Anterior N2 Research Articles

P.3.023 Prebiotic intake reduces the waking cortisol response and alters emotional bias in healthy volunteers

The N2 subcomponents of event-related potentials are known to reflect early attentional processes. The anterior N2 may reflect conflict monitoring, whereas the posterior N2 may be involved in target detection. The aim of this study was to identify the brain areas involved in the generation of the N2 subcomponents, in order to define the spatiotemporal dynamics of these attentional processes. We recorded 128-channel electroencephalograms in 15 healthy controls performing a three-stimulus visual oddball task and identified standard-, distracter- and target-elicited N2 components. Individual N2 sources were localized using standardized-weighted-low-resolution-electromagnetic-tomography (swLORETA). Comparative analyses were performed with a non-parametric permutation technique. Common N2 generators were observed in the Brodmann area (BA) 24 of the anterior cingulate cortex (ACC). The posterior cingulate cortex and the central precuneus were more involved in distracter processing, whereas the anterior precuneus and BA 32 of the ACC were target-specific. In accordance with previous demonstration of the frontoparietal cortex’s critical role in attentional processes, these new data shed light on the ACC’s role in conflict monitoring and its interaction with other median and frontoparietal structures in early attentional processes.

Novelty detection is enhanced when attention is otherwise engaged: an event-related potential study

Novel stimuli are detected and evaluated quickly, suggesting that processing them is a priority for the brain. In the present study, the effects of attention on this early visual novelty processing were investigated in two experiments using the event-related potential (ERP) technique. In the first experiment, participants performed two tasks that varied in the amount of attention available for novel stimuli. In the Visual Oddball task, participants responded to an infrequent target presented among standard and novel stimuli. In the Working Memory task, participants saw the same stimuli, but they could ignore them. Instead, participants had to keep six letters in working memory and report one of these letters at the end of the trial; attention was thus maximally allocated away from the visual oddball stimuli. In line with attention being fully occupied in the Working Memory task, the P3a to the visual oddball stimuli was smaller in the Working Memory than in the Visual Oddball task. In contrast, the anterior N2 component to task-irrelevant stimuli was enhanced in the Working Memory task. These findings suggest that the initial detection of novel stimuli is enhanced (large anterior N2) when few attentional resources are available, which is inconsistent with earlier findings that if anything, the N2 is enhanced by attention. In a second experiment, a condition was added in which working memory load was low, but visual oddball stimuli were task-irrelevant. Results from this experiment showed that while the reduction in P3a amplitude was due to task irrelevance, the enhanced anterior N2 was linked to a high working memory load. This suggests that novelty detection is enhanced when attention is otherwise engaged.

Expecting the unexpected: the effects of deviance on novelty processing.

Novelty is often prioritized and detected automatically. It attracts attention-eliciting the orienting response. However, novelty is not a unitary concept, and the extent to which the orienting response is elicited depends on several factors. In the present study we investigated how stimulus novelty, deviance from the context, and complexity of the stimulus context contribute to the anterior N2 and novelty P3 event-related potential components, using the visual novelty oddball paradigm. In the first experiment the novelty P3 was drastically reduced when the stimulus context was complex compared with simple, and in a second experiment when novels were frequent rather than deviant. No such effect was found for the anterior N2, suggesting it is a function of stimulus characteristics, not deviance. In contrast, the novelty P3 depended on deviance and contextual complexity.

The electrophysiological locus of the redundant target effect on visual discrimination in a dual singleton search task

Task performance can be enhanced by the addition of extra information to a visual environment in which observers search for a target stimulus. One example of such information is the repetition of the searched-for stimulus; a form of target redundancy. In the present study, the electrophysiological correlates of such target redundancy were investigated in a visual discrimination task. Observers were asked to look for targets in displays that always contained two salient singletons (tilted lines; targets and/or nontargets) against a background of vertical distractor lines. Displays contained either two redundant targets, two nontargets, or a single target and nontarget, at opposite sides of the visual field. Search was most efficient when two targets were shown, and effects of target redundancy were observed on the event-related potential as well. Target redundancy modulated the anterior N2, and the P3 in both an early and a late window. The results are compatible with models of visual attention that support a relatively late (i.e., central or decisional) locus of redundancy processing.

