Updating and validating a new framework for restoring and analyzing latency‐variable ERP components from single trials with residue iteration decomposition (RIDE)

Trial‐to‐trial latency variability pervades cognitive EEG responses and may mix and smear ERP components but is usually ignored in conventional ERP averaging. Existing attempts to decompose temporally overlapping and latency‐variable ERP components show major limitations. Here, we propose a theoretical framework and model of ERPs consisting of temporally overlapping components locked to different external events or varying in latency from trial to trial. Based on this model, a new ERP decomposition and reconstruction method was developed: residue iteration decomposition (RIDE). Here, we describe an update of the method and compare it to other decomposition methods in simulated and real datasets. The updated RIDE method solves the divergence problem inherent to previous latency‐based decomposition methods. By implementing the model of ERPs as consisting of time‐variable and invariable single‐trial component clusters, RIDE obtains latency‐corrected ERP waveforms and topographies of the components, and yields dynamic information about single trials.     

S‐R compatibility effects on motor potentials associated with hand and foot movements

Two four‐choice reaction time (RT) experiments used the lateralized readiness potential (LRP) and the limb selection potential (LSP) to assess the effects of spatial S‐R compatibility on motor processes. Individual stimuli were presented at one corner of a square centered at fixation, and each response was made with the left or right hand or foot. In Experiment 1, the correct response was determined by stimulus location, whereas in Experiment 2 it was determined by stimulus identity. Horizontal and vertical compatibility affected both RT and response accuracy, but the LRP and LSP results suggested that compatibility had little or no direct effect on the duration of motor processes. In addition, the results suggest that the relatively new LSP measure is a useful index of motor activation processes. Its insensitivity to horizontal stimulus artifacts makes it especially useful for studying the effects of horizontal spatial compatibility.     

Similarities and differences between interference from stimulus position and from direction of an arrow: Behavioral and event-related potential measures

Studies with stimulus–response compatibility (SRC) tasks used the stimulus position (SRC-p) and/or the direction indicated by a central arrow (SRC-d) as irrelevant dimensions. Despite behavioral differences revealed by the distributional analysis (DA), both interferences were established at similar loci on the basis of modulations in the lateralized readiness potential (LRP) and P3b components. Consequently, similar underlying mechanisms were proposed for both interferences. However, comparison of motor processes associated with each task is problematical because each involves different components. In addition, previous studies have frequently used different proportions of trials between conditions, which complicate interpretation of the results because the stimulus probability may modulate P3b. Taking these problems into account, the present study investigated the effects of interference in SRC-p and SRC-d tasks, in which the participants responded to the color of a stimulus while ignoring the position and the direction indicated by a central arrow, respectively. The interference was greater in the SRC-p than in the SRC-d task. The DA showed that stimulus position affected the performance more quickly than the direction of the arrow. The P3b latency was longer and the P3b amplitude was smaller when stimulus position was incompatible. However, no differences in P3b were found in the SRC-d task. Moreover, both types of interference affected response-related processes (LRP-r) similarly. Therefore, the stimulus position and the direction indicated by the stimulus may share a common locus of interference (response execution), but only stimulus position affects P3b component, which constitutes a link between stimulus evaluation and the response selection.     

Electrophysiological dynamics reveal distinct processing of stimulus‐stimulus and stimulus‐response conflicts

The present study examined electroencephalogram profiles on a novel stimulus‐response compatibility (SRC) task in order to elucidate the distinct brain mechanisms of stimulus‐stimulus (S‐S) and stimulus‐response (S‐R) conflict processing. The results showed that the SRC effects on reaction times (RTs) and N2 amplitudes were additive when both S‐S and S‐R conflicts existed. We also observed that, for both RTs and N2 amplitudes, the conflict adaptation effects—the reduced SRC effect following an incongruent trial versus a congruent trial—were present only when two consecutive trials involved the same type of conflict. Time‐frequency analysis revealed that both S‐S and S‐R conflicts modulated power in the theta band, whereas S‐S conflict additionally modulated power in the alpha and beta bands. In summary, our findings provide insight into the domain‐specific conflict processing and the modular organization of cognitive control.     

