Enhancement of conflict processing activity in human brain under task relevant condition

Distinct multisensory perceptual processes guide enhanced auditory recognition memory in older cochlear implant users

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Congruent audio-visual encoding enhances later auditory processing in the elderly.

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CI users benefit from additional congruent visual information, similar to controls.

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CI users show distinct neurophysiological processes, compared to controls.

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CI users show an earlier modulation of event-related topographies, compared to controls.

In naturalistic situations, sounds are often perceived in conjunction with matching visual impressions. For example, we see and hear the neighbor’s dog barking in the garden. Still, there is a good chance that we recognize the neighbor’s dog even when we only hear it barking, but do not see it behind the fence. Previous studies with normal-hearing (NH) listeners have shown that the audio-visual presentation of a perceptual object (like an animal) increases the probability to recognize this object later on, even if the repeated presentation of this object occurs in a purely auditory condition. In patients with a cochlear implant (CI), however, the electrical hearing of sounds is impoverished, and the ability to recognize perceptual objects in auditory conditions is significantly limited. It is currently not well understood whether CI users – as NH listeners – show a multisensory facilitation for auditory recognition. The present study used event-related potentials (ERPs) and a continuous recognition paradigm with auditory and audio-visual stimuli to test the prediction that CI users show a benefit from audio-visual perception. Indeed, the congruent audio-visual context resulted in an improved recognition ability of objects in an auditory-only condition, both in the NH listeners and the CI users. The ERPs revealed a group-specific pattern of voltage topographies and correlations between these ERP maps and the auditory recognition ability, indicating a different processing of congruent audio-visual stimuli in CI users when compared to NH listeners. Taken together, our results point to distinct cortical processing of naturalistic audio-visual objects in CI users and NH listeners, which however allows both groups to improve the recognition ability of these objects in a purely auditory context. Our findings are of relevance for future clinical research since audio-visual perception might also improve the auditory rehabilitation after cochlear implantation.

Transcranial Magnetic Stimulation Over the Right Posterior Superior Temporal Sulcus Promotes the Feature Discrimination Processing

Attention is the dynamic process of allocating limited resources to the information that is most relevant to our goals. Accumulating studies have demonstrated the crucial role of frontal and parietal areas in attention. However, the effect of posterior superior temporal sulcus (pSTS) in attention is still unclear. To address this question, in this study, we measured transcranial magnetic stimulation (TMS)-induced event-related potentials (ERPs) to determine the extent of involvement of the right pSTS in attentional processing. We hypothesized that TMS would enhance the activation of the right pSTS during feature discrimination processing. We recruited 21 healthy subjects who performed the dual-feature delayed matching task while undergoing single-pulse sham or real TMS to the right pSTS 300 ms before the second stimulus onset. The results showed that the response time was reduced by real TMS of the pSTS as compared to sham stimulation. N270 amplitude was reduced during conflict processing, and the time-varying network analysis revealed increased connectivity between the frontal lobe and temporo-parietal and occipital regions. Thus, single-pulse TMS of the right pSTS enhances feature discrimination processing and task performance by reducing N270 amplitude and increasing connections between the frontal pole and temporo-parietal and occipital regions. These findings provide evidence that the right pSTS facilitates feature discrimination by accelerating the formation of a dynamic network.

Task relevance effect on number/shape conflict detection in the number-matching task: An ERP study

It is debatable whether the task relevance effect on a conflict occurs in the detection or in the inhibition underlying sequential matching. To explore this issue, three types of number pairs, identical (e.g., 12, 12), conserved (e.g., 12, ), and non-conserved (e.g., 12, 15) pairs, were displayed to be judged as perceptually (identical shape condition) or quantitatively (identical value condition) the same. Both error rates and RTs for the three types of number pairs showed different patterns to detect perceptual mismatch in the identical shape condition and number inequivalence in the identical value conditions. The event-related potential (ERP) results showed that increased N200 and N400 as well as decreased P300 were triggered by the conserved and non-conserved pairs in contrast to identical pairs in the identical shape condition and by the non-conserved pairs relative to the conserved and identical pairs in the identical value condition. These results showed that task-relevant mismatches were attended to and detected in both conditions. Therefore, for the task-relevance effect on a conflict, attention is selectively directed to task-relevant features rather than inhibiting task-irrelevant conflict.

Does the aura surrounding healthy-related imported products fade in China? ERP evidence for the country-of-origin stereotype

Chinese consumers’ craze about imported products, especially foods and drugs, peaked after various safety incidents, such as the contamination of Chinese dairy products. Recently, this boom has gradually receded because of the constant quality problems of imported products and the stricter safety supervision of domestic products. Researchers have measured consumer’s perception toward domestic and imported products in various ways. In the current research, we investigated whether the country-of-origin stereotype has weakened in Chinese young consumers at the neurological level. By using a word-pair paradigm, 21 young participants were required to classify positive or negative words while event-related potentials were recorded. The results showed that reaction time to identify negative words following presentation of imported products (imported-negative condition) was longer than domestic products (domestic-negative condition). The amplitudes of N270 and LPP evoked in the imported-negative condition were significantly larger than those in the domestic-negative condition, possibly reflecting the higher expectation conflict when participate identified the adjectives as negative primed by imported healthy-related products. These findings revealed that young Chinese consumers still evaluated imported products better than domestic products.

