Effects of rearranged vision on event-related lateralizations of the EEG during pointing

We used event-related lateralizations of the EEG (ERLs) and reversed vision to study visuomotor processing with conflicting proprioceptive and visual information during pointing. Reversed vision decreased arm-related lateralization, probably reflecting the simultaneous activity of left and right arm specific neurons: neurons in the hemisphere contralateral to the observed action were probably activated by visual feedback, neurons in the hemisphere contralateral to the response side by the somatomotor feedback. Lateralization related to the target in parietal cortex increased, indicating that visual to motor transformation in parietal cortex required additional time and resources with reversed vision. A short period of adaptation to an additional lateral displacement of the visual field increased arm-contralateral activity in parietal cortex during the movement. This is in agreement with the, which showed that adaptation to a lateral displacement of the visual field is reflected in increased parietal involvement during pointing.     

Visual search for biological motion: an event-related potential study

To investigate the neural response to detection of biological motion (BM) surrounded by distractors, event-related potentials (ERPs) were recorded. Scrambled motion with the same velocity vector as the BM but randomized initial starting points was used as the distractor. The number of distractors was varied to control the difficulty of the task. The behavioral data showed that the reaction time increased with the number of distractors. Moreover, the ERP results showed that enhanced negativity was elicited at posterior electrodes contralateral to the location of the BM as with the conventional N2pc-like component, which is related to selection of the target. The increment of reaction time indicated that the attentional process is involved in the detection of BM. Furthermore, the ERP waveforms suggest that, even when detection of the target requires form-from-motion processing, similar neural mechanisms to those involved in conventional visual search tasks were employed here.     

Attention modulates auditory pattern memory as indexed by event-related brain potentials

The role of selective attention on auditory pattern processing was investigated using the mismatch negativity, an event-related brain potential component associated with sensory memory. Participants responded to changes in an alternating tone pattern in a designated ear while a similar auditory pattern was presented in the opposite ear. Participants were also presented with the same sequences while reading a book (no response required). In all conditions, changes in the pattern elicited a mismatch negativity (MMN) that peaked at 160–220 ms poststimulus. MMN amplitude varied with attention: the amplitude was higher in response to deviant stimuli presented in the attended ear than to the deviant stimuli presented in the unattended ear or during reading. The results show that selective attention modulates auditory pattern memory.     

Effects of nicotine on visuo-spatial selective attention as indexed by event-related potentials

Nicotine has been shown to specifically reduce reaction times to invalidly cued targets in spatial cueing paradigms. In two experiments, we used event-related potentials to test whether the facilitative effect of nicotine upon the detection of invalidly cued targets is due to a modulation of perceptual processing, as indexed by early attention-related event-related potential components. Furthermore, we assessed whether the effect of nicotine on such unattended stimuli depends upon the use of exogenous or endogenous cues. In both experiments, the electroencephalogram was recorded while non-smokers completed discrimination tasks in Posner-type paradigms after chewing a nicotine polacrilex gum (Nicorette 2 mg) in one session and a placebo gum in another session. Nicotine reduced reaction times to invalidly cued targets when cueing was endogenous. In contrast, no differential effect of nicotine on reaction times was observed when exogenous cues were used. Electrophysiologically, we found a similar attentional modulation of the P1 and N1 components under placebo and nicotine but a differential modulation of later event-related potential components at a frontocentral site. The lack of a drug-dependent modulation of P1 and N1 in the presence of a behavioral effect suggests that the effect of nicotine in endogenous visuo-spatial cueing tasks is not due to an alteration of perceptual processes. Rather, the differential modulation of frontocentral event-related potentials suggests that nicotine acts at later stages of target processing.     

Deficient auditory processing in children with Asperger Syndrome,as indexed by event-related potentials

Conflicting inputs from visual and vestibular afferents produce motion sickness and postural instability. However, the relationship of visual and vestibular inputs to each other remains obscure. In this study, we examined the development of subjective sickness- and balance-related symptoms and objective equilibrium ataxia induced by visual–vestibular conflict (VVC) stimulation using virtual reality. The subjective symptoms evaluated by Graybiel's and Hamilton's criteria got gradually worse during the VVC. The objective postural instability was not observed during the VVC, but it occurred immediately after the VVC. There was a time lag between the subjective symptoms and objective ataxia induced by VVC. Our study suggests that the VVC inputs are processed in different pathways causing subjective autonomic symptoms and postural instability in humans.     

