Time effects on event-related brain potentials and vigilance performance

Electrophysiological correlation between executive vigilance and attention network based on cognitive resource control theory

Attention is comprised of three independent and interacting attention networks: phasic alertness, orienting, and executive control. Previous studies have explored event-related potentials associated with these attention networks and executive vigilance, there is a lack of research on the relationship between executive vigilance and the three attention networks. However, there is a lack of research on the relationship between executive vigilance and the three attention networks. The present study aims to investigate this relationship. Based on the theory of cognitive resource control, two experimental blocks were designed with the vigilance task as the control variable. A total of 39 participants completed both ANTI and ANTI-V trials (two variants of the traditional attention network test ANT) in the same period. Through analysis of behavior measures (RT) and electrophysiological results related to phasic alertness (N1, P2, and contingent negative variation), orienting (P1, N1, and P3), and executive control (N2 and slow positive potential), we found that the reaction time of the ANTI block was lower than that of the ANTI-V block under all conditions, This suggests that adding a vigilance task may lead to reduced allocation of attention resources across all three attention networks. Furthermore, the orienting ability was weaker in the ANTI-V experimental block compared to that in the ANTI block due to effects on P1 and P3 regulation by the vigilance task. The N2 amplitude of the ANTI-V block was consistently reduced under similar conditions, indicating a weakening of executive control ability. The electrophysiological results revealed that executive vigilance inhibited the component of early attention perception related to the orienting network and was also related to the ability to detect conflict in the executive control network.

Persistence of Mental Fatigue on Motor Control

The effects of mental fatigue on both cognitive and physical performance are well described in the literature, but the recovery aspects of mental fatigue have been less investigated. The present study aimed to fill this gap by examining the persistence of mental fatigue on behavior and electrophysiological mechanisms. Fifteen participants performed an arm-pointing task consisting of reaching a target as fast as possible, before carrying out a 32-min cognitively demanding task [Time Load Dual Back (TLDB) task], and immediately, 10 and 20 min after completion of the TLDB task. During the experiment, electroencephalography was continuously recorded. The significant increase in mental fatigue feeling after the TLDB task was followed by a decrease during the 20 min of recovery without returning to premeasurement values. Brain oscillations recorded at rest during the recovery period showed an increase in both theta and alpha power over time, suggesting a persistence of mental fatigue. Arm-pointing movement duration increased gradually over time during the recovery period, indicating that behavioral performance remained impaired 20 min after the end of the cognitively demanding task. To conclude, subjective measurements indicated a partial recovery of mental fatigue following a cognitively demanding task, whereas electrophysiological and behavioral markers suggested that the effects of mental fatigue persisted for at least 20 min. While the subjective evaluation of mental fatigue is a very practical way to attest the presence of mental fatigue, electrophysiological and behavioral measures seem more relevant to evaluate the time course of mental fatigue effects.

Neural anomalies during vigilance in schizophrenia: Diagnostic specificity and genetic associations

Impaired vigilance is a core cognitive deficit in schizophrenia and may serve as an endophenotype (i.e., mark genetic liability). We used a continuous performance task with perceptually degraded stimuli in schizophrenia patients (N = 48), bipolar disorder patients (N = 26), first-degree biological relatives of schizophrenia patients (N = 55) and bipolar disorder patients (N = 28), as well as healthy controls (N = 68) to clarify whether previously reported vigilance deficits and abnormal neural functions were indicative of genetic liability for schizophrenia as opposed to a generalized liability for severe psychopathology. We also examined variation in the Catechol-O-methyltransferase gene to evaluate whether brain responses were related to genetic variation associated with higher-order cognition. Relatives of schizophrenia patients had an increased rate of misidentification of nontarget stimuli as targets when they were perceptually similar, suggestive of difficulties with contour perception. Larger early visual responses (i.e., N1) were associated with better task performance in patients with schizophrenia consistent with enhanced N1 responses reflecting beneficial neural compensation. Additionally, reduced N2 augmentation to target stimuli was specific to schizophrenia. Both patients with schizophrenia and first-degree relatives displayed reduced late cognitive responses (P3b) that predicted worse performance. First-degree relatives of bipolar patients exhibited performance deficits, and displayed aberrant neural responses that were milder than individuals with liability for schizophrenia and dependent on sex. Variation in the Catechol-O-methyltransferase gene was differentially associated with P3b in schizophrenia and bipolar groups. Poor vigilance in schizophrenia is specifically predicted by a failure to enhance early visual responses, weak augmentation of mid-latency brain responses to targets, and limited engagement of late cognitive responses that may be tied to genetic variation associated with prefrontal dopaminergic availability. Experimental results illustrate specific neural functions that distinguish schizophrenia from bipolar disorder and provides evidence for a putative endophenotype that differentiates genetic liability for schizophrenia from severe mental illness more broadly.

