The Effects of Stimulus Expectancy on Evoked Brain Potentials

The effects of self-generated expectancy of stimulus content on the visual evoked potential to physically identical stimuli were studied in college students. The subject set up his own internal expectant; by choosing to see either a bright or dim Hash. When a bright or dim Hash was anticipated, the potentials evoked by u medium stimulus intensity resembled the responses elicited by an actual bright or dim flash, respectively. Significant differences in visual evoked potential amplitude were obtained between identical medium intensity stimuli depending on the stimulus intensity expected, despite (he constant physical properties of the stimulus. 1 In1 results suggest that a subject's expectancy of certain physical parameters of a stimulus are as important In determining (he resultant visual evoked potential as the actual physical features of the stimulus.     

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.     

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.     

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.     

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.     

Effects of Amplitude-Frequency Characteristics of a Noise-Masked Test Stimulus on the Shapes of Visual Evoked Potentials

Visual evoked potentials produced in response to a reversive checkerboard pattern presented in conditions of additive noise were recorded. Changes induced by noise in both the shapes of evoked potentials and the structure of the test stimulus were compared. The nature of changes in the shapes of evoked potentials was found to correlate with the nature of changes in the amplitude-frequency spectrum of the stimulus. These results support the gestalt psychology point of view that the visual system uses spatial frequency rather than discrete means for describing information. Translated from Rossiiskii Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 94, No. 8, pp. 928–944, August, 2008.     

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。     

Spectral Analysis of the Visual Evoked Potential (VEP): Effects of Stimulus Luminance

Power spectral analysis was performed on the visual evoked potentials (VEPs) of subjects who had participated in an augmenting-reducing study. Six flash luminances were used (0.31, 0.65, 1.25, 2.5, 5.0, and 10.0 fL). EEG recordings were taken from C_z O₁, O₂, T₃, and T₄ scalp locations. Power in six frequency ranges was examined (0–2, 2–6, 6–10, 10–14, 14–18, and 18–22 Hz). Power in the lowest three frequency ranges increased linearly with stimulus luminance at all electrode sites. Power in the highest three ranges increased linearly with luminance at occipital sites only. Power was greater in the left hemisphere than in the right for 18–22 Hz activity recorded at occipital locations. The reverse asymmetry occurred for 6–14 Hz activity recorded at temporal locations. The results suggest that individual differences in stimulus control in EEG recordings taken from scalp locations overlying nonspecific cortex are due primarily to the contributions of higher frequency components of the VEP spectrum. A thalamo-cortical model of stimulus control is described.     

Peak Identification in Visual Evoked Potentials

Waveform patterns evoked by 4 intensities of flash in normal subjects were studied in relation to intersubject variability. Time-frequency distribution curves of all peaks occurring between 11 and 280 msec after flash onset and meeting minimal criteria were obtained from 46 males. These distributions closely corresponded to similar data reported by others for single intensity stimulation. An algorithm was developed which identified in 67 to 100% of instances a single “peak event’ within the time ranges of each of 6 peak distributions. Many peak events appeared and disappeared within the 4 intensity sets of individuals. Latencies were obtained for these peak events. Application of the algorithm to a replicate sample of 29 Ss, which included 8 females, indicated generalizability. Test-retest data on 15 Ss showed its reliability. The data suggest that methodology significantly contributes to the variability of peak identification among subjects. This may be reduced by employing multiple intensities of stimulation.     

Reflection of an Orienting Reflex in the Phases of Evoked Potentials in the Rabbit Visual Cortex and Hippocampus during Substitution of Stimulus Intensity

Experiments on conscious rabbits were performed using the oddball paradigm, in which a rare (deviant) and common (standard) stimuli were of the same color but different intensities. Deviant stimuli were of lesser intensity. Recordings were made of evoked potentials induced by series of uniform deviant stimuli (without using standard stimuli), which were presented at the beginning and end of stimulation. Visual evoked potentials recorded in response to deviant stimuli in the visual cortex and hippocampus showed increases in the amplitudes of phases, shifted towards positivity as compared with responses to standard stimuli and uniform deviant stimuli at the beginning and end of stimulus blocks. Significant changes affected phases P1 and P2 of visual evoked potentials in the cortex and phases P1, N1, and P2 in the hippocampus. The most significant increase in evoked potentials in the cortex was seen for the P2 peak (P130). It is suggested that changes in responses to oddball-deviant stimuli result from an orienting reflex to rare, unexpected stimuli and that the P2 (P130) peak in the cortex is associated with transmission of information regarding changes in the intensity of the light. The amplitude of this peak was shown to be decreased in responses to uniform deviant stimuli at the beginning and end of stimulus blocks. It was also demonstrated that the clearest and most contrasting changes in visual evoked potentials in responses to deviant and standard stimuli were seen with the smallest differences in intensity between these types of stimulus, this reflecting increases in the orienting reflex at threshold differences.     

