|
Perceptual Control Theory (PCT) of William T. Powers
Basic Ideas:
Perceptual Control Theory (PCT) of William T. Powers dates back to 1973 and describes
behavior as a control system making continual adjustments based upon perceptions (feedback) from
the environment. Attempts to first present the attendant jargon (such as "disturbances" and "reference
signals") for explanation will likely lose most folks, but Powers has a simple example which clearly
shows the attributes of a control system:
"... We say, commonly, that a driver controls the path of a car by steering it. ... If something tends to
disturb the path of the car, like a crosswind, will the driver produce an action that opposes the effect of
the crosswind on the path of the car? Definitely yes. This is a true example of control as we use the
term in PCT."
(Powers, 1998).
For Powers, staying in the middle of the highway lane would be the driver's internal "reference signal".
That is, the perception of the middle of the road is what the driver wants to see. Any deviation from
this "picture" would be, again in Powers' terms, a disturbance. Whether the car hits some ice and
begins sliding toward the shoulder or a sudden gust of wind pushes the car to the left or right, the
perceived image through the windshield will suddenly no longer match the "reference signal" (driving
down the middle of the lane). Given the disturbance, the driver immediately tries to counteract the
disturbance by steering opposite to the unwanted drifiting. If sliding right, the driver steers left. If
veering left, the driver steers right. In the case of the highway altering its image such as when it curves
left or right, the driver will again alter steering behavior to keep the car running down the middle of the
road. In both cases, steering either against the sliding or with the curving, the driver is monitoring and
altering behavior to keep the car such that the desired perception, or what he wants to see, is always
maintained. And the driver wants to see the middle of the lane in front of the car. This image is the
"reference signal" of the driver, and the driver is a "control system" under constant vigilence to
counteract disturbances to this "reference signal".
Theory Roots:
Powers gives credit for the origin of his ideas to work by W. Ross Ashby and Norbert Wiener
in the 1950s as well as to the development of "control system" concepts in the 1940s. The idea of
all behavior being acts of control can be traced at least back to B.F. Skinner in the the early 1970s and
perhaps even earlier to others. But credit must also be given to Walter Cannon who, in the early 1930s,
coined the term "homeostasis" to discribe the body and mind's attempt to maintain a stable internal
state.
"... the sympathetic nervous system acts to modify and adjust conditions in the body so as to
preserve constancy and stability."
(Cannon, 1932. pg. 37)
Importance:
Perceptual Control Theory (PCT) by itself may be just another competing theory of behavior
and mind, but when underlying neurobiological mechanisms are recognized and compared, PCT becomes
very compelling. Specifially, it is well established that the hypothalamus acts as a control system. Only
when disturbances occur to its biochemical equilibrium does it alter the mind and behavior until the
chemical imbalance is corrected.
"The main function of the hypothalamus is homeostasis, or maintaining the
body's status quo. ... Ultimately, the hypothalamus can control every
endocrine gland in the body, and alter blood pressure (through vasopressin
and vasoconstriction), body temperature, metabolism (through TSH), and
adrenaline levels (through ACTH)."
(Molavi, et al., 1997. pg. 1,2)
|
