Figure 1.

Optimal feedback control (OFC) framework

(A) The control policy consists of time-varying feedback gains that transform the estimated states into motor commands. According to stochastic OFC, the feedback gains depend on a cost function that accounts for the goal of the task (task selection) while minimizing the motor cost. Efference copies of motor commands are combined with delayed sensory feedback to estimate the current state of the limb. The estimated states are continuously fed into the control policy to update the outgoing motor commands (modified from¹). Robust OFC extends the framework and imposes an additional cost to maximize the controller’s response to disturbances that may arise from unmodeled dynamics or variable external disturbances. In turn, the controller’s time-varying feedback gains increase (control policy) and the influences of internal feedback (efference copy) are downregulated during state estimation.²

(B) Robust OFC and stochastic OFC lie on opposite ends of a continuum of control strategies that trade-off the controller’s movement efficiency and stability against errors (modified from²).