Automatic Conflict Monitoring by Event-Related Potentials Could be used to Estimate Visual Acuity Levels

Numerous studies have explored the physical attribute features or face perceptions in conflict processing, while complicate gradient conflicts were rarely discussed. The aim of the study was to discuss the relationship between the event-related potential (ERP) component features and different visual acuity levels by using the modified S1-S2 task under non-attention status. Three visual acuity levels were applied, each with four orientations of "E" optotype stimuli randomly presented in the center of the visual field while participants were required to concentrate on listening to stories. The results showed that the amplitudes of P1 and P3 as well as difference P3 were larger in supra-threshold condition. In threshold condition, larger amplitudes for both N2 and difference N2 exhibited in frontal and central areas. In sub-threshold condition, there was no endogenous component elicited by mismatch stimuli except smaller anterior N1. Meanwhile, the specific distributions of N1 and N2 were presented and compared with previous face processing. The findings showed that visual conflict processing took place not only at an early stage but also at the late period, which might be as the consequences of interaction between conflict strength and involuntary attention. We concluded that automatic conflict detecting of visual icons by the serial ERP components could distinguish different visual acuity levels. The involvement of endogenous components could reveal the specific mechanism of more precise and fine conflict identification of complex physical attributes under non-attention status, furthermore could be used as valid markers to estimate the magnitude of visual acuity objectively.

Neural processes underlying the"same"-"different" judgment of two simultaneously presented objects--an EEG study

The present study investigated the neural processes underlying “same” and -“different” judgments for two simultaneously presented objects, that varied on one or both, of two dimensions: color and shape. Participants judged whether or not the two objects were “same” or “different” on either the color dimension (color task) or the shape dimension (shape task). The unattended irrelevant dimension of the objects was either congruent (same-same; different-different) or incongruent (same-different). ERP data showed a main effect of color congruency in the time window 190–260 ms post-stimulus presentation and a main effect of shape congruency in the time window 220–280 ms post-stimulus presentation in both color and shape tasks. The interaction between color and shape congruency in the ERP data occurred in a later time window than the two main effects, indicating that mismatches in task-relevant and task-irrelevant dimensions were processed automatically and independently before a response was selected. The fact that the interference of the task-irrelevant dimension occurred after mismatch detection, supports a confluence model of processing.

The effects of visual imagery on face identification: an ERP study

The present study tested the hypothesis that the effects of mental imagery on subsequent perception occur at a later matching stage in perceptual identification, but not in the early perceptual stage as in perceptual detection. The behavioral results suggested that the effect of visual imagery on visual identification is content-specific, i.e., imagining a congruent face facilitates face identification, whereas a mismatch between imagery and perception leads to an interference effect. More importantly, the ERP results revealed that a more negative N2 response to the subsequent visual face stimuli was elicited over fronto-central sites in the mismatch and no-imagery conditions as compared to that in the match condition, with the early P1 and N170 components independent of manipulations. The latency and distribution of the neural effects demonstrate that the matching step, but not the earlier perceptual process, is affected by the preceding visual imagery in the context of face identification. We discuss these results in a broader context that the imagery-perception interaction may depend on task demand.

Arithmetic mismatch negativity and numerical magnitude processing in number matching

Background

This study examined the relationship of the arithmetic mismatch negativity (AMN) and the semantic evaluation of numerical magnitude. The first question was whether the AMN was sensitive to the incongruity in numerical information per se, or rather, to the violation of strategic expectations. The second question was whether the numerical distance effect could appear independently of the AMN. Event-related potentials (ERPs) were recorded while participants decided whether two digits were matching or non-matching in terms of physical similarity.

Results

The AMN was enhanced in matching trials presented infrequently relative to non-matching trials presented frequently. The numerical distance effect was found over posterior sites during a 92 ms long interval (236-328 ms) but appeared independently of the AMN.

Conclusions

It was not the incongruity in numerical information per se, but rather, the violation of strategic expectations that elicited the AMN. The numerical distance effect might only temporally coincide with the AMN and did not form an inherent part of it.

Electrophysiological correlates of hypothesis evaluation: revealed with a modified Wason's selection task

A modified Wason's selection task was used to explore brain correlates of hypothesis evaluation, a core process of hypothesis testing. Twenty-two undergraduate participants (11 males, 11 females) were provided with a proposition (hypothesis) and a card. They were asked to evaluate whether the card verified or falsified the given proposition while event related potentials (ERP) were measured. Behavioral results showed that participants required less time to make correct responses in verification conditions than in falsification conditions. The ERPs time-locked to the second side of each card showed that (1) smaller amplitudes of P2 were elicited in backward falsification than in backward verification, which reflected a lower intensity of perception; (2) a profound negative deflection was found in falsification conditions compared to verification conditions during the N2 time window, which implied the processing of conflicting information; (3) in comparison to verification conditions, falsification conditions evoked a decreased P3 component, which was linked to the process of hypothesis evaluation; and (4) a late positive component (400-600 ms) was only triggered in the forward falsification condition, reflecting the manipulation of cognitive context.

