Welber Marinovic, James Tresilian, Jack L. Chapple, Stephan Riek, Timothy J. Carroll

A loud acoustic stimulus (LAS) is often used as a tool to investigate motor preparation in simple reaction time (RT) tasks, where all movement parameters are known in advance. In this report, we used a LAS to examinedirection specification in simple and choice RT tasks. This allowed us toinvestigatehow the specification of movement direction unfolds during the preparation period. In two experiments, participants responded to the appearance of an imperative stimulus (IS) with a ballistic wrist force directed towards one of two targets. In probe trials, a LAS (120 dBa) was delivered around the time of IS presentation. In Experiment 1, reaction times in the simple RT task were faster when the LAS was presented, but the effect on the movement kinematics was negligible. In the Choice RT task, however,movement direction variability increased when the LAS was presented. In Experiment 2, when we primed movements towards one direction, our analyses revealed that the longer participants took to start a movement, the more accurate their responses became. Our results show not only that movement direction reprogramming occurs quickly and continuously, but also that LAS can be a valuable tool to obtain meaningful readouts of the motor system's preparatory state.