Emotional distraction in boys with ADHD: Neural and behavioral correlates

Although, in everyday life, patients with attention deficit hyperactivity disorder (ADHD) are frequently distracted by goal-irrelevant affective stimuli, little is known about the neural and behavioral substrates underlying this emotional distractibility. Because some of the most important brain responses associated with the sudden onset of an emotional distracter are characterized by their early latency onset and short duration, we addressed this issue by using a temporally agile neural signal capable of detecting and distinguishing them. Specifically, scalp event-related potentials (ERPs) were recorded while 20 boys with ADHD combined type and 20 healthy comparison subjects performed a digit categorization task during the presentation of three types of irrelevant, distracting stimuli: arousing negative (A−), neutral (N) and arousing positive (A+). Behavioral data showed that emotional distracters (both A− and A+) were associated with longer reaction times than neutral ones in the ADHD group, whereas no differences were found in the control group. ERP data revealed that, compared with control subjects, boys with ADHD showed larger anterior N2 amplitudes for emotional than for neutral distracters. Furthermore, regression analyses between ERP data and subjects’ emotional ratings of distracting stimuli showed that only in the ADHD group, emotional arousal (ranging from calming to arousing) was associated with anterior N2: its amplitude increased as the arousal content of the visual distracter increased. These results suggest that boys with ADHD are more vulnerable to the distracting effects of irrelevant emotional stimuli than control subjects. The present study provides first data on the neural substrates underlying emotional distractibility in ADHD.

The neural signature of spatial frequency-based information integration in scene perception

Spatial frequency-based information plays an important role in visual perception. By combining behavioral and electroencephalogram (EEG) measurements, we investigated the mechanisms of the interaction and information integration between different spatial frequency bands. The observers performed a scene categorization task on hybrid images that were generated by combining the low spatial frequency (LSF) component of one image with the high spatial frequency (HSF) component of another image. The results showed that the recognition of the HSF component was interfered by the non-attended LSF component at semantic level. The strength of the semantic interference was modulated by the physical similarity between the LSF and HSF components. Analyses of the EEG data revealed an early anterior N1 component (122ms from stimulus onset) that was related to the observed interaction of the semantic and physical information between the LSF and HSF components. These findings demonstrate that the semantic information from different spatial frequency bands can be integrated at early stage of the perceptual processing. This early integration is likely to occur at frontal areas in order to initiate top-down facilitation.

Detecting self-produced speech errors before and after articulation: an ERP investigation

It has been argued that speech production errors are monitored by the same neural system involved in monitoring other types of action errors. Behavioral evidence has shown that speech errors can be detected and corrected prior to articulation, yet the neural basis for such pre-articulatory speech error monitoring is poorly understood. The current study investigated speech error monitoring using a phoneme-substitution task known to elicit speech errors. Stimulus-locked event-related potential (ERP) analyses comparing correct and incorrect utterances were used to assess pre-articulatory error monitoring and response-locked ERP analyses were used to assess post-articulatory monitoring. Our novel finding in the stimulus-locked analysis revealed that words that ultimately led to a speech error were associated with a larger P2 component at midline sites (FCz, Cz, and CPz). This early positivity may reflect the detection of an error in speech formulation, or a predictive mechanism to signal the potential for an upcoming speech error. The data also revealed that general conflict monitoring mechanisms are involved during this task as both correct and incorrect responses elicited an anterior N2 component typically associated with conflict monitoring. The response-locked analyses corroborated previous observations that self-produced speech errors led to a fronto-central error-related negativity (ERN). These results demonstrate that speech errors can be detected prior to articulation, and that speech error monitoring relies on a central error monitoring mechanism.

