Feedback 11545 221859687 2008-06-26T12:13:40Z Mdd 113850 [[WP:UNDO|Undid]] revision 221826601 by [[Special:Contributions/210.49.100.187|210.49.100.187]] ([[User talk:210.49.100.187|talk]]) Nonsense {{otheruses}} '''Feedback''' is a [[process]] whereby some proportion of the output signal of a system is passed (fed back) to the [[input]]. This is often used to control the dynamic behavior of the [[system]]. Examples of feedback can be found in most [[complex system]]s, such as [[engineering]], [[architecture]], [[economics]], [[thermodynamics]], and [[biology]]. [[Negative feedback]] was applied by [[Harold Stephen Black]] to electrical amplifiers in 1927, but he could not get his idea patented until 1937.<ref name=Spencer> {{cite book |author=Richard R Spencer & Ghausi MS |title=Introduction to electronic circuit design |year= 2003 |publisher=Prentice Hall/Pearson Education |location=Upper Saddle River NJ |isbn=0-201-36183-3 |pages=p. 661 |url=http://worldcat.org/isbn/0-201-36183-3}} </ref> [[Arturo Rosenblueth]], a Mexican researcher and physician, co-authored a seminal 1943 paper ''Behavior, Purpose and Teleology''<ref>[http://links.jstor.org/sici?sici=0031-8248(194301)10%3A1%3C18%3ABPAT%3E2.0.CO%3B2-8 Rosenblueth A, Wiener N & Bigelow J: ''Behavior, Purpose and Teleology'' ]</ref> that, according to [[Norbert Wiener]] (another co-author of the paper), set the basis for the new science of [[cybernetics]]. Rosenblueth proposed that behavior controlled by negative feedback, whether in animal, human or machine, was a determinative, directive principle in nature and human creations.{{Fact|date=November 2007}}. This kind of feedback is studied in [[cybernetics]] and [[control theory]]. In [[organization]]s, feedback is a process of sharing observations, concerns and suggestions between persons or divisions of the organization with an intention of improving both personal and organizational performance. Negative and positive feedback have different meanings in this usage, where they imply criticism and praise, respectively. == Overview == Feedback is both a mechanism, process and signal that is looped back to control a [[system]] within itself. This loop is called the feedback loop. A [[control system]] usually has input and output to the system; when the output of the system is fed back into the system as part of its input, it is called the "feedback." Feedback and regulation are self related. The negative feedback helps to maintain stability in a system in spite of external changes. It is related to [[homeostasis]]. Positive feedback amplifies possibilities of divergences (evolution, change of goals); it is the condition to change, evolution, growth; it gives the system the ability to access new points of [[equilibrium]]. For example, in an organism, most positive feedback provide for fast autoexcitation of elements of endocrine and nervous systems (in particular, in stress responses conditions) and play a key role in regulation of morphogenesis, growth, and development of organs, all processes which are in essence a rapid escape from the initial state.{{Fact|date=November 2007}} Homeostasis is especially visible in the [[nervous system|nervous]] and [[endocrine system]]s when considered at organism level. == Types of feedback == [[Image:Ideal feedback model.svg|thumb|Figure 1: Ideal feedback model. The feedback is negative if B < 0|300px|right]] {{main|Negative feedback|positive feedback}} Types of feedback are: * [[negative feedback]]: which tends to reduce output (but in amplifiers, stabilizes and linearizes operation), * [[positive feedback]]: which tends to increase output, or * [[bipolar]] feedback: which can either increase or decrease output. Systems which include feedback are prone to ''hunting'', which is [[oscillation]] of output resulting from improperly tuned inputs of first positive then negative feedback. Audio feedback typifies this form of oscillation. Bipolar feedback is present in many natural and human systems. Feedback is usually bipolar—that is, positive and negative—in natural environments, which, in their diversity, furnish synergic and antagonistic responses to the output of any system. == Applications == === In biology === In [[biology|biological]] systems such as [[organism]]s, [[ecosystem]]s, or the [[biosphere]], most parameters must stay under control within a narrow range around a certain optimal level under certain environmental conditions. The deviation of the optimal value of the controlled parameter can result from the changes in internal and external environments. A change of some of the environmental conditions may also require change of that range to change for the system to function. The value of the parameter to maintain is recorded by a reception system and conveyed to a regulation module via an information channel. Biological systems contain many types of regulatory circuits, both positive and negative. As in other contexts, ''positive'' and ''negative'' don't imply consequences of the feedback have good or bad final effect. A negative feedback loop is one that tends to slow down a process, while the positive feedback loop tends to accelerate it. The [[mirror neuron]]s are part of a social feedback system, when an observed action is ´mirrored´ by the brain - like a self performed action. Feedback is also central to