基于非正弦激励的模拟电路故障诊断

传统交流故障字典法通过施加不同频率的正弦激励,以获得对待测电路中频率敏感元件更高的故障覆盖率。为减少多次对待测电路施加激励的时间开销,该文提出可将多个不同频率激励进行叠加,得到非正弦的激励信号作为待测电路激励。在此背景下,讨论了产生一个非正弦激励信号,使之能够包含所需测试频率分量的方法。并分析了在施加非正弦激励下情形下,对待测电路响应中不同频率分量进行解耦,识别各分量交流参数的可行性和需要解决的问题。结果表明:在已知叠加前波形频域特征时,可以反推出叠加前各个原始波形的特征参数。因此,可以在实现压缩传统交流故障字典法测试时间的同时,达到与传统方法相近的诊断能力。     

A possible neuronal basis for Doppler-shift compensation in echo-locating horseshoe bats

The auditory system of the horseshoe bat is finely tuned to the bat's individual vocalization frequency. To compensate for flight-induced Doppler shifts in the echo frequency, the horseshoe bat adjusts the frequency of its echo-location call to maintain the echo frequency within the narrow range to which its auditory system is best tuned. In this report I describe neurons in the midbrain tegmentum of the horseshoe bat, with properties that strongly indicate their involvement in this Doppler-shift compensation. The activity of these neurons was influenced by both sound emission and auditory stimuli. Neuronal discharges in response to vocalization, however, differed from those in response to purely auditory stimuli that mimicked the bat call. When an auditory stimulus was temporally locked to a preceding vocalization, the response was dependent on the time delay between the two. This delay-sensitivity completely disappeared when vocalizations were simulated acoustically. Only those vocalization and 'echo' parameters were encoded that occur in Doppler-shift compensation. In conclusion, I suggest a model for the regulation of the vocalization frequency through auditory feedback.     

视、听偏差刺激选择性注意的ERPs研究

本实验采用了视听双通道伪同时呈现的oddball模式,以汉字和简单几何图形为视觉刺激,1000Hz和800Hz的纯音为听觉刺激,使用注意通道(注意和非注意条件)×刺激概率(偏差刺激概率均为15%,标准刺激的概率均为85%)的2×2因素设计,来研究视觉和听觉偏差刺激在注意和非注意条件下诱发的事件相关电位(ERPs)。实验中视觉和听觉刺激随机序列地呈现给被试(刺激间隔ISI为700～1300ms),被试被要求注意某一通道如视觉通道,而相应地忽视另一通道即听觉通道,以左右手触键反应,如左手反应视觉偏差刺激,右手反应视觉标准刺激。结果表明,听觉偏差刺激在注意和非注意条件下均诱发了类似的不匹配负波(MMN);而视觉偏差刺激在注意和非注意条件下没有诱发MMN或类似MMN的成分,这是因为视觉系统的平行加工特性和难以对视觉影像产生记忆痕迹。听觉偏差刺激在注意条件下重迭了N2b成分并跟随了P3a成分,这种重迭和跟随反映了选择注意中的定向反应。注意条件下听觉和视觉的偏差刺激诱发了较大波幅的P300成分,反映了工作记忆中的表象更新。本实验的结果支持Naatanen对MMN所做的观察,听觉偏差刺激所诱发的MMN与注意条件的无关性反映了听觉通道中感觉刺激特征的自动化加工。     

Receptive field plasticity of neurons in rat auditory cortex

Using conventional electrophysiological technique, we investigated the plasticity of the frequency receptive fields (RF) of auditory cortex (AC) neurons in rats. In the AC, when the frequency difference between conditioning stimulus frequency (CSF) and the best frequency (BF) was in the range of 1--4 kHz, the frequency RF of AC neurons shifted. The smaller the differences between CSF and BF, the higher the probability of the RF shift and the greater the degree of the RF shift. To some extent, the plasticity of RF was dependent on the duration of the session of conditioning stimulus (CS). When the frequency difference between CSF and BF was bigger, the duration of the CS session needed to induce the plasticity was longer. The recovery time course of the frequency RF showed opposite changes after CS cessation.The RF shift could be induced by the frequency that was either higher or lower than the control BF, demonstrating no clear directional preference. The frequency RF of some neurons showed bidirectional shift, and the RF of other neurons showed single directional shift. The results suggest that the frequency RF plasticity of AC neurons could be considered asan ideal model for studying plasticity mechanism. The present study also provides important evidence for further study of learning and memory in auditory system.     

