Abs & Winstein (feedback too slow)

[Avery Andrews 930127.1710]
  Rick Marken (930112.0800)

> If you want
>to read more amusing statements about feedback being "too slow" made by
>authoritative leaders in the study of human movement control , try the article
>by
>Abbs and Winstein in M. Jeannerod (ED) Attention and Performance XIII,
>Hilldale, Erlbaum, 1990

I had a look at it, and didn't find the discussion about speed silly
at all. They debunked the 200ms myth, showed that feedback
thru the oral track could occur in as little as 12 msec, noted
that feedback from the distal arms was faster than the proximal
arms, maybe in the 30 msec range, etc. It isn't my field, but I
didn't see any figures that were at variance with common sense, &
the generaltrend of the literature.

What I did find intriguing was the following assertion:

"Technically, a feedback system is one in which an error signal
  directly drives a corrective adjustment >at the site where the
  error is introduced<" (p. 366, my emphasis)

This was supposed to entail that compensetory lip adjustment couldn't
be feedback (this is when someone is trying to make, say, a /w/,
which requires the lips to come close together, and one lip is
disturbed, & the other goes further to make up for it).

Does anyone know any basis for this `technical' restriction on the
scope of feedback? It seems patently wrong, even on the basis
of the classic examples of thermostat and ships rudder, where
the error might be introduced in front hall, when Fred leaves
the front door open for a while, and the compensatory adjustment
is made in the basement by the furnace starting.

I didn't have the time to read the whole article carefully, but I
did notice that the authors are caught up in the stampede of
enthusiasm for `motor programs', which still appear to me to be
a rather vague and woolly concept that we might hope to get somewhere
by replacing with the ECS.

Avery.Andrews@anu.edu.au