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White Noise (white + noise)
Selected AbstractsIntroduction: White Noise: Bringing Language into Whiteness StudiesJOURNAL OF LINGUISTIC ANTHROPOLOGY, Issue 1 2001Sara Trechter [source] A Study on the Effects of Damage Models and Wavelet Bases for Damage Identification and Calibration in BeamsCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 8 2007Vikram Pakrashi A numerical study has been performed in this article addressing these issues for single and multispan beams with an open crack. The first natural modeshapes of single and multispan beams with an open crack have been simulated considering damage models of different levels of complexity and analyzed for different crack depth ratios and crack positions. Gaussian white noise has been synthetically introduced to the simulated modeshape and the effects of varying signal-to-noise ratio have been studied. A wavelet-based damage identification technique has been found to be simple, efficient, and independent of damage models and wavelet basis functions, once certain conditions regarding the modeshape and the wavelet bases are satisfied. The wavelet-based damage calibration is found to be dependent on a number of factors including damage models and the basis function used in the analysis. A curvature-based calibration is more sensitive than a modeshape-based calibration of the extent of damage. [source] Age-related changes in transient and oscillatory brain responses to auditory stimulation during early adolescenceDEVELOPMENTAL SCIENCE, Issue 2 2009Catherine Poulsen Maturational changes in the capacity to process quickly the temporal envelope of sound have been linked to language abilities in typically developing individuals. As part of a longitudinal study of brain maturation and cognitive development during adolescence, we employed dense-array EEG and spatiotemporal source analysis to characterize maturational changes in the timing of brain responses to temporal variations in sound. We found significant changes in the brain responses compared longitudinally at two time points in early adolescence, namely 10 years (65 subjects) and 11.5 years (60 of the 65 subjects), as well as large differences between adults, studied with the same protocol (Poulsen, Picton & Paus, 2007), and the children at 10 and 11.5 years of age. The transient auditory evoked potential to tone onset showed decreases in the latency of vertex and T-complex components, and a highly significant increase in the amplitude of the N1 wave with increasing age. The auditory steady state response to a 40-Hz frequency-modulated tone increased in amplitude with increasing age. The peak frequency of the envelope-following response to sweeps of amplitude-modulated white noise also increased significantly with increasing age. These results indicate persistent maturation of the cortical mechanisms for auditory processing from childhood into middle adulthood. [source] Extinction risk under coloured environmental noiseECOGRAPHY, Issue 2 2000Mikko Heino Positively autocorrelated red environmental noise is characterized by a strong dependence of expected sample variance on sample length. This dependence has to be taken into account when assessing extinction risk under red and white uncorrelated environmental noise. To facilitate a comparison between red and white noise, their expected variances can be scaled to be equal, but only at a chosen time scale. We show with a simple one-dimensional population dynamics model that the different but equally reasonable choices of the time scale yield qualitatively different results on the dependence of extinction risk on the colour of environmental noise: extinction risk might increase as well as decrease when the temporal correlation of noise increases. [source] Changes in the Frequency Structure of a Mating Call Decrease Its Attractiveness to Females in the Cricket Frog Acris crepitans blanchardiETHOLOGY, Issue 8 2001Klaudia Witte In many species, females often prefer male signals that are more complex than in nature or beyond the range of calls naturally produced by conspecific males in spectral, temporal and amplitude features. In this study we examined both the ability of females to recognize signals outside the normal range of spectral frequency variation seen in male advertisement calls, and the influence of increasing call complexity by adding spectral components to enhance the attractiveness of a male advertisement call in the cricket frog Acris crepitans blanchardi, while keeping its amplitude constant. We used two different natural male call groups and created the following synthetic call groups: with a dominant frequency at 3500 Hz, i.e. at the normal dominant frequency with a frequency band within the sensitivity range of the inner ear basilar papilla; with a dominant frequency at 700 Hz, i.e. outside the normal range of variation and with a frequency band outside the sensitivity range of the basilar papilla but within the range of the amphibian papilla; with two dominant frequencies, one at 700 Hz and another at 3500 