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Changes in F-actin labeling in the outer hair cell and the Deiters cell in the chinchilla cochlea following noise exposure.

It has been found that 'conditioning' noise exposures can render the inner ear more resistant to traumatic noise exposures. To explore the possible mechanisms underlying this phenomenon, filamentous actin (F-actin), labeled by rhodamine-phalloidin, was examined in the chinchilla cochlea using confocal fluorescence microscopy. The conditioning noise was 0.5 kHz octave band noise (OBN) at 90 dB SPL for 6 h/day and the high-level noise was the same noise but at 105 dB SPL for 4 h. A variety of pathological changes were found in the chinchilla cochlea after exposure to noise. Subjects exposed to conditioning noise (1 day or 10 days) and only high-level noise showed an increase in F-actin labeling than unexposed controls. By contrast, subjects who had 5 days quiet after the 10-day conditioning exposure exhibited a decrease in F-actin labeling. Interestingly, subjects exposed to high-level noise with prior 10-day conditioning exposure also showed a decrease in F-actin labeling in the cuticular plate and the stereocilia. The F-actin decreases in the stereocilia and the cuticular plates may decrease the mechanical rigidity of the organ of Corti. A more pliable organ of Corti may have reduced the possibility of fracture or ripping of cell junctions during the motion of the basilar membrane induced by acoustic overstimulation.

Acoustic Stimulation↗

Signal-to-noise ratio in microelectrode-array-based electrochemical detectors.

The signal-to-noise ratio at an electrode array depends on the electrode area, the perimeter-to-area ratio of the electroactive portion of the surface, the mass transfer coefficient of the analyte-electrode combination, the measurement bandwidth, and the sources and magnitudes of the noises. Simple models for chronoamperometry with an array in quiescent solution and for hydrodynamic current at an array in one wall of a rectangular conduit through which analyte-containing solution is following are given. Noises from seven sources, including environmental noises, are considered in a noise model. The signal and noise models are combined to yield a model for signal-to-noise ratio at array-based electrochemical detectors. There exists an optimum array density for a given area that depends on the noise power, noise resistance, the current density at a sparse array, and the current density at a solid electrode of the same area. Approximations that lead to simple expressions for the optimum electroactive area fraction and noise resistance lead to results that are in good agreement with more complex and less approximate calculations. Electrodes of millimeter dimensions consisting of about 1% active surface with electroactive "pieces" of micrometer dimensions are anticipated to yield detection limits of about 1 fmol injected into a typical packed-column liquid chromatograph. This corresponds to about 10(-10) M analyte in the detector and about an order of magnitude improvement over solid electrodes.

Electrochemistry↗

Development of ultra-low-noise spectrophotometry for analytical applications.

Methodology and instrumentation that dramatically increase the signal-to-noise ratio of scanning spectrophotometers over present commercial instruments is presented. The increase was accomplished by greatly reducing all important noise components. The random noise from an incoherent light source, which is the dominant noise source for most commercial spectrophotometers, was effectively removed by use of unique noise cancellation circuitry implemented with a dual-beam spectrophotometer configuration. Several other noise sources were also minimized by appropriate instrumental design, so that the observed noise level was attributable to the shot noise of the detectors. Single-wavelength measurements taken with a home-built prototype instrument have achieved a signal-to-noise ratio increase near 100-fold over commercial instruments. A spectrum taken in the visible region with a home-built retrofit detector installed in a commercial instrument showed a 10-fold signal-to-noise ratio increase over the standard commercial instrument. Widespread implementation of the methodology should enable many new types of research activities.

Journal Article↗

The influence of selected masking noises on Lombard and sidetone amplification effects.

The present experiments were designed to test the notion that the Lombard and sidetone amplification effects are related to the masking ability of a presented background noise. In Experiment 1, eight normal-hearing college students spoke in quiet and while listening to five frequency bands of noise which were equated for intensity but differed in ability to interfere with speech intelligibility. Vocal intensity increased as the frequency band, and thus the masking ability of the noise increased. In Experiment 2, eight additional students spoke in quiet and while listening to four of the frequency bands of noise used in Experiment 1. The noises were equated for loudness rather than intensity. Again, vocal intensity increased as the masking ability of the noise increased. In Experiment 3, 20 additional students spoke while listening to 0 and 20 dB of sidetone amplification mixed with three of the noise bands from Experiment 1. The noises were equated for intensity and mixed with sidetone. The sidetone amplification effect increased as the masking ability of the noise increased. The results of these experiments indicate that interference with speech intelligibility is directly related to elicitation of the Lombard and sidetone amplification effects. The loudness or intensity of a noise has little control over vocal intensity independent of the contribution to masking of speech.

