Book Review

I've just finished reading Bill Powers' book "Making Sense of Behavior: The
Meaning of Control." It presents a much more satisfying view of human
beings than the "black box" view of the behaviorists or the computer-inside
view of the cognitivists. I've posted a review of it on my articles web
site under the General Interest heading. You can go to it directly at
http://home.att.net/~nickols/behavior.htm.

···

--

Fred Nickols
The Distance Consulting Company
"Assistance at A Distance"
http://home.att.net/~nickols/distance.htm
nickols@worldnet.att.net
(609) 490-0095

[From Rick Marken (2002.11.26.0850)]

I have finally completed my review of the book "Control theory for humans" by
Jagacinski and Flach. I posted the review at
http://www.mindreadings.com/BookReview.htm. I hope you find it helpful.

Best regards

Rick

···

--
Richard S. Marken, Ph.D.
The RAND Corporation
PO Box 2138
1700 Main Street
Santa Monica, CA 90407-2138
Tel: 310-393-0411 x7971
Fax: 310-451-7018
E-mail: rmarken@rand.org

[From Rick Marken (2002.11.27.0900)]

Bruce Abbott (2002.11.27.0930 EST)--

Rick, although I appreciate the point you make in this paper,

I appreciate the appreciation. I'd rather get _agreement_ , but appreciation will
do;-)

I must say
that it doesn't really qualify as a review of Jagacinski and Flach's
book. It conveys very little about the contents of the book.

I agree. It wasn't that kind of review, I guess.

We learn
that it describes the tools used by engineers to analyze control systems
(such as Bode plots), and that's it. The rest of the paper is a lament
over what it does NOT contain.

Well, I didn't mean it to be a lament. I wrote the review from the point of view
of PCT oriented behavioral science researcher (I found it difficult to write it
from any other perspective;-)) advising a student regarding this new new book
introducing the application of control theory to the study of behavior. My review
is what I would tell students who came to me asking about "Control theory for
humans"; whether they should read it as an introduction to the application to
control theory to behavioral science. I think that, in this sense, the review is
informative about the book.

Best regards

Rick

···

--
Richard S. Marken, Ph.D.
The RAND Corporation
PO Box 2138
1700 Main Street
Santa Monica, CA 90407-2138
Tel: 310-393-0411 x7971
Fax: 310-451-7018
E-mail: rmarken@rand.org

[From Bruce Abbott (2002.11.27.0930 EST)]

Rick Marken (2002.11.26.0850) --

I have finally completed my review of the book "Control theory for humans" by
Jagacinski and Flach. I posted the review at
http://www.mindreadings.com/BookReview.htm. I hope you find it helpful.

Rick, although I appreciate the point you make in this paper, I must say
that it doesn't really qualify as a review of Jagacinski and Flach's
book. It conveys very little about the contents of the book. We learn
that it describes the tools used by engineers to analyze control systems
(such as Bode plots), and that's it. The rest of the paper is a lament
over what it does NOT contain.

On a more positive note, CSGneters might enjoy taking a look at the control
system simulations posted on the web by John Flach. In one, you can try to
keep a motorcycle on a road by controlling position, velocity,
acceleration, or two higher-order levels (1st derivative of acceleration,
etc.). (Be sure to check out "older demos" for more.)

Bruce A.

[From Bruce Abbott (2002.11.27.0950 EST)]

Me:

On a more positive note, CSGneters might enjoy taking a look at the
control system simulations posted on the web by John Flach. In one, you
can try to keep a motorcycle on a road by controlling position, velocity,
acceleration, or two higher-order levels (1st derivative of acceleration,
etc.). (Be sure to check out "older demos" for more.)

I forgot to mention the Web address. It's

http://studiolab.io.tudelft.nl/controltheory/

Bruce A.

