This glossary contains a vocabulary used by CPER concerning the overall site, regarding: meaning of scientific words, useful definitions, short explanations of some concepts, and references to reliable external sources of information on the Internet or on paper.

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  1. Communication / education: (critical) assessment on information produced (verbal of lexical).
  2. Cybernetics: the signal that is looped back to control a system within itself.
    (see: Positive Feedback Loop or Negative Feedback Loop).
  3. Music / electronics: the high-pitched howling noise heard when there's a loop between a microphone and a speaker.




Feedback occurs when outputs of a system are "fed back" as inputs as part of a chain of cause-and-effect that forms a circuit or loop. The system can then be said to "feed back" into itself. The notion of 'cause-and-effect' has to be handled carefully when applied to feedback systems: Simple causal reasoning about a feedback system is difficult because the first system influences the second and second system influences the first, leading to a circular argument. This makes reasoning based upon cause and effect tricky, and it is necessary to analyze the system as a whole. In this context, the term "feedback" has also been used as an abbreviation for:

  • Feedback signal: the conveyance of information fed back from an output, or measurement, to an input, or effector, that affects the system.
  • 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).



Simple Feedback Loop without sign

Figure: Simple feedback loop showing circular cause-effect relationship.

Positive - Negative

The terms positive and negative feedback are defined in different ways within different disciplines:

  1. The altering of the gap between reference and actual values of a parameter, based on whether the gap is widening (positive) or narrowing (negative) [in physics, cybernetics, biology].
  2. The valence of the action or effect that alters the gap, based on whether it has a happy (positive) or unhappy (negative) emotional connotation to the recipient or observer [in didactics, comunication training].


Fields of Application


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. An example of this is Insulin oscillations.

Biological systems contain many types of regulatory circuits, both positive and negative. As in other contexts, positive and negative do not imply that the feedback causes good or bad effects. A negative feedback loop is one that tends to slow down a process, whereas the positive feedback loop tends to accelerate it.

Feedback is also central to the operations of genes and gene regulatory networks. 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. 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).

On a larger scale, feedback can have a stabilizing effect on animal populations even when profoundly affected by external changes, although time lags in feedback response can give rise to predator-prey cycles.
In zymology, feedback serves as regulation of activity of an enzyme by its direct product(s) or downstream metabolite(s) in the metabolic pathway.
The hypothalamic–pituitary–adrenal axis is largely controlled by positive and negative feedback.


In psychology, the body receives a stimulus from the environment or internally that causes the release of hormones. Release of hormones then may cause more of those hormones to be released, causing a positive feedback loop. This cycle is also found in certain behaviour. For example, "shame loops" occur in people who blush easily. When they realize that they are blushing, they become even more embarrassed, which leads to further blushing, and so on.


External Sources




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