Auditory Perception↗

[Comparison of methods for reducing residual noise in suprathreshold early auditory evoked potential registration].

BACKGROUND: The level of residual noise in auditory brainstem responses (ABR) depends not only on the number of averages but also on the amplitude of background noise and on the frequency of artifacts. This paper describes the influence of digital filtering and of different methods of artifact suppression on the residual noise of ABRs. METHOD: Amplitude of background noise was estimated for 1033 ABRs recorded under suprathreshold stimulation (70 and 90 dB nHL) in 251 subjects. In 45 ABR recordings in 15 subjects, all 4000 individual sweeps were stored for off-line simulation. The power spectrum of background noise was investigated using an FFT analyzer. RESULTS: A great variability of mean noise amplitude was found both between subjects and in the recordings for each subject. Depending on the slope of the analogue 100-Hz high-pass filter, mean RMS values of background noise of 4.2 microV (6 dB/Oct.) and 2.5 microV (12 dB/Oct.), respectively, were found. Digital high pass filtering before averaging was found to increase the signal-to-noise ratio (SNR) considerably. CONCLUSIONS: Results indicate that (i) effective suppression of low-frequency noise components can only be achieved by zero phase digital filtering and (ii) if clipping of noise amplitude to 25 microV is used, optimized artifact rejection as weighted averaging or adopted artifact rejection levels have only small effect on the SNR.

Adolescent↗

The Gray-Scott model under the influence of noise: reentrant spatiotemporal intermittency in a reaction-diffusion system.

We investigate the influence of noise on the spatiotemporal behavior of the Gray-Scott model, a prototype for a simple reaction-diffusion system. In the parameter regime studied it is characterized deterministically by a stable fixed point. As the noise increases a regular periodic pattern is replaced first by an irregularly oscillating periodic pattern and then by spatiotemporal intermittency. With further increasing noise strength the spatiotemporal intermittency is first replaced by a low amplitude noisy regime followed by spatiotemporal intermittency (STI) embedded into a noisy background. At sufficiently high noise intensity high amplitude noise prevails. We point out that the transition from spatiotemporal intermittency to low amplitude noise can be traced back to the fact that the spatially homogeneous state is a global attractor. As the noise strength grows further the "noisy" fixed point starts to communicate with STI leading to noise-induced spatiotemporal intermittency as an excitable state. At high enough noise strength high amplitude noise is left over wiping out all details of the underlying deterministic dynamical system.

Journal Article↗

Fast accurate MEG source localization using a multilayer perceptron trained with real brain noise.

Iterative gradient methods such as Levenberg-Marquardt (LM) are in widespread use for source localization from electroencephalographic (EEG) and magnetoencephalographic (MEG) signals. Unfortunately, LM depends sensitively on the initial guess, necessitating repeated runs. This, combined with LM's high per-step cost, makes its computational burden quite high. To reduce this burden, we trained a multilayer perceptron (MLP) as a real-time localizer. We used an analytical model of quasistatic electromagnetic propagation through a spherical head to map randomly chosen dipoles to sensor activities according to the sensor geometry of a 4D Neuroimaging Neuromag-122 MEG system, and trained a MLP to invert this mapping in the absence of noise or in the presence of various sorts of noise such as white Gaussian noise, correlated noise, or real brain noise. A MLP structure was chosen to trade off computation and accuracy. This MLP was trained four times, with each type of noise. We measured the effects of initial guesses on LM performance, which motivated a hybrid MLP-start-LM method, in which the trained MLP initializes LM. We also compared the localization performance of LM, MLPs, and hybrid MLP-start-LMs for realistic brain signals. Trained MLPs are much faster than other methods, while the hybrid MLP-start-LMs are faster and more accurate than fixed-4-start-LM. In particular, the hybrid MLP-start-LM initialized by a MLP trained with the real brain noise dataset is 60 times faster and is comparable in accuracy to random-20-start-LM, and this hybrid system (localization error: 0.28 cm, computation time: 36 ms) shows almost as good performance as optimal-1-start-LM (localization error: 0.23 cm, computation time: 22 ms), which initializes LM with the correct dipole location. MLPs trained with noise perform better than the MLP trained without noise, and the MLP trained with real brain noise is almost as good an initial guesser for LM as the correct dipole location.

