Event-related Potential Waveforms Research Articles

Inter-hemispheric frontal alpha synchronization of event-related potentials reflects memory-induced mental fatigue.

Mental fatigue is often associated with continuous brain activities in our daily life. It can diminish efficiency and increase errors. However, the related physiological features are still not clear and under exploration. The present study investigated changes of inter-hemispheric synchronization in event-related potentials (ERPs) due to mental fatigue during sustained memory processing. Twenty-six participants performed a continuous two-back memory task for around 2.5h. Prefrontal and frontal synchronies in the alpha frequency band (8-13Hz) were analyzed because of their close relationships with memory functions. Coherence was used to examine bilateral synchronization changes of ERP power and phase. We compared ERP coherences in both non-fatigued and fatigued states. We also observed the variation of ERP coherences during the continuous task. High overlaps of inter-hemispheric ERP waveforms were observed at prefrontal and frontal cortex in both non-fatigued and fatigued conditions. During the whole experimental procedure, ERP alpha coherences at frontal regions (FP1-FP2 and F3-F4) were significantly higher than at central (C3-C4), parietal (P3-P4) and occipital (O1-O2) regions. Alpha synchronization in anterior electrode pairs showed significant declines with increasing mental fatigue during the memory task. Our findings about changes in frontal ERP alpha synchronization might be used as biomarkers to assess mental fatigue induced by prolonged memory demands.

Concealed Around-the-Ear EEG Captures Cognitive Processing in a Visual Simon Task.

In theory, miniaturized systems such as the around-the-ear electrode arrays (cEEGrids) enable mobile monitoring of the electroencephalogram (EEG) in a variety of real life situations without interfering with the natural setting. However, the research benefit of such cEEGrid recordings critically depends on their validity. To investigate whether visual and motor processing are reflected in the cEEGrid-EEG, a direct comparison of EEG that was concurrently recorded with the cEEGrids and with a high-density cap setup was conducted. Thirteen participants performed a classic Simon task in which letters were presented laterally and a lateralized choice response was executed. N1, P1 and P300 event-related potential (ERP) waveforms were extracted from cEEGrid-EEG: they were found to be strongly correlated with corresponding waveforms extracted from cap-EEG but with lower signal strength and lower signal-to-noise-ratio (SNR). Event-related lateralizations (ERLs) recorded at posterior scalp sites were well reflected in middle cEEGrid pairs. Moreover, the effect size of the Simon correspondence effect on the extracted ERLs was similar between the two systems. However, lateralizations at central cap sites were less well reflected in the cEEGrid-EEG indicating a difficulty in capturing motor response preparation and execution. These results show that well-described visual and cognitive ERPs and ERLs can be measured using the cEEGrids, while motor-related cortical potentials are not well captured. This study further demonstrates the potential and possible limitations of unobtrusive cEEGrid-EEG recordings.

From neuro-pigments to neural efficiency: The relationship between retinal carotenoids and behavioral and neuroelectric indices of cognitive control in childhood

Lutein and zeaxanthin are plant pigments known to preferentially accumulate in neural tissue. Macular Pigment Optical Density (MPOD), a non-invasive measure of retinal carotenoids and surrogate measure of brain carotenoid concentration, has been associated with disease prevention and cognitive health. Superior MPOD status in later adulthood has been shown to provide neuroprotective effects on cognition. Given that childhood signifies a critical period for carotenoid accumulation in brain, it is likely that the beneficial impact would be evident during development, though this relationship has not been directly investigated. The present study investigated the relationship between MPOD and the behavioral and neuroelectric indices elicited during a cognitive control task in preadolescent children. 49 participants completed a modified flanker task while event-related potentials (ERPs) were recorded to assess the P3 component of the ERP waveform. MPOD was associated with both behavioral performance and P3 amplitude such that children with higher MPOD had more accurate performance and lower P3 amplitudes. These relationships were more pronounced for trials requiring greater amounts of cognitive control. These results indicate that children with higher MPOD may respond to cognitive tasks more efficiently, maintaining high performance while displaying neural indices indicative of lower cognitive load. These findings provide novel support for the neuroprotective influence of retinal carotenoids during preadolescence.