Sustaining attention for a prolonged period of time increases temporal variability in cortical responses

Our ability to stay focused is limited: prolonged performance of a task typically results in mental fatigue and decrements in performance over time. This so-called vigilance decrement has been attributed to depletion of attentional resources, though other factors such as reductions in motivation likely also play a role. In this study, we examined three electroencephalography (EEG) markers of attentional control, to elucidate which stage of attentional processing is most affected by time-on-task and motivation. To elicit the vigilance decrement, participants performed a sustained attention task for 80 min without breaks. After 60 min, participants were motivated by an unexpected monetary incentive to increase performance in the final 20 min. We found that task performance and self-reported motivation declined rapidly, reaching stable levels well before the motivation manipulation was introduced. Thereafter, motivation increased back up to the initial level, and remained there for the final 20 min. While task performance also increased, it did not return to the initial level, and fell to the lowest level overall during the final 10 min. This pattern of performance changes was mirrored by the trial-to-trial consistency of the phase of theta (3-7 Hz) oscillations, an index of the variability in timing of the neural response to the stimulus. As task performance decreased, temporal variability increased, suggesting that attentional stability is crucial for sustained attention performance. The effects of attention on our two other EEG measures-early P1/N1 event-related potentials (ERPs) and pre-stimulus alpha (9-14 Hz) power-did not change with time-on-task or motivation. In sum, these findings show that the vigilance decrement is accompanied by a decline in only some facets of attentional control, which cannot be fully brought back online by increases in motivation. The vigilance decrement might thus not occur due to a single cause, but is likely multifactorial in origin.

The neural correlation of sustained attention in performing conjunctive continuous performance task: an event-related potential study

Owing to great improvements in cognitive neuroscience, the study of brain functions during different types of cognitive tasks has attracted much attention. Recording event-related potentials (ERPs) is an appropriate tool for such a purpose, as it is noninvasive and affordable. Attention is among the most studied cognitive processes. In this study, a visual version of the conjunctive continuous performance task-visual was used to examine the differences of cognitive processes in target and nontarget stimuli. Twenty healthy individuals (average age: 23 years) participated in the study. Electroencephalogram signals were recorded from all participants during conjunctive continuous performance task-visual. After preprocessing, the ERPs were calculated by averaging the epochs that were time-locked to the stimulus onset. Then, the ERPs of the two groups of target and nontarget stimuli, from the aspects of differences in the P300 and N200 morphological features, were analyzed in three midline channels: Pz, Fz, and Cz. According to the results, the P300 amplitudes were significantly larger in the target than those in the nontarget stimuli. The P300 latencies were also larger in the target than in the nontarget stimuli, but the difference was only significant in the Pz channel ERPs. For the N200 component, the negativity of amplitudes was significantly more enhanced in the target than in the nontarget stimuli. However, for the N200 latencies, no significant difference was found based on the data obtained from the groups. Furthermore, the findings suggest that the distribution of the P300 component is more centroparietal for the target stimuli, and more centrofrontal for the nontarget ones. In addition, the distribution of the N200 component is more frontoparietal for both the target and nontarget stimuli.

Independent contributions of theta and delta time-frequency activity to the visual oddball P3b

A growing body of work suggests that the P300 (P3) event-related potential (ERP) component is better understood as a mixture of task-relevant processes (Polich, 2007). This converges with earlier time-frequency work suggesting that the P3b is primarily composed of centroparietal delta (0.5-3 Hz) and frontocentral theta (3-7 Hz) activity. Within this study (N = 229), we hope to re-affirm these prior ideas and expand upon them in several crucial ways, reassessing how delta and theta contribute to the visual oddball P3b through the lens of several recent decades of additional P3b research. We provide a comprehensive assessment of how theta and delta time-frequency activity contribute to several common variants of the time-domain P3b, specifically measuring the target and non-target P3b, as well as differences between targets and non-targets, target-to-target interval (TTI), and target habituation. Results replicate and extend earlier work indicating that delta and theta account for a majority of variance in both the target and non-target P3b as well as their respective amplitude differences. They also newly indicate that theta and delta activity can have unique contributions to TTI differences and target habituation effects. Results in target habituation particularly demonstrate how time-frequency analyses can disentangle nuanced changes in P3b activity, shedding new light on these complicated phenomena. Findings suggest that delta and theta measures index separable processes occurring during the P3b, and provide additional support for the idea that they index theoretical frontocentral and centroparietal P3 subcomponents.

