William T. Powers

29 August 1926, Salem, Oregon, United States – 24 May 2013, Lafayette, Colorado, United States (aged 86)

American engineer and independent scientist who developed perceptual control theory: the idea that living things act to control what they perceive, not what they do.

Life

Powers trained as an electronics technician in the US Navy during the Second World War and then studied physics at Northwestern University. He worked as an engineer in medical physics and on astronomical instruments in Chicago, while developing his theory of behaviour largely outside academic institutions. Later he lived in Colorado, first in Durango and then in Lafayette, where he died at 86. He remained active in the community that grew around his theory until the end of his life.

Influences

Reading Norbert Wiener’s cybernetics alongside his own experience with control systems led Powers to notice something psychologists had missed. In an engineering control loop, the variable that is held constant is the system’s input, a sensed quantity, while its output varies to achieve this.

Contributions

In papers from 1960 with R. K. Clark and R. L. McFarland, and then in Behavior: The Control of Perception (1973), Powers argued that organisms are hierarchies of negative feedback loops, each controlling a perception against an internal reference. Behaviour is the means by which perceptions are controlled, so it varies from moment to moment, while the perceptual outcome stays stable. Higher levels set the references for lower ones, from muscle tension up to principles and system concepts.

The theory, perceptual control theory (PCT), was supported by computer simulations and tracking experiments that predicted human behaviour with very high accuracy. It has been applied in psychotherapy (the Method of Levels), education and robotics.

Why it matters today

PCT shares its central idea with active inference: organisms act to make their senses match their expectations. It offers a clear account of why people resist pressure to change behaviour, because they are defending perceptions that matter to them.

Further reading

  • William T. Powers, Behavior: The Control of Perception (1973)
  • William T. Powers, Making Sense of Behavior (1998)
  • Warren Mansell (ed.), The Interdisciplinary Handbook of Perceptual Control Theory (2020)

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