Dissociated mechanisms of extracting perceptual information into visual working memory

Background

The processing mechanisms of visual working memory (VWM) have been extensively explored in the recent decade. However, how the perceptual information is extracted into VWM remains largely unclear. The current study investigated this issue by testing whether the perceptual information was extracted into VWM via an integrated-object manner so that all the irrelevant information would be extracted (object hypothesis), or via a feature-based manner so that only the target-relevant information would be extracted (feature hypothesis), or via an analogous processing manner as that in visual perception (analogy hypothesis).

Methodology/Principal Findings

High-discriminable information which is processed at the parallel stage of visual perception and fine-grained information which is processed via focal attention were selected as the representatives of perceptual information. The analogy hypothesis predicted that whereas high-discriminable information is extracted into VWM automatically, fine-grained information will be extracted only if it is task-relevant. By manipulating the information type of the irrelevant dimension in a change-detection task, we found that the performance was affected and the ERP component N270 was enhanced if a change between the probe and the memorized stimulus consisted of irrelevant high-discriminable information, but not if it consisted of irrelevant fine-grained information.

Conclusions/Significance

We conclude that dissociated extraction mechanisms exist in VWM for information resolved via dissociated processes in visual perception (at least for the information tested in the current study), supporting the analogy hypothesis.

Effects of discrepancy between imagined and perceived sounds on the N2 component of the event-related potential

Two experiments were conducted to examine whether the N2 component of the event-related potential (ERP), typically elicited in a S1-S2 matching task and considered to reflect mismatch process, can still be elicited when the S1 was imagined instead of perceived and to investigate how N2 amplitude varied with the degree of S1-S2 discrepancy. Three levels of discrepancy were defined by the degree of separation between the heard (S2) and imagined (S1) sounds. It was found that the N2 was reliably elicited when the perceived S2 differed from the imagined S1, but whether N2 amplitude increased with the degree of discrepancy depended in part on the S1-S2 discriminability (as evidenced by reaction time). Specifically, the effect of increasing discrepancy was attenuated as discriminability increased from hard to easy. These results, together with the dynamic ERP topography observed within the N2 window, suggest that the N2 effect reflects two sequential but overlapping processes: automatic mismatch and controlled detection.

Electrophysiological Correlates of Inductive Generalization

The cognitive mechanism of inductive generalization has been studied broadly, although the neural correlates are still unclear. In the present study, participants were provided with battery quadruplets. Within each quadruplet, some batteries were charged while others were not. Participants were asked to generate a hypothesis about what kinds of batteries were charged. The results revealed that the reaction times and the latencies of frontal N1 were shorter in the Generalizable condition than in the Nongeneralizable condition. After 420 ms onset of stimuli, the late positive complex (LPC) was increased significantly in the generalizable condition, reflecting a process of hypothesis generation and subsequent updating.

Attention changes in epilepsy patients following 3-month topiramate or valproate treatment revealed by event-related potential

The present study was designed to reveal changes of cognitive processes in epilepsy (EP) patients with Topiramate (TPM) or Valproate (VPA) treatment using Wechsler Adult Intelligence Scale (WAIS-CR) and event-related potential (ERP). Thirty untreated epilepsy patients were randomly divided into two groups receiving TPM or VPA, respectively. Fifteen healthy volunteers were included as controls. All the patients were examined by WAIS-CR and ERP before and 3 months after drug treatment. Controls were examined by ERP at the time recruited into the study and 3 months later. Unfamiliar grey-scale photographs of faces (front view) were used as stimuli. ERP were recorded at the same time. Mean Intelligence Quotient (IQ) in TPM group decreased after the 3-month treatment (90.40 vs. 81.00, P<0.05). One component of ERP-P300 was smaller in epilepsy patients than controls (P<0.05), but remained unchanged after TPM or VPA treatment (P>0.05). A delayed and smaller N270 was detected in patients compared to controls (P<0.05). After 3 months TPM treatment, it decreased further compared to before treatment (P<0.05). N170 was lower in patient groups, and it became lower after TPM treatment than before. Our results demonstrate that in all epilepsy patients with mild cognitive impairment ERP changes were found. TPM affected the cognitive functions in epilepsy patients reflected by the decreased full-scale intelligence quotient (FIQ). The imperative effects of TPM on visual perception function reflected by N170 were more obvious than that of VPA. Attention reflected by N270 was impaired after TPM treatment.

