Overview: What is Perceptual Control Theory?

What it Is

Perceptual control theory (PCT) is a theory of behavior with wide applications in fields ranging from psychology and sociology to robotics, biology, and engineering.

Perceptual control theory is "a model of how a human being must be internally organized to accomplish this process called controlling. It is a technical theory that involves neurology and physiology and mathematical theories of control systems developed some 60 years ago by engineers" (from The Nature of PCT).

For an overview of how PCT works and the basic terminology of PCT, see William Powers' The Nature of PCT, a talk given by William Powers and presented in transcript on this site.

The definitive statement of PCT is found in the 1973 book, Behavior: The Control of Perception, by William Powers.

A perhaps more friendly, less mathematical description of the theory is in Making Sense of Behavior (Powers, 1998). More about these books is on our Explanations and Demos: Getting Started with PCT page.

What It Does

Stated broadly, PCT explains how entities control what happens to them. It explains the relationships between actions and goals, perceptions and actions, and perceptions and reality, and it does so within a single, testable concept of how living systems work.

PCT says that:

• Behavior is controlled input
• Organisms do not produce behavior by computing output. Instead, they produce behavior by comparing inputs with desired inputs, and using the difference to drive output
• Organisms do not "respond to stimuli" rather they control input variables
• 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).
• Behavior is goal directed and purposeful, not mechanical and responsive

PCT focuses on how we look at and experience things, and the way these perceptions are compared with experiences we want. The difference produces action and physiology. Thus PCT explains how thoughts become actions, feelings and results, and its principles can be applied to any activity involving human experience.

PCT has been modeled with several freely available computer software demos.

How It's Different

PCT stands in contrast to the stimulus-response model of behavior associated with B. F. Skinner, and to the cognitive science model. These older models attempt to explain behavior either do not recognize or do not clearly understand control. Behavior is neither just caused by stimuli in the environment nor is it blind execution of internal plans. Behavior is not an end result. It is an integral part of the closed loop process which controls perception.

Why It's Exciting