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Perceptual control theory (PCT) is a model of the psychological and behavioral processes occurring within living beings, including humans. It demonstrates that animals are goal-driven, purposeful entities rather than automata repeating conditioned responses to external stimuli or computers planning commands that will produce desired actions. Behavior, in PCT, is the means by which an organism controls its perceptions; and actions are not controlled, they are varied so as to cancel the effects that unpredictable environmental disturbances would otherwise have on controlled perceptions. PCT is grounded in the principles of negative feedback but differs in important respects from engineering control theory. Numerous computer simulations of specific behavioral situations demonstrate its efficacy,[1] with extremely high correlations to observational data (0.95 or better), such as are routinely expected in physics and chemistry.

The place of purpose (intention) and causation in psychology[edit | edit source]

A tradition from Aristotle through William James recognizes that behavior is purposeful rather than merely reactive. However, the only evidence for intentions was subjective. Behaviorists following Wundt, Thorndyke, Watson, and others rejected introspective reports as data for an objective science of psychology. Only observable behavior could be admitted as data.[2]

There follows from this stance the assumption that environmental events (stimuli) cause behavioral actions (responses). This assumption persists in cognitive psychology, which interposes cognitive maps between stimulus and response, but otherwise retains the assumption of linear causation from environment to behavior.

Another, more specific reason for rejecting notions of purpose or intention was that they could not see how a goal (a state that did not yet exist) could cause the behavior that led to it.

PCT provides a model of the functioning of organisms in which purpose has objective status without recourse to introspection, and in which causation is circular around feedback loops, resolving philosophical arguments about teleology.

Methodology[edit | edit source]

The principal datum in PCT methodology is the controlled variable. The fundamental step of PCT research, the Test for controlled variables, is the slow and gentle application of disturbing influences to the state of a variable in the environment which the researcher surmises is already under control by the observed organism. It is essential not to overwhelm the organism's ability to control, since that is what is being investigated. If the organism changes its actions just so as to prevent the disturbing influence from having the expected effect on that variable, that is strong evidence that the experimental action disturbed a controlled variable. It may take a number of variations of the disturbance to isolate just which aspect of the environmental situation is under control, as perceived by the observed organism.

The controlled variable as measured by the observer corresponds to a reference value for a perception that the organism is controlling. The controlled variable is thus an objective index of the purpose or intention of those particular behavioral actions by the organism—the goal which those actions consistently work to attain despite disturbances.

Data for individuals are not aggregated for statistical analysis;[3] instead, a generative model is built which replicates the data observed for individuals with very high fidelity (0.95 or better). With two variables specified, the controlled input and the reference (a variable ′setpoint′), a properly designed control system, simulated on a digital computer, produces outputs that almost precisely oppose unpredictable disturbances to the controlled input. Further, the variance from perfect control (which would result in zero effect of the disturbance) accords well with that observed for living organisms.[4]

History[edit | edit source]

The unaffiliated scientist William T. Powers recognized that to be purposeful implies control, and that the concepts and methods of engineered control systems could be applied to biological control systems. Powers recognized further that in any control system the variable that is controlled is not the output of the system (the behavioral actions), but its input, that is, a sensed and transformed function of some state of the environment that could be affected by the control system's output. Because some of these sensed and transformed inputs appear as consciously perceived aspects of the environment, Powers labelled the controlled variable "perception". The theory came to be known as "Perceptual Control Theory" or PCT rather than "Control Theory Applied to Psychology" because control theorists often assert or assume that it is the system's output that is controlled. In PCT it is the internal representation of the state of some variable in the environment—a "perception" in everyday language—that is controlled.[5] The basic principles of PCT were first published by Powers, Clark, and MacFarland as a "general feedback theory of behavior" in 1960,[6] with credits to cybernetic authors Wiener and Ashby, and has been systematically developed since then in the research community that has gathered around it. Initially, it received little general recognition, but is now better known.

Example[edit | edit source]

A simple negative feedback control system is a cruise control system for a car. A cruise control system has a sensor which "perceives" speed as the rate of spin of the drive shaft directly connected to the wheels. It also has a driver-adjustable 'goal' specifying a particular speed. The sensed speed is continuously compared against the specified speed by a device (called a "comparator") which subtracts the currently-sensed input value from the stored goal value. The difference (the error signal) determines the throttle setting (the accelerator depression), so that the engine output is continuously varied to counter variations in the speed of the car. This type of classical negative feedback control was worked out by engineers in the 1930s and 1940s.