Who needs a referee? How incorrect basketball actions are automatically detected by basketball players' brain

While the existence of a mirror neuron system (MNS) representing and mirroring simple purposeful actions (such as reaching) is known, neural mechanisms underlying the representation of complex actions (such as ballet, fencing, etc.) that are learned by imitation and exercise are not well understood. In this study, correct and incorrect basketball actions were visually presented to professional basketball players and naïve viewers while their EEG was recorded. The participants had to respond to rare targets (unanimated scenes). No category or group differences were found at perceptual level, ruling out the possibility that correct actions might be more visually familiar. Large, anterior N400 responses of event-related brain potentials to incorrectly performed basketball actions were recorded in skilled brains only. The swLORETA inverse solution for incorrect–correct contrast showed that the automatic detection of action ineffectiveness/incorrectness involved the fronto/parietal MNS, the cerebellum, the extra-striate body area, and the superior temporal sulcus.

Are there sex differences in ERPs related to processing empathy-evoking pictures?

ObjectiveThis study aimed to investigate sex differences in the temporal dynamics of experiencing empathy by using electrophysiological measurements. MethodsTwenty-five females and 27 males viewed 414 pictures of the International affective picture system varying in emotional valence (positive, negative and neutral) and presence of humans (human and scenes). EEG event related potentials (ERPs) were obtained and correlations were computed with self-reported empathy. ResultsCompared to males, females showed increased anterior N2 and parietal LPP amplitudes to humans contrasted with scenes (independent of emotional valence) and to negative contrasted with neutral emotions (independent of human presence). Independent of sex the N1 and anterior N2 were specifically increased for positive human emotions and the parietal LPP for negative human emotions. Across sexes, the N2 and LPP human emotion effects and LPP human effects were associated with self-reported affective empathy, but not with cognitive empathy. ConclusionsThis study provides electrophysiological evidence that women prioritize the processing of socially relevant and negative emotional information, but that women did not show enhanced brain potentials to pictures with positive or negative emotions in humans.

Common N1 and mismatch negativity neural evoked components are revealed by independent component model‐based clustering analysis

Mismatch negativity (MMN) is an event-related brain potential that appears when an auditory regularity is violated. Two main hypotheses have been proposed to explain it: the adaptation hypothesis and the memory-based hypothesis. Critically, they differ in whether the MMN can be distinguished from the N1. In this study, we assessed the differential contribution of the N1 and the MMN using independent component analysis (ICA) combined with model-based clustering. Our results show that the neural responses associated with the standard and deviant tones are explained by three clusters of reliable ICs with frontocentral scalp distribution. Two of these clusters exhibited a common N1 for both the standard and deviant tones and one cluster showed an enhancement of the anterior N1 at the MMN time range. These results support the adaptation hypothesis, which proposes that MMN is generated by neural mechanisms similar to those associated with auditory N1.

Hemispheric differences in VEPs to lateralised stimuli are a marker of recovery from neglect

Visual-evoked potentials (VEPs) were recorded in seventeen patients with unilateral lesions of the right hemisphere (RH) and visuospatial neglect. Hemispheric differences were detected for VEP components in the time window from 130 to 280 msec; this result replicates data from a previous study using a larger group of patients (Di Russo et al., 2008). Three patients were tested twice; their hemispheric differences, i.e., the differences in latency and amplitude of VEPs to ipsilesional and contralesional stimuli, were evaluated at the beginning and end of visuospatial rehabilitation training for neglect. The hemispheric differences were limited to components anterior N1 (N1a), posterior N1 (N1p) and P2 (not C1 and P1) and showed a significant decrease after training; amelioration at the behavioural level was also observed. Fourteen patients were tested only once, at different steps of their training. For the overall group, we determined the correlation between VEP hemispheric differences and the number of sessions attended by the patients at the time of VEP recording. The correlation was negative, the higher the number of sessions, the lower the hemispheric asymmetry, and high, ranging from .45 to .64, for both the latency and amplitude of the N1p and P2 components, and for the amplitude of the N1a component. The correlation between VEP hemispheric differences and time from onset (TFO) of the pathological event was not significant. Overall, the hemispheric differences between specific components of the VEP responses to lateralised stimuli appear to be a good marker of recovery from neglect.