Age-related changes in cognitive conflict processing: An event-related potential study

Cognitive tasks involving conflicting stimuli and responses are associated with an early age-related decline in performance. Conflict and conflict-induced interference can be stimulus- or response-related. In classical stimulus-response compatibility tasks, such as the Stroop task, the event-related potential (ERP) usually reveals a greater negativity on incongruent versus congruent trials which has often been linked with conflict processing. However, it is unclear whether this negativity is related to stimulus- or response-related conflict, thus rendering the meaning of age-related changes inconclusive. In the present study, a modified Stroop task was used to focus on stimulus-related interference processes while excluding response-related interference. Since we intended to study work-relevant effects ERPs and performance were determined in young (about 30 years old) and middle-aged (about 50 years old) healthy subjects (total n=80). In the ERP, a broad negativity developed after incongruent versus congruent stimuli between 350 and 650 ms. An age-related increase of the latency and amplitude of this negativity was observed. These results indicate age-related alterations in the processing of conflicting stimuli already in middle age.

Activation of the posterior cingulate by semantic priming: a co-registered ERP/fMRI study

Although the N400 is the best understood semantically sensitive component of the event-related potential (ERP), others have been observed as well. In an earlier lexical decision study, an N300 ERP was found to be enhanced to unprimed targets, although the effect could also be characterized as a prolonged P2 to primed targets as described in other reports. Because its scalp topography suggested its neural source might be of interest, a source localization was conducted that suggested that this component emanated from the dorsal posterior cingulate cortex (dPCC). In order to confirm this word N300 localization, a functional magnetic resonance imaging (fMRI) study was conducted to replicate the ERP study with a separate sample of 17 participants in an event-related design, using a 3-T scanner. A significant activation in the right dPCC was found corresponding to the N300 localization. The activation was greater on the related prime trials, supporting the characterization of the ERP component as being a P2 rather than an N300. A review is provided which suggests that a number of separate lines of ERP research regarding the word N300, the picture N300, the word P2, the phonological mismatch negativity, and the word midline frontal negativity may be most parsimoniously regarded as dealing with the same ERP component and that they all therefore emanate from the dPCC. It is suggested that this region plays a role in stimulus-response mapping in polymodal fashion. It is also suggested that the ERP component be termed a P2-dPCC.

Brain activities immediately after finding rare targets

It is generally assumed that the prior knowledge about the frequency of the target occurrence would influence the identification of a stimulus. Nevertheless, whether this influence occurs immediately after finding a rare target is unknown as yet. To clarify this issue, Event-related brain potentials were recorded in the present study while subjects were presented with thousands of pictures and were required to indicate whether a categorical target such as a tool was in the display. The results showed that participants responded more quickly to the posttarget nontargets (PNTs, i.e. the nontargets that immediately followed the rare targets) than to the common nontargets (CNTs, i.e. the nontargets that did not immediately follow the rare targets). Compared with CNTs, PNTs elicited enhanced amplitudes at N1, N2, and parietal P2 components. Moreover, the N2 latency was longer overall for PNTs than for CNTs. These results suggested that the prior knowledge did not affect observer's judgment immediately; instead, the event of finding a rare target strengthened the processing of PNTs.

Event-related potential N270 correlates of brand extension

The aim of this study is to investigate the neural mechanism of extending a brand in a specific product category to other product categories. Facing two sequential stimuli in pairs consisting of beverage brand names (stimulus 1) and product names (stimulus 2) in other categories, 16 participants were asked to indicate the suitability of extending the brand in stimulus 1 to the product category in stimulus 2. These stimulus pairs were divided into four conditions depending on the product category in stimulus 2: beverage, snack, clothing, and household appliance. A negative component, N270, was recorded for each condition on the participants' scalps,whereas the maximum amplitude was observed at the frontal area. Greater N270 amplitude was observed when participants were presented with stronger conflict between the brand product category (stimulus 1) and the extension category (stimulus 2). It suggests that N270 can be evoked not only by a conflict of physical attributes (different shapes of words of brand and product names) but also by that of lexical content. From the marketing perspective, N270 can be potentially used as a reference measure in brand-extension attempts.

Antiepileptic Drugs and the Significance of Event-Related Potentials

The authors compared cognitive changes in epilepsy patients with or without antiepileptic drugs using event-related potential (ERP) N270 and P300. The patients were divided into three groups according to treatment type: carbamazepine, valproate acid (VPA), or no treatment. One control group composed of healthy subjects was included. The Mini-Mental State Examination detected no clinical dementia in all subjects. A modified Sternberg paradigm was used as a task when an ERP was recorded. When a stimulus was different from the memorized item (conflict condition), N270 was elicited in both controls and patients. All the three patient groups showed a delayed and smaller N270 than the control group. P300 was elicited when a stimulus was the same one as the memorized item (match condition), and its amplitude decreased in the VPA group. P300 latency did not differ among the four groups. ERP (N270 and P300) was abnormal in patients with epilepsy. These results indicate that antiepileptic drugs, especially VPA, might enhance the impairment of cognitive processing. N270 is more sensitive than P300 in the early detection of minor cognitive impairment in epileptics.

