Feedback - Types of Feedback

Types of Feedback

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

1. the context of the gap between reference and actual values of a parameter, based on whether the gap is widening (positive) or narrowing (negative).
2. the context of the action or effect that alters the gap, based on whether it involves reward (positive) or non-reward/punishment (negative).

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, reinforcing/balancing, discrepancy-enhancing/discrepancy-reducing or regenerative/degenerative respectively. And within context 2, some authors advocate describing the action or effect as positive/negative reinforcement rather than feedback. 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. 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."

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. 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. Harold Stephen Black's classic 1934 paper first details the use of negative feedback in electronic amplifiers. According to Black:

"Positive feed-back increases the gain of the amplifier, negative feed-back reduces it."

According to Mindell (2002) confusion in the terms arose shortly after this:

"...Friis and Jensen had made the same distinction Black used between 'positive feed-back' and 'negative feed-back', based not on the sign of the feedback itself but rather on its effect on the amplifier’s gain. In contrast, Nyquist and Bode, when they built on Black’s work, referred to negative feedback as that with the sign reversed. Black had trouble convincing others of the utility of his invention in part because confusion existed over basic matters of definition."

Even prior to the terms being applied, James Clerk Maxwell had described several kinds of "component motions" associated with the centrifugal governors used in steam engines, distinguishing between those that lead to a continual increase in a disturbance or the amplitude of an oscillation, and those which lead to a decrease of the same.