Crossing the hands disrupts tactile spatial attention but not motor attention: evidence from event-related potentials

During covert shifts of tactile spatial attention both somatotopic and external reference frames are employed to encode hand location. When participants cross their hands these frames of references produce conflicting spatial codes which disrupt tactile attentional selectivity. Because attentional shifts are triggered not only in Attention tasks but also during covert movement preparation, the present study aimed at investigating the reference frame employed during such 'motor shifts of attention'. Event related brain potentials (ERPs) were recorded during a Motor task where a visual cue (S1) indicated the relevant hand for a manual movement prior to a tactile Go/Nogo stimulus (S2). For comparison, we ran a tactile Attention task where the same cue (S1) now indicated the relevant hand for a tactile discrimination (S2). Both tasks were performed under uncrossed and crossed hands conditions. In both Attention and Motor tasks similar lateralized components were observed following S1 presentation. Anterior and posterior ERP components indicative of covert attention shifts were exclusively guided by an external reference frame, while a later central negativity operated according to a somatotopic reference frame in both tasks. In the Motor task, this negativity reflected selective activation of the motor cortex in preparation for movement execution. In the Attention task, this component might reflect activity in the somatosensory cortex in preparation for the subsequent tactile discrimination. The presence of multiple and conflicting spatial codes resulted in disruption of tactile attentional selection in the Attention task where attentional modulations of tactile processing were delayed and attenuated with crossed hands as indicated by the analysis of ERPs elicited by S2. In contrast, attentional modulations of S2 processing in the Motor task were largely unaffected by the hand posture manipulation, suggesting that motor attention employs primarily one spatial coordinate system.     

Auditory attention processing in 5-year-old children born preterm: evidence from event-related potentials

The assumption that children born preterm have difficulties in maintaining active attention was tested in passive and active tasks. Twenty 5-year-old children born preterm at 26 to 32 weeks gestational age were compared with 20 children born at term, matched for age and IQ, using an auditory paradigm. In the passive task participants had to watch a videotape of a cartoon and ignore auditory stimuli. In the active task they had to detect a rare tone (the 'target' tone; 10% of the tones presented) among frequent tones (the 'standard' tone; 90%). Accuracy and reaction time were analysed, and event-related potentials (ERPs) were recorded at the scalp sites Fz, Cz, T3, T4, Pz, Oz, and two electrodes for the left mastoid (passive task); and Fz, F7, F8, Cz, T3, T4, Pz, and Oz (for the active task). Behavioural and electrophysiological data were analysed with repeated-measure ANOVAs. The results showed a significant group effect only on the active task. The preterm group scored fewer correct hits (correct detection of target tone) and were less efficient in their attentional strategy as assessed by ERP components.     

Automatic activation of the semantic network in schizophrenia: evidence from event-related brain potentials.

BACKGROUND: Language disorder associated with schizophrenia might be due to disturbances in both automatic activation and mechanisms of controlled attention. The contribution of each process to semantic memory dysfunction has not been determined for schizophrenia, and the semantic priming paradigm is well-suited for addressing this question. In the present report, event-related potentials (ERPs) elicited under conditions assumed to reveal automatic activation (short prime-target interval and low proportion of related words) are compared directly with ERPs elicited under conditions associated with controlled processing (long prime-target interval and high proportion of related words). METHODS: Visual ERPs were recorded during a lexical decision task, in which semantic relationship (associated and unassociated words), expectancy (relatedness proportions), and prime-target interval (250- and 850-msec inter-stimulus intervals [ISIs]) were varied. Diagnosis and expectancy were between-subjects factors; semantic relationship and ISI were repeated measures. The N400 priming effect (enhanced negativity to unassociated words) was compared between 34 male normal control subjects tested once and 37 male schizophrenia inpatients evaluated during their participation in a double-blind haloperidol maintenance therapy and placebo replacement protocol. RESULTS: The N400 priming effect for patients was significantly reduced during both pharmacologic phases, compared with controls. During haloperidol treatment, however, patients showed a significant N400 priming effect over the anterior scalp region and additionally under the automatic activation condition. The N400 priming effect was enhanced under the controlled processing condition for control subjects; this effect was not observed for patients. N400 amplitude elicited under the rapid presentation rate (250-msec ISI) differed between medicated patients and controls; groups did not differ for the 850-msec ISI. CONCLUSIONS: Findings suggest that automatic activation and mechanisms of controlled attention are both disrupted during semantic memory access for schizophrenia patients. Pharmacologic agents, such as haloperidol, might enhance automatic activation of the semantic network in this patient population, as indexed by the N400 component of the ERP.     