Brain↗

The influence of hearing and age on speech recognition scores in noise in audiological patients and in the general population.

OBJECTIVE: To describe the influence of pure-tone audiometry and age on the speech recognition score in noise, both in audiological patients and also in a random population sample. DESIGN: In a cross-sectional study, speech recognition scores (SRS) using monosyllabic words presented in a fixed background noise were evaluated on 1895 audiological patients of both genders with normal hearing or sensorineural hearing losses. The background noise was speech weighted and presented with a signal to noise ratio of +4 dB. In 291 participants, SRS in quiet was estimated as well. A female random population sample also was tested (N = 513). RESULTS: The major predictor for the SRS-noise was high-frequency hearing thresholds. If hearing was normal, age had no effect on speech recognition. Young persons with hearing loss had higher SRS-noise than older persons with the same degree of hearing loss. The difference between young and old persons became larger the greater the hearing loss. Predictive SRS-noise with consideration taken to hearing function and age are presented. SRS-noise correlated stronger with pure-tone audiometry and age than SRS-quiet. Controls performed better (by 10 to 20%) than their same-aged peers with similar hearing loss. CONCLUSION: It is recommended that speech recognition tests be performed in background noise. SRS-noise is a valuable tool for audiologists and audiological physicians to identify patients in need of pedagogic rehabilitation programs or further diagnostic investigations.

Adult↗

Noise-induced chaos in an optically injected semiconductor laser model

The chaos induced by an intrinsic spontaneous-emission noise in an optically injected semiconductor laser is investigated through a single-mode injection model. A method is developed to quantitatively study the scale-dependent noise effect in general, and the noise-induced chaotic feature in particular. We find that noise at an experimentally measured level can induce chaos in the system. This suggests that noise-induced chaos may indeed exist in real systems. Certain required characteristics for noise to induce chaos are identified: the periodic state itself, when subject to weak noise, should undergo a process that is much more diffusive than the Brownian motion, and the adjacent chaotic states should still behave chaotically on certain finite scales when subject to noise. We believe they are generic features for noise to induce chaos. The correlation dimension of the clean and noisy attractors is also calculated to study noise-induced changes in the geometrical structure of the attractors.

Journal Article↗

Robust estimation of ultrasound pulses using outlier-resistant de-noising.

A different approach to the problem of estimation of the ultrasound pulse spectrum, which usually arises as a part of ultrasound image restoration algorithms, is presented. It is shown that this estimation problem can be reformulated in terms of a de-noising problem. In this formulation, the log-spectrum of a radio-frequency line (RF-line) is viewed as a noisy measurement of the signal that needs to be estimated, i.e., the ultrasound pulse log-spectrum. The log-spectrum of the tissue reflectivity function (i.e., tissue response) is considered as the noise to be rejected. The contribution of the paper is twofold. First, it provides statistical description of the reflectivity function log-spectrum for the case, when the samples of the reflectivity function are independent identically distributed (i.i.d.) Gaussian random variables. Moreover, it is shown that the problem of the pulse spectrum recovery is essentially a de-noising problem. Consequently, it is suggested to solve the problem within the framework of the de-noising by wavelet shrinkage. Second, a computationally efficient algorithm is proposed for the pulse-spectrum estimation, which can be viewed as a modified version of the classical Donoho's three-step de-noising procedure. This modification is necessary, because of specific properties of the noise to be rejected. It is shown, that whenever the samples of the reflectivity function can be assumed to be i.i.d. Gaussian random variables, the samples of its log-spectrum obey the Fisher-Tippet distribution. For this type of noise, straightforward implementation of the standard de-noising can cause serious estimation errors. In order to overcome this difficulty, an outlier-resistant de-noising is performed. The unique properties of this modified de-noising algorithm allow estimating the pulse spectrum adaptively to its properties, as they are continuously influenced by the frequency-dependent attenuation process. The performance of the proposed algorithm is examined in a series of computer-simulations. It is shown that this algorithm, developed on the assumption of the "Gaussian" reflectivity function, remains applicable for broader classes of distributions. The results obtained in a series of in vivo experiments reveal superior performance of the novel approach over some of alternative estimation techniques, e.g., cepstrum-based estimation.