the operations of [[gene]]s and [[gene regulatory network]]s. [[Repressor protein|Repressor]] (see [[Lac repressor]]) and [[activator protein|activator]] [[protein]]s are used to create genetic [[operon]]s, which were identified by [[Francois Jacob]] and [[Jacques Monod]] in 1961 as ''feedback loops''. These feedback loops may be positive (as in the case of the coupling between a sugar molecule and the proteins that import sugar into a bacterial cell), or negative (as is often the case in metabolic consumption). Any self-regulating natural process involves feedback and is prone to hunting. A well known example in [[ecology]] is the oscillation of the population of [[snowshoe hare]]s due to predation from [[lynx]]es. In [[fermentation (biochemistry)|zymology]], feedback serves as regulation of activity of an enzyme by its direct product(s) or downstream metabolite(s) in the metabolic pathway (see [[Allosteric regulation]]). [[Hypothalamic-pituitary-adrenal axis|Hypothalamo-pituitary-adrenal]] and ovaraian or testicular axis is largely controlled by positive and negative feedback, much of which is still unknown. ===In climate science=== The climate system is characterized by strong feedback loops between processes that affect the state of the atmosphere, ocean, and land. A simple example is the ice-albedo positive feedback loop whereby melting snow exposes more dark ground (of lower [[albedo]]), which in turn absorbs heat and causes more snow to melt. ===In control theory=== Feedback is extensively used in [[control theory]], using a variety of methods including [[state space (controls)]], [[pole placement]] and so forth. The most common general-purpose [[controller]] using a control-loop feedback mechanism is a [[PID controller|proportional-integral-derivative]] (PID) controller. Each term of the PID controller copes with time. The proportional term handles the present state of the system, the integral term handles its past, and the derivative or slope term tries to predict and handle the future. === In economics and finance === A [[system]] prone to hunting (oscillating) is the [[stock market]], which has both positive and negative feedback mechanisms. This is due to cognitive and emotional factors belonging to the field of [[behavioral finance]]. For example, * When stocks are rising (a [[bull market]]), the belief that further rises are probable gives investors an incentive to buy (positive feedback, see also [[stock market bubble]]); but the increased price of the [[stock|shares]], and the [[knowledge]] that there must be a peak after which the market will fall, ends up deterring buyers (negative feedback). * Once the market begins to fall regularly (a [[bear market]]), some investors may expect further losing days and refrain from buying (positive feedback), but others may buy because stocks become more and more of a bargain (negative feedback). [[George Soros]] used the word "reflexism" to describe feedback in the financial markets and developed an investment theory based on this principle. The conventional [[economic equilibrium]] model of [[supply and demand]] supports only ideal linear negative feedback and was heavily criticized by [[Paul Ormerod]] in his book "[[The Death of Economics]]" which in turn was criticized by traditional economists. This book was part of a change of perspective as economists started to recognise that [[Chaos Theory]] applied to nonlinear feedback systems including financial markets. === In education === Young students will often look up to instructors as experts in the field and take to heart most of the things instructors say. Thus, it is believed that spending a fair amount of time and effort thinking about how to respond to students may be a worthwhile time investment. Here are some general types of feedback that can be used in many types of student assessment: <table border="1" cellspacing="0" cellpadding="10"> <tr> <td width="139" valign="top"><p>Confirmation</p></td> <td width="432" valign="top"><p>Your answer was incorrect.</p></td> </tr> <tr> <td width="139" valign="top"><p>Corrective</p></td> <td width="432" valign="top"><p>Your answer was incorrect. The correct answer was Jefferson.</p></td> </tr> <tr> <td width="139" valign="top"><p>Explanatory</p></td> <td width="432" valign="top"><p>Your answer was incorrect because Carter was from Georgia; only Jefferson called Virginia home.</p></td> </tr> <tr> <td width="139" valign="top"><p>Diagnostic</p></td> <td width="432" valign="top"><p>Your answer was incorrect. Your choice of Carter suggests some extra instruction on the home states of past presidents might be helpful.</p></td> </tr> <tr> <td width="139" valign="top"><p>Elaborative</p></td> <td width="432" valign="top"><p>Your answer, Jefferson, was correct. The University of Virginia, a campus rich with Jeffersonian architecture and writings, is sometimes referred to as Thomas Jefferson’s school.