Temporal attention enhances early visual processing: a review and new evidence from event-related potentials

Two fundamental cognitive functions, selective attention and processing of time, have been simultaneously explored in recent studies of temporal orienting of attention. A temporal-orienting procedure may consist of a temporal analogue to the Posner's paradigm, such that symbolic cues indicate the most probable moment for target arrival. Behavioral measures suggest that performance is improved for events appearing at expected vs. unexpected moments. However, there is no agreement on the locus of stimulus processing at which temporal attention operates. Thus, it remains unclear whether early perceptual or just late motor processes can be modulated. This article reviews current ERP research on temporal orienting, with an emphasis on factors that might determine the modulation of temporal orienting at early stages of processing. We conclude that: First, late components (N2 and P300) are consistently modulated by temporal orienting, which suggests attentional preparation of decision and/or motor processes. Second, early components (e.g., N1) seem to be modulated only when the task is highly demanding in perceptual processing. Hence, we conducted an ERP experiment which aimed to observe a modulation of early visual processing by using a perceptually demanding task, such as letter discrimination. The results show, for the first time, that targets appearing at attended moments elicited a larger P1 component than unattended targets. Moreover, temporal attention modulated the amplitude and latency of N2 and P300 components. This suggests that temporal orienting of attention not only modulates late motor processing, but also early visual processing when perceptually demanding tasks are used.     

Attention in essential tremor: evidence from event-related potentials

Clinically subtle executive dysfunctions have recently been described in essential tremor (ET), though the presence of attentional deficits is still unclear. We investigated the psychophysiological aspects of attention in ET, using event-related potentials (ERPs). Twenty-one non-demented patients with ET and 21 age- and sex-matched healthy controls underwent a psychophysiological evaluation. P300 components and the Contingent Negative Variation (CNV) were recorded. The latencies and amplitudes of the P3a and P3b subcomponents and CNV areas were evaluated. Possible correlations between clinical parameters and ERP data were investigated. P3a latency was significantly longer in the ET group (p < 0.05), while no differences emerged between patients and controls in P3b latency. No differences were observed between the two groups in the CNV parameters. ET patients display a difficulty in the response to novelty and in the recruitment of prefrontal attentive circuits, while the memory context-updating process appears to be spared. This selective cognitive dysfunction does not appear to interfere with the attentional set linked to the expectancy evaluated during a complex choice-reaction time task, which is preserved in ET. This multitask psychophysiological approach reveals the presence of a peculiar attentional deficit in patients with ET, thus expanding the clinical features of this disease.     

The role of spatial selective attention in working memory for locations: evidence from event-related potentials

We investigated the hypothesis that the covert focusing of spatial attention mediates the on-line maintenance of location information in spatial working memory. During the delay period of a spatial working-memory task, behaviorally irrelevant probe stimuli were flashed at both memorized and nonmemorized locations. Multichannel recordings of event-related potentials (ERPs) were used to assess visual processing of the probes at the different locations. Consistent with the hypothesis of attention-based rehearsal, early ERP components were enlarged in response to probes that appeared at memorized locations. These visual modulations were similar in latency and topography to those observed after explicit manipulations of spatial selective attention in a parallel experimental condition that employed an identical stimulus display.     

Semantic and syntactic processes during sentence comprehension in patients with schizophrenia: evidence from event-related potentials

Language and thought disorders are core symptoms in schizophrenia. We therefore studied language comprehension processes in patients with schizophrenia and control subjects during a sentence processing paradigm using event-related potentials (ERPs). In the ERP, assignment of syntactic structure to a string of words is reflected by an early left anterior negativity (ELAN) at about 80 ms after stimulus onset. Integration of syntactic and semantic information into a coherent representation is indexed by a positive potential at 600 ms (P600). Amplitudes of the ELAN and the P600 components are higher for grammatically incorrect sentences. Semantic processes are associated with a negative deflection peaking at 400 ms (N400). N400 amplitude is higher in semantically incongruent sentences. Nineteen patients with DSM IV schizophrenia and 19 healthy controls were presented with correct, semantically incorrect (semantic mismatch) and grammatically incorrect sentences (syntactic mismatch). Syntactic mismatch elicited an ELAN component in both subject groups. However, only controls but not patients with schizophrenia exhibited a P600 syntactic mismatch effect. Semantic mismatch was associated with a larger N400 potential which did not differ between groups. These results suggest that patients with schizophrenia are not impaired in syntactic structure assignment as reflected by the ELAN, but show deficits in semantic-syntactic integration processes underlying the P600.     

