William T. Powers

William T. Powers (August 29, 1926 – May 24, 2013) was a medical physicist and an independent scholar of experimental and theoretical psychology[1][2][3] who developed the perceptual control theory (PCT) model of behavior as the control of perception. PCT demonstrates and explains how[4] rather than controlling their behavioral outputs, living things vary their behavior as the means of controlling their sensory inputs (perceptions). Living control systems differ from those specified by Engineering control theory (a thermostat is a simple example), for which the reference value (setpoint) for control is specified outside the system by what is called the controller,[5] whereas in living systems the reference variable for each feedback control loop in a control hierarchy[6] is generated within the system, usually as a function of error output from a higher-level system or systems.[7] Powers and his students and colleagues in diverse fields have developed many demonstrations of negative feedback control, and computer models or simulations that replicate observed and measured behavior of living systems (human and animal, individuals and groups of individuals) with a very high degree of fidelity (0.95 or better),[1] and corresponding control structures have been demonstrated neurophysiologically.[8][9]

Powers also designed the board game Trippples,[10] produced by Aladdin Industries and granted US Patent 3,820,791 in 1974[11]

Selected bibliography

  • Powers, William T. (1973). Behavior: The control of perception. Chicago: Aldine de Gruyter. ISBN 0-202-25113-6. 2nd ed. (2005) New Canaan: Benchmark Publications. Chinese tr. (2004) Guongdong Higher Learning Education Press, Guangzhou, China. ISBN 7-5361-2996-3.
  • 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 0-9647121-5-6
  • 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.


  1. Runkel, Philip J. (1990). Casting nets and testing specimens: Two grand methods of psychology. New York: Praeger. p. 103. ISBN 978-0-275-93533-7.
  2. 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, p. 9, ISBN 978-0-262-03277-3
  3. Powers, William (3 November 2017). "Northwestern University Archival and Manuscript Collections: William T. Powers Papers". Northwestern University Library. Northwestern University. Retrieved 18 May 2018.
  4. Marken, Richard S. (August 1986). "Perceptual organization of behavior: A hierarchical control model of coordinated action". Journal of Experimental Psychology: Human Perception and Performance. 12 (3): 267–276. doi:10.1037/0096-1523.12.3.267., Marken, Richard S. (2001). "Controlled variables: psychology as the center fielder views it". American Journal of Psychology. 114 (2): 259–281. CiteSeerX doi:10.2307/1423517. JSTOR 1423517., Marken, Richard S.; William T., Powers (1989), "Levels of intention in behavior", in Hershberger, Wayne (ed.), Volitional Action, Advances in psychology, 62, Amsterdam: Elsevier B.V., pp. 409–430, ISBN 978-0-444-88318-6, and the interactive demonstrations in (Powers 2008)
  5. Åström, Karl J.; Murray, Richard M. (2008). Feedback Systems: An Introduction for Scientists and Engineers (PDF). Princeton University Press. ISBN 978-0-691-13576-2.
  6. Marken, Richard S. and Powers, William T., "Levels of intention in behavior", Chapter 18 in Hershberger, Wayne A. (1989). Volitional action. Amsterdam: Elsevier Science Publishers, B.V. ISBN 9780444883186.
  7. Runkel, Philip J. (2003). People as living things. Hayward, CA: Living Control Systems Publishing. ISBN 978-0-9740155-0-7.
  8. Powers (1973:88-92).
  9. Yin, Henry H. (18 November 2014). "How Basal Ganglia Outputs Generate Behavior". Advances in Neuroscience. 2014 (768313): 1–28. doi:10.1155/2014/768313.
  10. "About William T. (Bill) Powers".
  11. US 3820791, "Board Game"
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