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Abstract:
The presented experiments demonstrate that the lateralized
readiness potential (LRP)does not only reflect the absolute number
of a priori known movement parameters but is also linked to the
degree to which advance task information is used strategically for
motor preparation. In a 2-choice reaction task, subjects were
requested to respond to numbers with extions and flexions of their
left or right index finger. The imperative stimulus was always
preceded by a precue indicating either response hand alone (partial
precue) or response hand and direction (full precue). In Experiment
1, the two precue types were presented mixed or blocked. Blocked
presentation of partial precues was assumed to enhance the degree
to which hand information was used for advance response
preparation. The results indicate neither faster responses nor
larger LRP amplitudes in the foreperiod preceding the imperative
stimulus in blocked as compared to mixed presentation. However,
during mixed presentation immediate precue repetitions decreased
response latencies and increased LRP amplitudes as compared to
precue alternations. Experiment 2 compared two subject groups being
rewarded for speeded responding specifically in either full or
partial precue trials. Irrespectively of the assignment, all
subjects showed larger foreperiod LRPs for the stressed precue
category than for the lenient condition. Therefore, time pressure
enhances motor preparedness (as indicated by the LRP) independently
of the amount of precued response information.
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