[From Rick Marken (960324.1500)]
Martin Taylor (960324 13:00) --
Where I have a problem, and why I jumped in with what I thought would have
been an innocuous comment the other day, is in your statement that "the
results of action are unpredictable." As I see it, that's not true. Only
the direction of movement following a "tumble" (hit on the space-bar,
mouseclick, ...) is unpredictable. The result of the action "do nothing"
is ordinarily totally predictable.
You can look at it that way, but the demo I keep mentioning (and
describe in more detail below) shows that the "predictability" of
movement after the press is irrelevant; if the dot just stays put in
a new position after a press (so there is no continuation of movement
to predict) you can still control the position of the dot.
If you couldn't predict where it would be going next instant, on
what ground would you choose to press or not to press the
space-bar/mouse?
On the usual ground: the _error signal_, which represents the difference
between reference (goal) and actual position of the dot: if the dot is
not at the reference position (error) then press, otherwise (no error)
don't press.
In your sense, the "results of action" are always unpredictable in the
real world outside the laboratory.
Indeed, this is exactly true; the results of our actions would be
completely unpredictable if it were not for the fact that we _are_
control systems. Controlling can be thought of as the way we make the
results of our actions precisely predictable; when we are in control,
we are forcing the results of our actions into "predictable" (reference)
states.
When you turn a door-knob, you don't know that the latch will
actually move and the door-handle not fall off
Right. The result you wanted was an open latch; instead you got a
handle on the floor (and a latch that was still closed, I presume);
so it looks like you lost control of the perception of "latchedness"
of the door. But I bet you will regain control of that variable soon.
That particular loss of control was the result of a large disturbance
(the broken handle); ordinarily the handle doesn't break but the amount
of force required to open the latch is unpredictable; since you can
control "lachedness", you adjust your actions (force exerted on the
handle) as necessary to produce the intended result (an open latch).
The result of controlling "latchedness" is usually quite predictable;
if you want the latch open it ends up open;if you want it closed, it
ends up closed. There is no prediction of the force needed to produce
the intended result; just closed loop control.
All I'm doing is pointing out the surface facts of the situation,
noting that control is possible when the e-coli path is predictable
_after_ the bar press, but would not be if the future path could not
be predicted from current observation.
But these "surface facts" are not facts at all; that's why I keep
replying. It is simply not true that control would not be possible
"if the future path could not be predicted from current observation".
The "predictability" of the path of dot movement after a press has
nothing to so with the possibility of control in this task.
Try setting up this version of the E. coli demo: after a mouse click
the dot moves randomly to one of 10 positions (marked with circles)
on the screen. Select one of those 10 circles as the reference (target)
position. Now see if you can control the dot (get it to the target
circle) by clicking the mouse.
Easy, isn't it? Especially if the dot happens to be on the target circle
on the first trial. In this demo, the position of the dot after a
press is completely unpredictable (although the dot stays put after
a press so maybe you will say it's still predictable; you can predict
that it will stay where it ends up; but then you have to explain how
that kind of predictability makes it possible to decide on the appropiate
action to take; after all, the dot stays where it is after a mouse
click whether it lands on a target or a non-target circle).
So I think we really have no disagreement here, except for your finding
quagmires where there are only little spots of dampness.
I'm afraid that we have a real disagreement; you say that control is
only possible if the results of action are predictable to some extent;
I say that control is possible whether or not the results of action are
predictable.
I submit that the best way to solve this disagreement is for you to
start agreeing with me;-)
Best
Rick