MIT professor Norbert Wiener describes two discrete flavors of feedback in hs 1947 book Cibornetcs. One form maintains equilibrium ond preserves ereuahon though maximum adoplabity. This is NEGATIVE feedback, It's schematically drawn like this :
In a NEGATIVE feedback loop, C (control) reads the current value of B (output), compares this 1 an ieal value, then instructs A (input) to send ether a higher or lower signal to B. This produces a new value whch C reads again and so on. In an air-conditioned room, for example, the thermostat (C) reads the current temperature (B), which is then compared against an ideal value, corrections are made (A) and more or less cold air is pumped in. The new fomperature is read ond the negative feedback loop continues, the roam reeching something, close to a constant temperature, or adaptive equilibrium.
POSITIVE feedback, on the other hand, works *against adaptability.* To produce posive feedback, one simply removes the control functions that are atherwise located where the information loop would meet itself to control its dynamic behavior. It Iooks something ike ths :
In the diagram above, there is no C fo interrupt the continuous escalation of the loop: A increases B which increases A which increases B... No self-regulating decison maker exists in the loop and more action leads only to more action, indefinitely. Phiosopher Manuel De Landa offers an easy mage :
“ The turbulent dynamics behind an explosion are the clearest example ofa system governed by postive feedbock. nthis case the loop is esteblshed between the explosive substance and ils temperature. The velocity of on explosion is often determined by the intensity of is temperature (the hotter the faster), bul because the explosion self generates heat, the process is self accelerating. Unlike the thermostat, where the errangement helps to keep temperature under central, bee posive feedback forces temperature to go out of control. ”
The prinapal characteristic of negative feedback in the thermostat example iis HOMOGENIZING effect ; all deviations are fllered and eliminated. Postve feedback instead, as De Landa explains,
“ tends to increase helerogeneity, as smal orignal differences are amplifed by the loop into large discrepancies. ” So the diagram actually ought to look somethng more like this :
– " INNNNNNWAHHHHH! ” Lars Bang Lersen, Bulletins of The Serving Litrary #4, 2012
Liam Gilick, Monument to democracy, 2012, digital print, 89.3 x 69cm