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.     

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.     

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     

听觉和视觉认知电位P300系列成分的临床电生理学特征

目的:通过对视觉和听觉事件相关电位P300系列成分的研究,了解其临床电生理学特征,从而为临床评价脑认知功能的状态提供依据。方法:使用经典的Odball P300刺激范式对29名志愿者分别进行视觉、听觉刺激,采用64导ERP数据采集分析系统进行数据采集及离线分析。使用SPSS 17.0对所得数据进行统计分析。结果:听觉P1波幅和潜伏期的性别主效应均显著(F=5.44,22.45;P=0.02,0.00),N1波幅的性别和电极部位主效应也均显著(F=4.50,17.85;P=0.04,0.00),P2波幅的电极部位主效应明显(F=17.64,P=0.00);而视觉P1、N1、P2的波幅和潜伏期中,仅P2波幅的电极部位主效应显著(F=3.51,P=0.04)。视觉性P1、N1、P2电位潜伏期明显小于听觉性P1、N1、P2(F=20.45,104.12,107.26;P=0.00),P1和N1的波幅明显低于听觉性P1、N1(F=7.05,133.82;P=0.01,0.00),听觉性N2、P300电位潜伏期明显大于视觉性N2和P300(F=52.43,52.64;P=0.00),视觉N2的波幅也明显高于听觉性N2(F=26.00,P=0.00),但视觉性P300波幅与听觉性P300无差异(F=0.00,P=0.989)。结论:听觉诱发电位具有早期外源性感知电位影响因素较多,P300等晚期内源性认知电位虽然相对稳定,但有波幅较低的缺点;视觉诱发电位早期外源性感知电位同样结果较稳定但波幅低,而晚期内源性认知电位具有波幅高和波形分化好的优点。因此同时检测视觉和听觉P300能够更加准确地评价大脑的认知功能。     

Emitted and Evoked P300 Potentials and Variation in Stimulus Probability

There have been a number of reports of a cerebral potential occurring at about the time of an expected but absent stimulus when absence provided significant information for the subject. This potential consists primarily of a positive peak occurring with a latency of about 300 msec with respect to the time of stimulus absence and is referred to as an emitted P300 potential. It has been conjectured that the emitted P300 is a manifestation of the same process that underlies the evoked P300 . Evidence supporting this hypothesis is provided by demonstrating that both the evoked and emitted P300 potentials are similarly affected by variation in event probability. A paradigm was used in which click presence and absence provided information. The relative probability of click presence and absence was experimentally manipulated. Both evoked and emitted p300 amplitude responded in the same way to event probability, larger for the less frequent event and smaller for the more frequent event.     

脊椎体感诱发电位中的高频抑制

本文介绍了脊椎体感诱发电位的记录装置及记录方法,并在家兔脊椎处体表记录到了体感诱发电位波形。研究了高频脉冲电刺激所引起的神经兴奋对诱发电位刺激所引起的神经兴奋在脊髓发生的影响,证明了高频抑制在脊髓就能发生。同时也阐明了体表记录的脊椎体感诱发电位完全能反映出脊髓中高频抑制这样的电活动,这对理解体表记录的诱发电位所能表示的生理信息量是很有意义的。     

Auditory Evoked Potentials and Divided Attention

In a multi-channel divided attention task, 8 subjects listened to a sequence of tones delivered at one of two stimulation rates and at one of three spatial locations (channels): left ear, right ear, and an apparent position midway between left and right ears. Subjects were instructed to monitor one, two, or all three channels and detect slightly louder target tones in the monitored channel(s). Seven listening conditions were used, three in which subjects monitored one channel and ignored the others, another three in which two channels were simultaneously monitored and the third ignored, and a further condition in which all three channels were monitored. With a high stimulation rate, the N1 component of the vertex evoked potential (latency 70–130 msec) in both attended and unattended channels significantly decreased in amplitude with an increase in the number of monitored channels. At the same time, N1 was significantly larger when a channel was attended than when it was ignored. There were no significant effects under slow stimulation rate conditions. Like N1, target detectability (d') declined with increasing monitoring load only with a fast stimulation rate, but the correspondence between these two measures was not upheld in every condition. The results indicate that with a high “information load” in a multi-channel task, selective attention increases the vertex response in all attended channels, while divided attention decreases the response in both attended and unattended channels, thus suggesting that the N1 component of the auditory evoked potential reflects the apparent division of attentional capacity among competing auditory inputs.     

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.