</p></td> </tr> </table> (Adapted from Flemming and Levie<ref name=Fleming> {{cite book |author=Fleming, M., & Levie, W.H. |title=Instructional message design: principles from the behavioral and cognitive sciences |year= 1993 |edition=Second Edition |publisher=Educational Technology Publications |location=Englewood Cliffs NJ |isbn=0877782539 |url=http://books.google.com/books?id=vLxPAAAAMAAJ&dq=intitle:Instructional+intitle:message+intitle:design&lr=&as_brr=0&pgis=1}} </ref>.) A different application of feedback in education is the system for "continuous improvement" of engineering curricula monitored by the Accreditation Board for Engineering and Technology (ABET)<ref>[http://www.vanth.org/curriculum/twoloop.html ''Accreditation provides you with a structured mechanism to assess and improve the quality of your program: The two-loop feedback diagram'']</ref> === In electronic engineering === The processing and control of feedback is engineered into many [[electronics|electronic]] [[Electronic component|device]]s and may also be [[embedded]] in other [[technology|technologies]]. If the signal is inverted on its way round the control loop, the system is said to have [[negative feedback amplifier|''negative feedback'']]; otherwise, the feedback is said to be ''positive''. Negative feedback is often deliberately introduced to increase the [[BIBO stability|stability]] and accuracy of a system. 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 feedback signal results in positive feedback, causing the output to [[oscillation|oscillate]] or [[Hunting (engineering)|''hunt'']]<ref>With mechanical devices, hunting can be severe enough to destroy the device.</ref> Positive feedback is usually an unwanted consequence of system behaviour. [[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_plot#Gain_margin_and_phase_margin|Bode plot]]s (contributed by [[Hendrik_Wade_Bode| Hendrik Bode]]). Design to insure stability often involves [[frequency compensation]], one method of compensation being [[pole splitting]]. ===In government=== Examples of feedback in government are: * [[Elections]] * [[Mass media]] * [[Revolution]] * [[Curfews]] === In mechanical engineering === In ancient times, the [[float valve]] was used to regulate the flow of water in Greek and Roman [[water clock]]s; similar float valves are used to regulate fuel in a [[carburetor]] and also used to regulate tank water level in the [[flush toilet]]. The [[windmill]] was enhanced in 1745 by blacksmith Edmund Lee who added a fantail to keep the face of the windmill pointing into the [[wind]]. In 1787 [[Thomas Mead]] regulated the speed of rotation of a windmill by using a centrifugal pendulum to adjust the distance between the bedstone and the runner stone (i.e. to adjust the load). The use of the [[centrifugal governor]] by [[James Watt]] in 1788 to regulate the speed of his [[steam engine]] was one factor leading to the [[Industrial Revolution]]. Steam engines also use float valves and pressure release valves as mechanical regulation devices. A [[mathematical analysis]] of Watt's governor was done by [[James Clerk Maxwell]] in 1868. The [[SS Great Eastern|Great Eastern]] was one of the largest steamships of its time and employed a steam powered rudder with feedback mechanism designed in 1866 by J.McFarlane Gray. Joseph Farcot coined the word [[servo]] in 1873 to describe steam powered steering systems. Hydraulic servos were later used to position guns. [[Elmer Ambrose Sperry]] of the [[Sperry Corporation]] designed the first [[autopilot]] in 1912. Nicolas Minorsky published a theoretical analysis of automatic ship steering in 1922 and described the [[PID controller]]. Internal combustion engines of the late 20th century employed mechanical feedback mechanisms such as vacuum advance (see: [[Ignition timing]]) but mechanical feedback was replaced by electronic [[engine control unit|engine management systems]] once small, robust and powerful single-chip [[microcontroller]]s became affordable. === In organizations === As an [[organization]] seeks to improve its performance, feedback helps it to make required adjustments. Examples of feedback in organizations: * [[Financial audit]] * [[Performance appraisal]] * [[Shareholders' meeting]]s * [[Marketing research]] * [[360-degree feedback]] * [[Walkout]]s * [[Lockout (industry)|Lockout]]s == See also == {{Wiktionary}} *[[Negative feedback amplifier]] *[[Audio feedback]] *[[Interaction]] *[[Low-key feedback]] *[[Optical feedback]] *[[Perverse incentive]] *[[Stability criterion]] *[[Tactile]] *[[Unintended consequence]] *[[Resonance]] == References == {{reflist}} == Further reading == * Katie Salen and [[Eric Zimmerman]]. ''Rules of Play''. [[MIT Press]]. 2004. ISBN 0-262-24045-9. Chapter 18: Games as Cybernetic Systems. * [[Korotayev]] A., Malkov A., Khaltourina D. ''Introduction to Social Macrodynamics: Secular Cycles and Millennial Trends.'' Moscow: URSS, 2006. ISBN 5-484-00559-0 *Dijk, E., Cremer, D.D., Mulder, L.B., and Stouten, J. "How Do We React to Feedback in Social Dilemmas?" In Biel, Eek, Garling & Gustafsson, (eds.), ''New Issues and Paradigms in Research on Social Dilemmas'', New York: Springer, 2008. [[Category:Control theory]] [[Category:Electronic feedback]] [[ca:Realimentació]] [[cs:Zpětná vazba]] [[da:Feedback]] [[de:Rückkopplung]] [[es:Realimentación]] [[fr:Rétroaction]] [[ko:피드백]] [[id:Loloh balik]] [[it:Retroazione]] [[he:משוב]] [[lt:Grįžtamasis ryšys]] [[nl:Terugkoppeling]] [[ja:フィードバック]] [[no:Tilbakekobling]] [[pl:Sprzężenie zwrotne]] [[pt:Retroalimentação]] [[ru:Обратная связь]] [[simple:Feedback]] [[sk:Spätná väzba]] [[sl:Povratna zanka]] [[sr:Фидбек]] [[fi:Takaisinkytkentä]] [[sv:Återkoppling]] [[tr:Geri besleme]] [[uk:Зворотний зв'язок]] [[zh:反馈]]