User:Trevithj/sandbox

Feedback: LEDE


Feedback  is the return of information about a system or process that may effect a change in the process, for example, the regulation or optimization of performance. "Feedback" originally referred to the action of feeding the output of a process back to the input[], and "feedback" is still used in that sense in some disciplines such as control theory.

Subsequent authors defined feedback more generally in terms of circular causality. When components of a system form part of a chain of cause-and-effect that forms a circuit or loop, the system is said to "feed back" into itself.

The term "feedback" is also used as an abbreviation for:
 * Feedback signal – the embodiment of feedback information in some form: electrical, neural, mechanical, chemical etc.
 * Feedback mechanism – the action or means used to act upon feedback information
 * Feedback loop – the closed path made up of the system itself and the path that transmits the feedback about the system from its origin (for example, a sensor) to its destination (for example, an actuator).

Negative Feedback: HISTORY
Self-regulating mechanisms have existed since antiquity, and were used to maintain a constant level in the reservoirs of water clocks as early as 200 BCE. Cornelius Drebbel had built thermostatically-controlled incubators and ovens in the early 1600s, James Watt employed centrifugal governors to regulate the speed of steam engines, and James Clerk Maxwell in 1868 described "component motions" associated with these governors that lead to a decrease in a disturbance or the amplitude of an oscillation.

The general idea of feedback was well established by the 1920s, in reference to a means of boosting the gain of an electronic amplifier. Friis and Jensen described this action as "positive feedback" and made passing mention of a contrasting "negative feed-back action" in 1924. Harold Stephen Black detailed the use of negative feedback in electronic amplifiers in 1934, where he defined negative feedback as a type of coupling that reduced the gain of the amplifier, in the process greatly increasing its stability. Nyquist and Bode built on Black’s work to develop a theory of amplifier stability, but chose to define "negative" as applying to the polarity of the loop (rather than the effect on the gain) which gave rise to confusion over basic definitions.

Early researchers in the area of cybernetics generalised the idea of negative feedback to cover any goal-seeking or purposeful behavior. "All purposeful behavior may be considered to require negative feed-back. If a goal is to be attained, some signals from the goal are necessary at some time to direct the behavior."

Cybernetics pioneer Norbert Wiener helped to formalize the concepts of feedback control, defining feedback in general as "the chain of the transmission and return of information", and negative feedback as the case when: "The information fed back to the control center tends to oppose the departure of the controlled from the controlling quantity..."

While the view of feedback as any "circularity of action" helped to keep the theory simple and consistent, Ashby pointed out that it can clash with definitions in other fields that require "a more tangible connexion." "[The] practical experimenters and constructors ... want to use the word to refer, when some forward effect from P to R can be taken for granted, to the deliberate condition of some effect back from R to P by some connexion that is physically or materially evident."

Further confusion arose after BF Skinner introduced the terms positive and negative reinforcement, both of which can be considered negative feedback mechanisms in the sense that they try to minimize deviations from the desired behavior. In the context of human behaviour, Herold and Greller used the term "negative" to refer to the valence of the feedback: that is, cases where a subject receives an evaluation with an unpleasant emotional connotation. "A common theme for the 10 items [in the feedback analysis] is their valence, all representing negative feedback. Examples are being removed from a job or suffering some adverse consequence due to poor performance or receiving more or less direct indications of dissatisfaction from co-workers or the supervisor."

To reduce confusion, some authors have used alternative terms such as degenerative, self-correcting, balancing, or discrepancy-reducing in place of "negative".