Misallocation of variance in event-related potentials: simulation studies on the effects of test power, topography, and baseline-to-peak versus principal component quantifications

Exploring the Activation of Target Words in Picture Naming in Children Who Stutter: Evidence From Event-Related Potentials

PURPOSE

Target word activation in picture naming was explored in children who stutter (CWS) and typically fluent children (TFC) using event-related potentials (ERPs).

METHOD

A total of 18 CWS and 16 TFC completed a task combining picture naming and probe word identification. On each trial, a picture-to-be-named was followed by an auditory probe word-to-be-identified; the probe was identical (Identity condition) or Unrelated to the picture name. ERPs were recorded from probe onset. Attenuation of the N400 ERP component was predicted to Identity versus Unrelated trials (N400 priming). Between-groups differences in amplitude, timing, and topography of N400 priming were explored.

RESULTS

Naming was more accurate on Identity versus Unrelated trials. Probe word identification accuracy was not affected by Condition. N400 priming was detected, indicating that self-generated picture names facilitated semantic processing of identical probes. This effect was larger in amplitude in CWS versus TFC. Unexpectedly, an N400-preceding, frontally maximal, positive-going ERP component-associated with expectancy processing-was larger in amplitude to Unrelated versus Identity trials. This effect was smaller in CWS versus TFC.

CONCLUSIONS

A larger N400 priming effect in CWS versus TFC reflects a tendency toward more extensive semantic processing in picture naming in CWS. A smaller Condition effect on frontally maximal, positive-going, N400-preceding ERP activity in CWS versus TFC indicates a reduced ability to form expectancies about the lexical and/or phonological identity of probe words in CWS. Both effects may point to inefficient activation of target words in picture naming in CWS.

Reliability of the P3 component in a 3-stimulus concealed information test with known and unknown stimuli

The parietal P3 amplitude of the event-related potential (ERP) has been highlighted to signal stimulus salience in concealed information tests (CITs) with known and unknown stimuli. To extend previous validity investigations in deception research, the reliability of the early parietal P3 amplitude in a 3-stimulus CIT including known and unknown stimuli has been investigated in a sample of N = 68 participants. Variations of Cronbach's Alpha and split-half reliability (odd-even, 1st vs. 2nd half) of the early parietal P3 amplitude were considered for ERP quantification method (peak-to-peak, mean, baseline-to-peak), epoch selection strategies (chronological vs. random) and number of epochs (10-40) in three stimulus types (probe, target, irrelevant). Excellent reliability coefficients have been summarized for number of epochs, P3 quantifications, and epoch selection strategies. Moreover, the best-practice recommendations highlight mandatory combinations of epoch selection strategy, number of epochs and P3 quantifications to ensure robust and excellent reliabilities of the early parietal P3 amplitude in a 3-stimulus CIT with known (probe, target) and unknown (irrelevant) stimuli. The robustness of mandatory excellent reliability coefficients for the early parietal P3 has been discussed for two data tracks in single-case analyses.

Single-trial-based temporal principal component analysis on extracting event-related potentials of interest for an individual subject

BACKGROUND

Temporal principal component analysis (tPCA) has been widely used to extract event-related potentials (ERPs) at group level of multiple subjects ERP data and it assumes that the underlying factor loading is fixed across participants. However, such assumption may fail to work if latency and phase for one ERP vary considerably across participants. Furthermore, effect of number of trials on tPCA decomposition has not been systematically examined as well, especially for within-subject PCA.

NEW METHOD

We reanalyzed a real ERP data of an emotional experiment using tPCA to extract N2 and P2 from single-trial EEG of an individual. We also explored influence of the number of trials (consecutively increased from 10 to 42 trials) on PCA decomposition by comparing temporal correlation, the statistical result, Cronbach's alpha, spatial correlation of both N2 and P2 for the proposed method with the conventional time-domain analysis, trial-averaged group PCA, and single-trial-based group PCA.

RESULTS

The results of the proposed method can enhance spatial and temporal consistency. We could obtain stable N2 with few trials (about 20) for the proposed method, but, for P2, approximately 30 trials were needed for all methods.

COMPARISON WITH EXISTING METHOD(S)

About 30 trials for N2 were required and the reconstructed P2 and N2 were poor correlated across participants for the other three methods.

CONCLUSION

The proposed approach may efficiently capture variability of one ERP from an individual that cannot be extracted by group PCA analysis.

A tutorial on the use of temporal principal component analysis in developmental ERP research – opportunities and challenges

Developmental researchers are often interested in event-related potentials (ERPs). Data-analytic approaches based on the observed ERP suffer from major problems such as arbitrary definition of analysis time windows and regions of interest and the observed ERP being a mixture of latent underlying components. Temporal principal component analysis (PCA) can reduce these problems. However, its application in developmental research comes with the unique challenge that the component structure differs between age groups (so-called measurement non-invariance). Separate PCAs for the groups can cope with this challenge. We demonstrate how to make results from separate PCAs accessible for inferential statistics by re-scaling to original units. This tutorial enables readers with a focus on developmental research to conduct a PCA-based ERP analysis of amplitude differences. We explain the benefits of a PCA-based approach, introduce the PCA model and demonstrate its application to a developmental research question using real-data from a child and an adult group (code and data openly available). Finally, we discuss how to cope with typical challenges during the analysis and name potential limitations such as suboptimal decomposition results, data-driven analysis decisions and latency shifts.