Sustained firing in auditory cortex evoked by preferred stimuli

It has been well documented that neurons in the auditory cortex of anaesthetized animals generally display transient responses to acoustic stimulation, and typically respond to a brief stimulus with one or fewer action potentials. The number of action potentials evoked by each stimulus usually does not increase with increasing stimulus duration. Such observations have long puzzled researchers across disciplines and raised serious questions regarding the role of the auditory cortex in encoding ongoing acoustic signals. Contrary to these long-held views, here we show that single neurons in both primary (area A1) and lateral belt areas of the auditory cortex of awake marmoset monkeys (Callithrix jacchus) are capable of firing in a sustained manner over a prolonged period of time, especially when they are driven by their preferred stimuli. In contrast, responses become more transient or phasic when auditory cortex neurons respond to non-preferred stimuli. These findings suggest that when the auditory cortex is stimulated by a sound, a particular population of neurons fire maximally throughout the duration of the sound. Responses of other, less optimally driven neurons fade away quickly after stimulus onset. This results in a selective representation of the sound across both neuronal population and time.     

Cortical remodelling induced by activity of ventral tegmental dopamine neurons.

Representations of sensory stimuli in the cerebral cortex can undergo progressive remodelling according to the behavioural importance of the stimuli. The cortex receives widespread projections from dopamine neurons in the ventral tegmental area (VTA), which are activated by new stimuli or unpredicted rewards, and are believed to provide a reinforcement signal for such learning-related cortical reorganization. In the primary auditory cortex (AI) dopamine release has been observed during auditory learning that remodels the sound-frequency representations. Furthermore, dopamine modulates long-term potentiation, a putative cellular mechanism underlying plasticity. Here we show that stimulating the VTA together with an auditory stimulus of a particular tone increases the cortical area and selectivity of the neural responses to that sound stimulus in AI. Conversely, the AI representations of nearby sound frequencies are selectively decreased. Strong, sharply tuned responses to the paired tones also emerge in a second cortical area, whereas the same stimuli evoke only poor or non-selective responses in this second cortical field in naive animals. In addition, we found that strong long-range coherence of neuronal discharge emerges between AI and this secondary auditory cortical area.     

Top-down gain control of the auditory space map by gaze control circuitry in the barn owl

High-level circuits in the brain that control the direction of gaze are intimately linked with the control of visual spatial attention. Immediately before an animal directs its gaze towards a stimulus, both psychophysical sensitivity to that visual stimulus and the responsiveness of high-order neurons in the cerebral cortex that represent the stimulus increase dramatically. Equivalent effects on behavioural sensitivity and neuronal responsiveness to visual stimuli result from focal electrical microstimulation of gaze control centres in monkeys. Whether the gaze control system modulates neuronal responsiveness in sensory modalities other than vision is unknown. Here we show that electrical microstimulation applied to gaze control circuitry in the forebrain of barn owls regulates the gain of midbrain auditory responses in an attention-like manner. When the forebrain circuit was activated, midbrain responses to auditory stimuli at the location encoded by the forebrain site were enhanced and spatial selectivity was sharpened. The same stimulation suppressed responses to auditory stimuli represented at other locations in the midbrain map. Such space-specific, top-down regulation of auditory responses by gaze control circuitry in the barn owl suggests that the central nervous system uses a common strategy for dynamically regulating sensory gain that applies across modalities, brain areas and classes of vertebrate species. This approach provides a path for discovering mechanisms that underlie top-down gain control in the central nervous system.     

近视与视觉事件相关电位P300关系的研究

对8名无其他眼科疾病的近视眼患者在摘除和佩戴眼镜两种情况下分别进行视觉oddball模式刺激,并记录其脑电信号.刺激分为两组:一组为形状相同但颜色不同的几何图形,另一组为颜色相同但形状不同的图形.在每组刺激中,分别比较在摘除与佩戴眼镜两种情况下由该刺激诱发的视觉事件相关电位P300.结果发现在这两组刺激中,近视眼患者在摘除与佩戴眼镜两种情况下的P300无显著性差异.这说明大脑对颜色与二维图形的认知功能基本上不会受到视力的影响.     

