Hemispheric asymmetry in visual discrimination and memory: ERP evidence for the spatial frequency hypothesis

Event related potentials (ERPs) were recorded during delayed discrimination of simple spatial frequency gratings in the high and low frequency bands. Analyses of the waveforms N170, P220, N310, P400, and slow wave (SW) indicated significant and regionally specific interaction of spatial frequency and hemisphere for N170 amplitude. This interaction was independent of memory conditions, and appeared to be in the opposite direction of what is predicted by the spatial frequency model of hemispheric asymmetry. Additional interactions between spatial frequency and hemisphere were observed for N310 in the encoding process (reference stimulus) and for SW in the retrieval process (test stimulus). The general hypothesis of an interaction of spatial frequency and hemisphere in visual cognition is supported, but the findings indicate caution in interpreting an increase in physiological measures as an indication of more efficient brain processing. Moreover, several stages of information processing may contribute to the asymmetry observed in behavioral studies, and hemispheric balance may change dynamically during the time course of processing.     

Aiming for the bull's eye: Preparing for throwing investigated with event-related brain potentials

We explored the feasibility of investigating complex goal-directed actions with event-related brain potentials by studying the aiming phase of throwing. A virtual reality environment was set up, allowing aimed throws at distant targets, with participants standing upright and moving relatively unrestrained. After a separate practice session, the contingent negative variation (CNV) was measured during preparation for a simple button release, unaimed throws, and aimed throws at targets of two levels of difficulty. Consistent with expectations, CNV amplitude was larger for all throwing conditions compared to button release. It further increased with task difficulty in the aimed throwing conditions, reflecting the increasing motor programming demands for more difficult goal-directed actions. Therefore, investigating throwing as an instance of complex goal-directed action with ERPs is feasible, opening interesting perspectives for future research.     

The role of arousal in the preparation for voluntary movement

Planning and readiness for action are associated with pre-movement brain activity reflected in the readiness potential (RP). Previous research suggests that RP is affected by higher-order cognitive functions. The present study investigated the relationship between arousal and RP. Twenty participants performed a RP paradigm in which they executed self-paced movements approximately every 4-5 s. Participants’ arousal level was directly manipulated through interaction with the experimenter during the rest breaks preceding the movement task. Skin conductance level (SCL) differed between arousal conditions, indicating that the arousal manipulation was effective. RP was significantly higher under the low arousal than the high arousal condition. This arousal effect also changed depending on whether RP was measured at overall high or low levels of arousal. Our data indicate that arousal does not directly activate structures underlying action preparation. We suggest that the arousal effect may be mediated by the attentional resources allocated to the movement.     

脑电源的空间谱及其在视觉空间选择性注意研究中的应用

研究了三层球模型中脑电源的空间谱和它的初步应用。以基于等效分布偶极源的球谐谱反演方法为基础 ,提出了新的纬向谱 S(l)和经向谱 S(m)作为脑电源的空间谱刻画 ,然后应用于视觉空间选择注意的诱发脑电(ERP)数据。应用研究发现 ,在纬向谱 S(l)和经向谱 S(m )的时变曲线上 ,介于 10 0～ 2 0 0 ms间的成分的延时和幅度变化能较好地反映出注意的影响 ,从而显示了纬向谱和经向谱在认知科学研究中的应用价值     

Movement-related potentials preceding voluntary movement are modulated by the mode of movement selection

In two experiments movement-related cortical potentials preceding voluntary movement were recorded. In experiment 1, subjects performed four motor tasks involving joystick movements. The four tasks differed in complexity (single vs sequential movements) and in the mode of movement selection, i.e., whether a movement or movement sequence was made in fixed or in self-determined directions. The choice of these tasks was based, firstly, on previous electrophysiological studies suggesting an effect of task-complexity on the amplitude of the readiness potential (RP) and, secondly, on previous positron emission tomography (PET) studies showing that activity of the supplementary motor area (SMA) is influenced by the mode of movement selection. The results show that, for single movements, RP amplitude is higher preceding freely selected movements than preceding movements in a fixed direction. In experiment 2 this effect was replicated using button presses instead of joystick movements. The results converge with PET evidence obtained in similar tasks and establish that the RP is modulated by the mode of movement selection. This modulation is probably related to differential involvement of the SMA.     