Positive Effects of Mindfulness-Based Training on Energy Maintenance and the EEG Correlates of Sustained Attention in a Cohort of Nurses

Mindfulness based training (MBT) is becoming increasingly popular as a means to improve general wellbeing through developing enhanced control over metacognitive processes. In this preliminary study, we tested a cohort of 36 nurses (mean age = 30.3, SD = 8.52; 2 male) who participated in an 8-week MBT intervention to examine the improvements in sustained attention and its energetic costs that may result from MBT. Changes in sustained attention were measured using the psychomotor vigilance task (PVT) and electroencephalography (EEG) was collected both during PVT performance, and during a brief period of meditation. As there was substantial variability in training attendance, this variable was used a covariate in all analyses. Following the MBT program, we observed changes in alpha power across all scalp regions during meditation that were correlated with attendance. Similarly, PVT performance worsened over the 8-week period, but that this decline was mitigated by good attendance on the MBT program. The subjective energy depletion due to PVT performance (measured using self-report on Likert-type scales) was also less in regular attendees. Finally, changes in known EEG markers of attention during PVT performance (P300 and alpha-band event-related desynchronization) paralleled these behavioral shifts. Taken together, our data suggest that sustained attention and its associated costs may be negatively affected over time in the nursing profession, but that regular attendance of MBT may help to attenuate these effects. However, as this study contained no control condition, we cannot rule out that other factors (e.g., motivation, placebo effects) may also account for our findings.

Relationship of Event-Related Potentials to the Vigilance Decrement

Cognitive fatigue emerges in wide-ranging tasks and domains, but traditional vigilance tasks provide a well-studied context in which to explore the mechanisms underlying it. Though a variety of experimental methodologies have been used to investigate cognitive fatigue in vigilance, relatively little research has utilized electroencephalography (EEG), specifically event-related potentials (ERPs), to explore the nature of cognitive fatigue, also known as the vigilance decrement. Moreover, much of the research that has been done on vigilance and ERPs uses non-traditional vigilance paradigms, limiting generalizability to the established body of behavioral results and corresponding theories. In this study, we address concerns with prior research by (1) investigating the vigilance decrement using a well-established visual vigilance task, (2) utilizing a task designed to attenuate possible confounding ERP components present within a vigilance paradigm, and (3) informing our interpretations with recent findings from ERP research. We averaged data across electrodes located over the frontal, central, and parietal scalp. Then, we generated waveforms locked to the onset of critical low-frequency or non-critical high-frequency events during a 40 min task that was segregated into time blocks for data analysis. There were three primary findings from the analyses of these data. First, mean amplitude of N1 was greater during later blocks for both low-frequency and high-frequency events, a contradictory finding compared to past visual vigilance studies that is further discussed with respect to current interpretations of the N1 in visual attention tasks. Second, P3b mean amplitude following low-frequency events was reduced during later blocks, with a later onset latency. Third and finally, the decrease in P3b amplitude correlated with individual differences in the magnitude of the vigilance decrement, assessed using d′. The results provide evidence for degradations of cognitive processing efficiency brought on by extended time on task, leading to delayed processing and decreased discriminability of critical stimuli from non-critical stimuli. These conclusions are discussed in the context of the vigilance decrement and corresponding theoretical accounts.

Sustained Attention Ability Affects Simple Picture Naming

Sustained attention has previously been shown as a requirement for language production. However, this is mostly evident for difficult conditions, such as a dual-task situation. The current study provides corroborating evidence that this relationship holds even for simple picture naming. Sustained attention ability, indexed both by participants’ reaction times and individuals’ hit rate (the proportion of correctly detected targets) on a digit discrimination task, correlated with picture naming latencies. Individuals with poor sustained attention were consistently slower and their RT distributions were more positively skewed when naming pictures compared to individuals with better sustained attention. Additionally, the need to sustain attention was manipulated by changing the speed of stimulus presentation. Research has suggested that fast event rates tax sustained attention resources to a larger degree than slow event rates. However, in this study the fast event rate did not result in increased difficulty, neither for the picture naming task nor for the sustained attention task. Instead, the results point to a speed-accuracy trade-off in the sustained attention task (lower accuracy but faster responses in the fast than in the slow event rate), and to a benefit for faster rates in the picture naming task (shorter naming latencies with no difference in accuracy). Performance on both tasks was largely comparable, supporting previous findings that sustained attention is called upon during language production.

