用奇异性检测技术提取诱发电位

本文介绍了用 小波变换模极大 值检测信号奇 异性的方法， 讨论了 信号与 白噪声 的小 波变换 和奇 异性指数之间区 别，模极大值沿 尺度 传递 的不同 特点 ，并 利用它 们的 区别 消除 诱发 电位 信号 中的噪 声，重 构出消 噪后 的信号， 取得 了较好 的效果 ，利用 较少的 刺激 次数就 可获取 诱发电 位信 号，有 效地提高 了信 噪比，大 大减 少了迭 加次数 ，特征 波的潜 伏期 及幅值 容易辨 认，易 于测量 ，且无 信号 失真。奇异性检 测技术有望成为 临床实用的诱 发电位提取 技术，并 可应用 于其他 生物 医学信 号的 消噪。     

ERP单次提取中的小波变换模极大值恢复算法

自发脑电的频谱不规则,与有效信号ＥＲＰ频谱相重叠,传统滤波方法难以奏效。但由于随机噪声奇异性指数与有效信号奇异性指数大小不一样,小波变换模极大值在不同尺度下传播行为也不一样,据此可将有效信号从随机噪声中提取出来。我们发现利用小波变换模极大值算法可以提取出单次ＥＲＰ,并将此方法用于１１名被试听觉的实时提取研究。     

基于小波变换的R波奇异性分析的研究

奇异性是生物信号的基本特征。依据小波变换模在多尺度上的变化特征,研究了信号奇异性分析的基本定理,在此基础上提出了奇异度Lipschitz指数的估计算法,并将之用于心电图(ECG)的R波奇异性分析。研究发现,随机选取的10名健康受试者与10名心律不齐患者的ECG的R波的奇异性存在显著的差异,健康受试者的奇异性结果显著高于心律不齐的患者。     

磁共振截断频谱图像的层析法边缘检测技术

本文提出一种适合于含有截断伪影磁共振图像的边缘检测新算法。按奇异函数分析理论 ,把任何有截断伪影的信号表示为以奇异点为参量的截断奇异函数的加权和 ,奇异点和加权系数由该信号决定。层析边缘检测的关键在于一层层地剥去奇异点上的加权截断奇异函数 ,从而一层层地检测出奇异点。这些奇异点可以构成图像的边缘。本方法可以有效地剔除由截断伪影而引入的虚假边缘。实际和仿真结果都表明这种方法效果高于现有方法     

心音信号检测的一种新方法

本文为实现第一心音（Ｓ１）和第二心音（Ｓ２）的定位的一种新方法，对心音图（ＰＣＧ）信号进行预处理后，再利用小波变换原理检测信号的奇异点，达到准确定位的目的。这一检测方法已在心功能仪上成功地应用于测试Ｑ－Ｓ１和Ｑ－Ｓ２间期。     

A local measure for modeling contrast discrimination: response to Katkov, Tsodyks and Sagi

Katkov, et al. [Katkov, M., Tsodyks, M., & Sagi, D. (2007). Singularities explained: Response to Klein. Vision Research, preceding article] commented on my comments [Klein, S. A. (2006). Separating transducer nonlinearities and multiplicative noise in contrast discrimination. Vision Research, 46, 4279-4293] regarding fitting the Kontsevich, et al. [Kontsevich, L. L., Chen, C. C., & Tyler, C. W. (2002). Separating the effects of response nonlinearity and internal noise psychophysically. Vision Research, 42, 1771-1784] contrast discrimination data. Klein [Klein, S. A. (2006). Separating transducer nonlinearities and multiplicative noise in contrast discrimination. Vision Research, 46, 4279-4293] focused on the question of whether the singularity associated with the constant noise model makes it difficult to reject that model. The present paper acknowledges the presence of a singularity but shows that even in the presence of a strong singularity and using a reasonable number of 2AFC trials, it is possible to not only reject the constant noise hypothesis, but also to place confidence limits on estimates of the magnitude of the multiplicative noise. Our analysis is based on measuring contrast discrimination among triplet of contrast levels.     