[From Rick Marken (2002.11.27.1530)]

Ray (2002.11.28.0750)

An interesting way of writing a review Rick.
I hope that “interesting” isn’t a nice way of saying “awful”:wink:
It seems clear what it
is you are controlling for.
Thank you. I’ve been trying to make it clear for over 20 years. I’m beginning
to like this review more and more.
Where else is the book
review being published?
Nowhere else, to my knowledge. I sent a copy of the review to Erlbaum (the
publisher of “Control theory for humans”) and the person who read it loved
it. I was thinking of sending it to Contemporary Psychology (a journal
of reviews of books on psychological topics) but I don’t think they publish
unsolicited reviews.
Thanks again for the comments, Ray

Best regards

Rick

···

Richard S. Marken, Ph.D.

The RAND Corporation

PO Box 2138

1700 Main Street

Santa Monica, CA 90407-2138

Tel: 310-393-0411 x7971

Fax: 310-451-7018

E-mail: rmarken@rand.org

[From Rick Marken (2002.11.27.1615)]

Bruce Abbott (2002.11.27.1830 EST)--

I'm left wondering whether you have actually read the book. Were there no
ideas presented in it that would be worth discussing here, on CSGnet?

I did read the book, some parts more carefully than others. There are probably
topics worth discussing on CSGNet. But I think the topics would pertain to
technical details that would probably not be of great interest to many people on
CSGNet. It's hard to judge the pertinence of ideas to CSGNEt when those ideas are
not based on an understanding of behavior as the control of perceptual variables.
That's what I was trying to communicate in the report.

Was it written at a level appropriate for its intended audience (behavioral
researchers and their students)?

Again, it's hard to say. Since the target audience is behavioral scientists and
since the book is the second part of what should be a two part series (with BCP
and MMR as the first part) I guess I'd say it's too advanced for the target
audience. It's kind of like teaching people calculus before they've been taught
algebra. But then again it's not. It's weird.

Would CSGnetters who want do do
quantitative modeling benefit from reading it?

Again, it's not easy to say. I would say it would benefit people who already know
PCT quite well. I would say no if people don't. In fact, I think it would be very
confusing to learn quantitative modeling from the book, and the reason would,
again, be related to the theme of my review: the absence of any discussion of
controlled perceptual variables and where those variables fit into the design of
control models.

Do you think it worth owing
a copy?

I would say , if you already understand PCT quite well then, yes, it would be
worth owning it. If you don't understand PCT quite well then I'd wait on it
because the book could lead to confusion.

(I've been seriously considering plunking down the $39.95 for the
softcover edition, and was hoping your review would help me to decide.)

I think it would _definitely_ be worth it for you to get it. There are things in
there that could be useful to someone, like you, who understands the basics of
PCT. I think that's the point of my review: if you are a behavioral scientist
who understands what a controlled variable is and how it fits into a control model
of behavior then my review says "Control theory for humans" (CTH) should be on
your shelf. If, however, you are a little fuzzy about the nature of control or
perceptual variables or such stuff, then you should probably master B:CP and MSB
(and MR and MMR, but I was too self- effeacing to mention those;-)) before
tackling CTH.

Best regards

Rick

···

--
Richard S. Marken, Ph.D.
The RAND Corporation
PO Box 2138
1700 Main Street
Santa Monica, CA 90407-2138
Tel: 310-393-0411 x7971
Fax: 310-451-7018
E-mail: rmarken@rand.org

[From Ray 2002.11.28.0750]

An interesting way of writing a review Rick.
It seems clear what it is you are controlling for. I hope it works and
that students understand what control theory for humans should really be
about and that they will take a look at Bill’s books. Where else is the
book review being published?

Regards,

Ray
Richard Marken wrote:

···

[From Rick Marken (2002.11.26.0850)]
I have finally completed my review of the book “Control theory for humans”
by

Jagacinski and Flach. I posted the review at

http://www.mindreadings.com/BookReview.htm.
I hope you find it helpful.

Best regards

Rick

Richard S. Marken, Ph.D.