Effect of Different Attentional Conditions on ERP Detection of Visual Acuity

To study the effect of different attentional conditions on the event-related potential （ERP） components generated by the visual information stimuli related to visual acuity, and provide a theoretical reference for clinical forensic visual objective evaluation. With visual acuity optotypes as normal form of visual information stimuli, 15 volunteers as study subjects were supposed to account the visual acuity optotypes under the attentional condition of visual stimuli. Furthermore, the subjects were required to listen to the storytelling carefully under the non-attentional condition of visual stimuli, and after the examination, they needed to answer the story-related questions. All the EEG results of two different attentional conditions from the subjects were recorded by 32 channel ERP system. Under two attentional conditions, P₁ and P₃₀₀ components were evoked by the visual acuity optotypes on supra-threshold and threshold visual acuity levels, while only P₁ component were evoked by the visual acuity optotypes on sub-threshold levels. In the ERP waveforms evoked by the visual acuity optotypes on supra-threshold, P₁ and P₃₀₀ amplitudes under attentional condition were larger than that under non-attentional condition. Attentional conditions can influence the detection of visual acuity. P₃₀₀ component can be used to distinguish the visual acuity levels with supra-threshold and sub-threshold under non-attentional condition.

Event-related potential data from a guess the number brain-computer interface experiment on school children

Guess the number is a simple P300-based brain-computer interface experiment. Its aim is to ask the measured participant to pick a number between 1 and 9. Then, he or she is exposed to corresponding visual stimuli and experimenters try to guess the number thought while they are observing event-related potential waveforms on-line. 250 school-age children participated in the experiments that were carried out in elementary and secondary schools in the Czech Republic. Electroencephalographic data from three EEG channels (Fz, Cz, Pz) and stimuli markers were stored. Additional metadata about the participants were collected (gender, age, laterality, the number thought by the participant, the guess of the experimenters, and various interesting additional information). Consequently, we offer the largest publicly available odd-ball paradigm collection of datasets to neuroscientific and brain-computer interface community.

Neural evidence that inhibition is linked to the affective devaluation of distractors that match the contents of working memory

Stimuli appearing as visual distractors subsequently receive more negative affective evaluations than novel items or prior targets of attention. Leading accounts question whether this distractor devaluation effect occurs through evaluative codes that become associated with distractors as a mere artefact of attention-task instructions, or through affective consequences of attentional inhibition when applied to prevent distractor interference. Here we test opposing predictions arising from the evaluative-coding and devaluation-by-inhibition hypotheses using an electrophysiological marker of attentional inhibition in a task that requires participants to avoid interference from abstract-shape distractors presented while maintaining a uniquely-colored stimulus in memory. Consistent with prior research, distractors that matched the colour of the stimulus being held in memory elicited a Pd component of the event-related potential waveform, indicating that their processing was being actively suppressed. Subsequent affective evaluations revealed that memory-matching distractors also received more negative ratings than non-matching distractors or previously-unseen shapes. Moreover, Pd magnitude was greater on trials in which the memory-matching distractors were later rated negatively than on trials preceding positive ratings. These results support the devaluation-by-inhibition hypothesis and strongly suggest that fluctuations in stimulus inhibition are closely associated with subsequent affective evaluations. In contrast, none of the evaluative-coding based predictions were confirmed.

A multi-dimensional functional principal components analysis of EEG data.