Physiological signal analysis for fatigue level of experienced and inexperienced drivers

OBJECTIVE

We studied the changes in driving fatigue levels of experienced and inexperienced drivers at 3 periods of the day: 9:00 a.m.-12:00 p.m., 12:00 p.m.-2:00 p.m., and 4:00 p.m.-6:00 p.m.

METHODS

Thirty drivers were involved in 120-min real-car driving, and sleepiness ratings (Stanford Sleepiness Scale, SSS; Hoddes et al. 1973 ), electroencephalogram (EEG) signals, and heart rates (HRs) were recorded. Together with principal component analysis, the relationship between EEG signals and HR was explored and used to determine a comprehensive indicator of driving fatigue. Then the comprehensive indicator was assessed via paired t test.

RESULTS

Experienced and inexperienced drivers behaved significantly differently in terms of subjective fatigue during preliminary trials. At the beginning of trials and after termination, subjective fatigue level was aggravated with prolonged continuous driving. Moreover, we discussed the changing rules of EEG signals and HR and found that with prolonged time, the ratios of δ and β waves significantly declined, whereas that of the θ wave significantly rose. The ratio of (α + θ)/β significantly rose both before trials and after termination, but HR dropped significantly. However, one-factor analysis of variance shows that driving experience significantly affects the θ wave, (α + θ)/β ratio, and HR.

CONCLUSIONS

We found that in a monotonous road environment, fatigue symptoms occurred in inexperienced drivers and experienced drivers after about 60 and 80 min of continuous driving, respectively. Therefore, as for drivers with different experiences, restriction on continuous driving time would avoid fatigued driving and thereby eliminate traffic accidents. We find that the comprehensive indicator changes significantly with fatigue level. The integration of different indicators improves the recognition accuracy of different driving fatigue levels.

Differences in Sustained Attention Capacity as a Function of Aerobic Fitness

PURPOSE

We investigated the relationship between aerobic fitness and sustained attention capacity by comparing task performance and brain function, by means of event-related potentials (ERP), in high- and low-fit young adults.

METHODS

Two groups of participants (22 higher-fit and 20 lower-fit) completed a 60-min version of the Psychomotor Vigilance Task (PVT). Behavioral (i.e., reaction time) and electrophysiological (ERP) (i.e., contingent negative variation and P3) were obtained and analyzed as a function of time-on-task. A submaximal cardiorespiratory fitness test confirmed the between-groups difference in terms of aerobic fitness.

RESULTS

The results revealed shorter reaction time in higher-fit than in lower-fit participants in the first 36 min of the task. This was accompanied by larger contingent negative variation amplitude in the same period of the task in higher-fit than in lower-fit group. Crucially, higher-fit participants maintained larger P3 amplitude throughout the task compared to lower-fit, who showed a reduction in the P3 magnitude over time.

CONCLUSIONS

Higher fitness was related to neuroelectric activity suggestive of better overall sustained attention demonstrating a better ability to allocate attentional resources over time. Moreover, higher fitness was related to enhanced response preparation in the first part of the task. Taken together, the current data set demonstrated a positive association between aerobic fitness, sustained attention, and response preparation.

Statistical modeling of time-dependent fMRI activation effects

Functional magnetic resonance imaging (fMRI) activation detection within stimulus-based experimental paradigms is conventionally based on the assumption that activation effects remain constant over time. This assumption neglects the fact that the strength of activation may vary, for example, due to habituation processes or changing attention. Neither the functional form of time variation can be retrieved nor short-lasting effects can be detected by conventional methods. In this work, a new dynamic approach is proposed that allows to estimate time-varying effect profiles and hemodynamic response functions in event-related fMRI paradigms. To this end, we incorporate the time-varying coefficient methodology into the fMRI general regression framework. Inference is based on a voxelwise penalized least squares procedure. We assess the strength of activation and corresponding time variation on the basis of pointwise confidence intervals on a voxel level. Additionally, spatial clusters of effect curves are presented. Results of the analysis of an active oddball experiment show that activation effects deviating from a constant trend coexist with time-varying effects that exhibit different types of shapes, such as linear, (inversely) U-shaped or fluctuating forms. In a comparison to conventional approaches, like classical SPM, we observe that time-constant methods are rather insensitive to detect temporary effects, because these do not emerge when aggregated across the entire experiment. Hence, it is recommended to base activation detection analyses not merely on time-constant procedures but to include flexible time-varying effects that harbour valuable information on individual response patterns.