Development of children's performance and ERP components in the equiprobable Go/NoGo task

Since the equiprobable Go/NoGo task lacks the dominant Go imperative of the usual Go/NoGo (with more Go than NoGo stimuli), it is generally regarded as involving little inhibition. However, children have relative difficulty with this task, and have a large frontal NoGo N2. We previously found that this 'child N2' does play an inhibitory role, with larger frontal N2b associated with fewer commission errors. Here we investigated age-related developmental differences in the N2b and other components in the equiprobable Go/NoGo task. Two groups of eighteen Younger children (aged 8.0 to 10.3 years) and eighteen Older children (aged 10.4 to 12.8 years), matched on sex, were presented with three stimulus blocks each containing 100 Go and 100 NoGo tone stimuli in random order. Four temporal PCAs, each with unrestricted VARIMAX rotation, separately quantified the Go and NoGo ERPs of each group, and similar components were extracted from each set. Most identified components were differentially enhanced to either Go or NoGo, as in adults, supporting a previously-proposed differential sequential processing schema. The Older group had Go component latencies that were systematically reduced by some 7.4% from the Younger group, and they displayed faster RT and fewer omission and commission errors. Between subjects in the Older group, larger frontocentral NoGo N2b was associated with fewer commission errors. Hence the NoGo N2b in this paradigm can be interpreted as an individual marker of inhibition in older, but not young, children.

Using temporo-spatial principal component analysis as tool to dissociate latent ERP components of episodic memory retrieval: Objectifying time-window selection for overlapping ERP components

This report details how principal component analysis (PCA) can be used as a valuable tool to dissociate latent ERP components, even when considerable temporal and spatial overlap makes it difficult to discern ERP effects in standard time windows. We illustrate our methodological approach in a data set from a recognition memory paradigm, in which event-related potential (ERP) correlates of familiarity, recollection and the late parietal negativity (LPN) were partially overlapping. By adapting standard time windows based on the results of a temporo-spatial PCA, small yet reliable ERP correlates reflecting familiarity and recollection for identical items and late recollection for changed items were identified, complementing the result pattern observed in behavioral performance. Due to similar temporo-spatial characteristics and opposing polarities in late parietal ERP correlates associated with memory retrieval, component overlap is often observed in this field of research. Hence, the complex interplay of several processes underlying higher cognitive functions such as memory retrieval may interfere with standard ERP assessment. In such instances, PCA can provide promising ways to objectively assess time window selection for subsequent ERP analyses.

Test-Retest Reliability of Event-Related Potentials Across Three Tasks

Abstract. Event-related potentials (ERPs) constitute a useful and cost-effective method to assess the neural underpinnings of multiple cognitive processes. ERPs have been used to track changes in cognitive processes in longitudinal and clinical studies. However, few studies have assessed their test-retest reliability (i.e., their consistency across time). Therefore, in the current study, we aimed to assess the test-retest reliability of ERPs (P100, N100, P200, N200, P3b, lateralized readiness potentials) across three tasks. In two assessments separated by approximately 4 months, ERPs were recorded in 26 healthy participants, during two oddball tasks (motor and counting) and a stimulus-response compatibility paradigm. Pearson’s correlations and intraclass correlations were used to assess the test-retest reliability of ERPs. Correlations between ERPs elicited by the three tasks were assessed with Pearson’s correlations. Our analyses revealed moderate to very strong test-retest reliability for most ERP components across the three tasks. Test-retest reliability did not differ between the motor and counting oddball tasks. Most ERPs were also correlated across paradigms. Therefore, these results confirm that ERPs have the potential to be reliable markers to serve as robust assessment tools in longitudinal or clinical studies.

Inhibitory Control of Lexical Selection in Adults who Stutter

PURPOSE

Based on previous evidence that lexical selection may operate differently in adults who stutter (AWS) versus typically-fluent adults (TFA), and that atypical attentional processing may be a contributing factor, the purpose of this study was to investigate inhibitory control of lexical selection in AWS.

METHOD

12 AWS and 12 TFA completed two tasks. One was a picture naming task featuring High and Low Agreement object naming. Naming accuracy and reaction times (RT), and event-related potentials (ERPs) time-locked to picture onset, were recorded. Second was a flanker task featuring Congruent and Incongruent arrow arrays. Push-button accuracy and RTs, and ERPs time-locked to arrow array onset, were recorded.

RESULTS

Low Agreement pictures were named less accurately and slower than High Agreement pictures in both Groups. The magnitude of the Agreement effect on naming RTs was larger in AWS versus TFA. Delta-plot analysis revealed that the Agreement effect was positively correlated with individual differences in inhibition in TFA but not in AWS. Moreover, Low Agreement pictures elicited negative-going ERP activity relative to High Agreement pictures in both Groups. However, the scalp topography of this effect was markedly reduced in AWS versus TFA. For the Flanker task, Congruency affected push-button accuracy and RTs, and N2 amplitudes, similarly between groups.

CONCLUSIONS

Results point to a selective deficit in inhibitory control of lexical selection in AWS. Potential pathways between diminished inhibitory control of lexical selection, speech motor control and stuttering are discussed.

