ABSTRACT
There is evidence that the CNS contains transformations, or internal models, which mimic aspects of one’s own body and the external world (Wolpert et al. 1995; Wolpert 1997). Here we shall be concerned with two varieties of internal model, predictors and controllers (also known as forward and inverse models, respectively). Whenever a movement is made, a motor command is generated by the CNS and a predictor estimates the sensory consequences of that motor command. A controller, on the other hand, captures the relationship between the desired state and the motor command required to achieve that state. An important issue to stress in our discussion of such representations is that they do not need to be detailed or accurate models of the external world. Often an internal model need only provide a rough approximation of some external transformation in order to play a useful role. The function of predictors and controllers requires that at least three states of the motor system are represented: the current state of the system, the desired state of the system and the predicted state of the system.