If the speed of the car starts to drop below the goal-speed, for example when climbing a hill, the small increase in the error signal, amplified, causes engine output to increase, which keeps the error very nearly at zero. If the speed exceeds the goal, e.g. when going down a hill, the engine is throttled back so as to act as a brake, so again the speed is kept from departing more than a barely-detectable amount from the goal speed (brakes are needed only if the hill is too steep). The result is that the cruise control system maintains a speed close to the goal as the car goes up and down hills, and as other disturbances such as wind affect the car's speed. This is all done without any advance planning of specific actions, and without any blind reactions to stimuli.

The same principles of negative feedback control (including the ability to nullify effects of unpredictable external or internal disturbances) apply to living control systems. The thesis of PCT is that animals and people do not control their behavior; rather, they vary their behavior as their means for controlling their perceptions, with or without external disturbances. This directly contradicts the historical and still widespread assumption that behavior is the final result of stimulus inputs or cognitive plans.

A hierarchy of control[edit | edit source]

Perceptions, in PCT, are constructed and controlled in a hierarchy of levels. For example, visual perception of an object is constructed from differences in light intensity or differences in sensations such as color at its edges. Controlling the shape or location of the object requires altering the perceptions of sensations or intensities (which are controlled by lower-level systems). This organizing principle is applied at all levels, up to the most abstract philosophical and theoretical constructs.

The Russian physiologist Nicolas Bernstein[7] independently came to the same conclusion that behavior has to be multiordinal—organized hierarchically, in layers. A simple problem led to this conclusion at about the same time both in PCT and in Bernstein's work. The spinal reflexes act to stabilize limbs against disturbances. Why do they not prevent centers higher in the brain from using those limbs to carry out behavior? Since the brain obviously does use the spinal systems in producing behavior, there must be a principle that allows the higher systems to operate by incorporating the reflexes, not just by overcoming them or turning them off. The answer is that the reference value (setpoint) for a spinal reflex is not static; rather, it is varied by higher-level systems as their means of moving the limbs. This principle applies to higher feedback loops, as each loop presents the same problem to subsystems above it.

Whereas an engineered control system has a reference value or setpoint adjusted by some external agency, the reference value for a biological control system cannot be set in this way. The setpoint must come from some internal process. If there is a way for behavior to affect it, any perception may be brought to the state momentarily specified by higher levels and then be maintained in that state against unpredictable disturbances. In a hierarchy of control systems, higher levels adjust the goals of lower levels as their means of approaching their own goals set by still-higher systems. This has important consequences for any proposed external control of an autonomous living control system (organism). At the highest level, reference values (goals) are set by heredity or adaptive processes.

Reorganization in evolution, development, and learning[edit | edit source]

If an organism controls inappropriate perceptions or controls some perceptions to inappropriate values, it is less likely to bring progeny to maturity, and may die. Consequently, by Natural Selection successive generations of organisms evolve so that they control those perceptions that, when controlled with appropriate setpoints, tend to maintain critical internal variables at optimal levels, or at least within non-lethal limits. Powers called these critical internal variables "intrinsic variables" (Ashby's "essential variables").

The mechanism that influences the development of structures of perceptions to be controlled is termed "reorganization", a process within the individual organism that is subject to natural selection just as is the evolved structure of individuals within a species.[8]

This "reorganization system" is proposed to be part of the inherited structure of the organism. It changes the underlying parameters and connectivity of the control hierarchy in a random-walk manner. There is a basic continuous rate of change in intrinsic variables which proceeds at a speed set by the total error (and stops at zero error), punctuated by random changes in direction in a hyperspace with as many dimensions as there are critical variables. This is a more or less direct adaptation of Ashby's "homeostat", first adopted into PCT in the 1960 paper and then changed to use E. coli's method of navigating up gradients of nutrients, as described by Koshland (1980).[9]

Reorganization may occur at any level when loss of control at that level causes intrinsic (essential) variables to deviate from genetically-determined set points. This is the basic mechanism that is involved in trial-and-error learning, which leads to the acquisition of more systematic kinds of learning processes.[10]

Conflict[edit | edit source]

In a hierarchy of interacting control systems, different systems at one level can send conflicting goals to one lower system. When two systems are specifying different goals for the same lower-level variable, they are in conflict. Protracted conflict is experienced by human beings as many forms of psychological distress such as anxiety, obsession, depression, confusion, and vacillation. Severe conflict prevents the affected systems from being able to control, effectively destroying their function for the organism.

