Event-related Potential Waveforms Research Articles

Study on the effect of nontarget types on name based auditory event-related potentials.

Exploring the brain response to stimuli of healthy people in passive state is helpful to understand the brain response mechanism of unresponsive people. Event-related potential (ERP) can reflect the time synchronization of potentials, which is a feasible objective electrophysiological index reflecting the functional status of the brain. In this paper, we used the subjects' own name (SON) as target stimuli and compared with the nontarget stimuli (others' name) of Three Chinese Characters (3CC) and Two Chinese Characters (2CC) with the same stimuli duration (600ms) and inter stimuli interval (500ms-800ms）. Thirteen healthy subjects attended in this study with four conditions ( [active, passive]×[3CC, 2CC] ). We compared the ERP waveforms, the behavior performance, and the classification of four different conditions. ERP results show that the P300 amplitude of conditions with 3CC nontargets is higher than that of conditions with 2CC nontargets. Behavioral results show that the grand accuracy is 97% when the nontargets are 3CC, while the grand accuracy is only 94% when the nontargets are 2CC. The reaction time is also different from the two nontargets (605ms with 3CC vs 635ms with 2CC). Classification results illustrate that in active condition, the accuracy rate is 82.1% when the nontarget is 3CC, and that is 80.9% in passive condition, which are 4.2% and 6.4% higher than the accuracy rate under 2CC cases in both active and passive conditions. This study can provide a scheme for grading diagnosis of consciousness detection, and further applying to clinical evaluation.Clinical Relevance- This study can provide a better paradigm basis for clinical evaluation of unresponsive patients (such as disorder of consciousness, DOC) and may become an effective auxiliary means for clinical rating scales.

Spatial covariance improves BCI performance for late ERPs components with high temporal variability

Objective. Event Related Potentials (ERPs) reflecting cognitive response to external stimuli, are widely used in brain computer interfaces. ERP waveforms are characterized by a series of components of particular latency and amplitude. The classical ERP decoding methods exploit this waveform characteristic and thus achieve a high performance only if there is sufficient time- and phase-locking across trials. The required condition is not fulfilled if the experimental tasks are challenging or if it is needed to generalize across various experimental conditions. Features based on spatial covariances across channels can potentially overcome the latency jitter and delays since they aggregate the information across time. Approach. We compared the performance stability of waveform and covariance-based features as well as their combination in two simulated scenarios: 1) generalization across experiments on Error-related Potentials and 2) dealing with larger latency jitter across trials. Main results. The features based on spatial covariances provide a stable performance with a minor decline under jitter levels of up to ± 300 ms, whereas the decoding performance with waveform features quickly drops from 0.85 to 0.55 AUC. The generalization across ErrP experiments also resulted in a significantly more stable performance with covariance-based features. Significance. The results confirmed our hypothesis that covariance-based features can be used to: 1) classify more reliably ERPs with higher intrinsic variability in more challenging real-life applications and 2) generalize across related experimental protocols.

Finding Suitable Clinical Endpoints for a Potential Treatment of a Rare Genetic Disease: the Case of ARID1B

There is a lack of reliable, repeatable, and non-invasive clinical endpoints when investigating treatments for intellectual disability (ID). The aim of this study is to explore a novel approach towards developing new endpoints for neurodevelopmental disorders, in this case for ARID1B-related ID. In this study, twelve subjects with ARID1B-related ID and twelve age-matched controls were included in this observational case–control study. Subjects performed a battery of non-invasive neurobehavioral and neurophysiological assessments on two study days. Test domains included cognition, executive functioning, and eye tracking. Furthermore, several electrophysiological assessments were performed. Subjects wore a smartwatch (Withings® Steel HR) for 6 days. Tests were systematically assessed regarding tolerability, variability, repeatability, difference with control group, and correlation with traditional endpoints. Animal fluency, adaptive tracking, body sway, and smooth pursuit eye movements were assessed as fit-for-purpose regarding all criteria, while physical activity, heart rate, and sleep parameters show promise as well. The event-related potential waveform of the passive oddball and visual evoked potential tasks showed discriminatory ability, but EEG assessments were perceived as extremely burdensome. This approach successfully identified fit-for-purpose candidate endpoints for ARID1B-related ID and possibly for other neurodevelopmental disorders. Next, results could be replicated in different ID populations or the assessments could be included as exploratory endpoint in interventional trials in ARID1B-related ID.