A Comparison of Simple Structure Rotation Criteria in Temporal Exploratory Factor Analysis for Event-Related Potential Data

Abstract. It is challenging to apply exploratory factor analysis (EFA) to event-related potential (ERP) data because such data are characterized by substantial temporal overlap (i.e., large cross-loadings) between the factors, and, because researchers are typically interested in the results of subsequent analyses (e.g., experimental condition effects on the level of the factor scores). In this context, relatively small deviations in the estimated factor solution from the unknown ground truth may result in substantially biased estimates of condition effects (rotation bias). Thus, in order to apply EFA to ERP data researchers need rotation methods that are able to both recover perfect simple structure where it exists and to tolerate substantial cross-loadings between the factors where appropriate. We had two aims in the present paper. First, to extend previous research, we wanted to better understand the behavior of the rotation bias for typical ERP data. To this end, we compared the performance of a variety of factor rotation methods under conditions of varying amounts of temporal overlap between the factors. Second, we wanted to investigate whether the recently proposed component loss rotation is better able to decrease the bias than traditional simple structure rotation. The results showed that no single rotation method was generally superior across all conditions. Component loss rotation showed the best all-round performance across the investigated conditions. We conclude that Component loss rotation is a suitable alternative to simple structure rotation. We discuss this result in the light of recently proposed sparse factor analysis approaches.

Varimax Rotation Based on Gradient Projection Is a Feasible Alternative to SPSS

Gradient projection rotation (GPR) is an openly available and promising tool for factor and component rotation. We compare GPR toward the Varimax criterion in principal component analysis to the built-in Varimax procedure in SPSS. In a simulation study, we tested whether GPR-Varimax yielded multiple local solutions by creating population simple structure with a single optimum and with two optima, a global and a local one (double-optimum condition). The other conditions comprised the number of components (k = 3, 6, 9, and 12), the number of variables per component (m/k = 4, 6, and 8), the number of iterations per rotation (i = 25 and 250), and whether loadings were Kaiser normalized before rotation or not. GPR-Varimax was conducted with unrotated and multiple (q = 1, 10, 50, and 100) random start loadings. We found equal results for GPR-Varimax and SPSS-Varimax in most conditions. The few very small differences in favor of SPSS-Varimax were eliminated when Kaiser-normalized loadings and 250 iterations per rotation were used. Selecting the best solution out of multiple random starts in GPR-Varimax increased proximity to population components in the double-optimum condition with Kaiser normalized loadings, for which GPR-Varimax recovered population structure better than SPSS-Varimax. We also included an empirical example and found that GPR-Varimax and SPSS-Varimax yielded highly similar solutions for orthogonal simple structure in a real data set. We suggest that GPR-Varimax can be used as an alternative to Varimax rotation in SPSS. Users of GPR-Varimax should allow for at least 250 iterations, normalize loadings before rotation, and select the best solution from at least 10 random starts to ensure optimal results.

Exploratory structural equation modeling for event-related potential data-An all-in-one approach?

ERP data are characterized by high dimensionality and a mixture of constituting signals and are thus challenging for researchers to analyze. To address these challenges, exploratory factor analysis (EFA) has been used to provide estimates of the unobserved factors and to use these estimates for further statistical analyses (e.g., analyses of group effects). However, the EFA approach is prone to biases due to assigning individual factor scores to each observation as an intermediate step and does not properly consider participants, electrodes, and groups/conditions as differentiable sources of factor variance, with the consequence that factor correlations are inaccurately estimated. Here, we suggest exploratory structural equation modeling (ESEM) as a potential approach to address these limitations. ESEM may handle the complexity of ERP data more appropriately because multiple sources of variance can be formally taken into consideration. We demonstrate the application of ESEM to ERP data (in comparison with EFA) with an illustrative example and report the results of a small simulation study in which ESEM clearly outperformed EFA with respect to accurate estimation of the population factor loadings, population factor correlations, and group differences. We discuss how robust statistical inference can be conducted within the ESEM approach. We conclude that ESEM naturally extends the current EFA approach for ERP data and that it can provide a coherent and flexible analysis framework for all kinds of ERP research questions.

Principles behind variance misallocation in temporal exploratory factor analysis for ERP data: Insights from an inter-factor covariance decomposition

Temporal exploratory factor analysis (EFA) is commonly applied to ERP data sets to reduce their dimensionality and the ambiguity with respect to the underlying components. However, the risk of variance misallocation (i.e., the incorrect allocation of condition effects) has raised concerns with regard to EFA usage. Here, we show that variance misallocation occurs because of biased factor covariance estimates and the temporal overlap between the underlying components. We also highlight the consequences of our findings for the analysis of ERP data with EFA. For example, a direct consequence of our expositions is that researchers should use oblique rather than orthogonal rotations, especially when the factors have a substantial topographic overlap. A Monte Carlo simulation confirms our results by showing, for instance, that characteristic biases occur only for orthogonal Varimax rotation but not for oblique rotation methods such as Geomin or Promax. We discuss the practical implications of our results and outline some questions for future research.

Demonstrating test-retest reliability of electrophysiological measures for healthy adults in a multisite study of biomarkers of antidepressant treatment response

Growing evidence suggests that loudness dependency of auditory evoked potentials (LDAEP) and resting EEG alpha and theta may be biological markers for predicting response to antidepressants. In spite of this promise, little is known about the joint reliability of these markers, and thus their clinical applicability. New standardized procedures were developed to improve the compatibility of data acquired with different EEG platforms, and used to examine test-retest reliability for the three electrophysiological measures selected for a multisite project-Establishing Moderators and Biosignatures of Antidepressant Response for Clinical Care (EMBARC). Thirty-nine healthy controls across four clinical research sites were tested in two sessions separated by about 1 week. Resting EEG (eyes-open and eyes-closed conditions) was recorded and LDAEP measured using binaural tones (1000 Hz, 40 ms) at five intensities (60-100 dB SPL). Principal components analysis of current source density waveforms reduced volume conduction and provided reference-free measures of resting EEG alpha and N1 dipole activity to tones from auditory cortex. Low-resolution electromagnetic tomography (LORETA) extracted resting theta current density measures corresponding to rostral anterior cingulate (rACC), which has been implicated in treatment response. There were no significant differences in posterior alpha, N1 dipole, or rACC theta across sessions. Test-retest reliability was .84 for alpha, .87 for N1 dipole, and .70 for theta rACC current density. The demonstration of good-to-excellent reliability for these measures provides a template for future EEG/ERP studies from multiple testing sites, and an important step for evaluating them as biomarkers for predicting treatment response.