The electroencephalography (EEG) data created in event-related potential (ERP) experiments have a complex high-dimensional structure. Each stimulus presentation, or trial, generates an ERP waveform which is an instance of functional data. The experiments are made up of sequences of multiple trials, resulting in longitudinal functional data and moreover, responses are recorded at multiple electrodes on the scalp, adding an electrode dimension. Traditional EEG analyses involve multiple simplifications of this structure to increase the signal-to-noise ratio, effectively collapsing the functional and longitudinal components by identifying key features of the ERPs and averaging them across trials. Motivated by an implicit learning paradigm used in autism research in which the functional, longitudinal, and electrode components all have critical interpretations, we propose a multidimensional functional principal components analysis (MD-FPCA) technique which does not collapse any of the dimensions of the ERP data. The proposed decomposition is based on separation of the total variation into subject and subunit level variation which are further decomposed in a two-stage functional principal components analysis. The proposed methodology is shown to be useful for modeling longitudinal trends in the ERP functions, leading to novel insights into the learning patterns of children with Autism Spectrum Disorder (ASD) and their typically developing peers as well as comparisons between the two groups. Finite sample properties of MD-FPCA are further studied via extensive simulations.

Motivated attention and family risk for depression: Neuronal generator patterns at scalp elicited by lateralized aversive pictures reveal blunted emotional responsivity.

Behavioral and electrophysiologic evidence suggests that major depression (MDD) involves right parietotemporal dysfunction, a region activated by arousing affective stimuli. Building on prior event-related potential (ERP) findings (Kayser et al. 2016 NeuroImage 142:337–350), this study examined whether these abnormalities also characterize individuals at clinical high risk for MDD. We systematically explored the impact of family risk status and personal history of depression and anxiety on three distinct stages of emotional processing comprising the late positive potential (LPP). ERPs (72 channels) were recorded from 74 high and 53 low risk individuals (age 13–59 years, 58 male) during a visual half-field paradigm using highly-controlled pictures of cosmetic surgery patients showing disordered (negative) or healed (neutral) facial areas before or after treatment. Reference-free current source density (CSD) transformations of ERP waveforms were quantified by temporal principal components analysis (tPCA). Component scores of prominent CSD-tPCA factors sensitive to emotional content were analyzed via permutation tests and repeated measures ANOVA for mixed factorial designs with unstructured covariance matrix, including gender, age and clinical covariates. Factor-based distributed inverse solutions provided descriptive estimates of emotional brain activations at group level corresponding to hierarchical activations along ventral visual processing stream. Risk status affected emotional responsivity (increased positivity to negative-than-neutral stimuli) overlapping early N2 sink (peak latency 212 ms), P3 source (385 ms), and a late centroparietal source (630 ms). High risk individuals had reduced right-greater-than-left emotional lateralization involving occipitotemporal cortex (N2 sink) and bilaterally reduced emotional effects involving posterior cingulate (P3 source) and inferior temporal cortex (630 ms) when compared to those at low risk. While the early emotional effects were enhanced for left hemifield (right hemisphere) presentations, hemifield modulations did not differ between risk groups, suggesting top-down rather than bottom-up effects of risk. Groups did not differ in their stimulus valence or arousal ratings. Similar effects were seen for individuals with a lifetime history of depression or anxiety disorder in comparison to those without. However, there was no evidence that risk status and history of MDD or anxiety disorder interacted in their impact on emotional responsivity, suggesting largely independent attenuation of attentional resource allocation to enhance perceptual processing of motivationally salient stimuli. These findings further suggest that a deficit in motivated attention preceding conscious awareness may be a marker of risk for depression.