Event-related brain potentials during visual sentence reading and picture recognition memory tasks

It is uncertain if different brain areas in response to pre-semantic picture processing are functionally homogeneous. Using event-related potentials (ERPs), we aimed to explore the neural activities in different brain regions in relation to processing of sentence memory and picture identification. Healthy subjects were chosen to discriminate visual stimulus pairs, and the ERPs were recorded from the scalp. Two kinds of stimuli were provided for each subject in the present study. One was Chinese sentence reading, referred as task 1. Another one was watching a line-drawing picture to judge if the picture matched the meaning of the sentence before. When the line-drawing picture received by the subject was inconsistent with the meaning of the sentence before, it was called as task 2, otherwise, if incongruous, it was called as task 3. Our findings implicate that stimuli of sentence memory and picture identification may exert neural activities on different working memory areas in the brain of human.

Electroencephalography effects to semantic and non-semantic mismatch in properties of visually presented single-characters: The N2b and the N400

Event-related potential (ERP) correlates of semantic and non-semantic mismatch in the 200-400ms time interval were dissociated. Twelve subjects observed pairs of single letters and digits presented serially, and decided whether the colour (blue or red) or the category membership (letter or number) of the second item in a pair matched the first one. In both tasks mismatch elicited central N2b components (220ms peak latency in the colour matching task, and 280ms peak latency in the category matching task). Furthermore, in the category matching task a centro-parietal negativity (N400) emerged. The topography of the N2b effect was clearly distinct from that of the N400 effect. Analysis of event-related spectral perturbations confirmed that N400 time-range effects were specific to category matching. We conclude that while the N400 effect is a specific marker of semantic mismatch, the N2b effect is a general correlate of detecting mismatch between the representations of task-relevant features.

Event-Related Potential N270 in Detecting Cognitive Impairment in Patients With Transient Ischemic Attack

Latency and amplitude of the visual P300 and N270 were examined in patients with transient ischemic attack (TIA) and in age-matched healthy control subjects to investigate the feasibility of N270 as a clinical examination method to evaluate the cognitive status of patients with TIA. Stimulus pairs with identical (match condition) or different (conflict condition) colors were randomly presented to subjects. Each pair consisted of two sequential stimuli (S1 and S2) that lasted for 300 ms; the onset interval between them was 700 ms. Thirty TIA patients without clinical dementia and 30 age-matched control subjects determined if the two stimuli in a pair had the same color. Subjects were required to press a button in the match condition and another button in the conflict condition. Event-related potentials (ERPs) were recorded from their scalp electrodes at the same time. N270 was evoked by the second stimulus (S2) of the conflict condition in either control subjects or patients. The patient group exhibited a delayed N270 than the control group. TIA patients as a group showed cognitive decline. N270 is an effective index to detect the cognitive impairment of TIA patients.

Various conflicts from ventral and dorsal streams are sequentially processed in a common system

Event-related potentials (ERPs) were recorded in subjects while they were matching two sequentially presented color spots. The two spots might be presented in the same position of the same color, or different colors (color conflict). They might be in different positions of the same color (position conflict), or different colors (color and position conjunction conflicts). Subjects matched the stimuli in three different sessions according to different attention tasks: attending to color, attending to position, or attending to both color and position. A negative one-peak brain potential, N270, was elicited in all the conflict conditions with amplitude enhanced in the task-relevant conflict. Two negative effects, N270 and N400, were recorded when attending to the conjunction conflicts concurrently. Visual spatial information is processed through the dorsal stream, while the feature information is processed through the ventral stream in the brain. The results suggest that all kinds of conflicts might be processed in a common system above the level of the two streams, which processes the conjunction conflict information from ventral and dorsal stream in series.

An ERP study of visual change detection: effects of magnitude of spatial frequency changes on the change-related posterior positivity

In event-related brain potential (ERP) studies using a visual S1-S2 matching task, change stimuli elicit a posterior positivity at around 100-200 ms. In the present study, we investigated the effects of magnitude of spatial frequency changes on change-related positivity. Each trial consisted of two sequentially presented stimuli (S1-S2), where S2 was either (1) the same as S1 (i.e., NO-change, p=.40), (2) different from S1 in spatial frequency only (SF-change, .40), (3) different in orientation only (OR-change, .10), or (4) different in both spatial frequency and orientation (BOTH-change, .10). Further, three magnitude conditions (Large, Medium, and Small) were used to examine the effect of the magnitude of the spatial frequency change. Participant's (N=12) task was to respond to S2 with a change in orientation (from vertical to horizontal, or from horizontal to vertical) regardless of the spatial frequency of the stimulus. Changes in the spatial frequency elicited change-related positivity at a latency range of about 120-180 ms, which was followed by a central negativity (N270) and a late positive component (LPC). The amplitude of the change-related positivity tends to be enhanced as the magnitude of the change is increased. These results support the notion that the change-related positivity reflects memory-based change detection in the human visual system.