Effect of Sleep Deprivation on the Working Memory-Related N2-P3 Components of the Event-Related Potential Waveform.

Working memory is very sensitive to acute sleep deprivation, and many studies focus on the brain areas or network activities of working memory after sleep deprivation. However, little is known about event-related potential (ERP)-related changes in working memory after sleep loss. The purpose of this research was to explore the effects of 36 h of total sleep deprivation (TSD) on working memory through ERPs. Sixteen healthy college students performed working memory tasks while rested and after 36 h of TSD, and electroencephalography (EEG) data were simultaneously recorded while the subjects completed working memory tasks that included different types of stimulus materials. ERP data were statistically analyzed using repeated measurements analysis of variance to observe the changes in the working memory-related N2-P3 components. Compared with baseline before TSD, the amplitude of N2-P3 components related to working memory decreased, and the latency was prolonged after TSD. However, the increased amplitude of the P2 wave and the prolonged latency were found after 36 h of TSD. Thus, TSD can impair working memory capacity, which is characterized by lower amplitude and prolonged latency.

S138. A PRELIMINARY STUDY ON ILLNESS INSIGHT MEASURED BY THE RELATIONSHIP BETWEEN ERN PATTERNS AND MMPI RESULTS IN PATIENTS WITH SCHIZOPHRENIA

BackgroundThe error-related negativity (ERN) is an event-related brain potential waveform peaking about 50 ms after error commission in choice-response tasks and may indicate a conflict between neural representations of correct and incorrect responses as stimulus processing continues after an error. Most previous studies consistently reported a reduced event-related potential (ERP) amplitude in patients with schizophrenia compared with normal controls. Some self-report measures derived from the Minnesota Multiphasic Personality Inventory (MMPI) are known to be associated with clinical observations in carefully diagnosed schizophrenia patients. In the MMPI, an elevation of the validity scales in the MMPI best distinguishes patients with schizophrenia from patients feigning schizophrenia, and the MMPI validity scales are known to provide a good reflection of illness insight in schizophrenia.Both the amplitudes of the Pe of the ERN and the scores of the MMPI validity scales are supposed to reflect, directly or indirectly, the illness insight of patients with schizophrenia.When the abovementioned results obtained in studies on the ERN or MMPI in patients with schizophrenia are taken together, we may presume that a certain relationship exists between the results of the ERN and the MMPI validity scales in terms of illness insight.Interestingly, as far as we know, there are no published studies that looked at the results of the ERN and the MMPI at the same time.We tried to perform an integrative examination of the relationship between the results of the ERN and MMPI tests in patients with schizophrenia as a method of measuring illness insight in patients with schizophrenia.MethodsWe reviewed the medical records of who were diagnosed as having schizophrenia based on the DSM-5.The protocol for the general ERP and ERN are as follows.64 channels with M1 and M2 as reference electrodesImpedance: < 1 kΩERN: 1000 msERPs were recorded while the patients were performing the Stroop test. Independently of the ERP recording, the patients received an MMPI test.The relationship between the latency and amplitude of the ERN and the demographic and clinical variables was analyzed by a t-test, and correlation analyses were used for categorical and continuous variables. The statistical significance was set at p < 0.05.ResultsOf the total 18 patients (8 men and 10 women; age = 41.6 ± 15.8) whose data were reviewed, 5 were excluded due to poor understanding of the ERN instructions.Table 1. Demographic and clinical information of participated patientswith schizophreniaTable 2. Partial correlation coefficients on variables after controlling for age and gender.DiscussionThe results for the association of ERN amplitude and latency with the MMPI validity scales showed that latency measures were positively associated with the MMPI validity scales that were related to the assessment of the overestimation of responses. Individuals who tended to exaggerate problems through over-responses showed increased ERN amplitude but decreased ERN Pe amplitude. Although caution is needed to interpret the results of this study due to limitations, our results suggest that ERP measurement could act as a biological marker for endophenotype in schizophrenia. Furthermore, ERP measurement might be used to visualize or to make concrete illness insight, which by its nature is difficult to measure objectively.ReferencesYeung N, Botvinick MM, Cohen JD. The neural basis of error detection: conflict monitoring and the error-related negativity. Psychol Rev. 2004 Oct;111(4):931–959.Kansal V, Patriciu I, Kiang M. Illness insight and neurophysiological error-processing deficits in schizophrenia. Schizophr Res. 2014 Jun;156(1):122–7.

