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"...'feedback' exists between two parts when each affects the other..."[1](p53)


Feedback is also a synonym for:

  • Feedback signal - the measurement of the actual level of the parameter of interest.
  • Feedback mechanism - the action or means used to subsequently modify the gap.
  • Feedback loop - the complete causal path that leads from the initial detection of the gap to the subsequent modification of the gap.



The verb phrase "to feed back", in the sense of returning to an earlier position in a mechanical process, was in use in the US by the 1860s,[3][4] and in 1909, Nobel laureate Karl Ferdinand Braun used the term "feed-back" as a noun to refer to (undesired) coupling between components of an electronic circuit.[5]

By the end of 1912, researchers using early electronic amplifiers (audions) had discovered that deliberately coupling part of the output signal back to the input circuit would boost the amplification (through regeneration), but would also cause the audion to howl or sing.[6] This action of feeding back of the signal from output to input gave rise to the use of the term "feedback" as a distinct word by 1920.[6]


"[Practical experimenters] object to the mathematician's definition, pointing out that this would force them to say that feedback was present in the ordinary pendulum ... between its position and its momentum—a 'feedback' that, from the practical point of view, is somewhat mystical. To this the mathematician retorts that if feedback is to be considered present only when there is an actual wire or nerve to represent it, then the theory becomes chaotic and riddled with irrelevancies."[1](p54)



Feedback is commonly divided into two types—usually termed positive and negative. The terms can be applied in two contexts:


The two contexts may cause confusion, such as when an incentive (reward) is used to boost poor performance (narrow a gap). Referring to context 1, some authors use alternative terms, replacing 'positive/negative' with self-reinforcing/self-correcting,[9] reinforcing/balancing,[10] discrepancy-enhancing/discrepancy-reducing[11] or regenerative/degenerative[12] respectively. And within context 2, some authors advocate describing the action or effect as positive/negative reinforcement or punishment rather than feedback.[7][13] Yet even within a single context an example of feedback can be called either positive or negative, depending on how values are measured or referenced.[14] This confusion may arise because feedback can be used for either informational or motivational purposes, and often has both a qualitative and a quantitative component. As Connellan and Zemke (1993) put it:

"Quantitative feedback tells us how much and how many. Qualitative feedback tells us how good, bad or indifferent."[15](p102)

The terms "positive/negative" were first applied to feedback prior to WWII. The idea of positive feedback was already current in the 1920s with the introduction of the regenerative circuit.[16] Friis and Jensen (1924) described regeneration in a set of electronic amplifiers as a case where the "feed-back" action is positive in contrast to negative feed-back action, which they mention only in passing.[17] Harold Stephen Black's classic 1934 paper first details the use of negative feedback in electronic amplifiers. According to Black:












Hypothalamo-pituitary-adrenal and gonadal axis is largely controlled by positive and negative feedback, much of which is still unknown.


Climate science[edit]


Computer Science[edit]

Recursion is a computer programming technique whereby a function is defined so as to invoke itself, or a data structure is defined by reference to itself. This allows an elegant solution to problems such as searching a tree or calculating factorials.

Control theory[edit]



Mechanical engineering[edit]






Electronic engineering[edit]

The simplest form of a feedback amplifier can be represented by the ideal block diagram.[25]

The use of feedback is widespread in the design of electronic amplifiers, oscillators, and logic circuit elements. Electronic feedback systems are also very commonly used to control mechanical, thermal and other physical processes.

If the signal is inverted on its way round the control loop, the system is said to have negative feedback; otherwise, the feedback is said to be positive. Negative feedback is often deliberately introduced to increase the stability and accuracy of a system by correcting unwanted changes. This scheme can fail if the input changes faster than the system can respond to it. When this happens, the lag in arrival of the correcting signal can result in over-correction, causing the output to oscillate or "hunt".[26] While often an unwanted consequence of system behaviour, this effect is used deliberately in electronic oscillators.

Harry Nyquist contributed the Nyquist plot for assessing the stability of feedback systems. An easier assessment, but less general, is based upon gain margin and phase margin using Bode plots (contributed by Hendrik Bode). Design to ensure stability often involves frequency compensation, one method of compensation being pole splitting.


