人类颞叶皮层与视、听信息加工:Ⅱ.左颞叶癫痫病人的脑事件相关电位

记录7名左颞叶癫痫病人和9名正常人在四种实验条件下的事件相关电位：（1）听觉脑子诱发电位,（2）红色闪光刺激,（3）陌生人嗓音识别,（4）陌生人面孔识别。实验结果发现,两组被试在视觉信息加工中无差异,在嗓音识别中病人的N150和P300波潜伏期大于正常人,表明其复杂听觉认知功能受到影响．红色闪光刺激和噪音识别条件下,病人的P100波幅大于正常人,说明病人对强刺激的物理强度有较高的反应水平,不易习惯化。     

Differential effects of inferior temporal cortex lesions upon visual and auditory-evoked potentials in the amygdala of the squirrel monkey (Saimiri sciureus)

Visual-evoked potentials (VEPs) and auditory-evoked potentials (AEPs) were elicited from amygdala nuclei and inferior temporal (IT) cortex in chaired, alert squirrel monkeys to diffuse flash and click stimuli. VEPs were recorded from electrodes placed in basalis lateralis amygdalae (BLA) and basalis medialis amygdalae (BMA) while AEPs could also be obtained from additional electrode sites in basalis accessorius medialis (BAM), centralis amygdalae (CeA), and lateralis amygdalae (LA). The amygdala-evoked potentials resulting from stimulation of the two modalities were similar in terms of component configuration. AEPs recorded from the IT cortex had shorter latencies than the amygdala VEPs that were recorded. Both modalities of stimulation elicited potentials with shorter onset latencies in the amygdala than those recorded from the surface of IT cortex. Bilateral ablation of the IT cortex eliminated VEPs recorded from the BMA but not the BLA amygdala region. AEPs recorded from BMA as well as other amygdala areas were not consistently affected by these IT cortical ablations.     

Visual adaptation to a spatial contrast enhances visual evoked potentials

The effects of adaptation to the visual contrast of a counterphase grating were studied with visual evoked potentials (VEPs). The spatial frequency of the grating was 4 cpd, and its temporal frequency was 4 or 12 Hz. Steady-state VEPs were analyzed through an FFT (fast Fourier transform) algorithm. In the first experiment, contrast thresholds rose strongly just after the end of adaptation and declined regularly over time. The VEPs recorded in the medio-occipital lead showed an initial decrease in amplitude after adaptation, followed by an enhancement well above the preadaptation level and then a return to that level. The paradoxical enhancement of the VEP was found at both high and low contrast in both the medio-occipital lead and the right temporal lead of a right-handed subject. The left temporal leads showed a VEP enhancement at high contrast and a decline at a low value.     

Visual evoked potentials to the geometric forms in the randomized presentation

Two outlined geometric figures, an equilateral triangle and a circle, of equal contour length, were randomly presented at a fixed position in the lower or upper part of the visual field (LVF and UVF). Transient visual evoked potentials (VEPs) were recorded monopolarly from the inion (I), 5, 10, 15 cm above it (I5, I10, I15) and Fz, for 12 subjects. Grand-averaged VEPs were computed. A negative (N) wave (averaged peak latency 155 ms) was identified in the LVF and a positive (P) wave (130 ms) in the UVF. In the LVF, the N amplitude of the triangle was significantly larger than that of the circle at I5 and I. Regarding the P wave in the UVF, the triangle was of a significantly longer latency than the circle at I15, I10 and I5. The enhancement of the N amplitude for the triangle in the LVF is not attributable to the arousal caused by the preparatory state for the figure, since the subject could not predict the figure to be presented next or its position.     

Hemispheric Asymmetry in Transient Visual Evoked Potentials Induced by the Spatial Factor of the Stimulation

In order to enhance the effect of spatial frequency on the hemispheric asymmetry of visual evoked potentials (VEP), the response amplitudes to ON-OFF modulated gratings were compared with the responses to pattern reversal stimulation. Sinusoidal gratings of different spatial frequencies were presented to six righthanders. VEPs were recorded from temporal leads on each hemisphere. In the left hemisphere, the amplitude was constant for the two modes of presentation and independent of spatial frequency. In the right hemisphere, the response amplitude was larger to the ONSET stage of ON-OFF stimulation than to reversal and presented the characteristic spatial frequency tuning curve. This asymmetry is assumed to reflect a difference in sensitivity of the two hemispheres to the spatiotemporal characteristics of the stimulus. The relevance of these findings is discussed in relation to the other hemispheric specialization models.     

