The Influence of Unequal Numbers of Trials on Comparisons of Average Event-Related Potentials

Stimulus expectations do not modulate visual event-related potentials in probabilistic cueing designs

Humans and other animals can learn and exploit repeating patterns that occur within their environments. These learned patterns can be used to form expectations about future sensory events. Several influential predictive coding models have been proposed to explain how learned expectations influence the activity of stimulus-selective neurons in the visual system. These models specify reductions in neural response measures when expectations are fulfilled (termed expectation suppression) and increases following surprising sensory events. However, there is currently scant evidence for expectation suppression in the visual system when confounding factors are taken into account. Effects of surprise have been observed in blood oxygen level dependent (BOLD) signals, but not when using electrophysiological measures. To provide a strong test for expectation suppression and surprise effects we performed a predictive cueing experiment while recording electroencephalographic (EEG) data. Participants (n=48) learned cue-face associations during a training session and were then exposed to these cue-face pairs in a subsequent experiment. Using univariate analyses of face-evoked event-related potentials (ERPs) we did not observe any differences across expected (90% probability), neutral (50%) and surprising (10%) face conditions. Across these comparisons, Bayes factors consistently favoured the null hypothesis throughout the time-course of the stimulus-evoked response. When using multivariate pattern analysis we did not observe above-chance classification of expected and surprising face-evoked ERPs. By contrast, we found robust within- and across-trial stimulus repetition effects. Our findings do not support predictive coding-based accounts that specify reduced prediction error signalling when perceptual expectations are fulfilled. They instead highlight the utility of other types of predictive processing models that describe expectation-related phenomena in the visual system without recourse to prediction error signalling.

Predicting phonological information in language comprehension: evidence from ERP representational similarity analysis and Chinese idioms

Do comprehenders predict the meaning and even the phonological form of upcoming words during language comprehension? With a growing body of evidence suggesting that semantic representations may be predicted, the evidence for phonological prediction is less clear and largely derived from studies conducted in languages utilizing an alphabetic script. In this research, we aim to examine the prediction of phonological information in the processing of Chinese idioms through the use of ERP representational similarity analysis (RSA). The study utilizes four-character Chinese idioms, and phonological overlap was manipulated by varying the syllable at the idiom-final part between idiom pairs so that pairs of idioms share a syllable (i.e. within-pairs) or not (between-pairs). We quantified the similarity between patterns of neural activity of idioms for within- and between-pairs. RSA results revealed greater similarity in neural activity patterns for idioms within-pairs, compared with between-pairs, and critically this similarity effect was observed prior to the presentation of the phonological similarity, providing evidence for the pre-activation of upcoming phonological information, under circumstances that encourage predictive processing.

Sex differences in automatic emotion regulation in adolescents with autism spectrum disorder

Autism may be underdiagnosed in females because their social difficulties are often less noticeable. This study explored sex differences in automatic facial emotion processing in 45 adolescents with autism spectrum disorder (22 female, 23 male), age 10-16 years, performing active target detection task and Go/NoGo tasks where faces with positive and negative emotional expressions served as irrelevant distractors. The combined sample demonstrated more accurate performance on the target detection (response initiation) than the Go/NoGo task (response inhibition), replicating findings previously reported in typical participants. Females exhibited greater difficulty than males with response initiation in the target detection task, especially in the context of angry faces, while males found withholding a response in the Go/NoGo block with happy faces more challenging. Electrophysiological data revealed no sex differences or emotion discrimination effects during the early perceptual processing of faces indexed by the occipitotemporal N170. Autistic males demonstrated increased frontal N2 and parietal P3 amplitudes compared to females, suggesting greater neural resource allocation to automatic emotion regulation processes. The associations between standardized behavioral measures (autism severity, theory of mind skills) and brain responses also varied by sex: more adaptive social functioning was related to the speed of perceptual processing (N170 latency) in females and the extent of deliberate attention allocation (P3 amplitudes) in males. Together, these findings suggest that males and females with autism may rely on different strategies for social functioning and highlight the importance of considering sex differences in autism. LAY SUMMARY: Females with autism may exhibit less noticeable social difficulties than males. This study demonstrates that autistic females are more successful than males at inhibiting behavioral responses in emotional contexts, while males are more likely to initiate a response. At the neural level, social functioning in females is related to the speed of automatic perceptual processing of facial cues, and in males, to the extent of active attention allocation to the stimuli. These findings highlight the importance of considering sex differences in autism diagnosis and treatment selection.

