Spatial Separation Of Signals Research Articles

Neural encoding for spatial release from informational masking and its correlation with behavioral metrics.

The central auditory system encompasses two primary functions: identification and localization. Spatial release from masking (SRM) highlights speech recognition in competing noise and improves the listening experience when a spatial cue is introduced between noise and target speech. This assessment focuses on the integrity of auditory function and holds clinical significance. However, infants or pre-lingual subjects sometimes provide less reliable results. This study investigates the value of cortical auditory evoked potentials (CAEPs) onset and acoustic change complex (ACC) as an objective measurement of SRM. Thirty normal-hearing young adults (11 males) were recruited. We found the spatial separation of signals and noise (±90° symmetrically) resulted in a signal-to-noise ratio (SNR) improvement of 9.00 ± 1.71 dB behaviorally. It significantly enhanced cortical processing at all SNR levels, shortened CAEP latencies, and increased amplitudes, resulting in a greater number of measurable peaks for ACC. SRM showed mild to moderate correlations with the differences between two conditions in CAEP measures. The regression model combining N1'-P2' amplitude at 5 dB SNR (R2 = 0.26), P1 amplitude at 0 dB SNR (R2 = 0.14), and P1 latency at -5 dB SNR (R2 = 0.15), explained 45.3% of the variance in SRM. Our study demonstrates that introducing spatial cues can improve speech perception and enhance central auditory processing in normal-hearing young adults. CAEPs may contribute to predictions about SRM and hold potential for practical application.NEW & NOTEWORTHY The neural encoding of spatial release from masking (SRM) can be observed in normal-hearing young adults. Spatial separation between target and masker improves speech perception in noise and enhances central auditory processing. The behavioral results showed mild-to-moderate correlations with electrophysiological measures, with acoustic change complex (ACC) amplitude being a better indicator than onset components. Cortical auditory evoked potentials (CAEPs) may contribute to predictions about spatial release from masking, especially when behavioral tests are less reliable.

Human brain 7Li-MRI following low-dose lithium dietary supplementation in healthy participants

BackgroundLithium is an effective mood stabiliser, but its mechanism of action is incompletely defined. Even at very low doses, lithium may have neuroprotective effects, but it is not clear if these relate to brain lithium concentration in vivo. We have developed magnetic resonance imaging (7Li-MRI) methods to detect lithium in the brain following supplementation at a very low dose. MethodsLithium orotate supplements were taken by nine healthy adult male subjects (5 mg daily) for up to 28 days, providing 2–7 % of the lithium content of a typical therapeutic lithium carbonate dose. One-dimensional 7Li-images were acquired on a 3.0 T MRI scanner. All subjects were scanned on day 14 or 28; seven were scanned on both, one at baseline and one after 7-days washout. Results7Li-MR signal amplitude was broadly stable between days 14 and 28. Two subjects had notably higher 7Li-signal intensities (approximately 2–4×) compared to other study participants. LimitationsLithium adherence was self-reported by all participants without formal validation. The coarse spatial resolution necessary for detection of low concentrations of 7Li exhibits imperfect spatial separation of signal from adjacent pixels. Conclusions7Li-MRI performed using a clinical 3T scanner demonstrated detection of lithium in the brain at very low concentration, in the range of approximately 10–60 mM. The methods are suited to studies assessing low dose lithium administration in psychiatric and neurodegenerative disorders, and permit the comparison of different lithium salt preparations at a time of emerging interest in the field.

Distinct protocerebral neuropils associated with attractive and aversive female-produced odorants in the male moth brain.

The pheromone system of heliothine moths is an optimal model for studying principles underlying higher-order olfactory processing. In Helicoverpa armigera, three male-specific glomeruli receive input about three female-produced signals, the primary pheromone component, serving as an attractant, and two minor constituents, serving a dual function, that is, attraction versus inhibition of attraction. From the antennal-lobe glomeruli, the information is conveyed to higher olfactory centers, including the lateral protocerebrum, via three main paths - of which the medial tract is the most prominent. In this study, we traced physiologically identified medial-tract projection neurons from each of the three male-specific glomeruli with the aim of mapping their terminal branches in the lateral protocerebrum. Our data suggest that the neurons' widespread projections are organized according to behavioral significance, including a spatial separation of signals representing attraction versus inhibition - however, with a unique capacity of switching behavioral consequence based on the amount of the minor components.