Experimental research on the tactile perception from fingertip skin friction

Skin friction is a main perception channel for humankind to recognize object surface properties. However, the relationship between tactile perception and skin friction is a typical bio-tribology interdisciplinary problem, which is rarely studied both in biology and tribology fields. In order to study the brain stimulation response to the fingertips sliding friction, cognitive related fingertip friction testing was carried out, and the tactile perception evoked by the friction and vibration of various surface textures was investigated in this paper, human subjective tactile experiments was carried out through twenty volunteers testing for the tactile perception of surface properties, focused on three fabric samples (cotton, linen and silk) and three paper samples (photo paper, kraft paper and normal paper). The friction coefficient and frictional vibration signals were measured, and the brain response signals stimulated by the fingertip friction were simultaneously recorded and analyzed. The research works in this paper are beneficial for the deep understanding of tactile perception mechanism by fingertips, and building up a biomimetic model for smart robotic fingers.The research results indicate that the cerebral cortex responds sensitively to the variations in fingertips frictional force and vibration amplitudes. The human tactile perception is very sensitive to the fabric texture properties, which are described by the dimensions such as rough-smooth, coarse-fine and complex-uniform. The higher values of the fabric texture dimensions, the lower values in friction coefficient, and the more sensitive of tactile perception for the surface textures. Furthermore, it is noticed that the amplitude and distribution of brain signals response, i.e. ERPs (event related potentials) evoked by fingertip friction, is affected by the surface texture or friction coefficient. It is found that the response sensibility shown on the beginning peaks of ERP waveform has strong relation to the frictional stimulus on fingertip friction. The parameter of P3 latency (i.e. the third positive peak of ERP) is the distinct identifying information for the tactile perception of surface textures.

Total variation for the analysis of event-related potentials

BackgroundEvent-related potential waveforms are often analysed in the time-domain for changes of striking morphological features, like amplitudes or latencies of extrema, at the expense of missing less obvious changes in overall morphology. New methodThe measure of total variation can capture a variety of changes in curve morphology. We show analytical examples, and the application to two sets of EEG data (n1=41, n2=19) difficult to analyse with more traditional methods. ResultsTotal variation can be used to identify the effects of experimental manipulations on event-related potential waveforms, and can additionally be used to identify the respective time windows by means of hierarchical subdivision of longer signals. Comparison with existing methodsThe ANOVA of total variation provided additional insights into effects already hinted at by the ANOVA of global field power in the first experiment, and identified a number of interactions missed by an ANOVA of amplitude as well as a topographic ANOVA in the second one. ConclusionsThe analysis of total variation can be an interesting complement to more traditional analyses, especially when changes are hard to assess with traditional methods, e.g. in the absence of pronounced extrema, or the presence of noise or large interindividual variations of latency.

Distinguishing Neural Adaptation and Predictive Coding Hypotheses in Auditory Change Detection.

The auditory mismatch negativity (MMN) component of event-related potentials (ERPs) has served as a neural index of auditory change detection. MMN is elicited by presentation of infrequent (deviant) sounds randomly interspersed among frequent (standard) sounds. Deviants elicit a larger negative deflection in the ERP waveform compared to the standard. There is considerable debate as to whether the neural mechanism of this change detection response is due to release from neural adaptation (neural adaptation hypothesis) or from a prediction error signal (predictive coding hypothesis). Previous studies have not been able to distinguish between these explanations because paradigms typically confound the two. The current study disambiguated effects of stimulus-specific adaptation from expectation violation using a unique stimulus design that compared expectation violation responses that did and did not involve stimulus change. The expectation violation response without the stimulus change differed in timing, scalp distribution, and attentional modulation from the more typical MMN response. There is insufficient evidence from the current study to suggest that the negative deflection elicited by the expectation violation alone includes the MMN. Thus, we offer a novel hypothesis that the expectation violation response reflects a fundamentally different neural substrate than that attributed to the canonical MMN.