Neural correlates of preattentive and attentive processing of visual changes

To identify electrophysiological correlates of pre-attentive and attentive processing of visual changes, we compared event-related brain potentials in response to color changes at attended and unattended spatial locations using a visual S1-S2 matching task. The results showed that compared to no change, change stimuli elicited occipito-temporal positivity at around 100-160 ms (change-related positivity) and subsequent central negativity at around 220-300 ms (N270). Change-related positivity was observed in response to changes at both attended and unattended locations, while N270 was observed only when attention was directed to the location of the changes. These results suggest that change-related positivity reflects the pre-attentive processing of visual changes and N270 reflects the attentive processing of visual changes in the human brain.

Positive difference in ERPs reflects independent processing of visual changes

To elucidate the nature of the processing of visual stimulus changes, ERPs were recorded while 12 participants performed an S1-S2 matching task with multifeature stimuli. Each trial consisted of two sequentially presented stimuli (S1-S2), where S2 was either the same as S1, different from S1 only in color, different only in shape, or different in both color and shape. The four trial types were presented in random order with equal probability, and participants responded to one of these types in separate blocks. Relative to the no-change stimuli, the change stimuli elicited posterior positivity with different topography according to changing features ranging from 100 to 180 ms in all tasks. The amplitude and topography of the positivity in response to the both changes were the respective sums of those to changes in the corresponding single features. These results suggest that a feature-specific change detection system exists in the human visual system.

Independent processing of visual stimulus changes in ventral and dorsal stream features indexed by an early positive difference in event-related brain potentials

In event-related brain potential (ERP) studies of brain activity using a visual S1-S2 matching task, change stimuli elicit a posterior positive component with a latency of 100-200 ms. To elucidate the hierarchical organization of the processing of a visual stimulus change based on multiple stimulus features, ERPs were recorded in 12 participants performing an S1-S2 matching task with stimuli defined by color (mediated by the ventral stream) and motion direction (mediated by the dorsal stream). Each trial consisted of two sequentially presented stimuli (S1-S2), where S2 was either (1) the same as S1 (i.e., no change), (2) different from S1 in color only (color change), (3) different in motion direction only (motion direction change), or (4) different in both color and motion direction (color-motion direction change). These trials were presented in random order with equal probability, and the participants were asked to respond to one of these trials in separate blocks. Relative to the no-change stimulus, the three types of change stimuli elicited posterior positivities. The scalp-topography of change positivities differed according to the feature changed. In addition, the amplitude and scalp-topography of change positivities in response to a conjunction change were the respective sums of those in response to changes in the corresponding single features. These results suggest that the change detection system reflected by the change positivity is separate for each feature dimension, and these operate independently.

Distinctive conflict processes associated with different stimulus presentation patterns: an event-related potential study

Twelve subjects were asked to perform visual stimulus presentation tasks. Two figures were presented either simultaneously or sequentially. They were either in congruity (same shapes) or in conflict (different shapes) with each other. Conflicting stimulus pairs presented sequentially evoked a negative event-related component with a fronto-central and bilateral posterior scalp distribution, referred to as N270. In contrast, stimuli displayed simultaneously elicited a N220 with fronto-central prominence, irrespective of whether they were in conflict or in congruity. The results suggest that the N270 may be associated with the processing of a conflict with working memory information whereas the N220 might reflect the detection and evaluation of attention to visual information in the human brain.

The effect of numerical distance and stimulus probability on ERP components elicited by numerical incongruencies in mental addition

In two experiments, we investigated the effect of the numerical distance of incongruous results from correct results and stimulus probability on the N270/N400 event-related brain potential components. In Experiment 1, 12 subjects saw two one-digit addends and a possible solution and signaled if the proposed result (falling in the range of 3-17) was true or false. Incorrect results could deviate by +/-2 or by +/-9 from the correct answer. The probability of correct results was 50%. Twelve subjects carried out a similar task in Experiment 2 without giving behavioral responses. The probability of incorrect results was 20%, 50% or 80% in different conditions. Both raw potentials and incorrect minus correct difference potentials were analyzed. A fronto-central N3 and a centro-parietal dN3 (incorrect-correct difference) were present for incongruous results in both experiments. The amplitude of the dN3 was not sensitive to numerical distance, but the latency of the dN3 was longer when numerical distance was larger. The overall amplitude of the N3 and of the dN3 was not sensitive to the probability manipulation. However, there was a parietally localized effect of probability on N3 amplitude. The dN3 in mental addition is most probably identical to the arithmetic N400 effect reported earlier in mental multiplication. The distance effect in latency may be a correlate of the discrimination of correct vs. incorrect results. A parietally localized probability effect (right greater than left) was found in the N3 amplitude. The dN3 was insensitive to the probability manipulation. In accord with its insensitivity to stimulus probability, the dN3 seems to be more related to the N400 than to the N2b. Posterior attentional processes sensitive to the allocation of attentional resources may have contributed to the topography of the dN3. The N3 is more related to the detection of expectation violation, while the P3 reflects the ease of identifying stimulus categories.

