[Lateralized readiness potential and reaction time in partial preliminary information of a psychomotor parameter]

An overt response with a single hand is preceded by a change in the relative activation of the left and right motor cortices. The resulting lateral shift in the distribution of electrical potential at the scalp is known as the Lateralized Readiness Potential (LRP). The LRP is thought to reflect the differential preparation of the two hands and has been used to study the time-course of such preparation. A number of questions concerning the interpretation of the LRP still remain, however. The present study sought to discover whether the LRP reflects only the preparation of actual muscles or can arise from a more abstract muscle-independent form of preparation. In a choice reaction time (RT) task, either hand (left or right) or movement direction (finger flexion or extension) was precued before the response signal appeared. The hand precue induced an LRP, even though the remaining response alternatives involved different roles for the same muscles. Surprisingly, RT was correlated with the amplitude of the LRP following the direction precue, but not the hand precue. The results support the assumption that the LRP reflects an abstract muscle-independent form of response preparation. It is argued that this preparation works in an all-or-none fashion.