Evaluating the evidence for expectation suppression in the visual system

Reports of expectation suppression have shaped the development of influential predictive coding-based theories of visual perception. However recent work has highlighted confounding factors that may mimic or inflate expectation suppression effects. In this review, we describe four confounds that are prevalent across experiments that tested for expectation suppression: effects of surprise, attention, stimulus repetition and adaptation, and stimulus novelty. With these confounds in mind we then critically review the evidence for expectation suppression across probabilistic cueing, statistical learning, oddball, action-outcome learning and apparent motion designs. We found evidence for expectation suppression within a specific subset of statistical learning designs that involved weeks of sequence learning prior to neural activity measurement. Across other experimental contexts, whereby stimulus appearance probabilities were learned within one or two testing sessions, there was inconsistent evidence for genuine expectation suppression. We discuss how an absence of expectation suppression could inform models of predictive processing, repetition suppression and perceptual decision-making. We also provide suggestions for designing experiments that may better test for expectation suppression in future work.

Auditory event-related potentials index faster processing of natural speech but not synthetic speech over nonspeech analogs in children

Given the crucial role of speech sounds in human language, it may be beneficial for speech to be supported by more efficient auditory and attentional neural processing mechanisms compared to nonspeech sounds. However, previous event-related potential (ERP) studies have found either no differences or slower auditory processing of speech than nonspeech, as well as inconsistent attentional processing. We hypothesized that this may be due to the use of synthetic stimuli in past experiments. The present study measured ERP responses during passive listening to both synthetic and natural speech and complexity-matched nonspeech analog sounds in 22 8-11-year-old children. We found that although children were more likely to show immature auditory ERP responses to the more complex natural stimuli, ERP latencies were significantly faster to natural speech compared to cow vocalizations, but were significantly slower to synthetic speech compared to tones. The attentional results indicated a P3a orienting response only to the cow sound, and we discuss potential methodological reasons for this. We conclude that our results support more efficient auditory processing of natural speech sounds in children, though more research with a wider array of stimuli will be necessary to confirm these results. Our results also highlight the importance of using natural stimuli in research investigating the neurobiology of language.

Controlling Unpleasant Thoughts: Adjustments of Cognitive Control Based on Previous-Trial Load in a Working Memory Task

Dynamic cognitive control adjustments are important for integrating thoughts and actions that take place during dynamic changes of environmental demands and support goal-directed behavior. We investigated, in a working memory (WM) paradigm, whether dynamic adjustments in cognitive control based on previous trial load influence the neural response to neutral or unpleasant distracters. We also investigated whether individual self-reported abilities in controlling thoughts influence this effect. Participants performed a WM change detection task with low or high WM-related cognitive demands. An unpleasant or a neutral distractive image was presented at the beginning of each trial, prior to the WM task. We tested for control adjustments that were associated with the load level of the preceding trial task (N-1) on the neural response to the subsequent distractive image. We found an effect of the prior WM task load on a parieto-occipital waveform event-related potential (ERP) that appeared between 200 and 300 ms after the neutral distracter onset. This effect was not observed for the unpleasant distracter. Individual ability for controlling thoughts may influence the effect of cognitive control adjustments on distracter processing during the unpleasant condition. These findings provide evidence that: (1) dynamic cognitive control adjustments are impaired by unpleasant distracters; and (2) the ability to control unpleasant thoughts is linked to individual differences in flexible cognitive control adjustments and shielding of WM representations from unpleasant distracters.

