The lateralized readiness potential preceding brief isometric force pulses of different peak force and rate of force production.

Previous studies have reported that the lateralization of the readiness potential is unaffected by force amplitude of brief unimanual responses. However, because those studies did not specify rate of force production, response force probably was mainly controlled by force unit duration rather than by recruitment of force units, which may explain this negative finding. To enforce recruitment control, we factorially combined peak force (10% or 50% of maximal voluntary finger force) and time to peak force (100 or 200 ms). A precue provided advance information about the responding index finger (left vs. right). After 1 s, the imperative stimulus followed, requiring a brisk isometric flexion of the specified index finger. Symmetric effects, maximal at the vertex, of both force and rate of force production were observed 200-100 ms before the imperative stimulus in stimulus-synchronized averages and 200-100 ms before response onset in response-synchronized averages. However, neither force nor rate of force production affected the lateralized readiness potential. We conclude that this measure does not reflect movement parameters but appears to indicate an abstract preparation of lateralized response channels.