Influence of the movement parameter to be controlled on manual RT asymmetries in right-handers

In this experiment we test whether the effects of manual asymmetries on mov ement preparation depend on the parameter (amplitude or direction) to be pr ogrammed. In two experiments, only the amplitude, or the direction, of aimi ng movements was constrained. Reaction and movement times were measured. Re sults show that RTs are always shorter for left-hand than for right-hand mo vements. There is an effect of target extent in the amplitude condition, bu t not in the direction one. RTs for ipsilateral movements are shorter than RTs for contralateral movements. These results are discussed in the light o f the processes involved in setting the amplitude or direction of the movem ent and with regard to the competency of the two hemispheres regarding thes e processes, (C) 2000 Academic Press.