Background Of White Noise Research Articles

Optimal reception of a rectangular pulse with unknown appearance and disappearance times

We obtain the maximum-likelihood and optimum (Bayesian) algorithms for detecting and estimating the appearance and disappearance times of a rectangular pulse against the white-noise background. Rigorous expressions for the characteristics of the maximum-likelihood algorthms are found. The characteristics of the Bayesian algorithms are obtained using computer simulations.

Music effects on event-related potentials of humans on the basis of cultural environment

Auditory oddball responses were recorded from Turkish subjects in a silent environment or superimposed on white noise, or music played with violoncello or a similar music played with ney, a reed flute frequently listened by the Turkish population. P3 amplitudes with ney music in the background were significantly larger than both the white noise and violoncello backgrounds. The topography of the P3 response changed significantly between the ney and silent background conditions, indicating a relatively higher participation of frontal areas during hearing ney. Our results showed that hearing music of a familiar style increases the allocation of attentional resources during memory updating processes which is supposed to determine the P3 amplitude, and therefore showed the effects of cultural environment on the cognitive processes.

Spectral Narrowing of Atomic Resonance by Recurrent Excitation Spectroscopy: Feedback from Atom to Radiation Field via Digital-Data Processing

We describe the theoretical analysis and experimental detail of recurrent excitation spectroscopy (RES), which contributes to precise determination of atomic resonance frequency. The basic idea of RES lies in the iterative excitation of the atomic system by radiation. During the preceding excitation, the output field emitted from the atom is recorded in the form of digital data, and the next excitation field is generated in accordance with these data. This recurrent interaction between the atomic system and the radiation field significantly reduces the spectral width of the atomic resonance, while the signal-to-noise ratio remains sufficiently high. To reflect the actual experimental situation, we present a theoretical model in the presence of background white noise, and using this model, analytical and numerical calculations are performed. We find that RES gives a better signal-to-noise ratio compared to the conventional averaging technique until spectral narrowing is terminated. The combination of RES and the digital-data processing technique has been successfully applied to the magnetic resonance of Rb atoms in the sub-MHz region, where our theoretical findings are experimentally confirmed.

Influences of the solar activity on the correlation dimension of underground muon time series at 34 MWE

The correlation dimension d GP of cosmic ray muon time series recorded at Misato underground station at a depth of 34 hg/cm 2 has been calculated by means of the Grassberger and Procaccia algorithm. From the time series, background white noise which is caused by the counting-rate error and gives a serious impact on the estimation of d GP is removed by means of a technique of the wavelet expansion. Marked periodic variations which are caused by cosmic ray anisotropies and make it difficult to obtain a reliable value of d GP are also removed from the time series by means of a recursive digital filter. Using the muon time series which is apparently free from both the background white noise and the daily variation, we could estimate a reliable value of the correlation dimension for three different periods which correspond to different levels of solar activity. It is found that the correlation dimension changes only slightly with the level of solar activity.

Poor P50 suppression among schizophrenia patients and their first-degree biological relatives.

This study's goal was to replicate the finding that family members of schizophrenia patients show poor P50 suppression during a paired-click auditory evoked response paradigm. The paired-click paradigm was used to test 44 schizophrenia patients, 60 of their clinically unaffected first-degree relatives, and 45 normal subjects. Two clicks (83 dB[A] over a 60-dB[A] white noise background) separated by 500 msec were presented 60 times to all subjects. P50 responses to the first and second clicks were selected from the digitally filtered data by using standard methods and the Cz recording site. The schizophrenia patients had smaller P50 responses to click 1 than either their relatives or the normal subjects; the patients and their relatives, who did not significantly differ, had larger P50 responses to click 2 than the normal subjects. Schizophrenia patients had worse P50 suppression than either their family members or the normal subjects; the patients' family members had worse P50 suppression than the normal subjects. Family members of schizophrenia patients have worse P50 suppression than normal subjects. To the authors' knowledge, this is the first demonstration independent of the group associated with the University of Colorado that schizophrenia patients' family members have poor P50 suppression. This result is intrinsically important, perhaps especially because a recent report suggests genetic linkage of poor P50 suppression to the cholinergic receptor's alpha7 nicotinic subunit.

The influence of broadband noise on the precedence effect.