事件相关电位在精神分裂症中的应用及研究进展

事件相关电位（event related potentials,ERP）是根据现代心理学原理发展起来的一种与刺激事件呈“锁时”关系的脑电活动分析技术,临床常规ERP包括失匹配负波（MMN）、P300、关联负变（CNV）、感觉门控（P50）等,现就近年来事件相关电位在精神分裂症方面的研究作一综述。     

Involuntary attention in children as a function of sound source location: evidence from event-related potentials.

OBJECTIVES: The present study addressed the question of whether location of the auditory stimulation source affects an involuntary attention triggering to the deviant sounds in a passive oddball paradigm in 8-10-year-old children. METHODS: Using free-field stimulation two late event-related potentials components were examined: the mismatch negativity (MMN), indexing preconscious sound change detection and the P3a, indexing involuntary attention switch. Data were registered to frequency changes in sounds of different complexities in two experimental conditions. In the 'in-front' condition, the sound sequences were presented through the loudspeakers situated in front of a participant on both sides of the video display. In the 'on-sides' condition, the sources of auditory and visual stimuli were separated by moving the loudspeakers to the sides of the participant. RESULTS: The MMN amplitude or the MMN and P3a latencies varied in neither stimulus class significantly as a function of sound location. However, significantly larger P3 amplitude was found in the 'in-front', as compared to the 'on-sides' condition. CONCLUSIONS: The present results indicate enhanced involuntary attention switching in children when unattended auditory events occur within the space attended actively for visual modality. Such study design favouring cross-modal integration can be advantageous when studying involuntary auditory attention and its impairment in children.     

Predictive learning, prediction errors, and attention: evidence from event-related potentials and eye tracking

Prediction error ("surprise") affects the rate of learning: We learn more rapidly about cues for which we initially make incorrect predictions than cues for which our initial predictions are correct. The current studies employ electrophysiological measures to reveal early attentional differentiation of events that differ in their previous involvement in errors of predictive judgment. Error-related events attract more attention, as evidenced by features of event-related scalp potentials previously implicated in selective visual attention (selection negativity, augmented anterior N1). The earliest differences detected occurred around 120 msec after stimulus onset, and distributed source localization (LORETA) indicated that the inferior temporal regions were one source of the earliest differences. In addition, stimuli associated with the production of prediction errors show higher dwell times in an eye-tracking procedure. Our data support the view that early attentional processes play a role in human associative learning.     

Visuo-verbal interactions in working memory: evidence from event-related potentials

Working memory is thought to involve separate modality-specific storage systems. Interactions between these storage systems were investigated using a novel cross-modal 2-back paradigm. 2-back, 1-back and target items were presented either visually as a verbalizable linedrawing or auditorily as a digitized spoken word. ERPs for auditory targets were primarily modulated by the presentation modality of the 2-back item, whereas ERPs for visual targets were largely modulated by presentation modality of the 1-back item. Results indicate that verbalizable pictures are only partially transformed into a phonological code for rehearsal in working memory. Furthermore, results support the idea of a more stable and persistent auditory short-term store as opposed to a more transiently activated visual store for verbalizable material.     

Crossmodal links in spatial attention between vision, audition, and touch: evidence from event-related brain potentials

Results from event-related potential (ERP) studies are reviewed that investigated crossmodal links in spatial attention between vision, audition and touch to find out which stages in the processing of sensory stimuli are affected by such crossmodal links. ERPs were recorded in response to visual, auditory, and tactile stimuli under conditions where attention was directed to a specific location within one (primary) modality, while stimuli in another (secondary) modality were to be ignored regardless of their position. Systematic ERP effects of spatial attention were observed not only in the primary modality, but also for secondary modality stimuli, thus revealing crossmodal links in spatial attention. These links affected relatively early sensory-specific ERP components between 100 and 200 ms post-stimulus. Beyond 200 ms, ERPs to secondary modality stimuli were little affected by the current focus of attention within another modality. This pattern of results suggests that crossmodal links in spatial attention may affect sensory-perceptual processes within modality-specific cortical regions, but have little impact on later post-perceptual processing stages.     