The Effects of Different Hands?? Responses on Main ERP Components

The authors recorded event-related potentials (ERPs) in 14 subjects to explore the effects of different hands'responses on ERP components. Subjects used two different fingers of one hand to indicate whether the two sequentially presented visual stimuli were of the same color (match) or not (conflict) in the first half of the test, while they used the other hand in the last half. ERP components of contingent negative variation (CNV), P100, N160, N200, and late positive component (LPC) were recorded in either the match or conflict condition. Component N270 was recorded only in the conflict condition mainly on the centrofrontal area (F3, F4). The mean amplitude of the CNV was significantly higher when subjects used the right hand to respond. The mean amplitudes of N160 in the two conditions and N200 in the conflict condition were significantly higher when the left hand was used to indicate a response. There was no significant difference in the amplitude of N270 between the left-hand and right-hand responses. The N270 is thought to reflect activity in a conflict processing system. The LPC component was not affected by different hands'response-effect.

Cognitive impairment in major depressive disorder revealed by event-related potential N270

Major depressive disorder (MDD) is a mood disorder that is often accompanied by the impairment of cognitive functions. The aim of this study was to investigate the feasibility of N270 as an index for evaluating the cognitive impairment in MDD patients. Twenty-five patients with MDD diagnosed according to DSM-IV and 25 age matched normal controls performed a matching task while event-related potentials (ERPs) were recorded from their scalp. There were two kinds of stimulus pairs in this study: match condition, the second stimulus (S2) in a pair was identical to the first one (S1); mismatch condition, S2 conflicted with S1 in the color attribute. Subjects were required to press a button in the match condition and to press another button in the mismatch condition. A negative ERP component, N270, which was considered to reflect conflict processing activity in human brain, was evoked by S2 of the mismatch condition. The patient group showed a delayed and smaller N270 than the control group. The prolongation of its peak latency was significant at P3 and P4 electrodes, and the reduction of its peak amplitude was significant at F3, F4, P3 and P4 electrodes. The amplitude of P300 elicited in the match condition was decreased in the patient group at P3 and P4 electrodes, but its latency did not differ from the control group. The results indicate that MDD patients as a group showed cognitive decline. N270 is a sensitive index in revealing cognitive impairment.

Access to numerical information is dependent on the modality of stimulus presentation in mental addition: a combined ERP and behavioral study

We investigated whether the mental representation of numbers is abstract amodal or modality-dependent. Subjects verified simple additions. In an event-related potential (ERP) experiment, subjects added an Arabic digit (S2) to a preceding number (S1) offsetting 3 s before S2. S1 was either a visually shown Arabic digit, a written number word or an acoustically presented number word. In a behavioral experiment, we measured the speed of addition using a modified paradigm. In the ERPs to S2, the amplitude of the parietal N1, the fronto-central P2, and the late positivity between 320 and 460 ms were more positive and RTs were faster when S1 was a heard number word than when S1 was a written number word. ERP amplitudes and reaction times took intermediate positions between the other two conditions when S1 was an Arabic digit. Between the Arabic and heard number conditions, this so-called numeral modality effect (NME) was present at electrodes Pz, P4, P3 and Cz when number size was small, whereas it was significant over electrode C4 and P4 when number size was large. Our results suggest that numbers presented in different surface-formats have differential access to number representations. Conclusions for models of number processing are drawn and the possible role of parietal number representations is discussed. We replicated the N270 ERP component and elicited the ERP numerical distance effect in response to incongruent arithmetical results.

The sequential processing of visual feature conjunction mismatches in the human brain

To clarify the brain mechanism for multifeature stimulus comparison, subjects matched the features of two serial visual stimuli in pairs. Stimulus pairs were of four categories: C-S-, color same, shape same (match); C-S+, color same, shape different (shape mismatch); C+S-, color different, shape same (color mismatch); C+S+, color different, shape different (conjunction mismatches). Subjects matched the stimuli in three different sessions according to different attention tasks: attending to color (Ac), attending to shape (As), or attending to both color and shape (Acs). A negative one-peak brain potential, N270, was elicited in all the mismatch conditions with amplitude enhanced in the task-relevant mismatch. Negative potential with two peaks, N270 and N400, appeared when attending to the conjunction mismatches concurrently. The two serial negativities in response to attended feature conjunctions might reflect the temporal different stages for processing conjunction mismatches or conflicts.

Event-related potential N270, a negative component to identification of conflicting information following memory retrieval

OBJECTIVE

N270, an endogenous ERP component of conflict effect, was evoked in previous studies with S1-S2 paradigm. The present experiment is designed to confirm the speculation that this conflict-related negativity could also be elicited by stimulus probes having conflict with a memorized item in a visual post-retrieval comparison task.