Hemifield-dependent N1 and event-related theta/delta oscillations: An unbiased comparison of surface Laplacian and common EEG reference choices

Surface Laplacian methodology has been used to reduce the impact of volume conduction and arbitrary choice of EEG recording reference for the analysis of surface potentials. However, the empirical implications of employing these different transformations to the same EEG data remain obscure. This study directly compared the statistical effects of four commonly-used (nose, linked mastoids, average) or recommended (reference electrode standardization technique [REST]) references and their spherical spline current source density (CSD) transformation for a large data set stemming from a well-understood experimental manipulation. ERPs (72 sites) recorded from 130 individuals during a visual half-field paradigm with highly-controlled emotional stimuli were characterized by mid-parietooccipital N1 (125 ms peak latency) and event-related synchronization (ERS) of theta/delta (160 ms), which were most robust over the contralateral hemisphere. All five data transformations were rescaled to the same covariance and submitted to a single temporal or time-frequency PCA (Varimax) to yield simplified estimates of N1 or theta/delta ERS. Unbiased nonparametric permutation tests revealed that these hemifield-dependent asymmetries were by far most focal and prominent for CSD data, despite all transformations showing maximum effects at mid-parietooccipital sites. Employing smaller subsamples (signal-to-noise) or window-based ERP/ERS amplitudes did not affect these comparisons. Furthermore, correlations between N1 and theta/delta ERS at these sites were strongest for CSD and weakest for nose-referenced data. Contrary to the common notion that the spatial high pass filter properties of a surface Laplacian reduce important contributions of neuronal generators to the EEG signal, the present findings demonstrate that instead volume conduction inherent in surface potentials weakens the representation of neuronal activation patterns at scalp that directly reflect regional brain activity.

Olfaction in the psychosis prodrome: electrophysiological and behavioral measures of odor detection

Smell identification deficits (SIDs) are relatively specific to schizophrenia and its negative symptoms, and may predict transition to psychosis in clinical high-risk (CHR) individuals. Moreover, event-related potentials (ERPs) to odors are reduced in schizophrenia. This study examined whether CHR patients show SIDs and abnormal olfactory N1 and P2 potentials. ERPs (49 channels) were recorded from 21 CHR and 20 healthy participants (13 males/group; ages 13-27 years) during an odor detection task using three concentrations of hydrogen sulfide (H2S) or blank air presented unilaterally by a constant-flow olfactometer. Neuronal generator patterns underlying olfactory ERPs were identified and measured by principal components analysis (unrestricted Varimax) of reference-free current source densities (CSD). Replicating previous findings, CSD waveforms to H2S stimuli were characterized by an early N1 sink (345 ms, lateral-temporal) and a late P2 source (600 ms, mid-frontocentroparietal). N1 and P2 varied monotonically with odor intensity (strong > medium > weak) and did not differ across groups. Patients and controls also showed comparable odor detection and had normal odor identification and thresholds (Sniffin' Sticks). However, olfactory ERPs strongly reflected differences in odor intensity and detection in controls, but these associations were substantially weaker in patients. Moreover, severity of negative symptoms in patients was associated with reduced olfactory ERPs and poorer odor detection, identification and thresholds. Three patients who developed psychosis had poorer odor detection and thresholds, and marked reductions of N1 and P2. Thus, despite the lack of overall group differences, olfactory measures may be of utility in predicting transition to psychosis among CHR patients.

Attention in children with obstructive sleep apnoea: an event-related potentials study

BACKGROUND

Obstructive sleep apnoea (OSA) in children has been causally implicated in neurobehavioural and cognitive dysfunction. Consequently, the American Academy of Paediatrics highlighted the need to study pertinent functional cognitive outcomes before and after treatment. However, neurocognitive function has thus far only been assessed by caregiver-completed questionnaires, which can be labour intensive and time consuming, such that the need for complementary and more objective measures has emerged.

OBJECTIVE

The study aimed to identify electrophysiological correlates of neurocognitive alterations in children with OSA and investigate utility as a predictive tool.

PATIENTS AND METHODS

Twenty-eight children (14 OSA and 14 matched controls) underwent overnight sleep studies and neurocognitive testing, as well as the oddball attention task while event-related potentials (ERPs) were recorded. ERPs were analysed using temporal principal components and source analyses that provided dependent variables for the subsequent repeated measures analysis of variance (ANOVA) and multiple regressions. Time-locked waveforms formed spatial models that localised electrical activity in the brain. ERP differences between groups were then correlated to neurocognitive outcomes.

RESULTS

OSA children exhibited significantly altered ERP patterns of neural activation and impaired neurocognitive performance. Specific ERP variables exhibited accurate predictive ability regarding performance on neurobehavioural measures.

CONCLUSION

Specific ERP events during a single attention task can reliably identify the presence of OSA-associated cognitive dysfunction. Electrophysiological approaches during specific cognitive tasks may serve as simple, complementary, and reliable reporters of cognitive dysfunction associated with OSA in children.