Visual change detection: event-related potentials are dependent on stimulus location in humans

Infrequent colored patterns within sequences of patterns of frequent color elicited a posterior negative event-related potential component only in case of lower half-field stimulation. This negativity in the 140-200 ms latency range is considered as a correlate of automatic visual change detection (visual mismatch negativity, vMMN). Retinotopic prestriate visual areas are suggested to be the generating loci of vMMN.     

Visual event-related potentials and depression in the elderly

Event-related potentials (ERPs) were recorded during a visual discrimination task from nine elderly individuals (mean=68.1 years), diagnosed as having major depressive disorder, and nine age-matched controls (mean=68.0 years). During the task, subjects pressed a switch to targets (the number 9) and ignored background (the number 6) and novel stimuli (random designs). Novel and target stimuli were both interspersed infrequently in the sequence of background stimuli. Scalp electrical activity was recorded from midline frontal (F_z), central (C_z), and parietal (P_z) sites. Depressives were characterized by lengthened response times and increased number of errors across the session. Speed of response was also found to vary directly with clinical status. Additionally, ERP correlates of depression in the elderly were found: N₁ was more prolonged for target than non-target stimuli in the depressed group; P₂ was larger for all conditions; N₂ was uniformly small across the scalp, whereas the controls showed small N₂ amplitudes only at F_z; large P₃s appeared in trials following the novel stimuli in the depressed but not in the control group. These results are interpreted in terms of the symptomatology associated with depression (i.e., distractability, impaired short-term memory or concentration, indecisiveness) and possible age-related changes in the ERP scalp distribution.     

Visual and auditory event-related potentials elicited by linguistic and non-linguistic incongruities

To test the hypothesis that violation of overlearned relations between stimuli in a sequence is critical for eliciting the event-related potential (ERP) N400, we recorded scalp ERPs in sequences where interstimulus relations were either overlearned (sentences or famous songs) or not (geometric figures or scale notes): 25% of the sequences ended with an incongruous stimulus. N400 occurred after incongruous words in sentences only. It seems to index the further processing necessary to specify the nature of the mismatch detected between attended and expected stimuli, when complex information is involved. Earlier components also varied as a function of experimental factors.     

Towards the measurement of event-related EEG activity in real-life working environments

In applied contexts, psychophysiological measures have a long tradition to evaluate the user state. EEG correlates that indicate mechanisms of information processing, however, are hardly accessible since discrete time stamps that are necessary for this approach are commonly not available in natural situations. However, eye blinks may close this gap. Eye blinks are assumed to mark distinct points in information processing, necessary to segment the incoming data stream. By using mobile EEG in a simulated working situation we demonstrate that eye-blink-related potentials provide reliable information about cognitive processing in distinct working environments. During cognitive tasks, an increase in the fronto-central N2 component as well as evoked theta activity can be shown, both indices of enhanced cognitive control. The posterior P3 is reduced during physical tasks (sorting of boxes), probably reflecting the more continuous nature of this task. The data are discussed within a model of dopaminergic modulation of blink activity that involves both task specific aspects like executive control and modulating influences of motivation or fatigue.     

Neural network based classification of non-averaged event-related EEG responses

Classification of non-averaged task-related EEG responses with different types of classifier, including self-organising feature map and learning vector quantiser, K-mean, back-propagation and a combination of the last two, is reported. EEG data are collected from approximately one second periods prior to movement of the right or left index finger. A cue stimulus indicating which hand to use is employed. Feature vectors are formed by concatenating spatial information from different EEG electrodes and temporal information from different time incidents during the planning of hand movement. Power values of the most reactive frequencies within the extended alpha-band (5–16 Hz) are used as features. The features are derived from an autoregressive model fitted to the EEG signals. The performance of the classifiers and their ability to learn and generalise is tested with 200 arbitrarily selected event-related EEG data from a normal subject. Classification accuracies as high as 85–90% are achieved with the methods described here. A comparison of the classifiers is made.     

