1. a. The return of a portion of the output of a process or system to the input, especially when used to maintain performance or to control a system or process. b. The portion of the output so returned.
2. The return of information about the result of a process or activity; an evaluative response: asked the students for feedback on the new curriculum.
According to cybernetics, the human brain and nervous system coordinate information to determine which actions will be performed; control mechanisms for self-correction in machines serve a similar purpose. This principle, known as feedback, is the fundamental concept of automation. One of the basic tenets of cybernetics is that information can be statistically measured in accordance with the laws of probability. Purposive behavior in humans or in machines requires control mechanisms that maintain order by counteracting the natural tendency toward disorganization.
In a system where a transformation occurs, there are inputs and outputs. The inputs are the result of the environment's influence on the system, and the outputs are the influence of the system on the environment. Input and output are separated by a duration of time, as in before and after, or past and present.
there's a neat little video trick that's commonly known. point your camcorder at a television set connected to the camera, and play with the zoom and angles and lighting. eventually you'll fall into some sort of strange loop that is very psychedelic. a fractal wormhole of sorts. i had plenty of fun with this coming down off of acid a couple of times. - @Om* 12/3/99
give feedback re: fUSION Anomaly by emailing me.
"...in perfecting feedback and the means of rapid data manipulation, the science of cybernetics was gaining a deeper understanding of life itself as being, at its core, the processing of information."
- Theodore Roszak, _The Cult of Information_
Daybreak topped off my mug with more tea. "When the Buddha spoke of control, he wasn't talking about clamping down on our urges, but about cultivating a homeostatic sense of feedback, an ethics of constant modulation. Shakyamuni once compared meditation to a musician constantly tuning a string that keeps going flat or sharp. That's the trickóconstant negative feedback. A Buddhist gun-freak I knew likens zazen to the flight of F-14s, which are aerodynamically unstable. Computers must constantly adjust the surfaces of the plane's wings and fuselage in response to atmospheric conditions in order to keep the plane aloft. That's the Middle Way. The trap is the vicious escalation of positive feedback, whether it's a barfight or the arms race or consumer culture. For Buddhists, satisfying ordinary desires is like a thirsty man drinking sea-water. More positive feedback. But what if we introduce a minus sign into the loop? What if we become the minus sign? Rather than respond to anger with more anger, what if can realize that there is no human being there to be angry at, just the resonance of countless molecular machines producing the complexity of life?"
- selections from the notebooks of Lance Daybreak, curated by Erik Davis in _Shards Of The Diamond Matrix_
"We shape our tools and thereafter they shape us." - Marshall McLuhan
"It is my thesis that the physical functioning of
the living individual and the operation of some of the newer communication
machines are precisely parallel in their analogous attempts to control
entropy through feedback." - Norbert
In every feedback loop, as
the name suggests, information
about the result of a transformation or an action is sent back to the input
of the system in the form of input data. If these new data facilitate and
accelerate the transformation in the same direction as the preceding results,
they are positive feedback - their effects are cumulative. If the new data
produce a result in the opposite direction to previous results, they are
negative feedback - their effects stabilize the system. In the first case
there is exponential growth or decline; in the second there is maintenance
of the equilibrium.
Positive feedback leads to
divergent behavior: indefinite expansion or explosion (a running away toward infinity)
or total blocking of activities (a running away toward zero).
Each plus involves another plus; there is a snowball effect. The examples
are numerous: chain reaction, population explosion, industrial expansion,
capital invested at compound interest, inflation, proliferation of cancer
cells. However, when minus leads to another minus, events come to a standstill.
Typical examples are bankruptcy and economic depression.
In either case a positive feedback loop left to itself can lead only to the destruction of the system, through explosion or through the blocking of all its functions. The wild behavior of positive loops - a veritable death wish - must be controlled by negative loops. This control is essential for a system to maintain itself in the course of time.
Negative feedback leads to
adaptive, or goal-seeking behavior: sustaining the same level, temperature,
concentration, speed, direction. In some cases the goal is self-determined
and is preserved in the face of evolution:
the system has produced its own purpose (to maintain, for example, the
composition of the air or the oceans in the ecosystem or the concentration
of glucose in the blood). In other cases man has determined the goals of
the machines (automats and servomechanisms). In a negative loop every variation
toward a plus triggers a correction toward the minus, and vice versa. There
is tight control; the system oscillates
around an ideal equilibrium that it never attains. A thermostat or a water
tank equipped with a float are simple examples of regulation by negative
Peter Jackson echoes the sentiment, but he also feels that the intense feedback enabled by the Internet is worthwhile. "Fans have so much information and communicate about films for so long that it will hopefully force filmmakers to make much better movies. The voice of the audience is heard: They don't want crap."
- Erik Davis - _The Fellowship Of The Ring_ in _Wired_ 9.10 - October 2001 re: J.R.R. Tolkien
In engineering, economics and biology, feedback is a process whereby some proportion of the output signal of a system is fed back to the input, in order to change the dynamic behaviour of the system.
Feedback may be negative, thus tending to reduce output, or positive, thus increasing 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.
Feedback in electronic engineering
Feedback is designed into many electronic and other technical devices.
In engineering control theory, feedback is a process in which a signal generated from the output of a system is applied as an input to the same system.
The most common general-purpose controller is a proportional-integral-derivative 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.
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, as in the feedback amplifier invented by Harold Stephen Black. This scheme can fail if the input changes faster than the system can respond to it. When this happens, the negative feedback signal begins to act as positive feedback, causing the output to oscillate or hunt. Positive feedback is usually an unwanted consequence of system behaviour.
A well-known example of runaway positive feedback in electronic systems is called "howl" or "howl-round". This occurs in public address systems when sound from the loudspeakers reaches the microphone, is amplified by the system, and is then fed back into the system at even higher volume. All electrical systems contain capacitance and inductance and so act as band-pass filters responding better to certain frequencies. In a single loop through the system, this effect is negligible, but it becomes severe when the signal passes through the system repeatedly. This effect is the basis of the simplest kinds of analogue electrical oscillator.
With mechanical devices, hunting can be severe enough to destroy the device.
Feedback in economics
A system prone to hunting is the stock market, which has both positive and negative feedback mechanisms. For example, when stocks are rising (a bull market), the belief that further rises are probable gives investors an incentive to buy (positive feedback); but the increased price of the shares, and the knowledge that there must be a peak after which the market will fall, deter 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).
Feedback in nature
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. 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, among which positive and negative feedbacks. Positive and negative don't imply consequences of the feedback have positive or negative final effect. The negative feedback loop tends to slow down a process, while the positive feedback loop tends to accelerate it.
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 feedbacks 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.
Feedback is also central to the operations of genes and gene regulatory networks. repressor and activator proteins are used to create genetic operons, which were identified by Francois Jacob and Jacques Monod in 1961 as feedback loops.
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.
Compare with: feed-forward
Feedback 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
* shareholder meetings
* customer surveys