Influence of spatial structure of the field on a signal-to-interference ratio in communication systems with spatial signal separation

This article presents research results of the signal-to-interference ratio dependence (S/I) on the spatial structure of the radiation field of a three-element linear sparse antenna array in communication systems with spatial signal separation. As a result of the research, it was stated that when the receiving linear antenna is located in the region of the zero order maximum of the field of the useful signal, the formation of the S/I ratio does not depend on whether the field distribution is considered on a straight line or on a circular arc. The location of the receiving antenna in the region of the first-order maximum of the field of the useful signal gives the best results in the formation of the S/I ratio if the field distribution is used on circular arc and not on a straight line.

Nonlinear spin wave switches in layered structure based on magnonic crystals

The features of spin wave processes in a layered structure based on two magnonic crystals (MC-1 and MC-2) separated by a dielectric layer have been studied theoretically and experimentally at different levels of input power. The theoretical model has been developed for the cases of magnetic field oriented in-plane and out-of-plane to MC surfaces in order to identify the mechanisms of nonlinear interactions. Two types of nonlinear switching are implemented in the structure MC-1/MC-2 with increasing input power. Depending on parameters of the structure the input signal can exit from three (“double nonlinear switching”) or two (“single nonlinear switching”) outputs. This feature allows to consider MC-1/MC-2 structure as a basic element in a multifunctional device for the spatial separation of signals with different power levels.

The spatial separation of signals by the curvature of the wave front

The spatial separation of signals by the curvature of the wave front

Improving the quality of spatial separation of signals in radio communication systems

The article presents the research results of dependence of the signal-to-interference ratio in the focus area of the reflecting antenna array on its length, as well as the influence of the center displacement of the antenna array of different sizes on the signal-to-interference ratio. The research results show that short-focus reflecting antenna arrays have better characteristics than long-focus ones. By displacing the center of the antenna array, the signal-to-interference ratio can be increased by almost 20 dB.

False Discovery Rate Smoothing

ABSTRACTWe present false discovery rate (FDR) smoothing, an empirical-Bayes method for exploiting spatial structure in large multiple-testing problems. FDR smoothing automatically finds spatially localized regions of significant test statistics. It then relaxes the threshold of statistical significance within these regions, and tightens it elsewhere, in a manner that controls the overall false discovery rate at a given level. This results in increased power and cleaner spatial separation of signals from noise. The approach requires solving a nonstandard high-dimensional optimization problem, for which an efficient augmented-Lagrangian algorithm is presented. In simulation studies, FDR smoothing exhibits state-of-the-art performance at modest computational cost. In particular, it is shown to be far more robust than existing methods for spatially dependent multiple testing. We also apply the method to a dataset from an fMRI experiment on spatial working memory, where it detects patterns that are much more biologically plausible than those detected by standard FDR-controlling methods. All code for FDR smoothing is publicly available in Python and R (https://github.com/tansey/smoothfdr). Supplementary materials for this article are available online.

The increase of signal-to-noise ratio in the spatial separation of signals by the curvature of the wavefront

The article presents the results of the research of the dependence of the signal-to-noise ratio in the focal spot of the reflecting passive phased antenna array (PPAA), made of planar diffraction elements, on the orientation of the PPAA relative to the structure of the interference field, its dimensions and distance from PPAA plane to the focal spot. The results of the research show that the signal-to-noise ratio mainly depends on the horizontal size of the PPAA. The increase of the vertical size of the array leads to the fact that the focal distance corresponding to the maximum of the signal-to-noise ratio increases with the practically unchanged value of this maximum.