Hz, stimulating the basilar and amphibian papilla simultaneously. In double choice experiments we tested all combinations of the three call groups, and we tested the 3500 Hz call groups against the same natural call groups. Additionally, we tested the 700 Hz call groups against white noise to see whether these signals are meaningful in mate choice. Females preferred 3500 Hz call groups over all other call groups. The synthetic call group was as attractive to females as the same natural call group. The 700 Hz call group was not meaningful in mate choice. The combined (700 Hz + 3500 Hz) call group was significantly less attractive to females than the 3500 Hz call group. Thus, making a call more spectrally complex without increasing its overall amplitude decreases its attractiveness to cricket frog females. [source] The Frequency Accrual Speed Test (FAST): psychometric intelligence and personality correlatesEUROPEAN JOURNAL OF PERSONALITY, Issue 2 2001Ulrich Ettinger Performance on a putative psychophysical measure of information processing related to intelligence (Vickers' 1995 Frequency Accrual Speed Test, FAST) was assessed in relation to two psychometric measures of intelligence (Raven's Advanced Progressive Matrices and the Mill Hill vocabulary test). Participants (N,=,57) completed the Eysenck Personality Questionnaire , Revised (EPQ-R), and performed the FAST task under either low (70 dB) or high (90 dB) levels of white noise. FAST correlated with Raven's (r,=,0.56) and Mill Hill (r,=,0.28), as expected. FAST total scores were not affected by personality or personality-by-noise interactions. However, a measure of consistency of FAST performance (i.e. the standard deviation) was correlated negatively with total FAST scores (r,=,,0.37) and positively with (EPQ-R) extraversion (r,=,0.34). The results are discussed in terms of the validity of the FAST to explicate the information processing variables in psychometric intelligence. Copyright © 2001 John Wiley & Sons, Ltd. [source] Role of differential changes in sympathetic nerve activity in the preparatory adjustments of cardiovascular functions during freezing behaviour in ratsEXPERIMENTAL PHYSIOLOGY, Issue 1 2010Kenju Miki Freezing behaviour is associated with a distinct pattern of changes in cardiovascular function, which has been considered as a preparatory reflex for ,fight or flight' behaviour. However, the detailed mechanisms underlying preparatory cardiovascular adjustments and their physiological implications have received less attention. We studied responses in renal and lumbar sympathetic nerve activity and cardiovascular function during freezing behaviour in conscious rats, which was induced by exposure to loud white noise. Freezing behaviour was associated with regionally specific alterations in sympathetic nerve activity, in that renal sympathetic nerve activity increased while lumbar sympathetic nerve activity did not change. Moreover, freezing behaviour was associated with differential shifts in baroreflex control of sympathetic outflows, which could help to explain the selective responses in renal and lumbar sympathetic nerve activity during freezing behaviour. These differential changes in sympathetic outflows would result in a visceral vasoconstriction without having any impact on the skeletal muscle vasculature. These cardiovascular adjustments during freezing behaviour may help to explain the immediate and massive increase in muscular blood flow that occurs at the onset of fight or flight behaviour. It is hypothesized that central command originating from the defence area could somehow modulate separate baroreflex pathways, causing differential changes in sympathetic nerve activity to generate the preparatory cardiovascular adjustments during the freezing behaviour. [source] Parameter identification for lined tunnels in a viscoplastic mediumINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 12 2002B. Lecampion Abstract This paper is dedicated to the identification of constitutive parameters of elasto-viscoplastic constitutive law from measurements performed on deep underground cavities (typically tunnels). This inverse problem is solved by the minimization of a cost functional of least-squares type. The exact gradient is computed by the direct differentiation method and the descent is done using the Levenberg,Marquardt algorithm. The method is presented for lined or unlined structures and is applied for an elastoviscoplastic constitutive law of the Perzyna class. Several identification problems are presented in one and two dimensions for different tunnel geometries. The used measurements have been obtained by a preliminary numerical simulation and perturbed with a white noise. The identified responses match the measurements. We also discuss the usage of the sensitivity analysis of the system, provided by the direct differentiation method, for the optimization of in situ monitoring. The sensitivity distribution in space and time assess the location of the measurements points as well as the time of observation needed for reliable identification. Copyright © 