Examining the relationships between self-efficacy, task-relevant attentional control , and task performance: Evidence from event-related brain potentials

Self-efficacy (SE) is a modifiable psychosocial factor related to individuals' beliefs in their capabilities to successfully complete courses of action and has been shown to be positively associated with task performance. The authors hypothesized that one means through which SE is related with improved performance is through enhanced task-relevant attentional control during task execution. To assess this hypothesis, we examined the relationships between SE and behavioural and neural indices of task performance and task-relevant attentional control for 76 young adults during the completion of a flanker task. Results showed that greater SE was associated with greater response accuracy and P3b amplitude across task conditions, and faster RT under more difficult task conditions. Additionally, P3b amplitude was found to mediate the relationship between SE and task performance in the difficult condition. These findings suggest that greater attentional allocation to task-relevant processes, including monitoring stimulus-response relationships and focusing attention on working memory operations, may help explain the association between SE and improved task performance.

Drivers' misjudgement of vigilance state during prolonged monotonous daytime driving

To investigate the effects of monotonous daytime driving on vigilance state and particularly the ability to judge this state, a real road driving study was conducted. To objectively assess vigilance state, performance (auditory reaction time) and physiological measures (EEG: alpha spindle rate, P3 amplitude; ECG: heart rate) were recorded continuously. Drivers judged sleepiness, attention to the driving task and monotony retrospectively every 20 min. Results showed that prolonged daytime driving under monotonous conditions leads to a continuous reduction in vigilance. Towards the end of the drive, drivers reported a subjectively improved vigilance state, which was contrary to the continued decrease in vigilance as indicated by all performance and physiological measures. These findings indicate a lack of self-assessment abilities after approximately 3h of continuous monotonous daytime driving.

Visual event-related potentials in elite and amateur athletes

In the present study, we tested the hypothesis that the neural synchronization estimated in visual cortex during visuo-spatial demands shows different features in elite karate athletes when compared to amateur karate athletes and non-athletes. EEG recordings (56 channels; EB-Neuro) were performed from 17 elite karate athletes, 14 amateur karate athletes, and 15 non-athletes, during the observation of pictures with basket and karate attacks. They clicked a right (left) keyboard button for basket or karate attacks at right (left) monitor side. Results pointed to no difference of late occipital VEPs/ERPs after basket versus karate attacks in the non-athletes (300-800 ms post-stimulus). In the amateur karate athletes, occipital VEPs/ERPs at 300-450 ms post-stimulus (P3-P4 components) were lower in amplitude for the karate than basket attacks. In the elite karate athletes, the occipital VEPs/ERPs further declined in amplitude at 300-450 ms post-stimulus (P3 and P4 components) and enhanced at about 800 ms post-stimulus ("N2" component) for the karate than basket attacks. A control study showed that in 10 elite fencers, the same was true for the fencing compared to the karate attacks. These results support the hypothesis that peculiar mechanisms of occipital neural synchronization can be observed in elite athletes during visuo-spatial demands, possibly to underlie sustained visuo-spatial attention and self-control.

Time-on-task analysis using wavelet networks in an event-related potential study on attention-deficit hyperactivity disorder

OBJECTIVE

The aim of this event-related potential (ERP) study was to test time-on-task analysis at the level of single sweeps in a clinical trial. Since inattentiveness is one of the main symptoms of attention-deficit hyperactivity disorder (ADHD), this child psychiatric disorder was chosen as an exemplary application.

METHODS

Twenty-four healthy and 24 ADHD boys, aged 9--15 years, performed an auditory selective attention task for about 5 min. ERP single trials were analyzed using wavelet networks. Time-on-task analysis was applied to omission errors, reaction time and slow ERP components (frontal negativity, parietal positivity), represented by a low-frequency wavelet component.