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

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

Reduced premovement positivity during the stimulus‐response interval precedes errors: Using single‐trial and regression ERPs to understand performance deficits in ADHD

Brain mechanisms linked to incorrect response selections made under time pressure during cognitive task performance are poorly understood, particularly in adolescents with attention‐deficit hyperactivity disorder (ADHD). Using subject‐specific multimodal imaging (electroencephalogram, magnetic resonance imaging, behavior) during flanker task performance by a sample of 94 human adolescents (mean age = 15.5 years, 50% female) with varying degrees of ADHD symptomatology, we examined the degree to which amplitude features of source‐resolved event‐related potentials (ERPs) from brain‐independent component processes within a critical (but often ignored) period in the action selection process, the stimulus‐response interval, were associated with motor response errors (across trials) and error rates (across individuals). Response errors were typically preceded by two smaller peaks in both trial‐level and trial‐averaged ERP projections from posterior medial frontal cortex (pMFC): a frontocentral P3 peaking about 390 ms after stimulus onset, and a premovement positivity (PMP) peaking about 110 ms before the motor response. Separating overlapping stimulus‐locked and response‐locked ERP contributions using a “regression ERP” approach showed that trial errors and participant error rates were primarily associated with smaller PMP, and not with frontocentral P3. Moreover, smaller PMP mediated the association between larger numbers of errors and ADHD symptoms, suggesting the possible value of using PMP as an intervention target to remediate performance deficits in ADHD.     

Overcoming limitations of the ERP method with Residue Iteration Decomposition (RIDE): A demonstration in go/no‐go experiments

The usefulness of the event‐related potential (ERP) method can be compromised by violations of the underlying assumptions, for example, confounding variations of latency and amplitude of ERP components within and between conditions. Here we show how the ERP subtraction method might yield misleading information due to latency variability of ERP components. We propose a solution to this problem by correcting for latency variability using Residue Iteration Decomposition (RIDE), demonstrated with data from representative go/no‐go experiments. The overlap of N2 and P3 components in go/no‐go data gives rise to spurious topographical localization of the no‐go–N2 component. RIDE decomposes N2 and P3 based on their latency variability. The decomposition restored the N2 topography by removing the contamination from latency‐variable late components. The RIDE‐derived N2 and P3 give a clearer insight about their functional relevance in the go/no‐go paradigm.     

Contextual cueing effects despite spatially cued target locations

Reaction times (RT) to targets are faster in repeated displays relative to novel ones when the spatial arrangement of the distracting items predicts the target location (contextual cueing). It is assumed that visual–spatial attention is guided more efficiently to the target resulting in reduced RTs. In the present experiment, contextual cueing even occurred when the target location was previously peripherally cued. Electrophysiologically, repeated displays elicited an enhanced N2pc component in both conditions and resulted in an earlier onset of the stimulus‐locked lateralized readiness potential (s‐LRP) in the cued condition and in an enhanced P3 in the uncued condition relative to novel displays. These results indicate that attentional guidance is less important than previously assumed but that other cognitive processes, such as attentional selection (N2pc) and response‐related processes (s‐LRP, P3) are facilitated by context familiarity.     

The N2cc component as an electrophysiological marker of space‐based and feature‐based attentional target selection processes in touch

An electrophysiological correlate of attentional target selection processes in touch (N2cc component) has recently been discovered in lateralized tactile working memory experiments. This tactile N2cc emerges at the same time as the visual N2pc component but has a different modality‐specific topography over central somatosensory areas. Here, we investigated links between N2cc components and the space‐based versus feature‐based attentional selection of task‐relevant tactile stimuli. On each trial, a pair of tactile items was presented simultaneously to one finger on the left and right hand. Target stimuli were defined by their location (e.g., left index finger; Spatial Attention Task), by a nonspatial feature (continuous vs. pulsed; Feature‐Based Attention Task), or by a combination of spatial and nonspatial features (Conjunction Task). Reliable N2cc components were observed in all three tasks. They emerged considerably earlier in the Spatial Attention Task than in the Feature‐Based Attention Task, suggesting that space‐based selection mechanisms in touch operate faster than feature‐guided mechanisms. The temporal pattern of N2cc components observed in the Conjunction Task revealed that space‐based and feature‐based attention both contributed to target selection, which was initially driven primarily by spatial location. Overall, these findings establish the N2cc component as a new electrophysiological marker of the selective attentional processing of task‐relevant stimuli in touch.     

