Feedback is a process whereby some proportion of the output signal of a system is passed (fed back) to the input. Input is the term denoting either an entrance or changes which are inserted into a System and which activate/modify a Process. This is often used to control the dynamic behavior of the system. System (from Latin systēma, in turn from Greek systēma is a set of interacting or interdependent Entities, real or abstract Examples of feedback can be found in most complex systems, such as engineering, architecture, economics, thermodynamics, and biology. This article describes complex system as a type of system For other meanings see Complex systems. Engineering is the Discipline and Profession of applying technical and scientific Knowledge and The term architecture (from Greek αρχιτεκτονικήarchitektoniki) can be used to mean a process a profession or documentation Economics is the social science that studies the production distribution, and consumption of goods and services. In Physics, thermodynamics (from the Greek θερμη therme meaning " Heat " and δυναμις dynamis meaning " Foundations of modern biology There are five unifying principles

Negative feedback was applied by Harold Stephen Black to electrical amplifiers in 1927, but he could not get his idea patented until 1937. Negative Feedback feeds part of a System 's output inverted into the system's input generally with the result that fluctuations are attenuated Harold Stephen Black (1898-1983 was an American Electrical engineer, who revolutionized the field of applied electronics by inventing the Negative feedback amplifier ^[1] Arturo Rosenblueth, a Mexican researcher and physician, co-authored a seminal 1943 paper Behavior, Purpose and Teleology^[2] that, according to Norbert Wiener (another co-author of the paper), set the basis for the new science of cybernetics. Arturo Rosenblueth Stearns ( October 2, 1900 – September 20, 1970) was a Mexican researcher physician and physiologist Norbert Wiener ( November 26, 1894, Columbia Missouri – March 18, 1964, Stockholm, Sweden) was an American Cybernetics is the interdisciplinary study of the Structure of Complex systems especially Communication processes control mechanisms and Feedback Rosenblueth proposed that behavior controlled by negative feedback, whether in animal, human or machine, was a determinative, directive principle in nature and human creations. . This kind of feedback is studied in cybernetics and control theory. Cybernetics is the interdisciplinary study of the Structure of Complex systems especially Communication processes control mechanisms and Feedback Control theory is an interdisciplinary branch of Engineering and Mathematics, that deals with the behavior of Dynamical systems The desired output

In organizations, 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. An organization (or organisation &mdash see spelling differences) is a social arrangement which pursues collective goals which controls its own performance and Negative and positive feedback have different meanings in this usage, where they imply criticism and praise, respectively.

Contents 1 Overview 2 Types of feedback 3 Applications 3.1 In biology 3.2 In climate science 3.3 In control theory 3.4 In economics and finance 3.5 In education 3.6 In electronic engineering 3.7 In government 3.8 In mechanical engineering 3.9 In organizations 4 See also 5 References 6 Further reading

Overview

Feedback is both a mechanism, process and signal that is looped back to control a system within itself. System (from Latin systēma, in turn from Greek systēma is a set of interacting or interdependent Entities, real or abstract 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. A control system is a device or set of devices to manage command direct or regulate the behavior of other devices or systems "

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. Homeostasis (from Greek: ὅμος hómos, "equal" and ιστημι istēmi, "to stand" lit 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. Homeostasis is especially visible in the nervous and endocrine systems when considered at organism level. The nervous system is a Network of specialized cells that communicate information about an animal's surroundings and itself The endocrine system is an integrated system of small organs that involve the release of extracellular signaling molecules known as Hormones The endocrine system is instrumental

Types of feedback

Main articles: Negative feedback and 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. Negative Feedback feeds part of a System 's output inverted into the system's input generally with the result that fluctuations are attenuated Positive feedback, sometimes referred to as "cumulative causation" is a Feedback loop system in which the system responds to perturbation in the same direction Negative Feedback feeds part of a System 's output inverted into the system's input generally with the result that fluctuations are attenuated Positive feedback, sometimes referred to as "cumulative causation" is a Feedback loop system in which the system responds to perturbation in the same direction

