Brainstem circuits that mirror the muscles

1. A direct phasic command from burst neurons which is scaled by R to match the viscosity (r) of the muscles & globe. This command moves the eye quickly to the desired position.
2. An indirect input through the neural integrator which is scaled by K to match the elasticity of the muscles (k). This command holds the eye in its new position.

The internal estimates of the plant characteristics, K & R, must match that of the actual plant, k & r.