Effects of angularity of the figures with sharp and round corners on visual evoked potentials

Following a study in which equilateral triangles elicited larger visual evoked potentials (VEPs) than either squares or circles, we examined the effect of single-line angular figures with a sharp or a round corner at angles of 45°, 90°, 135° or 180°. VEPs were recorded monopolarly at four locations on the midline of scalp for 10 subjects, while the figure was tachiscopically presented to the lower visual field. Subtracted waves were obtained between figure and control (blank) conditions. N1 (peak latency 135–142 ms) and P2 (235–237 ms) waves were identifiable. N1 amplitude tended to decrease as a function of angularity, irrespective of orientation (angle pointing up or down). The effect of the sharpness/roundness of the corner was much smaller than that of its angularity. These findings suggest that the greater VEP response with triangles than with squares and circles may be attributable to the acute angularity of triangles. Related cortical processes and VEP components are also discussed.     

Binocular summation in the evoked cortical potential

Computer-averaged evoked potentials were recorded from six subjects presented with flashes under conditions of binocular and monocular viewing, with a device fitted over each eye to produce ganzfeld conditions. Tests were run with red light and with blue. Analysis of the evoked potentials indicates a substantially larger amplitude with binocular stimulation.     

Binocular interaction of orientation and spatial frequency channels: Evoked potentials and observer sensitivity

The interaction between size and orientation feature processing in the human visual system was investigated. Both observer sensitivity (d’ss) and the visual evoked potential (VEP) to test gratings flashed to one eye were investigated as a function of the nature of a continuously presented suppressing grating viewed either by that same eye or the opposite eye. The test and suppressing gratings were varied both in bar width (9′ss vs. 36′ss) and orientation (vertical vs. horizontal). The continuous grating intra- and interocularly suppressed the monocular VEPs to the flashed grating, the specificity of the suppression depending on the latency at which VEP amplitude was measured. VEP amplitude measured at early latencies (100–125 msec) was suppressed primarily when the flashed and continuous gratings were the same orientation, regardless of size. Starting at about 200 msec, and thereafter, VEP amplitudes were suppressed when the continuous bars were either the same orientationor size as the flashed bars. Late latencies, starting at 220 msec, and thereafter, were suppressed primarily when the bars in the two gratings were the same orientation and size. The reduction in observer sensitivity (d′ss) paralleled the changes found in the late VEP measures. These effects were evident under both the intraocular and interocular suppressing conditions. This pattern of VEP suppression, measured across eight points in the VEP waveform, was interpreted as indicating the existence of a sequence of channels that are specific first to a particular grating orientation, then to either a particular grating spatial frequency or orientation, and finally to the conjunction of a particular orientation and spatial frequency. Both sequential and parallel feature processing appears to take place in the human visual cortex, with grating orientation being encoded earlier than grating size.     

The orientation anisotropy and orientation constancy: a visual evoked potential study.

Two experiments were conducted on the orientation anisotropy in which averaged visual evoked potentials (VEPs) were recorded from the occipital scalp. The first experiment confirmed the findings of Maffei and Campbell (1970) that obliquely oriented gratings alternated back and forth produced smaller-amplitude VEPs than when the gratings were oriented horizontally or vertically. Since no asymmetry was found in VEPs produced by a Julesz figure presented under identical conditions, it was concluded that direction of displacement could not have been contributing to the effect. In a second experiment head tilt of the subject was manipulated together with grating orientation and the results indicated that the orientation anisotropy is retinally rather than gravitationally referenced. It was concluded that the site of orientation constancy is located either at higher levels of the primary visual system or in the second visual system.     

Differentiation of retinal and nonretinal contributions to averaged evoked responses obtained with electrodes placed near the eyes

Recent visual evoked potential (VEP) studies suggest that during sustained voluntary attention, irrelevant or unattended visual stimuli may be filtered precortically. Testing of this hypothesis in humans requires knowledge of the origin of specific components of the VEP that are affected by selective attention. This study describes techniques and procedures for distinguishing between retinal and nonretinal components of VEPs recorded from electrodes placed strategically around the eyes and on the forehead. By visually stimulating one eye at a time while recording simultaneously from both, and by stimulating a given retinal area with the eyes fixated on the target at different angular deviations from the normal line of regard, components of the VEPs around the eyes can be distinguished as of retinal or nonretinal origin. The results are discussed in terms of volume conduction theory.     