Systems which include feedback are prone to hunting, which is oscillation of output resulting from improperly tuned inputs of first positive then negative feedback. Oscillation is the repetitive variation typically in Time, of some measure about a central value (often a point of Equilibrium) or between two or more different states 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 biological systems such as organisms, ecosystems, or the biosphere, most parameters must stay under control within a narrow range around a certain optimal level under certain environmental conditions. Foundations of modern biology There are five unifying principles An ecosystem is a natural unit consisting of all plants animals and micro-organisms( Biotic factors in an area functioning together with all of the non-living physical ( The biosphere is the broadest level of ecological study the global sum of all Ecosystems. 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 neurons are part of a social feedback system, when an observed action is ´mirrored´ by the brain - like a self performed action. A mirror neuron is a Neuron which fires both when an animal acts and when the animal observes the same action performed by another (especially Conspecific

Feedback is also central to the operations of genes and gene regulatory networks. History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance A Gene regulatory network (also called a GRN or genetic regulatory network) is a collection of DNA segments in a cell which interact with each Repressor (see Lac repressor) and activator proteins are used to create genetic operons, which were identified by Francois Jacob and Jacques Monod in 1961 as feedback loops. For other uses see Repression A repressor is a DNA-binding protein that regulates the expression of one or more genes by decreasing The lac repressor is a DNA-binding protein which inhibits the expression of Genes coding for Proteins involved in the Metabolism of An activator is a DNA-binding protein that regulates one or more Genes by increasing the rate of transcription. Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl An operon is a functioning unit of key Nucleotide sequences including an operator, a common Promoter, and one or more structural Genes, François Jacob (born 17 June 1920 in Nancy France) is a French Biologist who together with Jacques Monod, originated See also Jacques-Louis Monod, French-born composer and cousin of Jacques Monod 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 hares due to predation from lynxes. Ecology (from Greek grc οἶκος oikos, "house(hold" and grc -λογία -logia) is the scientific study of The Snowshoe Hare ( Lepus americanus) also called the Varying Hare, is a species of Hare found in North America. A lynx is any of four medium-sized wild cats. All are members of the Genus Lynx, but there is considerable confusion about the best way to classify

In 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). Fermentation is the process of deriving energy from the oxidation of organic compounds such as carbohydrates using an endogenous electron acceptor which is In Biochemistry, allosteric regulation is the regulation of an Enzyme or other Protein by binding an effector molecule at the protein's allosteric

Hypothalamo-pituitary-adrenal and ovaraian or testicular axis is largely controlled by positive and negative feedback, much of which is still unknown. The hypothalamic-pituitary-adrenal axis ( HPA or HTPA axis) also known as the Limbic -hypothalamic-pituitary-adrenal axis (LHPA axis is a complex set of direct influences

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. The albedo of an object is the extent to which it diffusely reflects light from the sun This is part of the evidence of the danger of global warming. Global warming is the increase in the average measured temperature of the

In control theory

Feedback is extensively used in control theory, using a variety of methods including state space (controls), pole placement and so forth. Control theory is an interdisciplinary branch of Engineering and Mathematics, that deals with the behavior of Dynamical systems The desired output In Control engineering, a state space representation is a mathematical model of a physical system as a set of input output and state variables related by first-order Differential

The most common general-purpose controller using a control-loop feedback mechanism is a proportional-integral-derivative (PID) controller. A proportional–integral–derivative controller (PID controller is a generic Control loop Feedback mechanism widely used in industrial Control systems 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. System (from Latin systēma, in turn from Greek systēma is a set of interacting or interdependent Entities, real or abstract A stock market, or (equity market is a private or public market for the trading of company Stock and derivatives of company This is due to cognitive and emotional factors belonging to the field of behavioral finance. Behavioral economics and behavioral finance are closely related fields which apply scientific research on human and social cognitive and emotional factors to better 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 shares, and the knowledge that there must be a peak after which the market will fall, ends up deterring buyers (negative feedback). In Investing, Financial markets are commonly believed to have market trends that can be classified as primary trends secondary trends (short-term and secular trends A stock market bubble is a type of Economic bubble taking place in Stock markets when price of Stocks rise and become overvalued by any measure of Stock Software for Fixed assets management and Stock control developed in 2004. Knowledge is defined ( Oxford English Dictionary) variously as (i expertise and skills acquired by a person through experience or education the theoretical or practical understanding
• 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). In Investing, Financial markets are commonly believed to have market trends that can be classified as primary trends secondary trends (short-term and secular trends

