[Avery Andrews 920121.1030]
Here's some evidence that Schmidt and a number of other people don't
understand feedback very well:
Cruse, H, J. Dean, H. Heuer and R.A. Schmidt (1990) `Utilization of
Sensory Information for Motor Control', in O. Neumannn & W. Prinz,
Springer-Verlag, pp 43-`79.
This article covers a lot of ground, and makes some proposals that may
well be right, as far as I know, but the smoking guns of ignorance
appear on p. 60, where they are discussing a model in which
commands are sent out to effectors on a `feedforward' basis,
with a feedback system supplying corrections (sort of like what I've
speculated for driving). The bloopers:
1. "The advantage of an open loop system is that it responds quickly
to an input signal, and cannot become unstable like a closed loop
system subject to a delay in the feedback signal."
The first statement being wrong, since a reference level and
a current perception can be compared monosynaptically, which
is trivial in the overall time-budget. The second is true,
but irrelevant, since you get the possiblity of instability
once a feedback system is included.
2. "Owing to the operation of the open-loop system, the closed-loop
system only has to deal with small error signals, so the gain
(S) can be relatively low."
Wrong because you need a high-gain sysem to compensate for
small errors.
There's lots more here to mull over, but I can't do it today.
Avery.Andrews@anu.edu.au