This study examined the influence of background noise on the localization of lead-lag noise-burst pairs and on echo threshold for the same stimuli. Experiments were conducted in an anechoic chamber with a leading stimulus delivered from a loudspeaker at 45 degrees to the right of center and a lagging stimulus from 45 degrees left. Lead and lag stimuli were 4-ms bursts of Gaussian noise. In experiment 1, with lead and lag at equal levels and the lag delay fixed at 2 ms, the perceived location of the image produced by the lead-lag stimulus was estimated from subjects' left/right judgments relative to bursts from a "comparitor" loudspeaker whose position could be adjusted. In experiment 2, the dominance of the leading burst on perceived location was measured by determining the increase in level of the lagging burst necessary to produce an image estimated to be centered at 0 degree azimuth. Experiment 3 was concerned with echo threshold. Subjects reported whether or not they heard a sound in the vicinity of the lagging loudspeaker as the lag-burst delay was varied. In all three experiments, data were obtained for four to five stimulus levels in quiet and for three levels of background white noise from a loudspeaker at 180 degrees. The results revealed a substantial weakening effect of background noise on the precedence effect in experiments 2 and 3, and a nonsignificant effect in experiment 1.

620 The effects of interstimulus intervals on mismatch negativity and P50 wave to long duration auditory stimuli

The present study explored effects of background noise on the cerebral functional asymmetry of speech perception. The magnetic equivalent (MMNm) of mismatch negativity (MMN) elicited by consonant-vowel syllable change presented in silence and during background white noise was measured with a whole-head magnetometer. It was found that in silence MMNm to speech stimuli, registered from the auditory cortex, was stronger in the left than in the right hemisphere. However, when speech signals were presented in white noise background, MMNm in the left hemisphere diminished while that in the right hemisphere increased in amplitude and dipole moment. These results confirm that in silence, speech signals are mainly discriminated in the left hemisphere's auditory cortex. However, in noisy conditions the involvement of the left hemisphere's auditory cortex in speech discrimination is considerably decreased, while that of the right hemisphere increases.

Optimal estimation of the appearance time of a pulsed signal with random substructure

An algorithm for optimum estimation of the appearance time of a pulsed signal with random substructure, which is observed against the background of white Gaussian noise, is synthesized. The comparative analysis of the Bayesian and maximum likelihood meters of the appearance time is performed. The results of statistical modeling of estimation algorithms are presented.

Background acoustic noise and the hemispheric lateralization of speech processing in the human brain: magnetic mismatch negativity study

The present study explored effects of background noise on the cerebral functional asymmetry of speech perception. The magnetic equivalent (MMNm) of mismatch negativity (MMN) elicited by consonant-vowel syllable change presented in silence and during background white noise was measured with a whole-head magnetometer. It was found that in silence MMNm to speech stimuli, registered from the auditory cortex, was stronger in the left than in the right hemisphere. However, when speech signals were presented in white noise background, MMNm in the left hemisphere diminished while that in the right hemisphere increased in amplitude and dipole moment. These results confirm that in silence, speech signals are mainly discriminated in the left hemisphere's auditory cortex. However, in noisy conditions the involvement of the left hemisphere's auditory cortex in speech discrimination is considerably decreased, while that of the right hemisphere increases.

Nonlinear filtering for recognition of phase-encoded images

We investigate the use of Fourier plane nonlinear filtering for phase-encoded images. We investigate the performance of the nonlinear joint transform correlator and the nonlinearly transformed matched filter for phase-encoded images with different types of input noise. We use the peak-to-output-energy ratio, peak-to-sidelobe ratio, and discrimination ratio as the metrics for measuring the performances. We mathematically analyze the peak-to-output-energy ratio of the nonlinearly transformed matched filter for phase-encoded images with spatially nonoverlapping white noise. Computer simulations are provided to show the performance improvements of the nonlinear filtering techniques for the phase-encoded images. In comparison with linear filtering techniques, we find that the nonlinear filtering techniques substantially improve the performance metrics. From the computer-simulation results it can be seen that the nonlinear joint transform correlator performs better than the nonlinearly transformed matched filter in detecting phase-encoded targets in the presence of different types of noise, such as additive overlapping white noise, spatially nonoverlapping white background noise, spatially nonoverlapping colored background noise, and nontarget objects.