George Soros used the word "reflexism" to describe feedback in the financial markets and developed an investment theory based on this principle. George Soros (ˈsɔroʊs or /ˈsɔrəs/ Hungarian ˈʃoroʃ (born August 12, 1930, in Budapest, Hungary, as György Schwartz) is

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. In Economics, economic equilibrium is simply a state of the world where economic forces are balanced and in the absence of external influences the (equilibrium values of economic Supply and demand is an Economic model describing effects on price and quantity in a Market. Paul Ormerod is a Economist who is currently researching Complexity, Complex systems Nonlinear Feedback, the Boom and bust The Death of Economics is a book written by Paul Ormerod attacking a particular form of Economics, which remains dominant in the Teaching 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 Mathematics, chaos theory describes the behavior of certain dynamical systems – that is systems whose state evolves with time – that may exhibit dynamics that

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:

Confirmation	Your answer was incorrect.
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.
Diagnostic	Your answer was incorrect. Your choice of Carter suggests some extra instruction on the home states of past presidents might be helpful.
Elaborative	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.

(Adapted from Flemming and Levie^[3]. )

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)^[4]

In electronic engineering

The processing and control of feedback is engineered into many electronic devices and may also be embedded in other technologies. Electronics refers to the flow of charge (moving Electrons through Nonmetal conductors (mainly Semiconductors, whereas electrical An electronic component is a basic electronic element usually packaged in a discrete form with two or more connecting leads or metallic pads Technology is a broad concept that deals with a Species ' usage and knowledge of Tools and Crafts and how it affects a species' ability to control and adapt

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. When a fraction of the output of an amplifier is combined with the input Feedback exists if the feedback opposes the original signal it is negative feedback and if it increases Negative feedback is often deliberately introduced to increase the stability and accuracy of a system. Bibo redirects here For the Egyptian football player nicknamed Bibo see Mahmoud El-Khateeb. 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 oscillate or hunt^[5] Positive feedback is usually an unwanted consequence of system behaviour. Oscillation is the repetitive variation typically in Time, of some measure about a central value (often a point of Equilibrium) or between two or more different states Hunting is a self-exciting Oscillation of a system and is common in systems which incorporate Feedback.

Harry Nyquist contributed the Nyquist plot for assessing the stability of feedback systems. Harry Nyquist ( né Harry Theodor Nyqvist pron, not as often pronounced ( February 7, 1889 – April 4, 1976) was an important A Nyquist plot is used in automatic control and Signal processing for assessing the stability of a system with Feedback. An easier assessment, but less general, is based upon gain margin and phase margin using Bode plots (contributed by Hendrik Bode). A Bode plot, named after Hendrik Wade Bode, is usually a combination of a Bode magnitude plot and Bode phase plot A Bode magnitude plot is a graph of log Hendrik Wade Bode (pronounced Boh-dee in English, Boh-dah in Dutch) ( 24 December 1905 &ndash 21 June Design to insure stability often involves frequency compensation, one method of compensation being pole splitting. In Electrical engineering, frequency compensation is a technique used in Amplifiers, and especially in amplifiers employing negative feedback Pole splitting is a type of Frequency compensation used in an Electronic amplifier in which a Capacitor is introduced between the input and output sides