The error-related negativity (ERN) moderates the association between interpersonal stress and anxiety symptoms six months later

Anxiety disorders are often preceded by interpersonal stress; however, most individuals who experience stress do not develop anxiety, making it difficult to predict who is most susceptible to stress. One proposed trans-diagnostic neural risk marker for anxiety is the error-related negativity (ERN), a negative deflection in the event-related potential waveform occurring within 100 ms of error commission. The present study sought to investigate whether interpersonal stress experienced over the course of a year interacts with ERN magnitude to prospectively predict anxiety symptoms. A sample of 57 emerging adults performed an arrow flanker task to elicit the ERN at the start of the academic school year (time one). Toward the end of the academic year (time two), participants reported on past-year interpersonal stress and anxiety symptoms. Stress interacted with ERN magnitude to predict anxiety symptoms, whereby, for individuals with an enhanced ERN at time one, greater interpersonal stress over the course of a year was significantly associated with increased anxiety symptoms at time two, even controlling for anxiety symptoms at time one. These findings suggest that enhanced performance monitoring may render individuals more susceptible to the adverse effects of interpersonal stress, thereby increasing risk for heightened anxiety.

Neural differences between chromatic- and luminance-driven attentional salience in visual search.

Previous electroencephalographic research on attentional salience did not fully capture the complexities of low-level vision, which relies on both cone-opponent chromatic and cone-additive luminance mechanisms. We systematically varied color and luminance contrast using a visual search task for a higher contrast target to assess the degree to which the salience-computing attentional mechanisms are constrained by low-level visual inputs. In our first experiment, stimuli were defined by contrast that isolated chromatic or luminance mechanisms. In our second experiment, targets were defined by contrasts that isolated or combined achromatic and chromatic mechanisms. In both experiments, event-related potential waveforms contralateral and ipsilateral to the target were qualitatively different for chromatic- compared to luminance-defined stimuli. The same was true of the difference waves computed from these waveforms, with isoluminant stimuli eliciting a mid-latency posterior contralateral negativity (PCN) component and achromatic stimuli eliciting a complex of multiple components, including an early posterior contralateral positivity followed by a late-latency PCN. Combining color with luminance resulted in waveform and difference wave patterns equivalent to those of achromatic stimuli. When large levels of chromaticity contrast were added to targets with small levels of luminance contrast, PCN latency was speeded. In conclusion, the mechanisms underlying attentional salience are constrained by the low-level inputs they receive. Furthermore, speeded PCN latencies for stimuli that combine color and luminance signals compared to stimuli that contain luminance alone demonstrate that color and luminance channels are integrated during pre-attentive visual processing, before top-down allocation of attention is triggered.