2002 John Wiley & Sons, Ltd. [source] Identification of autoregressive models in the presence of additive noiseINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 5 2008Roberto Diversi Abstract A common approach in modeling signals in many engineering applications consists in adopting autoregressive (AR) models, consisting in filters with transfer functions having a unitary numerator, driven by white noise. Despite their wide application, these models do not take into account the possible presence of errors on the observations and cannot prove accurate when these errors are significant. AR plus noise models constitute an extension of AR models that consider also the presence of an observation noise. This paper describes a new algorithm for the identification of AR plus noise models that is characterized by a very good compromise between accuracy and efficiency. This algorithm, taking advantage of both low and high-order Yule,Walker equations, also guarantees the positive definiteness of the autocorrelation matrix of the estimated process and allows to estimate the equation error and observation noise variances. It is also shown how the proposed procedure can be used for estimating the order of the AR model. The new algorithm is compared with some traditional algorithms by means of Monte Carlo simulations. Copyright © 2007 John Wiley & Sons, Ltd. [source] Identification and adaptive control of some stochastic distributed parameter systemsINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 6 2001B. Pasik-Duncan Abstract An important class of controlled linear stochastic distributed parameter systems is that with boundary or point control. A survey of some existing adaptive control problems with their solutions for the boundary or the point control of a partially known linear stochastic distributed parameter systems is presented. The distributed parameter system is described by an analytic semigroup with cylindrical white noise and a control that occurs only on the boundary or at discrete points. The unknown parameters in the model appear affinely in both the infinitesimal generator of the semigroup and the linear transformation of the control. The noise in the system is a cylindrical white Gaussian noise. Strong consistency is verified for a family of least-squares estimates of the unknown parameters. For a quadratic cost functional of the state and the control, the certainty equivalence control is self-optimizing, that is the family of average costs converges to the optimal ergodic cost. Copyright © 2001 John Wiley & Sons, Ltd. [source] On stochastic modelling of linear circuitsINTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS, Issue 3 2010Tarun Kumar Rawat Abstract In this paper, the deterministic modelling of linear circuits is replaced by stochastic modelling by including variance in the parameters (resistance, inductance and capacitance). Our method is based on results from the theory of stochastic differential equations. This method is general in the following sense. Any electrical circuit that consists of resistances, inductances and capacitances can be modelled by ordinary differential equations, in which the parameters of the differential operators are the functions of circuit elements. The deterministic ordinary differential equation can be converted into a stochastic differential equation by adding noise to the input potential source and to the circuit elements. The noise added in the potential source is assumed to be a white noise and that added in the parameters is assumed to be a correlated process because these parameters change very slowly with time and hence must be modelled as a correlated process. In this paper, we model a series RLC circuit by using the proposed method. The stochastic differential equation that describes the concentration of charge in the capacitor of a series RLC circuit is solved. Numerical simulations in MATLAB are obtained using the Euler,Maruyama method. Copyright © 2008 John Wiley & Sons, Ltd. [source] Global analysis of runs of annual precipitation and runoff equal to or below the median: run lengthINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 7 2004Murray C. Peel Abstract The investigation of fluctuations of wet and dry years has a long history in the climatology and hydrology literature. In this, the first of two papers investigating runs of consecutive dry years, the lengths (persistence) of dry runs are investigated. In the second paper the magnitude/intensity and severity (length × magnitude) of dry runs will be investigated. Consecutive dry years are associated with drought, which is a significant physical and economic phenomenon that imposes great stress on ecosystems and societies. Run lengths of consecutive years equal to or below the median were analysed for 3863 precipitation and 1236 runoff stations from around the world. Run lengths were found to be similar across all continents and Köppen climate zones, expect for tropical and arid North Africa (Sahel), which showed a distinct bias toward longer run lengths than any other region of the world. Generally, the