feedback

feedback arrangement for the automatic self-regulation of an electrical, mechanical, or biological system by returning part of its output as input. A simple example of feedback is provided by a governor on an engine; if the speed of the engine exceeds a preset limit, the governor reduces the supply of fuel, thus decreasing the speed. Electronic control systems employ feedback extensively. In voltage and current regulators, part of the output is used as a control input, providing self-regulation. For example, if the output becomes too great, it acts through the feedback loop to reduce itself. The use of feedback as the fundamental control mechanism for machinery occurs in automation . Living organisms possess feedback control systems of great complexity. For example, when the hand reaches for an object, information about its position is continuously fed back to the brain, both by the eyes and by position-sensing nerves in the arm; the brain uses the position information to guide the hand to the object. Such feedback can be termed voluntary, since it is to some extent under conscious control. Automatic, involuntary feedback is constantly taking place as well, controlling processes such as respiration, circulation, digestion, and maintenance of body temperature. Feedback is one of the main concerns of cybernetics . See control systems . See also biofeedback .

feedback The use of part of the output of a system to control its performance. In positive feedback, the output is used to enhance the input; in negative feedback, the output is used to reduce the input. Many biological processes rely on negative feedback. As the population of a species expands, so its food supply per individual is diminished; the result is that the population then begins to fall. Many biochemical processes are controlled by feedback inhibition. Feedback mechanisms play an important role in maintaining a state of equilibrium within an organism (see homeostasis).

feedback Response to operator input that indicates that the input has been understood and the desired action accomplished. See also acknowledgment, prompt, echoing.