Age-Related Changes in the Processing of To-be-Ignored Stimuli: Preserved Selective Attention Does Not Prevent Subsequent Allocation of Excessive Processing Resources (IN4-1.004)

Objective: To investigate age-related changes in attentional operations involved in the processing of to-be-ignored stimuli. Background A critical mechanism for conserving capacity-limited resources and efficiently carrying out task demands is to limit the allocation of resources to stimuli that are supposed to be ignored. Design/Methods: ERPs were measured in 12 young (mean age 23) and 15 old (mean age 74) well-matched adults during a color-selective attention task. Subjects responded to target letters in a specified color (Attend) while ignoring letters in a different color (Ignore). Results: There were minimal age-associated differences in selective attention (Attend-Ignore), as indexed by the size of the posterior Selection Negativity (SN) and anterior Selection positivity (SP). In stark contrast to their younger counterparts, old subject appropriated a similar amount of resources to targets under the Attend and Ignore conditions for operations involved with orienting and decision-making, as measured by the size of the P3a and P3b components. Old subjects demonstrated a decline of attentional control, as indexed by a smaller anterior N2 to target-like stimuli under Ignore. Old subjects also exhibited prolonged latencies of the SP, SN, P3a, and P3b components, suggestive of delays in carrying out pertinent operations. Prolongation of SN latency did not correlate with subsequent delays in P3 latency, but did predict larger P3 responses to targets under the Ignore condition. Conclusions: Despite the relative preservation of early selective attention, old subjects appropriated substantially more controlled processing resources in response to target-like stimuli under Ignore. Although inefficiencies in selective attention may undermine the quality of information available for subsequent operations, they do not fully account for the strikingly increased allocation of resources in response to to-be-ignored targets. One consequence of this age-related deficit is that older adults are at high risk for running out of processing resources to manage increased task demands. Supported by: R01 AGO17935. Disclosure: Dr. Alperin has nothing to disclose. Dr. Haring has nothing to disclose. Dr. Zhuravleva has nothing to disclose. Dr. Holcomb has nothing to disclose. Dr. Rentz has received personal compensation for activities with Elan Pharmaceuticals as a consultant. Dr. Daffner has nothing to disclose.

The neural mechanisms of percept–memory comparison in visual working memory

Researchers have revealed that comparing the perceptual input with the representations stored in visual working memory initiates a rapid attention-shift, which is predominantly triggered by the relevant-feature change. The comprehension of the change contents further necessitates a follow-up comparison that contrasts all the object features regardless of the task relevancy. However, whether such a distinct stage exists and how the process is carried on need further verification. We explored this issue by investigating the underlying neural mechanisms of the percept–memory comparison. By recording EEG, we found that both the task-relevant and -irrelevant feature changes elicited significantly more negative anterior N2 waves (230–340ms) rooting in the anterior cingulate cortex (ACC), and meanwhile activated the frontal theta (5–8Hz, 250–550ms). These results suggest that a distinct comparison stage does exist, which is supported by the anterior N2, ACC and frontal theta.

Dynamic cultural modulation of neural responses to one's own and friend's faces.

Long-term cultural experiences influence neural response to one's own and friend's faces. The present study investigated whether an individual's culturally specific pattern of neural activity to faces can be modulated by temporary access to other cultural frameworks using a self-construal priming paradigm. Event-related potentials were recorded from British and Chinese adults during judgments of orientations of one's own and friend's faces after they were primed with independent and interdependent self-construals. We found that an early frontal negative activity at 220–340 ms (the anterior N2) differentiated between one's own and friend's faces in both cultural groups. Most remarkably, for British participants, priming an interdependent self-construal reduced the default anterior N2 to their own faces. For Chinese participants, however, priming an independent self-construal suppressed the default anterior N2 to their friend's faces. These findings indicate fast modulations of culturally specific neural responses induced by temporary access to other cultural frameworks.

The influence of executive capacity on selective attention and subsequent processing.

Recent investigations that suggest selective attention (SA) is dependent on top-down control mechanisms lead to the expectation that individuals with high executive capacity (EC) would exhibit more robust neural indices of SA. This prediction was tested by using event-related potentials (ERPs) to examine differences in markers of information processing across 25 subjects divided into two groups based on high vs. average EC, as defined by neuropsychological test scores. Subjects performed an experimental task requiring SA to a specified color. In contrast to expectation, individuals with high and average EC did not differ in the size of ERP indices of SA: the anterior Selection Positivity (SP) and posterior Selection Negativity (SN). However, there were substantial differences between groups in markers of subsequent processing, including the anterior N2 (a measure of attentional control) and the P3a (an index of the orienting of attention). EC predicted speed of processing at both early and late attentional stages. Individuals with lower EC exhibited prolonged SN, P3a, and P3b latencies. However, the delays in carrying out SA operations did not account for subsequent delays in decision making, or explain excessive orienting and reduced attentional control mechanisms in response to stimuli that should have been ignored. SN latency, P3 latency, and the size of the anterior N2 made independent contributions to the variance of EC. In summary, our findings suggest that current views regarding the relationship between top-down control mechanisms and SA may need refinement.