run length observed in annual runoff was found to be similar to that observed in annual precipitation for the same location. Both annual precipitation and runoff data were found to be well described by the lag-one autoregressive (AR(1)) model or by white noise. The influence of the El Niño,southern oscillation on run lengths was not observed to be significant. The presence of decadal and multi-decadal oscillations was weakly observed in the results of the precipitation runs analysis. The faintness of the decadal and multi-decadal oscillation signal may be due to the sample sizes not being long enough and/or the runs analysis not being sensitive enough to detect their presence. Copyright © 2004 Royal Meteorological Society [source] Testing against smooth stochastic trendsJOURNAL OF APPLIED ECONOMETRICS, Issue 3 2001Jukka Nyblom A trend estimated from an unobserved components model tends to be smoother when it is modelled as an integrated random walk rather than a random walk with drift. This article derives a test of the null hypothesis that the trend is deterministic against the alternative that it is an integrated random walk. It is assumed that the other component in the model is normally distributed white noise. Critical values are tabulated, the asymptotic distribution is derived and the performance of the test is compared with the test against a trend specified as a random walk with drift. The test is extended to allow for serially correlated and evolving seasonal components. When there is a stationary process containing a single autoregressive unit root close to one, a bounds test can be applied. In the case of a first-order autoregressive disturbance, it is shown that a consistent test can still be obtained by carrying out estimation of the nuisance parameters under the null hypothesis. The overall conclusion is that the most effective test against an integrated random walk is a parametric one based on the random walk plus drift test statistic, constructed from innovations, with the nuisance parameters estimated in the unrestricted model. Copyright © 2001 John Wiley & Sons, Ltd. [source] Precision of prediction in second-order calibration, with focus on bilinear regression methodsJOURNAL OF CHEMOMETRICS, Issue 1 2002Marie Linder Abstract We consider calibration of hyphenated instruments with particular focus on determination of the unknown concentrations of new specimens. A hyphenated instrument generates for each specimen a two-way array of data. These are assumed to depend on the concentrations through a bilinear regression model, where each constituent is characterized by a pair of profiles to be determined in the calibration. We discuss the problem of predicting the unknown concentrations in a new specimen, after calibration. We formulate three different predictor construction methods, a ,naive' method, a least squares method, and a refined version of the latter that takes account of the calibration uncertainty. We give formulae for the uncertainty of the predictors under white noise, when calibration can be seen as precise. We refine these formulae to allow for calibration uncertainty, in particular when calibration is carried out by the bilinear least squares (BLLS) method or the singular value decomposition (SVD) method proposed by Linder and Sundberg (Chemometrics Intell. Lab. Syst. 1998; 42: 159,178). By error propagation formulae and previous results on the precision of and we can obtain approximate standard errors for the predicted concentrations, according to each of the two estimation methods. The performance of the predictors and the precision formulae is illustrated on both real (fluorescence) and simulated data. Copyright © 2002 John Wiley & Sons, Ltd. [source] The price paid for the second-order advantage when using the generalized rank annihilation method (GRAM)JOURNAL OF CHEMOMETRICS, Issue 9 2001Nicolaas (Klaas) M. Faber Abstract In a ground-breaking paper, Linder and Sundberg developed a statistical framework for the calibration of bilinear data (Chemometrics Intell. Lab. Syst. 1998; 42: 159,178). Within this framework they formulated three different predictor construction methods (J. Chemometrics accepted), namely a so-called naive method, a least squares (LS) method and a refined version of the latter that takes account of the calibration uncertainty. They showed that the naive method is statistically less efficient than the others under the assumption of white noise. In the current work a close relationship is established between the generalized rank annihilation method (GRAM) and the naive method by comparing expressions for prediction variance. The main conclusion is that the relatively poor efficiency of GRAM is the price one pays for obtaining the second-order advantage with a single calibration sample. Copyright © 2001 John Wiley & Sons, Ltd. [source] NEURAL NETWORK PREDICTION OF PERMEABILITY IN THE EL GARIA FORMATION, ASHTART OILFIELD, OFFSHORE TUNISIAJOURNAL OF PETROLEUM GEOLOGY, Issue 4 2001J.H. Ligtenberg The Lower Eocene El Garia Formation forms the reservoir rock at the Ashtart