Specific lexico-semantic predictions are associated with unique spatial and temporal patterns of neural activity

We used Magnetoencephalography (MEG) in combination with Representational Similarity Analysis to probe neural activity associated with distinct, item-specific lexico-semantic predictions during language comprehension. MEG activity was measured as participants read highly constraining sentences in which the final words could be predicted. Before the onset of the predicted words, both the spatial and temporal patterns of brain activity were more similar when the same words were predicted than when different words were predicted. The temporal patterns localized to the left inferior and medial temporal lobe. These findings provide evidence that unique spatial and temporal patterns of neural activity are associated with item-specific lexico-semantic predictions. We suggest that the unique spatial patterns reflected the prediction of spatially distributed semantic features associated with the predicted word, and that the left inferior/medial temporal lobe played a role in temporally 'binding' these features, giving rise to unique lexico-semantic predictions.

Cortical response of the projected-thumb tactile sensation under TENS by MEG

The existence of projected finger territories (PFTs) near the stump provides an essential way to realize the tactile sensation of lost fingers by transcutaneous electrical nerve stimulation (TENS). After amputation, the somatosensory cortex corresponding to lost fingers might be invaded by other cortical areas due to cortical plasticity. However, it was seldom observed how the amputees could feel the projected or lost finger tactile sensation in the cerebral cortex under TENS. To answer this question, by using magnetoencephalography (MEG), we investigated the cortical response under TENS of the projected thumb territory and normal thumb with 2 Hz current pulses. One subject with long-term left forearm amputation was recruited. The temporal and spatial characteristics of the activated cortical magnetic signals were analyzed. The Equivalent Current Dipoles (ECDs) corresponding to the strongest strength were mapped in the cerebral cortex, and the current density distribution were clearly illustrated. We found that the latencies at the maximum ECD strength were 60 ± 1.41 ms for the projected thumb and 46 ± 1.25 ms for the normal counterpart. The strongest ECD corresponding to projected thumb was located in the central sulcus near the mirror location of the normal thumb counterpart. And the response strengths of projected thumb cortex were stronger than normal thumb counterpart.

Speech-Processing Fatigue in Children: Auditory Event-Related Potential and Behavioral Measures

PURPOSE

Fatigue related to speech processing is an understudied area that may have significant negative effects, especially in children who spend the majority of their school days listening to classroom instruction.

METHOD

This study examined the feasibility of using auditory P300 responses and behavioral indices (lapses of attention and self-report) to measure fatigue resulting from sustained listening demands in 27 children (M = 9.28 years).

RESULTS

Consistent with predictions, increased lapses of attention, longer reaction times, reduced P300 amplitudes to infrequent target stimuli, and self-report of greater fatigue were observed after the completion of a series of demanding listening tasks compared with the baseline values. The event-related potential responses correlated with the behavioral measures of performance.

CONCLUSION

These findings suggest that neural and behavioral responses indexing attention and processing resources show promise as effective markers of fatigue in children.

Processing of stimulus content but not of emotional valence is altered in persons with Williams syndrome

BACKGROUND

Individuals with Williams syndrome (WS) exhibit hypersociability and may respond atypically to emotional information in social and nonsocial stimuli. It is not yet clear whether these difficulties are specific to emotional content or stimulus type. This study examined the neural processes supporting social and emotional information processing in WS.

METHOD

Visual event-related potentials were recorded in 19 adults with WS and 10 typical peers during a picture-viewing task requiring detection of smiling faces among other social and nonsocial images with positive and negative emotional content.

RESULTS

The participant groups were not significantly different in affective processing of positive and negative stimuli and perceived faces as different from nonsocial images. Participants with WS showed subtle differences in face-specific perceptual processes (e.g. face inversion, N170 lateralisation), suggesting a more feature-based processing. They also demonstrated reduced attention and arousal modulation (P3, late positive potential) in response to faces vs. nonsocial images. These differences were independent of intelligence quotient.

CONCLUSIONS

There was no evidence of greater than typical perceptual, attentional or affective processing of social information in WS. The results support the idea that altered face perception processes and not the increased salience of social stimuli or difficulties with emotion discrimination may contribute to the hypersocial phenotype in WS.

