Biomedical subjects

M N Verbaten

Publications and source records attributed to M N Verbaten.

At least 55 records · Page 3Linked to original sources

PubMed1995

Auditory event-related brain potentials in autistic children and three different control groups.

ERPs to auditory stimuli, generated during an oddball task, were obtained in a group of autistic children and three control groups (normal, ADDH, and dyslectic children, respectively). The task included the presentation of standards, deviants, and novels and had a (between-group) passive vs. active (counting) condition. It was examined whether 1) it was possible to replicate several earlier findings, 2) autistics manifest an abnormal lateralization pattern of ERPs, 3) autistics have an abnormal mismatch negativity (MMN), and 4) differences between autistics and normals are really specific to the autistic group. The only finding that could be replicated was that autistics have a smaller A/Pcz/300. There was no evidence for abnormal lateralization or abnormal MMN; however, there was an unexpected effect of the task manipulation on the amplitude of the P3: in autistics, the occipital P3 to deviant stimuli was significantly larger in the active than in the passive condition, a finding, like the replication of the smaller A/Pcz/300, specific to the autistic group. It was suggested that the auditory occipital task effect is related to understimulation of the occipital lobe by visual stimuli in autistic children.

Adolescent↗

PubMed1995

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.

Adult↗

PubMed1994

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.

Adolescent↗

PubMed1994

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.

Adult↗

PubMed1994

Effects of oxazepam on performance and event-related brain potentials in vigilance tasks with static and dynamic stimuli.

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 (40 mg) caused impaired performance in the early part of a task with stimuli inducing frequent saccadic eye movements (dynamic task), relative to a task in which the stimuli remained at the same location (static task). This could not be explained by effects of the drug on oculomotor behavior. A larger diameter of the pupil in the dynamic task indicated that performance on this task may have required more effort. Stimulus processing requirements were higher in the dynamic task, as suggested by event-related brain potentials (ERPs), in particular the P3 wave; i.e., more resources had to be allocated in this task. This (additional) investment of resources appeared impossible after administration of oxazepam (40 mg). The conclusion was that tasks eliciting frequent eye movements require more effort and processing resources.

Adult↗

PubMed1994

Visual and somatosensory event-related brain potentials in autistic children and three different control groups.

Event-related potentials (ERPs) to visual and somatosensory stimuli, generated during an oddball task, were obtained in a group of autistic children and 3 control groups (normal, attention-deficit, and dyslectic children, respectively). The task included the presentation of standard, deviant, and novel stimuli and had a (between-group) passive vs. active (counting) condition. Research questions were whether (a) autistic children differ from other children with respect to the processing of visual and/or somatosensory stimuli, as measured in the amplitude of the N1, mismatch activity, and P3, (b) autistic children specifically have problems in the processing of distal (visual) stimuli, compared to the processing of proximal (somatosensory) stimuli, and (c) autistic children have an atypical lateralization pattern of ERP activity. Only in the autistic group a task effect on the visual P2N2 (mismatch activity) and larger P3s to novels than to deviants were found, in both the visual and the somatosensory modality. There also was a smaller occipital P3 to visual standard stimuli in the passive condition in the autistic group than in 2 control groups. We concluded that autistics (a) differ from several other groups of children with respect to the visual P2N2 and the visual and somatosensory P3, (b) show abnormalities in the processing of both proximal and distal stimuli, and (c) show no indication of abnormal lateralization of ERPs.

Adolescent↗

PubMed1992

Effects of bromazepam on single-trial event-related potentials in a visual vigilance task.