The RAND Corporation

PO Box 2138

1700 Main Street

Santa Monica, CA 90407-2138

Tel: 310-393-0411 x7971

Fax: 310-451-7018

E-mail: rmarken@rand.org

[From Bruce Abbott (2002.11.27.1830 EST)]

Rick Marken (2002.11.27.0900) --

> Bruce Abbott (2002.11.27.0930 EST)--
>
> Rick, although I appreciate the point you make in this paper,

I appreciate the appreciation. I'd rather get _agreement_ , but
appreciation will
do;-)

O.K., allow me to rephrase. I agree with the point you make in this
paper. A major part of applying control theory to human behavior is
testing to determine what is actually being controlled. If the book
doesn't mention that, it misses something important.

> I must say
> that it doesn't really qualify as a review of Jagacinski and Flach's
> book. It conveys very little about the contents of the book.

I agree. It wasn't that kind of review, I guess.

What kind of review is it, that doesn't review?

> We learn
> that it describes the tools used by engineers to analyze control systems
> (such as Bode plots), and that's it. The rest of the paper is a lament
> over what it does NOT contain.

Well, I didn't mean it to be a lament. I wrote the review from the point
of view
of PCT oriented behavioral science researcher (I found it difficult to
write it
from any other perspective;-)) advising a student regarding this new new book
introducing the application of control theory to the study of behavior. My
review
is what I would tell students who came to me asking about "Control theory for
humans"; whether they should read it as an introduction to the application to
control theory to behavioral science. I think that, in this sense, the
review is
informative about the book.

I'm left wondering whether you have actually read the book. Were there no
ideas presented in it that would be worth discussing here, on CSGnet? Was
it written at a level appropriate for its intended audience (behavioral
researchers and their students)? Would CSGnetters who want do do
quantitative modeling benefit from reading it? Do you think it worth owing
a copy? (I've been seriously considering plunking down the $39.95 for the
softcover edition, and was hoping your review would help me to decide.)

Bruce A.

[From Bruce Abbott (2002.11.28.1000 EST)]

Rick Marken (2002.11.27.1615) --

> Bruce Abbott (2002.11.27.1830 EST)--
>
> (I've been seriously considering plunking down the $39.95 for the
> softcover edition, and was hoping your review would help me to decide.)

I think it would _definitely_ be worth it for you to get it.

O.K., thanks!

Bruce

[From Bill Williams UMKC 28 November 2002 6:00 PM CST]

I'm finding the Jagacinski and Flach book interesting reading.

However, I would point out a minor error on page 274. where the stall speed
is defined as "A wing stall is a situation where the lift generated by the
wing is less than the force of gravity." This is not correct. Actually a
stall is defined in terms of the angle of attack between an airfoil ( wing)
and an airflow at which their is an abrupt increase in the ratio between
aerodynamic drag and lift. THis statement occurs in a passage which
considers "controlled flight into terrain." A properly trained pilot uses
an airspeed indicator as the primary indicator of airspeed, not a
perception of speed over the ground. But, J & F treat this problem in terms
of a "Global Optical Flow Rate" of travel over the ground. The GOFR may
well be a part of the initial problem they discuss in this section where
pilots transitioning to the 747 initially taxied the aircraft at an
excessive speed. However as far as I know this has not been a signficant
contributor to controlled flight into terrain accidents. This isn't
neccesarily an indicator of the quality of J&F's typical treatment of
issues-- but they don't appear to be dependablely familiar with the actual
character of perceptual problems involved in operating an aircraft.

I would be interested in observations where it is perceived that J&F make
similar errors in regard to material with which I wouldn't neccesarily be a
position to assess the correctness of what they are saying.

Rick's review tells us J&F didn't write the book the way PCT people would
have written the book-- which is important to recognize. What, I'd would
also be interested in is how accurate and well done is the book they
actually wrote.

Bill Williams

[From Bruce Gregory (2002.11.28.2008)]

Bill Williams UMKC 28 November 2002 6:00 PM CST

However, I would point out a minor error on page 274. where the
stall speed
is defined as "A wing stall is a situation where the lift generated
by the
wing is less than the force of gravity." This is not correct.