Slow EEG potentials preceding self-paced plantar flexions of hand and foot

Slow EEG shifts preceding voluntary self-paced plantar flexions of hand and foot were studied in five healthy right handed subjects. The EEG was recorded from a coronal electrode chain at the central areas. The movements were preceded by slow negative shifts beginning even as early as one second before the movement and culminating in fast slopes during the early EMG activity at the onset of the movements. The EEG shifts preceding hand and foot movements were differently distributed over the scalp: hand movements were preceded by contralaterally maximal shifts a few hundred milliseconds before the movement, whereas the potential distributions preceding foot movements were symmetrical or ipsilaterally dominant. It is suggested that the differences in the scalp distributions are due to the different orientation of the current dipoles at the cortical motor areas of hand and foot     

Unintentional covert motor activations predict behavioral effects: Multilevel modeling of trial‐level electrophysiological motor activations

The present experiment measured an EEG indicator of motor cortex activation, the lateralized readiness potential (LRP), while participants performed a speeded category classification task. The LRP data showed that visually masked words triggered covert motor activations. These prime‐induced motor activations preceded motor activations by subsequent (to‐be‐classified) visible target words. Multilevel statistical analyses of trial‐level effects, applied here for the first time with electrophysiological data, revealed that accuracy and latency of classifying target words was affected by both (a) covert motor activations caused by visually masked primes and (b) spontaneous fluctuations in covert motor activations. Spontaneous covert motor fluctuations were unobserved with standard subject‐level (multi‐trial) analyses of grand‐averaged LRPs, highlighting the utility of multilevel modeling of trial‐level effects.     

Emotional content modulates response inhibition and perceptual processing

In this study, event‐related potentials were used to investigate the effect of emotion on response inhibition. Participants performed an emotional go/no‐go task that required responses to human faces associated with a “go” valence (i.e., emotional, neutral) and response inhibition to human faces associated with a “no‐go” valence. Emotional content impaired response inhibition, as evidenced by decreased response accuracy and N2 amplitudes in no‐go trials. More importantly, emotional expressions elicited larger N170 amplitudes than neutral expressions, and this effect was larger in no‐go than in go trials, indicating that the perceptual processing of emotional expression had priority in inhibitory trials. In no‐go trials, correlation analysis showed that increased N170 amplitudes were associated with decreased N2 amplitudes. Taken together, our findings suggest that emotional content impairs response inhibition due to the prioritization of emotional content processing.     

Effect of the irrelevant location of the response signal on choice reaction time: an electromyographic study in humans.

Choice reaction time (RT) is shorter when the stimulus corresponds spatially to the response than when the stimulus does not, even when the stimulus location is irrelevant to the task. We used electromyographic measures to document that this effect is the result of a response conflict. The activity of the prime movers of two alternative responses was recorded during the performance of a visual RT task in which the irrelevant spatial correspondence between the stimuli and the responses was varied. Only the premotor component of RT was affected by the stimulus-response correspondence. Correct trials were distinguished according to whether or not the activation of the prime mover involved in the required response was preceded by an activation of the prime mover involved in the alternative response. Double muscular activation trials were more numerous for noncorresponding than for corresponding stimulus-response associations. Furthermore, these trials yielded longer RTs than the single muscular activation trials.     

Age‐related changes in ERP correlates of visuospatial and motor processes

Although previous ERP studies have demonstrated slowing of visuospatial and motor processes with age, such studies frequently included only young and elderly participants, and lacked information about age‐related changes across the adult lifespan. The present research used a Simon task with two irrelevant dimensions (position and direction of an arrow) to study visuospatial (N2 posterior contralateral, N2pc) and motor (response‐locked lateralized readiness potential, LRP‐r) processes in young, middle‐aged, and elderly adults. The reaction time and motor execution stage (LRP‐r) increased gradually with age, while visuospatial processes (N2pc latency) were similarly delayed in the older groups. No age‐related increase in interference was observed, probably related to a delay in processing the symbolic meaning of the direction in older groups, which was consistent with age‐related differences in distributional analyses and N2pc amplitude modulations.     

