[From Hank Folson (920826)]
(Chris Malcolm 920825)
Clearly these apparent paradoxes arise because the "folk" theories of
how control is learnt and executed are wrong.
Is there really a paradox here? As you described, the only way to get a
motorcycle/bicycle to turn right is to get it leaning to the right before
initiating the final steering actions. The only reason we make a big deal about
counter-steering is because i
t is not obvious that we must do it and do do it. IsnUt the use of the term
"counter-steering" a stimulus-response sort of description?
What is required is a theory of control which can be applied to the >phenomena
of counter-steering in which the paradoxes become predicted.
How about this, Chris: One thing that I am coming to understand about control
theory is that purpose is all that counts. Method is secondary, just a means
to the intended end. The motorcycle/bicycle steering scenario is a good example
of this, I think.
The first time someone without a physics degree or an experienced tutor tries to
ride a bike/motorcycle, they will steer right when they want to turn right. The
desired perception is turning right, and turning the handlebars to the right
seems like a good
idea at the time. The result is a fall or a moment of panic and wobbling with
no turn. The purpose/goal of turning right remains, however. Steering right
didn't work, so I suspect that our control systems simply try another
controlling action AT RANDOM.
Handlebars only go right or left, so the next controlling action is to turn the
bars to the left. NOTE THAT THE SYSTEM HAS NO INKLING OF WHY THIS SHOULD WORK
ANY BETTER THAN TURNING THE BARS TO THE RIGHT JUST DID. The bike now falls to
the right side in r
esponse to God and Newton. Whatever level of our hierarchy controls for not
falling quickly takes over. The most recent output was to turn the handlebars
to the left. So now the system corrects, and turns the bars to the right. This
is the only controllin
g action option available, fortunately. (In other words there are not so many
degrees of freedom that all options could not be tried before you fall to the
ground.)
Now the bike has velocity, and is leaning to the right, and the bars are turned
to the right. With the centrifugal (or is it centripedal?) force, and the human
control system hopefully in a stable range, there is no fall, just a
beautifully controlled rig
ht turn EVEN THOUGH THE CONTROL SYSTEM DOES NOT UNDERSTAND WHY.
There is not much in the way of planned output in my perception of how a control
system functions. The initial controlling action chosen may be selected for
some reason (e.g. If I want to turn right, it makes sense to turn the bars to
the right, based on
what is stored in the mind from past experiences, such as steering a tricycle.),
but if that first choice does not produce the desired input as the process goes
around the control loop, or if there is no reason to choose a particular
action, the control s
ystem will try one at random. And if that doesn't work, it will continue to
control by trying another action. One thing I like about this suggested
interpretation is that a living control system can survive a great many complex
and/or new situations, with
out requiring a lot of computing power, and can react very fast. Perhaps those
lucky enough to randomly pick the best controlling actions first survive better
than others!
The bicycle steering example is, to me, a good example how a control system can,
by random actions, handle something that its sensors and internal logic would
never figure out. The way E. coli tumbles and takes off in a random direction
when controlling f
or a new food source is a lower level example.
In the going right by steering left scenario, I did not mention another
controlling action the system has available: putting a foot down. This is
perfectly valid, and many beginners probably do this. This takes care of the
error signal of falling down, bu
t doesn't do anything about turning right. Those who put their foot down will
probably take longer to learn how to ride, because their control systems will
not get the opportunity to complete the steering left to go right strategy.
Another thought to ponder: The system has just learned by trial and error how to
turn right. How will the system respond to the next new goal which would be to
turn left? Will the rider try steering left to go left, or will he immediately
steer right to
go left? Is this a prediction of your paradox, Chris?
Hank Folson, Henry James Bicycles, Inc.
704 Elvira Avenue, Redondo Beach, CA 90277
310-540-1552 (Day & Evening) MCI MAIL: 509-6370 Internet: 5096370@MCIMAIL.COM