The upper spatial limit for perception of displacement is affected by preceding motion.

The upper spatial limit D(max) for perception of apparent motion of a random dot pattern may be strongly affected by another, collinear, motion that precedes it [Mateeff, S., Stefanova, M., &.

Flanker interference in young and older participants as reflected in event-related potentials.

The present study investigates behavioural and event-related potential (ERP) differences between young and older participants in two variants of a flanker task. Flankers preceded the target by 100 ms (Experiment 1) or were presented simultaneously with the target (Experiment 2). In both experiments the response times showed an age-related slowing and a compatibility effect, which did not differ significantly across age.

Error processing in patients with Parkinson's disease: the influence of medication state.

One of the hallmarks of Parkinson's disease (PD) is a depletion of dopamine. Error processing, as reflected in a component of the event-related potential, the so-called error (related) negativity (Ne or ERN) is likely dependent on the midbrain dopaminergic system. In case of an unfavourable event such as an error, this system is assumed to send an error signal to the mediofrontal cortex, which elicits the Ne.

Perceived global direction of a compound of real and apparent motion.

We presented a random dot pattern that moved horizontally for 1.6s within a stationary invisible aperture. The dots were periodically visible for 50 ms (visible phase) with lengths of the real motion 0-1.

Effects of ageing on cognitive task preparation as reflected by event-related potentials.

Objective: The anticipation of complex cognitive tasks involves effortful preparation being reflected in the contingent negative variation (CNV) of the event-related potential. In the literature there are contradictory results concerning the effect of age on this potential. We wanted to investigate effects of age, time-on-task, and task difficulty on the CNV.

Effects of stimulus-response compatibility in Parkinson's disease: a psychophysiological analysis.

The present study investigated the mechanisms underlying stimulus-response compatibility effects in Parkinson's disease patients and matched controls. Since basal ganglia are involved in the selection and inhibition of competing responses we examined whether basal ganglia dysfunction in Parkinson's disease leads to greater interference effects compared to the control subjects. Reaction times and lateralized movement-related cortical potentials (lateralized readiness potential: LRP) were recorded in two modified Eriksen flanker tasks.

Visual analysis of changes of motion in reaction-time tasks.

Subjects observed a random-dot pattern moving uniformly in the vertical direction (vector V1). The motion vector abruptly changed to V2, both in speed and direction simultaneously. It was found that the time of simple reaction to such changes V1 --> V2 can be described by a function of a single variable, [w(V1 - V2c) + (1 - w) V2N], 0 < w < 0.

Central and parietal event-related lateralizations in a flanker task.

Recently Wascher et al. (1999) reported that in a flanker task with arrow stimuli not only the known lateralized readiness potential (LRP) that reflects lateralized response activation was induced, but also a parietal lateralized activation (direction encoding lateralization; DEL) that was interpreted as reflecting an earlier coding of a response side. However, the Wascher study did not exclude that the DEL could have also been due to lateralized stimulus- or attention-related factors.

Effects of spatial attention on the brain stem frequency-following potential.

Can spatial attention or orienting affect human auditory information processing as peripheral as on the brain stem level? More specifically, is the reduction of the latency of the frequency-following potential (FFP; an evoked lower brain stem response) that we described in an earlier Neuroreport article really specifically attention-related? Here we demonstrate that, indeed, exogenous intramodal (auditory) spatial orienting, but not a transient modulation of general arousal, reduced the latency of the FFP by 27 micros; there were no effects on the FFP-amplitude. Although it might seem small, this reduction may be relevant in spatial hearing. We conclude that under certain conditions spatial attention can affect auditory information processing already on the brain stem level.

Parallel systems of error processing in the brain.

Major neurophysiological principles of performance monitoring are not precisely known. It is a current debate in cognitive neuroscience if an error-detection neural system is involved in behavioral control and adaptation. Such a system should generate error-specific signals, but their existence is questioned by observations that correct and incorrect reactions may elicit similar neuroelectric potentials.

Short-term mobilization of processing resources is revealed in the event-related potential.

This study investigates whether an occasional effortful improvement of performance, as asked for by a precue, is reflected in event-related potential (ERP) changes. To estimate the limits of possible effort-induced behavioral and ERP changes, we manipulated the time between precue and imperative stimulus (IS; precue interval, PCI). The subjects could, in fact, improve their performance in the effort trials, with all but the shortest PCI.

Sensorimotor slowing with ageing is mediated by a functional dysregulation of motor-generation processes: evidence from high-resolution event-related potentials.

The objective of the present study was to identify the origin(s) of ageing-related behavioural slowing in sensorimotor tasks. For this aim, event-related potentials (ERPs) were analysed at 64 electrodes to evaluate the strength and timing of different stages of information processing in the brain. Electrophysiological indices of stimulus processing, sensorimotor integration/response selection and motor-related processing were used to compare the processing speed of young (n = 13, mean age = 22.

The time it takes to detect changes in speed and direction of visual motion.