The processing of emotional facial expression is gated by spatial attention: evidence from event-related brain potentials

To investigate whether the processing of faces and emotional facial expression can be modulated by spatial attention, ERPs were recorded in response to stimulus arrays containing two faces and two non-face stimuli (houses). In separate trials, attention was focused on the face pair or on the house pair, and facial expression was either fearful or neutral. When faces were attended, a greater frontal positivity in response to arrays containing fearful faces was obtained, starting about 100 ms after stimulus onset. In contrast, with faces located outside the attentional focus, this emotional expression effect was completely eliminated. This differential result demonstrates for the first time a strong attentional gating of brain processes involved in the analysis of emotional facial expression. It is argued that while an initial detection of emotionally relevant events mediated by the amygdala may occur pre-attentively, subsequent stages of emotional processing require focal spatial attention. The face-sensitive N170 component was unaffected by emotional facial expression, but N170 amplitudes were enhanced when faces were attended, suggesting that spatial attention can modulate the structural encoding of faces.     

Executive control is disturbed in schizophrenia: evidence from event-related potentials in a Go/NoGo task.

BACKGROUND: Schizophrenic patients suffer from cognitive and attentional deficits, particularly from failure of executive control functions. METHODS: This study investigated the cortical organization of executive control in schizophrenic patients and healthy control subjects using event-related potentials (ERPs). Event-related potentials were collected while subjects performed an auditory Go/NoGo task that required response inhibition. To exclude stimulus discriminability and early stimulus processing to confound results, stimuli were adjusted to the subject's individual discrimination ability and were presented in a simple and a difficult version. RESULTS: Schizophrenic patients performed similar to control subjects in the Go condition but worse than control subjects in the NoGo condition that required response inhibition. Event-related potentials revealed the neurophysiological substrate of this dysfunction. In the Go conditions, both healthy control subjects and schizophrenic patients showed the same voltage pattern. In the NoGo condition, control subjects and patients showed similar cortical activation only during early processing (N2 time window). However, in later stages of processing (P3 time window), healthy subjects showed left lateralization of ERPs over frontal areas while schizophrenic patients did not. CONCLUSIONS: We conclude that schizophrenic patients exhibit deficient processing in a neuronal network, including left frontal areas, that is involved in later stages of executive control function.     

Dynamics of task sets: evidence from dense-array event-related potentials

Prior research suggests that task sets facilitate coherent, goal-directed behavior by providing an internal, contextual frame that biases selection toward context-relevant stimulus attributes and responses. Questions about how task sets are engaged, maintained, and shifted have recently become a major focus of research on executive control processes. We employed dense-array (128-channel) event-related potential (ERP) methodology to examine the dynamics of brain systems engaged during the preparation and implementation of task switching. The EEG was recorded while participants performed letter and digit judgments to pseudorandomly-ordered, univalent (#3, A%) and bivalent (G5) stimulus trials, with the appropriate task cued by a colored rectangle presented 450 ms before target onset. Results revealed spatial and temporal variations in brain activity that could be related to preparatory processes common to both switch and repeat trials, switch-specific control processes engaged to reconfigure and maintain task set under conflict, and visual priming benefits of task repetition. Despite extensive practice and improvement, both behavioral and ERP results indicated that subjects maintained high levels of executive control processing with extended task engagement. The patterns of ERP activity obtained in the present study fit well with functional neuroanatomical models of self-regulation of action. The frontopolar and right-lateralized frontal switch effects obtained in the present study are consistent with the role of these regions in adapting to changing contextual contingencies. In contrast, the centroparietal P3b and N384 effects related to the contextual ambiguity of bivalent trials are consistent with the context monitoring and updating functions associated with the posterior cingulate learning circuit.     

Processing pronouns without antecedents: evidence from event-related brain potentials

Pronouns that do not have explicit antecedents typically cause processing problems. We investigate a specific example in which this may not be the case, as in "At the interview, they asked really difficult questions," where the plural pronoun they has no explicit antecedent, yet is intuitively easy to process. Some unspecified but constrained set of individuals (the interview panel or the company) can be inferred as the referent, but it is not crucial to determine specifically which entities are being referred to. We propose that this contrasts with the processing of singular pronouns (he or she), for which it is necessary to determine a specific referent. We used event-related brain potentials to investigate how readers process the pronoun (they vs. he/she) in these cases. Sentences were placed in a context that either did or did not contain an explicit antecedent for the pronoun. There were two key findings. Firstly, when there was no explicit antecedent, a larger fronto-central positivity was observed 750 msec after pronoun onset for he/she than they, possibly reflecting the additional difficulty involved in establishing a referent for he/she than for they when no explicit referent is available. Secondly, there was a larger N400-like deflection evoked by he/she than they, regardless of whether there was an explicit antecedent for the pronoun. We suggest that this is due to the singular pronouns bringing about a greater integration effort than the plural pronoun. This observation adds to a growing body of research revealing fundamental differences in the way these pronouns are handled by the language processor.     