Positive Affect Processing and Joint Attention in Infants at High Risk for Autism: An Exploratory Study

Few behavioral indices of risk for autism spectrum disorders (ASD) are present before 12 months, and potential biomarkers remain largely unexamined. This prospective study of infant siblings of children with ASD (n = 16) and low-risk comparison infants (n = 15) examined group differences in event-related potentials (ERPs) indexing processing of facial positive affect (N290/P400, Nc) at 9 months and their relation to joint attention at 15 months. Group differences were most pronounced for subtle facial expressions, in that the low-risk group exhibited relatively longer processing (P400 latency) and greater attention resource allocation (Nc amplitude). Exploratory analyses found associations between ERP responses and later joint attention, suggesting that attention to positive affect cues may support the development of other social competencies.

Effects of Valence and Origin of Emotions in Word Processing Evidenced by Event Related Potential Correlates in a Lexical Decision Task

This paper presents behavioral and event-related potential (ERP) correlates of emotional word processing during a lexical decision task (LDT). We showed that valence and origin (two distinct affective properties of stimuli) help to account for the ERP correlates of LDT. The origin of emotion is a factor derived from the emotion duality model. This model distinguishes between the automatic and controlled elicitation of emotional states. The subjects' task was to discriminate words from pseudo-words. The stimulus words were carefully selected to differ with respect to valence and origin whilst being matched with respect to arousal, concreteness, length and frequency in natural language. Pseudo-words were matched to words with respect to length. The subjects were 32 individuals aged from 19 to 26 years who were invited to participate in an EEG study of lexical decision making. They evaluated a list of words and pseudo-words. We found that valence modulated the amplitude of the FN400 component (290-375 ms) at centro-frontal (Fz, Cz) region, whereas origin modulated the amplitude of the component in the LPC latency range (375-670 ms). The results indicate that the origin of stimuli should be taken into consideration while deliberating on the processing of emotional words.

A Permutation Test for Unbalanced Paired Comparisons of Global Field Power

Global field power is a valuable summary of multi-channel electroencephalography data. However, global field power is biased by the noise typical of electroencephalography experiments, so comparisons of global field power on data with unequal noise are invalid. Here, we demonstrate the relationship between the number of trials that contribute to a global field power measure and the expected value of that global field power measure. We also introduce a statistical testing procedure that can be used for multi-subject, repeated-measures (also called within-subjects) comparisons of global field power when the number of trials per condition is unequal across conditions. Simulations demonstrate the effect of unequal trial numbers on global field power comparisons and show the validity of the proposed test in contrast to conventional approaches. Finally, the proposed test and two alternative tests are applied to data collected in a rapid serial visual presentation target detection experiment. The results show that the proposed test finds global field power differences in the classical P3 range; the other tests find differences in that range but also at other times including at times before stimulus onset. These results are interpreted as showing that the proposed test is valid and sensitive to real within-subject differences in global field power in multi-subject unbalanced data.

Tracking the sensory environment: an ERP study of probability and context updating in ASD

We recorded visual event-related brain potentials from 32 adult male participants (16 high-functioning participants diagnosed with autism spectrum disorder (ASD) and 16 control participants, ranging in age from 18 to 53 years) during a three-stimulus oddball paradigm. Target and non-target stimulus probability was varied across three probability conditions, whereas the probability of a third non-target stimulus was held constant in all conditions. P3 amplitude to target stimuli was more sensitive to probability in ASD than in typically developing participants, whereas P3 amplitude to non-target stimuli was less responsive to probability in ASD participants. This suggests that neural responses to changes in event probability are attention-dependant in high-functioning ASD. The implications of these findings for higher-level behaviors such as prediction and planning are discussed.

Illusory and veridical mapping of tactile objects in the primary somatosensory and posterior parietal cortex

While several behavioral and neuroscience studies have explored visual, auditory, and cross-modal illusions, information about the phenomenology and neural correlates of somatosensory illusions is meager. By combining psychophysics and somatosensory evoked potentials, we explored in healthy humans the neural correlates of 2 compelling tactuo-proprioceptive illusions, namely Aristotle (1 object touching the contact area between 2 crossed fingers is perceived as 2 lateral objects) and Reverse illusions (2 lateral objects are perceived as 1 between crossed-fingers object). These illusions likely occur because of the tactuo-proprioceptive conflict induced by fingers being crossed in a non-natural posture. We found that different regions in the somatosensory stream exhibit different proneness to the illusions. Early electroencephalographic somatosensory activity (at 20 ms) originating in the primary somatosensory cortex (S1) reflects the phenomenal rather than the physical properties of the stimuli. Notably, later activity (around 200 ms) originating in the posterior parietal cortex is higher when subjects resist the illusions. Thus, while S1 activity is related to illusory perception, PPC acts as a conflict resolver that recodes tactile events from somatotopic to spatiotopic frames of reference and ultimately enables veridical perception.