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 clocks; similar float valves are used to regulate fuel in a carburetor and also used to regulate tank water level in the flush toilet. An election is a Decision-making process by which a population chooses an individual to hold formal office "Popular press" redirects here note that the University of Wisconsin Press publishes under the imprint "The Popular Press" A revolution (from the Latin revolutio, "a turnaround" is a fundamental change in power or organizational structures that takes place in a relatively A curfew can be one of the following An order by a Government for certain persons to return home daily before a certain time A float valve is a mechanical Feedback mechanism that regulates fluid level by using a float to drive an inlet valve so that a higher fluid level will force the valve closed A water clock or clepsydra ( Greek kleptein to steal; hydro water) is any timekeeper operated by means of a regulated flow of liquid into (inflow A carburetor (North American spelling or carburettor ( Commonwealth spelling) is a device that blends air and Fuel for an Internal A flush toilet or Water Closet (WC is a Toilet that disposes of human waste by using water to flush it through a drainpipe to another location

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. A windmill is a machine that is powered by the energy of the wind Wind is the flow of Air or other Gases that compose an Atmosphere (including but not limited to the Earth's) 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. Thomas Francis Mead ( 4 May 1918 - 22 January 2004) was an Australian politician elected as a member of the New South Wales Legislative 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. A centrifugal governor is a specific type of governor that controls the Speed of an Engine by regulating the amount of Fuel (or Working James Watt ( 19 January 1736 &ndash 25 August 1819 Boulton proved to be an excellent businessman and both men eventually made fortunes A steam engine is a Heat engine that performs Mechanical work using Steam as its Working fluid. The Industrial Revolution was a period in the late 18th and early 19th centuries when major changes in agriculture manufacturing and transportation had a profound effect on the 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. Analysis has its beginnings in the rigorous formulation of Calculus. James Clerk Maxwell (13 June 1831 &ndash 5 November 1879 was a Scottish mathematician and theoretical physicist.

The 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. History Concept After the Great Exhibition of 1851 which had publicized Australia's wealth and natural resources waves of people were eager to emigrate from 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. Elmer Ambrose Sperry ( October 12, 1860 – June 16, 1930) was a prolific Inventor and Entrepreneur, most famous as co-inventor Sperry Corporation (1910-1986 was a major American equipment and Electronics company whose existence spanned more than seven decades of the twentieth century An autopilot is a mechanical electrical or hydraulic system used to guide a vehicle without assistance from a human being Nicolas Minorsky published a theoretical analysis of automatic ship steering in 1922 and described the PID controller. A proportional–integral–derivative controller (PID controller is a generic Control loop Feedback mechanism widely used in industrial Control systems

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 management systems once small, robust and powerful single-chip microcontrollers became affordable. Ignition timing in an Internal combustion engine is the process of setting the time that a spark will occur in the combustion chamber (during the Power stroke) relative An engine control unit (ECU is an Electronic control unit which controls various aspects of an Internal combustion engine 's operation A microcontroller (also MCU or µC is a functional Computer system-on-a- chip.

In organizations

As an organization seeks to improve its performance, feedback helps it to make required adjustments. An organization (or organisation &mdash see spelling differences) is a social arrangement which pursues collective goals which controls its own performance and

Examples of feedback in organizations:

• Financial audit
• Performance appraisal
• Shareholders' meetings
• Marketing research
• 360-degree feedback
• Walkouts
• Lockouts

See also

• Negative feedback amplifier
• Audio feedback
• Interaction
• Low-key feedback
• Optical feedback
• Perverse incentive
• Stability criterion
• Tactile
• Unintended consequence
• Resonance

References

Further reading

• Katie Salen and Eric Zimmerman. Eric Zimmerman (born 1969) is a Game designer and the co-founder and CEO of Gamelab, a computer game development company which is Rules of Play. MIT Press. The MIT Press is a University press affiliated with the Massachusetts Institute of Technology (MIT in Cambridge Massachusetts ( USA) 2004. ISBN 0-262-24045-9. Chapter 18: Games as Cybernetic Systems.
• Korotayev A. Andrey Korotayev (born in 1961 is an anthropologist, economic Historian, and sociologist. , 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.

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