[Martin Taylor 950501 17:10]
Mayday, Mayday...
Bill Powers (950427.1038 MDT)
Martin Taylor (950420 11:00)--
Rick sez:
but its present time perceptions are also (and simultaneously) based on
it present time actions.And you say:
Sorry. Should say "based on the actions at such past times as now
are affecting the perceptual signal." Its present time actions
have not yet affected the perceptual signal. You are mixing up the
fact that all functions in the loop are acting simultaneously
(which they do) with the notion that all signals in the loop have
simultaneous effects all around the loop (which they don't).And you have missed the fact that Rick's statement is literally true:
present-time perceptions are also and simultaneosly based on present-
time actions. If all functions in the loop are acting simultaneously,
then it follows that at the time any perception is varying, it is
subject to the effects of present-time actions that are going on.
Absolutely NOT so. At the very least there is the light-speed limitation
that ensures that the effects of present action are not yet represented
in perception. In any practical control system the delays are many,
many orders of magnitude longer. Eyes take time to deliver signals
after photons arrive (Parenthetically, have you ever tried playing
table-tennis by the light of the full moon? It's a very edifying experience
in that regard*). Actions don't move things instantaneously. No, the effect
of present time actions never, ever, form part of present time perception.
Yes, all functions in the loop are acting simultaneously. The amalgamated
effects of possibly a long period of past action older than some minimum age
is represented in present perception (if the output is a pure integrator,
the effect of ALL past action older than the minimum age is part of present
perception). But that minimum age is intrinsic to the limitations on the
control system.
To focus too much on the loop delays is to miss
the important fact, which is that all perceptions are affected by
actions all of the time.
These are orthogonal concepts. Why should the recognition of one affect
the understanding of the other? And "that all perceptions are affected by
actions all of the time" is different from saying "that all perceptions
are affected by _present_ actions all of the time," which was the thrust
of my mild correction to Rick.
In real human control systems, lags are
relatively unimportant because inertial effects and integrations that
would be there anyway take care of most of their deleterious effects.
Yes, we animals have evolved in an efficient way in many respects. We don't
waste many resources on actions or processing that would ordinarily be useless.
Evolution is often neat that way, to the extent that there are still people
who insist that its neatness is evidence for the existence of a personal
Designer.
The inertial effects and such like provide limits on the bandwidths of
disturbances that can be countered, so why waste resources on perceptual
processing at higher bandwidths than those lags allow for control?
Likewise, why provide muscular efforts that would allow for faster action
than the related perceptual processes admit? These things co-evolve so
that they usually fit together reasonably well, to a first approximation.
You think I concentrate too much on loop delay or external transport lag.
I think you slough over it too much, and disregard its critical nature in
the dynamics of control.
Martin
*(Moonlight table tennis CAN be played, if one attempts to hear the bat
hit the ball at the same time as one sees the ball passing over the net
on its way to you. You have to "predict" where the ball will be when you
hit it, from a visual appearance that in normal lighting would have been
seen a few hundred msec earlier. Quite a trick, but doable. And I do
recognize that there is no more "prediction" involved than in catching a
high fly ball--in other words, none if you look at the right perceptual
level of control).