Neural correlates of cognitive set shifting in amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) has been associated with executive dysfunction, particularly in the domain of cognitive set shifting. In a recent event-related potential (ERP) study, shifting-related cortical activity on a complex set-shifting paradigm was found to be attenuated in patients with ALS. Here, we investigated whether this ERP change could also be observed in a simplified set-shifting task adapted for potential clinical use, and in ALS patients without overt cognitive impairment. Twenty-six patients and 28 matched healthy controls (HC) completed a set-shifting paradigm involving two task rules and explicit task cues. Cue-locked ERPs were analyzed. ALS patients and HC did not differ in response latency or accuracy. In HC, cues that required shifting task rules elicited more positive parietal ERP waveforms than cues that signaled a rule repetition. This shifting-related amplitude modulation was absent in patients with ALS. The attenuation of ERP activity in ALS patients remained significant when participants with possible cognitive impairment were excluded. Electrophysiological measures can detect ALS-related changes in the neural substrates of set shifting even when these changes do not become apparent in neuropsychological assessment. These findings illustrate the potential utility of ERPs as indicators of cognitive change in ALS.

Reconstructing ERP amplitude effects after compensating for trial-to-trial latency jitter: A solution based on a novel application of residue iteration decomposition

Stimulus-locked averaged event-related potentials (ERPs) are among the most frequently used signals in Cognitive Neuroscience. However, the late, cognitive or endogenous ERP components are often variable in latency from trial to trial in a component-specific way, compromising the stability assumption underlying the averaging scheme. Here we show that trial-to-trial latency variability of ERP components not only blurs the average ERP waveforms, but may also attenuate existing or artificially induce condition effects in amplitude. Hitherto this problem has not been well investigated. To tackle this problem, a method to measure and compensate component-specific trial-to-trial latency variability is required. Here we first systematically analyze the problem of single trial latency variability for condition effects based on simulation. Then, we introduce a solution by applying residue iteration decomposition (RIDE) to experimental data. RIDE separates different clusters of ERP components according to their time-locking to stimulus onsets, response times, or neither, based on an algorithm of iterative subtraction. We suggest to reconstruct ERPs by re-aligning the component clusters to their most probable single trial latencies. We demonstrate that RIDE-reconstructed ERPs may recover amplitude effects that are diminished or exaggerated in conventional averages by trial-to-trial latency jitter. Hence, RIDE-corrected ERPs may be a valuable tool in conditions where ERP effects may be compromised by latency variability.

Event-Related Potential Effects of Object Repetition Depend on Attention and Part-Whole Configuration.

The effects of spatial attention and part-whole configuration on recognition of repeated objects were investigated with behavioral and event-related potential (ERP) measures. Short-term repetition effects were measured for probe objects as a function of whether a preceding prime object was shown as an intact image or coarsely scrambled (split into two halves) and whether or not it had been attended during the prime display. In line with previous behavioral experiments, priming effects were observed from both intact and split primes for attended objects, but only from intact (repeated same-view) objects when they were unattended. These behavioral results were reflected in ERP waveforms at occipital–temporal locations as more negative-going deflections for repeated items in the time window between 220 and 300 ms after probe onset (N250r). Attended intact images showed generally more enhanced repetition effects than split ones. Unattended images showed repetition effects only when presented in an intact configuration, and this finding was limited to the right-hemisphere electrodes. Repetition effects in earlier (before 200 ms) time windows were limited to attended conditions at occipito-temporal sites during the N1, a component linked to the encoding of object structure, while repetition effects at central locations during the same time window (P150) were found for attended and unattended probes but only when repeated in the same intact configuration. The data indicate that view-generalization is mediated by a combination of analytic (part-based) representations and automatic view-dependent representations.

The magnitude of the central visual field could be detected by active middle-late processing of ERPs

This study investigated the changes in event-related potential (ERP) waveforms under different central visual field conditions using a three-stimulus oddball paradigm. Circular checkerboards were presented in the center of a computer screen with a visual angle of 5°, 10°, 20°, or 30°, which were regarded as target stimuli. The ERP waveforms were analyzed separately for different stimulus conditions. Participants responded more slowly and had lower accuracy for the 30° visual field level than the other three visual field levels. The ERP results revealed that the amplitudes of target P2 gradually increased from the 5° to 20° visual field conditions, while they decreased abruptly in the 30° visual field condition. Regional effects showed that the amplitudes of target P2 were larger from the occipital electrodes than that from the temporal sites. Besides the negative-going deflection of target N2 and visual mismatch negativity (vMMN) components having an increasing tendency with expansion of the visual field, there was also a trend that the amplitudes of target P3 were decreased and the peak latencies were prolonged with increasing visual field ranges. In addition, the latencies of the difference P3 had a similar trend to the latencies of the target P3, and all the differences were more obvious at the 30° visual field level. The study demonstrated that middle-late components of ERPs can reflect changes in the visual field to some extent.

