Abstract Real world actions often comprise a series of movements that cannot be entirely planned before initiation. When these actions are executed rapidly, planning of future movements needs to occur simultaneously with ongoing execution. However, it remains unknown how the human brain solves this task and whether planning processes of subsequent movements interact. Here we introduce a new sequential reaching paradigm in humans (N=10, 7 sessions each) with a horizon manipulation that allows us to study this interaction by controlling the timing and the overlap of the planning processes for individual movements embedded in the sequence. We show that at least two future reaches are planned simultaneously with the ongoing reach. Two results indicate that these planning processes are not independent of one another. First, correcting an ongoing reach is slower when future movements are planned. Second, the curvature of the current reach is modified based on the next reach only when the planning processes of the two reaches overlap sufficiently. The interactions between future planning processes may enable smooth production of sequential actions.

Interaction of multiple future movement plans in sequential reaching