Indeed. If it were correct, the wings of an aircraft would be stalled
when it was parked at the gate, taxiing or on a takeoff roll! You
take off by increasing the angle of attack, not by unstalling the
wing (which normally requires one to _decrease_ the angle of attack).

What, I would
also be interested in is how accurate and well done is the book they
actually wrote.

Me too.

[From Rick Marken (2002.11.29.0910]

Bill Williams (UMKC 28 November 2002 6:00 PM CST)

I'm finding the Jagacinski and Flach book interesting reading.

However, I would point out a minor error on page 274. where the stall speed
is defined as "A wing stall is a situation where the lift generated by the
wing is less than the force of gravity." This is not correct. Actually a
stall is defined in terms of the angle of attack between an airfoil ( wing)
and an airflow at which their is an abrupt increase in the ratio between
aerodynamic drag and lift.

I think the J&F definition of wing stall is a more general than yours but both
are correct. It's true that wing stall is often defined in terms of angle of
attack but I think this is because angle of attack is the main determiner of
stall in-flight. But you can certainly stall a plane in-flight by reducing the
speed of the plane sufficiently while keeping the wing angle of attack
constant. Wing stall does mean that lift force is less than gravitational
force. Wing stall (J&G definition) is influenced by many variables (speed,
aileron position, load, altitude, etc.) the main one of which is angle of
attack. So it's also correct to say that wing stall occurs occurs when the
angle of attack of the wing produces an abrupt increase in drag relative to
lift. It's just a narrower definition, though it's the one that is probably
most useful to a pilot.

THis statement occurs in a passage which
considers "controlled flight into terrain." A properly trained pilot uses
an airspeed indicator as the primary indicator of airspeed, not a
perception of speed over the ground. But, J & F treat this problem in terms
of a "Global Optical Flow Rate" of travel over the ground.The GOFR may
well be a part of the initial problem they discuss in this section where
pilots transitioning to the 747 initially taxied the aircraft at an
excessive speed. However as far as I know this has not been a signficant
contributor to controlled flight into terrain accidents.

Did J&F say that GOFR was a significant contributor to controlled flight into
terrain accidents, without presenting any evidence that it is? If so, then I
agree that that would be a shortcoming of the text. But as I recall (the book
is in my office at the moment) the chapter on GOFR was a discussion of GOFR as
a possible controlled variable. Of course, J&F never use the term "controlled
variable" but I think that is what they were trying to get at.

Best regards

Rick

···

--
Richard S. Marken
MindReadings.com
marken@mindreadings.com
310 474-0313

[From Bruce Gregory (2002.11.29.1255)]

Rick Marken (2002.11.29.0910)

I think the J&F definition of wing stall is a more general than
yours but both are correct. It's true that wing stall is often
defined in terms of angle of attack but I think this is because
angle of attack is the main determiner of stall in-flight. But you
can certainly stall a plane in-flight by reducing the speed of the
plane sufficiently while keeping the wing angle of attack constant.

I'm afraid not. If you reduce power and keep the angle of attack
constant, the plane will descend rather than stall.

[From Rick Marken (2002.11.29.1130)]

Bruce Gregory (2002.11.29.1255)--

> But you
>can certainly stall a plane in-flight by reducing the speed of the
>plane sufficiently while keeping the wing angle of attack constant.

I'm afraid not. If you reduce power and keep the angle of attack
constant, the plane will descend rather than stall.

I thought that if you powered down completely while keeping angle of
attack constant you would eventually be moving so slowly that you would
stall. Isn't this basically what "stall speed" is? The speed at which
gravitational force exceeds lift force for some constant angle of
attack? Doesn't angle of attack basically just affect the speed at
which a stall would occur? And isn't "descent" just a gradual "stall"
anyway?

Anyway, it doesn't seem to me like it was much of a mistake for J&F to
define a stall as gravitational force exceeding lift force. That is what
happens when a plane stalls, after all, isn't it?