Healthy Restrained Eaters Diminish Consummatory Food Reward and Inhibit Prepotent Feeding Responses: An EEG Study

Background: Some individuals with modest elevations in dietary restraint exhibit the ability to diminish consummatory and anticipatory food reward. In this paper we aim to identify the underlying mechanisms of food-specific cortical inhibition responses in restrained vs unrestrained eaters. Methods: Restrained (n = 43) and unrestrained eaters (n = 38) completed self-report surveys and a food- vs non-food Stroop task protocol with record of electroencephalography (EEG). Cortical rhythms and EEG ERPs were assessed. Results: Compared to their unrestrained peers, restrained eaters showed several differences in food task-related event-related potential (ERP) waveform presentation: ERP P300 component latency was significantly longer during food image viewing over the left parietal cortex (P3), and the amplitudes of the ERP P300 and LPP components were significantly greater over the right central electrode (C4) whilst responding to Stroop color-word cues. Food task-related conflict cue elicited ERP P300 amplitude correlated positively with eating restraint, and negatively with bioelectrical impedance assessed % body fat. Conclusions: Restrained eaters free of eating pathology attenuate conscious visual food cue processing and show enhanced executive brain functioning during late attentional processing despite the presence of distractor food cues. Our data propose robust executive governance as the primary underlying neurophysiological mechanism by which healthy restrained eaters diminish consummatory food reward and inhibit prepotent feeding responses.

A new method to detect event-related potentials based on Pearson's correlation.

Event-related potentials (ERPs) are widely used in brain-computer interface applications and in neuroscience. Normal EEG activity is rich in background noise, and therefore, in order to detect ERPs, it is usually necessary to take the average from multiple trials to reduce the effects of this noise. The noise produced by EEG activity itself is not correlated with the ERP waveform and so, by calculating the average, the noise is decreased by a factor inversely proportional to the square root of N, where N is the number of averaged epochs. This is the easiest strategy currently used to detect ERPs, which is based on calculating the average of all ERP’s waveform, these waveforms being time- and phase-locked. In this paper, a new method called GW6 is proposed, which calculates the ERP using a mathematical method based only on Pearson’s correlation. The result is a graph with the same time resolution as the classical ERP and which shows only positive peaks representing the increase—in consonance with the stimuli—in EEG signal correlation over all channels. This new method is also useful for selectively identifying and highlighting some hidden components of the ERP response that are not phase-locked, and that are usually hidden in the standard and simple method based on the averaging of all the epochs. These hidden components seem to be caused by variations (between each successive stimulus) of the ERP’s inherent phase latency period (jitter), although the same stimulus across all EEG channels produces a reasonably constant phase. For this reason, this new method could be very helpful to investigate these hidden components of the ERP response and to develop applications for scientific and medical purposes. Moreover, this new method is more resistant to EEG artifacts than the standard calculations of the average and could be very useful in research and neurology. The method we are proposing can be directly used in the form of a process written in the well-known Matlab programming language and can be easily and quickly written in any other software language.Electronic supplementary materialThe online version of this article (doi:10.1186/s13637-016-0043-z) contains supplementary material, which is available to authorized users.

The Relationship Between Engagement and Neurophysiological Measures of Attention in Motion-Controlled Video Games: A Randomized Controlled Trial.

