When Optimal Feedback Control Is Not Enough: Feedforward Strategies Are Required for Optimal Control with Active Sensing

摘要

Movement planning is thought to be primarily determined by motor costs such as inaccuracyand effort. Solving for the optimal plan that minimizes these costs typically leads to specifying a time-varying feedback controller which both generates the movement and can optimally correct for errors that arise within a movement. However, the quality of the sensoryfeedback during a movement can depend substantially on the generated movement. Weshow that by incorporating such state-dependent sensory feedback, the optimal solutionincorporates active sensing and is no longer a pure feedback process but includes a significant feedforward component. To examine whether people take into account such statedependency in sensory feedback we asked people to make movements in which we controlled the reliability of sensory feedback. We made the visibility of the hand state-dependent, such that the visibility was proportional to the component of hand velocity in aparticular direction. Subjects gradually adapted to such a sensory perturbation by makingcurved hand movements. In particular, they appeared to control the late visibility of themovement matching predictions of the optimal controller with state-dependent sensorynoise. Our results show that trajectory planning is not only sensitive to motor costs but takessensory costs into account and argues for optimal control of movement in which feedforwardcommands can play a significant role.