[From Rick Marken (970418.2340)]
Me:
If I am not able to design an experiment so that it produces clear
and consistent results, I give up on the experiment until a
cleverer person comes along and does it right.
Bruce Abbott (970418.1100 EST)--
Well, that explains why PCT has not advanced beyond simple
tracking experiments in over 25 years. You leave all the
really hard work to others -- and there ain't no others.
How true. But I reassure myself with the knowledge that
reinforcement theory has not advanced beyond simple feeding experiments
in over 60 years.
Me:
Even when there is an observed correlation between d and p it is
still not correct to say that p reduces the system's uncertainty
about d.
Bruce Abbott (970418.2005 EST) --
there is no use arguing about it; it is an empirical question. We
could answer it with appropriate data from a simple tracking study.
I doubt it. We did such studies a couple years ago; Martin is convinced
that they showed that there is information about the disturbance in the
perceptual signal; I (and I think Bill and Tom)
am convinced that they showed that there is no such information in
the perceptual signal.
We can design such studies again if you like. But I think it
might be nice to first discuss a higher level question: Why should
anyone care whether or not there is information about the disturbance in
perception? If there is such information it is certainly not
clear what it would be doing there. If, as you say, the information
about the disturbance is proportional to the correlation between
disturance and perceptual signal (higher correlation means more
information) then the _better_ the system controls, the _less_
information there is about the disturbance. This is a peculiar
relationship if the information about the disturbance is used by
the control system as the basis for generating the outputs that counter
that disturbance; the more information there is about the disturbance,
the more poorly the system does at generating outputs that counter the
disturbance.
It may be, however, that the information about the disturbance is
something that control systems don't want. All control systems might
have a reference level of 0 for the amount of information about the
disturbance that they want to receive. This seems to be Martin's
position and I have to agree with Bruce Gregory that it seems awfully
strange. It is certainly something I have never heard in the literature
on control theory -- even the literature on MCT.
I can tell you why I _don't_ like the idea that there is information
about the disturbance in perception. I don't like it because it
sounds to me like an attempt to conceptualize control in S-R terms.
The information-based models of control that I have seen assume that
information about the disturbance is an aspect of the sensory input
to the system. This information _guides_ the outputs that compensate
for that disturbance. This conception of the control process is
consistent with the fundamental assumption of conventional psychology --
that inputs guide or cause outputs. It is completely inconsistent with
the way control systems actually work. A control system guides
or _controls_ its input; inputs don't guide or control the control
system.
Of course, there might actually be information about the disturbance in
perception. If so, then I wonder what is it there for? If there
is information in the perceptual signal then how can it be anything
other than a side effect -- like the buzz that a neuron makes when
it is hooked up to an amplifier?
I note that you had _no_ comment about my claim that a system
provided a sensor to detect the effect of its own actions on
its perception of the CV would be capable of providing almost
full information about the disturbance. Don't want to admit I
have it right?
Both Bill and I noted that if a system (other than the one doing the
controlling) has access to both the perceptual signal, p, and output
variable, o, (assuming all other functions are constants) then it would
be trivially easy for that system to deduce the disturbance, since p = o
+ d and d = o - p. The system doing the controlling
could compute the estimated value of d too, of course, and everything
would be fine as long as the system "provided" this information to some
other system and didn't use it itself as its perceptual or
output signal.
Of course, in a real situation, you would have to know a lot more
than just the output signal to deduce the disturbance variable(s);
you would have to know the feedback function, the number of
disturbing variables influencing the controlled variable and the
function relating EACH disturbing variable to the controlled
variable.
Best
Rick