That should do it

[From Rick Marken (931113.1000)]

Powers (931112.1750 MST), (931112.0815 MST) --

This is the resolution I was after. Does it work for you, Chuck?
I can't imagine it being said more clearly and completely. Bill's
wonderful posts should put feedforward (at least, as a possible
explanation of behavior) in its proper place (ie. down the toilet).

But the discussion has suggested a useful point that should be
included in the PCT repetoire of demonstrations, experiments and
models. The point is that a heirarchicy of feedback control systems
can "survive" for some time intermittant losses of sensory input
about controlled variables. Psychologists who, for whatever reason,
want to show that "feedback" (really, perception) is not a necessary
component of behavior (a point of view that tends to make it hard
to convince psychologists that behavior is the control of perception)
point to studies where behavioral results are produced with sensory
loss as evidence of their point of view. I think that it is very
important to show that a control system will behave just like a living
system when both are subjected to the same kinds of sensory loss. So
I am planning to do a version of the experiment suggested by Hans and
Bill P. -- tracking a predictable target and having the corsor disappear
for periods of time that can be adjusted by the experimenter. I plan to
compare the behavior of subjects to that of a control system model AND
an open loop model. I hope to put to rest the idea that behavior during
sensory loss rules out a feedback model (and rules IN an open-loop,
feedforward model). But I am under no illusions about this; I am well
aware of the fact that open-loop ideas can be put to rest no more
easily than PCT fanatics or rust. But, it's something to do.