Negative feedback loops
When the fed-back output signal is out of phase with the input signal. This occurs when the fed-back signal is anywhere from 90° to 270° with respect to the input signal. Negative feedback is generally used to correct output errors or to lower device output gain to a pre-determined level. In feedback amplifiers, this correction is generally for waveform distortion reduction or to establish a specified gain level. A general expression for the gain of a negative feedback amplifier is the asymptotic gain model.
Positive feedback loops


Software engineering and computing systems[edit]

Feedback loops provide generic mechanisms for controlling the running, maintenance, and evolution of software and computing systems.[28] Feedback-loops are important models in the engineering of adaptive software, as they define the behaviour of the interactions among the control elements over the adaptation process, to guarantee system properties at run-time. Feedback loops and foundations of control theory have been successfully applied to computing systems.[29] In particular, they have been applied to the development of products such as IBM's Universal Database server and IBM Tivoli. From a software perspective, the autonomic (MAPE, monitor analyze plan execute) loop proposed by researchers of IBM is another valuable contribution to the application of feedback loops to the control of dynamic properties and the design and evolution of autonomic software systems.[30][31]

Social sciences[edit]

A feedback loop to control human behaviour involves four distinct stages.[32]

  1. Evidence. A behaviour must be measured, captured, and data stored.
  2. Relevance. The information must be relayed to the individual, not in the raw-data form in it was captured in, but in a context that makes it emotionally resonant.
  3. Consequence. The information must illuminate one or more paths ahead.
  4. Action. There must be a clear moment when the individual can recalibrate a behavior, make a choice, and act. Then that action is measured, and the feedback loop can run once more, every action stimulating new behaviors that inch the individual closer to their goals.

Reflexive feedback[edit]

A sociological concept that states a feedback association is created within a certain relationship whereby the subject/object that delivers a stimulus to a second subject/object, receives the stimulus back in response. This first impulse is reflected back and forth repeatedly.

Economics and finance[edit]





World-system development[edit]

The hyperbolic growth of the world population observed till the 1970s has recently been correlated to a non-linear second-order positive feedback between the demographic growth and technological development that can be spelled out as follows: technological growth—increase in the carrying capacity of land for people—demographic growth—more people—more potential inventors—acceleration of technological growth—accelerating growth of the carrying capacity—the faster population growth—accelerating growth of the number of potential inventors—faster technological growth—hence, the faster growth of the Earth's carrying capacity for people, and so on.[33]


In the majority of universities, teachers decide learning objectives and feedbacks to students.[34] Learners have different conceptions of learning activities and preconceptions about hierarchy in education. Some may look up to instructors as experts in the field and take to heart most of the things instructors say. This is the subject of study in the field of "formative feedback" or "formative assessment".

Types of reinforcement that operate in student assessment[35]
Reinforcement Example
Confirmation Your answer was correct.
Corrective Your answer was incorrect. The correct answer was Jefferson.
Explanatory Your answer was incorrect because Carter was from Georgia; only Jefferson called Virginia home.
Elaborative Your answer, Jefferson, was correct. The University of Virginia, a campus rich with Jeffersonian architecture and writings, is sometimes referred to as "Mr. Jefferson's University".



Examples of feedback in government are:

Email administration[edit]

A mechanism to alert the purported sender of an email with information about the email.

In organizations[edit]

As an organization seeks to improve its performance, feedback helps it to make required adjustments. Feedback motivates many people in the work place. People who receive negative or positive feedback must decide how to apply it to their job. Joseph Folkman says that to find the greatest level of success in an organization, working with other people, a person should learn how to accept any kind of feedback, analyze it in the most constructive manner possible, and use it to further impact future decision making.[37]

Sterman (2000, p 14) makes the point that the use of the term feedback in organizations can sometimes be misleading.