The functional locus of the lateralized readiness potential

The lateralized readiness potential (LRP) is considered to reflect motor activation and has been used extensively as a tool in elucidating cognitive processes. In the present study, we attempted to more precisely determine the origins of the LRP within the cognitive system. The response selection and motor programming stages were selectively manipulated by varying symbolic stimulus response compatibility and the time to peak force of an isometric finger extension response. Stimulus response compatibility and time to peak force affected response latency, as measured in the electromyogram, in a strictly additive fashion. The effects of the experimental manipulations on stimulus- and response-synchronized LRPs indicate that the LRP starts after the completion of response-hand selection and at the beginning of motor programming. These results allow a more rigorous interpretation of LRP findings in basic and applied research.     

Event‐related EEG time‐frequency PCA and the orienting reflex to auditory stimuli

We recently reported an auditory habituation series with counterbalanced indifferent and significant (counting) instructions. Time‐frequency (t‐f) analysis of electrooculogram‐corrected EEG was used to explore event‐related synchronization (ERS)/desynchronization (ERD) in four EEG bands using arbitrarily selected time epochs and traditional frequency ranges. ERS in delta, theta, and alpha, and subsequent ERD in theta, alpha, and beta, showed substantial decrement over trials, yet effects of stimulus significance (count vs. no‐task) were minimal. Here, we used principal components analysis (PCA) of the t‐f data to investigate the natural frequency and time combinations involved in such stimulus processing. We identified four ERS and four ERD t‐f components: six showed decrement over trials, four showed count > no‐task effects, and six showed Significance × Trial interactions. This increased sensitivity argues for the wider use of our data‐driven t‐f PCA approach.     

The Brain Computer Interface Using Flash Visual Evoked Potential and Independent Component Analysis

In this study flashing stimuli, such as digits or letters, are displayed on a LCD screen to induce flash visual evoked potentials (FVEPs). The aim of the proposed interface is to generate desired strings while one stares at target stimulus one after one. To effectively extract visually-induced neural activities with superior signal-to-noise ratio, independent component analysis (ICA) is employed to decompose the measured EEG and task-related components are subsequently selected for data reconstruction. In addition, all the flickering sequences are designed to be mutually independent in order to remove the contamination induced by surrounding non-target stimuli from the ICA-recovered signals. Since FVEPs are time-locked and phase-locked to flash onsets of gazed stimulus, segmented epochs from ICA-recovered signals based on flash onsets of gazed stimulus will be sharpen after averaging whereas those based on flash onsets of non-gazed stimuli will be suppressed after averaging. The stimulus inducing the largest averaged FVEPs is identified as the gazed target and corresponding digit or letter is sent out. Five subjects were asked to gaze at each stimulus. The mean detection accuracy resulted from averaging 15 epochs was 99.7%. Another experiment was to generate a specified string ‘0287513694E’. The mean accuracy and information transfer rates were 83% and 23.06 bits/min, respectively.     

Reaction‐time binning: A simple method for increasing the resolving power of ERP averages

Stimulus‐locked, response‐locked, and ERP‐locked averaging are effective methods for reducing artifacts in ERP analysis. However, they suffer from a magnifying‐glass effect: they increase the resolution of specific ERPs at the cost of blurring other ERPs. Here we propose an extremely simple technique—binning trials based on response times and then averaging—which can significantly alleviate the problems of other averaging methods. We have empirically evaluated the technique in an experiment where the task requires detecting a target in the presence of distractors. We have also studied the signal‐to‐noise ratio and the resolving power of averages with and without binning. Results indicate that the method produces clearer representations of ERPs than either stimulus‐locked and response‐locked averaging, revealing finer details of ERPs and helping in the evaluation of the amplitude and latency of ERP waves. The method is applicable to within‐subject and between‐subject averages.     

