Bill Powers occasionally discussed the possibility that the gain of a control system might itself be a controlled variable. For those who may be interested, such gain control has been documented in the stick insect’s femur-tibia joint. The relevant article is:
Kittmann, R. (1991). Gain control in the femur-tibia feedback system of the stick insect. Journal of Eperimental Biology, 151, 503-522. (Gain control was discussed on the CSG listserv in July 1992 (Bill Powers (920722.800) replying to Martin Taylor.) In the stick insect, gain control was speculated to keep the system at maximum sensitivity to error, just short of instability, under varying environmental conditions.
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