oilfield, offshore Tunisia. It comprises a thick package of mainly nummulitic packstones and grainstones with variable reservoir quality. Although porosity is moderate to high, permeability is often poor to fair with some high permeability streaks. The aim of this study was to establish relationships between log-derived data and core data, and to apply these relationships in a predictive sense to uncored intervals. An initial objective was to predict from measured logs and core data the limestone depositional texture (as indicated by the Dunham classification), as well as porosity and permeability. A total of nine wells with complete logging suites, multiple cored intervals with core plug measurements together with detailed core interpretations were available. We used a fully-connected Multi-Layer-Perceptron network (a type of neural network) to establish possible non-linear relationships. Detailed analyses revealed that no relationship exists between log response and limestone texture (Dunham class). The initial idea to predict Dunham class, and subsequently to use the classification results to predict permeability, could not therefore be pursued. However, further analyses revealed that it was feasible to predict permeability without using the depositional fabric, but using a combination of wireline logs and measured core porosity. Careful preparation of the training set for the neural network proved to be very important. Early experiments showed that low to fair permeability (1,35 mD) could be predicted with confidence, but that the network failed to predict the high permeability streaks. "Balancing " the data set solved this problem. Balancing is a technique in which the training set is increased by adding more examples to the under-sampled part of the data space. Examples are created by random selection from the training set and white noise is added. After balancing, the neural network's performance improved significantly. Testing the neural network on two wells indicated that this method is capable of predicting the entire range of permeability with confidence. [source] How does the pitch and pattern of a signal affect auditory arousal thresholds?JOURNAL OF SLEEP RESEARCH, Issue 2 2009DOROTHY BRUCK Summary How arousal thresholds vary with different sounds is a critical issue for emergency awakenings, especially as sleepers are dying in fires despite having a working smoke alarm. Previous research shows that the current high-pitched (3000+ Hz) smoke alarm signal is significantly less effective than an alternative signal, the 520 Hz square wave, in all populations tested. However, as the number of sounds tested has been small further research is needed. Here we measured auditory arousal thresholds (AATs) across signals with a range of characteristics to determine the most effective waking signal. Thirty-nine young adults participated over three nights. In Part A, nine signals were presented in stage 4 sleep with ascending decibel levels. Signals were short beeps in the low- to mid-frequency range with different spectral complexities: square waves, pure tones, whoops and white noise. Part B manipulated temporal patterns, inserting silences of 0, 10 and 21 s after each 12 s of beeps. It was found that the low-frequency (400 and 520 Hz) square waves yielded significantly lower AATs than the alternatives. A trend was found across the three temporal manipulations, with a 10 s intervening silence showing some advantage. These findings support earlier research indicating that the best sound for awakening from deep sleep is a low-frequency square wave. It is argued that the signal with the lowest response threshold when awake may be the same as the most arousing signal when asleep, especially where the sleeper processes the signal as meaningful. [source] A Note on Non-Negative Arma ProcessesJOURNAL OF TIME SERIES ANALYSIS, Issue 3 2007Henghsiu Tsai Abstract., Recently, there has been much research on developing models suitable for analysing the volatility of a discrete-time process. Since the volatility process, like many others, is necessarily non-negative, there is a need to construct models for stationary processes which are non-negative with probability one. Such models can be obtained by driving autoregressive moving average (ARMA) processes with non-negative kernel by non-negative white noise. This raises the problem of finding simple conditions under which an ARMA process with given coefficients has a non-negative kernel. In this article, we derive a necessary and sufficient condition. This condition is in terms of the generating function of the ARMA kernel which has a simple form. Moreover, we derive some readily verifiable necessary and sufficient conditions for some ARMA processes to be non-negative almost surely. [source] Efficient use of higher-lag autocorrelations for estimating autoregressive processesJOURNAL OF TIME SERIES ANALYSIS, Issue 3 2002LAURENCE BROZE The Yule,Walker estimator is commonly used in time-series analysis, as a simple way to estimate the coefficients of an autoregressive process. Under strong assumptions