单通道脑电信号中诱发电位的单次提取

我们正在构建一个脑控拼写装置，直接利用脑信号与计算机进行交互。在这种实时通信模式中，作为通信载体的特征脑信号淹没在自发的脑电背景中，不能采用常规的叠加平均方法来提取，而必须实现特征信号的单次识别。为使这种技术走出实验室，记录脑电的导联数应越少越好。我们采用独特的“模拟自然阅读”诱发模式，让被试从平滑移过小视窗的刺激符号串中识别靶刺激符号，以产生视觉诱发电位（VEP）。利用支持向量机方法，对三名被试位于导联Pz处EEG信号中的VEP进行了单次提取，正确识别率分别为92．1％、94．1％和91．5％，达到了较为满意的效果，为系统的实现打下了基础。     

基于视觉诱发电位的脑机接口实验研究

脑机接口是一种新颖的基于脑电信号实现人脑与计算机或其他电子设备进行通讯和控制的系统 ,在康复医学工程等领域具有重要意义。作者开展了基于视觉诱发电位的脑机接口实验研究。采用计算机编程 ,在屏幕产生多种刺激模式图案 ,屏幕上闪烁的不同图案代表多种选择 ,受试者通过注视其中一个目标来作出选择。头皮电极采集枕骨粗隆部位的诱发电位信号 ,分析诱发电位信号 ,可以判别出受试者注视的目标。采用小波滤波及累加平均方法提高信噪比 ,用于提取微弱的脑电信号。离线实验数据分析表明 ,采用本文提出的方法可以有效地实现脑机接口 ,并达到较高的正确率和通信速度 ,目标为 12个时 ,通信率高于 30 bit/ min     

Operant Conditioning of Visual Evoked Potentials in Man

The operant conditioning technique was used to produce visual evoked response modifications in man. Our results show that: 1) 50% of our subjects are able to modify a definite component of their evoked potential. 2) These modifications still occur with irregular evoked potential intervals. 3) The criterion segment is the only part of the response which is modified; other components are not affected. 4) All components ranging from 90 to 385 msec can be modified; however, the second part of the response (after 200 msec) seems to be more easily modified.     

Visual Cortical Evoked Potentials as a Function of Intensity Variations in Sequential Blanking

A sequential blanking paradigm was used to determine the effects of more intense, later appearing, stimuli upon the visual evoked potential (VEP) to earlier appearing stimuli. In sequential blanking the presentation of a sequence of visual stimuli at certain rates, and in certain orders, results in the perceptual blanking of approximately one-half of the stimuli. The precise timing and location requirements for this effect are conveniently produced with a digital computer and associated cathode ray tube display. Further evidence was found for the inhibiting effect of later occurring (more intense) stimuli on the VEP response to earlier occurring (less intense) stimuli. This effect revealed itself in the delayed appearance of the major components of the VEP. In addition, it was found that the amount of delay was related to the ratio of the intensity difference between the earlier (blanked) and later occurring (blanking) stimuli, i.e., the greater the intensity difference between them the greater the temporal displacement produced in the VEP components.     

A Factor Analysis of Visual Evoked Responses

A factor analysis was performed on 19 visual evoked response (VER) variables and age, in order to identify patterns of relationships among the variables. The analysis resulted in a 7-factor Varimax solution. Subjects were 98 kindergarten children (50 girls and 48 boys) in upper-middle socio-economic class. Mean IQ was 119.5; mean age, 67.16 mo. The five cortical measures of amplitude, latency, correlation, complexity, and linearity, the latter two of which had not been previously measured, were recorded from three scalp locations in response to three types of visual stimulation. Four factors (amplitude, linearity, and two latency factors-one for each of two stimulus conditions) were obtained which showed significant loadings only within a given cortical measure. Three factors (one for each of the stimulus conditions) were obtained which showed significant loadings across different cortical measures. Examination of the correlation matrix, as well as the orthogonal (independent) factor solution, supported the main hypothesis that the VER is a multidimensional domain. Specifically, different stimulus conditions and/or different cortical measures of VER often produced variables which were uncorrelated across subjects.     

Stimulus Intensity Expectation and Visual Evoked Brain Potentials

In a sample of 32 adult subjects, we examined the relationship between amplitude measures of the visual evoked potential (VEP) and a subject's expectation that a stimulus would be either brighter or dimmer than the others in a series. It was found that when subjects expected a bright light flash, the VEP waveform changed in the direction associated with a stimulus intensity increase even though no actual intensity change occurred. Conversely, when subjects expected a dim light flash, the VEP waveform changed in the direction associated with a stimulus intensity decrease even though no actual intensity change occurred. The amplitude changes to the expected stimulus intensities occurred in specific VEP peaks and were related to the position of the stimulus in the sequence.     

