# Bridges

**URL:** <http://discourse.iapct.org/t/bridges/1961>\
**Category:** CSG1998\
**Created:** [January 1, 1998, 4:37pm UTC](http://discourse.iapct.org/t/bridges/1961 "1998-01-01T16:37:56Z")\
**Posts on this page:** 20\
**Page:** 1

<div class="post-metadata">

**Author:** ![Bill\_Powers1](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/b/8e7dd6/32.png) [@Bill\_Powers1](http://discourse.iapct.org/u/Bill_Powers1)\
**Post date:** [January 1, 1998, 4:37pm UTC](http://discourse.iapct.org/t/bridges/1961/1 "1998-01-01T16:37:56Z")

</div>

[From Bill Powers (980101.0754 MST)]

Hmm. Looks just like 1997 out there. Oh, well.

Martin Taylor 971231 17:45 --

> > S.S. Stevens actually thought that  
> > perceptions were quantized; a control-system experiment would show that  
> > they are not.
> 
> It's interesting to know that even if the perceptual input function is  
> quantized, a control system experiment would show that it is not. Why  
> bother with the experiment, if the result would be the same no matter  
> what the fact of the matter investigated?

I should have said "low-order" perceptions. Of course higher-order  
perceptions such as categories are quantized. But as far as I know,  
lower-order perceptions are continuously variable. The lower and upper  
points between which a JND is measured would not repeat from one experiment  
to another (unless the experimenter forced them to repeat). At least they  
didn't when other people tried to replicate S.S. Stevens' results.

> > Signal-to-noise ratio is not the same thing as perceptions  
> > that occur in discrete steps.
> 
> No, indeed. That's why a d' (d-prime) measure is substituted for the notion  
> of jnd in respectable psychophysics. Nevertheless, this says nothing about  
> whether or not perception is quantized. That's a different issue.

I should know better to use physicists' terms. What S. S. Stevens thought  
was that subjective estimates of stimulus magnitude were such that the true  
plot would be a staircase rather than a smooth line. In other words, he  
asserted that changes in perceived stimulus magnitude would occur only at  
specific repeatable discretely-separated magnitudes of the stimulus.

> (Parenthetically, d' is a measure of the separability of the signal state  
> from the non-signal state. It is more akin to the magnitude of the  
> perceptual signal than it is to "the slope of the input function"  
> (Bill Powers 971230.1012 MST). "Bias" (usually labelled "beta") is the  
> willingness of the person to assert that a signal is present. It is  
> not the threshold, though changes in beta are associated with changes  
> in what would be called a threshold in a casual "is it there or is it not"  
> study.)

Just out of curiousity, what in standard parlance would correspond to the  
slope of the stimulus-magnitude-to-perception function?

> Psychophysical experiments \_are\_ control system experiments, though not in  
> the sense you intend. In a psychophysical experiment (other than one using  
> the method of adjustment) the subject is unable to influence what the  
> experimenter thinks of as the "stimulus," but is able to control an  
> important perception--the perception of the experimenter's satisfaction  
> with the subject's performance. The \_mechanism\_ for controlling this  
> perception is consistency of relation between stimulus and response. The  
> overt experiment is S-R. If the subject can hear the tone in an auditory  
> sensitivity experiment and randonly says "yes" or "no", the experimenter  
> will not be perceived as very satisfied.

Unfortunately, the degree of the experimenter's satisfaction is a second  
perception with its own unknown relation between actual and perceived  
satisfaction. This has been the problem with psychophysical experiments all  
along. We can estimate the scaling of one perception relative to another,  
but there is no absolute scale. If all perceptual input functions share the  
same nonlinearity (in addition to differences between functions of  
different kinds), there is no psychophysical way to find out what that  
nonlinearity is.

> There are real problems with a lot of psychophysical studies, but not being  
> control system experiments is not among them.

What a control-system experiment (method of adjustment) can do that no  
other kind of experiment can do is reveal the actual level of input that  
the subject considers to have some characteristic. If you say "Now make the  
stimulus twice as large as before," you can measure the external correlate  
of what the subject perceives as "twice as large." This doesn't tell you  
what the ratio of perceptions is, but it does tell you what the subject  
means by the verbal statement "twice as large" in terms of the external  
measurement.

If you try to do the same thing open-loop, you may or may not get the same  
results. The only way to find out is to re-do all the open-loop experiments  
in a closed-loop form and see if you do get the same results.