Principle ERP reduction and analysis: Estimating and using principle ERP waveforms underlying ERPs across tasks, subjects and electrodes

Event-related potentials (ERP) waveforms are the summation of many overlapping signals. Changes in the peak or mean amplitude of a waveform over a given time period, therefore, cannot reliably be attributed to a particular ERP component of ex ante interest, as is the standard approach to ERP analysis. Though this problem is widely recognized, it is not well addressed in practice. Our approach begins by presuming that any observed ERP waveform — at any electrode, for any trial type, and for any participant — is approximately a weighted combination of signals from an underlying set of what we refer to as principle ERPs, or pERPs. We propose an accessible approach to analyzing complete ERP waveforms in terms of their underlying pERPs. First, we propose the principle ERP reduction (pERP-RED) algorithm for investigators to estimate a suitable set of pERPs from their data, which may span multiple tasks. Next, we provide tools and illustrations of pERP-space analysis, whereby observed ERPs are decomposed into the amplitudes of the contributing pERPs, which can be contrasted across conditions or groups to reveal which pERPs differ (substantively and/or significantly) between conditions/groups. Differences on all pERPs can be reported together rather than selectively, providing complete information on all components in the waveform, thereby avoiding selective reporting or user discretion regarding the choice of which components or windows to use. The scalp distribution of each pERP can also be plotted for any group/condition. We demonstrate this suite of tools through simulations and on real data collected from multiple experiments on participants diagnosed with Autism Spectrum Disorder and Attention Deficit Hyperactivity Disorder. Software for conducting these analyses is provided in the pERPred package for R.

Distant Sensor Prediction of Event-Related Potentials.

The ability to measure event-related potentials (ERPs) as practical, portable brain vital signs is limited by the physical locations of electrodes. Standard electrode locations embedded within the hair result in challenges to obtaining quality signals in a rapid manner. Moreover, these sites require electrode gel, which can be inconvenient. As electrical activity in the brain is spatially volume distributed, it should be possible to predict ERPs from distant sensor locations at easily accessible mastoid and forehead scalp regions. An artificial neural network was trained on ERP signals recorded from below hairline electrode locations (Tp9, Tp10, Af7, Af8 referenced to Fp1, Fp2) to predict signals recorded at the ideal Cz location. The model resulted in mean improvements in intraclass correlation coefficient relative to control for all stimulus types (Standard Tones: +9.74%, Deviant Tones: +3.23%, Congruent Words: +15.25%, Incongruent Words: +25.43%) and decreases in RMS Error (Standard Tones: -26.72%, Deviant Tones: -17.80%, Congruent Words: -28.78%, Incongruent Words: -29.61%) compared to the individual distant channels. Measured vs predicted ERP amplitudes were highly and significantly correlated with control for the N100 (R = 0.5, padj < 0.05), P300 (R = 0.75, padj < 0.01), and N400 (R = 0.75, padj < 0.01) ERPs. ERP waveforms at distant channels can be combined using a neural network autoencoder to model the control channel features with better precision than those at individual distant channels. This is the first demonstration of feasibility of predicting evoked potentials and brain vital signs using signals recorded from more distant, practical locations. This solves a key engineering challenge for applications that require portability, comfort, and speed of measurement as design priorities for measurement of event-related potentials across a range of individuals, settings, and circumstances.

Brief report on the relationship between temporal discount rate and error related negativity for immediate versus future choice options

It is well documented that individuals vary in their economic patience – their willingness to choose delayed larger rewards (e.g., $100 in a month) over immediate smaller rewards (e.g., $25 now) – and that high levels of impatience, or temporal discounting, can be behaviorally problematic. Using event-related potential (ERP) method, we investigated error monitoring, as indexed by the error related negativity (ERN) component, as a function of discounting behavior. This work builds on prior work on risky decision making that revealed that individuals have greater ERNs for trials in which they select a risky option over a certain one (Yu and Zhou 2009), especially individuals not inclined towards risk taking (Martin and Potts 2009). In the present study, participants completed a temporal discounting task (choosing between a fixed immediate reward versus a future reward that varied across trials) while electroencephalogram (EEG) activity was recorded. We found an asymmetric relationship between discounting and the ERN: the greater an individual's overall rate of discounting, the greater the ERN component of the ERP waveform on trials where the future reward was selected, but not on trials in which the immediate reward was selected. The ERN may reflect an early warning signal alerting high discounters to potential negative consequences of future-oriented choices.