Sustained target-driven interference under optimal preparation in a cued task switching paradigm using orthogonal polynomial trend analysis (OPTA)

Event Abstract Back to Event Sustained target-driven interference under optimal preparation in a cued task switching paradigm using orthogonal polynomial trend analysis (OPTA) Alexander Provost1, Andrew Heathcote2, Scott Brown2, Sharna Jamadar3 and Frini Karayanidis1* 1 University of Newcastle, School of Psychology, Australia 2 University of Newcastle, School of Psychology, Australia 3 Monash University, School of Psychology and Psychiatry, Australia Dual process models of cognitive control posit the existence of both proactive and reactive control processes. Cued task switching paradigms have differentiated these processes by measuring ERPs linked to advance preparation during the cue-target interval (CTI) and ERPs linked to resolution of target-driven interference after target onset. Using Orthogonal Polynomial Trend Analysis (OPTA) to extract cue-locked ERP waveforms corresponding to semi-deciles of each participant’s RT distribution, Karayanidis et al. (2011, Psychophysiology, 48, 559–568) showed that proactive control involves both switch-specific and general task preparation processes. A significant residual RT switch cost remained even at the fastest semi-decile that was associated with greater proactive control, suggesting that reactive control may be required to resolve post-target interference even on optimally prepared trials. In this paper, we use OPTA to examine target-locked ERP waveforms associated with different levels of preparation. Fast ‘prepared’ switch trials (i.e., large cue-locked switch-positivity and small RT switch cost) showed no anterior N2 and a large prominent P3b. Slow ‘unprepared’ switch trials (i.e., small switch-positivity and large switch cost) showed a large anterior N2 and a very small P3b. Similar variability in N2 and P3b amplitude was evident across the RT distribution for repeat trials. At the fastest percentile, switch trials produced a larger N2 and smaller P3b than repeat trials, indicating that fully prepared switch trials continue to show greater interference than fully prepared repeat trials. These findings are consistent with the notion that proactive control can reduce but does not eliminate post-target interference for switch trials. Keywords: cognitive control, task switching, OPTA, ERP, interference control Conference: ACNS-2012 Australasian Cognitive Neuroscience Conference, Brisbane, Australia, 29 Nov - 2 Dec, 2012. Presentation Type: Oral Presentation Topic: Executive Processes Citation: Provost A, Heathcote A, Brown S, Jamadar S and Karayanidis F (2012). Sustained target-driven interference under optimal preparation in a cued task switching paradigm using orthogonal polynomial trend analysis (OPTA). Conference Abstract: ACNS-2012 Australasian Cognitive Neuroscience Conference. doi: 10.3389/conf.fnhum.2012.208.00184 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 25 Oct 2012; Published Online: 17 Nov 2012. * Correspondence: Prof. Frini Karayanidis, University of Newcastle, School of Psychology, Newcastle, NSW 2308, Australia, frini.karayanidis@newcastle.edu.au Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Alexander Provost Andrew Heathcote Scott Brown Sharna Jamadar Frini Karayanidis Google Alexander Provost Andrew Heathcote Scott Brown Sharna Jamadar Frini Karayanidis Google Scholar Alexander Provost Andrew Heathcote Scott Brown Sharna Jamadar Frini Karayanidis PubMed Alexander Provost Andrew Heathcote Scott Brown Sharna Jamadar Frini Karayanidis Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

The time course of contextual effects on visual word recognition.