RESULTS

Both performance and ERP measures showed distinct temporal dynamics. Time-on-task effects were not only linear, but also of higher order and started after less than 1 min. For ADHD children, earlier time-on-task effects, i.e. an earlier increase of omission errors and frontal negativity, resulted. Healthy children could allocate more attentional resources during the course of the experiment.

CONCLUSION

Time-on-task analysis at the level of single trials revealed phenomena probably reflecting ADHD children's attentional deficits. Thus, a more differentiated ERP analysis may provide a better understanding of the pathophysiological background in neuropsychiatric disorders.

Visual sustained attention in a child psychiatric population

OBJECTIVE

To increase knowledge of the diversity and specificity of sustained attention deficits in children with attention-deficit hyperactivity disorder (ADHD), with special reference to the issue of distinguishing between children with ADHD and children with other psychiatric diagnoses.

METHOD

A visual sustained attention task was used to compare 52 boys with ADHD with 55 normal controls, 29 boys with oppositional defiant disorder or conduct disorder (ODD/CD), 29 boys with anxiety or dysthymia (ANX/DYS), 43 boys with pervasive developmental disorder, 24 boys with ADHD plus ODD/CD, and 14 boys with ADHD plus ANX/DYS.

RESULTS

Compared with normal controls, children with ADHD were slower, were more inaccurate, were more impulsive, were less responsive to feedback, and showed less perceptual sensitivity and stability of performance, resulting in a marked decrease in vigilance over time. Unresponsiveness to feedback and the extent of the decrease in vigilance during time on task were found to be the only factors that distinguished children with ADHD from children with other diagnoses.

CONCLUSION

Although only children with ADHD are characterized primarily by "attention deficit," sustained attention deficit is common to a certain extent to all children with psychiatric disorders.

On P300 measurement stability: habituation, intra-trial block variation, and ultradian rhythms

P300 event-related brain potentials (ERPs) were elicited using a simple discrimination task in which participants discriminated two different equiprobable visual stimuli with button-press responses (n = 20). A total of ten trial blocks were presented at 10-min intervals. P300 amplitude declined significantly, but peak latency did not change reliably across trial blocks. P300 amplitude demonstrated a reliable cyclical fluctuation across trial blocks, although P300 latency did not. Intra-trial block ERP variability was assessed by computing the correlation coefficients between the target and standard stimuli for amplitude and latency measures across participants within each trial block. P300 amplitude correlations were weakest at the Fz electrode, more strongly associated at Cz, and were most strongly correlated at Pz across trial blocks. P300 latency correlations were somewhat weaker and similar in strength across electrodes sites. The correlational patterns for both P300 amplitude and latency demonstrated reliable cyclical variation. The N100 component produced strong and consistent correlations for both amplitude and latency, whereas the P200 and N200 component measures evinced cyclical correlational patterns similar to the P300 across trial blocks. These results suggest that the stability of P300 and other component measures can vary appreciably within and across trial blocks in a manner that reflects ultradian variation in arousal level.

Habituation of P300 from visual stimuli

The P300 event-related brain potential (ERP) was elicited with visual stimuli using an oddball task in which the subjects made button press responses to discriminate target and standard stimuli. Each stimulus occurred randomly with a 0.50 probability, and 10 trial blocks were presented at 10-min inter-block-intervals (IBIs). P300 amplitude declined reliably across trial blocks, and an interaction between trial block number and electrode site was observed. No habituation effects were found for P300 latency or for N100, P200, or N200 amplitude. The results suggest that P300 amplitude from visual stimuli habituates when short IBIs and a sufficient number of trial blocks are employed. Theoretical implications are discussed with respect to attentional resource allocation and context updating.

Event-related potentials and performance of attention-deficit hyperactivity disorder: children and normal controls in auditory and visual selective attention tasks

Attention-deficit hyperactivity disorder (ADHD) children and normal controls (7-13 yrs old) performed an auditory and visual selective attention task. Subjects were instructed to respond to the infrequent (10%) stimuli in the relevant channel. Processing negativity (PN) and several other ERP peaks were scored at the midline electrodes. In the auditory task, controls had more correct detections (hits), less false alarms, larger P3b amplitudes to nontarget stimuli (but not to hits), a larger central PN and larger early frontal positivity (100-250 ms) to target stimuli than ADHD subjects. In the visual modality, controls had more correct detections, less false alarms, larger P3b amplitudes to nontarget stimuli (but not to hits), and larger frontal P3(1) amplitudes to infrequent than to frequent stimuli. It was hypothesized that in ADHD children in both the auditory and the visual task, there is a deficit in the activation of the P3b process. Incorrect triggering of the P3b process might be caused by disturbances in other aspects of the attention process, preceding the P3b.