Controlling parenting and perfectionism is associated with an increased error-related negativity (ERN) in young adults.

A substantial amount of research focuses on the error-related negativity (ERN)—a negative deflection in the event-related potential waveform that occurs when individuals commit errors on lab-based tasks. The ERN has been link to concurrent and prospective risk for psychopathology and is thought to index sensitivity or reactivity to errors. The ERN can be potentiated in the lab with punishment and has been shown to be increased among offspring of harsh or controlling parents. A separate line of work has demonstrated that the ERN is increased among individuals high in perfectionism. In the current study, we integrate these separate lines of work by examining parenting styles, perfectionism and the ERN in a sample of young adults. Results suggest that the ERN is increased among offspring of controlling parents (both maternal and paternal). Additionally, the ERN is increased among individuals who report being high in perfectionism—specifically, the concerns over mistake and the personal standard perfectionism subscales of the Frost Multidimensional Perfectionism Scale. Moreover, results supported a mediation model wherein the indirect pathway from controlling parenting style to perfectionism (personal standard subscale) was mediated by the ERN—for paternal parenting.

Error-related negativity (ERN) and ‘hot’ executive function in bilingual and monolingual preschoolers

AbstractEarly regular experience with dual-language management is thought to shape executive function (EF) circuitry during development. However, previous investigations of bilingual children's EF have largely focused on behavioral measures, or on cognitive aspects of EF. The first part of this study compared monolingual and bilingual preschoolers’ performance on more purely cognitive and more affective versions of a card-sort task, and the second part investigated Error-related negativity (ERN) event-related potential (ERP) waveforms to understand error-awareness mechanisms underlying task performance. Behavioral results showed bilingual advantages in reaction times but not accuracy, and interaction effects of language background, level of challenge, and affective/motivational salience on reaction times. Electrophysiological results revealed smaller ERN peak amplitudes in bilinguals compared to monolinguals in frontal and frontocentral midline regions. Results highlight that bilingualism may shape motivational mechanisms and neural learning mechanisms such as error-detection, such that bilinguals may be less focused on their errors.

Sensitivity of Reality Monitoring to Fluency: Evidence from Behavioral Performance and Event-Related Potential (ERP) Old/New Effects.

BackgroundItem memory and source memory are differently processed with both behavioral and event-related potential (ERP) evidence. Reality monitoring, a specific type of source memory, which refers to the ability to differentiate external sources from internal sources, has been drawing much attention. Among factors that have an impact on reality monitoring, fluency has not been well-studied. Therefore, the current study aimed to investigate whether fluency could affect reality monitoring, through observations on both behavioral performance and electrophysiological patterns.Material/MethodsAdopting ERP techniques, participants were required either to watch the presentation of a name/picture pair, or to imagine a picture for each displayed name, once (low fluency) or twice (high fluency). Later they completed a reality monitoring task of identifying names as perceived, imagined, or novel items. Behavioral performance was measured, and ERP waveforms were recorded.ResultsBehaviorally, high fluency items were faster and more accurately attributed to the sources than low fluency items. ERP waveforms revealed that late positive component (LPC) occurred for all 4 types of items, while imagined items of low fluency did not record a robust FN400 or late frontal old/new effect.ConclusionsAs results revealed, the factor of fluency does influence reality monitoring in terms of accuracy and responding speed. Meanwhile, for imagined items of low fluency, the absence of FN400 and frontal old/new effect also suggests the sensitivity of reality monitoring to fluency, because these representatives of familiarity-based processing and post-retrieval monitoring are inevitably involved in the process of differentiating internal source from external source.