Event-related potentials for 7-month-olds' processing of animals and furniture items

Event-related potentials (ERPs) to single visual stimuli were recorded in 7-month-old infants. In a three-stimulus oddball paradigm, infants watched one frequently occurring standard stimulus (either an animal or a furniture item) and two infrequently occurring oddball stimuli, presenting one exemplar from the same and one from the different superordinate category as compared to the standard stimulus. Additionally, visual attributes of the stimuli were controlled to investigate whether infants focus on category membership or on perceptual similarity when processing the stimuli. Infant ERPs indicated encoding of the standard stimulus and discriminating it from the two oddball stimuli by larger Nc peak amplitude and late-slow-wave activity for the infrequent stimuli. Moreover, larger Nc latency and positive-slow-wave activity indicated increased processing for the different-category as compared to the same-category oddball. Thus, 7-month-olds seem to encode single stimuli not only by surface perceptual features, but they also regard information of category membership, leading to facilitated processing of the oddball that belongs to the same domain as the standard stimulus.

Recording infant ERP data for cognitive research

Researchers from different backgrounds have an increasing interest in investigating infant cognitive development using electroencephalogram (EEG) recordings. Although EEG measurements are suitable for infants, the method poses several challenges including setting up an infant-friendly, but interference-free lab environment and designing age-appropriate stimuli and paradigms. Certain specifics of infant EEG data have to be considered when deriving event-related potentials (ERPs) to investigate cognitive processes in the developing brain. The present article summarizes the practical aspects of conducting ERP research with infants and describes how researchers typically deal with the specific challenges entailed in this work.

Same but different: 9-month-old infants at average and high risk for autism look at the same facial features but process them using different brain mechanisms

The study examined whether 9-month-old infants at average vs. high risk for autism spectrum disorder (ASD) process facial features (eyes, mouth) differently and whether such differences are related to infants' social and communicative skills. Eye tracking and visual event-related potentials (ERPs) were recorded in 35 infants (20 average-risk typical infants, 15 high-risk siblings of children with ASD) while they viewed photographs of a smiling unfamiliar female face. On 30% of the trials, the eyes or the mouth of that face was replaced with corresponding features from a different female. There were no group differences in the number, duration, or distribution of fixations, and all infants looked at the eyes and mouth regions equally. However, increased attention to the mouth was associated with weaker receptive communication skills and increased attention to the eyes correlated with better interpersonal skills. ERP results revealed that all infants detected eye and mouth changes but did so using different brain mechanisms. Changes in facial features were associated with changes in activity of the face perception mechanisms (N290) for the average-risk group but not for the high-risk infants. For all infants, correlations between ERP and eye-tracking measures indicated that larger and faster ERPs to feature changes were associated with fewer fixations on the irrelevant regions of stimuli. The size and latency of the ERP responses also correlated with parental reports of receptive and expressive communication skills, suggesting that differences in brain processing of human faces are associated with individual differences in social-communicative behaviors.

Processing of novel and familiar faces in infants at average and high risk for autism

The study investigated whether infant siblings of children with autism (sibs-ASD) process familiar and novel faces differently from typical infants and whether sensitivity to face familiarity is associated with infants' social and communicative behaviors. Visual event-related potentials (ERPs) were recorded in 35 infants, age 9 months ± 15 days (20 typical infants, 15 sibs-ASD) using an oddball paradigm presenting photographs of infants' mothers (70% of trials) and an unfamiliar female (30% of trials). Eye tracking responses to a different unfamiliar face were recorded to determine whether differences in gaze patterns might account for any ERP differences found. There were no group differences in the distribution, number or duration of fixations. Both infant groups differentiated between mothers and strangers, as reflected in amplitude modulations of posterior N290/P400 and frontal/central Nc responses. Group differences were present in the latency of the P400 response, where a delayed response to the stranger face was observed only in typical infants. Across both groups, shorter Nc latency to mother's face was associated with parental reports of stronger interpersonal skills. Individual differences in the speed of processing for novel vs. familiar faces may be an informative early marker of risk for atypical social development.