Sentence comprehension depends on continuous prediction of upcoming words. However, when and how contextual information affects the bottom-up streams of visual word recognition is unknown. This study examined the effects of word frequency and contextual predictability (cloze probability of a target word embedded in the sentence) on N1, P200, and N400 components, which are related to various cognitive operations in early visual processing, perceptual decoding, and semantic processing. The data exhibited a significant interaction between predictability and frequency at the anterior N1 component. The predictability effect, in which the low predictability words elicited a more negative N1 than high predictability words, was only observed when reading a high frequency word. A significant predictability effect occurred during the P200 time window, in which the low predictability words elicited a less positive P200 than high predictability words. There is also a significant predictability effect on the N400 component; low predictability words elicited a greater N400 than high predictability words, although this effect did not interact with frequency. The temporal dynamics of the manner in which contextual information affects the visual word recognition is discussed. These findings support the interactive account, suggesting that contextual information facilitates visual-feature and orthographic processing in the early stage of visual word processing and semantic integration in the later stage.

Is It a Baby? Perceived Age Affects Brain Processing of Faces Differently in Women and Men

It is known that infant faces stimulate visual and anterior brain regions belonging to the mesocortical limbic system (orbito-frontal cortex, anterior cingulate cortex, and nucleus accumbens) as well as the fusiform gyrus during face coding, suggesting a preferential response to baby schema. In the present investigation, faces of infants, children, and adults were presented to 40 male and female right-handed university students with technological objects (and inanimate scenarios to serve as targets) in a randomly mixed fashion. EEG was recorded from 128 scalp sites. In both sexes, the N1 response to infant faces was larger than the response to adult faces; however, the baby-specific N1 response was much larger in women than in men across the left hemisphere. The anterior N2 response to infants was greater than the response to children only in women, whereas the response to children of any age was larger than the response to adults in men. LORETA identified the intracranial sources of N2 response to infants in the left fusiform gyrus (FG), as well as the uncus, cingulate, and orbito-frontal cortices. The FG, the limbic, and especially the orbito-frontal sources were much larger in women than in men. The data suggest a sex difference in the brain response to faces of different ages and in the preferential response to infants, especially with regard to activation of the mesocorticolimbic system.

Dissociating action inhibition, conflict monitoring and sensory mismatch into independent components of event related potentials in GO/NOGO task

The anterior N2 and P3 waves of event related potentials (ERPs) in the GO/NOGO paradigm in trials related to preparatory set violations in previous studies were inconsistently associated either with action inhibition or conflict monitoring operations. In the present study a paired stimulus GO/NOGO design was used in order to experimentally control the preparatory sets. Three variants of the same stimulus task manipulated sensory mismatch, action inhibition and conflict monitoring operations by varying stimulus-response associations. The anterior N2 and P3 waves were decomposed into components by means of independent component analysis (ICA). The ICA was performed on collection of 114 individual ERPs in the three experimental conditions. Three of the independent components were selectively affected by the task manipulations indicating association of these components with sensory mismatch, action inhibition and conflict monitoring operations. According to sLORETA the sensory mismatch component was generated in the left and right temporal areas, the action suppression component was generated in the supplementary motor cortex, and the conflict monitoring component was generated in the anterior cingulate cortex.

Effects of visual stimulus complexity on event-related brain potentials and viewing duration in a free-viewing task

The anterior N2 is a component of the event-related brain potential (ERP) elicited by visual novel stimuli. Previous studies have reported that the stimuli that were viewed for longer periods of time elicited a larger anterior N2 than the stimuli viewed for shorter periods of time. To scrutinize this relationship between the ERP and viewing duration in response to visual materials, 18 university students were asked to look at various random polygons one-by-one for as long as they wished. ERPs time-locked to stimulus onset were averaged separately for three levels of complexity (12-, 24-, and 48-sided polygons). We found that the more complex the stimulus, the larger the anterior negativity (N2, 200–300ms) and the posterior positivity (late positive potential [LPP], 400–800ms), and the longer the viewing duration. However, when ERPs were calculated separately for the stimuli viewed for longer or shorter than the median viewing time of each participant at each complexity level, no amplitude differences were found in either component. These results suggest that the previously reported correlation between the anterior N2 and visual duration is spurious and produced by a third variable, namely, the perceptual demand of the eliciting stimulus such as complexity.