From: The World In Your Head by Steven Lehar
Fig. 10.4 (A) The imbalance due to misalignment between center of gravity and center of support can be expressed as a field, indicated by the gray arrows, which can be used as a motor field to restore the balance, moving parts of the body in the direction indicated by the arrows of the motor field. (B) Maintaining a constant imbalance or tilt results in locomotion in the direction of tilt. (C) A more generalized motion field is expressed by a directed motion of the core of the body, with a balancing countermotion of the limbs in the periphery. (D) A phasic component to the motor field defines a rotating vortex that directs the two feet to rotate in counterphase.