Perceptual control theory

William T. Powers, 1960–1973

William T. Powers's theory that behaviour is the control of perception: organisms are hierarchies of feedback loops, each acting to keep a perceived quantity at a reference value.

Perceptual control theory (PCT) was developed by the engineer William T. Powers, beginning with papers in 1960 and set out fully in Behavior: The Control of Perception (1973).

The idea

Standard psychology describes behaviour as a response to stimuli, or as planned output. Powers pointed out that in any control system, what is held constant is a sensed quantity, an input, and the output varies as needed to keep it there. A driver keeps the car in the centre of the lane (a perception) by moving the wheel in whatever way the wind and road require (behaviour). The same perception can be achieved by very different actions.

So behaviour is the control of perception. Each control loop compares a perception with a reference value and acts to reduce the difference. Loops are organised in a hierarchy: higher levels control more abstract perceptions (relationships, sequences, principles, self-image) by setting the references for lower levels.

Evidence and applications

PCT was tested with computer simulations of tracking tasks, which predicted individual human behaviour with high accuracy. It has been applied in psychotherapy (the Method of Levels, developed by Timothy Carey), in education, in social theory, and in robotics. A community of researchers continues the work through the International Association for Perceptual Control Theory.

PCT anticipates central ideas of Karl Friston’s free energy principle and active inference, which also explain action as bringing sensations in line with expectations.

Further reading

  • William T. Powers, Behavior: The Control of Perception (1973)
  • Warren Mansell (ed.), The Interdisciplinary Handbook of Perceptual Control Theory (2020)

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