Adult↗

Membrane current noise in dark-adapted and light-adapted isolated retinal rods of the larval tiger salamander.

1. Low-frequency light-sensitive membrane current noise in isolated rod photoreceptors of the larval tiger salamander was recorded using suction electrodes, in the dark, and during light adaptation by backgrounds or by bleaching visual pigment. 2. In background light, noise variance increases and then decreases. For rods desensitized to similar levels by bleaching visual pigment, the noise variance either does not change (weak adaptation) or decreases (with stronger adaptation). 3. The power spectral density of the current noise in dark-adapted rods shows a component with half-power cut-off frequency at about 0.1 Hz, attributed to spontaneous single events and continuous noise from dark phosphodiesterase activity. A second component, with half-power cut-off frequency at about 1 Hz, may be due to slow components in the light-sensitive channel gating. 4. The power spectral density of the noise in background light is dominated by noise generated by the background. Background light adapts at least the first component of the noise seen in dark-adapted cells. For cells desensitized by bleaching, light adaptation of both components of the dark-adapted noise is observed. 5. The results confirm that the low-frequency noise in dark-adapted cells arises from the transduction mechanism of the rod, in that both components can be light adapted, and show that, for rods permanently desensitized by bleaching, the desensitization is not due to the presence of active visual pigment molecules similar to those produced by background light.

Adaptation, Ocular↗

Comparison of signal-averaged electrocardiograms with different levels of noise: time-domain, frequency-domain, and spectrotemporal analysis.

In order to test the effect of noise on the various parameters of the SAECG, 83 patients underwent three consecutive recordings at different noise levels. The high noise (HN) recordings had a noise level of 0.60-0.74 microV, the intermediate noise (IN) had 0.31-0.59 microV, and the low noise (LN) had < or = 0.30 microV. For the calculation of noise we used the standard deviation of the mean noise of the composite lead high pass filtered at 40 Hz. The recordings were compared using time-domain, frequency-domain, and spectrotemporal analysis. The time-domain parameters of the LN recordings, using 25-Hz, 40-Hz, and 60-Hz high pass cutoffs, were significantly different from those of the HN or IN recordings (P < 0.05). In the frequency-domain analysis, significant differences were found in some of the parameters of the LN compared to the HN. The spectrotemporal analysis of the X and Z leads also showed significant differences among the LN and the other recordings. In the time-domain analysis, both at 40 Hz and 25 Hz, there were more abnormal LN compared to the HN recordings (P < 0.05). In the spectrotemporal analysis, there were significantly more abnormal HN and IN recordings compared to the LN (P < 0.001 and P < 0.01, respectively). Therefore, the level of noise, even within the acceptable range, can significantly affect the SAECG. In the time domain at the lower noise levels the parameters become more abnormal, while the opposite seems to occur in the spectral and the spectrotemporal analysis.

Electrocardiography↗

Whole-cell current noise produced by excitatory and inhibitory amino acids in large cerebellar neurones of the rat.