We studied the ability of human observers to detect abrupt changes in velocity of motion of a random dot pattern. The pattern moved horizontally for 0.9 s at velocity V0, then changed to V1 either in speed, or in direction for a time T and returned to the initial motion.

Speed decrements are seen better than increments through small apertures.

Five subjects observed a random dot pattern that moved horizontally within a rectangular, 40 deg x 4 deg invisible aperture. The long side of this aperture was either parallel or perpendicular to the direction of motion. A two-interval forced-choice procedure was employed for measuring the thresholds for detection of 100-ms speed increments and decrements superimposed on uniform motion of 1.

Changes of error-related ERPs with age.

Errors in reaction tasks are followed by a negative component of the event-related brain potential (ERP), the error negativity (Ne), which is thought to be a correlate of error detection. In the present study we show that, in tasks that induce different types of errors, the amplitude of the Ne was reduced in elderly (54-65 years old) compared with young subjects (19-25 years old). This reduction was also seen in single trials, as were computed for one of the visual tasks.

Action monitoring, error detection, and the basal ganglia: an ERP study.

The error negativity (Ne or ERN) is an event-related brain potential component, which is assumed to reflect error detection. Recently it has been hypothesized that the basal ganglia are assumed to play a crucial role in error detection. In the present study we ask whether the Ne is altered in patients with Parkinson's disease (PD), who have an impaired function of the basal ganglia.

Mechanisms of simple and choice reaction to changes in direction of visual motion.

Experiments are presented in which a random dot pattern moved vertically upwards (velocity vector V(1)) and then abruptly changed its direction of motion by the angle alpha (velocity vector V(2)), either to the left or to the right, without changing the speed. Subjects performed simple reactions to the direction change, disregarding its sign. In another experiment choice reactions to the same stimuli were performed: the subjects pushed a left button when the direction change was to the left and a right button when the change was to the right.

The discrimination of abrupt changes in speed and direction of visual motion.

A random dot pattern that moved within an invisible aperture was used to present two motions contiguously in time. The motions differed slightly either in speed (Experiments 1 and 3) or in direction (Experiments 2 and 4) and the subject had to discriminate the sign of the change (e.g.

Early attention effects in human auditory-evoked potentials.

A fundamental question in attention theory concerns the earliest processing stages that can be modulated by selective attention. A series of experiments is reported in which very early attention effects are found under specific conditions in the frequency-following potential (FFP), a brain stem response to low-frequency tone stimuli. In two experiments, stimuli of two different modalities were applied, and attention directed to one of the modalities.

Different error types and error processing in spatial stimulus-response-compatibility tasks: behavioural and electrophysiological data.

We tested the hypothesis that in spatial stimulus-response-compatibility (SRC) tasks two different error types occur: A noise-induced 'general error' independent of SRC and reaction time and a 'position driven error' in incompatible trials with short RT being driven by the irrelevant stimulus position. A second issue was whether error detection is different for these two types of errors, which should be reflected by differences in the error negativity (Ne), since the Ne is seen as a neural correlate of error detection. To study these issues, we used a Simon- and a spatial Stroop-task.

ERP components on reaction errors and their functional significance: a tutorial.

Some years ago we described a negative (Ne) and a later positive (Pe) deflection in the event-related brain potentials (ERPs) of incorrect choice reactions [Falkenstein, M., Hohnsbein, J., Hoormann, J.

ERP components in Go/Nogo tasks and their relation to inhibition.

In visual Go/Nogo tasks the ERP usually shows a frontal negativity after Nogo stimuli ("Nogo-N2"), which possibly reflects an inhibition process. However, the Nogo-N2 appears to be very small after auditory stimuli, which is evidence against the inhibition hypothesis. In the present study we tested this hypothesis by evaluating performance differences between subjects.

The simple reaction time to changes in direction of visual motion.

Recently Dzhafarov et al. presented a model explaining data on simple reaction time (RT) to unidimensional velocity changes. The authors suggested that having a motion with an initial velocity V0, the velocity change detection system is reinitialized by means of a "subtractive normalization" process.

Performance differences in reaction tasks are reflected in event-related brain potentials (ERPs).

Event-related potentials (ERPs), which can be extracted from the electroencephalogram (EEG), are assumed to reflect distinct cognitive processes in real time. Hence ERP analysis could be used in cognitive ergonomics as a tool to specify, for example, bottlenecks or sources of individual performance differences. Such specific results may be helpful to change the tasks or train the subjects specifically.

A method to improve the latency estimation of the frequency-following potential (FFP).

If the latency of a noisy frequency-following potential (FFP) is estimated by determining the shift of the (periodical) cross-correlation function (CCF) between the stimulus and the FFP, the result may be unambiguous only within +/-1 or +/-2 periods of the CCF, because the absolute maximum and adjacent local maxima may not be significantly different. Here we present a method to amplify this difference by applying amplitude modulated stimuli. Using this method we first illustrate the effect of the method by a simulation and then demonstrate its usefulness by measuring real FFPs and estimating their latencies.