A 1.3 mW 48 MHz 4 Channel MIMO Baseband Receiver With 65 dB Harmonic Rejection and 48.5 dB Spatial Signal Separation

A four-channel multi-input multi-output (MIMO) complex baseband receiver for spectrum and space-aware cognitive radio applications is presented. The MIMO baseband receiver comprises a capacitive harmonic-rejection downconverting mixer (HRM) receiver and a signal-separation multi-input multi-output analog core (MAC) on a single integrated circuit. The HRM receiver performs frequency selection of the incoming RF signals by programmable spectral downconversion and filtering with minimal harmonic folding. The subsequent MAC separates the spectrally overlapping but spatially diverse signals by weighted complex matrix multiplication. The entire signal path is implemented using energy-efficient $g_m$ - $C$ analog circuits with digitally controlled capacitive weighting for configurable baseband down-/upconversion ranging from $-$ 24 to $+$ 24 MHz in the HRM, and programmable spatial filtering with 4 $\times$ 4 complex (8 $\times$ 8 real) 14-bit coefficients in the MAC. Measurements demonstrate greater than 65 dB harmonic-folding rejection by the HRM, and greater than 48.5 dB spatial signal separation by the MAC. The 65 nm CMOS IC occupies 3.27 $\text{mm}^{2}$ active area, and consumes 480 $\upmu$ W digital power at 45 MHz LO and 840 $\upmu$ W analog power at 3 MHz baseband from a 1.2 V supply.

Improving the efficiency of multi-channel voice recognition system

The use of methods of noisy signal treatment in voice recognition is discussed and some of the research results in this area are given. The main aim of the study is improving the effectiveness of recognition system of voice commands in a difficult acoustic environment by improving the signal / noise ratio due to the use of the spatial separation of signals using multiple directional microphones and digital signal processing on the basis of adaptive interference cancellation. The use of modern methods of language voice recognition together with the adaptive compensation method for processing a noisy signal can improve the accuracy of voice recognition. The algorithmic and structural approaches to solving the problems of sound processing, resulting in difficult acoustic conditions for further recognition of voice commands are discussed in the article. The presented method allows increasing the accuracy of the definition of basic and auxiliary channels of multi-channel voice recognition system to increase the efficiency of adaptive compensation. The method and the algorithm are designed to automatically determine the most appropriate channel for base and support channels in accordance with the method of adaptive interference cancellation. We propose to use proximity measure between the received signal and the standard obtained at command recognition on the basis of non-linear time alignment as a criterion for determining the base channel. The research results can be applied to voice recognition in the voice control systems of equipment and vehicles.

An efficient integrated two-color source for heralded single photons

We present a pulsed and integrated, highly non-degenerate parametric down-conversion (PDC) source of heralded single photons at telecom wavelengths, paired with heralding photons around 800 nm. The active PDC section is combined with a passive, integrated wavelength division demultiplexer on-chip, which allows for the spatial separation of signal and idler photons with efficiencies of more than 96.5%, as well as with multi-band reflection and anti-reflection coatings which facilitate low incoupling losses and a pump suppression at the output of the device of more than 99%. Our device is capable of preparing single photons with efficiencies of 60% with a coincidences-to-accidentals ratio exceeding 7400. Likewise, it shows practically no significant background noise compared to continuous wave realizations. For low pump powers, we measure a conditioned second-order correlation function of g(2) = 3.8 × 10−3, which proves almost pure single-photon generation. In addition, our source can feature a high brightness of 〈npulse〉 = 0.24 generated photon pairs per pump pulse at pump power levels below 100 μW. The high quality of the pulsed PDC process in conjunction with the integration of highly efficient passive elements makes our device a promising candidate for future quantum networking applications, where an efficient miniaturization plays a crucial role.

Effect of Harmonicity on the Detection of a Signal in a Complex Masker and on Spatial Release from Masking

The amount of masking of sounds from one source (signals) by sounds from a competing source (maskers) heavily depends on the sound characteristics of the masker and the signal and on their relative spatial location. Numerous studies investigated the ability to detect a signal in a speech or a noise masker or the effect of spatial separation of signal and masker on the amount of masking, but there is a lack of studies investigating the combined effects of many cues on the masking as is typical for natural listening situations. The current study using free-field listening systematically evaluates the combined effects of harmonicity and inharmonicity cues in multi-tone maskers and cues resulting from spatial separation of target signal and masker on the detection of a pure tone in a multi-tone or a noise masker. A linear binaural processing model was implemented to predict the masked thresholds in order to estimate whether the observed thresholds can be accounted for by energetic masking in the auditory periphery or whether other effects are involved. Thresholds were determined for combinations of two target frequencies (1 and 8 kHz), two spatial configurations (masker and target either co-located or spatially separated by 90 degrees azimuth), and five different masker types (four complex multi-tone stimuli, one noise masker). A spatial separation of target and masker resulted in a release from masking for all masker types. The amount of masking significantly depended on the masker type and frequency range. The various harmonic and inharmonic relations between target and masker or between components of the masker resulted in a complex pattern of increased or decreased masked thresholds in comparison to the predicted energetic masking. The results indicate that harmonicity cues affect the detectability of a tonal target in a complex masker.

