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Objectives: A problem with the topographic mapping of MEG data recorded with axial gradiometers is that field extrema are measured at sensors located at either side of a neuronal generator instead of at sensors directly above the source. This is problematic for the computation of event-related desynchronization (ERD) on MEG data, since ERD relies on a correspondence between the signal maximum and the location of the neuronal generator. Methods: We present a new method based on computing spatial derivatives of the MEG data. The limitations of this method were investigated by means of forward simulations, and the method was applied to a 150-channel MEG dataset. Results: The simulations showed that the method has some limitations. (1) Fewer channels reduce accuracy and amplitude. (2) It is less suitable for deep or very extended sources. (3) Multiple sources can only be distinguished if they are not too close to each other. Applying the method in the calculation of ERD on experimental data led to a considerable improvement of the ERD maps. Conclusions: The proposed method offers a significant advantage over raw MEG signals, both for the topographic mapping of MEG and for the analysis of rhythmic MEG activity by means of ERD.

In the present paper, event-related desynchronization (ERD) in the alpha and beta frequency bands is quantified in order to investigate the processes related to the anticipation of a knowledge of results (KR) stimulus. In a time estimation task, 10 subjects were instructed to press a button 4 s after the presentation of an auditory stimulus. Two seconds after the response they received auditory or visual feedback on the timing of their response. Preceding the button press, a centrally maximal ERD is found. Preceding the visual KR stimulus, an ERD is present that has an occipital maximum. Contrary to expectation, preceding the auditory KR stimulus there are no signs of a modalityspecific ERD. Results are related to a thalamo-cortical gating model which predicts a correspondence between negative slow potentials and ERD during motor preparation and stimulus anticipation. Ó 1999 Elsevier Science Ireland Ltd. All rights reserved.

What is the neurophysiological locus of inhibition when preparation for a manual response is countermanded? This paper evaluates data and models that pertain to inhibitory mechanisms operating in stop paradigms. In a model of De Jong, Coles and Logan (1995), (Strategies and mechanisms in nonselective and selective inhibitory motor control. Journal of Experimental Psychology: Human Perception and Performance, 21, 3, 498-511), a mechanism for nonselective inhibition operates peripheral to the motor cortex, while a selective mechanism operates at a central cortical level. We argue, however, that a peripheral mechanism of inhibition is incorrectly inferred from inhibition data available to date. Neurophysiological and psychophysiological data suggest that inhibitory processes always involve the cortex, and inhibitory effects are exerted upstream from the primary motor cortex. The prefrontal cortex and basal ganglia are candidate agents of response inhibition, whereas possible sites of inhibition are the thalamus and motor cortex.

In this study the relationship between perceived change implementation in an organization is related to employee self‐rated behaviour. The change implementation processes measured were communication, support and participation. The relationship between these processes and employee behaviour was examined by testing a theoretical model, in which two mediating concepts are used: the psychological contract and employee job attitudes. The research was carried out in two main divisions of a large telecommunications firm on a sample of 220 employees. The theoretical model (perceived change implementation influencing the psychological contract, influencing employee attitudes, influencing employee behaviour) had a better fit with the data, compared to alternative models.

AIM—To examine the spectrum of neurological dysfunction and perceptual-motor difficulties at school age in a cohort of prematurely born children, and the relation of these measures to neonatal brain lesions, intelligence quotient, and behavioural adjustment. METHOD—One hundred and eighty three children were tested at the age of 6 years using Touwen's Examination of the Child with Minor Neurological Dysfunction, the Movement Assessment Battery for Children (Movement ABC), the Developmental Test of Visual-Motor Integration (VMI), British Ability Scales, and Rutter Scales. RESULTS—Twenty six children had definite cerebral palsy and one was blind. Of the remaining 156, the proportions falling below the 15th centile point were 31% on Touwen's Examination, 44% on the Movement ABC, and 17% on the VMI. Forty two passed all three tests. No child with a normal ultrasound scan developed cerebral palsy, whereas nearly all those with major lesions did. Minor lesions, however, were not generally predictive of later outcome. Correlations between the tests were generally low. CONCLUSIONS—These findings stress the need to assess neurological and perceptual motor functioning separately at school age and to monitor relationships with other aspects of development. Keywords: neurological signs; perceptual-motor difficulties; prematurity; follow up.

Two alternative explanations were examined for why selective response activation sometimes starts before stimulus identification is complete (e.g., J. O. Miller & S. A. Hackley, 1992) and sometimes starts only after stimulus identification is complete (e.g., R. De Jong, M. Wierda, G. Mulder, & L. J. M. Mulder, 1988). Distinct psychophysiological methods related to stimulus identification and response selection provided evidence suggesting that partial stimulus information is identified but is or is not used before the stimulus is identified more fully, depending on task requirements. This result (a) suggests strategic adaptation of task performance, (b) is inconsistent with particular discrete and continuous models of information processing, and (c) shows the existence of a central selection mechanism that can prevent the automatic activation of responses associated with preliminary available stimulus information.

This chapter discusses the reasons behind a unilateral movement being preceded by a bilateral readiness potential (RP). Unilateral self-paced movements and warned stimulus-triggered movements are preceded by bilateral slow brain waves, RP, and the contingent negative variation. The chapter proposes two possibilities. The first possibility is that the RP is the consequence of a unilateral cortical activation contra-lateral to the movement side. The bilateral emergence could be because of volume conduction or to a mirror activation via the corpus callosum. The second possibility is that there is a bilateral activation of cortical motor areas. This might be because of a bilateral corticocortical activation, for example, from the prefrontal cortex to the motor cortex or to a bilateral subcortico-cortical activation via a cerebello-thalamocortical circuit or via a basal ganglia-thalamocortical circuit.

Rhythmic properties of spoken language such as metrical stress, that is, the alternation of strong and weak syllables, are important in speech recognition of stress-timed languages such as Dutch and English. Nineteen subjects listened passively to or discriminated actively between sequences of bisyllabic Dutch words, which started with either a weak or a strong syllable. Weak-initial words, which constitute 12% of the Dutch lexicon, evoked more negativity than strong-initial words in the interval between P2 and N400 components of the auditory event-related potential. This negativity was denoted as N325. The N325 was larger during stress discrimination than during passive listening. N325 was also larger when a weak-initial word followed a sequence of strong-initial words than when it followed words with the same stress pattern. The latter difference was larger for listeners who performed well on stress discrimination. It was concluded that the N325 is probably a manifestation of the extraction of metrical stress from the acoustic signal and its transformation into task requirements.

In 2 experiments, 64 male students worked almost continuously for 20 hr without sleep under varying social conditions. In Experiment 1, participants worked either individually or as a group. As hypothesized, performance deteriorated over time, especially in the group condition, which allowed participants to loaf. In Experiment 2, all participants worked in groups. They were instructed that public feedback would be provided either on the group result only or on the individual results of all group members. As expected, when individual results were made public, performance deteriorated less. Overall, the data suggest that fatigue increases social loafing. However, both individualizing the task and providing public individual feedback seem to counteract these effects.