Noise Cancellation for Brainstem Auditory Evoked Potentials

A technique for cancelling background noise in sensory evoked potential recordings is described. Since sensory evoked potentials are generally much smaller than the background noise, a large number of individual responses must be averaged. The proposed technique uses a second recording channel to estimate the background noise; a cancellation filter function is derived for each individual response in the average. The filter can vary from response to response; however, it does not attempt to adapt to long-term changes in the noise. The technique is intended for situations where the noise is intermittent or rapidly varying, as is often found in the operating room and intensive care unit. The technique was evaluated by a simulation using a known brainstem auditory evoked potential signal plus EEG samples obtained from a patient in the intensive care unit during an evoked potential test. The results showed that the technique could provide improvements in signal-to-noise ratio of 3-6 when the dominant noise component was external electrical interference. The effect was less when the background noise was muscle activity or spontaneous EEG, but there was still significant improvement. It was also found that the improvement obtained was approximately equal to the improvement that could be predicted from the formulation of the filter function.     

Signals and Noise in Evoked Brain Potentials

Event-related brain potentials measured with scalp electrodes are always corrupted by unrelated electrical discharges occurring in the brain. These unrelated electrical discharges, generally referred to as noise, have temporal and spectral characteristics similar to evoked potential waveforms, and they greatly increase the difficulty of detecting and estimating the parameters of the evoked potential waveforms themselves. This problem has been analyzed by computing the probability distributions for measured amplitudes and latencies of ERP components measured in the presence of the ongoing EEG. The analytical results have been verified over a wide range of signal-to-noise ratios by computer simulation. Comparisons of theoretical results to measured data indicate that the latency variations found experimentally greatly exceed what would be expected if they were due only to additive noise. It may be concluded, therefore, that the single ERP is not a signal whose components are deterministically related to the stimulus, but is made up of components that shift significantly in both amplitude and latency from one stimulus application to the next. Using the expressions developed in the paper, it is possible to separate the contributions to the variance due to interference from the ongoing EEG and that inherent in the ERP.     

A Fundamental Investigation of the Composition of Auditory Evoked Potentials

An investigation, carried out to establish whether auditory evoked potentials (AEP's) are due to phase reordering of the background electroencephalogram or to an additive signal, is described. New phase reordered and additive models of the AEP were introduced and used in conjunction with the techniques of angular statistics. It was established that all of the AEP's studied contained additive energy in at least one harmonic component.     

Effectiveness of Earphone Shielding for Artifact Control in Auditory Evoked Potentials

Control of the electromagnetic artifact produced by earphones is a major problem in the acquisition of surface-recorded auditory evoked responses, especially short latency responses (0-10 ms). Several investigators have used magnetically shielded earphones to reduce the artifact. In this paper, a method for measuring shielding effectiveness is described, and results obtained with a TDH-39 earphone are presented. Two layers of shielding were found to provide 10-15 dB of shielding effectiveness; the resulting artifact is less than 0.1 ?V for acoustic stimuli below 120 dB sound pressure level (SPL). The shielding also affects the response of the transducer, especially at low frequencies. It is concluded that shielding is effective in controlling artifact for high-frequency transient stimuli. However, for low-frequency stimuli, for which the response begins while the stimulus is present, results obtained with shielded earphones should be interpreted with caution.     

Adaptive Filterng of Evoked Potentials

We present an adaptive filtering (AF) technique for rapid processing of evoked potentials (EP). The AF algorithm minimizes the mean-square error (MSE) between successive ensembles. We demonstrate theoretically that the filter output converges to the least square estimate of the underlying signal. Computer simulations with known signal and added noise show that AF produces lower MSE than ensemble averaging. We also compare results of AF to those obtained by ensemble averaging for some EP recorded from animals and humans. For very noisy EP recordings, we propose techniques that combine AF and ensemble averaging. The AF technique shows promise for requiring fewer ensembles than averaging to attain adequate signal quality.     

诱发电位中α稳定分布噪声参数的动态估计新方法

针对诱发电位潜伏期变化检测中信号噪声的非平稳特性,本文提出了一种新的参数估计方法,实现了诱发电位中α稳定分布噪声的动态参数估计.计算机仿真结果表明,这种方法可以有效地跟踪信号噪声特性的变化,且进一步完善了EP潜伏期变化的动态检测方法.     