Bypassing Orthogonal Relaying Transmissions via Spatial Signal Separation

We argue for incorporating Space Division Multiple Access (SDMA) into cooperative relaying, in order to bypass orthogonal relaying transmissions and thus achieve diversity gain without any cost on the available degrees of freedom. In particular, we propose a cooperative relaying scheme that utilizes two single-antenna relays and multiple antennas at the destination terminal, in order to spatially separate the concurrently arriving signals. The whole concept is based upon two key elements: a) To combat the half-duplex constraint by having two relays transmitting alternatively, i.e., the one receiving while the other transmitting and vice versa, and b) to spatially separate the signals arriving concurrently at the destination using the well-known optimum combining technique. Closed-form expressions for the average capacity and outage probability are provided. Numerical results manifest that the proposed model outperforms orthogonal relaying as well as distributed space-time coding in terms of average capacity and outage probability, owing to the former's advantage of higher spectral efficiency.

Some brain mechanisms for auditory scene analysis.

Detection and discrimination of sounds in complex auditory environments is facilitated by knowledge of the locations of sound sources and by spatial separation of signals and maskers. In studies of the spatial sensitivity of auditory cortical neurons in anesthetized cats, we find that location‐dependent variation in temporal spike patterns can signal sound‐source locations throughout up to 360 deg of space. In awake cats, spatial receptive fields can be similarly broad, although cortical neurons show a greater diversity of temporal patterns than is seen in anesthetized conditions. Our recent results demonstrate that spatial tuning tends to sharpen when a cat is engaged in an auditory task, compared to idle conditions, and that tuning can sharpen even further when the task involves sound localization. In human psychophysical studies, spatial hearing permits perceptual “stream segregation” of multiple temporally interleaved sequences of sounds. In parallel studies of the auditory cortex in anesthetized cats...

Accommodating natural and sexual selection in butterfly wing pattern evolution

Visual patterns in animals may serve different functions, such as attracting mates and deceiving predators. If a signal is used for multiple functions, the opportunity arises for conflict among the different functions, preventing optimization for any one visual signal. Here we investigate the hypothesis that spatial separation of different visual signal functions has occurred in Bicyclus butterflies. Using phylogenetic reconstructions of character evolution and comparisons of evolutionary rates, we found dorsal surface characters to evolve at higher rates than ventral characters. Dorsal characters also displayed sex-based differences in evolutionary rates more often than did ventral characters. Thus, dorsal characters corresponded to our predictions of mate signalling while ventral characters appear to play an important role in predator avoidance. Forewing characters also fit a model of mate signalling, and displayed higher rates of evolution than hindwing characters. Our results, as well as the behavioural and developmental data from previous studies of Bicyclus species, support the hypothesis that spatial separation of visual signal functions has occurred in Bicyclus butterflies. This study is the first to demonstrate, in a phylogenetic framework, that spatial separation of signals used for mate signalling and those used for predator avoidance is a viable strategy to accommodate multiple signal functions. This signalling strategy has important ramifications on the developmental evolution of wing pattern elements and diversification of butterfly species.

