Prospective Sky Guides (Fixed Wing Aircraft)

Tau Theory

One of the key facets of the ecological approach to visual perception is that the motion of the observer and the perception of the environment are inextricably linked.  Motion leads to an optic flow-field that contains optical invariants that the observer can utilise to perceive that motion.  The observer must use the invariant information about the perceived environment to navigate around and survive within it.  There must be an optical invariant available to an observer to prospectively guide the observer whilst performing these actions.  Such an invariant must be biologically plausible [14].  Such an invariant comes in the form of the time to close a motion-gap at its current closure rate, designated tau [15].

Some of the key principles of Tau Theory are [15]:

1. Motion is guided by the coupling of taus;
2. Coupling can be extrinsic (the coupling of two externally perceived variables) or intrinsic (an externally perceived variable is coupled to a hypothesized mechanism generate by the observer’s central nervous system, a tau-guide).

Coupling onto a constant velocity or deceleration tau-guide is equivalent to the observer adopting a constant rate of change of tau motion strategy.  This strategy was one of the earliest hypothesised methods of motion guidance and was used extensively in this research project.