Combining information: Probability summation and probability averaging in detection and discrimination.

Detection may improve if a stimulus offers 2 cues rather than 1. This is sometimes attributed to probability summation of independent detections, which provides an especially simple model for sensory information combination. However, this model assumes a strong bias toward the positive response, which is not appropriate for discrimination. The probability summation model is here extended to apply to discrimination and to allow different degrees of summation, ranging from complete through partial to probability averaging, and the use of this model is illustrated for the method of constant stimuli. It allows performance based on independent decisions to be distinguished from performance (e.g., integration) that is better than summation can explain. Models for the discrimination of complex stimuli may provide a tool for studying the development of expertise in areas where this involves a perceptual component, such as clinical judgment. The detection and discrimination of stimuli is the main subject matter of psychophysics , and study of these processes has given researchers a sophisticated understanding of them. Unfortunately, the benefit of applying this knowledge to areas of research or application other than psychophysics has not been fully realized. This article examines and extends a simple model of how information is combined when one detects or discriminates stimuli that are defined by more than one sensory component or feature. The application of these ideas to a wider range of problems is also considered. A laboratory detection task may require a subject to decide, for example, whether a faint sound was presented. A discrimination task may require the participant to judge whether a given line is longer or shorter than a 5-in (12.7 cm) standard. In each case the task is made difficult because of noise. This noise may be external, such as a background of white noise, or it may arise internally, from the variability of the response of the sensory organ and the nervous system to the stimulus input.

Effect of acoustic stimulus characteristics on the startle response in hooded rats.

The acoustic startle response (ASR) depends on stimulus parameters such as duration, intensity and particularly on the stimulus rise time. The aim of our study was to determine to what extent the ASR parameters are affected by the spectral characteristics of the stimulus. Therefore, in this experiment the amplitude and the latency of the acoustic startle reflex were assessed for a fixed pulse duration and for a variety of stimulus frequencies ranging between 3 and 23 kHz. The ASRs were studied in 11 adult hooded rats exposed to 2-ms (120 dB SPL) tone pulses of different frequencies presented in random order, with or without 70 dB white noise background. Statistical analysis of the data revealed significant differences between ASR amplitudes for different frequencies. In our experimental situation the rats responded more readily to a low frequency stimulus. The startle amplitude decreased with tonal frequencies and distinguishable difference were seen for 3, 7, and 10 kHz pulses. However, such differences were not readily observed for higher frequencies i.e. 15, 20, 23 kHz. The same pattern of differences was observed when the acoustic stimulus was presented with the white noise background. The observed differences may be attributed, firstly, to a spectral characteristic of the stimulus and thus to an audibility in rats and secondly to a behavioral meaning of a stimulus of a different frequency.

Optimum reception of a signal with unknown duration against the background of white noise

An algorithm for optimum (Bayesian) detection and measurement of the duration of a rectangular pulse observed against the background of white Gaussian noise is developed. The potential characteristics of reception are obtained as a result of computer modeling of the synthesized algorithms.

Effects of music and white noise on working memory performance in monkeys.

It has been suggested that Mozart's music may have beneficial effects on the performance of cognitive tasks in humans. In the present study the effects of Mozart's piano music, white noise, simple rhythm and silence were studied on the performance of a delayed response (DR) task in monkeys. The acoustic treatments were given for 15 min, either before or during DR testing. The acoustic treatments did not affect DR performance when given before testing. However, Mozart's piano music played during DR testing caused a significant deterioration in the performance of the monkeys, whereas white noise improved it. It is suggested that Mozart's music serves as distractive stimulation during DR performance thus affecting working-memory-related neuronal processing and performance. White background noise, on the other hand, may improve DR performance by protecting against environmental distraction during testing.

