Timothy C. Hain, This document reviews the literature concerning
feedback control of pitch, and also is meant to be a place where
one can look at several mathematical models of central auditory
feedback control in one place. Fairbanks (1954) reviewed
historical ideas in a concept paper concerning auditory
feedback, going as far back as 1931. His servomechanism
incorporated a desired signal, a storage unit, a multi-input
comparator, a summing junction where the desired signal and
error are added, and a plant. Fairbanks recognized that there
might be multisensory inputs, and implemented auditory, tactile
and proproceptive inputs. This is a modern idea, reminiscent of
"internal estimator" theory, although Fairbanks did not discuss
the problem of dealing with multiple inputs in a quantitative
way. Although his "model" had a memory circuit, it was used to
extrapolate future performance where error was driven to zero
instead of matching delays of input to output. Ringel and Steer
(1963) examined the effect of anest