on the noise process, this estimator possesses the same asymptotic properties as the Gaussian maximum likelihood estimator. However, when the noise is a weak one, other estimators based on higher-order empirical autocorrelations can provide substantial efficiency gains. This is illustrated by means of a first-order autoregressive process with a Markov-switching white noise. We show how to optimally choose a linear combination of a set of estimators based on empirical autocorrelations. The asymptotic variance of the optimal estimator is derived. Empirical experiments based on simulations show that the new estimator performs well on the illustrative model. [source] "A Discovered Dissembler Can Achieve Nothing Great"; Or, Four Theses on the Death of Presidential Rhetoric in an Age of EmpirePRESIDENTIAL STUDIES QUARTERLY, Issue 4 2007STEPHEN JOHN HARTNETT Because of the explosion of mass media, we have entered a new age of white noise; because of the disastrous extension of U.S. imperial ambitions, we have entered a new age of political deception; when these two historical factors are combined with the peculiar communicative habits of President George W. Bush, Americans are left with what we call a post-rhetorical presidency. This is an anti-democratic condition wherein presidential discourse is not meant to mobilize, educate, and uplift the masses; rather, by marshaling ubiquitous public chatter, waves of disinformation, and cascades of confusion-causing misdirection, post-rhetorical presidential discourse attempts to confuse public opinion, prevent citizen action, and frustrate citizen deliberation. Under these new conditions, the president defines fantasy, not reality; he numbs citizens rather than energizing them; instead of informing and teaching, he chooses to dumb down and stupefy. We pursue this thesis by offering four philosophical theses and three rhetorical case studies of the president's public speaking, thus combining critical theory and rhetorical criticism to help map what may represent the death of democracy. [source] Communalities and differences in fear potentiation between cardiac defense and eyeblink startlePSYCHOPHYSIOLOGY, Issue 6 2009María B. Sánchez Abstract This study examines similarities and differences in fear potentiation between two protective reflexes: cardiac defense and eyeblink startle. Women reporting intense fear of animals but low fear of blood or intense fear of blood but low fear of animals viewed pictures depicting blood or the feared animal for 6 s in 2 separate trials in counterbalanced order. An intense burst of white noise, able to elicit both a cardiac defense response and a reflexive startle blink, was presented 3.5 s after picture onset. Both cardiac and blink responses were potentiated when highly fearful individuals viewed fearful pictures. However, differences appeared concerning picture order. This pattern of results indicates communalities and differences among protective reflexes that are relevant for understanding the dynamics of emotional reflex modulation. [source] Time adaptive denoising of single trial event- related potentials in the wavelet domainPSYCHOPHYSIOLOGY, Issue 6 2000Arndt Effern We present a new wavelet-based method for single trial analysis of transient and time variant event-related potentials (ERPs). Expecting more accurate filter settings than achieved by other techniques (low-pass filter, a posteriori Wiener filter, time invariant wavelet filter), ERPs were initially balanced in time. By simulation, better filter performance could be established for test signals contaminated with either white noise or isospectral noise. To provide an example of real application, the method was applied to limbic P300 potentials (MTL-P300). As a result, variance of single trial MTL-P300s decreased, without restricting the corresponding mean. The proposed method can be regarded as an alternative for single-trial ERP analysis. [source] Detection of patterns in noisy time seriesTHE CANADIAN JOURNAL OF STATISTICS, Issue 2 2001M. A. Tingley Abstract In the context of a research project in ergonomy, myoelectric signals monitored over two to three hour periods gave rise to long noisy time series, which were smoothed using running medians. Tests developed by the authors show that the patterns displayed by the smoothed time series are not artifacts of smoothed white noise. Indeed, the smoothed series show amplitude fluctuations and short-term correlations which are larger than those obtained by applying running medians to independent, identically distributed data. The key idea is that of reduction of data to binary signals. [source] Listen to the noise: noise is beneficial for cognitive performance in ADHDTHE JOURNAL OF CHILD PSYCHOLOGY AND PSYCHIATRY AND ALLIED DISCIPLINES, Issue 8 2007Göran Söderlund Background:, Noise is typically conceived of as being detrimental to cognitive performance. However, given the mechanism of stochastic resonance, a certain amount of noise can benefit performance. We investigate cognitive performance in noisy environments in relation to a neurocomputational