devils bathtub

[Avery Andrews 930119.730]

  Rick Marken (920119.1200)

Houk & Rymer (and even Arbib) don't suggest that feedforward can be
effective on its own - in their diagram it acts in concert with a
feedback system (like turning the steering wheel on the basis of
the perceived curvature of the upcoming road, which can be done in
accord with a formula posted by Bill during the steering discussion
a few months ago. So I'd put H&R on the goodguy list (after all,
Houk & Milhorn (1984) described the posture-control circuitry that
Bill & Greg simulated a simplified version of).

(Greg Williams (30119))

Wow! The page 210-211 quotes are really off the wall. It seems to me
that this stuff can be used in arm documentation. E.g. Jordan &
Rosenbaum dismiss feedback as too slow citing only Schmidt, but judging
from these quotes he's demonstrably so ignorant that they seriously
discredit themselves by doing this.

`Event-based' analysis seems to be a common thread running through many
of these DB entries, & it's interesting that that's where Beth Preston's
Synthese paper falls apart too, in my judgement. Also assuming that
reaction times for voluntary activity have much to do with the existence
of lower level closed-loop mechanisms. I think that a lot of the
movement-control schemes in Jordan & Rosenbaum are event-based too,
but I'm not sure, since the prose is fairly vague (or my math too
feeble).

But, it does seem like at the vicinity of 212 Schmidt might be getting
around to making sense, but I don't get a clear conception of what
overall conclusions he's coming to there.

Avery.Andrews@anu.edu.au

[From Rick Marken (930119.1400)]

Avery Andrews 930119.730

Houk & Rymer (and even Arbib) don't suggest that feedforward can be
effective on its own - in their diagram it acts in concert with a
feedback system.

Oh, all right. They can have the tub in the PCT corner of heaven which
has a thermometer that shows current temp, derivative of temp and
a "predictive display" of up to 10 minutes of estimated future temp --
constantly revised based on changing outputs (ice cubes, boiling water
and atmospheric conditions) -- the delux model. I agree that this kind
of "feedforward" could be used to improve control (the predicted infor-
mation is still part of a closed control loop -- the word "feedforward" may
be what is misleading; predicted future information is just a present time
perceptual input that can be a controlled variable -- or part of a controlled
variable -- like any other controlled variable).

Best

Rick