> One way of studying any  
> feedback structure is to break the loop somehwere and to look at the  
> input-output relations among the components of the loop. That's what  
> a psychophysical experiment (other than method of adjustment) does.

Breaking the loop works fine for an artificial nonadaptive control  
organization. It is much harder to use with a living control system,  
because breaking the loop means loss of control, and loss of control  
usually leads to an immediate switch to a different mode of control. So  
when you think you're measuring the same system open-loop, you're probably  
looking at a different system.

Think about trying this with a tracking experiment. If you actually break  
the loop in the middle of a run and present a convincingly similar picture  
of cursor and target, you will see essentially the same output actions for  
some short period of time. But the difference will soom magnify and the  
person will discover that control has actually been lost. At that point  
you'll see the control handle start to produce experimental wiggles, and  
then go into some completely different mode of movement, or stop.

If you simply tried to measure the dependence of handle movement on  
cursor-target separation without first having the person actively tracking  
for some considerable time, the results would be completely meaningless.  
What would you tell the subject to do? "When you see the cursor and target,  
move the handle in the way you think it should move?" It would be very hard  
to avoid giving instructions that tell the subject how you want to see the  
handle moving.

> The  
> loop component we call "environmental feedback function" is broken,  
> permitting the internal component to be studied in isolation. I think  
> that is useful, and the results help to establish parameters for the  
> functioning of completed control loops using the same perceptions.

This would be possible only in special circumstances.

> The question arises as to whether the perceptual input functions operate  
> the same way when the resulting perception is being controlled as when it  
> isn't. This issue is not ordinarily considered within HPCT, since normally  
> the perceptual input function is taken to be whatever it is, and only the  
> magnitude of its output is controlled. But it is an issue, one that might  
> invalidate the uncritical use of the results of psychophysical studies  
> to assess the elements of related control loops.

Yes. But it's not only the input function you have to worry about. Suppose  
a tracking system could go on working in the same way without the  
environmental feedback function. If you were to present the cursor a  
certain distance from the target, the output action would be quite extreme;  
it would become something like 30 times as large as needed to correct that  
error, and it would change along something like a decelerating exponential  
path. I think you must know that we would actually observe nothing of the  
sort. I can tell you we wouldn't, because I've tried it, but I suppose that  
my observations could be considered biased. You should try it yourself. You  
can't just break the loop when a living control system is involved, and  
assume that you're still looking at the same system.

> **···**
>
> ------------------------------------  
> To whom it may concern:
> 
> I don't think that my real message is getting across here. Some people are  
> acting as if I said that all psychological facts discovered through  
> traditional methods are wrong. That's not my point at all. What I'm saying  
> is that because control-system considerations were not taken into account  
> when those experiments were done, WE DON'T KNOW WHICH RESULTS ARE RIGHT AND  
> WHICH ARE WRONG. There might be selected cases in which we could review the  
> methodology and look at the data and conclude that a control-system  
> experiment was in fact (unwittingly) done, or that if the loop were closed  
> we could reasonably expect that the results would be the same. But even to  
> do that requires that we review everything.
> 
> My mother used to come up with little jokes that had a point I didn't get  
> until much later in life. One was about a bank teller who was counting a  
> stack of dollar bills that was supposed to have $300 in it. He counted  
> "one, two, three, four ... 151, 152, 153 ... well, it's right so far, it  
> must be right the rest of the way."
> 
> Perhaps my point would be easier to accept we we stipulate that we're  
> talking only about \_other people's\_ results in fields of psychology \_other  
> than your own\_. And specifically, whoever is reading this, we're exempting  
> from consideration any experiment you have done yourself, or have publicly  
> accepted as methodologically correct and factually reliable. All I'm asking  
> is that we revisit experiments done in other fields with the idea of seeing  
> whether control processes were properly taken into account, and whether a  
> re-design of the experiments as closed-loop experiments might lead to  
> different outcomes.
> 
> And in all cases where there is any doubt, I'm asking that we either  
> actually re-do the experiments using PCT methods, or put the findings on  
> the shelf until such time as the tests can be done, not using them as facts  
> until then.
> 
> Does that sound like a reasonable proposal?
> 
> Best,
> 
> Bill P.

---

<div class="post-metadata">

**Author:** ![R\_Marken](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/r/8797f3/32.png) [@R\_Marken](http://discourse.iapct.org/u/R_Marken)\
**Post date:** [January 1, 1998, 5:24pm UTC](http://discourse.iapct.org/t/bridges/1961/2 "1998-01-01T17:24:51Z")

</div>

[From Rick Marken (980101.0930)]

Bill Powers (980101.0754 MST) --

> What S. S. Stevens thought was that subjective estimates of  
> stimulus magnitude were such that the true plot would be a  
> staircase rather than a smooth line.