Thirty females performed a visual vigilance task under the influence of bromazepam (6 and 12 mg) in a placebo-controlled, double blind, experiment. Measures employed were percentage of hits, percentage of false alarms, response latency (RT), A' (sensitivity), B" (cautiousness), and RI (responsivity), as well as signal- and non-signal event-related potentials (ERPs). Bromazepam did not aggravate the normally occurring decrement in performance in vigilance tasks, but had an effect on overall level of performance: accuracy was reduced under the influence of the drug, but speed improved. A Drug x Period interaction for cautiousness (B") indicated increasingly less cautiousness with bromazepam, which probably contributed to faster motor responses (and more errors) than in the placebo group. The ERP data suggest that the effects of bromazepam are already manifest in the early stages of information processing (attention-detection) as mirrored by a drug effect on N1 amplitude. Deterioration at this early stage may affect later processing stages (P2-N2 amplitudes). As a result, subjects under the influence of the drug probably accumulate less signal evidence for their final evaluation.

Adult↗

PubMed1992

Time effects on event-related brain potentials and vigilance performance.

A review of the literature showed that in vigilance or oddball tasks, changes over time in event-related potentials (ERPs) and performance measures often seem to be unrelated, but a number of studies had some shortcomings. In the present study a visual vigilance experiment was carried out, in which single-trial ERPs and performance data of 40 males were obtained. A relationship between time trends in behavioral and ERP measures was found: an early P3 amplitude and response latency (RT) showed an inversely varying relation over time. Analysis of covariance showed that the two linear trends tap the same aspect of processing: both trends became insignificant when adjusted for common variance. A negative correlation between mean values of P3 amplitude and RT rather than for change scores has been observed in previous studies, but has been ignored in the literature. However, correlations with RT have also been reported for other ERP deflections. Although there were several correlations between mean scores, most time-induced changes in ERP parameters appeared to be unrelated to worsening performance, for which several explanations are advanced. The ERP results do not support the hypothesis that a decrement in performance is caused by increasing difficulty discriminating targets from nontargets. A gradual decline in effort or resources allocated to the task might be an alternative explanation of performance deterioration. However, an effort-hypothesis cannot easily be tested. Effort is often invoked post hoc, and has previously been associated with many ERP components. The relationship between ERPs and the signal detection measures "sensitivity" d' and "response bias" beta is discussed.

Adolescent↗

PubMed1992

Visual stimulus change and the orienting reaction: event-related potential evidence for a two-stage process.

In a previous study it was found that infrequent deviant visual stimuli, in a series of standards, elicited event-related potentials (ERPs) with enhanced P2-N2s and P3 amplitudes, suggesting that these parameters reflect processes related to the orienting reaction (OR). In the present study a similar oddball series was presented against the background of a second class of stimuli. With respect to the latter stimuli, subjects had to perform either a very involved (hard) or an easy task. EEG was recorded to oddball (probe) stimuli from Oz, Pz, Cz, and Fz. Analysis of average ERPs revealed that, in the easy condition, deviant probes elicited both enhanced P2-N2s and enhanced P3s, relative to the standards. In contrast, in the hard condition P2-N2, but not P3, was enhanced by stimulus change. In addition, overall P3 amplitude to probes was smaller in the hard condition (sequence-independent load effect). Analysis of single-trial ERPs (SERPs) with orthogonal polynomial trend analysis largely replicated these effects. In addition, SERP analysis also revealed a sequence-independent load effect on P2, as well as a decreasing P3 to deviant stimuli in the Easy condition, which was observed at Cz and Fz, but not at Pz or Oz. The results are interpreted as suggesting that P2-N2 and P3 reflect different stages of the OR, one of automatic and one of capacity-limited processing.

Adult↗

PubMed1991

Abnormal visual event-related potentials of autistic children.

This study compared the visual ERPs and concurrently measured fixation times of autistic children with those of normal children and two psychiatric control groups (so-called "externalizers" and "internalizers"). Autistic children had, in contrast with normal control groups, smaller P3 waves (occipital maximum) to visual target stimuli but did not differ in this respect from the two psychiatric control groups. When the autistic group was split into "good" and "bad" performers, the latter group had significantly smaller amplitudes than the former. No difference was found between the groups in electrophysiological reactivity to the first, novel stimulus of a habituation series. However, an unexpected change in stimulus location induced an increased Fz N400 in the normal group but not in the autistic group or the two psychiatric control groups. In addition, in a non-task-relevant habituation condition, the autistic group fixated complex visual stimuli for shorter times and had smaller occipital P3 waves than the control groups. Analysis of covariance showed that the smaller P3s could not be explained by the shorter fixation times. In none of the ERP parameters were there differences in habituation rate between the controls and the autistic children.