字典训练结合形态分量分析的诱发电位少次提取方法

诱发电位的少次提取对于研究大脑活动规律以及临床诊断等均有重要意义。根据诱发电位与自发脑电信号的不同特点,本文提出一种基于形态分量分析的诱发电位少次提取方法,在不同的过完备字典上对诱发电位与自发脑电信号进行稀疏表示。为了改善在稀疏表示过程中的错误分解问题,提出使用几次带噪观测信号的叠加平均结果作为模板信号,并使用K-SVD算法训练得到合适的过完备字典,再对当前观测信号进行混合稀疏表示。实验结果表明,该方法能够有效地降低由通用过完备字典进行稀疏表示时的错分程度,较好地实现对诱发电位信号的提取。      

Application of Pseudorandom Noise to DPCM

The conventional DPCM compression algorithm has been substantially improved by the substitution of a tapered, noisy quantizer for the usual tapered quantizer. This markedly reduces the visibility of defects caused by granular noise and leak. The quantizer characteristic can then be modified to achieve less slope overload, thus significantly improving image quality.     

A Multivariate Approach to the Analysis of Average Evoked Potentials

An approach to the quantitative analysis of average evoked potential data is presented. An average evoked potential is assumed to be a sample from a multivariate normal distribution. Using this assumption, multivariate statistical techniques can be applied to test hypotheses about the similarity or difference of evoked potentials obtained under different conditions.     

联合稀疏表示的双次诱发电位提取算法

诱发电位少次提取对于研究大脑活动规律以及临床诊断等具有重要意义.根据脑电信号的特点,本文提出一种基于联合稀疏表示的双次诱发电位信号估计算法.利用诱发电位信号的准周期性和自发脑电信号的随机性,该算法将脑电信号看作为相似成分和相异成分的叠加.神经系统通过相同刺激产生的诱发电位主要在潜伏期和波幅两方面发生变化,因此该算法利用平均诱发电位进行建模,得到稀疏字典,通过联合稀疏表示算法实现双次诱发电位信号的提取.实验结果表明,该算法和其他算法相比获得了更好的效果.     

船舶噪声合成与听觉感知分析

船舶噪声人耳听觉感知训练是提高声呐员目标识别能力的重要手段,但是实录各类船舶在各个状态下的辐射噪声作为训练噪声样本根本无法实现,而且实录船舶辐射噪声易受环境噪声和海洋声信道传播的影响,无法清晰且不失真地呈现船舶的状态信息。依据人耳听觉感知的临界带通特性,提出了通过临界带通滤波和线谱迭加合成方法合成船舶辐射噪声的方法,并对舰船辐射噪声的原始声和合成声进行了听觉感知特性分析。研究结果表明辐射噪声的合成声与原始声在尖锐度、粗糙度和波动强度三个音色属性方面一致,可以作为船舶噪声人耳听觉感知训练中的噪声样本。     

Analysis and Digital Realization of a Pseudorandom Gaussian and Impulsive Noise Source

This paper presents results on the analysis and digital hardware realization of a non-Gaussian impulse noise source which can be used to model the impulsive noise present in wide-band communications systems. The impulse noise appearing in practical systems is characterized by bursts of much higher amplitudes than would be predicted by a normal- or Gaussian-distribution law. A need exists for a better characterization of this non-Gaussian impulsive noise as well as actual noise generators which can be used for evaluation of present and future communications equipment under realistic system-operating conditions. The impulse noise model and the realization of the noise generator described in this paper are capable of producing Gaussian background noise, lognormal impulsive noise, and burst timing to set prescribed starting and ending times of the bursts and impulse density within each of the burst periods. The techniques used in this paper are based on first generating a basic pseudorandom binary sequence (PRBS) and then from this deriving the Gaussian background noise by adding samples from the PRBS generator. The lognormal noise is then derived from the same sequence by using an incremental exponential generator. The burst timing signals which realize an approximate Poisson distribution are obtained by observing the occurrences of specific subsequences from the PRBS generator.     