I'm not familiar with this aspect of S. S. Stevens' psychophysics.  
I believe that neither Stevens nor Fechner viewed the the perceptual  
representation of stimulus magnitude as discrete. Fechner concluded  
that perception (p) was a \_continuous\_ log function of stimulus  
magnitude (s); Fechner's law -- p = k log (s) -- was derived under  
the \_assumption\_ the just noticeable differences in stimulus magnitude  
(Weber's jnd's, measured in physical units) are subjectively equal  
(same size in perceptual units). Stevens wanted to measure the  
relationship between p and s "directly" -- without assuming that  
jnd's are perceptually equal. He developed a very simple  
technique called "magnitude estimation" to do this; in magnitude  
estimation a person uses numbers (or some another perceptual  
variable) to indicate the perceived magnitude of s. The results  
of magnitude estimation of various physical stimulus dimensions  
showed that magnitude estimates varied as a power funtion of s.  
Stevens assumed that the magnitude estimates were direct measures  
of perceptual magnitude and concluded that the actual relationship  
between p and s was p = s ^ k -- where the exponent, k, varied  
across stimulus dimensions.

Psychophysics will unquestionably benefit from an understanding  
of control theory and the methods of studying perceptual control  
implied by that theory. But I don't think Fechner and Stevens  
can be blamed for the non-analog view of lower level perception  
that seems to be prevalent in psychology today. I think the  
real culprit was the computer model of the brain, with it's  
emphasis on "information processing" and "symbol manipulation".  
Stevens was actually a rather analog guy -- as, of course, was  
Fechner. Both did their work well before the unfortunate "digital  
revolution" in psychology.

Martin Taylor (971231 17:45) --

> Psychophysical experiments \_are\_ control system experiments

This is not true at all. Psychophysical experiments are no more  
control system experiments than are any other kinds experiments  
in psychology. Of course, people are controlling variables in  
psychophysical (and \_all\_) experiments -- because people control.  
The reason these are not control \_experiments\_ is that you have  
no way of telling \_what\_ subjects are controlling. There is no  
systematic attempt to test (by disturbing hypothetical controlled  
variables) what perceptions are under control.

We can identify possible controlled variables in \_any\_  
psychological experiment. This is particularly easy to do  
in operant experiments where the organism is given the ability  
to produce certain results. But identifying \_possible\_ controlled  
variables (like "seeing the experimenter pleased") is nothing  
like finding out what variable(s) the organism is \_actually\_  
controlling. It is simply not a control experiment unless we  
can identify a controlled variable, monitor it's behavior  
under disturbance and monitor the way in which the subject  
manages to keep the variable under control. That is why there  
are hardly any conventional psychology experiments \_of any kind\_  
that are \_control experiments\_, Bruce Abbott notwithstanding.

Happy New Year

Rick

> **···**
>
> --
> 
> Richard S. Marken Phone or Fax: 310 474-0313  
> Life Learning Associates e-mail: rmarken@earthlink.net  
> [http://home.earthlink.net/~rmarken/](http://home.earthlink.net/~rmarken/)

---

<div class="post-metadata">

**Author:** ![Bill\_Powers1](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/b/8e7dd6/32.png) [@Bill\_Powers1](http://discourse.iapct.org/u/Bill_Powers1)\
**Post date:** [January 1, 1998, 7:31pm UTC](http://discourse.iapct.org/t/bridges/1961/3 "1998-01-01T19:31:41Z")

</div>

[From Bill Powers (980101.1217 MST)]

Rick Marken (980101.0930)--

> I'm not familiar with this aspect of S. S. Stevens' psychophysics.  
> I believe that neither Stevens nor Fechner viewed the the perceptual  
> representation of stimulus magnitude as discrete.

I don't have a reference on this; it's something that came up late in  
Stevens' career, and as I remember it didn't convince anyone else. If you  
had a suitable library handy you could probably dredge it up.

> Fechner concluded  
> that perception (p) was a \_continuous\_ log function of stimulus  
> magnitude (s); Fechner's law -- p = k log (s) -- was derived under  
> the \_assumption\_ the just noticeable differences in stimulus magnitude  
> (Weber's jnd's, measured in physical units) are subjectively equal  
> (same size in perceptual units).

