EFFECTS OF RESPONSE PROBABILITY ON RESPONSE FORCE IN SIMPLE RT

Response force (RF) was measured in a simple reaction time (RT) experi ment varying response uncertainty by cuing the probability of the resp onse on each trial. In all cases, RF decreased as response probability increased. The dependence of RF on response probability was insensiti ve to foreperiod length and to the use of loud auditory response signa ls, although the dependence of RT on response probability was sensitiv e to both of these manipulations. In combination with previous finding s, these results provide evidence that RT and RF can be dissociated. W e describe an extension of Naatanen's readiness model that can account for the effects of response probability on RF and RT According to thi s model, the distance between motor activation and a threshold for act ion is relatively large when subjects are unprepared, and a large incr ement is needed to exceed this threshold, resulting in slow but forcef ul responses. A possible neurophysiological implementation of this mod el is suggested.