The OODA Loop as John Boyd sketched it toward the end of his life
Late in 1992, John Boyd sketched the version of the OODA Loop reproduced above. In it, he plays with the notion that a scientist grappling with a problem goes through roughly the same mental processes as a fighter pilot bounced by an enemy aircraft. Each begins with Observation: he sees the situation as it is. The pilot (or soldier or footballer or chess or tennis player) goes on to Orientation, but in a manner much more complex than the OODA Loop is usually understood. In the popular view, the combatant simply orients himself with respect to the new information (NI, on the sketches) acquired through Observation. Elsewhere, Boyd employs the more evocative term "unfolding circumstances," which makes the point that the process is a fluid one.
But in fact, that's only the beginning. The new information is necessarily filtered through the lenses of the combatant's previous experiences (PE), genetic heritage (GH), and cultural traditions (CT). On this basis, he decides what to do; then he acts upon his decision. So: Observation > Orientation > Decision > Action, as shown in the topmost diagram.
For the scientist, Boyd speculates, the preliminary Observation is processed through a somewhat different process, which he calls Synthesis / Analysis, though it involves the same galaxy of forces as the combatant applies in the Orientation stage of his OODA Loop. Again, based on the insights gained in that process, the scientist formulates a Hypothesis and subjects it to Test, thus completing his own, analogous Loop. No less than aerial combat, science turns out to be "a self-correcting process of observations, analyses / synthesis, hypothesis, and test." He shows this in the second diagram, with the two variants more or less combined in the bottom sketch.