Neuronal generator patterns of olfactory event-related brain potentials in schizophrenia

To better characterize neurophysiologic processes underlying olfactory dysfunction in schizophrenia, nose-referenced 30-channel electroencephalogram was recorded from 32 patients and 35 healthy adults (18 and 18 male) during detection of hydrogen sulfide (constant-flow olfactometer, 200 ms unirhinal exposure). Event-related potentials (ERPs) were transformed to reference-free current source density (CSD) waveforms and analyzed by unrestricted Varimax-PCA. Participants indicated when they perceived a high (10 ppm) or low (50% dilution) odor concentration. Patients and controls did not differ in detection of high (23% misses) and low (43%) intensities and also had similar olfactory ERP waveforms. CSDs showed a greater bilateral frontotemporal N1 sink (305 ms) and mid-parietal P2 source (630 ms) for high than low intensities. N1 sink and P2 source were markedly reduced in patients for high intensity stimuli, providing further neurophysiological evidence of olfactory dysfunction in schizophrenia.

ERP generator patterns in schizophrenia during tonal and phonetic oddball tasks: effects of response hand and silent count

Greater left than right reductions of P3 amplitude in schizophrenia during auditory oddball tasks have been interpreted as evidence of left-lateralized dysfunction. However, the contributions of methodological factors (response mode, stimulus properties, recording reference), which affect event-related potential (ERP) topographies, remain unclear. We recorded 31-channel ERPs from 23 schizophrenic patients and 23 age- and gender-matched healthy controls (all right-handed) during tonal and phonetic oddball tasks, varying response mode (left press, right press, silent count) within subjects. Performance accuracy was high in both groups but patients were slower. ERP generator patterns were summarized by temporal Principal Components Analysis (PCA; unrestricted Varimax) from reference-free current source density (CSD; spherical spline Laplacians) waveforms, which sharpen scalp topographies. CSD represents the magnitude of the radial current flow entering (source) and leaving (sink) the scalp. Both patients and controls showed asymmetric frontolateral and parietotemporal N2 sinks peaking at 240 ms and asymmetric parietal P3 sources (355 ms) for targets (tonal R > L, phonetic L > R), but frontocentral N2 sinks and parietal P3 sources were bilaterally reduced in patients. A response-related midfrontal sink and accompanying centroparietal source (560 ms) were highly comparable across groups. However, a superimposed left temporal source was larger for silent count compared to button press, and this difference was smaller in patients. In both groups, left or right press produced opposite, region-specific asymmetries originating from central sites, modulating the N2/P3 complex. The results suggest bilaterally reduced neural generators of N2 and P3 in schizophrenia during auditory oddball tasks, but both groups showed comparable topographic effects of task and response mode. However, additional working memory demands during silent count may partially overlap in time the generation of the N2/P3 complex and differentially affect the asymmetry of P3 subcomponents, particularly when employing conventional ERP measures.

Impairments in attention in occasionally snoring children: an event-related potential study

OBJECTIVE

To determine whether minimal snoring is benign in children.

PROCEDURE

22 rarely snoring children (mean age = 6.9 years, 11 females) and age- and sex-matched controls participated in an auditory oddball task wearing 128-electrode nets. Parents completed the Conners Parent Rating Scales-Revised Long (CPRS-R:L).

RESULTS

Snorers scored significantly higher on four CPRS-R:L subscales. Stepwise regression indicated that two ERP variables from a region of the ERP that peaked at 844 msec post-stimulus onset predicted CPRS-R:L Attention Deficit Hyperactivity Disorder (ADHD) Index scores.

CONCLUSIONS

Occasional snorers, according to parental report, do exhibit ADHD-like behaviors. Basic sensory processing is longer than in controls, suggesting that delayed frontal activation requires more effort in snorers.

Executive Function Skills of 6 to 8 Year Olds: Brain and Behavioral Evidence and Implications for School Achievement

Academic and social success in school has been linked to children's self-regulation. This study investigated the assessment of the executive function (EF) component of self-regulation using a low-cost, easily administered measure to determine whether scores obtained from the behavioral task would agree with those obtained using a laboratory-based neuropsychological measure of EF skills. The sample included 74 children (37 females; M = 86.2 months) who participated in two assessments of working memory and inhibitory control: Knock-Tap (NEPSY: Korkman, Kirk, and Kemp, 1998), and participation in event-related potential (ERP) testing that included the Directional Stroop Test (Davidson, Cruess, Diamond, O'Craven, & Savoy, 1999). Three main findings emerged. First, children grouped as high versus low performing on the NEPSY Knock-Tap Task were found to performed differently on the more difficult conditions of the DST (the Incongruent and Mixed Conditions), suggesting that the Knock-Tap Task as a low-cost and easy to administer assessment of EF skills may be one way for teachers to identify students with poor inhibitory control skills. Second, children's performance on the DST was strongly related to their ERP responses, adding to evidence that differences in behavioral performance on the DST as a measure of EF skills reflect corresponding differences in brain processing. Finally, differences in brain processing on the DST task also were found when the children were grouped based on Knock-Tap performance. Simple screening procedures can enable teachers to identify children whose distractibility, inattentiveness, or poor attention spans may interfere with classroom learning.