基于独立分量分析的失匹配负波快速提取

失匹配负波(MM N)是一种由刺激变化所诱发的听觉诱发电位成分,其过低的信噪比造成检测和提取比较困难。提出利用独立分量分析(ICA)方法对多导听觉诱发电位信号进行多次分解,根据MM N产生的生理机制及其信号特征,设计合理的独立分量选取原则,提取MM N。该方法通过仿真实验验证,能有效提高信噪比。在真实数据的处理中,仅用传统方法20%左右的实验时间,实现MM N成分波的提取。这将促进MM N在认知神经科学及临床上的应用。     

听觉诱发电位信号分析中小波基函数的确定

声舒适是评价建筑室内环境的重要部分,听觉诱发电位是声环境舒适度评价的客观生理指标,听觉诱发电位信号的时频能量特征可以用来评价声环境的舒适性.小波包分析可以探究听觉诱发电位信号时频能量分布规律,分析时运用的小波基不同,产生的结果也不同.为了更好地研究听觉诱发电位信号的时频能量分布,比较了5种小波基函数的时域特点和幅频特性.对16名正常成年人进行了脑干听觉诱发电位实验,将所测16组听觉诱发电位的平均值进行小波包时频能量分析.结果表明,dmey小波分析结果在时频分布上可与实际信号的能量信息相匹配,可以减少各个频带信号分解后的失真问题.选择dmey小波对听觉诱发电位信号进行处理,能够更准确地分析听觉诱发电位信号的时频能量分布,为声环境的舒适性研究提供理论依据.     

卷积编码TH-UWB通信系统对抗ISI的性能仿真及分析

针对UWB(超宽带)无线传感器网络中由多径效应引起的ISI(码间干扰)问题,在两个不同UWB信道环境下仿真了TH-PPM-UWB(跳时脉位调制超宽带)通信系统传输有无ISI及是否采用编码调制共8种情况下的误码性能,结果表明采用卷积编码的TH-PPM-UWB系统抵抗ISI的能力较无编码系统有较大的提高,并且ISI越严重,卷积编码调制越有效.     

家鸽前脑声反应神经元的分布及其特性的研究

实验在61只家鸽上完成。动物用三碘季胺酚麻痹,记录了前脑36个神经元的电活动。实验结果表明,对短声刺激具有反应的前脑神经元分散地分布在旧纹状体、上纹状体以及新纹状体内,但是大多数听神经元集聚在相当于Karten和Hodos氏鸽脑立体定位图谱P_(1-3),L或R_(1-3)以及H_(2-6)的坐标范围之内。这些对声刺激有反应的听神经元的潜伏期为5～42msec。在正常情况下,神经元的潜伏期很少变化。前脑听神经元既可以接受对侧耳的信息,也可以接受同侧耳的信息。在旧纹状体内来自双耳信息的聚合可能引起相互抑制的结果。     

家鸽前脑声反应神经元的分布及其特性的研究

实验在61只家鸽上完成。动物用三碘季胺酚麻痹,记录了前脑36个神经元的电活动。实验结果表明,对短声刺激具有反应的前脑神经元分散地分布在旧纹状体、上纹状体以及新纹状体内,但是大多数听神经元集聚在相当于Karten和Hodos氏鸽脑立体定位图谱P_(1～3),L或R_(1～3)以及H_(2～6)的坐标范围之内。这些对声刺激有反应的听神经元的潜伏期为5～42msec。在正常情况下,神经元的潜伏期很少变化。前脑听神经元既可以接受对侧耳的信息,也可以接受同侧耳的信息。在旧纹状体内来自双耳信息的聚合可能引起相互抑制的结果。     

Gamma-band synchronization in visual cortex predicts speed of change detection

Our capacity to process and respond behaviourally to multiple incoming stimuli is very limited. To optimize the use of this limited capacity, attentional mechanisms give priority to behaviourally relevant stimuli at the expense of irrelevant distractors. In visual areas, attended stimuli induce enhanced responses and an improved synchronization of rhythmic neuronal activity in the gamma frequency band (40-70 Hz). Both effects probably improve the neuronal signalling of attended stimuli within and among brain areas. Attention also results in improved behavioural performance and shortened reaction times. However, it is not known how reaction times are related to either response strength or gamma-band synchronization in visual areas. Here we show that behavioural response times to a stimulus change can be predicted specifically by the degree of gamma-band synchronization among those neurons in monkey visual area V4 that are activated by the behaviourally relevant stimulus. When there are two visual stimuli and monkeys have to detect a change in one stimulus while ignoring the other, their reactions are fastest when the relevant stimulus induces strong gamma-band synchronization before and after the change in stimulus. This enhanced gamma-band synchronization is also followed by shorter neuronal response latencies on the fast trials. Conversely, the monkeys' reactions are slowest when gamma-band synchronization is high in response to the irrelevant distractor. Thus, enhanced neuronal gamma-band synchronization and shortened neuronal response latencies to an attended stimulus seem to have direct effects on visually triggered behaviour, reflecting an early neuronal correlate of efficient visuo-motor integration.     

