes in the stimulus level and an increase of about 5 dB was sufficient to release the neurons from adaptation. The temporal recovery could best be described by two time constants, one short time constant of 3.03 ms, and one longer time constant of 300 ms. Additionally, the spike-frequency adaptation in the neuron’s response to the masker and probe stimuli were investigated. Spike-frequency adaptation (SFA) describes the dynamics of the instantaneous spike rate during stimulus presentation. For the elicited spikes at steady state, the responses to the masker stimulus were reduced by about 70% compared to the maximum peak response at stimulus onset. Furthermore, the decay of SFA acted on time scales in the range of tens of millisec-onds. SFA to the probe stimuli was much more complex and generally influenced by the proceeding response to the masker, by the silent interval between the two stimuli and by the intensity of the stimulus. Thus, the results of this thesis demonstrate that neurons in the barn owl’s ICC are capable to respond to changing stimulus parameters with high precision and the coding properties of these neurons contribute to the underlying processing of auditory signals, which finally are involved in the computation of auditory space needed for precise sound localization

Coding of auditory signals in narrowband neurons in the inferior colliculus of the barn owl

The barn owl (Tyto alba) is a well-known model system for auditory processing and sound localization. Several morphological and neuronal adaptations enable these birds to catch prey even in total darkness solely by using acoustic information such as the rustling of a mouse moving on the ground. Performing this task requires many complex computational processes as to discriminate time differences between both ears in the range of a few microseconds or exploiting level differences of only a few decibels. One of the nuclei involved in auditory processing is located in the midbrain and is called inferior colliculus. This nucleus can be roughly subdivided into a central nucleus (ICC) and an external nucleus (ICX) both with separate functions in neuronal processing of auditory information. Two major goals were pursued in this doctoral thesis. First, an alternative model of sound localization in reference to the Jeffress model was tested. Second, the response properties of ICC neurons to double-stimulation that mimics snapshots of complex signals varying either in temporal or level-dependent manner were recorded. Both approaches served to shed light on the complex processing in the auditory midbrain and to contribute to the long lasting debate on the different competing models of auditory processing. The first part of this thesis tackles the question of whether an alternative model to the Jeffress model for sound localization could be involved in the encoding of extremely large interaural time differences (ITDs). While the animal’s head size limits the range of naturally experienced ITDs to the so-called physiological range, a neuronal response to ITDs far exceeding this range can be recorded in the IC of barn owls. Although the Jeffress model of sound localization is well established in the auditory system of the barn owl, the model is insufficient to explain the recorded responses to large ITDs. As an alternative to the Jeffress model, the stereausis model was tested for its ability to explain the described responses to large ITDs. This model assumes a systematic mismatch of frequencies between both ears that vary as a function of ITD. For the barn owl, neither the data recorded in ICC nor a comparison of the recorded data with the predictions of a cross-correlation model for sound localization could support the stereausis model. The second part of the thesis investigated the effect of adaptation in the ICC. When tested with tonal double-stimulation, the response of recorded units to the second stimulus (probe) was generally reduced compared to the response to the first stimulus (masker). This effect is known as response adaptation. Subsequently, it was tested how response adaptation could be compensated for by changing the stimulus paradigm. Two different paradigms were applied: first, the stimulus level of the probe was varied to investigate how much increase in stimulus level was necessary to overcome response adaptation. Second, the interval between masker offset and probe onset was increased from 25 ms to 1600 ms to test for the recovery periods. It turned out that ICC neurons were very sensitive to faint changes in the stimulus level and an increase of about 5 dB was sufficient to release the neurons from adaptation. The temporal recovery could best be described by two time constants, one short time constant of 3.03 ms, and one longer time constant of 300 ms. Additionally, the spike-frequency adaptation in the neuron’s response to the masker and probe stimuli were investigated. Spike-frequency adaptation (SFA) describes the dynamics of the instantaneous spike rate during stimulus presentation. For the elicited spikes at steady state, the responses to the masker stimulus were reduced by about 70% compared to the maximum peak response at stimulus onset. Furthermore, the decay of SFA acted on time scales in the range of tens of millisec-onds. SFA to the probe stimuli was much more complex and generally influenced by the proceeding response to the masker, by the silent interval between the two stimuli and by the intensity of the stimulus. Thus, the results of this thesis demonstrate that neurons in the barn owl’s ICC are capable to respond to changing stimulus parameters with high precision and the coding properties of these neurons contribute to the underlying processing of auditory signals, which finally are involved in the computation of auditory space needed for precise sound localization