model of attention deficit hyperactivity disorder (ADHD) and dopamine. The Moderate Brain Arousal model (MBA; Sikström & Söderlund, 2007) suggests that dopamine levels modulate how much noise is required for optimal cognitive performance. We experimentally examine how ADHD and control children respond to different encoding conditions, providing different levels of environmental stimulation. Methods:, Participants carried out self-performed mini tasks (SPT), as a high memory performance task, and a verbal task (VT), as a low memory task. These tasks were performed in the presence, or absence, of auditory white noise. Results:, Noise exerted a positive effect on cognitive performance for the ADHD group and deteriorated performance for the control group, indicating that ADHD subjects need more noise than controls for optimal cognitive performance. Conclusions:, The positive effect of white noise is explained by the phenomenon of stochastic resonance (SR), i.e., the phenomenon that moderate noise facilitates cognitive performance. The MBA model suggests that noise in the environment, introduces internal noise into the neural system through the perceptual system. This noise induces SR in the neurotransmitter systems and makes this noise beneficial for cognitive performance. In particular, the peak of the SR curve depends on the dopamine level, so that participants with low dopamine levels (ADHD) require more noise for optimal cognitive performance compared to controls. [source] Chronologic Changes of Nitric Oxide Concentration in the Cochlear Lateral Wall and Its Role in Noise-Induced Permanent Threshold ShiftTHE LARYNGOSCOPE, Issue 5 2008Yuh-Shyang Chen MD Abstract Objective: The objective of this study was to investigate the chronologic changes of nitric oxide (NO) concentration in the cochlear lateral wall and to explore its possible role in permanent threshold shift (PTS) after intense noise exposure. Materials and Methods: Seventeen guinea pigs were subjected to a single continuous exposure to broadband white noise at 105 ± 2 dB sound pressure level (SPL) for 40 hours and were divided into four groups according to various postnoise recovery periods. Another 12 guinea pigs were not exposed to noise and served as controls. The hearing status of all animals was evaluated with auditory brainstem responses (ABR) evoked by condensation "click" sounds. ABR were recorded both prior to noise exposure and immediately before killing the animal. After death, NO concentration in the cochlear lateral wall was directly measured with an NO/ozone chemiluminescence technique. Results: An approximately 1.7-fold increase in NO concentration was observed immediately postnoise exposure, which persisted for up to 28 days. The threshold of ABR elevation (mean, 30 dB SPL) peaked immediately after cessation of noise exposure and gradually resolved to a PTS (mean, 14.5 dB SPL) 56 days after noise exposure when NO concentration had returned to its prenoise exposure level. Conclusion: Noise-induced threshold shift, which resolved to a mild PTS, can be partially attributed to NO elevation in the cochlear lateral wall. Our results revealed a nonlinear correlation between ABR recovery and depletion of NO, indicating that the mechanisms of NO changes in the cochlear lateral wall may be more complicated than previously conceived and that other pathophysiologic mechanisms may also play important roles in noise-induced PTS. [source] Olivocochlear Activity and Temporary Threshold Shift-Susceptibility in HumansTHE LARYNGOSCOPE, Issue 11 2005W Wagner MD Abstract Study Objectives: Animal studies (guinea pig, cat, chinchilla) have shown that activity of the medial olivocochlear efferents can exert noise-protective effects on the cochlea. It is not yet known whether such effects are also existent in humans. Olivocochlear activity can be estimated indirectly by contralateral suppression (CS) of otoacoustic emissions (OAE). Material and Methods: We measured Input/Output functions of distortion products of OAE (DPOAE), with and without contralateral acoustic stimulation by white noise, in 94 normal hearing young male subjects. Seven stimuli with L2 between 20 and 60 dB SPL and L1 = 39 dB + 0.4 L2 ("scissor paradigm") were used at f2 = 2, 3, 4, 5, and 6 kHz. The measurement was repeated 2 weeks later. In 83 subjects of the same group, pure tone audiometry was registered before and 6 minutes after shooting exercises to evaluate individual susceptibility to develop a temporary threshold shift (TTS). Results: Test-retest repeatability of CS was generally good. CS averaged 0.98 dB SPL (SD 1.19 dB, median 0.56 dB). As expected, CS was greatest at low stimulus levels (median 1.06 dB at L2 = 20 dB, as compared with 0.33 dB at L2 = 60 dB). The smallest average CS was found at 4 kHz, and the greatest CS appeared at 2 kHz. A TTS occurred in 7 of 83 (8.5%) subjects. Statistical analysis did not reveal any correlation between the amount of CS and individual TTS susceptibility. Conclusions and Outlook: 1) Measurement of CS of DPOAE using an extensive measurement paradigm revealed