Stimulus-locked ERP Research Articles

Validation of the g.tec Unicorn Hybrid Black wireless EEG system.

Although dry and hybrid-style electrode technology has been well validated, systems utilizing these electrodes have not been widely adopted. One reason for this may be that the systems incorporating such technology present limitations that are fundamental to the EEG approach. The g.tec Unicorn Hybrid Black system, a low density Bluetooth EEG amplifier, however, attempts to address many of these limitations to allow greater flexibility to replicate methods used with traditional EEG amplifiers and extend them to more novel applications. The aim of the present investigation was to validate the g.tec Unicorn Hybrid Black amplifier to determine if it provides comparable data to a traditional laboratory-based system when no electrode preparation is utilized or if a saline-based solution is necessary to obtain sufficient signal quality. Stimulus-locked ERPs and EEG power spectrum data were concurrently recorded using both the Unicorn Hybrid Black amplifier and a traditional high-end laboratory-based low-impedance wired system. Findings suggest that the Unicorn Hybrid Black provides valid measures for investigations of frequency spectra even with no conductive solution applied. However, to obtain valid assessments of event-related brain potentials, it appears necessary to use a conductive solution for electrode preparation. This system appears well suited to allow for high-quality and flexible EEG measures available outside of traditional laboratory environments.

Effects of motor restrictions on preparatory brain activity

Modifying established motor skills is a challenging endeavor due to proactive interference from undesired old to desired new actions, calling for high levels of cognitive control. Motor restrictions may facilitate the modification of motor skills by rendering undesired responses physically impossible, thus reducing demands to response inhibition. Here we studied behavioral and EEG effects of rule changes to typing in skilled touch-typists. The respective rule change—typing without using the left index finger—was either implemented per instruction only or with an additional motor restriction. In both groups, the rule change elicited delays and more errors in typing, indicating the occurrence of proactive interference. While stimulus-locked ERPs did not exhibit prominent effects of rule change or group, response-locked ERPs revealed that the time courses of preparatory brain activity preceding typing responses depended on the presence of motor restriction. Although further research is necessary to corroborate our findings, they indicate a novel brain correlate that represents changes in inhibitory response preparation induced by short-term motor restrictions.

Electrophysiological correlates underlying interference control in motor tasks

Changing pre-existing, automatized motor skills often requires interference control. Prepotent response inhibition – one subdimension of inhibition – has been theorized to be particularly associated with successful interference control in motor skills. Recent evidence suggests that different inhibition subdimensions elicit distinct ERP patterns (with larger P3 components for response inhibition). Therefore, we examined whether a similar ERP pattern would arise in a task demanding participants to overcome interference emerging from strong motor automatisms. This was realized within a typing paradigm involving a letter switch manipulation which is able to produce strong, immediate interference effects. Most importantly, stimulus-locked ERP analyses revealed an enhanced P3 component at frontal, central and most pronouncedly parietal sites for interference trials, in line with previous reported patterns for response inhibition. Together, different analyses provide first insights into the electrophysiological correlates of motor skill change, corroborating the pivotal role of response inhibition for successful interference control.

Test–Retest Reliability of Electroencephalographic Measures of Performance Monitoring in Children and Adults

ABSTRACT This study examined the test–retest reliability of the error-related negativity (ERN) and error positivity (Pe) amplitudes using a Flanker task in 118 neurotypical children and 53 adults before and after latency jitter adjustments. The reliability of the ERN and Pe amplitudes was moderate for children and moderate to strong for adults. The latency variability adjustment did not improve the reliability of the ERN and Pe amplitudes for either group, suggesting that latency variability may be a trait-like measure. For comparison purposes, the reliability of the stimulus-locked ERPs was strong for correct trials, yet the reliability was weak for incorrect trials.

Social comparison impacts stimulus evaluation in a competitive social learning task.

When we perform an action, the outcome that follows it can change the value we place on that behaviour, making it more or less likely to be repeated in the future. However, the values that we learn are not objective: we interpret the outcomes that we receive for ourselves relative to those that share our environment, i.e. we engage in social comparison. The temporal dynamics of physiological responses to stimulus valuation in social learning tasks are poorly understood, particularly in human participants. Therefore, we recorded stimulus-locked event-related potentials with 64-channel EEG to examine stimulus valuation, following the design of a study previously used in macaques. Pairs of participants performed a social learning task in which they received outcomes sequentially for a presented stimulus (partner first) by pressing a button in response to a cue. There were two conditions: one in which stimulus values varied for the participant but output a constant rate of reward for the partner (self-variable blocks), and another condition in which this payout was reversed (other-variable blocks). We then measured participants’ self-reported competitiveness. Approximately 200 ms post-stimulus, an ERP related to stimulus evaluation and attentional processing appeared to encode own stimulus value in self-variable blocks. In other-variable blocks the same pattern of activity was reversed, even though the value of the stimulus for the participant did not depend on the stimulus presented. Outcome-locked analyses further showed that attention dedicated to the partner’s outcome was greater in more competitive participants. We conclude that subjective stimulus value can be reflected in early stimulus-locked ERP responses and that competitive participants may be more invested in their own performance relative to the other player, hence their increased interest in the outcome of their partner.

