I mailed this last night -- to the wrong address. Ooops.
[From Rick Marken (960311.2100)]
Re: the notion that asking a patient to worry _more_ is an example of
positive feedback I said:
Not necessarily. It looks to me like you are asking a person to change the
reference for a perception (worrying) that is presumably under control.
Scott Graham (960311) replies:
She actually tried to control worrying before -- along a continuum
(negative feedback -- reduce the error). She actually did not try to
control or reduce worrying but exagerate the worry -- amplify the error.
This is why it seems to be positve feedback to me...
"Worry" and "error" are not the same thing. "Worry" is a perceptual
variable; it is something we perceive (experience) and it varies (from
none to alot). You suggest that it is a controllable perception (which it
may be) and you describe a situation where a patient is asked to maintain
(control) that percpetion at a particular reference level (alot of worry).
If worry is controllable, then any difference between the level of worry
we are experiencing and the level of worry we want to experience is
"error" that drives whatever it is we are doing to increase or decrease
the perception of worry. We don't control this error; we control the
perception of worry. If our reference for worry is low (as it usually
is) then we will try to keep our perception of worry low (control it
relative to a low reference); if our reference for worry is high (as,
presumably, was the patient's in your example) then we will try to keep
our percpetion of worry high (control it relative to a high reference).
Negative feedback control doesn't mean trying to keep a perception (like
the perception of worry) low; it means trying to keep a perception at a
reference (desired) level, whatever that reference level might be. A
thermostat that's keeps the room temperature at a sweltering 120 degrees
is controlling just as well as is one that keeps the room temperature
at a comfortable 68 degrees (assuming that the reference setting of
the first thermostat is 120 degrees and that of the second is 68 degrees).
Error is not necessarily something we try to control; but if we did
try to control error, it would be the perception of error (difference
between actual and wanted worry) that is the variable to be controlled.
There would, indeed, be positive feedback if any increase in the
perception of error led to actions that further increased the error.
If the patient were actually in a positive feedback relationship with
respect to perceived error, then any increase in error would continuously
drive what she was doing to increase the error, thus further increassing
the error. What we would see is a rapid and unstoppable increase in the
level of worry felt by the patient until the patient could do no more to
increase her worry.
Perhaps this is what the patient did. But, from your description, it seems
more like the patient was able to change her reference for the amount of
worry she wanted to perceive and she was apparently also doing a pretty
good job of moving the percetion of worry to the new reference level.
This suggests negative feedback control of worry rather than a positive
feedback _loss of control_ of worry.
As Bill Powers suggested, perhaps the patient stopped worrying when she
learned to see the situation from the point of view of the systems
in herself that set the reference level for worry; she learned that
she was in control of how much worry she felt.
Here's another situation (from a phsyiological perspective):
A person with a heart condition takes nitroglycerin regularly and when
they experience chest pains (negative feedback -- reduce the error). Now,
for the sake of this illustration, suppose the error-reducing effects
don't happen' the patient's electrical impuses to the heart increase,
their BP goes up, etc.
They get rushed to the hopital where some vasodilating drugs are given
(another attempt to reduce the error). Still no effect...the patient's
electrical impusles go besurk and they enter v-fib.... The MDs now
introduce positive feedback -- amplify the electrical error -- hit the
patient with some voltage...the system collapses, recalibrates --
hopefully...
Yes / No?
Maybe.
I can't tell what the variables and functional relationships in
the loop might be. But I can imagine a case where this situation
would involve positive feedback -- though I don't know if this is
realistic. Positive feedback would exist if the doctors hit
the patient with a voltage that increased electrical activity in
the heart whenever they saw that the scope indicated increased
electrical activity in the heart. So an increase in a perceived
variable (indication of electrical activity on the scope) leads
to actions (hitting the patient with a voltage) that further
increases the electrical activity on the scope. I think this is
a pretty far-fetched scenario, however, In fact, the doctors are
probably trying to control heart activity and hit the patient (or
stop hitting) as necessary to get the perceived heart activity to
the desired level.
I think you may be using the term "positive feedback" to refer to
something other than positive feedback (as that term is used in
control theory). Positive feedback is rare in behavior and it's not
easy to voluntarily be in a positive feedback relationship with
respect to a variable (like worry) that one cares about.
Best
Rick