Engines of Our Ingenuity

No. 977:
FEEDBACK

by John H. Lienhard

Click here for audio of Episode 977.

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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