Arousal↗

PubMed1991

Abnormal electrodermal reactivity to novel visual stimuli in autistic children.

Skin conductance responses and eye-fixation behavior to visual stimuli were measured in high-functioning autistic children, normal children, children with externalizing disorders, and children with internalizing disorders. Novelty, complexity, and subjective significance of the stimuli were manipulated. Autistic children were electrodermally hyporesponsive to novel stimuli. In all groups, manipulation of stimulus complexity only influenced fixation time. Manipulation of subjective significance influenced fixation time as well as skin conductance response in all groups. In the autistic group, adding subjective significance to a stimulus changed electrodermal nonresponders into responders, indicating that nonresponsiveness or hyporesponsiveness in autistic children does not imply a loss of (novel) stimulus detection, filtering, or orientation reaction capability, per se.

Arousal↗

PubMed1991

Removal of the ocular artifact from the EEG: a comparison of time and frequency domain methods with simulated and real data.

Frequency-dependent transfer from EOG to EEG may be insufficiently accounted for by simple time domain regression methods (Gasser, Sroka, & Möcks, 1986; Woestenburg, Verbaten, & Slangen, 1983). In contrast, a multiple-lag time domain regression analysis, using lagged regression of EEG on EOG, must theoretically account for both frequency dependence and independence. Two data sets were constructed, in which the transfer from EOG to EEG was either frequency-independent (constant gain) or frequency-dependent. Subsequently, three different correction methods were applied: 1) a simple regression analysis in the time domain; 2) a multiple-lag regression analysis in the time domain; and 3) a regression analysis in the frequency domain. The major results were that, for data set 1, the three methods constructed the original EEG equally well. With data set 2, reconstruction of the original EEG was achieved reasonably well with the frequency domain method and the time domain multiple-lag method, but not with simple time domain regression. These three correction procedures were also applied to real data, consisting of concomitantly recorded EEG and high-variance EOG series. No appreciable differences in outcome of the three methods were observed, and estimated transfer parameters suggested that these data were marked by weak frequency dependence only, which can be accounted for by simple time domain regression (and also by the other two methods).

Blinking↗

PubMed1991

Event-related brain potentials and vigilance performance: dissociations abound, a review.

Event-related brain potentials (ERPs) have been suggested as a brain correlate of attention in sustained task performance. However, a review of the literature shows that changes in ERPs and performance measures over time often are dissociated. It is suggested that this may partly be caused by the simultaneous occurrence of several, separate processes in ERP trends over time. Further, it has been claimed that ERP recordings are more finely textured than behavioral measures such as hits, RT, sensitivity or response bias. Shortcomings of some studies are discussed and an approach is suggested which may more validly be employed in the search for relationships between time effects in ERP measures and measures of performance.

Arousal↗

PubMed1990

Dynamic vs static stimuli in their effect on visual vigilance performance.

This report describes a test of the prediction, made by Teichner in 1974, that on visual vigilance tasks dynamic stimuli result in greater performance decrements than do static stimuli. For correct detections and sensitivity there was only a nonsignificant trend in the predicted direction, but for response latency (RT) the prediction was supported. Positional uncertainty within displays did not affect vigilance performance. Teichner's assumption that ocular demand is responsible for the impairing effect of dynamic stimuli is questioned. Depletion of central capacity rather than an ocular effect may explain deteriorating performance. Just as in studies of visual fatigue, the contributions of central and modality-specific impairing effects are difficult to separate.

Adolescent↗

PubMed1989

"Initial-" and "change-orienting reactions": an analysis based on visual single-trial event-related potentials.

