William T. Powers

William T. Powers (August 29, 1926 – May 24, 2013) was an independent scholar of experimental and theoretical psychology who developed the perceptual control theory (PCT) model of behavior as the control of perception. PCT demonstrates and explains how 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, whereas in living systems the reference variable for each control loop in a control hierarchy is generated within the system, usually as a function of error output from a higher-level system or systems. 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), and corresponding control structures have been demonstrated neurophysiologically.

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