[From Bruce Abbott (970419.1450 EST)]
Rick Marken (970418.2340) --
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.
No, those "feeding experiments" have become quite sophisticated, and what
has been learned from them could fill many large volumes. Why has there not
been a similar explosion in the tracking field? Most studies can be
implemented with nothing more than a PC and a single willing participant,
and an enormous amount of data can be produced in short order (e.g., 3600
data points in 2 minutes). (For comparison, those "simple feeding
experiments" usually take months to complete, sometimes over a year.) Even
ol' unfunded Rick Marken should be able to crank out several such studies a
year in his spare time. So why the lack of activity?
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.
How can this be a matter of opinion if you have the data? Did anyone
compute the quantity of information? What was it?
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.
Martin Taylor already answered that question. You are reifying
"information" into a "something" that has something to "do." Information is
just a metric for system performance. If I said that the output of a sensor
conveys information about the termperature, would you ask me what the
information is "doing there" in the wire?
The question is whether this alternative metric provides insights into
system performance that are not as easy to obtain using other metrics (like
the correlation between d and p). I'd like to see Martin give it a shot.
What can it hurt?
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.
You seem to be on a reification _binge_, Rick. Control systems don't have
wants with respect to information, nor reference levels. In fact, control
systems don't "want" anything. They just do what they do. If this action
happens to bring p near to r, they don't become any happier, and they don't
feel sad or upset when these actions fail. They are not little people.
But a perfect control system _would_ allow _no_ information about a
disturbance to p to show up in p. That's what control systems _do_:
ideally, they isolate their controlled inputs from the effects of
disturbance, and isolation means that one could learn nothing about the
disturbance merely by monitoring p. On the other hand, if r were known to
be constant, then any wiggles in p would indicate a disturbance to p.
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.
That's just metaphorical speech. Information is just a metric. It implies
nothing whatever about S-R or causality. You should be objecting to the
concept of gain: it sounds like an attempt to conceptualize control in
capitalist economic terms. (No doubt the term was invented by a Republican
Of course, there might actually be information about the disturbance in
perception. If so, then I wonder what is it there for?
Arrgh. Let's rephrase this. "Of course, there might actually be some
shared variance between the disturbance and the perception. If so, then I
wonder what it is there for?" The steering wheel on my daughter's care
shakes at under 20 mph. I wonder what the shaking is there for. Do these
questions make any sense? No.
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
Well, you know Rick, the lack of comment does not indicate agreement; in
fact it _can_ be interpreted as the opposite, if one is disposed to do so.
I for one would find it most helpful if you explicitly indicate when you
_agree_ with some observation or conclusion of mine as well as when you
disagree. I'm not a mind reader.
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
Yes, of course, with respect to the first. As for the rest, that depends on
whether you need to know each disturbance individually or only their