Postperceptual effects and P300 latency

P300 latency is commonly thought to provide a chronometric index of the duration of perceptual processing. Because the evidence in favor of this assumption is controversial, we examined whether P300 latency is influenced by perceptual processes, response selection, and by motoric processes in two experiments using a two-choice spatial stimulus-response compatibility (SRC) task. Both experiments revealed additive effects of perceptual difficulty with spatial SRC in reaction time and P300 latency. In addition, Experiment 2 showed that P300 latency measured in average waveforms is insensitive to motoric processes. The influence of spatial SRC on P300 latency disagrees with the view that P300 latency is sensitive only to stimulus evaluation processes. However, P300 latency may be used to discriminate between influences on premotoric and motoric processing stages. A response conflict account for the SRC effect on P300 latency is suggested.     

Resting state intrinsic EEG impacts on go stimulus‐response processes

Neuropsychological research and practice rely on cognitive task performance measures as indicators of brain functioning. The neural activity underlying stimulus‐response processes can be assessed with ERPs, but the relations between these cognitive processes and the brain's intrinsic resting state EEG activity are less understood. This study focused on the neurocognitive functioning of 20 healthy young adults in an equiprobable go/no‐go task to map the ERP correlates of behavioral responses and examine contributions of the resting state intrinsic EEG to task‐related outcomes. Continuous EEG was recorded during pretask eyes‐closed (EC) and eyes‐open (EO) conditions, and in the subsequent task. Delta, theta, alpha, and beta band amplitudes were assessed for the EC state and also for the reactive change to EO. Go/no‐go ERPs were submitted to temporal principal components analysis, where the P2, N2, P3, and slow wave components of interest were extracted. The performance measure of reaction time (RT) variability was positively correlated with no‐go and go errors, and also with go P2 amplitude, linking these to stimulus discrimination efforts involved in appropriate response selection. An N2c‐P3b pairing was enhanced for shorter mean RTs, supporting their involvement in the decision to execute a response. A stepwise regression model identified EC midline delta as a predictor of P3b positivity, highlighting the relevance of delta in the neural mechanisms of attentional processes. These findings clarify the electrophysiology underlying decision‐making processes in executive function, and provide a platform for further research assessing performance outcomes in larger samples and in developmental/clinical contexts.     

Stimulus sequence context differentially modulates inhibition‐related theta and delta band activity in a go/no‐go task

Recent work suggests that dissociable activity in theta and delta frequency bands underlies several common ERP components, including the no‐go N2/P3 complex, which can better index separable functional processes than traditional time‐domain measures. Reports have also demonstrated that neural activity can be affected by stimulus sequence context information (i.e., the number and type of preceding stimuli). Stemming from prior work demonstrating that theta and delta index separable processes during response inhibition, the current study assessed sequence context in a go/no‐go paradigm in which the number of go stimuli preceding each no‐go was selectively manipulated. Principal component analysis of time‐frequency representations revealed differential modulation of evoked theta and delta related to sequence context, where delta increased robustly with additional preceding go stimuli, while theta did not. Findings are consistent with the view that theta indexes simpler initial salience‐related processes, while delta indexes more varied and complex processes related to a variety of task parameters.     

Comparing P300 modulations: Target‐to‐target interval versus infrequent nontarget‐to‐nontarget interval in a three‐stimulus task

This study examined temporal determinants of the P300 component of the ERP in a three‐stimulus visual oddball task. Frequent standards, with equiprobable targets and infrequent nontargets, were utilized. We tested whether the infrequent nontarget‐to‐nontarget interval (infrequent NNI) influences P300 amplitudes and latencies analogously to the target‐to‐target interval (TTI). EEG was recorded from 27 participants, and response time and P300 effects of TTIs and infrequent NNIs were assessed. Increases in TTI augmented target P300 amplitudes and decreased latencies and response times. However, this modulation of P300 amplitude was weak for manipulations of infrequent NNI. P300 latencies increased initially before decreasing across infrequent NNI levels. Together, these findings support the notion that the P300 has an underlying temporal mechanism that is modulated by motivationally significant events. Theoretical implications are discussed.     