Conditions for view invariance in the neural response to visual symmetry

Symmetry detection is slow when patterns are distorted by perspective, perhaps due to a time‐consuming normalization process, or because discrimination relies on remaining weaker regularities in the retinal image. Participants viewed symmetrical or random dot patterns, either in a frontoparallel or slanted plane (±50°). One group performed a color discrimination task, while another performed a regularity discrimination task. We measured a symmetry‐related event‐related potential (ERP), beginning around 300 ms. During color discrimination, the ERP was reduced for slanted patterns, indexing only the remaining retinal structure. During regularity discrimination, the same ERP was view invariant, and identical for frontoparallel or slanted presentation. We conclude that normalization occurs rapidly during active symmetry discrimination, while symmetry‐sensitive networks respond only to regularity in the retinal image when people are attending to other features.     

Perceptual load modifies processing of unattended stimuli both in the presence and absence of attended stimuli

This study explored effects of perceptual load on stimulus processing in the presence and absence of an attended stimulus. Participants were presented with a bilateral or unilateral display and asked to perform a discrimination task at either low or high perceptual load. Electrophysiological responses to stimuli were then compared at the P100 and N100. As in previous studies, perceptual load modified processing of attended and unattended stimuli seen at occipital scalp sites. Moreover, perceptual load modulated attention effects when the attended stimulus was presented at high perceptual load for unilateral displays. However, this was not true when the attended and unattended stimulus appeared simultaneously in bilateral displays. Instead, only a main effect of perceptual load was found. Reductions in processing contralateral to the unattended stimulus at the N100 provide support for Lavie's (1995) theory of selective attention.     

Waiting in readiness: Gating in attention and motor preparation

In this paper the similarities in the structural and functional organization of motor preparation and attension are discussed. A crucial structure in this organization is the thalamus, a complex of sensory and motor nuclei that transmits information from subcortical origins to the cortex. For the most part, the thalamus is overlapped by the nucleus reticularis, which has a local inhibitory influence on the underlying nuclei. This serves as a gating mechanism for the transmission of sensory information to the cortex. Skinner and Yingling (1977) have provided arguments in favor of a frontal control in the gating of sensory information. The present paper extends their suggestions to the motor system: a similar gating mechanism for the transmission of subcortical motor information to the cortex is hypothesized, also under frontal control. Slow potentials recorded during motor preparation and attention for an upcoming stimulus show a different distribution over the scalp. These distributions are interpreted as an indication of which thalamic gates are open to transmit information to the cortex. Probe responses (spinal reflexes, evoked potentials, and the startle reflex) can also be used to investigate which thalamocortical gates are open under certain experimental conditions. It is concluded that the sensory and motor input to the cortex are subjected to a similar control mechanism.     

癫（疒/间）大鼠听觉事件相关电位P3样波的研究

目的 :研究正常大鼠听觉事件相关电位 (ERP)的P3样波 (下简称听觉P3样电位 )特点及癫大鼠P3样电位变化。方法 :癫组大鼠每日予戊四氮腹腔注射 ,直至达到点燃标准 ;正常组大鼠每日注射生理盐水。记录并分析两组动物听觉ERP特点及其P3样电位的变化。结果 :①在大鼠可发现与人类听觉ERP的P3电位波形、潜伏期及反应特点相似的ERP ;②癫大鼠与正常大鼠相比 ,其P3样电位的听觉ERP的P3电位潜伏期明显延长 (P <0 0 1) ,波幅相对降低 (P >0 0 5 ) ,波形分化不清。结论 :P3样电位的产生具有跨越种属的相似性 ,提示P3样电位在哺乳动物中可能具有共同的神经回路     

The absence of a visual stimulus can trigger task-set-independent attentional capture

We investigated whether the absence of one item in a regularly spaced visual array (gap cue) captures attention in a task-set-independent fashion. Participants searched for a large target among medium-size distractors (size task) or a red target among gray distractors (color task). Target arrays were preceded by uninformative cue arrays that contained a color singleton or a gap cue. The N2pc component was measured as an index of attentional capture. Color singleton cues captured attention only in the color task, but gap cues captured attention in both tasks. For cue arrays containing a color singleton and a gap cue on opposite sides, an N2pc was triggered by the color singleton in the color task. The absence of an item in a regular array triggered task-set-independent attentional capture when it was the only unique display feature, but not when a competing set-matching singleton was simultaneously present.     