Task difficulty modulates voluntary attention allocation, but not distraction in an auditory distraction paradigm

Keeping task-relevant sensory events in the focus of attention while ignoring irrelevant ones is crucial for optimizing task behavior. This attention-distraction balance might change with the perceptual demands of the ongoing task: while easy tasks might be performed with low attentional effort, difficult ones require enhanced attention. The goal of the present study was to investigate how task difficulty affected allocation of attention and distractibility in an auditory distraction paradigm. Participants performed a tone duration discrimination task in which tones were rarely, occasionally presented at a rare pitch (distracters), and task difficulty was manipulated by the duration difference between short and long tones. Short tones were consistently 200 ms long, while long tone duration was 400 ms in the easy, and 260 ms in the difficult condition. Behavioral results and deviant-minus-standard event-related potential (ERP) waveforms suggested similar magnitudes of distraction in both conditions. ERPs without such a subtraction showed that tone onsets were preceded by a negative-going trend, suggesting that participants prepared for tone onsets. In the difficult condition, N1 amplitudes to tone onsets were enhanced, indicating that participants invested more attentional resources. Increased difficulty also slowed down tone offset processing as reflected by significantly delayed offset-related P1 and N1/N2 waveforms. These results suggest that although task difficulty compels participants to attend the tones more strongly, this does not have significant impact on distraction-related processing.

Acute Moderate-Intensity Exercise Generally Enhances Attentional Resources Related to Perceptual Processing

The present study aimed to investigate whether acute moderate-intensity exercise led to a selective effect on executive function tasks or general effect on cognitive tasks that involve executive function and basic information processing in young adults. Besides, we also aimed to examine acute exercise’s effect on multiple ERP components (e.g., P2, N2, P3b, and N450) to expand previous research. Seventy-two young adults were randomly assigned to the exercise or control groups. The Stroop task was administrated before and after treatments (exercise or reading), and the P2, N2, P3b, and N450 components of the Event-Related Potential (ERP) waveform were recorded and analyzed. Larger P2 amplitudes on both congruent and incongruent tasks were observed following acute exercise. Acute exercise did not influence accuracy or response time, and no effects on N2, P3b, and N450 components were found. These findings suggest that acute moderate-intensity exercise may have a generally beneficial effect on mobilization of attentional resources related to perceptual processing and exercise-related physiological arousal.

Neither wrong nor right: Theta and delta power increase during performance monitoring under conditions of uncertainty

The brain's performance monitoring system monitors ongoing actions and signals the need for cognitive control to optimize behavior under uncertainty. In the lab, performance monitoring has been studied using the flanker task, wherein a single optimal behavior exists. However, in the real world, the majority of performance monitoring occurs in contexts where there is not a single best option, and these uncertain contexts may be especially aversive for some individuals. To that end, the present study sought to examine performance monitoring in the context of certain and uncertain responses in 62 adults. Specifically, we modified the flanker task such that, in addition to arrows pointing left or right, we explicitly instructed participants that they would have to respond to some stimuli for which there would be no right or wrong responses (i.e., ambiguous trials). Neural indices of performance monitoring were examined in both the temporal (error-related negativity (ERN), correct-response negativity (CRN), and stimulus-locked N2) and spectral domains (theta and delta power). Associations between intolerance of uncertainty (IU) and performance monitoring were also assessed. Ambiguous trials elicited a relative negativity in the event-related potential waveform that was smaller than both the ERN and CRN. However, these ambiguous trials elicited increases in both theta and delta power relative to correct responses. Increased inhibitory IU was uniquely associated with diminished performance monitoring on ambiguous trials. These findings indicate ongoing performance monitoring and execution of cognitive control under conditions where the accuracy of our actions is neither known nor important.