Brain ERP components predict which individuals progress to Alzheimer's disease and which do not

Predicting which individuals will progress to Alzheimer's disease (AD) is important in both clinical and research settings. We used brain Event-Related Potentials (ERPs) obtained in a perceptual/cognitive paradigm with various processing demands to predict which individual Mild Cognitive Impairment (MCI) subjects will develop AD versus which will not. ERP components, including P3, memory "storage" component, and other earlier and later components, were identified and measured by Principal Components Analysis. When measured for particular task conditions, a weighted set of eight ERP component_conditions performed well in discriminant analysis at predicting later AD progression with good accuracy, sensitivity, and specificity. The predictions for most individuals (79%) had high posterior probabilities and were accurate (88%). This method, supported by a cross-validation where the prediction accuracy was 70-78%, features the posterior probability for each individual as a method of determining the likelihood of progression to AD. Empirically obtained prediction accuracies rose to 94% when the computed posterior probabilities for individuals were 0.90 or higher (which was found for 40% of our MCI sample).

Dynamic links between emerging cognitive skills and brain processes

The goal of the present study was to investigate whether advanced cognitive skills in one domain impact the neural processing of unrelated skills in a different cognitive domain. This question is related to the broader issue of how cognitive-neurodevelopment proceeds as different skills are mastered. To address this goal, event-related brain potentials (ERPs) were used to assess linkages between cognitive skills of preschool children as reflected in their performance on a pre-reading screening test (Get Ready To Read) and their neural responses while engaged in a geometric shape matching task. Sixteen children (10 males) participated in this study. The children ranged from 46 to 60 months (SD = 4.36 months). ERPs were recorded using a 128-electrode high-density array while children attended to presentations of matched and mismatched shapes (triangles, circles, or squares). ERPs indicated that children with more advanced pre-reading skills discriminated between matched and mismatched shapes earlier than children with poorer pre-readings skills. The earlier discrimination effect observed in the advanced group was localized over the occipital electrode sites whereas in the Low Group such effects were present over frontal, parietal, and occipital sites. Modeled magnetic resonance images (MRIs) of the ERP component sources identified differences in neural generators between the two groups. Both sets of findings support the hypothesis that processing in a poorer-performing group is more distributed temporally and spatially across the scalp, and reflects the engagement of more distributed brain regions. These findings are seen as support for a theory of neural-cognitive development that is advanced in the present article.

ERP correlates of noun and verb processing in preschool-age children

Indices of discrimination between words of different syntactic classes were examined in a group of 22 preschool-age children utilizing event-related potential (ERP) procedures. Video taped scenes depicted an actor performing actions with a set of toys. ERPs were recorded to spoken nouns or verbs that either matched or failed to match the action name or object name in the video scene. ERPs were analyzed using peak amplitude-ANOVA procedures and principal components analysis-ANOVA. Results indicated good convergence across analysis approaches. More specifically, P100 and N220 varied bilaterally over frontal electrode sites and discriminated between different syntactic classes for both match and mismatch situations. Based on comparisons with adult data from previous work [Molfese, D.L., Burger-Judisch, L., Gill, L.A., Golinkoff, R.M., Hirsh-Pasek, K., 1996. Electrophysiological correlates of noun-verb processing in adults. Brain and Language 54 388-413], it is suggested that the pattern of brain involvement underlying syntactic class discriminations undergo developmental changes between the preschool years and adulthood.

Evaluation of PCA and ICA of simulated ERPs: Promax vs. Infomax rotations

Independent components analysis (ICA) and principal components analysis (PCA) are methods used to analyze event-related potential (ERP) and functional imaging (fMRI) data. In the present study, ICA and PCA were directly compared by applying them to simulated ERP datasets. Specifically, PCA was used to generate a subspace of the dataset followed by the application of PCA Promax or ICA Infomax rotations. The simulated datasets were composed of real background EEG activity plus two ERP simulated components. The results suggest that Promax is most effective for temporal analysis, whereas Infomax is most effective for spatial analysis. Failed analyses were examined and used to devise potential diagnostic strategies for both rotations. Finally, the results also showed that decomposition of subject averages yield better results than of grand averages across subjects.

Breast-Fed Infants Process Speech Differently From Bottle-Fed Infants: Evidence From Neuroelectrophysiology

Numerous studies report positive effects of breast-feeding on infant development. Such effects are apparent early in development as well as in later years. Recently, elements in breast milk, polyunsaturatred fatty acids (PUFAs), have been identified as having great potential for increasing nutritional benefits. PUFAs are long-chain fatty acids containing two or more double bonds. While some scientists are enthusiastic about the long-term benefits of PUFAs on brain and cognitive development, many of the positive pharmacological effects attributed to PUFAs remain unsubstantiated. The present study investigated the differential impact of breast-feeding vs. PUFA-enriched formula in a small but well-matched population of 12 infants tested at 6 months of age. Event-related potential (ERP) and a range of behavior measures were recorded. ERP waveforms identified marked differences between the breast-fed and PUFA-fed infants by 6 months of age. When a range of biological, perinatal, and cognitive factors were equated between the two groups, only the ERPs recorded from breast-fed infants changed throughout their recorded period (700 msec), differentiated between all speech sounds, and generated differences in scalp recordings across all regions recorded across both hemispheres. Such differences in the range of their brain responses could signal an advantage for the breast-fed infants for later linguistic and cognitive development.

Smoking during pregnancy affects speech-processing ability in newborn infants

BACKGROUND

Tobacco smoking during pregnancy is known to adversely affect development of the central nervous system in babies of smoking mothers by restricting utero-placental blood flow and the amount of oxygen available to the fetus. Behavioral data associate maternal smoking with lower verbal scores and poorer performance on specific language/auditory tests.

OBJECTIVES

In the current study we examined the effects of maternal smoking during pregnancy on newborns' speech processing ability as measured by event-related potentials (ERPs).