The recognition potential and word priming

The effect of priming on the latency of the recognition potential (RP) was tested using rapid stream stimulation. Subjects detected five-letter words in a stream of nonword images. Lifting the right index finger signalled detection of a word. Rapid responses were rewarded and false alarms were penalized. Just before generating an image stream, a computer briefly displayed either the specific target word or or five-letter string that indicated the target was any one of ten previously studied words. Precise target specification was expected to produce more rapid detection than the provision of less definite information. Since the RP was thought to reflect the speed of perception, it was predicted that its latency would be less when the target word was beforehand than when less specific information was provided. The results for 10 subjects confirmed the hypothesis.

P3(00) habituation from auditory and visual stimuli

The P3(00) event-related brain potential (ERP) was elicited with auditory and visual stimuli using an oddball task in which the subject indicated with a button-press response the occurrence of a target stimulus that occurred randomly on 20% of the trials and refrained from responding to a standard stimulus. A total of four trial blocks were collected for each stimulus modality condition. P3 amplitude from the target stimuli decreased reliably across trial blocks for both the auditory and visual stimulus condition, with no interaction obtained between stimulus modality and trial block. P3 latency was shorter for the auditory compared to visual stimulus conditions, but did not vary with trial block. No changes in amplitude or latency independent of the P3 effects were obtained for the other ERP components with trial block, although the usual modality differences were observed. The results suggest that P3 components elicited by auditory and visual stimuli both habituate for actively discriminated target stimuli. The theoretical implications are discussed in the context of previous findings.

Effects of oxazepam on event-related brain potentials, EEG frequency bands, and vigilance performance

Eighteen males performed two vigilance tasks with static and dynamic stimuli under the influence of oxazepam (20 and 40 mg) in a placebo-controlled, double blind, crossover design. Oxazepam dose-dependently impaired overall level of performance and aggravated the decrement with time in measures of accuracy and sensitivity relative to placebo. The drug reduced the amplitudes of the P1, N1, P2N2, and P3 (dose-dependently) waves of event-related potentials (ERPs). Oxazepam aggravated the linear decline with time of the P3 amplitude only. Oxazepam impaired accuracy was related to deterioration of central processing involved in stimulus discrimination (P2N2). Impairment of response-related performance measures (RT and RI) was associated with processing manifest in the P1, N1, and P3 waves. Oxazepam effects on the amplitudes of N1 and P3 correlated with drug effects on power in alpha 1 (8-10 Hz). Drug effects on overall performance and alpha were also related; the drug effect on response speed correlated only with the drug effect on beta 1 (12.5-21 Hz). Effects of time-on-task on performance and EEG were unrelated, but oxazepam induced performance declines with time may have been caused by declines in resource allocation, as manifest in the amplitude of P3. Time effects on EEG power bands and ERP amplitudes were not significantly related to the time course of oxazepam activity. A curious dissociation emerged: both oxazepam and time-on-task impaired performance, but the drug induced a decrease of theta and alpha 1 power, whereas time-on-task increased power. Various processes play a role in performance decrements with time, and various aspects of processing may be involved in signal-detection measures which makes terms such as sensitivity quite meaningless. So-called computational processing was indistinguishable from energetic processes, which questions the validity of the distinction between these two domains. Explanations of EEG activity in terms of a unidimensional theory of arousal are untenable.

Is the Continuous Performance Task useful in research with ADHD children? Comments on a review

A recent review of the Continuous Performance Task (CPT) as a research tool by Corkum and Siegel, Journal of Child Psychology and Psychiatry, 34, 1217-1239, 1993, is criticized for insufficient covering of the relevant literature, disregard of the question of differentiation among clinical groups, and inadequacy of explanations of Attention-Deficit-Hyperactivity Disorder (ADHD) in terms of arousal, activation, and effort. An attention-deficit in ADHD children cannot be inferred from poor performance on a CPT. Impaired performance is anything but specific to ADHD children and is caused by a host of variables among which "attention" probably plays a minor role.