good test-retest repeatability, confirming the reliability of this audiologic tool. 2) CS of DPOAE does not predict individual susceptibility to mild TTS induced by impulse noise in humans. Possible explanations for the missing association are discussed. Future perspectives include longitudinal studies to further elucidate the association between medial olivocochlear bundle-activity and permanent threshold shift in humans. The goal is to develop a diagnostic tool for the prediction of individual noise vulnerability in humans, thereby preventing noise-induced hearing loss. [source] Model error and sequential data assimilation: A deterministic formulationTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 634 2008A. Carrassi Abstract Data assimilation schemes are confronted with the presence of model errors arising from the imperfect description of atmospheric dynamics. These errors are usually modelled on the basis of simple assumptions such as bias, white noise, and first-order Markov process. In the present work, a formulation of the sequential extended Kalman filter is proposed, based on recent findings on the universal deterministic behaviour of model errors in marked contrast with previous approaches. This new scheme is applied in the context of a spatially distributed system proposed by Lorenz. First, it is found that, for short times, the estimation error is accurately approximated by an evolution law in which the variance of the model error (assumed to be a deterministic process) evolves according to a quadratic law, in agreement with the theory. Moreover, the correlation with the initial condition error appears to play a secondary role in the short-time dynamics of the estimation error covariance. Second, the deterministic description of the model error evolution, incorporated into the classical extended Kalman filter equations, reveals that substantial improvements of the filter accuracy can be gained compared with the classical white-noise assumption. The universal short-time quadratic law for the evolution of the model error covariance matrix seems very promising for modelling estimation error dynamics in sequential data assimilation. Copyright © 2008 Royal Meteorological Society [source] Wavelet transform in denoising magnetic archaeological prospecting dataARCHAEOLOGICAL PROSPECTION, Issue 2 2007B. Tsivouraki Abstract Magnetic measurements in archaeological prospecting are often affected by cultural noise having the same high-frequency content as anomalies arising from buried antiquities. Also, in many cases the microrelief of the ground surface causes a noise that is coherent, pseudorandom and periodic. The main cause of this kind of noise is the ploughing of the earth. In this paper the efficiency of a wavelet denoising scheme is tested with respect to these types of unwanted disturbances. The proposed scheme combines the cyclospinning algorithm with a variable threshold calculated in each cycle of the algorithm. Tests on synthetic and real data show a satisfactory performance of the technique in suppressing both the white noise and the coherent noise caused by the systematic undulations of the ground surface. Copyright © 2007 John Wiley & Sons, Ltd. [source] Application of Residence Time Distribution for Measuring the Fluid Velocity and Dispersion CoefficientCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 1 2007W. Zhang Abstract Most studies on residence time distribution (RTD) have focused on the tail of the RTD curve, and very little attention has been paid to the effect of white noise on the measured results. The aim of this work is to study the effect of white noise on the calculated parameters with different data processing methods. The anti-disturbance abilities of the moment method and the least squares method are compared. The results show that the anti-disturbance ability of the least squares method was better than that of the moment method. As a result of peak overlapping in the RTD curve of a loop reactor, the moment method cannot be used to calculate the fluid velocity and dispersion coefficient. Experiments show that the least squares method is still applicable in a loop reactor. [source] Reverse correlation in neurophysiologyCOGNITIVE SCIENCE - A MULTIDISCIPLINARY JOURNAL, Issue 2 2004Dario Ringach Abstract This article presents a review of reverse correlation in neurophysiology. We discuss the basis of reverse correlation in linear transducers and in spiking neurons. The application of reverse correlation to measure the receptive fields of visual neurons using white noise and m-sequences, and classical findings about spatial and color processing in the cortex resulting from such measurements, are emphasized. Finally, we describe new developments in reverse correlation, including "sub-space" and categorical reverse-correlation. Recent results obtained by applying such methods in the orientation, spatial-frequency and Fourier domains have revealed the importance of cortical inhibition in the establishment of sharp tuning selectivity in single neurons. [source] | |||||||||||||||||||||||||||||||