You have a real-life example of (a) in the space-flight program. At
one stage there was an effect that was publicised as a mystery that
the space physiologists were hard put to explain. Why did people
increase their leg muscle output when they first arrived at the
space station (or MIR?) rather than decreasing it as they expected,
since in space you don’t walk? When I first saw that, I said to
myself that it was obvious that the low-level feedback path through
the foot on the ground had been cut, and so the output would
naturally increase, at least until reorganization allowed the
astronaut to adapt to zero G. I don’t remember the details, but I do
remember what I thought about it. I wonder if they have figured it
out yet?
Martin
···
[From
Bruce Abbott (2015.02.13.1910 EST)]
BA: I’m basically concerned with
modeling the Level 1 system that controls the
perception of muscle length and force. What happens
when the feedback pathways are cut, leaving the
reference inputs intact? How will the system
respond to (a) changes in reference level and (b)
changes in load? The answer to the first question
is that there will be an exaggerated response to the
so-called motor commands that set the reference
levels, at least until reorganization has had a
chance to reduce the output gain.
BA: I’m basically concerned with modeling the Level 1 system that controls the perception of muscle length and force. What happens when the feedback pathways are cut, leaving the reference inputs intact? How will the system respond to (a) changes in reference level and (b) changes in load? The answer to the first question is that there will be an exaggerated response to the so-called motor commands that set the reference levels, at least until reorganization has had a chance to reduce the output gain.
You have a real-life example of (a) in the space-flight program. At one stage there was an effect that was publicised as a mystery that the space physiologists were hard put to explain. Why did people increase their leg muscle output when they first arrived at the space station (or MIR?) rather than decreasing it as they expected, since in space you don’t walk? When I first saw that, I said to myself that it was obvious that the low-level feedback path through the foot on the ground had been cut, and so the output would naturally increase, at least until reorganization allowed the astronaut to adapt to zero G. I don’t remember the details, but I do remember what I thought about it. I wonder if they have figured it out yet?
Another example from space flight, this one working in the opposite direction, is the weakening of the bones astronauts experience during extended weightlessness. Apparently bone cells respond to the reduced strains on the skeletal system by reducing bone-strength. I imagine that there is a feedback system causing the bone cells to add or remove material so as the make the bones strong enough to resist the typical stresses they experience without adding so much as to make the bone overly thick and brittle. Feedback everywhere!