Cognitive and biological determinants of P300: an integrative review

The P300 event-related brain potential (ERP) is thought to reflect neuroelectric activity related to cognitive processes such as attention allocation and activation of immediate memory. However, recent studies have provided evidence that the P300 also is influenced by biological processes such as fluctuations in the arousal state of subjects. The effects of natural (circadian, ultradian, seasonal, menstrual) and environmentally induced (exercise, fatigue, drugs) state variables on the P300 are reviewed. The findings suggest that these factors contribute to P300 measures and are discussed in terms of their theoretical and applied implications.

Methylphenidate influences on both early and late ERP waves of ADHD children in a continuous performance test

Although it has frequently been reported that hyperactive children have abnormally small P3 amplitudes of the event-related potential (ERP), which are normalized by the stimulant drug methylphenidate (MPH), the literature is inconsistent concerning earlier ERP waves. The aim of the present study was to investigate whether the normalizing effect of a 10-mg dose of MPH was also apparent on earlier waves, such as the N1, the P2, and the N2, besides the P3. Twelve attention deficit with hyperactivity disorder (ADHD) children performed a Continuous Performance Test involving a button-press response to the letter X (CPT-X) under the influence of MPH in a double-blind placebo controlled acute dosage design. ERPs were recorded at Oz, Pz, Cz, and Fz. The expected increase of the parietal P3, both to targets and nontargets, was apparent, as well as a significant increase in percentage of hits. There also was a significant increase of an earlier, negative going, wave, the N2, with a frontal maximum, under the influence of MPH. This wave was probably a manifestation of an increase in processing negativity for target stimuli only, after the intake of the stimulant drug. No effect of MPH was found on the N1 or the P2.

P300 habituation from visual stimuli?

The P3(00) event-related brain potential (ERP) was elicited with visual stimuli using an oddball task in which the subject indicated with a finger tap response the occurrence of a target stimulus that occurred randomly on 20% of the trials and refrained from responding to a standard stimulus. A total of six trial blocks were collected, with an equal number of artifact-free epochs averaged for both stimulus types. P3 amplitude from the target stimuli did not decrease across trial blocks; P3 amplitude from the standard stimuli did decrease across trial blocks. P3 latency from both the target and standard stimuli increased across trial blocks. No changes in amplitude or latency independent of the P3 effects were obtained for the other ERP components with trial block. The results suggest that P3 components elicited by visual stimuli do not readily habituate for actively discriminated target stimuli. The theoretical implications are discussed in the context of previous findings.

Effects of oxazepam on eye movements and performance in vigilance tasks with static and dynamic stimuli

The aim of the present study was to determine whether in a task with stimuli inducing frequent saccadic eye movements, ingestion of oxazepam impairs performance more than in a task in which the stimuli remained fixed at the same location, due to effects of oxazepam on the ocular system. Eighteen males performed a vigilance task with static and dynamic stimuli under the influence of oxazepam (20 and 40 mg) in a placebo-controlled, double blind, crossover design. Oxazepam (40 mg) had a larger effect on vigilance performance in the first part of the dynamic task, relative to its static counterpart. Oxazepam also had an effect on oculomotor behavior, but this effect was unrelated to impaired performance. There were dose-dependent effects of oxazepam on absolute, overall level of performance but not on the decrement with time. The non-dose-dependent aggravation of the decrement in correct detections, caused by the drug, could only partly be accounted for by pharmacokinetics and increased eyelid closures, and was also caused by pharmacodynamic effects of the drug, such as those on attention. Different effects were noted for the two signal detection measures of response behavior, B" and RI.

Stimulant drugs and vigilance performance: a review

The literature on the effects of some stimulant drugs (amphetamine, methylphenidate, caffeine, and nicotine) on vigilance performance is reviewed. Improvement of overall level of performance (both accuracy and speed) after the intake of amphetamine, caffeine, and nicotine has often been reported, and the decrement in performance with time has been shown to be prevented especially with amphetamine and nicotine. Effects on false alarms are negligible. In studies where a test battery was employed, vigilance tasks appeared to be the most sensitive performance tests in detecting the effects of stimulants; however, different vigilance tasks may measure different aspects of mental functions. There is no support for earlier conclusions that improvements are noticed only in fatigued subjects in protracted sessions. Evidence from several studies does not support the hypothesis that improvements are only a recovery of withdrawal-induced impairment. Because positive effects have been obtained with drugs possessing different mechanisms of action, there is as yet no clear support for a noradrenergic, dopaminergic, or cholinergic theory of sustained attention. Simple neurotransmitter theories of attention and information processing may be untenable.