[From Bill Powers (931116.0900 MST)]
Gavan Lintern (931115.1054) --
In response to my question about how the balance-of-forces model
handles disturbances, you say
as with a falling object that had reached terminal velocity, a
disturbance that perturbed the system from the attractor (as in
dynamical sytems theory) would have only a transient effect.
The falling-object analogy handles cases in which only blindly-
applied forces are involved (gravity and aerodynamic drag). To
make this into an example of actual human behavior, we might
consider a pair of skydivers, one of them a video photographer
adjusting bodily orientation to vary the drag coefficient and
thus remain level with the other while the other does stunts. A
disturbance would then be the variations in falling speed of the
other skydiver during the stunts. As the difference in vertical
position changes, the "chasing" skydiver adjusts his or her
bodily configuration, using the variable drag as a means of
correcting the altitute difference between the divers. There is
no constraint here forcing the disturbance to be transient, so we
have the general case: an arbitrary disturbance acting to alter
the state of a variable under control by one system. The person
doing the controlling of relative altitute acts in a way that
counteracts whatever disturbances of relative altitude show up.
How would the ecological approach analyze this situation without
using the concept of control?
Bill P.