Electrophysiological evidence of altered memory processing in children experiencing early deprivation

Associations between early deprivation and memory functioning were examined in 9- to 11-year-old children. Children who had experienced prolonged institutional care prior to adoption were compared to children who were adopted early from foster care and children reared in birth families. Measures included the Paired Associates Learning task from the Cambridge Neuropsychological Test and Automated Battery (CANTAB) and a continuous recognition memory task during which ERPs were also recorded. Children who experienced prolonged institutionalization showed deficits in both behavioral memory measures as well as an attenuated P300 parietal memory effect. Results implicate memory function as one of the domains that may be negatively influenced by early deprivation in the form of institutional care.

Voluntary control over prestimulus activity related to encoding

A new development in our understanding of human long-term memory is that effective memory formation relies on neural activity just before an event. It is unknown whether such prestimulus activity is under voluntary control or a reflection of random fluctuations over time. In the present study, we addressed two issues: (1) whether prestimulus activity is influenced by an individual's motivation to encode, and (2) at what point in time encoding-related activity emerges. Electrical brain activity was recorded while healthy male and female adults memorized series of words. Each word was preceded by a cue, which indicated the monetary reward that would be received if the following word was later remembered. Memory was tested after a short delay with a five-way recognition task to separate different sources of recognition. Electrical activity elicited by the reward cue predicted later memory of a word. Crucially, however, this was only observed when the incentive to memorize a word was high. Encoding-related activity preceded high-reward words that were later recollected. This activity started shortly after cue onset and persisted until word onset. Prestimulus activity thus not only signals cue-related processing but also an ensuing preparatory state. In contrast, reward-related activity was limited to the time period immediately after the reward cue. These findings indicate that engaging neural activity that benefits the encoding of an upcoming event is under voluntary control, reflecting a strategic preparatory state in anticipation of processing an event.

Predicting Reading Growth with Event-Related Potentials: Thinking Differently about Indexing "Responsiveness"

The purpose of this study was to determine if event-related potential (ERP) data collected during three reading-related tasks (Letter Sound Matching, Nonword Rhyming, and Nonword Reading) could be used to predict short-term reading growth on a curriculum-based measure of word identification fluency over 19 weeks in a sample of 29 first-grade children. Results indicate that ERP responses to the Letter Sound Matching task were predictive of reading change and remained so after controlling for two previously validated behavioral predictors of reading, Rapid Letter Naming and Segmenting. ERP data for the other tasks were not correlated with reading change. The potential for cognitive neuroscience to enhance current methods of indexing responsiveness in a response-to-intervention (RTI) model is discussed.

What do infants see in faces? ERP evidence of different roles of eyes and mouth for face perception in 9-month-old infants

The study examined whether face-specific perceptual brain mechanisms in 9-month-old infants are differentially sensitive to changes in individual facial features (eyes vs. mouth) and whether sensitivity to such changes is related to infants' social and communicative skills. Infants viewed photographs of a smiling unfamiliar female face. On 30% of the trials, either the eyes or the mouth of that face were replaced by corresponding parts from a different female. Visual event-related potentials (ERPs) were recorded to examine face-sensitive brain responses. Results revealed that increased competence in expressive communication and interpersonal relationships was associated with a more mature response to faces, as reflected in a larger occipito-temporal N290 with shorter latency. Both eye and mouth changes were detected, though infants derived different information from these features. Eye changes had a greater impact on the face perception mechanisms and were not correlated with social or communication development, whereas mouth changes had a minimal impact on face processing but were associated with levels of language and communication understanding.

