Thinking Tau: The Emergence of Intrinsic Guidance

Studies of sensory guidance of movement in animals show that large nervous systems are not necessary for accurate control, suggesting that guidance may be based on some simple principles. In search for those principles, a theory of guidance of movement is described, which has its roots in Gibson’s pathfinding work on visual control of locomotion (J. J. Gibson, 1958). The theory is based on the use of the simple but powerful variable tau, the time-toclosure of a “gap” at the current gap closure rate (whatever the gap’s dimension—distance, angle, force, etc.); and on the principle of tau-coupling (keeping two Ts in constant ratio). In this article, I show how tau-coupling could be used to synchronize movements and regulate their kinematics. Supportive experimental results are reported. I also show theoretically how sensory-taus, defined on sensory input arrays, can specify motion-taus through tau-coupling; how the braking procedure of keeping tau-dot stable is a particular case of taucoupling; and how tools for steering (e.g., limbs, whole bodies, cars, or aircraft) could be built from tau-couplings, which would enable steering control in a variety of situations, including steering straight and curved courses to goals, steering and controlling speed at the same time, steering around obstacles, and asymptoting on surfaces as when landing. Some movements also involve intrinsic guidance from within, and a hypothesis on intrinsic guidance by tau is introduced, supported by experiments spanning different activities. Animals have to guide their movement through the environment to avoid obstacles, reach destinations safely, intercept moving objects, and so forth. In his seminal article on “Visually Controlled Locomotion and Visual