I don't think that can be established. The way you measure JNDs is to make  
a change in the stimulus smaller and smaller until the person is wrong half  
of the time. But that doesn't tell you how large the perceptual signal is.  
Even if the perceptual signal were linear with stimulus magnitude, you'd  
see an increasing JND just because of signal statistics.

> Stevens wanted to measure the  
> relationship between p and s "directly" -- without assuming that  
> jnd's are perceptually equal. He developed a very simple  
> technique called "magnitude estimation" to do this; in magnitude  
> estimation a person uses numbers (or some another perceptual  
> variable) to indicate the perceived magnitude of s. The results  
> of magnitude estimation of various physical stimulus dimensions  
> showed that magnitude estimates varied as a power funtion of s.

That means only that they vary \_relative to each other\_ as power functions.  
How big is "2"? There's no way to measure that in absolute terms. Maybe all  
perceptions are essentially linear functions of stimulus magnitude, but in  
converting analog signals to symbolic numbers we insert a power function.  
There's just no way to tell. It's a non-question.

\< ... I don't think Fechner and Stevens

> can be blamed for the non-analog view of lower level perception  
> that seems to be prevalent in psychology today. I think the  
> real culprit was the computer model of the brain, with it's  
> emphasis on "information processing" and "symbol manipulation".  
> Stevens was actually a rather analog guy -- as, of course, was  
> Fechner. Both did their work well before the unfortunate "digital  
> revolution" in psychology.

I agree with all that. Stevens' downfall probably came about through  
wanting to say something "digitally correct" in the atmosphere that was  
building up around him. Fechner, I think, simply didn't realize that his  
methods couldn't uncover a nonlinearity common to \_all\_ perceptions.

Best,

Bill P.

---

<div class="post-metadata">

**Author:** ![Martin\_Taylor4](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/m/71c47a/32.png) [@Martin\_Taylor4](http://discourse.iapct.org/u/Martin_Taylor4)\
**Post date:** [January 2, 1998, 7:19am UTC](http://discourse.iapct.org/t/bridges/1961/4 "1998-01-02T07:19:33Z")

</div>

[Martin Taylor 990102 01:35]

> [From Bill Powers (980101.0754 MST)]

> Just out of curiousity, what in standard parlance would correspond to the  
> slope of the stimulus-magnitude-to-perception function?

I think it is sometimes called "the psychophysical function." But hardly  
any psychophysics is concerned with that, anyway. Most psychophysics is  
concerned with the conditions under which people can tell whether A is  
different from B. Is the area of that triangle bigger than of this disk;  
was there a beep in that time interval or not; is this colour redder  
than that one or not...

> > Psychophysical experiments \_are\_ control system experiments, though not in  
> > the sense you intend. In a psychophysical experiment (other than one using  
> > the method of adjustment) the subject is unable to influence what the  
> > experimenter thinks of as the "stimulus," but is able to control an  
> > important perception--the perception of the experimenter's satisfaction  
> > with the subject's performance. The \_mechanism\_ for controlling this  
> > perception is consistency of relation between stimulus and response. The  
> > overt experiment is S-R. If the subject can hear the tone in an auditory  
> > sensitivity experiment and randonly says "yes" or "no", the experimenter  
> > will not be perceived as very satisfied.
> 
> Unfortunately, the degree of the experimenter's satisfaction is a second  
> perception with its own unknown relation between actual and perceived  
> satisfaction.

That hardly matters, since it is the subject's perception of the  
experimenter's satisfaction that is being compared with the subject's  
reference for the exdperimenter's satisfaction--as with any other  
perceptual control. If "behaving well" in the experiment brings the  
subject's perception of the experimenter's satisfaction closer to its  
reference, the mechanism has served its purpose in controlling the  
relevant perception.