Representation of Evoked Potentials by Fourier-Bessel Expansions

Fourier-Bessel expansions and Fourier series are used to represent the average evoked cortical potentials obtained by stimulation of the olfactory tract in cats. The applicability of various mathematical representations of potentials to the modeling of neural systems is discussed.     

不同相位噪声谱对QPSK的性能影响分析

研究了相位噪声对QPSK系统的性能影响,利用高斯信道下带有相位噪声的条件误码率公式,分析了不同相位噪声谱所带来的解调损失。相位调制是一种恒包络调制方式,它对调制信号的相位偏移非常敏感,在单频相位噪声模型基础上,把相位噪声功率谱密度与相干解调的误码率公式相联系起来,计算了高斯信道条件下不同相位噪声谱对不同速率QPSK信号的解调损失。     

基于听感知特性的噪声分析与防护

噪声是造成听力损伤的重要因素。针对噪声分析侧重研究噪声源的特性,较少考虑噪声防护需求的现状。从人耳听觉系统的感知特性出发,采用Gammatone分析滤波器组对声音在频域上进行非均匀多子带分解,通过耳谱图、子带能量及通道相关特性,定量计算噪声信号听感知特性,并提出了相应的噪声防护建议。从听感知特性出发分析噪声特征,进而设计的噪声防护方法是一种有效途径。     

Estimation of Intracellular Potentials from Evoked Neural Pulse Trains

An algorithm is presented for estimating the time course of intracellular generator potentials on the basis of the times of occurrence of evoked neural impulses, under conditions of external sinusoidal stimulation, and assuming SS-IPFM encoding. Recorded neural pulses are applied to the output of a theoretical SS-IPFM encoder (``in reverse') and a least-squares criterion is adopted for estimating the input sinusoid and its harmonics which would have given rise to the same train of pulses. Illustrative simulation examples of the algorithm are given, and its practical applications are discussed.     

Dipole Localization of Average and Single Visual Evoked Potentials

A single dipole source was chosen as a model of the neurological generator of evoked potentials elicited by illuminated checker-board stimulation of halves and quadrants of the visual field, and a homogeneous sphere was chosen as a model for the head. Dipole locations and moments were calculated for the average evoked potentials and average dipole locations and moments were calculated for the preprocessed single evoked potentials. The average dipole locations for the single potentials appear to be more anatomically appropriate than the location due to the average evoked potentials. A relationship was demonstrated between the dipole parameters and polarity inversions in the average evoked potentials.     

Optimum Multielectrode A Posteriori Estimates of Single-Response Evoked Potentials

This paper discusses the design and performance of an optimum linear multielectrode filter for estimating the evoked potential contained in a single scalp-recorded brain response to a visual stimulus. The filter is derived under the criterion of minimum mean-square error and is time varying to allow for the nonstationarity of the brain response. Single-and two-channel filters are designed for simulated and human visual evoked potential data. Cross-correlation matrices required to design the filters are estimated "a posteriori" from multielectrode recordings of the prestimulus electroencephalogram and are derived from a multielectrode model of the evoked potential. Filter performance is evaluated using the criteria of mean-square error, signal bias, noise reduction, and output signal-to-noise ratio. The filter is shown to be very effective at suppressing the ongoing electroencephalogram and emphasizing the underlying evoked potential.     

微波固体噪声二极管噪声功率谱密度的理论分析

本文根据PN结雪崩噪声理论、有限倍增因子和合适的二极营模式提出了微波固体噪声二极管噪声功率谱密度的表示式,并对其谱特性进行分析.指出了提高微波固体噪声二极管噪声输出功率的途径.     

Measurements of Signal Components in Single Visualy Evoked Brain Potentials

A two step procedure is described for measuring the characteristics of visual evoked brain potentials. First, the recorded waveforms are processed by a filter designed to minimize the mean square error produced by the ongoing EEG. This filter is different for each subject and is based on certain statistical properties of the measured data. Second, the filtered potentials are searched automatically by a computer to determine the existence and location of the individual components in the responses. By aligning the corresponding components in different waveforms and averaging over the waveform segment in the immediate vicinity of the peak, a latency corrected average is obtained that provides a new representation of the response waveform.