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W Klimesch

Publications and source records attributed to W Klimesch.

7 recordsLinked to original sources
PubMed1992

Functional topography during a visuoverbal judgment task studied with event-related desynchronization mapping.

Event-related desynchronization (ERD) of alpha components was studied in 10 subjects in a visuoverbal judgment task. EEG was recorded from 29 electrodes; ERD, measured by percentage of alpha power decrease, was calculated in 125-ms intervals and displayed in a time course over 7-s intervals and in the form of topographical ERD maps. ERD, interpreted as a measure of activated cortical areas, was studied in the upper and lower alpha bands. It was found that upper alpha band ERD was short-lasting (less than 1 s), localized to the posterior region and not found before stimulation; in contrast to this, lower alpha band ERD was longer-lasting (greater than 1 s), more widespread, with a left hemisphere dominance, and was already present before stimulation. ANOVA revealed significant interactions among alpha frequency bands, scalp location, and pre-/poststimulus intervals. The self-organizing topological Kohonen network was used to analyze the stability of consecutive ERD maps. There is evidence that topographical ERD patterns can be stable for about 300-400 ms.

Adult↗
PubMed1992

Semantic memory: complexity or connectivity?

The complexity hypothesis predicts that concept-feature verification times should be directly related to the number of features associated with a concept (the fan effect). Conversely, the connectivity hypothesis predicts that for interconnected semantic relationships, this verification time should be inversely related to the number of closely associated features (the reversed fan effect). In the present experiments, although the time required for episodic recognition memory decisions tended to be directly related to the number of features associated with a concept, semantic verification times were inversely related to the complexity of the concept. In addition, the concept's complexity was at least as good a predictor of performance in semantic tasks as was the strength of association between the concept and feature. Both of these results are interpreted in terms of the connectivity hypothesis.

Adult↗
PubMed1992

[P300 and dementia: diagnostic relevance II].

Recent research on the relationship between ERP-latencies and reduced information process capabilities with demented subjects has yielded divergent results. In the present study P300-latencies and RT are used in an attempt to differentiate between demented and nondemented subjects. Based on the "feature-integration-theory" of Treisman an experiment was designed in order to investigate more complex cognitive processes. The results showed that both P300-latency and RT may be used as additional diagnostic indices for cognitive capability.

Adult↗
PubMed1990

Topographical display and interpretation of event-related desynchronization during a visual-verbal task.

Multichannel EEG recordings were performed during a visual-verbal judgement task with a verbal response using an event-related paradigm. EEG trials of 7 sec were first digitally band pass filtered (10-12 Hz, 10-11 Hz, 11-12 Hz), and the amplitudes were then squared and averaged over all trials. This processing method results in a time course of alpha power and allows us to quantify the event-related desynchronization (ERD) in each EEG channel and to compute series of ERD maps in intervals of 125 msec. Analyzing the 10-11 Hz band, it was possible to study the time course and topographical pattern of cortical activation during visual encoding and cognition. Analysis of the 11-12 Hz band has enabled us, for the first time, to study the time course, spatial localization and extent of activation of speech, premotor and motor areas. We found that the speech centers were activated maximally 250 to 375 msec before speech onset and the SMA about 250 msec before speech onset. The results are preliminary, but demonstrate how much information can be extracted from the scalp EEG.

Acoustic Stimulation↗
PubMed1990

[P300 and dementia: diagnostic relevance. I].

Visual evoked potentials, including the P300 response, and reaction time were recorded from 20 patients with multi-infarct dementia, 20 nondemented patients with brain-infarct diseases, and 20 age-matched control subjects. Additionally the patients were assessed using the WAIS-index. Prolonged P300 latency and reaction time occurred in both of the patient-groups, correlated significantly with the WAIS-index. However, effects regarding to P300 latency and reaction time were not strong enough to allow individual classifications.

Adult↗
PubMed1990

[Event-related desynchronization and the selection of an alpha-frequency band for quantifying cortical pre- and poststimulus activation].

The amount of event-related decrease of increase in alpha-band power is termed "Event-Related Desynchronization" or ERD. In this study, ERD is used as an index of cortical activation, which not only can be applied to monitor poststimulus but prestimulus processes as well. Usually, ERD is analyzed within a fixed range of alpha-frequency, typically within a range of 8-12 Hz. alpha-frequency, however, shows a considerable between subject variation, even in a sample of subjects with comparable age. The purpose of this study, thus is to show as to how the range of alpha-frequency affects the calculation of ERD. Two different methodological approaches were compared. First, ERD was calculated within a fixed range of 8-12 Hz. Second, ERD was calculated within an individual range, which was adjusted to the individually determined alpha-frequency of each subject. A sample of ten right handed subjects participated in an episodic memory experiment, in which target words, shown in a earlier session of the experiment, were to be identified. A time span of 375 ms preceding and following the presentation of a word was defined as the "pre-" and "poststimulus" interval. EEG-signals were recorded unipolarly from 29 leads. The results show a rather localized increase of ERD in the poststimulus interval. In the prestimulus interval on the other hand, the average magnitude of ERD is much lower and the topographical distribution less localized. Most importantly, however, when comparing the two methods of analyzing ERD, those ERD-values calculated within an individually determined alpha-band, are superior in order to differentiate between the pre- and poststimulus interval.

Adult↗