Visual search of heading direction

When we move along we frequently look around. How quickly and accurately can we gaze in the direction of heading? We studied the temporal aspects of heading perception in expanding and contracting patterns simulating self-motion. Center of flow (CF) eccentricity was 15°. Subjects had to indicate the CF by making a saccade to it. A temporal constraint on the response time was introduced, because stimuli were presented briefly (1 s). On average, subjects needed two saccades to find the CF. Initial saccades covered about 50–60% of the distance between the fixation point and the CF. Subjects underestimated the eccentricity of the CF. The systematic radial error ranged from –2.4° to –4.9°. The systematic tangential error was small (about 0.5°). The variable radial error ranged from 2.7° to 4.6°. We found a relation between saccade onset time and saccade endpoint error. Saccade endpoint error decreased with increasing saccade onset time, suggesting that saccades were often fired before the heading processing had been completed. From the saccade onset times, saccade endpoint errors and an estimate for the saccadic dead time (interval prior to the saccade during which modification is impossible 70 ms), we estimated the heading processing time (HPT 0.43 s). In three out of four subjects, HPT was longer for trials simulating backward movement than for trials simulating forward movement. For each saccade we determined whether it reduced the distance error. The second saccade reduced the error more effectively per time unit than the initial saccade. On the basis of this finding, we suggest that visual processing that occurs during the saccadic dead time of the first saccade is used in the preparation of the second saccade.     

EEG Correlates of the Afterimage of Visual Stimulation

Occipital EEG alpha activity following visual stimuli of varying intensity was studied with particular reference to the visual afterimage. Subjects each received three stimuli of differing intensity under two conditions: with and without reporting of afterimage onset and offset required. A third condition controlled for possible reporting effects on the EEG. Findings indicate that visual afterimages are a significant determinant of the duration of EEG alpha desynchronization following visual stimulation and that where visual stimuli are employed the duration of EEG alpha blocking is unsuitable as an indicator of the OR to such stimulation.     

Spectral analysis of event-related EEG responses during short-term memory performance

Summary Averaged event-related EEG frequency response profiles were generated from normalized spectral analysis data obtained in 2 studies of short-term memory. A continuous performance task was used requiring a keyboard response to targeted letter sequences presented on a video screen at 2 sec. intervals. Seven 2 Hz frequency bands between 5–15 Hz were evaluated. In the first study (n=14) response profiles from control and target stimuli were compared. This analysis disclosed 1) a short latency increase at 5–7 and 7–9 Hz in posterior cortex that was identical in both conditions and was attributed to frequency manifestations of the extrinsic visual evoked response (VEP), 2) a separate long-latency increase of uncertain origin at 5–7 Hz in anterior cortex only in the task condition, and 3) a generalized mid-latency alpha frequency suppression and recovery pattern (event-related desynchronization, or ERD) in all bands during both conditions. The ERD in bands between 9–13 Hz was significantly increased at left central and bilateral parietal cortex during target recall. The second study (n=26) compared good vs. poor performance in the target recall task. Findings disclosed significant differences at 7–9 Hz localized to posterior temporal cortex bilaterally. These differences included reduced magnitude in the VEP component and increased suppression in the ERD component among good performers.This work was supported by the Veterans Administration, the Northrop-Grumman Corporation, and the United States Air Force.     

Visual event-related potentials during movement imagery and the dipole analysis

Visual event-related potentials during an oddball paradigm with movement imagery tasks were recorded in 10 right-handed subjects from 32 scalp electrodes. Rare targets and non-targets elicited early (P3e) and late (P3l) P300 components. In the P3e there was no difference between the rare target and non-target. In the right-imagery task the rare target P3l amplitude was larger than the rare non-target one, whereas the rare non-target P3l amplitude was larger than the rare target one in the left-imagery task. Some of the 4 equivalent current dipole (ECD) sources were located at the subcortical regions, the cerebellum and the cingulate cortex, common to the P3e and the P3l. Moreover, another P3e dipole was localized to the parietal regions, while that of the P3l dipoles to the contralateral premotor cortex. This difference between the P3e and P3l dipoles might reflect two different neural networks related with the transformation of coordinates from visual to motor space.     

Bilateral Differences in Parietal-Occipital EEG Induced by Contingent Visual Feedback

If visual stimulation is made contingent on a unilateral occipital EEG, there is an increase in the control of the alternation between alpha and little or no alpha on the side used to control the visual stimuli as compared to the other side. Previous studies using a visual stimulus for feedback, did not control for the possibility that “feedback” effects might be produced by non-contingent intermittent stimulation. This experiment was a yoked-cortex control for intermittent non-contingent vs intermittent contingent stimulation. The result show that the effects observed are due to contingent stimulation and not merely due to intermittent stimulation.     