1. Membrane noise and current changes produced by glutamate and related excitatory amino acids have been examined in cultured large cerebellar neurones (including Purkinje cells), with whole-cell patch-clamp methods. The sensitivity of these neurones to the inhibitory amino acids gamma-aminobutyric acid (GABA) and glycine has also been studied. 2. The neurones formed inhibitory synapses in culture, and displayed spontaneous synaptic currents. Reducing the pipette Cl- concentration (i.e. intracellular synaptic currents. Reducing the pipette Cl- concentration (i.e. intracellular concentration) caused a negative shift in their reversal potential, and the currents could be blocked with bicuculline (10 microM), suggesting that they were mediated by GABAA receptors. Spontaneous synaptic activity was also considerably reduced in the presence of 3 microM-tetrodotoxin. 3. Analysis of the increase in whole-cell current noise produced by the application of GABA (3 microM) gave noise spectra that were fitted by two Lorentzian components with slow and fast time constants of 23.6 and 1.9 ms at a membrane potential (Vm) of -110 mV. The mean single-channel conductance estimated from GABA noise was gamma noise = 12 pS. Glycine (10 microM) whole-cell current responses were Cl(-)-mediated and reversibly abolished by 1 microM-strychnine. 4. Bath application of excitatory amino acids gave whole-cell current changes accompanied by an increase in synaptic activity. Postsynaptic responses to the excitatory amino acids were more readily seen after the inhibitory synaptic currents had been abolished by bicuculline. Membrane current changes were obtained in response to the putative transmitters glutamate and aspartate, and the agonists NMDA (N-methyl-D-aspartate), ibotenate, quisqualate and kainate. Their reversal potential was approximately -5 mV. 5. A majority of noise spectra produced by the various glutamate receptor agonists were fitted by two Lorentzian components; the rest were fitted with a single Lorentzian component. The noise time constants were apparently not dependent on the type of glutamate agonist used to activate the receptor channels. Pooling data for all agonists gave a mean time constant for single-component spectra of tau noise = 4.8 +/- 0.3 ms; for two-component spectra the time constants were tau 1 = 22.7 +/- 1.8 ms and tau 2 = 2.2 +/- 0.12 ms (Vm = -110 to -50 mV). It is likely that the two components present in whole-cell noise spectra reflect complex kinetics of glutamate receptor channels. 6. The mean single-channel conductance was estimated from whole-cell noise for the various excitatory amino acids.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗

Signal-to-noise ratio and spatial resolution in x-ray electronic imagers: is the MTF a relevant parameter?

In most imaging detectors, the modulation transfer function (MTF) is regarded as a good parameter to describe spatial resolution. This is undoubtedly valid for visual observation. However, the detectability of a detail is essentially a matter of signal-to-noise ratio, which is not accounted for by the MTF. In x-ray imaging, signal-to-noise ratio in the image is generally limited by incident photons statistics, often larger than readout noises. Therefore, the MTF of the detector applies to both signal and noise, and does not impair the image content. Contrast can easily be restored by image processing without altering the signal-to-noise ratio. However, a number of effects may alter very differently noise and signal: (i) If the MTF significantly extends beyond half the sampling frequency, the aliasing introduced by spatial sampling can severely enhance the noise and cancel the benefit of the good signal transfer. This is illustrated by synthetic images which simulate the response of imagers with different MTFs to the same test pattern in the presence of quantum noise. (ii) Parallax and blurring by the x-ray spot size or motion are shown to degrade the transfer properties of signal, but do not affect the quantum noise; they must be treated separately. Contrary to the x-ray converter MTF, parallax directly impacts the detective quantum efficiency (DQE). Finally, it is shown that only the detective quantum efficiency can reliably describe the spatial resolution of an x-ray imaging detector in the presence of noise, parallax and blurring.

Biophysical Phenomena↗

Comparison between the effects of continuous and impact noise on cochlear potentials in guinea pigs.

Cochlear microphonics (CM), action potentials (AP), and endocochlear potential (EP) were recorded from anesthetized, immobilized guinea pigs during potential (EP) were recorded from anesthetized, immobilized guinea pigs during and following 20 min periods of noise exposure. Changes in cochlear potentials were compared in guinea pigs exposed to continuous broadband noise or mechanically generated impact noise of equal energy content. Over a range of continuous noise levels from 95 to 105 dB SPL it was found that continuous noise produced less suppression of CM and a greater suppression of AP than did impact noise of equal energy. A reduction of EP did not accompany CM suppression with either type of noise exposure. Suppression of CM and AP was also compared in guinea pigs with chronically implanted round window electrodes. In these preparations, AP was suppressed to a similar extent by impact and continuous noise of equal energy, but CM was suppressed to a significantly greater extent by impact noise. The data from both series of experiments indicate that the suppression of cochlear responses is not predicted by an "equal energy" rule when impact and continuous noise are compared.

Acoustics↗

Detection of tones in noise and the "severe departure" from Weber's law.