> **···**
>
> --------------------
> 
> > This has been the problem with psychophysical experiments all  
> > along. We can estimate the scaling of one perception relative to another,  
> > but there is no absolute scale.
> 
> That's another question entirely, and one that has been of concern since  
> at least my summer student days in the late 50's. I tried to work around  
> it in a series of experiments in which I looked for "anchoring effects"  
> in different perceptual continua--time, grey-scale, colour along an arc  
> in colour space, location of a dot along a line, location of a nonsense  
> syllable in an incompletely learned list, and even cardinal number. Some  
> of these continua were open at one end, some closed at both ends (and as  
> you may have observed, some even had discrete stimulus possibilities, yet  
> acted as if the perceptual space was continuous--the opposite of what  
> you sat Stevens thought).
> 
> The basis of my experiment was the idea that you propose later in your  
> message:
> 
> > Breaking the loop works fine for an artificial nonadaptive control  
> > organization. It is much harder to use with a living control system,  
> > because breaking the loop means loss of control, and loss of control  
> > usually leads to an immediate switch to a different mode of control. So  
> > when you think you're measuring the same system open-loop, you're probably  
> > looking at a different system.
> 
> My idea was that when the subject had control of a stimulus it would look  
> different from when the stimulus was just "presented" by an experimenter.  
> What I did was to use one of the continua as "stimulus" and another as  
> "response". In the classic Stevens magnitude estimation, a number would  
> be the response. I might instead use a number as the stimulus, and ask  
> the person to make a grey that matched the number. Or to make the  
> angle of a pointer in a quadrant match the timing of a light flash between  
> two others. Anyway, the result was clearly that the perception \_was\_  
> different when the subject controlled it as compared to when the  
> experimenter controlled it (though, of course I was not thinking in PCT  
> terms).
> 
> For magnitude estimation studies, then, your comments are clearly justified.  
> And they might even be justified for the more usual type of psychophysical  
> studies in which the ability to discriminate is what is tested. However,  
> whether or not that is in fact so, any study, by any method, that shows  
> a subject \_can\_ discriminate A from B also shows that the difference  
> between A and B could correspond to a controllable attribute of perception.  
> It provides at least an upper bound on the least ability to distinguish,  
> and the ability to distibguish is fundamental to the ability to control.  
> That is why I think that such studies remain useful. And despite what I  
> say in the next paragraph, I don't think that there is much likelihood  
> of large discrepancies in the measured ability of people to discriminate,  
> regardless of the method.
> 
> Now, why I think it possible that direct control studies \_might\_ give  
> a different result even in discrimination experiments: Experimental  
> techniques known as "adaptive threshold" methods, especially one called  
> PEST that I developed (with Doug Creelman), give results that seem to show  
> subjects to be a bit more sensitive to delicate discriminations than the  
> results of fixed level studies. In a PEST study, the task gets easier  
> if the subject is performing worse than a target level, and harder if the  
> subject is performing better. It's a control study from the experimenter's  
> viewpoint, with a reference that the subject should get, say, 80% correct.  
> Under these conditions, the subject gets 80% correct with a more  
> difficult task than would be the case if the experimenter just randomly  
> chose a set of difficulty levels and found by interpolation the level  
> corresponding to 80% correct. The same might be true if the subject  
> directly controlled the difficulty. It's hard to know. But the differences  
> in the PEST and fixed-level studies are large only when the discrimination  
> gets \_very\_ difficult, and I don't think there would be much difference  
> between a optimum direct control study and PEST, since the results  
> with PEST are usually within about 4 or 5 dB of a mathematically ideal  
> observer, if the subject is well trained, which gives not much room for  
> further improvement.
> 
> ----------------
> 
> > > One way of studying any  
> > > feedback structure is to break the loop somehwere and to look at the  
> > > input-output relations among the components of the loop. That's what  
> > > a psychophysical experiment (other than method of adjustment) does.
> > 
> > Breaking the loop works fine for an artificial nonadaptive control  
> > organization. It is much harder to use with a living control system,  
> > because breaking the loop means loss of control, and loss of control  
> > usually leads to an immediate switch to a different mode of control. So  
> > when you think you're measuring the same system open-loop, you're probably  
> > looking at a different system.
> 
> Yes. That's what happens when the person is actually trying to control  
> the perception in question. But if control is not intended (reference  
> level zero, as you discussed in another message yesterday), asking the  
> subject to provide output relating to the stimulus is not \_necessarily\_  
> going to provide a different result than would be the case on another  
> (non-experimental) occasion when the subject is controlling the perception  
> corresponding to that stimulus.
> 
> > > The question arises as to whether the perceptual input functions operate  
> > > the same way when the resulting perception is being controlled as when it  
> > > isn't. This issue is not ordinarily considered within HPCT, since normally  
> > > the perceptual input function is taken to be whatever it is, and only the  
> > > magnitude of its output is controlled. But it is an issue, one that might  
> > > invalidate the uncritical use of the results of psychophysical studies  
> > > to assess the elements of related control loops.
> > 
> > Yes. But it's not only the input function you have to worry about.
> 
> Sure. But if you are trying to study the input function, it is what you  
> are worrying about at that moment.
> 
> > ------------------------------------  
> > To whom it may concern:
> > 
> > I don't think that my real message is getting across here. Some people are  
> > acting as if I said that all psychological facts discovered through  
> > traditional methods are wrong. That's not my point at all. What I'm saying  
> > is that because control-system considerations were not taken into account  
> > when those experiments were done, WE DON'T KNOW WHICH RESULTS ARE RIGHT AND  
> > WHICH ARE WRONG. There might be selected cases in which we could review the  
> > methodology and look at the data and conclude that a control-system  
> > experiment was in fact (unwittingly) done, or that if the loop were closed  
> > we could reasonably expect that the results would be the same. But even to  
> > do that requires that we review everything.
> 
> I can go along with this as stated. But you usually come across a bit  
> stronger. I think that we can make a fairly easy triage, separating  
> results/observations into a class that we are reasonably safe to accept,  
> a class that is obviously untrustworthy or makes no sense in the PCT  
> way of looking at things, and a class that needs to be examined closely  
> to see whether the results might be worth rechecking. How large those  
> three classes are might be a topic of some controversy, given the recent  
> Marken-Abbott interchange:-) I'd start by putting most results from  
> discriminative psychophysics into the "safe to accept" category.
> 
> Happy New Year.
> 
> Martin