虚拟现实沉浸式视觉体验引起脑疲劳的脑电信号分析

虚拟现实可以提供用户关于视、听、体等感官的模拟体验,使其产生沉浸感。随着虚拟现实的迅速普及,佩戴虚拟现实设备引起的脑疲劳问题受到广泛关注。选取16名健康受试者,同步采集观看相同题材传统平面及虚拟现实视频时的脑电信号。首先采用主观问卷对被试者的脑疲劳程度进行分析,使用判断疲劳标准的视屏终端综合症的主观问卷(VDT)和主观疲劳状态量表(SPFS)之后,对比分析两种观看方式引起脑电信号中α、β、θ和δ各波段相对能量以及疲劳因子R值和重心频率的变化差异。结果发现:在VDT主观问卷和SPFS主观量表中,被试观看虚拟视频后的平均分值为0.44±0.22和3.28±1.03,相比观看传统平面视频后的平均分值0.31±0.20和2.26±0.98有显著性增加(P<0.05);在脑电信号的分析中,观看虚拟现实视频后,T3电极位置的α波段相对能量显著减少(观看前后分别为0.249±0.007和0.234±0.005,P<0.05),δ波段相对能量显著性增加(观看前后分别为0.295±0.012和0.314±0.007, P<0.05),重心频率显著性降低(观看前后分别为(7.545±0.950)Hz和(3.717±0.398)Hz, P<0.05),并且这些参数的变化趋势与观看传统平面视频后的参数变化显著不同,呈现出相反的变化趋势;观看虚拟现实视频过程中,脑电信号中的α波段和β波段变化明显,左右后颞叶区和顶叶区到枕叶区中的α波相对能量随时间变化波动下降,β波相对能量随时间先增加后减少,有显著性差异(P<0.05)。相比观看传统平面视频,观看虚拟现实视频更容易从主观感受上产生脑疲劳,脑电信号中特征频段的节律活动变化可以为客观评估虚拟现实引起的脑疲劳提供理论依据。     

Visual stimulus locking of EEG is modulated by temporal congruency of auditory stimuli

Disparate sensory streams originating from a common underlying event share similar dynamics, and this plays an important part in multisensory integration. Here we investigate audiovisual binding by presenting continuously changing, temporally congruent and incongruent stimuli. Recorded EEG signals are used to quantify spectrotemporal and waveform locking of neural activity to stimulus dynamics. Spectrotemporal analysis reveals locking to visual stimulus dynamics in both a broad alpha and the beta band. The properties of these effects suggest they are a correlate of bottom-up processing in the visual system. Waveform locking reveals two cortically distinct processes that lock to visual stimulus dynamics with differing topographies and time lags relative to the stimuli. Most importantly, these are modulated in strength by the congruency of an accompanying auditory stream. In addition, the waveform locking found at occipital electrodes shows an increase over stimulus duration for visual and congruent audiovisual stimuli. Hence we argue that these effects reflect audiovisual interaction. We thus propose that spectrotemporal and waveform locking reflect different mechanisms involved in the processing of dynamic audiovisual stimuli.     

Golf putt outcomes are predicted by sensorimotor cerebral EEG rhythms

It is not known whether frontal cerebral rhythms of the two hemispheres are implicated in fine motor control and balance. To address this issue, electroencephalographic (EEG) and stabilometric recordings were simultaneously performed in 12 right-handed expert golfers. The subjects were asked to stand upright on a stabilometric force platform placed at a golf green simulator while playing about 100 golf putts. Balance during the putts was indexed by body sway area. Cortical activity was indexed by the power reduction in spatially enhanced alpha (8-12 Hz) and beta (13-30 Hz) rhythms during movement, referred to as the pre-movement period. It was found that the body sway area displayed similar values in the successful and unsuccessful putts. In contrast, the high-frequency alpha power (about 10-12 Hz) was smaller in amplitude in the successful than in the unsuccessful putts over the frontal midline and the arm and hand region of the right primary sensorimotor area; the stronger the reduction of the alpha power, the smaller the error of the unsuccessful putts (i.e. distance from the hole). These results indicate that high-frequency alpha rhythms over associative, premotor and non-dominant primary sensorimotor areas subserve motor control and are predictive of the golfer's performance.     

Visual awareness of low-contrast stimuli is reflected in event-related brain potentials

Visual awareness was studied in 11 subjects by using coherent and scrambled objects as stimuli. The stimuli were presented near the subjective perceptual threshold. Explicitly recognized stimuli elicited a specific negative ERP deflection peaking at 460 ms. Our reaction time experiment suggests that this visual awareness negativity (VAN) is similar to that found previously at a shorter latency. We propose that VAN might reflect the exact moment of becoming aware of the task-relevant stimulus properties and provide an online marker of the temporal dynamics of visual awareness.