METHOD

High-density ERPs were recorded within 48 hr of birth in healthy newborn infants of smoking (n = 8) and nonsmoking (n = 8) mothers. Participating infants were matched on sex, gestational age, birth weight, Apgar scores, mother's education, and family income. Smoking during pregnancy was determined by parental self-report and medical records. ERPs were recorded in response to six consonant-vowel syllables presented in random order with equal probability.

RESULTS

Brainwaves of babies of nonsmoking mothers were characterized by typical hemisphere asymmetries, with larger amplitudes over the left hemisphere, especially over temporal regions. Further, infants of nonsmokers discriminated among a greater number of syllables whereas the newborns of smokers began the discrimination process at least 150 msec later and differentiated among fewer stimuli.

CONCLUSIONS

Our findings indicate that prenatal exposure to tobacco smoke in otherwise healthy babies is linked with significant changes in brain physiology associated with basic perceptual skills that could place the infant at risk for later developmental problems.

Below-average, average, and above-average readers engage different and similar brain regions while reading

Event-related potentials (ERPs) were recorded from 27 children (14 girls, 13 boys) who varied in their reading skill levels. Both behavior performance measures recorded during the ERP word classification task and the ERP responses themselves discriminated between children with above-average, average, and below-average reading skills. ERP amplitudes and peak latencies decreased as reading skills increased. Furthermore, hemisphere differences increased with higher reading skill levels. Sex differences were also related to ERP amplitude variations across the scalp. However, ERPs recorded from boys and girls did not differ as a function of differences in the children's reading levels.

ERP indicators of learning in adults

This study investigated learning-related changes in the brain activity of young adults. A group of 29 undergraduate students (18-24 years) participated in a learning study that included a pretest, a training session, and a posttest. Each trial involved presentation of a complex visual stimulus and its spoken "name." Auditory event-related potentials (ERPs) were recorded in response to matching and mismatching names. In the pretest, the participants guessed whether the names were matching the figures. During training they learned the names of a set of simple elements making up the complex figures and were required to master a simple rule for combining the visual and auditory stimuli. The posttest included presentation of the combinations learned during training as well as novel pairings of the same elements. Following training the number of correct responses for learned items doubled and the amplitudes of the auditory ERPs to learned and rule transfer stimuli were more positive than brain waves to the not learned or novel items over most of the analysis window. The ERPs further differentiated between a familiarity response (late positive shift) and learning-specific changes (N2-P3 range). Overall, the findings suggest that ERPs can be a useful tool for learning assessment and offer new insights in the study of individual differences associated with the learning process.

Principal components analysis of Laplacian waveforms as a generic method for identifying ERP generator patterns: I. Evaluation with auditory oddball tasks

OBJECTIVE

To evaluate the effectiveness and comparability of PCA-based simplifications of ERP waveforms versus their reference-free Laplacian transformations for separating task- and response-related ERP generator patterns during auditory oddball tasks.

METHODS

Nose-referenced ERPs (31 sites total) were recorded from 66 right-handed adults during oddball tasks using syllables or tones. Response mode (left press, right press, silent count) and task was varied within subjects. Spherical spline current source density (CSD) waveforms were computed to sharpen ERP scalp topographies and eliminate volume-conducted contributions. ERP and CSD data were submitted to separate covariance-based, unrestricted temporal PCAs (Varimax) to disentangle temporally and spatially overlapping ERP and CSD components.

RESULTS

Corresponding ERP and CSD factors were unambiguously related to known ERP components. For example, the dipolar organization of a central N1 was evident from factorized anterior sinks and posterior sources encompassing the Sylvian fissure. Factors associated with N2 were characterized by asymmetric frontolateral (tonal: frontotemporal R > L) and parietotemporal (phonetic: parietotemporal L > R) sinks for targets. A single ERP factor summarized parietal P3 activity, along with an anterior negativity. In contrast, two CSD factors peaking at 360 and 560 ms distinguished a parietal P3 source with an anterior sink from a centroparietal P3 source with a sharply localized Fz sink. A smaller parietal but larger left temporal P3 source was found for silent count compared to button press. Left or right press produced opposite, region-specific asymmetries originating from central sites, modulating the N2/P3 complex.

CONCLUSIONS

CSD transformation is shown to be a valuable preprocessing step for PCA of ERP data, providing a unique, physiologically meaningful solution to the ubiquitous reference problem. By reducing ERP redundancy and producing sharper, simpler topographies, and without losing or distorting any effects of interest, the CSD-PCA solution replicated and extended previous task- and response-related findings.

SIGNIFICANCE

Eliminating ambiguities of the recording reference, the combined CSD-PCA approach systematically bridges between montage-dependent scalp potentials and distinct, anatomically-relevant current generators, and shows promise as a comprehensive, generic strategy for ERP analysis.

Optimizing principal components analysis of event-related potentials: matrix type, factor loading weighting, extraction, and rotations

OBJECTIVE

Given conflicting recommendations in the literature, this report seeks to present a standard protocol for applying principal components analysis (PCA) to event-related potential (ERP) datasets.

METHODS

The effects of a covariance versus a correlation matrix, Kaiser normalization vs. covariance loadings, truncated versus unrestricted solutions, and Varimax versus Promax rotations were tested on 100 simulation datasets. Also, whether the effects of these parameters are mediated by component size was examined.

RESULTS

Parameters were evaluated according to time course reconstruction, source localization results, and misallocation of ANOVA effects. Correlation matrices resulted in dramatic misallocation of variance. The Promax rotation yielded much more accurate results than Varimax rotation. Covariance loadings were inferior to Kaiser Normalization and unweighted loadings.