The glutamate induced phase shift in the SCN slice: a two pulse study

The short-term dynamics of resetting the circadian ‘clock' was assessed by a double-pulse paradigm in vitro. On day 1, single and double 1 h ‘pulses' of 1 mM -glutamate were applied to the rat suprachiamastic nuclei (SCN). On days 2 and 3, single unit activity (SUA) was recorded and time-of-peak SUA was used as a phase marker of the circadian rhythm. The time-of-peak in untreated slices at ‘Zeitgeber' time (ZT; hours after lights-on) 6, was used to evaluate effects of glutamate on phase. In accordance with published data, a single glutamate pulse at ZT 14 resulted in a 3 h delay of peak SUA on days 2 and 3. A 2nd pulse, given 3 h after a 1st pulse, resulted in two distinct peaks on day 2: a 1st at ZT 7 and a 2nd at ZT 12, i.e., a 6 h phase delay and hence twice the delay obtained after a single pulse. On day 3, no peak in SUA was observed which indicates that a new steady state was not reached on day 2. The bimodal distribution of SUA on day 2 corroborates other findings which suggest that the SCN comprises two distinct neuronal populations with circadian firing patterns that are normally coupled but, possibly due to different sensitivities to glutamate, can desynchronize. The additive phase-shifting effect of two consecutive glutamate pulses suggests that, at least for one sub-population of SCN neurons, the phase shift is completed within 3 h.     

Three-dimensional visual feature representation in the primary visual cortex

In the cat primary visual cortex, it is accepted that neurons optimally responding to similar stimulus orientations are clustered in a column extending from the superficial to deep layers. The cerebral cortex is, however, folded inside a skull, which makes gyri and fundi. The primary visual area of cats, area 17, is located on the fold of the cortex called the lateral gyrus. These facts raise the question of how to reconcile the tangential arrangement of the orientation columns with the curvature of the gyrus.In the present study, we show a possible configuration of feature representation in the visual cortex using a three-dimensional (3D) self-organization model. We took into account preferred orientation, preferred direction, ocular dominance and retinotopy, assuming isotropic interaction. We performed computer simulation only in the middle layer at the beginning and expanded the range of simulation gradually to other layers, which was found to be a unique method in the present model for obtaining orientation columns spanning all the layers in the flat cortex. Vertical columns of preferred orientations were found in the flat parts of the model cortex. On the other hand, in the curved parts, preferred orientations were represented in wedge-like columns rather than straight columns, and preferred directions were frequently reversed in the deeper layers. Singularities associated with orientation representation appeared as warped lines in the 3D model cortex. Direction reversal appeared on the sheets that were delimited by orientation-singularity lines. These structures emerged from the balance between periodic arrangements of preferred orientations and vertical alignment of the same orientations. Our theoretical predictions about orientation representation were confirmed by multi-slice, high-resolution functional MRI in the cat visual cortex. We obtained a close agreement between theoretical predictions and experimental observations. The present study throws a doubt about the conventional columnar view of orientation representation, although more experimental data are needed.     

Entrainment of the natural pacemakers of the heart precedes atrial fibrillation

A new measure of heart rate variability is proposed to investigate the interaction of the sino-atrial (SA) and atrio-ventricular (AV) pacemakers. Using electrocardiogram (ECG) fiduciary markers corresponding to the depolarization time of the SA and AV pacemakers, the variability of SA and AV depolarization rate is jointly analyzed by spectral analysis. The result of this joint analysis provides evidence of a distinct pattern of interaction between the SA and AV nodes prior to the onset of paroxysmal atrial fibrillation (PAF): frequency entrainment between the primary and secondary pacemakers of the heart, occurring at the respiratory frequency. We propose a measure of this entrainment as a diagnostic indicator for PAF, and compare it to standard diagnostic measures. The entrainment measure is found to have greater diagnostic power than five other common ECG-derived measures.