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Abstract:
The repetitive tapping task used in this experiment required
subjects to synchronize a finger movement with a metronome. On
average the inter-tap times equal the metronome period (ISI), but
contain variability. Wing and Kristofferson, and subsequent
synchronization models, have suggested that variability stems from
at least two sources, a central timing, or clock process, and the
implementation of the motor command. These models provide a method
of analysis to estimate the contribution of each source from
behavioral data. The validity of these models was addressed by
recording evoked electrical brain potentials from the scalp while
subjects perform the tapping task. Results indicate (1) that the
lateralized readiness potential (LRP) measured in single trials
occurs at approximately the same time prior to the response (motor
latency) regardless of the tapping rate, and (2) the variability
associated with the LRP correlates more highly with the behavioral
estimate of motor variability than with clock variability. Since
the LRP has previously been explicitly associated with response
implementation and neural activity in the motor and peri-motor
cortices, the current data support the framework proposed by
synchronization extensions of the Wing-Kristofferson model, which
posit a motor component latency which is approximately constant in
both mean and variance at different ISI values.
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