Time-till-breakdown and scalp electrical potential maps of long-range apparent motion

A series of psychophysical and electrophysiological experiments is reported using the apparent motion (AM) breakdown effect. Breakdown describes an effect in AM in which, during continuous viewing, the percept of smooth motion of a single stimulus alternates with the percept of two discrete alternating stimuli. Visual evoked potentials (VEPs) were recorded during periods of motion or breakdown (“nonmotion”) in horizontal and vertical displays. VEPs were compared with synthetic VEPs (“composite-flash”) produced by adding VEPs to each element of the display recorded in isolation. Subtraction of VEPs was used in an attempt to compare the electrical responses with the processing of information relating to the form of the stimulus, subthreshold motion processing, and suprathreshold motion processing. The results, presented as scalp electrical potential distribution maps, were interpreted as consistent with a central adaptation process underlying the breakdown effect. The results also indicated that the hemispheric asymmetries in AM VEPs described by Manning, Finlay, and Fenelon (1988) were most likely due to the position of the stimuli in the visual field, rather than as a lateralization of motion processes per se. The results also provided evidence that the subthreshold and suprathreshold motion responses to the display were the product of different populations of motion units.     

Visual evoked potentials elicited by subjective contour figures

In order to investigate the relationship between the appearance of illusory figures and the wave form of visual evoked potentials (VEPs), 8 different visual pattern stimuli were presented to 8 normal subjects. Four of the stimuli (experimental stimuli) produced subjective figures and contours (squares and discs). The 4 other stimuli (reference stimuli), although equal to the experimental stimuli in the amount of physical energy, did not produce the illusion of squares or discs. Electrodes were placed on the scalp at central and occipital locations. Three prominent peaks in the occipital record were observed in all subjects. An amplitude difference of VEP N180 (N2) between the subjective figures and the reference stimuli was found in the values for each subject. Enhancement of the VEP of the illusory figure stimuli was observed for a specific component (N2), whereas the amplitude values at the central components and the occipital P120 (P2) and P280 (P3) were almost the same as the reference values. The VEP (N2 component) amplitude enhancement at the occipital area for subjective figure stimuli suggests that illusory contour formation takes place at higher levels in the visual system. This was known from experiments using dichoptic presentation.     

Visual Evoked Potentials to Geometric Forms: Effects of Spatial Orientation

Five outlined geometric figures of equal contour length were presented monocularly below the fixation point (FP); an upright equilateral triangle (upright triangle), an inverted equilateral triangle (inverted triangle), an upright square (square), a 45°-tilted square (diamond) and a circle. The angular separation between FP and the top of the figures was held constant. Transient visual evoked potentials (VEPs) were recorded monopolarly from inion, 4, 7, 10 cm above it (l, l4, l7, l10) and Cz for ten subjects. The grand-averaged subtracted waves were obtained between the figure and blank (control) conditions. N1 (mean peak latency: 155 ms) and P2 (240 ms) waves were identified. ANOVAs were conducted for the latency and amplitude values. Main results were as follows: On the N1 amplitude at l4 and l, the upright triangle, inverted triangle and diamond figures evoked significantly larger responses than did the square and the circle. However, no significant difference was found among the former three figures. These findings on the N1 amplitude suggest that the effect of a triangle is orientation-free and that of a square is orientation-bound.     

Changes in spontaneous slow potentials and visually (flash) evoked potentials in response to stimuli with no performance implication]

The influence of spontaneous slow potential shifts (SPSs) on visual (flash-)evoked potentials (VEPs) was studied. Eighteen subjects received 100 flashes. The sequence of interstimulus-intervals (ISIs) was pseudo-randomized. ISI-durations were 3, 5, 7, 9 or 11 seconds. EEG was recorded from Fz, Cz, Pz and Oz with linked-mastoids as reference. EEG was EOG-corrected and VEPs were calculated for preceding positive SPSs. Averaging was done for local SPSs; VEP pairings as well as VEPs were calculated over occipital SPS-polarities. Results showed an influence of SPSs on VEP-amplitudes. Differences in amplitudes were interpreted with the 'activation-correction'-hypothesis and with the 'ceiling'-hypothesis. Negative SPSs were followed by smaller negative peaks, and positive SPSs were followed by smaller positive peak-amplitudes. Differences in latencies of N145-P300 peak-to-peak amplitudes after SPSs of different polarity were explained with the threshold-regulation hypothesis. Spectral-analysis were done for SPS-data. There were only poor effects, showing increased parietal alpha 2-power after negative SPSs.     