Visual Evoked Responses (VERs) in Normal and Disabled Readers

The present study investigated the possibility that reading disabled children exhibit abnormal visual evoked responses (VERs). Comparisons were made between a group of disabled children and two control groups of normals, one group matched on age and IQ, and the other on reading level and IQ. VERs were obtained for flashes of light and word stimuli. Results indicated that the reading disabled children showed a significantly smaller amplitude in the negative wave at 180 msec following stimulus onset, for an electrode placed in the region of the left angular gyrus, compared to the two controls. All three groups showed significantly greater negative amplitudes at this latency for the word stimulus compared to the light flash. The results confirm some earlier findings and suggest that a neurological origin of reading disability is likely.     

Visual Evoked Potentials and Reaction Time in Normal and Dyslexic Children

This investigation compared the visual evoked responses (VERs) and reaction time (RT) performance of 24 dyslexic boys and 24 controls at four different age levels (7, 9, 11, and 13 yrs). Prescreening and matching techniques were used to eliminate differences due to social or educational deprivation, gross sensory-motor handicaps, specific neurological deficiencies, or intellectual impairment. The VER was recorded from four scalp locations (O₁, O₂, P₃, and P₄) referenced to the vertex during a detection task in which subjects were required to respond to dim flashes occurring in a train of brighter flashes. An overall hemispheric asymmetry in VER amplitude (right > left) was observed in both experimental and control subjects. Dyslexics exhibited an increased amplitude to unattended stimuli and a slower RT to attended stimuli. Normals exhibited significant correlations between RT and VER latency, dyslexics did not. There were no significant VER-IQ correlations. The results are discussed in terms of an attentional deficit hypothesis.     

Visual Evoked Potentials to Illusory Reversals of the Necker Cube

Sensory adaptation and cognitive evaluation have been proposed as explanations of illusory figure reversals. The effect of variations in the perceived orientation of a Necker cube on visual evoked potentials (VEPs) was studied to test these two hypotheses. VEPs associated with perceptual reversals and non-reversals of a Necker cube were compared with VEPs elicited by a sequence of physically varying cubical figures. Amplitude differences in the early VEP components consistent with adaptation effects were not detected. Both types of reversals were associated with a late positive component (400–700 ms), which was smaller in amplitude in the illusory condition. The late positivity to illusory reversals was also distinguished by a broad (200–700 ms) positive component over frontal and central recording sites which was absent over Oz. These findings suggest that illusory reversals are more difficult to discriminate than physical reversals, and require additional cognitive resources for evaluation.     

Visual Evoked Potentials Before and After Kraepelin Performance Test in Schizophrenia

Visual evoked potentials of a group of 25 schizophrenic patients, a group of 13 neurotics, and a group of 24 healthy subjects were recorded before and after Kraepelin performance test. Soon after performance of the addition test for 15 min. amplitudes of later components (waves IV, V, and VI) of the potential were reduced in schizophrenics, while neurotic patients and healthy subjects did not show such changes.     

Orientation-Specific and Luminance Effects: Interocular Suppression of Visual Evoked Potentials in Man

The interocular transfer of orientation-specific effects was investigated using visual evoked potentials (VEPs). Monocular VEPs were obtained to either diffuse light or grids of 0° or 45° orientations flashed to one eye. The other eye continuously viewed either darkness, diffuse light or grids of 0°, 15°, 30°, or 45° orientations. Changing the continuous stimulus from darkness to diffuse light interocularly reduced the amplitude of a late VEP component (P200). Changing the orientation of the continuous stimulus primarily affected an earlier VEP component (N110). This interocular effect was orientation specific: the more similar the orientation of the flashed and continuously presented grids, the smaller the amplitude of the VEP components. The 1/2 bandwidths at 1/2 amplitude of the orientation tuning functions were 45° and 32° for the vertical and oblique test flashes respectively. This orientation-specific interocular suppression was discussed in terms of electrophysiological and psychophysical data indicating binocular orientation channels and the interactions among these channels.     

酒精依赖者视觉诱发电位的研究

目的：本研究旨在通过对酒精依赖者模式翻转视觉诱发电位（ＰＲＶＥＰ）的研究，为了解酒精依赖者的生理和心理功能损害提供客观指标。方法：酒精依赖者６２人，正常对照者４０人，采用日本产Ｎｅｕｒｏｐａｃｋ－２型诱发电位仪，分别对其进行模式翻转视觉诱发电位（ＰＲＶＥＰ）记录。结果：与正常对照组相比，酒精依赖者ＰＲＶＥＰ波潜伏期延长，波幅降低，主波群异常，晚成份出现率低，周期不明显及侧性优势现象消失，差异具有显     

Hemispheric Asymmetries in the Visual Cortical Evoked Potential as a Function of Stimulus Location

The averaged visual cortical evoked potential (VEP) was examined in two separate experiments us a function of stimulus location. The VEP was recorded from over left and right occipital hemispheres and stimuli were presented binocularly. The results of Experiment I, in which three stimulus locations were used, indicated that stimuli presented in the left visual field resulted in shorter VKP latencies at the right occipital area than the left, while for stimuli presented in the right visual field, the opposite occurred. In Experiment II, seven locations were used and similar VEP latency asymmetries were observed. White no hemispheric amplitude asymmetries were found, there was a trend toward a decrease of VEP amplitude with increasing distance of stimulation from the fovea. The latency asymmetries may he explained in terms of the angle at which the stimuli impinge upon the retinas of the two eyes from different locations. Direct stimulation is produced at the primary projection area, whereas indirect stimulation probably occurs at the secondary area, after crossover of impulses via the corpus callosum.     

