Title: Integration of Predictive Feedforward and Sensory Feedback Signals for Online Control of Visually- 1 Guided Movement 2

Online control of movement requires complex integration of predictive central feedforward 16 and peripheral sensory feedback signals. We studied the hand trajectories of human subjects pointing to 17 visual targets which abruptly changed locations by different amounts and modeled the mechanism of 18 rapid online correction using a dynamic model of a two-joint limb. Small unperceived and large de19 tected target displacements could be attributed to different origins (motor execution errors versus envi20 ronmental changes respectively) and compensated differently. However, the behavioral findings indi21 cate that the rapid feedback pathway is recruited regardless of the amplitude or subjective awareness of 22 target displacement, and that the size of the earliest correction is always proportional to the amplitude 23 of the target displacement over the tested range of perturbations. The modeling findings suggest that 24 the rapid online corrections can be accomplished by superimposing a dynamically appropriate error 25 correction signal onto the outgoing feedforward motor command to the original target. Furthermore, 26 the modeling shows that the online correction mechanism must include compensation for the dynamic 27 mechanical properties of the limb and for sensory delays in its error-correction pathway. 28