CONCLUSIONS

Based on the current simulation of two components, the evidence supports the use of a covariance matrix, Kaiser normalization, and Promax rotation. When these parameters are used, unrestricted solutions did not materially improve the results. We argue against their use. Results also suggest that optimized PCA procedures can measurably improve source localization results.

SIGNIFICANCE

Continued development of PCA procedures can improve the results when PCA is applied to ERP datasets.

Event-related potentials in cocaine-exposed children during a Stroop task

OBJECTIVE

Prenatal cocaine-exposure may interfere with the ontogeny of prefrontal cortical executive functions due to cocaine's effect on the developing monoaminergic system. This study presents findings regarding cortical functioning in 29 prenatally cocaine-exposed (CE) and non-drug-exposed (NDE) 7- to 9-year-old children participating in event related potential (ERP) studies.

METHODS

ERPs were recorded using 128-electrode high-density arrays while children responded to a standard Stroop paradigm.

RESULTS

In the Stroop paradigm, CE children generated prolonged responses to the words while the NDE children produced briefer responses. Effects were noted in the region of the initial positive peak (P1), the second negative peak (N2) and the later positive peak (P3).

CONCLUSIONS

Early cocaine exposure may inhibit the specialization and streamlining of brain region involvement during cognitive processing such that task processing is slower to begin, requires more diverse cortical involvement, and requires more time to complete. ERP methodology has considerable potential for studying frontal maturation and may provide additional information to clarify generally the specific effects of prenatal CE on cortical functioning and the developmental course of cognitive functions.

What is novel in the novelty oddball paradigm? Functional significance of the novelty P3 event-related potential as revealed by independent component analysis

To better understand whether voluntary attention affects how the brain processes novel events, variants of the auditory novelty oddball paradigm were presented to two different groups of human volunteers. One group of subjects (n=16) silently counted rarely presented 'infrequent' tones (p=0.10), interspersed with 'novel' task-irrelevant unique environmental sounds (p=0.10) and frequently presented 'standard' tones (p=0.80). A second group of subjects (n=17) silently counted the 'novel' environmental sounds, the 'infrequent' tones now serving as the task-irrelevant deviant events. Analysis of event-related potentials (ERPs) recorded from 63 scalp channels suggested a spatiotemporal overlap of fronto-central novelty P3 and centro-parietal P3 (P3b) ERP features in both groups. Application of independent component analysis (ICA) to concatenated single trials revealed two independent component clusters that accounted for portions of the novelty P3 and P3b response features, respectively. The P3b-related ICA cluster contributed to the novelty P3 amplitude response to novel environmental sounds. In contrast to the scalp ERPs, the amplitude of the novelty P3 related cluster was not affected by voluntary attention, that is, by the target/nontarget distinction. This result demonstrates the usefulness of ICA for disentangling spatiotemporally overlapping ERP processes and provides evidence that task irrelevance is not a necessary feature of novelty processing.

Dopamine D4 receptor exon III genotype influence on the auditory evoked novelty P3

The functional implications of the dopamine D4 receptor gene (DRD4) exon III polymorphism and its role in the modulation of temperament and in the pathophysiology of psychiatric disorders are still a matter of debate. Based on evidence from animal studies, we hypothesised that this polymorphism is involved in the modulation of the cortical response to novelty as reflected by the auditory evoked novelty P3 event-related potential. In a sample of 46 healthy volunteers, we observed an interactive effect of DRD4 exon III genotype and the eye-blink rate, a measure of central dopaminergic activity, on the novelty P3. These findings suggest that the DRD4 exon III polymorphism influences the processing of novelty and that this influence depends on tonic dopaminergic activity.

Neural correlates of bimodal speech and gesture comprehension

The present study examined the neural correlates of speech and hand gesture comprehension in a naturalistic context. Fifteen participants watched audiovisual segments of speech and gesture while event-related potentials (ERPs) were recorded to the speech. Gesture influenced the ERPs to the speech. Specifically, there was a right-lateralized N400 effect-reflecting semantic integration-when gestures mismatched versus matched the speech. In addition, early sensory components in bilateral occipital and frontal sites differentiated speech accompanied by matching versus non-matching gestures. These results suggest that hand gestures may be integrated with speech at early and late stages of language processing.

Optimizing PCA methodology for ERP component identification and measurement: theoretical rationale and empirical evaluation

OBJECTIVE

To determine how specific methodological choices affect "data-driven" simplifications of event-related potentials (ERPs) using principal components analysis (PCA). The usefulness of the extracted component measures can be evaluated by knowledge about the variance distribution of ERPs, which are characterized by the removal of baseline activity. The variance should be small before and at stimulus onset (across and within cases), but large near the end of the recording epoch and at ERP component peaks. These characteristics are preserved with a covariance matrix, but lost with a correlation matrix, which assigns equal weights to each sample point, yielding the possibility that small but systematic variations may form a factor.

METHODS

Varimax-rotated PCAs were performed on simulated and real ERPs, systematically varying extraction criteria (number of factors) and method (correlation/covariance matrix, using unstandardized/standardized loadings before rotation).

RESULTS

Conservative extraction criteria changed the morphology of some components considerably, which had severe implications for inferential statistics. Solutions converged and stabilized with more liberal criteria. Interpretability (more distinctive component waveforms with narrow and unambiguous loading peaks) and statistical conclusions (greater effect stability across extraction criteria) were best for unstandardized covariance-based solutions. In contrast, all standardized covariance- and correlation-based solutions included "high-variance" factors during the baseline, confirming findings for simulated data.

CONCLUSIONS

Unrestricted, unstandardized covariance-based PCA solutions optimize ERP component identification and measurement.