Best

Rick

···

---
Richard S. Marken
MindReadings.com
marken@mindreadings.com
310 474-0313

[From Bill Williams UMKC 29 November 2002 12:24 PM CST]

Rick says,

"... you can certainly stall a plane in-flight by reducing the speed of the
plane sufficiently while keeping the wing-angle of attack constant."

When I was a flight instructor, and my students would present this
argument, and they did, I used to take them out and show them that it is
possible to reduce the speed of an airplane to zero ( at least indicated
which since zero is far as for most purposes you can reduce an aircraft's
airspeed would meet your criteria for "sufficiently" ) and continue to fly
the airplane without its approaching a stall. The cost to them for such
instruction, over and above the normal hourly fee, was dinner. Since we
didn't have an angle of attack indicator, I didn't attempt to demonstrate
that I could keep the angle of attack constant, but given an AOA meter I
could do that too so the "certainity" you attribute to your argument is
misplaced. Upon what basis did you come up with this argument?

An aircraft stalls when its AOA exceeds a critical value-- period. Any
other "definition" is mistaken. Airspeed has nothing to do with a wing's
stalling. Too harbor such a misconception in the course of flight
operations is distinctly dangerous. One of the effects of such a
misconception is a belief that above a certain speed an aircraft is
going "too fast to stall." So, its important to be sure in training a pilot
that they are aware that airspeed and a wing's stalling are not connected.
The elementary flight instruction sylabus has over the years been
constructed with a great deal of care to weed out misconceptions such as
the basic misconception of thinking that an airplane can be stalled by
reducing its speed while holding the AOC constant. Such thinking is an
indication of a basic kinesmatic confusion. The impression that J&F's
discussion might give, to someone who wasn't familiar with aircraft
operations is that they are dealing with actual problems encountered in
aircraft operations. The discussion that lead into this passage about
excessive taxi speed appears to me to be correct, but then they go off on
speculations that have little or no actual relevance to actual problems,
and their discussion is the sort academics get into when they don't know
the field to which they which they wish to find applications for their
speculations. I'll repeat what I said about a properly trained pilot
relying upon an airspeed indicator rather than a visual flow for an
indicator of airspeed. One of the exercises which may be required for the
most basic private pilot's liciensure exam is flying a circle around a
point at low altitude in a significant wind. The point of the exercise is
to convince the student of the fact that the optical flow _does not_
correspond to airspeed. When this exercise is flown in a light airplane at
60 mph in a 40 mph wind the point of the exercise is dramatic. Ground speed
varies from 20 mph going upwind to 100 mph going downwind. My impression
based upon reading the accident reports for a number of years is that
contemporary pilots do not fly into the ground because they confuse visual
flow with airspeed.

When I made my point about J&F exhibiting some misconceptions, I also said
that I considered the errors "minor" in the context of their work. But,
the errors are by no means "minor" in the context of flight operations.
And, I expressed a curiousity about whether people with understandings
different than mine perceived similiar errors of which I might not be aware.

best

Bill Williams

[From Rick Marken (2002.11.29.1230)]

Bill Williams (UMKC 29 November 2002 12:24 PM CST)

Rick says,

"... you can certainly stall a plane in-flight by reducing the speed of the
plane sufficiently while keeping the wing-angle of attack constant."

When I was a flight instructor, and my students would present this
argument, and they did, I used to take them out and show them that it is
possible to reduce the speed of an airplane to zero ( at least indicated
which since zero is far as for most purposes you can reduce an aircraft's
airspeed would meet your criteria for "sufficiently" ) and continue to fly
the airplane without its approaching a stall. The cost to them for such
instruction, over and above the normal hourly fee, was dinner. Since we
didn't have an angle of attack indicator, I didn't attempt to demonstrate
that I could keep the angle of attack constant, but given an AOA meter I
could do that too so the "certainity" you attribute to your argument is
misplaced. Upon what basis did you come up with this argument?

It was an intuition based on my understanding of how a stall occurs. I guess
I'm surprised that a plane will stay up when its airspeed is zero. Does
airspeed include wind speed? If not, it sounds like you are saying that a plane
will not stall even when there is no movement of air relative to the plane. So
the only way to get a plane to stall is to change the angle of attack of the
wings (once the plane is up, I presume)?