BackgroundVideo games and virtual environments continue to be the subject of research in health sciences for their capacity to augment practice through user engagement. Creating game mechanics that increase user engagement may have indirect benefits on learning (ie, engaged learners are likely to practice more) and may also have direct benefits on learning (ie, for a fixed amount of practice, engaged learners show superior retention of information or skills).ObjectiveTo manipulate engagement through the aesthetic features of a motion-controlled video game and measure engagement’s influence on learning.MethodsA group of 40 right-handed participants played the game under two different conditions (game condition or sterile condition). The mechanics of the game and the amount of practice were constant. During practice, event-related potentials (ERPs) to task-irrelevant probe tones were recorded during practice as an index of participants’ attentional reserve. Participants returned for retention and transfer testing one week later.ResultsAlthough both groups improved in the task, there was no difference in the amount of learning between the game and sterile groups, countering previous research. A new finding was a statistically significant relationship between self-reported engagement and the amplitude of the early-P3a (eP3a) component of the ERP waveform, such that participants who reported higher levels of engagement showed a smaller eP3a (beta=−.08, P=.02).ConclusionsThis finding provides physiological data showing that engagement elicits increased information processing (reducing attentional reserve), which yields new insight into engagement and its underlying neurophysiological properties. Future studies may objectively index engagement by quantifying ERPs (specifically the eP3a) to task-irrelevant probes.

The effect of modulating top-down attention deployment on the N2pc/PCN

The N2pc (PCN) component of the event-related potential (ERP) waveform provides a useful tool for directly assessing the locus of spatial attention in visual search. It is still unclear whether the amplitude of the N2pc/PCN relates to the deployment of attentional resources. A key issue is the lack of evidence that top-down allocation of attention affects the N2pc/PCN amplitude. Previous findings could be explained if manipulating different expectancy strategies changes participants’ search mode, causing them to redefine the target’s features. In this study, we explored the relationship between N2pc/PCN amplitude and top-down attention allocation by manipulating the discriminative difficulty (differences in the response-defining feature) but leaving the search difficulty (target’s saliency) unchanged. Using the same sets of stimuli, in a blocked condition, participants showed the expected higher amplitude of N2pc/PCN in the hardest condition, compared to easier discrimination conditions. Importantly, there was no difference in the N2pc/PCN when the exact same stimulus sets were presented in a randomly interleaved mixed set. At a behavioral level, in both conditions performance was significantly slower for the hardest condition. This finding indicates that the N2pc/PCN component is modulated by the predictability of discriminative difficulty, which reflects the modulation of top-down attentional deployment.

Bootstrap Signal-to-Noise Confidence Intervals: An Objective Method for Subject Exclusion and Quality Control in ERP Studies.

Analysis of event-related potential (ERP) data includes several steps to ensure that ERPs meet an appropriate level of signal quality. One such step, subject exclusion, rejects subject data if ERP waveforms fail to meet an appropriate level of signal quality. Subject exclusion is an important quality control step in the ERP analysis pipeline as it ensures that statistical inference is based only upon those subjects exhibiting clear evoked brain responses. This critical quality control step is most often performed simply through visual inspection of subject-level ERPs by investigators. Such an approach is qualitative, subjective, and susceptible to investigator bias, as there are no standards as to what constitutes an ERP of sufficient signal quality. Here, we describe a standardized and objective method for quantifying waveform quality in individual subjects and establishing criteria for subject exclusion. The approach uses bootstrap resampling of ERP waveforms (from a pool of all available trials) to compute a signal-to-noise ratio confidence interval (SNR-CI) for individual subject waveforms. The lower bound of this SNR-CI (SNRLB) yields an effective and objective measure of signal quality as it ensures that ERP waveforms statistically exceed a desired signal-to-noise criterion. SNRLB provides a quantifiable metric of individual subject ERP quality and eliminates the need for subjective evaluation of waveform quality by the investigator. We detail the SNR-CI methodology, establish the efficacy of employing this approach with Monte Carlo simulations, and demonstrate its utility in practice when applied to ERP datasets.