Independent Planning of Timing and Sequencing for Complex Movements

The current studies examined the processes involved in response sequencing and timing initiation for complex, multiple-component movements. Participants performed a 3 key-press sequence in simple and choice reaction time (RT) paradigms (Experiment 1), or a study time paradigm that allowed the participants to control the foreperiod delay, which is thought to reflect advance preparation duration (Experiment 2). Sequencing complexity was manipulated by using either the same hand and effector for all key presses (low complexity) or different hands/effectors across key presses (high complexity) while timing initiation complexity was manipulated by using either an isochronous (low complexity) or nonisochronous (high complexity) timing pattern. Increasing sequencing complexity had little effect on simple RT but increased participant-controlled foreperiod delay (i.e., study time). Conversely, increasing timing initiation complexity had no effect on foreperiod delay but increased simple RT. These results provide compelling evidence that in a simple RT paradigm, sequencing preparation is performed during the foreperiod while preparation of timing initiation is delayed until the RT interval. Furthermore, choice RT increased with sequencing complexity and was relatively unaffected by timing initiation complexity, indicative of sequencing preparation occurring during the choice RT interval and preparation of timing initiation occurring online. Collectively, the data indicate a dissociation and independence of the preparation of timing initiation and sequencing for complex movements.