Higher level control systems often are able to use known strategies (which are themselves acquired through prior reorganizations) to seek perceptions that don't produce the conflict. Normally, this takes place without notice. If the conflict persists and systematic "problem solving" by higher systems fails, the reorganization system may modify existing systems until they bypass the conflict or until they produce new reference signals (goals) that are not in conflict at lower levels.

When reorganization results in an arrangement that reduces or eliminates the error that is driving it, the process of reorganization slows or stops with the new organization in place. (This replaces the concept of reinforcement learning.) New means of controlling the perceptions involved, and indeed new perceptual constructs subject to control, may also result from reorganization. In simplest terms, the reorganization process varies things until something works, at which point we say that the organism has learned. When done in the right way, this method can be surprisingly efficient in simulations.

PCT and psychotherapy: the Method of Levels (MOL)[edit | edit source]

The reorganization concept has led to a method of psychotherapy called the Method of Levels (MOL) currently being tested in England, the United States, and Australia.

Current situation and prospects[edit | edit source]

Perceptual control theory currently proposes a hierarchy of 11 levels of perceptions controlled by systems in the human mind and neural architecture. These are: intensity, sensation, configuration, transition, event, relationship, category, sequence, program, principle, and system concept. Diverse perceptual signals at a lower level (e.g. visual perceptions of intensities) are combined in an input function to construct a single perception at the higher level (e.g. visual perception of a color sensation). The perceptions that are constructed and controlled at the lower levels are passed along as the perceptual inputs at the higher levels. The higher levels in turn control by telling the lower levels what to perceive: that is, they adjust the reference levels (goals) of the lower levels. [11]

While many computer demonstrations of principles have been developed, the proposed higher levels are difficult to model because too little is known about how the brain works at these levels. Isolated higher-level control processes can be investigated, but models of an extensive hierarchy of control are still only conceptual, or at best rudimentary.

Perceptual Control Theory has not been widely accepted in mainstream psychology, but has been effectively used in a considerable range of domains[12] in human factors,[13] clinical psychology, and psychotherapy (the "Method of Levels"), and it has formed the conceptual foundation for the reference model used by a succession of NATO research study groups.[14] It is the basis for a considerable body of research in sociology.[15] It is being taught in several universities worldwide and is the subject of a number of PhD degrees.

References[edit | edit source]

  • Cziko, Gary. (1995). Without miracles: Universal selection theory and the second Darwinian revolution. Cambridge, MA: MIT Press (A Bradford Book). ISBN 0-262-53147-X (Online)
  • Cziko, Gary. (2000). The things we do: Using the lessons of Bernard and Darwin to understand the what, how, and why of our behavior. Cambridge, MA: MIT Press (A Bradford Book). ISBN 0-262-03277-5 (Online)
  • Marken, Richard S. (1992) Mind readings: Experimental studies of purpose. Benchmark Publications: New Canaan, CT.
  • Marken, Richard S. (2002) More mind readings: Methods and models in the study of purpose. Chapel Hill, NC: New View. ISBN 0-944337-43-0
  • Powers, William T. (1973). Behavior: The control of perception. Chicago: Aldine de Gruyter. ISBN 0-202-25113-6. [2nd exp. ed. = Powers (2005)].
  • Powers, William T. (1989). Living control systems. [Selected papers 1960-1988.] New Canaan, CT: Benchmark Publications. ISBN 0-9647121-3-X.
  • Powers, William T. (1992). Living control systems II. [Selected papers 1959-1990.] New Canaan, CT: Benchmark Publications.
  • Powers, William T. (1998). Making sense of behavior: The meaning of control. New Canaan, CT: Benchmark Publications. ISBN 0964712156.
  • Powers, William T. (2005). Behavior: The control of perception. New Canaan: Benchmark Publications. ISBN 0−9647121−7−2. [2nd exp. ed. of Powers (1973). Chinese tr. (2004) Guongdong Higher Learning Education Press, Guangzhou, China. ISBN 7-5361-2996-3.]
  • Powers, William T. (2008). Living Control Systems III: The fact of control. [Mathematical appendix by Dr. Richard Kennaway. Includes computer programs for the reader to demonstrate and experimentally test the theory.] New Canaan, CT: Benchmark Publications. ISBN 978-0-9647121-8-8.
  • Powers, William T. and Runkel, Philip J. 2011. Dialogues concerning two life sciences: Word pictures and correlations vs. working models. Hayward, CA: Living Control Systems Publishing. ISBN 0−9740155−1−2.
  • Robertson, R.J. & Powers, W.T. (1990). Introduction to modern psychology: the control-theory view. Gravel Switch, KY: Control Systems Group.
  • Robertson, R. J., Goldstein, D.M., Mermel, M., & Musgrave, M. (1999). Testing the self as a control system: Theoretical and methodological issues. Int. J. Human-Computer Studies, 50, 571-580.
  • Runkel, Philip J[ulian]. 1990. Casting Nets and Testing Specimens: Two Grand Methods of Psychology. New York: Praeger. ISBN 0275935337. [Repr. 2007, Haywood, CA: Living Control Systems Publishing, ISBN 0974015571.]
  • Runkel, Philip J[ulian]. (2003). People as living things. Hayward, CA: Living Control Systems Publishing. ISBN 0-9740155-0-4