After the P3: late executive processes in stimulus categorization

Two experiments examined the hypothesis that dual systems of stimulus evaluation for categorization can be observed in event-related potentials: one whose duration is indexed by the latency of the P3 component, and a second evident in a later frontal potential. Subjects categorized artificial animals by a "two out of three" rule. Stimuli with two visual features of their own category and one feature of a different category (i.e., near the boundary between categories) elicited very prolonged reaction times as compared to stimuli with three features from a single category. This response time (RT) delay was not accompanied by a delayed P3, suggesting that the P3 indexed only a first pass of stimulus evaluation. The near-boundary stimuli elicited more positive potentials than far-boundary stimuli at prefrontal and frontotemporal sites, suggesting that a secondary stage of stimulus evaluation was triggered when detection of single features or simple conjunctions was insufficient to support a correct decision. The frontal potential that was sensitive to categorization difficulty was of opposite polarity to frontal potentials previously observed in manipulations of working memory. The roles of frontal executive processes in categorization and memory tasks are discussed.     

Mental rotation strategies reflected in event‐related (de)synchronization of alpha and mu power

During a mental rotation task of hands, participants mentally rotate their hand into the orientation of the shown hand. These mental movements are subject to the body's biomechanical constraints. In this study, we investigated whether the involvement of motor processes during the mental rotation process, as reflected in mu‐power desynchronization, is also influenced by one's movement capabilities. We performed an EEG study and used a delayed response mental rotation task of hands to examine the event‐related desynchronization differences between movements that are biomechanically easy and difficult to perform. Our results show an increase in event‐related desynchronization of the mu power for biomechanically easy compared to difficult‐to‐adopt postures. These findings provide further evidence for the notion that motor simulations can only be performed for movements that can already be performed overtly.     

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.     

Role of the human motor cortex in rapid motor learning

Recent studies suggest that the human primary motor cortex (M1) is involved in motor learning, but the nature of that involvement is not clear. Here, learning-related changes in M1 excitability were studied with transcranial magnetic stimulation (TMS) while na subjects practiced either a ballistic or a ramp pinch task to the 0.5-Hz beat of a metronome. Subjects rapidly learned to optimize ballistic contractions as indicated by a significant increase in peak pinch acceleration and peak force after the 60-min practice epoch. The increase in force and acceleration was associated with an increase in motor evoked potential (MEP) amplitude in a muscle involved in the training (flexor policis brevis) but not in a muscle unrelated to the task (abductor digiti minimi). MEPs returned to their baseline amplitude after subjects had acquired the new skill, whereas no practice-induced changes in MEP amplitude were observed after subjects had overlearned the task, or after practicing slow ramp pinches. Since the changes in MEP amplitude were observed only after TMS of M1 but not after direct stimulation of the corticospinal tract, these findings indicate task- and effector-specific involvement of human M1 in rapid motor learning.     

Event-related potentials increase the discrimination performance of the autonomic-based concealed information test

The concealed information test (CIT) assesses an examinee's crime-relevant memory on the basis of physiological differences between crime-relevant and irrelevant items. The CIT based on autonomic measures has been used for criminal investigations, while the CIT based on event-related potentials (ERPs) has been suggested as a useful alternative. To combine these two methods, we developed a quantification method of ERPs measured in the autonomic-based CIT where each item was repeated only 5 times. Results showed that the peak amplitude of the ERP difference wave between crime-relevant and irrelevant items could discriminate between guilty and innocent participants effectively even when only 5 trials were used for averaging. This ERP measure could detect some participants who were missed by the autonomic measures. Combining the ERP and autonomic measures significantly improved the discrimination performance of the autonomic-based CIT.