Perceptual Control Theory is a theory developed by William Powers, concerning the organisation of living systems as hierarchies of control processes. The CSGNET web site has further information.
As an exploration of the principles of perceptual control theory, I have written a Java applet simulating a six-legged robot. It controls the position and orientation of its body, resisting random disturbing forces, and is capable of walking, turning around, and hunting for food.
I have made a more physically detailed simulation using the Vortex physical simulation library. and also modelled some other mechanisms using the same control architecture.
Since then I have ported the simulation to the PhysX (formerly called NovodeX) physics engine.
The Java applet has been described in a preliminary report.
More recent work has been published in a paper presented at the Control 2004 conference:
Paper
Powerpoint slides