Sociology[edit | edit source]

  • (1994). Perceptual Control and Social Power. Sociological Perspectives 37: 461–496.
  • (2004). The Collective Control of Perceptions: Constructing Order from Conflict. International Journal of Human-Computer Studies 60: 65–99.
  • McClelland, Kent and Thomas J. Fararo, eds. (2006). Purpose, Meaning, and Action: Control Systems Theories in Sociology. New York: Palgrave Macmillan.
  • McPhail, Clark. 1991. The Myth of the Madding Crowd. New York: Aldine de Gruyter.

External links[edit | edit source]

Notes[edit | edit source]

  1. For example in this collection.
  2. "The behaviorist asks: Why don't we make what we can observe the real field of psychology? Let us limit ourselves to things that can be observed, and formulate laws concerning only those things. Now what can we observe? We can observe behavior—what the organism does or says." Watson, J.B. (1924). Behaviorism. New York: People's Institute Publishing Company.
  3. See Runkel 1990 on the limitations of statistical methods and the value of data for individuals.
  4. Powers (2008).
  5. For additional information about the history of PCT, see interviews with William T. Powers in the "Audio" section under "External links".
  6. Powers. W.T., Clark, R.K., and McFarland, R.L. (1960). "A general feedback theory of human behavior". Perceptual and Motor Skills 11, 71-88 (Part 1) and 309-323 (Part 2). [Reprinted in General Systems V, 63-83, 1960. Partial reprint in Smith, A. G., Communication and Culture, New York: Holt, Rinehart, and Winston (1966).]
  7. Bernstein, Nicolas. 1967. Coordination and regulation of movements. New York: Pergamon Press.
  8. For an introduction, see the Byte articles on robotics and the article on the origins of purpose in this collection.
  9. Koshland, Daniel. (1980). Bacterial chemotaxis as a model behavioral system. New York: Raven Press.
  10. Cziko, Gary (1995). Without Miracles..
  11. Powers, William T. (1973). Behavior: The Control of Perception.Cziko, Gary (1995). Without Miracles..
  12. The June 1999 Issue of The International Journal of Human-Computer Studies contained papers ranging from tracking through cockpit layout to self-image and crowd dynamics.
  13. PCT lies at the foundation of Component-Based Usability Testing.
  14. Reports of these groups are available from the NATO Research and Technology Administration publications page <> under the titles RTO-TR-030, RTO-TR-IST-021, and RTO-TR-IST-059.
  15. For example: McClelland, Kent A. and Thomas J. Fararo, eds. 2006, Purpose, Meaning and Action: Control Systems Theories in Sociology, New York: Palgrave Macmillan. (McClelland is co-author of Chapter 1, "Control Systems Thinking in Sociological Theory," and author of Chapter 2, "Understanding Collective Control Processes."). McClelland, Kent, 2004, "Collective Control of Perception: Constructing Order from Conflict", International Journal of Human-Computer Studies 60:65-99. McPhail, Clark. 1991, The myth of the madding crowd New York: Aldine de Gruyter.
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