An aircraft stalls when its AOA exceeds a critical value-- period.

OK. That's quite a surprise, I must admit.

Any other "definition" is mistaken.

But when AOA exceeds a critical value, the gravitational force exceeds the lift
force, does it not? So it's really not a mistake to say "A wing stall is a
situation where the lift generated by the
wing is less than the force of gravity ". That is what happens when there is a
wing stall, is it not, regardless of _why_ it happens.

Airspeed has nothing to do with a wing's stalling.

Why, then, do they give an airplane's "stall speed" as one of it's
specifications?

Best regards

Rick

···

--
Richard S. Marken
MindReadings.com
marken@mindreadings.com
310 474-0313

[From Bruce Gregory (2002.11.29.0645)]

Rick Marken (2002.11.29.1130)

I thought that if you powered down completely while keeping angle of
attack constant you would eventually be moving so slowly that you
would stall. Isn't this basically what "stall speed" is?

Stall speed is a misnomer. An airplane can stall at any speed if you
pull back on the stick hard enough.

>And isn't "descent" just a gradual "stall" anyway?

I sure hope not! I'd hate to think of a 747 descending from 30,000
feet on the brink of a stall. Airline pilots don't like to be
anywhere near a stall anyplace higher than two feet off the runway.
Sometimes not even there.

Anyway, it doesn't seem to me like it was much of a mistake for J&F
to define a stall as gravitational force exceeding lift force. That
is what happens when a plane stalls, after all, isn't it?

No. See my earlier post. As a plane proceeds down the runway in a
takeoff run the gravitational force exceeds the lift force for most
of the roll, but the wing is not stalled -- air is flowing smoothly
over the wing and generating lift with minimal drag.

[From Rick Marken (2002.11.29.1520)]

Bruce Gregory (2002.11.29.0645)--

>Anyway, it doesn't seem to me like it was much of a mistake for J&F
>to define a stall as gravitational force exceeding lift force. That
>is what happens when a plane stalls, after all, isn't it?

No. See my earlier post. As a plane proceeds down the runway in a
takeoff run the gravitational force exceeds the lift force for most
of the roll, but the wing is not stalled -- air is flowing smoothly
over the wing and generating lift with minimal drag.

Ah, I think I get your (and Bill's) point! Defining a stall as
"gravitational force exceeding lift force" doesn't distinguish stall
from other flight regimes where gravitational force exceeds lift force.

I guess that is a mistake. Not being a pilot I'm afraid I was unable to
evaluate the sections of J&F that dealt with piloting.

Best regards

Rick

···

--
Richard S. Marken
MindReadings.com
marken@mindreadings.com
310 474-0313

[From Bill Powers (2002.12.03.1048 MST)]

Back from Thanksgiving with kids in Boulder County. My remote e-mail
access didn’t work.

Bill Williams UMKC 28 November 2002
6:00 PM CST

Not that it matters, but since committees always spend 90% of their time
on the smallest 10% of the budget …

As I understand it, a stall condition is defined as the velocity at which
laminar flow over the top of the wing begins to turn into turbulent flow:
“the boundary layer separates,” as they say. The angle of
attack (relative to the direction of travel, the relative wind, not to
the horizontal) at which this occurs depends on airspeed, lift, weight,
drag, thrust, and wing configuration. I was once co-owner of a Stinson
Station Wagon, with a high gull-wing having leading-edge slots which
could be opened with a lever. The leading-edge slots directed air
downward over the wing at high angles of attack, preserving laminar flow.
I remember flying it straight and level with the nose aimed at the sky
and the throttle wide open, at 45 MPH. Quite a sensation. Of course it
wasn’t in a stall.

I’m finding the Jagacinski and
Flach book interesting reading.