Acute exercise has a general facilitative effect on cognitive function: A combined ERP temporal dynamics and BDNF study.

This study examined whether acute moderate intensity exercise results in a general or selective improvement in cognitive function. In addition, multiple stimulus-locked ERP components and serum BDNF levels were assessed to investigate potential neurobiological mechanisms underlying acute exercise effects on select aspects of cognitive performance. Thirty young adults were recruited and participated in exercise and reading control sessions in a counterbalanced order. Following treatments, the Stroop task was administrated, and N1, N2, P3, and N450 components of the ERP waveform were recorded and analyzed. Additionally, blood samples were withdrawn immediately following exercise or rest conditions prior to administration of the Stroop task. Acute exercise facilitated response times for both Stroop congruent and incongruent task conditions, with a similar magnitude of improvement. Larger P3 and reduced N450 amplitudes as well as decreased N450 latency were observed following exercise, but no effects on N1 and N2 components were found. This dose of exercise also did not influence serum BDNF levels. These findings suggest that moderate intensity acute exercise results in a generalized rather than selective improvement in cognition. The facilitation may be related to an increase in attentional or neural resource allocation and conflict detection processes reflected by longer latency endogenous components (P3, N450), but is not influenced by earlier sensory and monitoring processes revealed by earlier ERP components or by serum levels of BDNF.

Spatio-temporal Dynamics of Referential and Inferential Naming: Different Brain and Cognitive Operations to Lexical Selection.

Picture naming tasks are largely used to elicit the production of specific words and sentences in psycholinguistic and neuroimaging research. However, the generation of lexical concepts from a visual input is clearly not the exclusive way speech production is triggered. In inferential speech encoding, the concept is not provided from a visual input, but is elaborated though semantic and/or episodic associations. It is therefore likely that the cognitive operations leading to lexical selection and word encoding are different in inferential and referential expressive language. In particular, in picture naming lexical selection might ensue from a simple association between a perceptual visual representation and a word with minimal semantic processes, whereas richer semantic associations are involved in lexical retrieval in inferential situations. Here we address this hypothesis by analyzing ERP correlates during word production in a referential and an inferential task. The participants produced the same words elicited from pictures or from short written definitions. The two tasks displayed similar electrophysiological patterns only in the time-period preceding the verbal response. In the stimulus-locked ERPs waveform amplitudes and periods of stable global electrophysiological patterns differed across tasks after the P100 component and until 400-500ms, suggesting the involvement of different, task-specific neural networks. Based on the analysis of the time-windows affected by specific semantic and lexical variables in each task, we conclude that lexical selection is underpinned by a different set of conceptual and brain processes, with semantic processes clearly preceding word retrieval in naming from definition whereas the semantic information is enriched in parallel with word retrieval in picture naming.

Brain potentials predict substance abuse treatment completion in a prison sample.

IntroductionNational estimates suggest that up to 80% of prison inmates meet diagnostic criteria for a substance use disorder. Because more substance abuse treatment while incarcerated is associated with better post‐release outcomes, including a reduced risk of accidental overdose death, the stakes are high in developing novel predictors of substance abuse treatment completion in inmate populations.MethodsUsing electroencephalography (EEG), this study investigated stimulus‐locked ERP components elicited by distractor stimuli in three tasks (VO‐Distinct, VO‐Repeated, Go/NoGo) as a predictor of treatment discontinuation in a sample of male and female prison inmates. We predicted that those who discontinued treatment early would exhibit a less positive P3a amplitude elicited by distractor stimuli.ResultsOur predictions regarding ERP components were partially supported. Those who discontinued treatment early exhibited a less positive P3a amplitude and a less positive PC4 in the VO‐D task. In the VO‐R task, however, those who discontinued treatment early exhibited a more negative N200 amplitude rather than the hypothesized less positive P3a amplitude. The discontinuation group also displayed less positive PC4 amplitude. Surprisingly, there were no time‐domain or principle component differences among the groups in the Go/NoGo task. Support Vector Machine (SVM) models of the three tasks accurately classified individuals who discontinued treatment with the best model accurately classifying 75% of inmates. PCA techniques were more sensitive in differentiating groups than the classic time‐domain windowed approach.ConclusionsOur pattern of findings are consistent with the context‐updating theory of P300 and may help identify subtypes of ultrahigh‐risk substance abusers who need specialized treatment programs.

An ERP study of inhibition of non-target languages in trilingual word production

The present study examined the locus where inhibition of non-target languages is exerted during trilingual word production by analyzing the cue-locked and stimulus-locked ERPs respectively in the n-2 language repetition paradigm. During the experiment, Uighur–Chinese–English trilinguals overtly named Arabic digits in one of their three languages according to a visually presented cue while their behavioral and electrophysiological responses were recorded. The behavioral data revealed insignificant n-2 repetition costs. Cue-locked ERPs revealed also only tiny or marginally significant n-2 repetition effects over some midline electrodes. The stimulus-locked ERP data showed a more negative ERP component elicited by the n-2 repetition trials than the n-2 non-repetition trials around 250ms after stimulus onset, but no significant difference in this ERP effect between different languages was found. The results indicate that inhibition of non-target languages occurs at the lemma selection phase rather than the language task schemas phase during trilingual language production.

