Living Control Systems III

The Fact of Control

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Contents

Modeling and Simulation Demonstration CD
     —Notation

ii

Foreword: The Fact of Control

xi

Modeling and Simulation Demonstration CD

Foreword: The Fact of Control

This work began in the second sub-basement of the Argonne Cancer Research Hospital at the University of Chicago in 1952, when I was all of 26 years old. That was the year I gave up my interest in dianetics and went back to physics, the same year my friend Kirk Sattley showed me a small book called Cybernetics: Control and communication in the animal and the machine, and unwisely let me borrow it. Kirk died in 2002, but I still have his book. In my new job as a very junior health physicist, I had time to do some experiments with human control systems. One of them was an attempt to use external positive feedback to measure the amount of internal negative feedback in the galvanic skin response to loud sounds. There is no need to inform me that this experiment was rather confused in its premises. So was I. But I did begin to study engineering texts on control theory, and the work started that led, over many years, to this book and four others before it.
     Now, with this book, I seem to have done about as much as I can to preserve my version of this thread of thinking and pass it on to those who will make the best use of it. It still seems to me, as it seemed an hour after putting down Norbert Wiener’s book 55 years ago, that negative feedback control is the ingredient that has been missing from the life sciences for as long as they have existed, and is the concept that will finally put those sciences on a par with physics and chemistry. I can’t begin to guess why it has taken so long, why so many people have explored the phenomena of negative feedback control in living systems without seeing that they were looking at a revolution straining to happen, and why so many more have simply refused to learn anything about it. But that’s their problem.
     In this book I have only one goal: to establish in the mind of the reader the literal reality of negative feedback control as the basic organizing principle of human behavior. Human beings do not plan actions and then carry them out; they do not respond to stimuli according to the way they have been reinforced. They control. They never produce any behavior except for the purpose of making what

This book is about control theory and its uses as a way of explaining how human behavior, and perhaps the behavior of all organisms, works. Before getting into the computer demonstrations, we’ll spend one chapter on some generalizations that may be helpful, and some claims with which I hope you will eventually agree.

I’ll make a deal with you. You can skip Chapter 1 if you will agree that before you raise objections about something said in later chapters, you will go back and read it. It’s a bit heavy on mathematical concepts and not strictly necessary for understanding what comes next, but I believe the mental exercise will be at least a little helpful. If you disagree, just skip to Chapter 2 and get started with the demonstrations.

Whatever method of control one proposes, the basic concept of control is the same. To control something is to act to bring it to a specified condition, and then maintain it close to that condition even if unpredictable external forces and changes in environmental properties tend to alter it. Human behavior, as later chapters will suggest through numerous examples, is control behavior. All of it.

Anyone encountering for the first time the brand of control theory used here, PCT (perceptual control theory), might be a little confused if some other kind of control theory has happened to

If Chapter 3 succeeded in its aims, you now have a considerably enhanced idea of what a negative feedback control system is and how it works (some readers, of course, already knew). This is only a building-block; a complete theory of behavior would use many of these control systems operating in parallel and at many levels of organization. But even one building-block can be applied to isolated behaviors of many kinds from the simple to the complex, in each case suggesting how some low or high level of control might be organized. The object of this chapter is to see how well the model in Chapter 3 can describe and predict what we observe in a simple tracking task.

SIMULATION AS A SCIENTIFIC METHOD

The strategy, which we saw briefly in Chapter 2, involves constructing a working model and using it to simulate human behavior in a set task. The model, when expressed as a simulation, is the equivalent of a detailed and quantitative prediction of behavior that can be compared with real behavior.
The two main aspects of a model are its architecture and its realization. The architecture is the block diagram in Figure 3-1 in Chapter 3, without any mathematics—just labels for the parts, the connections among parts, and general descriptions of what the parts are and do. A block diagram is really a whole family of models that can behave entirely differently depending on which realization

Now we will extend the model of reorganization beyond three dimensions, to show that it works as well in fourteen dimensions as in three. Then we will add a second layer of control systems to show how coordinations can be handled in this model, and a third to show how the two levels of coordinated control can be used to control a relationship of the arm to an independent object. The subject of reorganization will be left behind as we consider coordination> not because it doesn't apply but because it will take someone a little younger and possibly smarter than I to deal with all the problems involved. Reorganization will apply in the first demonstration that follows.

REORGANIZING IN FOURTEEN DIMENSIONS

Demo 8-1, Arm Control Reorganization, which I will now assume you have started, shows someone's disembodied right arm floating in space, as seen in Figure 8-1.

In this last chapter of demonstrations, we will look at some aids to understanding that were developed as various points of difficulty arose.

SQUARING THE CIRCLE

Control of perception means control of the state of an existing perception (as was seen in Chapter 2). It doesn't mean making one kind of perception into another kind. But there is another dimension to understanding control of perception: namely, understanding that we control perceptions rather than actions. In Demonstration 9-1 you will be controlling a perceptual variable, tracing a shape by moving a point of light around in two dimensions using the mouse. The mouse movements are your means of controlling the perceptual variable, but the movements themselves are not what is controlled in this task. By the time you have finished with the demonstration, you will know why we speak of controlling perceptions, not actions. Demo 9-1, Square Circle, concerns a perception of a pretty good square.

In this appendix we present some mathematical analysis of the control systems described in this book. We assume familiarity only with basic algebra and linear differential equations. In places we will use Laplace transforms to simplify the solution of linear differential equations in multiple variables. A good reference for the control theory used in this book is [Lei04].

1 THE PROPORTIONAL CONTROLLER

We shall begin with the control system demonstrated in Chapter 3, pictured in Figure 1.