Neurophysiological Differences in Emotional Processing by Cochlear Implant Users, Extending Beyond the Realm of Speech

Cochlear implants (CIs) restore a sense of hearing in deaf individuals. However, they do not transmit the acoustic signal with sufficient fidelity, leading to difficulties in recognizing emotions in voice and in music. The study aimed to explore the neurophysiological bases of these limitations. Twenty-two adults (18 to 70 years old) with CIs and 22 age-matched controls with normal hearing participated. Event-related potentials (ERPs) were recorded in response to emotional bursts (happy, sad, or neutral) produced in each modality (voice or music) that were for the most part correctly identified behaviorally. Compared to controls, the N1 and P2 components were attenuated and prolonged in CI users. To a smaller degree, N1 and P2 were also attenuated and prolonged in music compared to voice, in both populations. The N1-P2 complex was emotion-dependent (e.g., reduced and prolonged response to sadness), but this was also true in both populations. In contrast, the later portion of the response, between 600 and 850 ms, differentiated happy and sad from neutral stimuli in normal hearing but not in CI listeners. The early portion of the ERP waveform reflected primarily the general reduction in sensory encoding by CI users (largely due to CI processing itself), whereas altered emotional processing (by CI users) could be found in the later portion of the ERP and extended beyond the realm of speech.

Comparison of Common Amplitude Metrics in Event-Related Potential Analysis

Waveform data resulting from time-intensive longitudinal designs require careful treatment. In particular, the statistical properties of summary metrics in this area are crucial. We draw on event-related potential (ERP) studies, a field with a relatively long history of collecting and analyzing such data, to illustrate our points. In particular, three summary measures for a component in the average ERP waveform feature prominently in the literature: the maximum (or peak amplitude), the average (or mean amplitude) and a combination (or adaptive mean). We discuss the methodological divide associated with these summary measures. Through both analytic work and simulation study, we explore the properties (e.g., Type I and Type II errors) of these competing metrics for assessing the amplitude of an ERP component across experimental conditions. The theoretical and simulation-based arguments in this article illustrate how design (e.g., number of trials per condition) and analytic (e.g., window location) choices affect the behavior of these amplitude summary measures in statistical tests and highlight the need for transparency in reporting the analytic steps taken. There is an increased need for analytic tools for waveform data. As new analytic methods are developed to address these time-intensive longitudinal data, careful treatment of the statistical properties of summary metrics used for null hypothesis testing is crucial.

Evaluation of flashing stimuli shape and colour heterogeneity using a P300 brain-computer interface speller

Previous works using a visual P300-based speller have reported an improvement modifying the shape or colour of the presented stimulus. However, the effects of both blended factors have not been yet studied. Thus, the aim of the present work was to study both factors and assess the interaction between them. Fifteen naïve participants tested four different spellers in a calibration and online task. All spellers were similar except the employed illumination of the target stimulus: white letters, white blocks, coloured letters, and coloured blocks. Regarding the results, the block-shaped conditions offered an improvement versus the letter-shaped conditions in the calibration (accuracy) and online (accuracy and correct commands per minute) tasks. The analysis of the event-related potential waveforms showed a larger difference between target and no target stimuli waveforms for the block-shaped conditions versus the letter-shaped. The hypothesis regarding the colour heterogeneity of the stimuli was not found at any level of the analysis. Therefore, this first study combining block-shaped and colour factors, and offering an exhaustive evaluation of both, demonstrated the superiority of block-shaped illumination versus the standard letter-shaped flashing stimuli in classification performance.

Early signal from the hippocampus for memory encoding.

The mediotemporal lobe (MTL), including the hippocampus, is involved in all stages of episodic memory including memory encoding, consolidation, and retrieval. However, the exact timing of the hippocampus' involvement immediately after stimulus encounter remains unclear. In this study, we used high-density 156-channel electroencephalography to study the processing of entirely new stimuli, which had to be encoded, in comparison to highly overlearned stimuli. Sixteen healthy subjects performed a continuous recognition task with meaningful pictures repeated up to four consecutive times. Waveform and topographic cluster analyses of event-related potentials revealed that new items, in comparison to repetitions, were processed significantly differently at 220-300 ms. Source estimation localized activation for processing new stimuli in the right MTL. Our study demonstrates the occurrence of a transient signal from the MTL in response to new information already at 200-300 ms poststimulus onset, which presumably reflects encoding as an initial step toward memory consolidation.