page_title: Internal model (motor control)
section_title: Inverse models
hierarchical_section_title: Internal model (motor control) / Inverse models
caption_attribution_description: English: Inverse model of a reaching task
context_page_description: In the subject area of control theory, an internal model is a process that simulates the response of the system in order to estimate the outcome of a system disturbance. The internal model principle was first articulated in 1976 by B. A. Francis and W. M. Wonham as an explicit formulation of the Conant and Ashby good regulator theorem.
  It stands in contrast to classical control, in that the classical feedback loop fails to explicitly model the controlled system.
  The internal model theory of motor control argues that the motor system is controlled by the constant interactions of the “plant” and the “controller.” The plant is the body part being controlled, while the internal model itself is considered part of the controller. Information from the controller, such as information from the central nervous system, feedback information, and the efference copy, is sent to the plant which moves accordingly.
  Internal models can be controlled through either feed-forward or feedback control. Feed-forward control computes its input into a system using only the current state and its model of the system. It does not use feedback, so it cannot correct for errors in its control.
context_section_description: Inverse models  use the desired and actual position of the body as inputs to estimate the necessary motor commands which would transform the current position into the desired one. For example, in an arm reaching task, the desired position (or a trajectory of consecutive positions) of the arm is input into the postulated inverse model, and the inverse model generates the motor commands needed to control the arm and bring it into this desired configuration (Figure 2). Inverse internal models are also in close connection with the uncontrolled manifold hypothesis (UCM), see also here.
caption: Figure 2. Inverse model of a reaching task. The arm’s desired trajectory, Xref(t), is input into the model, which generates the necessary motor commands, ũ(t), to control the arm.
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