Visual evoked potentials and selective attention to points in space

Visual evoked potentials (VEPs) were recorded to sequences of flashes delivered to the right and left visual fields while subjects responded promptly to designated stimuli in one field at a time (focused attention), in both fields at once (divided attention), or to neither field (passive). Three stimulus schedules were used: the first was a replication of a previous study (Eason, Harter, & White, 1969) where left- and right-field flashes were delivered quasi-independently, while in the other two the flashes were delivered to the two fields in random order (Bernoulli sequence). VEPs to attended-field stimuli were enhanced at both occipital (O₂) and central (C_z) recording sites under all stimulus sequences, but different components were affected at the two scalp sites. It was suggested that the VEP at O₂ may reflect modality-specific processing events, while the response at C_z, like its auditory homologue, may index more general aspects of selective attention.     

C1调制效应的理论评述及影响因素

C1成分是对视觉刺激最早做出反应的视皮层诱发电位,C1调制效应是指注意等因素能够影响C1振幅的现象.以往多数研究未观察到注意等因素对C1振幅的影响,仅发现注意等因素对晚于C1的P1与N1等成分存在调制作用,并有研究者据此提出延迟反馈假说.但近期研究提示,注意等因素可能会对C1成分产生影响,提示初级视皮层(V1)可能在视觉信息加工初期直接受注意调制.目前,对C1调制效应的影响因素尚未完全确定,知觉学习、负载等因素的作用尚待考察.未来研究需进一步明确C1调制效应的影响因素及实验条件.     

Neural correlates of transformational apparent motion

Transformational apparent motion (TAM) arises when a shape that is abruptly flashed on and off next to a static shape of similar color or texture appears as a protrusion that extends and retracts smoothly from the static object. Here we report that the strength of the TAM percept can be predicted from the waveform of visual evoked potentials (VEPs) measured while observers rated their percepts. The VEPs at pattern onset and offset are maximally symmetric when the static inducer and the flashing patches of the display are of the same contrast. VEP symmetry is affected by how the two patches can be matched as a single surface and may reflect the relative contribution of different motion and object detection systems in visual cortex.     

Relationships between movement initiation times and movement-related cortical potentials in Parkinson's disease

Movement-related cortical potentials recorded from the scalp reveal increasing cortical activity occurring prior to voluntary movement. Studies of set-related cortical activity recorded from single neurones within premotor and supplementary motor areas in monkeys suggest that such premovement activity may act to prime activity of appropriate motor units in readiness to move, thereby facilitating the movement response. Such a role of early stage premovement activity in movement-related cortical potentials was investigated by examining the relationship between premovement cortical activity and movement initiation or reaction times. Parkinson's disease and control subjects performed a simple button-pressing reaction time task and individual movement-related potentials were averaged for responses with short compared with long reaction times. For Parkinson's disease subjects but not for the control subjects, early stage premovement cortical activity was significantly increased in amplitude for faster reaction times, indicating that there is indeed a relationship between premovement cortical activity amplitude and movement initiation or reaction times. In support of studies of set-related cortical activity in monkeys, it is therefore suggested that early stage premovement activity reflects the priming of appropriate motor units of primary motor cortex, thereby reducing movement initiation or reaction times.PsycINFO classification: 2330; 2520; 2530     

Planning of saccadic eye movements

Most theories of the programming of saccadic eye movements (SEM) agree that direction and amplitude are the two basic dimensions that are under control when an intended movement is planned. But they disagree over whether these two basic parameters are specified separately or in conjunction. We measured saccadic reaction time (SRT) in a situation where information about amplitude and direction of the required movement became available at different moments in time. The delivery of information about either direction or amplitude prior to another reduced duration of SRT demonstrated that direction and amplitude were specified separately rather than in conjunction or in a fixed serial order. All changes in SRT were quantitatively explained by a simple growth-process (accumulator) model according to which a movement starts when two separate neural activities, embodying the direction and amplitude programming, have both reached a constant threshold level of activity. Although, in isolation, the amplitude programming was faster than the direction programming, the situation reversed when two dimensions had to be specified at the same time. We conclude that beside the motor maps representing the desired final position of the eye or a fixed movement vector, another processing stage is required in which the basic parameters of SEM, direction and amplitude, are clearly separable.     

Corners,receptive fields,and visually evoked cortical potentials

Alternating stimuli with herringbone patterns were used to obtain visually evoked cortical potentials (VECPs) from three human Ss. Two sets of stimulus patterns were used, one with sharp corners and one with the corners rounded off. Each set ranged in angularity from 180 to 45 deg in 45-deg steps. Results showed that: (a)VECP response amplitude was greatest for the 90-deg-corner pattern, (b) response amplitude was greater for the 45-deg-corner pattern than for the 135-deg-corner pattern, and (c) cornered and rounded patterns evoked responses of greater amplitude than those evoked by the straight (180-deg) patterns. Also, the peak latency of responses to cornered patterns was shorter than that of responses to rounded and straight patterns.