Study of the stability of a kalman-bucy filter subjected to correlated disturbances

The stability of a Kalman-Bucy filter that is optimal in the case of filtering of signals against a background of white Gaussian noise and of a filter that is optimal for nonwhite noise from measurements when subjected to the action of correlated disturbances is investigated. The “innovation process” correlation function is calculated and a noise decorrelator is synthesized and subsequently incorporated into the filter structure

Analysis/systhesis-based microphone array speech enhancer with variable signal distortion

A microphone array speech enhancement algorithm based on analysis/synthesis filtering that allows for variable signal distortion. The algorithm is used to suppress additive noise and interference. The processing structure consists of delaying the received signals so that the desired signal components add coherently, filtering each of the delayed signals through an analysis filter bank, summing the corresponding channel outputs from the sensors, applying a gain function to the channel outputs, and combining the weighted channel outputs using a synthesis filter. The structure uses two different gain functions, both of which are based on cross correlations of the channel signals from the two sensors. The first gain yields the GEQ-I array, which performs best for the case of a desired speech signal corrupted by uncorrelated white background noise. The second gain yields the GEQ-II array, which performs best for the case where there are more signals than microphones. The GEQ-II gain allows for a trade-off on a channel-dependent basis of additional signal degradation in exchange for additional noise and interference suppression.

The influence of two-source noise on echo suppression

When listeners are presented with lead and lag pairs of clicks from two loudspeakers in an anechoic room, they hear a single image near the location of the lead loudspeaker, provided that the delay of the lag is only a few ms. However, Thurlow and Parks [Perceptual and Motor Skills 13, 7–12 (1961)] reported that the addition of a continuous background of noise from a single loudspeaker causes the lag click to become audible as a separate auditory event. The current experiment investigated whether this apparent breakdown of echo suppression would also occur if the background noise was presented from two loudspeakers with one delayed relative to the other. The signal was a pair of brief white-noise bursts presented from loudspeakers located at 45 deg right and 45 deg left in an anechoic chamber, with delays ranging from 2 to 14 ms. A continuous background white noise presented from the same two loudspeakers disrupted echo suppression only when the direction of its time delay was inconsistent with the signal delay. One interpretation is that echo suppression was broken because stimulus and noise provided conflicting information about the acoustics of the room. [Work supported by NIH DC01625.]

Methods for automatic detection of mysticete sounds

Methods for the automatic recognition of low‐frequency sounds of baleen whales are presented. Matched filtering is implemented with a synthetic filter kernel derived from measurements of whale sounds, and this method is found effective at detecting blue whale (Balaenoptera musculus) sounds in white background noise. Spectrogram correlation is implemented and found effective at detection of blue whale vocalizations in the presence of interfering sounds. Spectrogram correlation employs image correlation using spectrograms and carefully designed image kernels to give good performance in the presence of noise. The two methods are briefly compared. The effectiveness of the spectrogram correlator is also demonstrated with finback whale (B. physalus) sounds. A supplementary method for detecting regular, repetitive sequences of sounds is applied to minke whale (B. acutorostrata) pulse trains, and found to improve detection in conditions of high ambient noise.

Target detection in a shallow-water environment using pseudorandom bipolar phase coded pulses

Recent experiments with the Littoral Sea Mine Test Vehicle (LSMTV) have provided a direct comparison of the performance of pseudorandom bipolar phase coded (BPPC) pulses for use in detection and localization of near-surface shallow-water targets. A February 1996 experiment at Ft. Lauderdale utilized a triplane of known target strength and position to evaluate various BPPC pulses with different Doppler and range resolutions. The purpose of this experiment was to measure the signal-processing gain by these pulse types against slow moving targets (1–3 kn) and compare it with the theoretical values for this environment. The target return was immersed in a white Gaussian noise background with volume and surface reverberation. Runs were made with the LSMTV on the ocean floor at 535 ft and triplane depths of 50 and 110 ft. The range craft was positioned so that it would drift through the test area. This study evaluates the resolution performance of these BPPC pulses via direct comparison to 0.5- and 32-ms cw pulses against the same target by sequencing the pulses during each target opportunity. Comparative performance results are presented for the measured signal processing gains and resolutions versus theoretical calculations. [Work supported by ONR.]

Cooperative behavior in periodically driven noisy integrate-fire models of neuronal dynamics.

The dynamics of the standard integrate-fire model and a simpler model (that reproduces the important features of the integrate-fire model under certain conditions) of neural dynamics are studied in the presence of a deterministic external driving force, taken to be time-periodic, and white background noise. Both models possess resonant phenomena in the first passage probability distribution and mean first passage time, arising from the interplay of characteristic time scales in the system. \textcopyright{} 1996 The American Physical Society.