A synaptic memory trace for cortical receptive field plasticity

Receptive fields of sensory cortical neurons are plastic, changing in response to alterations of neural activity or sensory experience. In this way, cortical representations of the sensory environment can incorporate new information about the world, depending on the relevance or value of particular stimuli. Neuromodulation is required for cortical plasticity, but it is uncertain how subcortical neuromodulatory systems, such as the cholinergic nucleus basalis, interact with and refine cortical circuits. Here we determine the dynamics of synaptic receptive field plasticity in the adult primary auditory cortex (also known as AI) using in vivo whole-cell recording. Pairing sensory stimulation with nucleus basalis activation shifted the preferred stimuli of cortical neurons by inducing a rapid reduction of synaptic inhibition within seconds, which was followed by a large increase in excitation, both specific to the paired stimulus. Although nucleus basalis was stimulated only for a few minutes, reorganization of synaptic tuning curves progressed for hours thereafter: inhibition slowly increased in an activity-dependent manner to rebalance the persistent enhancement of excitation, leading to a retuned receptive field with new preference for the paired stimulus. This restricted period of disinhibition may be a fundamental mechanism for receptive field plasticity, and could serve as a memory trace for stimuli or episodes that have acquired new behavioural significance.     

Hearing visual motion in depth

Auditory spatial perception is strongly affected by visual cues. For example, if auditory and visual stimuli are presented synchronously but from different positions, the auditory event is mislocated towards the locus of the visual stimulus-the ventriloquism effect. This 'visual capture' also occurs in motion perception in which a static auditory stimulus appears to move with the visual moving object. We investigated how the human perceptual system coordinates complementary inputs from auditory and visual senses. Here we show that an auditory aftereffect occurs from adaptation to visual motion in depth. After a few minutes of viewing a square moving in depth, a steady sound was perceived as changing loudness in the opposite direction. Adaptation to a combination of auditory and visual stimuli changing in a compatible direction increased the aftereffect and the effect of visual adaptation almost disappeared when the directions were opposite. On the other hand, listening to a sound changing in intensity did not affect the visual changing-size aftereffect. The results provide psychophysical evidence that, for processing of motion in depth, the auditory system responds to both auditory changing intensity and visual motion in depth.     

A corollary discharge maintains auditory sensitivity during sound production

Speaking and singing present the auditory system of the caller with two fundamental problems: discriminating between self-generated and external auditory signals and preventing desensitization. In humans and many other vertebrates, auditory neurons in the brain are inhibited during vocalization but little is known about the nature of the inhibition. Here we show, using intracellular recordings of auditory neurons in the singing cricket, that presynaptic inhibition of auditory afferents and postsynaptic inhibition of an identified auditory interneuron occur in phase with the song pattern. Presynaptic and postsynaptic inhibition persist in a fictively singing, isolated cricket central nervous system and are therefore the result of a corollary discharge from the singing motor network. Mimicking inhibition in the interneuron by injecting hyperpolarizing current suppresses its spiking response to a 100-dB sound pressure level (SPL) acoustic stimulus and maintains its response to subsequent, quieter stimuli. Inhibition by the corollary discharge reduces the neural response to self-generated sound and protects the cricket's auditory pathway from self-induced desensitization.     

Neural mechanisms of perceptual grouping in human visual cortex

The current work examined neural substrates of perceptual grouping in human visual cortex using event-related potential (ERP) recording. Stimulus arrays consisted of local elements that were either evenly spaced (uniform stimuli) or grouped into columns or rows by proximity or color similarity (grouping stimuli). High-density ERPs were recorded while subjects identified orientations of perceptual groups in stimulus arrays that were presented randomly in one of the four quadrants of the visual field.Both uniform and grouping stimulus arrays elicited an early ERP component (C1), which peaked at about 70ms after stimulus onset and changed its polarity as a function of stimulated elevations. Dipole modeling based on realistichead boundary-element models revealed generators of the C1 component in the calcarine cortex. The C1 was modulated by perceptual grouping of local elements based on proximity, and this grouping effect was stronger in the upper than in the lower visual field. The findings provide ERP evidence for the engagement of human primary visual cortex in the early stage of perceptual grouping.     

豚鼠听觉频率跟随反应中的非线性特性

本文研究了豚鼠听觉频率跟随反应(FFR)的非线性特性,认为FFR的非线性主要呈倍频效应,且随着刺激频率的改变而变化。刺激频率改变对FFR的影响比刺激强度对FFR的影响大。     

端部圆锥形薄壁构件的抗撞性设计优化

基于显式有限元技术,采用响应面法,以结构的比吸能为优化函数,研究了圆形截面金属薄壁构件的端部锥形尺寸对抗撞性的影响;经过数值分析,得出了端部为锥形的圆形截面薄壁构件的比吸能关于锥形长度和锥边直径的变化规律,这些规律可以用于实际吸能原件的设计,并为进一步研究奠定了基础.