Today, we find out why positive feedback is a bad
thing. The University of Houston's College of
Engineering presents this series about the machines
that make our civilization run, and the people
whose ingenuity created them.
I met a friend from the
Music Department the other day. I asked what he
knew about composer Roger Sessions, who'd been a
child prodigy at Harvard along with Norbert Wiener.
"Who was Wiener?" he wondered. So instead of
Sessions we talked about Wiener and cybernetics.
When we were done, he said, "Fascinating! Tell your
audience about that." So that's what I'll do.
Wiener entered Tufts University when he was ten. He
had his Ph.D. from Harvard at 19. For 41 years he
taught at MIT and studied the analogy between human
brains and machines. He had been the overcontrolled
product of ambitious parents. It's small wonder he
focused on robotics and the machine-like aspects of
the mind.
Wiener created the word "cybernetics" from the
Greek word for the steersman of a boat,
kybernitis. A steersman sits with a
hand on the rudder and sights over the prow to see
where the boat's headed -- say a wharf. If the
boat's aimed a little to the right, he turns it
slightly to the left. When he finally overshoots,
he recorrects to the right again. And so on.
He constantly compares the actual direction with
the intended direction and applies a negative
correction -- one that opposes the error. That's
called negative feedback, and it's what all
automatic control devices do -- the level control
in your toilet tank, your thermostat, the ignition
control in your car.
The Romans picked up the Greek word
kybernitis and corrupted it into
gubernare, from which we get our word
"governor." Of course that's another term we use
for a feedback control device.
Wiener studied the mathematics of the feedback
process. Then he went on to deal with what might be
called the psychology of robots. He found, for
example, that he could create insane behavior in
machines by controlling them badly.
Psychologists have taken the term positive feedback
from Weiner's work, but they misuse it. True
positive feedback is unstable, destructive -- a
parent saying to a child, "Oh, Billy, you ran into
the street again! Have an M & M." Technically,
positive feedback is action that reinforces what it
seeks to correct.
What psychologists really mean is either positive
reinforcement or negative feedback applied with
good sense and courtesy. Little Norbert Wiener got
plenty of feedback as a child, but it was feedback
lacking in the courtesy we parents owe our
children.
Later in life Wiener wrote books on the
implications of the mind/machine analogy. He
devoted his life to getting beyond the machine to
find the human -- to transcending his own overly
controlled childhood. And we're hardly surprised
when we find that one of those book titles was
The Human Use of Human Beings.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
(Theme music)
Mayr, O., The Origins of Feedback
Control. Cambridge, MA, M.I.T. Press, 1970.
Wallace, A., The Prodigy: A Biography of
William James Sidis, America's Greatest Child
Prodigy, New York: E.P. Dutton, 1986.
Feldman, D.H., with Goldsmith, L.T., Nature's
Gambit: Child Prodigies and the Development of
Human Potential. New York: Basic Books,
Inc., Publications, 1986.
See also any engineering text in automatic control
theory for a technical discussion of feedback
control.
From the 1832 Edinburgh
Encyclopaedia
The flyball governor was originally invented by
James Watt to control the flow of steam. It is used
here to control the flow of water.
From the 1832 Edinburgh
Encyclopaedia
Watt's original flyball governor
The Engines of Our Ingenuity is
Copyright © 1988-1997 by John H.
Lienhard.
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