METHODS

A Sternberg probe-matching paradigm was modified in the present study. The stimuli consisted of a memory set of 3 different items (simple figures) and a retrieval set of 3 probe figures. Subjects matched each probe to its corresponding item in the memory set. The tasks were designed with different conflict loads of no-conflict, low-conflict and high-conflict in the probe retrieval test.

RESULTS

Probes of no-conflict elicited a major positive going component, P300, with bilateral parietal distribution. Probes of low- and high-conflict evoked N270, while N430 was elicited only in high-conflict condition. N270 was more negative in high-conflict condition than in low-conflict condition. The N270 was right hemispheric prominent in the low-conflict task and remarkably distributed over the right prefrontal areas. On the other hand, both N270 and N430 were distributed bilaterally on the scalp in the high-conflict task.

CONCLUSIONS

The present results demonstrate that the N270 is an index to the conflict identification, while the N430 of the high-conflict task reflects the processing for complex conflicts following probe retrieval. These negativities are related to the processing of conflicts.

Brain potentials elicited by matching global and occluded 3-dimensional contours

Subjects were instructed to match 3-dimensional forms while event-related potentials (ERPs) were recorded to explore the relationship between visual completion and conflict processing. Sequentially presented paired stimuli (S1 and S2) were identical in condition I, while in condition II the images were of the same contour, but S2 contained an invisible portion, and in condition III S1 and S2 were of different contours. Subjects indicated if stimuli were physically identical or contour similar in two separate sessions. Following the onset of S2, ERP components P100, N150, and LPC were recorded in all conditions. N150 was enhanced in condition II in both sessions, and N270 was elicited in conditions II and III. N150 is related to visual completion, while N270 is related to the evaluation of information discrepancy, belonging to independent systems.

Event-related potential N270 and its distribution in adults and school-age children

To compare the pattern and distribution of event-related potential (ERP) N270 in adults and school-age children and to explore the development of conflict processing systems in the human brain, pairs of colored numbers were sequentially presented on a screen to subjects. The subjects were instructed to discriminate whether the color or magnitude of the pairs of numbers were identical (match) or different (conflict), and ERPs were recorded at the same time. In adults, a negative potential peaking at 270ms (N270) was elicited when the second stimulus (S2) conflicted with the first stimulus (S1) in either task relevant or irrelevant conditions. N270 was distributed widely on the scalp in adults. In children, N270 was only elicited by a task-relevant conflict. N270 in the color conflict was distributed bilaterally on the scalp and N270 elicited by the magnitude conflict was found to be on the left central-frontal areas. In school-age children, ERP N270 is elicited under the control of attention. Its distribution on the scalp depends on the attributes of stimulus pairs.

The N270 component of the event-related potential reflects supramodal conflict processing in humans

It is unclear whether crossmodal information conflict can initiate the conflict processing system indexed by a component of the event-related potential (ERP) called the N270, which previously has been observed only for visual conflict. ERPs were recorded in ten subjects, while they were engaged in a visual-auditory discrimination task. A visual stimulus of a facial photograph was followed by an auditory stimulus of Chinese syllable [a] or [i], which might be sounded by the same gender of its preceding photograph (gender match) or by different gender (gender conflict). Subjects pressed a button for gender match and another for gender conflict. A prominent N270, similar to that evoked by visual conflicts, was elicited by the auditory stimuli in gender conflict condition. It is likely that N270 reflects the brain activity of a supra-modal conflict processing system.

Event-related potentials elicited by stimulus spatial discrepancy in humans

Sixteen subjects were instructed to discriminate whether the spatial locations of two visual stimuli presented in sequence were identical and event-related potentials (ERPs) were recorded from their scalps. The first and the second stimuli were presented in the same location in condition 1, but were in different locations in condition 2. ERP components of P100, N150, late positive component (LPC) and slow negative wave (SNW) were recorded in condition 1; in condition 2, N150 was enhanced and N270 was elicited before LPC. N150, N270 and SNW were all mainly distributed bilaterally over P3, P4, Pz, O1, O2, and Oz. N270 represents the brain activity for processing spatial discrepancy. There are several specialized brain areas involved in the generation of the N270.

Event-related potentials in a No-go task involving response-tendency conflict

Event-related potentials (ERPs) were recorded while 13 subjects completed a color discrimination task. In task one, subjects were asked to press a button when the presented stimulus was a red or a green spot (Go stimulus), and inhibited any motor response when the stimulus was a yellow or a white spot (No-go stimulus). In task two, subjects were instructed to count the number of the Go stimuli, not to count the No-go stimuli. In order to investigate the influence of probability on ERP components, two sessions were designed in each task. In session one, the probability of the four kinds of stimuli was equal. In session two, the probability of red, green, yellow, and white were 10%, 10%, 10%, and 70% respectively. An enhanced negative potential in the frontal area was recorded in the 200-400 ms range both following No-go stimuli and following No-count stimuli, which was not influenced by the stimulus probability. The result cast doubt on the interpretation of the frontal negative potential enhancement as reflecting response-inhibition processes. The potential might be related to the information processing of response-tendency conflict rather than the suppression of motor execution.