Yes, I did too, in both a positive and a negative way. Positively, they
have collected all of the main concepts of control developed over the
last 60 or 70 years, so we have something concrete against which to
compare PCT. Negatively, I think the model they have adopted from the old
engineering psychologists is not carefully thought-out even for the very
narrow tracking situation for which they use it (The “McReuer
Crossover Model”). They never realized that a subject in a tracking
experiment could create and maintain many different relationships between
cursor and target, so they thought that the error was right out there on
the display screen, rather than seeing that it had to result from
comparing a perception with an internal, not an external,
reference. In fact that point seems to have eluded practically all
control theorists in psychology.
Another interesting fact is that while Flach assures me that he has done
many simulations, even some with real analog computers, I haven’t found
any simulations in Control theory for humans. Models are
presented, but there are almost no plots of their behavior, or any
comparisons of their behavior with that of real people. There are some
Bode plots, and some examples of Fourier analysis, but these are global
representations of behavior and do not show how any variables change
through time. I don’t think it’s possible to judge how well a model fits
real behavior from a Bode plot or a Fourier analysis – the
representations are simply not detailed enough.
For those who have not seen some of the correspondence, the subject of
Bode plots comes up in Chapter 14 of the book, purporting to show that
subjects actually change their internal organization when the nature of
the external part of the loop (that we call the environmental feedback
function) is changed. The Bode plot shows the frequency response of a
control system given sine-wave variations in its reference signal, or
else sine-wave disturbances. In the simplest application, the frequency
of the sine wave is gradually raised, while a record is kept of the
amplitude and the phase of the output (as Flach defines the controlled
variable) relative to the input (the reference signal, as Flach defines
input). For human beings the data have to be obtained indirectly using
randomized inputs, but the results should be the same.
The connection between the control handle and the cursor is selected from
three choices: a direct, proportional connection, a single integration,
and a double integration. The experimental results for these conditions
are shown in Chapter 14, Figs. 14-3, 14-4, and 14-5, The conclusion is
that the human being changes internally so as to make the overall system
function look like a first-order lag in all three cases, or as we call it
in PCT, a leaky integrator. The data certainly show that this effect
occurs, no doubt about that.
I have been able to come up with a two-level model that reproduces these
effects without any changes in model parameters, a fact that calls
into doubt all conclusions about “adaptation” drawn from these
experimental findings. It is possible to set up a two-level control
system controlling velocity at the lower level and position at the higher
level, which shows the same effects as in Ch. 14 when the external part
of the loop is changed from a proportional to an integral to a double
integral response. Bode plots show the same phase behavior and the same
20-db per decade frequency rolloffs. While this does not prove that no
adaptation at all takes place, it does show that the major part of the
data can be accounted for without assuming any adaptation (that
is, any changes in the model’s parameter values from one case to
another).

At present, Flach and his people are attempting to reproduce my model by
using MatLab (as they learn it), and are having a few difficulties that
are probably temporary. When they have their simulation running, I think
we will have some interesting conversations. Flach’s remarks about a
possible link between frequency-domain and time-domain methods suggests
to me that he has somewhat limited experience with the time-domain side
(what we call simulations). I learned the frequency-domain and
time-domain stuff at the same time (possibly before Flach was born) and
decided I greatly preferred time-domain. So I probably have as much to
learn about frequency domain as Flach et. al. have to learn about time
domain. Somehow, though, I think I’m going to end up still preferring
time domain.

I don’t want to say too much now about how this exploration with Flach
will proceed. I’m about to send him a new model that shows the same
two-level control system being used to apply the brakes to a vehicle and
stop it at a specific place. Of course the kinds of control systems in
the book that would be used for this would be the sort that compute
decelerations from physical properties of the system and then apply the
braking forces open-loop. Oddly enough, if we assume that braking force
is proportional to velocity times the amount of pedal pressure applied,
the model shows the pedal pressure to be constant once the distance to
the target point has become small enough for any braking to occur. I have
now added a nonlinear braking function just to prove that the control
system can still stop at the right place, and to show that the constant
braking pressure isn’t a loophole in the model.

Best,

Bill P.