- What is Perceptual Control Theory (PCT)?
Please see our overview page for the
answer to this important question.
- How is PCT different from from other theories of behavior?
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
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
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
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.
- What fields of study can be informed by PCT?
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
- Who should be interested in PCT?
Anyone interested in a scientific understanding of the behavior
of living organisms in general and human beings in particular.
interests include a whole range of fields, from psychology, to
cybernetics and artificial intelligence, education, counseling, and
- What are the meanings of "perceptual" and "control" in PCT?
"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.
- Why use the word "control" when it has negative connotations?
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
- What is the relationship between research methods in the physical and behavioral sciences?
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.
- How does modeling with PCT differ from traditional approaches to research
in the behavioral sciences?
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.
- How does PCT inform the field of applied psychology? How can
helping professionals contribute to the understanding of PCT in
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
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.
- What is a theoretical model?
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
Click here to see some available computer demos
- One of the ways in which PCT research is being done is
through computer simulations. How are these experiments
If you know about differential equations, the basic idea is
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
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