3. Perceptual Control Introduction
4. Perceptual Control and imagination
5. Hierarchic Perceptual Control
9. Degress of Freedom in the individual
10. Degrees of Freedom in the organization
11 Modes of Perception (Reprise)
Basic Principle of Psychology
All behaviour is the control of perception. Why?
- If you perceive that something is as you want it to be, you do nothing about it.
- If it is does not appear to be as you would wish, you act so that you can perceive it to be more like your wishes
- The world changes for many reasons, altering what you perceive
- There are many ways to alter the world so that your perception becomes more like your wishes.
- Your actions control your perceptions, not the other way around.
W.T. Powers: Behavior—The Control of Perception. Aldyne, 1973
The fundamental difference between Perceptual Control Theory and most other approaches is that PCT asserts that all behaviour is to control some perception. In this context, the word "perception" has a meaning somewhat wider than normal. It refers to the output of any function that uses the sensory input or other perceptions as its input. This includes imaginary perceptions, as shown in the slide "The Commander's Two Loops."
According to PCT, every controlled perception is controlled so that the perception comes to match a reference signal. All actions are for this purpose in respect (usually) of several different perceptions. But not all perceptions are controlled. At any moment almost all perceptions are not being controlled, and it may be that some perceptions are never controlled.
Feedback: Positive and Negative
The disturbance to the world alters the perception, and thus the
error. The amplified error is the output. If the output opposes the
disturbance, the error is reduced, and the perception is stabilized But if the output reinforces the disturbance, the error can grow
without limit |
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Control involves feedback. Some current perception is compared with its reference, and the resulting error signal leads to output actions. If control is to be effective, these actions should affect the world in such a way as to bring the perception closer to its reference. If they do, the feedback is said to be negative. But it is possible that the actions may increase the error, leading to stronger actions that greatly increase the error, and so on. This unfortunate situation is called positive feedback.
Error is normally caused by effects in the world known in PCT as "disturbances." A disturbance is anything that changes the perception, and thus causes error. In a negative feedback system, actions oppose disturbances, to maintain the perception at or near its reference level. The effects of a disturbance are seen only momentarily in the perception, since actions nearly exactly compensate for them.
The basic element of PCT is the Elementary Control System (ECS). The job of an ECS is to control the value of a Perceptual Signal—i.e., to keep the perceptual signal at a value specified by a Reference Signal. Most ECS connect to the outer environment through other ECSs. Only at the very periphery is the output of an ECS connected to a sensor or an effector, if then. The output of an ECS contributes to the reference signal for (possibly many) lower-level ECSs, and the sensory input of an ECS is (usually) composed of the perceptual signals from lower-level ECSs. When models are built to test aspects of the theory, it is common that the output signal goes to the same set of lower ECSs that provide the perceptual signals, but this is not intrinsic to the theory, and cannot be true in all cases. At the very least, some perceptual input comes from sensor systems that have no direct connection to muscular outputs!
Part of a simple Control network
The outputs of any ECS contribute to the reference signals of ECSs at the next lower level. The result of the perceptual input function of any ECS is provided as part of the perceptual input at the next higher level. Normally, the output and input links are connected in parallel, so that each ECS receives input from the same ones to which it sends output.
The whole control system is a network of many thousand, millions, or perhaps billions of ECSs. There are many paths through which any one ECS can affect its sensory input and thus its perceptual signal. This is captured in the adage "There are many ways to skin a cat." If one way to achieve an end is blocked, another may serve, but the perceptual signal is controlled, either way. Likewise, since the perceptual signal is a function of many inputs, there are many states in the world that allow any single perceptual signal to match its reference value. Hence, it is possible for a large number of ECSs simultaneously to control their perceptions without interfering with each other.