In common parlance the term "feedback" has come to serve as a euphemism for criticizing others, as in "the boss gave me feedback on my presentation." This use of feedback is not what we mean in system dynamics. Further, "positive feedback" does not mean "praise" and "negative feedback" does not mean "criticism". Positive feedback denotes a self-reinforcing process, and negative feedback denotes a self-correcting one. ... Telling someone your opinion does not constitute feedback unless they act on your suggestions and thus lead you to revise your view.[10]

Examples of feedback in organizations:

In Psychology[edit]

One application of feedback in psychology, education, and organizations is feedback intervention; defined as "actions taken by (an) external agent(s) to provide information regarding some aspect(s) of one's task performance."[38] Despite common beliefs that such feedback is typically effective, Kluger & DeNisi (1996) reported a meta-analysis that showed that in 38% of the experiments published between 1905 and 1992, feedback caused a decline in performance.[38] Moreover, the decline in performance was not related to whether the feedback was positive or negative (i.e., encouraging or critical). This result was explained with Higgins' self-discrepancy theory. Specifically, positive feedback seems to improve motivation and performance when people are promotion-focused (doing things out of a desire; working on a task requiring creativity.) Whereas negative feedback improves performance when people are prevention-focused (doing things out of an obligation; working on a task requiring vigilance.)[39]

See also[edit]


  1. ^ a b W. Ross Ashby, "An introduction to cybernetics", Chapman & Hall, London, 1956. - Internet (1999)
  6. ^ a b Stuart Bennett (1979). A history of control engineering, 1800-1930. Stevenage; New York: Peregrinus for the Institution of Electrical Engineers. ISBN 0-906048-07-9.  [2]
  7. ^ a b c Arkalgud Ramaprasad, "On The Definition of Feedback", Behavioral Science, Volume 28, Issue 1. 1983. Online PDF last accessed 16 March 2012.
  10. ^ a b John D.Sterman, Business Dynamics: Systems Thinking and Modeling for a Complex World McGraw Hill/Irwin, 2000. ISBN 978-0-07-238915-9
  16. ^ a b David A. Mindell (2002). Between Human and Machine : Feedback, Control, and Computing before Cybernetics.. Baltimore, MD, USA: Johns Hopkins University Press. 
  17. ^ Friis,H.T., and A.G.Jensen. "High Frequency Amplifiers" Bell System Technical Journal 3 (April 1924):181-205.
  18. ^ H.S. Black, "Stabilized feed-back amplifiers", Electrical Engineering, vol. 53, pp. 114–120, Jan. 1934.
  19. ^ a b Maxwell, James Clerk (1868). On Governors 16. Proceedings of the Royal Society of London. pp. 270–283. 
  23. ^ Araki, M., PID Control 
  24. ^ Minorsky, Nicolas (1922). "Directional stability of automatically steered bodies". J. Amer. Soc of Naval Engineers 34: 280–309. 
  25. ^ Wai-Kai Chen, "Active Network Analysis", World Scientific, 1991. ISBN 997150913X. pp186-187
  26. ^ With mechanical devices, hunting can be severe enough to destroy the device.
  28. ^ H. Giese, Y. Brun, J. D. M. Serugendo, C. Gacek, H. Kienle, H. Müller, M. Pezzè, and M. Shaw (2009). "Engineering self-adaptive and self-managing systems". Springer-Verlag. 
  29. ^ J. L. Hellerstein, Y. Diao, S. Parekh, and D. M. Tilbury (2004). Feedback Control of Computing Systems. John Wiley & Sons. 
  30. ^ J. O. Kephart and D. M. Chess (2003). "The vision of autonomic computing". 
  31. ^ H. A. Müller, H. M. Kienle, and U. Stege, (2009). "Autonomic computing: Now you see it, now you don’t—design and evolution of autonomic software systems". 
  32. ^ Thomas, Goetz (19 June 2011). "Harnessing the power of Feedback Loops". Wired Magazine (Wired Magazine). Retrieved 20 June 2011. 
  33. ^ Introduction to Social Macrodynamics by Andrey Korotayev et al.
  35. ^ Fleming, M., & Levie, W.H. (1993). Instructional message design: principles from the behavioral and cognitive sciences (Second Edition ed.). Englewood Cliffs NJ: Educational Technology Publications. ISBN 0-87778-253-9. 
  36. ^ Accreditation provides you with a structured mechanism to assess and improve the quality of your program: The two-loop feedback diagram
  37. ^ Folkman, Joseph R. The Power of Feedback. 1st ed. New Jersey: John Wiley & Sons Inc., 2006. Print.
  39. ^ Van Dijk, D., & Kluger, A. N. (2011). Task type as a moderator of positive/negative feedback effects on motivation and performance: A regulatory focus perspective. Journal of Organizational Behavior, 32, 1084-1105. doi: 10.1002/job.725

Further reading[edit]