Action‐associated modulation of visual event‐related potentials evoked by abstract and ecological stimuli

This study investigated the influence of action‐associated predictive processes on visual ERPs. In two experiments, we sought evidence for sensory attenuation (SA) indexed by ERP amplitude reductions for self‐induced stimuli when compared to passive viewing of the same images. We assessed if SA is (a) present for both ecological and abstract stimuli (pictures depicting hands or checkerboards), (b) modulated by the degree of stimulus predictability (certain or uncertain action‐effect contingencies), and (c) sensitive to laterality of hand movements (dominant or subdominant hand actions). We found reduced occipital responses in the early 77–90 ms time interval (C1 component), irrespective of stimulus type, predictability, or the laterality of hand movements. However, the subsequent P1 component was increased (rather than reduced) for all action‐associated stimuli. In addition, this P1 effect was influenced by the degree of stimulus predictability for ecological stimuli only. Finally, the posterior N1 component was not modulated by self‐initiated actions. Overall, our findings indicate that movement‐related predictive processes attenuate early visual responses. Moreover, we propose that amplitude modulations in the P1 time range reflect the interaction between expectation‐based SA and attention‐associated amplitude enhancements. These results can have implications for assessing the influence of action‐associated predictions on visual processing in psychiatric disorders characterized by aberrant sensory predictions and alterations in hemispheric asymmetry, such as schizophrenia.     

Auditory‐visual integration modulates location‐specific repetition suppression of auditory responses

Space is a dimension shared by different modalities, but at what stage spatial encoding is affected by multisensory processes is unclear. Early studies observed attenuation of N1/P2 auditory evoked responses following repetition of sounds from the same location. Here, we asked whether this effect is modulated by audiovisual interactions. In two experiments, using a repetition‐suppression paradigm, we presented pairs of tones in free field, where the test stimulus was a tone presented at a fixed lateral location. Experiment 1 established a neural index of auditory spatial sensitivity, by comparing the degree of attenuation of the response to test stimuli when they were preceded by an adapter sound at the same location versus 30° or 60° away. We found that the degree of attenuation at the P2 latency was inversely related to the spatial distance between the test stimulus and the adapter stimulus. In Experiment 2, the adapter stimulus was a tone presented from the same location or a more medial location than the test stimulus. The adapter stimulus was accompanied by a simultaneous flash displayed orthogonally from one of the two locations. Sound‐flash incongruence reduced accuracy in a same‐different location discrimination task (i.e., the ventriloquism effect) and reduced the location‐specific repetition‐suppression at the P2 latency. Importantly, this multisensory effect included topographic modulations, indicative of changes in the relative contribution of underlying sources across conditions. Our findings suggest that the auditory response at the P2 latency is affected by spatially selective brain activity, which is affected crossmodally by visual information.     

Magnetic brain activity phase-locked to the envelope, the syllable onsets, and the fundamental frequency of a perceived speech signal

During speech perception, acoustic correlates of syllable structure and pitch periodicity are directly reflected in electrophysiological brain activity. Magnetoencephalography (MEG) recordings were made while 10 participants listened to natural or formant‐synthesized speech at moderately fast or ultrafast rate. Cross‐correlation analysis was applied to show brain activity time‐locked to the speech envelope, to an acoustic marker of syllable onsets, and to pitch periodicity. The envelope yielded a right‐lateralized M100‐like response, syllable onsets gave rise to M50/M100‐like fields with an additional anterior M50 component, and pitch (ca. 100 Hz) elicited a neural resonance bound to a central auditory source at a latency of 30 ms. The strength of these MEG components showed differential effects of syllable rate and natural versus synthetic speech. Presumingly, such phase‐locking mechanisms serve as neuronal triggers for the extraction of information‐bearing elements.