Thresholds were measured for the detection of 20-ms sinusoids, with frequencies 500, 4000, or 6500 Hz, presented in bursts of bandpass noise of the same duration and centered around the signal frequency. A range of noise levels from 35 to 80 dB SPL was used. Noise at different center frequencies was equated in terms of the total noise power in an assumed auditory filter centered on the signal frequency. Thresholds were expressed as the signal levels, relative to these noise levels, necessary for subjects to achieve 71% correct. For 500-Hz signals, thresholds were about 5 dB regardless of noise level. For 6500-Hz signals, thresholds reached a maximum of 14 dB at intermediate noise levels of 55-65 dB SPL. For 4000-Hz signals, a maximum threshold of 10 dB was observed for noise levels of 45-55 dB SPL. When the bandpass noises were presented continuously, however, thresholds for 6500-Hz, 20-ms signals remained low (about 1 dB) and constant across level. These results are similar to those obtained for the intensity discrimination of brief tones in bandstop noise [R. P. Carlyon and B. C. J. Moore, J. Acoust. Soc. Am. 76, 1369-1376 (1984); R. P. Carlyon and B. C. J. Moore, J. Acoust. Soc. Am. 79, 453-460 (1986)].

Auditory Threshold↗

Relationship between noise, dose, and pitch in cardiac multi-detector row CT.

In spiral computed tomography (CT), dose is always inversely proportional to pitch. However, the relationship between noise and pitch (and hence noise and dose) depends on the scanner type (single vs multi-detector row) and reconstruction mode (cardiac vs noncardiac). In single detector row spiral CT, noise is independent of pitch. Conversely, in noncardiac multi-detector row CT, noise depends on pitch because the spiral interpolation algorithm makes use of redundant data from different detector rows to decrease noise for pitch values less than 1 (and increase noise for pitch values > 1). However, in cardiac spiral CT, redundant data cannot be used because such data averaging would degrade the temporal resolution. Therefore, the behavior of noise versus pitch returns to the single detector row paradigm, with noise being independent of pitch. Consequently, since faster rotation times require lower pitch values in cardiac multi-detector row CT, dose is increased without a commensurate decrease in noise. Thus, the use of faster rotation times will improve temporal resolution, not alter noise, and increase dose. For a particular application, the higher dose resulting from faster rotation speeds should be justified by the clinical benefits of the improved temporal resolution.

Artifacts↗

On the attenuation and amplification of molecular noise in genetic regulatory networks.

BACKGROUND: Noise has many important roles in cellular genetic regulatory functions at the nanomolar scale. At present, no good theory exists for identifying all possible mechanisms of genetic regulatory networks to attenuate the molecular noise to achieve regulatory ability or to amplify the molecular noise to randomize outcomes to the advantage of diversity. Therefore, the noise filtering of genetic regulatory network is an important topic for gene networks under intrinsic fluctuation and extrinsic noise. RESULTS: Based on stochastic dynamic regulation equation, the intrinsic fluctuation in reaction rates is modeled as a state-dependent stochastic process, which will influence the stability of gene regulatory network, especially, with low concentrations of reacting species. Then the mechanisms of genetic regulatory network to attenuate or amplify extrinsic fluctuation are revealed from the nonlinear stochastic filtering point of view. Furthermore, a simple measure of attenuation level or amplification level of extrinsic noise for genetic regulatory networks is also introduced by nonlinear robust filtering method. Based on the global linearization scheme, a convenient method is introduced to measure noise attenuation or amplification for each gene of the nonlinear stochastic regulatory network by solving a set of filtering problems, which correspond to a set of linearized stochastic regulatory networks. Finally, by the proposed methods, several simulation examples of genetic regulatory networks are given to measure their robust stability under intrinsic fluctuations, and to estimate the genes' attenuation and amplification levels under extrinsic noises. CONCLUSION: In this study, a stochastic nonlinear dynamic model is developed for genetic regulatory networks under intrinsic fluctuation and extrinsic noise. By the method we proposed, we could determine the robust stability under intrinsic fluctuations and identify the genes that are significantly affected by extrinsic noises, which we call the weak structure of the network. This method will be potential for robust gene circuit design in future, on which a drug design could be based.

Animals↗