The present study was concerned with brain potentials elicited by, respectively, the first of a series of stimuli ("initial-orienting reaction", I-OR), and infrequent deviants ("change-orienting reaction", C-OR). Single-trial event-related potentials (ERPs) to visual stimuli were estimated from recordings at Oz, Pz, Cz and Fz. The design included both a habituation series as well as a series of occasional deviant trials against a background of standards. This was done with both task-relevant and neutral stimuli, and in two interstimulus interval (ISI) conditions: 2.45 s and 8.45 s. In the latter ISI condition, skin conductance responses (SCRs) were recorded as well. Decrease (Habituation) in the habituation series was found for a non-specific N1, a posteriorly distributed P3, and the SCR, but not for P2-N2. Deviant stimuli produced an enhancement of the central P2-N2, the P3, the N1 (on the first few deviant trials only, in both ISI conditions), and the SCR (with task-relevant stimuli only). Elongation of ISI delayed both short-term and long-term decrease of P3, but had no effect on enhancement of P2-N2 due to stimulus deviance. It was concluded that, with respect to ERP parameters, the I-OR is marked by the N1, whereas the C-OR coincides with the P2-N2.

Adult↗

PubMed1989

Processing demands, effort, and individual differences in four different vigilance tasks.

In an attempt to specify the limiting conditions of the taxonomy of vigilance tasks, four tasks differing in memory load and in stimuli employed (sensory or cognitive) were compared. Electrodermal activity and subjective measures were used to determine the investment of effort. The data show that vigilance level and vigilance decrement dissociate. The level seems to relate to effort demand and investment; the decrement seems to be task driven, determined mainly by the type of stimuli used. Tasks employing unfamiliar stimuli showed a decline in sensitivity; "cognitive" tasks employing alphanumeric stimuli did not. Principal components analyses suggest that measures of speed and accuracy may reflect relatively independent systems. Subjective data showed that good performers expand more effort in difficult and complex tasks. Effortful processing seems to prevent rather than induce a decline in efficiency.

Adolescent↗

PubMed1988

Effects of task relevance on habituation of visual single-trial ERPs and the skin conductance orienting response.

Single-trial event-related potentials were recorded at Oz, Pz, Cz, and Fz, concurrently with skin conductance reactions and fixation behavior in a habituation paradigm. A total of 48 subjects received 16 identical visual stimuli; 24 of them were instructed to pay attention, whereas the other half were given a neutral instruction. Two early negative components (N1 and N2), as well as a late positive component (P3) were identified. N1 and skin conductance reaction (SCR) showed fast decrement over trials, whereas N2 and P3 habituated slowly. Habituation of N1 and SCR was delayed by task instructions; N2 was hardly seen at all in the neutral condition. The task effects on N1 and N2 were observed only at Oz. It is concluded that the processing of relevant stimuli differs structurally from the processing of neutral stimuli; this difference may be observed even at a latency of 100 ms. The N1 appears to be related to the SCR, whereas this does not hold for P3; the N2 is related to selection negativities reported by other authors.

Adult↗

PubMed1988

Acute effects of bromazepam on signal detection performance, digit symbol substitution test and smooth pursuit eye movements.

Effects of 6 and 12 mg bromazepam on reaction time, stimulus sensitivity and response bias in a 1-hour visual attention task, on smooth pursuit eye movements, and on performance in the digit symbol substitution test (DSST) were investigated in 12 healthy male volunteers. It was a placebo-controlled, double-blind, crossover study that used repeated measures. Three saliva samples and a blood sample were taken for correlating drug concentration and performance. Bromazepam lowered stimulus sensitivity dose-dependently. Response times for hits and response bias were affected by the 12-mg dose only. DSST performance decreased dose-dependently. Smooth pursuit was equally impaired by 6 and 12 mg. Concentrations in serum correlated with concentrations in saliva, but serum and saliva concentrations did not correlate with task performance.

Adolescent↗