Effect of frequency deviance direction on performance and mismatch negativity

The mismatch negativity (MMN) component of the auditory event-related potential is associated with automatic perceptual inference concerning changes in auditory stimulation. Recent studies have addressed the question whether performance and MMN is affected by the direction of frequency deviance. In the present study, the frequency MMN and performance is investigated during an auditory identification task. Specifically, we examined the effect of positive and negative differences between the present stimulus and the previous response frequencies on performance as well as on the characteristics of stimulus-locked ERPs and brain activation maps. The results show that frequency deviants creating mismatch conditions increase the likelihood of error commission. The decrease in performance achieves statistical significance in the case of positive frequency deviants. In the latter case, ERP amplitude values of the Fz electrode at 164 ms after stimulus onset are statistically larger for mismatch as opposed to no-mismatch condition. This corresponds to significance differences in the activation maps at Brodmann area 11, superior frontal gyrus, and the frontal lobe. The present findings revealed dissociations in behavioral and ERP responses in the processing of positive and negative frequency deviance, lending support to the notion that MMN is more sensitive to increments than to decrements in frequency.

Emotionally positive stimuli facilitate lexical decisions—An ERP study

The influence of briefly presented positive and negative emotional pictures on lexical decisions on positive, negative and neutral words or pseudowords was investigated. Behavioural reactions were the fastest following all positive stimuli and most accurate for positive words. Stimulus-locked ERPs revealed enhanced early posterior and late parietal attention effects following positive pictures. A small neural affective priming effect was reflected by P3 modulation, indicating more attention allocation to affectively incongruent prime-target pairs. N400 was insensitive to emotion. Response-locked ERPs revealed an early fronto-central negativity from 480ms before reactions to positive words. It was generated in both fronto-central and extra-striate visual areas, demonstrating a contribution of perceptual and, notably, motor preparation processes. Thus, no behavioural and little neural evidence for congruency-driven affective priming with emotional pictures was found, but positive stimuli generally facilitated lexical decisions, not only enhancing perception, but also acting rapidly on response preparation and by-passing full semantic analysis.

Error negativity on correct trials: a reexamination of available data

The error negativity, an EEG wave observed when subjects commit an error in a choice reaction time (RT) task, is often considered as a sign of error detection. Recently, reports of Ne-like waves on correct responses did challenge this interpretation. It has been proposed, however, that these Ne-like waves result either from an artifactual contamination of response-locked activities by stimulus-locked ones, or from an implicit monitoring of the time elapsing during the RT. Our aim was to reprocess published data: (1) to compare the shape and amplitude of EMG-locked and stimulus-locked ERPs on correct trials, and (2) to compare the size of the EMG-locked Ne-like waves obtained on fast and slow trials. The results neither support the artifact hypothesis nor the RT monitoring one. Therefore, it seems that the Ne-like waves observed on correct trials do correspond to a Ne, which suggests that the Ne has a broader significance than just error detection.

Behavioral and cortical measures of infants' visual expectations

Features of the habituation paradigm were combined with the visual expectation paradigm to examine behavioral and cortical indexes of infants' visual expectations. Eight 3-month-old infants watched an alternating picture sequence while their eye movements were videotaped and their cortical electrophysiological activity (event-related potential [ERP]) was recorded. Two ERP epochs were examined: a 3,000-msec stimulus-locked epoch included 1,000 msec before stimulus onset through 1,000 msec after stimulus offset; and a 1,200-msec response-locked epoch included 700 msec before saccade onset through 500 msec after the saccade. All infants anticipated upcoming pictures, and eye movement latencies for pictures that were not anticipated were comparable to saccade latencies reported in other visual expectation studies of infants at this age. Three components were identified in the stimulus-locked ERP waveform: a slowly developing negativity prior to picture onset, a postonset negative slow wave, and a late negativ...

Overlap between P300 and movement-related-potentials: A response to Verleger

In reply to Verleger's commentary, I first clarify what the term “MRP overlap” implies; by means of a simple additive simulation it is shown that overlap between a stable P300 and a MRP that moves in time with reaction-time, may cause two types of artefacts — amplitude reduction and double peaking of P300. Following Verleger's suggestion, it is then argued that the effects of stimulus-degradation on P300 amplitude in our experiments was, at least in part, due to overlap with negative components of the MRP (in the go-intact condition), and with positive CNV return (in the nogo-intact condition). It is concluded that MRP overlap is not only an artefact but also a useful index of motor-preparation in reaction tasks, and that more refined methods should be developed in future research for accurate estimation of MRP overlap in stimulus-locked ERP waveforms.