Error processing in major depressive disorder: evidence from event-related potentials

In a previous study we showed that errors following errors activate a strategic (prefrontal) mechanism. In an error trial (trial n) following an erroneous previous trial (trial n - 1) healthy control subjects were found to have enlarged (more negative) amplitudes of the error related negativity (ERN)/error negativity (Ne), an electrophysiological correlate of response monitoring, in response to a negative feedback signal. Contrary to that, patients with major depressive disorder showed smaller (less negative) ERN/Ne amplitudes. It has been discussed controversially whether errors of choice (e.g., pressing an incorrect response button in an Eriksen flanker task) and errors of commission (e.g., pressing a button when one is not supposed to in a Go/Nogo task) are related to different ERN/Ne mechanisms. In the present study, we examined whether our previous result only holds for errors of choice in an Eriksen flankers task or extends to errors of commission in a Go/Nogo task, as well. Ten patients with DSM-IV major depressive disorder and 10 matched controls participated in a Go/Nogo task with performance feedback which signaled monetary reward. Patients with major depressive disorder again showed a less negative ERN/Ne amplitude in error trials following error trials. This result might reflect impaired response monitoring processes in major depressive disorder resulting from an impaired activation of a central reward pathway and/or a deficit in strategic reasoning.     

Error processing and impulsiveness in normals: evidence from event-related potentials

Electrophysiological correlates of impulsiveness were investigated in thirty-two healthy subjects using event-related potentials (ERP). Impulsiveness was determined by calculating individual reaction times (as a function of general response speed) in order to split the entire group into two subgroups with a more controlled (n = 16) and less controlled (n = 16) response style. Participants performed a Go/Nogo task while a 64 channel EEG was recorded. Artifact-free EEG segments were used to compute ERPs on correct Go trials and incorrect Nogo trials, separately. Three ERP components were of special interest: the error-related negativity (ERN)/error negativity (Ne) and the "early" error positivity (Pe) reflecting automatic error processing and the "late" error positivity (Pe) which is thought to mirror the awareness of erroneous responses. Subjects with higher impulsiveness showed smaller amplitudes than subjects with lower impulsiveness for the ERN/Ne component and the "early" Pe component. With regard to the "late" Pe groups did not differ. Hence, ERP measures appear suitable for detailed analyses of impulsiveness in healthy participants. Moreover, present results argue for the necessity of careful control of impulsiveness when including normal comparison groups in the context of clinical studies.     

Auditory event-related potentials in schizophrenia and depression

Event-related potentials in two auditory target detection paradigms and two auditory paradigms without overt tasks were studied in 22 schizophrenic, 21 depressed, and 28 matched control subjects meeting Research Diagnostic Criteria. In the target detection paradigms, schizophrenics showed a pattern of reduced N120 amplitude and shorter P200 latency to frequently occuring tones, and reduced P300 and Slow Wave amplitude to infrequent target and nontarget tones. This pattern is consistent with impaired selective attention for stimuli. For depressed patients these variables were generally intermediate between those of schizophrenics and controls. In the other paradigms N120 latency was greater for schizophrenics, and P200 amplitude was less for depressed patients.     

Mechanisms of human attention: event-related potentials and oscillations

Electrophysiological and hemodynamical responses of the brain allow investigation of the neural origins of human attention. We review attention-related brain responses from auditory and visual tasks employing oddball and novelty paradigms. Dipole localization and intracranial recordings as well as functional magnetic resonance imaging reveal multiple areas involved in generating and modulating attentional brain responses. In addition, the influence of brain lesions of circumscribed areas of the human cortex onto attentional mechanisms are reviewed. While it is obvious that damaged brain tissue no longer functions properly, it has also been shown that functions of non-lesioned brain areas are impaired due to loss of modulatory influence of the lesioned area. Both early (P1 and N1) and late (P3) event-related potentials are modulated by excitatatory and inhibitory mechanisms. Oscillatory EEG-correlates of attention in the alpha and gamma frequency range also show attentional modulation.