Three-Dimensional Auditory Display for Enhancing Detection of Passive Sonar Signals

The viability of a three-dimensional (3-D) auditory display for improving signal detection of passive sonar signals was investigated. Sonar operators usually have difficulty detecting targets because the sound received by the hydrophone has a low signal-to-noise ratio when coupled with the operator's headset that does not isolate well against the ambient noise. Release from masking was assessed by pairing a recording of a torpedo with diotic broadband pink noise that served as a masker, and a 400 Hz tone with the masker. Masked thresholds were measured for seven signal durations when each signal was presented dioticly and in 3-D auditory space at three positions on the horizontal plane. The spatial separation of signal and masker yielded a significant improvement in detection. A 3-D auditory display is a viable technology that could lead to a significant improvement in release from masking. The magnitude of the masking level difference will vary with respect to the characteristics of the hydrophone signal and masker and the synthesis capability of the 3-D auditory display. Potential applications of this research include enhanced auditory displays for processing passive sonar signals, leading to earlier detection of enemy targets.

The effect of spatial separation of signal and noise on masking in the free field as a function of signal frequency and age in the mouse.

Masking of low- (4 kHz) and high-frequency (25 kHz) signals by one-octave bandpass maskers either spatially coincident with the signal or contralateral to it was examined in mice, 4-6 and 20-22 months of age, in the free field. Signals were presented 120 ms prior to a startle stimulus and differences in their inhibition of the startle reflex, relative to startle stimulus alone trials, were used to measure the severity of masking. Inhibition was reduced or eliminated by spatially coincident noise for weak but not for relatively intense signals, providing the type of "loudness recruitment" effect characteristic of human listeners in similar stimulus conditions. The spatial separation of the signal and its masker relieved this maskinglike effect for the high-frequency pair in both young and old mice. In contrast there was no beneficial effect of the shift in spatial location for the low-frequency pair at either age. This finding of masking release for high- but not low-frequency stimuli supports the hypothesis that the sound shadow provided by the head and pinna would yield a favorable signal-to-noise level difference for a contralateral masker and an ipsilateral signal only at very high frequencies in the mouse. The presence of masking release in these old mice, a first generation hybrid strain with near-normal high-frequency hearing in ABR measures, agrees with reports that the masking release resulting from a similar manipulation in aged human listeners with minimal high-frequency hearing loss is the equal of that obtained in the young listener.

Release from masking due to spatial separation of sources in the identification of nonspeech auditory patterns.

A nonspeech pattern identification task was used to study the role of spatial separation of sources on auditory masking in multisource listening environments. The six frequency patterns forming the signal set were comprised of sequences of eight 60-ms tone bursts. Bursts of masking sounds were played synchronously with the signals. The main variables in the study were (1) the difference in spatial separation in the horizontal plane between signals and maskers and (2) the nature of the masking produced by the maskers. Spatial separation of signal and masker ranged from 0-180 degrees. The maskers were of two types: (1) a sequence of eight 60-ms bursts of Gaussian noise intended to produce predominantly peripherally based "energetic masking" and (2) a sequence of eight 60-ms bursts of eight-tone complexes intended to produce primarily centrally based "informational masking." The results indicated that identification performance improved with increasing separation of signal and masker. The amount of improvement depended upon the type of masker and the center frequency of the signal patterns. Much larger improvements were found for spatial separation of the signal and informational masker than for the signal and energetic masker. This was particularly apparent when the acoustical advantage of the signal-to-noise ratio in the more favorable of the two ears (the ear nearest the signal) was taken into account. The results were interpreted as evidence for an important role of binaural hearing in reducing sound source or message uncertainty and may contribute toward solving the "cocktail party problem."

Effects of a single reflection with varied horizontal angle and time delay on speech intelligibility

Previously, almost all physical measures for estimating speech intelligibility in a room have been derived from only temporal-monaural criteria. This paper shows that speech intelligibility for a sound field with a single reflection depends not only on the temporal-monaural factor but also on the spatial-binaural factor of the sound field. Articulation tests for sound fields simulated with a single reflection of delay time delta t1 after the direct sound were conducted changing the horizontal incident angle xi of the reflection. Remarkable findings are as followings: (1) speech intelligibility (SI) decreases with increasing delay time delta t1, (2) SI increases when xi approaches 90 degrees; the horizontal angle of the reflection causes a significant effect on SI, and (3) the analysis of variance for articulation test scores clearly demonstrated that the effects of both delta t1 and xi on SI are fully independent. Concerning result (2), if listeners get a spatial separation of signals at the two ears, then the listener's capability for speech perception is assumed to be improved due to "adding" further information to the temporal pattern recognition.