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 readines s potential is unaffected by force amplitude of brief unimanual respon ses. However, because those studies did not specify rate of force prod uction, response force probably was mainly controlled by force unit du ration rather than by recruitment of force units, which may explain th is negative finding. To enforce recruitment control, we factorially co mbined peak force (10% or 50% of maximal voluntary finger force) and t ime to peak force (100 or 200 ms). A precue provided advance informati on about the responding index finger (left vs. right). After 1 s, the imperative stimulus followed, requiring a brisk isometric flexion of t he specified index finger. Symmetric effects, maximal at the vertex, o f both force and rate of force production were observed 200-100 ms bef ore the imperative stimulus in stimulus-synchronized averages and 200- 100 ms before response onset in response-synchronized averages. Howeve r, neither force nor rate of force production affected the lateralized readiness potential. We conclude that this measure does not reflect m ovement parameters but appears to indicate an abstract preparation of lateralized response channels.