Two experiments assessed the preparatory effects
of advance information about response force and movement
direction on the lateralized readiness potential (LRP).
In a choice reaction time (RT) task, an imperative stimulus
required an isometric flexion or an extension of the left
or right index finger. Prior information about response
force or about movement direction reduced RT and shortened
the interval from the onset of the imperative stimulus
up to the onset of the LRP. Advance information, however,
about direction but not about force decreased the interval
from LRP onset to the onset of the overt response. The
identical pattern of results was obtained in a second experiment,
in which each participant performed both precue conditions.
The findings of both experiments support the notion that
response force is specified before movement direction.
These results are consistent with the view accordingly
different mechanisms are involved in the specification
of muscle force and movement direction.