Reduced error monitoring in children with autism spectrum disorder: an ERP study

This study investigated self-monitoring in children with autism spectrum disorder (ASD) with event-related potentials looking at both the error-related negativity (ERN) and error-related positivity (Pe). The ERN is related to early error/conflict detection, and the Pe has been associated with conscious error evaluation or attention allocation. In addition, post-error slowing in reaction times (RTs) was measured. Children with ASD and age- and IQ- matched controls were administered an easy and a hard version of an auditory decision task. Results showed that the ERN was smaller in children with ASD but localized in the anterior cingulate cortex (ACC) in both groups. In addition we found a negativity on correct trials (CRN) that did not differ between the groups. Furthermore, a reduced Pe and a lack of post-error slowing in RTs were found in children with ASD. The reduced ERN in children with ASD, in the presence of an intact CRN, might suggest a specific insensitivity to detect situations in which the chance of making errors is enhanced. This might in turn lead to reduced error awareness/attention allocation to the erroneous event (reduced Pe) and eventually in a failure in change of strategy to deal with a situation, as becomes evident from the lack of post-error slowing in the ASD group. This relates well to the perseverative behaviour that is seen in children with ASD. We discuss these results in terms of a general deficit in self-monitoring, underlying social disturbance in ASD and the involvement of the ACC.

The developmental pattern of stimulus and response interference in a color-object Stroop task: an ERP study

Background

Several studies have shown that Stroop interference is stronger in children than in adults. However, in a standard Stroop paradigm, stimulus interference and response interference are confounded. The purpose of the present study was to determine whether interference at the stimulus level and the response level are subject to distinct maturational patterns across childhood. Three groups of children (6–7 year-olds, 8–9 year-olds, and 10–12 year-olds) and a group of adults performed a manual Color-Object Stroop designed to disentangle stimulus interference and response interference. This was accomplished by comparing three trial types. In congruent (C) trials there was no interference. In stimulus incongruent (SI) trials there was only stimulus interference. In response incongruent (RI) trials there was stimulus interference and response interference. Stimulus interference and response interference were measured by a comparison of SI with C, and RI with SI trials, respectively. Event-related potentials (ERPs) were measured to study the temporal dynamics of these processes of interference.

Results

There was no behavioral evidence for stimulus interference in any of the groups, but in 6–7 year-old children ERPs in the SI condition in comparison with the C condition showed an occipital P1-reduction (80–140 ms) and a widely distributed amplitude enhancement of a negative component followed by an amplitude reduction of a positive component (400–560 ms). For response interference, all groups showed a comparable reaction time (RT) delay, but children made more errors than adults. ERPs in the RI condition in comparison with the SI condition showed an amplitude reduction of a positive component over lateral parietal (-occipital) sites in 10–12 year-olds and adults (300–540 ms), and a widely distributed amplitude enhancement of a positive component in all age groups (680–960 ms). The size of the enhancement correlated positively with the RT response interference effect.

Conclusion

Although processes of stimulus interference control as measured with the color-object Stroop task seem to reach mature levels relatively early in childhood (6–7 years), development of response interference control appears to continue into late adolescence as 10–12 year-olds were still more susceptible to errors of response interference than adults.

Methylphenidate improves deficient error evaluation in children with ADHD: An event-related brain potential study

Children with ADHD make more errors than control children in response-conflict tasks. To explore whether this is mediated by enhanced sensitivity to conflict or reduced error-processing, task-related brain activity (N2, Ne/ERN, Pe) was compared between 8- to 12-year-old children with ADHD and healthy controls during performance of a flanker task. Furthermore, effects of methylphenidate were investigated in ADHD children in a second study. ADHD children made more errors, especially in high-response-conflict conditions, without showing post-error slowing. N2 amplitudes were enhanced on trials resulting in an error response, Ne/ERN amplitude was unaffected and Pe amplitude was reduced in the ADHD group. Methylphenidate reduced errors in both low- and high-conflict conditions and normalized Pe amplitudes in children with ADHD. It was concluded that the inaccurate behaviour of ADHD children in conflict tasks might be related to reduced error-awareness and higher sensitivity to response conflict. Methylphenidate's ameliorating effects might be established through its influence on brain networks including posterior (parietal) cortex, enabling children with ADHD to allocate more attention to significant events.