Frequently Asked Questions about Perceptual Control Theory

Please see our overview page for the answer to this important question.

It's different because of what it assumes behavior to be.

Other theories of behavior see behavior as caused output: human behaviors such as talking and writing are seen as outputs that are caused by processes in a person's brain or by stimuli in a person's environment.

PCT, on the other hand, sees behavior as controlled input. Behaviors such as talking and writing are seen as the observable consequences of actions (vocal and hand movements, respectively) aimed at producing intended inputs (sounds, graphical patterns).

While other theories view behavior as mechanical and responsive, PCT views behavior as goal directed and purposeful. PCT is a theory that explains how purposeful behavior works. The basic process that underlies purposeful behavior is closed loop negative feedback control. Control involves the production of consistent results in the face of disturbances that would otherwise prevent those results from repeating. For example, control is involved when you consistently write your name in the face of disturbances, such as differences in the pen and your orientation to the paper on each occasion.

What is controlled in purposeful behavior, according to PCT, is not the outputs that produce the intended inputs but, rather, the intended results themselves. These intended results exist as input perceptions for the actor. So talking -- producing words -- involves control of the perception of the words we are producing with our vocal movements; writing involves control of the perception of the graphical patterns we are producing with our writing movements. Purposeful behavior, according to PCT, is the control of various perceptions, such as the perceptions of spoken and written words.

PCT informs all fields that involve the study of living systems: psychology, sociology, political science, economics, biology, neuroscience, physiology, etc. PCT can also inform fields of study aimed at building artifacts that imitate the behavior of living systems, such as robotics, artificial intelligence and control engineering.

Anyone interested in a scientific understanding of the behavior of living organisms in general and human beings in particular.

Our interests include a whole range of fields, from psychology, to cybernetics and artificial intelligence, education, counseling, and more.

"Perception" in PCT refers to the world as we experience it. The dimensions of our experience -- the colors, shapes, movements, relationships and so on that we experience as aspect of the world we live in -- are called perceptual variables. Perceptual variables are what we control. Perceptual variables, such as the color of a house, can have many different possible values, such as white, yellow, green, etc. Control refers to the process of bringing a perceptual variable to a pre-selected state and maintaining it in that state, protected from disturbances. When you decide to paint your house white and then do it (or have someone do it for you) you are controlling the perceived color of your house.

Because there is no other word that describes the particular phenomenon explained by PCT -- the phenomenon of purposeful behavior or control -- as well. But the word control does not always have negative connotations. Control is often a very good thing.

Being in control of your own life is good; being out of control is a sign of mental illness. Athletes like to have control of their bodies. Teachers like to have control of their classes.

Control is only considered bad when other people try to control you. PCT explains why attempts to control other people lead to problems.

In the physical sciences, the main goal of research is to find functional relationships between variables, such as the relationship between the time it takes for a ball to move a fixed distance down an inclined plane and the inclination of the plane. Physical scientists do research by manipulating variables -- the independent variables -- and measuring the effect of this manipulation on other variables -- the dependent variables.

This approach to research was adopted by the behavioral sciences under the assumption that the goal of the behavioral sciences was the same as that of the physical sciences: to determine functional relationships between variables. But PCT shows that the physical science approach to research produces misleading results when used to study closed loop control systems.

Research in the behavioral sciences should be aimed at determining what perceptual variables living systems control. This kind of research is done using a method based on control engineering called The Test for the Controlled Variable (or, simply, The Test).

Here are two descriptions and demonstrations of The Test from another web site (Rick Marken's MindReadings site). They should work for you if you have a Java-enabled web browser.

• The Test for the Controlled Variable
• Detection of Purpose Demo

Traditional approaches to research in the behavioral sciences have relied mainly on qualitative, verbal theorizing as the basis of research. PCT emphasizes the use of quantitative, computer models as the basis of research. Computer models allow the researcher to make precise, quantitative predictions, making for more definitive empirical tests of the theory.

PCT shows how efforts to control other people or even oneself lead to conflict. And yet PCT also shows that people are controllers so they can't help wanting to control others and themselves. So, according to PCT, conflict is a constant in inter- and intra-personal relations.

Helping professionals can contribute to a better understanding of how PCT applies to solving human problems by exploring methods for helping people do two things: 1) solve the conflicts they have and 2) prevent or reduce the conflicts that might occur in the future.

A theoretical model is a quantitative description of the processes that are assumed to produce an observed phenomenon. The PCT model is a quantitative description of the processes that are thought to produce the phenomenon of purposive behavior.

Most PCT models are implemented as computer programs, many of which are available as demonstrations on the web. PCT models have been built that imitate various purposeful behaviors with great accuracy. For example, you can find models on the net that imitate human tracking behavior, broom balancing, baseball catching and social interaction.

Click here to see some available computer demos

If you know about differential equations, the basic idea is rather simple.

A control loop can typically be described by two equations: one describing the relationship between input and output and the other describing the relationship between output and input.

A computer program represents these relationships as differential equations, where input and output variables change slightly on each iteration of the program. The result is a dynamically changing set of variables that imitates the continuous changes that occur in a real control loop over time.

There will soon be a book out on how to construct computer simulations of control phenomena.

Click here to see some available computer demos