基于小波变换的颜色视觉诱发电位检测去噪研究

为了提高检测的效率，将基于小波变换的信号分析方法引入到颜色视觉诱发电位（Visual evoked potential，VEP）的检测中，提出了基于多尺度条件下小波变换模极大值分布图的重建VEP信号的方法。该方法对初始采集信号采用Mallat快速算法进行离散小波变换得到模极大值分布图。根据信号噪声的Lipschitz指数特性进行去噪。最后按照POCS（Projections onto convex sets）方法进行信号的重建。仿真实验结果表明该方法对VEP信号的去噪效果比较理想。同时该方法极大地降低了测试次数。因此该方法与现有临床的叠加方法相比有明显的优披件．     

用小波变换提取视觉诱发电位信号

视觉诱发电位（ＶＥＰ）信号的动态提取及处理具有重要的临床意义。通过硬件采集的ＶＥＰ信号经过叠加平均处理后仍含有大量背景噪声，不能直接用于诊断分析。小波变换是一种新兴时频分析方法，适于分析非平稳信号。在我们研制的视觉生理地形图系统中，成功地用它从背景噪声中提取出ＶＥＰ信号，完成信号的预处理。     

Conditioning of Evoked Potentials in Children of Differing Intelligence

This study compared the conditioning of averaged evoked potentials in three groups of children (average age 11 yrs): (I) normals, (II) IQ between 50 and 60, (III) IQ between 20 and 50. Sound was the conditioned stimulus, light the unconditioned stimulus, 68 sessions were recorded in 34 children. Decrease in the number and in the amplitude of potentials evoked by sound was observed from group I to group III, whereas generalized slow waves increased from group I to group III. Conditioning was different in the three groups. In the normal child it modified the conditioned evoked potential to sound. In the mentally retarded child, it modified generalized slow waves and brought about the reproduction of a temporal sequence.     

The Influence of Cognitive Tasks on Different Frequencies Steady-state Visual Evoked Potentials

Previous studies suggested that there exists different neural networks for different frequency bands of steady-state visual evoked potential (SSVEP). What is the effect of the same cognitive task on different frequency SSVEPs? In this work, when a subject was conducting a graded memory task, a 8.3 or 20 Hz flicker was used as a background stimulation. The recorded EEGs were analyzed by the method of steady-state probe topography (SSPT), the results showed that SSVEPs under these two flicker conditions were similar to each other in the various stages of memory process, and were similar to the result of a high alpha band SSVEP as reported before. However, the SSVEP amplitude and latency in the lower frequency band is more clear and stable than that in the higher frequency band. These results suggest that the same cognitive task affects the different frequency SSVEP in a similar way, and the low frequency flicker is a better choice than the high frequency one in such as working memory study.     

基于独立分量分析的大脑视觉诱发电位单次提取

脑电 (Electroencephalography ,EEG)视觉诱发电位 (VisualEvokedPotential,VEP)的单次提取是当前生物医学信号处理领域的一个研究热点。提出一种基于独立分量分析 (IndependentComponentAnalysis,ICA)的多道脑电信号VEP单次提取方法 ,与多次叠加求平均的方法相比较 ,可以得到令人满意的结果。     

视听联合刺激的跨感觉通道诱发电位源的分析

运用偶极子源分析方法分析视听单独刺激和联合刺激下脑区的区别和联系.采用64道脑电采集系统,记录了7名被试者在视觉、听觉和视听联合刺激下的脑诱发电位,并分别在初期、早期和晚期时间段对这3种任务做偶极子源分析.通过比较视听联合刺激和视听单独刺激下偶极子源的变化,可以得到视听联合刺激下的源不等于单独视听刺激下的源的简单叠加,从而提示存在视听相互作用的区域.     

Effects of Light Intensity and Edge Density on Visually Evoked Potentials in Rhesus Monkeys

Visually evoked potentials were recorded from bipolar electrodes implanted in the foveal and parafoveal striate, prestriate and inferotemporal cortices of mature rhesus monkeys (Macaca mulatta). The stimuli used were a blank field and three checkerboard patterns containing checks whose sizes were 2° 24′, 36′, and 9′ of visual arc. In addition to the size of the checks within the patterns, the intensity at which the stimuli were presented was also varied. In all four regions studied, check size had a significant effect on the amplitude of the average evoked potential, but intensity showed an effect only in the two striate regions. Certain regions of the visual cortex can apparently process two dimensions of a stimulus concurrently, and the same mass of neuronal tissue can participate in the processing of different dimensions of a stimulus at different times. The results are discussed in the context of existing literature concerning the evoked potential as an indicator of sensory information processing.