---

<div class="post-metadata">

**Author:** ![Myrexsw](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/m/858c86/32.png) [@Myrexsw](http://discourse.iapct.org/u/Myrexsw)\
**Post date:** [January 2, 1998, 8:55am UTC](http://discourse.iapct.org/t/bridges/1961/5 "1998-01-02T08:55:39Z")

</div>

i.kurtzer (980102.0300)

> Psychophysical experiments \_are\_ control system experiments, though not in  
> the sense you intend.

What up, Martin? You knew someone was going to freak on this one. So this must  
be some weirdo intro thread, but to what?

> In a psychophysical experiment (other than one using  
> the method of adjustment) the subject is unable to influence what the  
> experimenter thinks of as the "stimulus," but is able to control an  
> important perception--the perception of the experimenter's satisfaction  
> with the subject's performance.

Who knows how important? In determining the believability of the data noone  
checks the "degree of importance" a subject has adopted. And so its always and  
only implicit. But this applies to all studies involving willing humans--they  
are willing to try to follow instructions; we assume as a means to an end.  
Ergo, So what gives?

> The \_mechanism\_ for controlling this  
> perception is consistency of relation between stimulus and \>response.

For the subject it is percept A and percept B, not percept A and response B;  
now, as an tester we have one \_more\_ unknown.  
Before, the tester wanted to know the relation between "objective" state 1  
(wavelength) and subject's percept A (red) . But the introduction of  
interpretive protocol lessens the findings tenability. Now there is also state  
2 (tester's heard yes) and subject's percept B (yes) . This is bad.

> The  
> overt experiment is S-R.

It is S-R to its core. It is S-R because they cast the PIF in behavioral  
terms.

&nbsp;&nbsp;\>There are real problems with a lot of psychophysical studies, but not being

> control system experiments is not among them

This effectively rewrites every concievable experiment in the history of  
psychology as control-system experiments.  
Is this the bridge?  
Is an experiment a control-system experiment if the authors acted as if it  
wasn't? If so, then that's replacing ontology with methodology and makes it an  
apologist to all theories thereafter as being anticipating, but misunderstood.

i.

---

<div class="post-metadata">

**Author:** ![Bill\_Powers1](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/b/8e7dd6/32.png) [@Bill\_Powers1](http://discourse.iapct.org/u/Bill_Powers1)\
**Post date:** [January 2, 1998, 4:18pm UTC](http://discourse.iapct.org/t/bridges/1961/6 "1998-01-02T16:18:51Z")

</div>

> [Martin Taylor 990102 01:35]
> 
> > [From Bill Powers (980101.0754 MST)]
> 
> > Just out of curiousity, what in standard parlance would correspond to the  
> > slope of the stimulus-magnitude-to-perception function?
> 
> I think it is sometimes called "the psychophysical function." But hardly  
> any psychophysics is concerned with that, anyway. Most psychophysics is  
> concerned with the conditions under which people can tell whether A is  
> different from B. Is the area of that triangle bigger than of this disk;  
> was there a beep in that time interval or not; is this colour redder  
> than that one or not...

So most psychophysics experiments are really concerned with perception of  
relationships? That's interesting; the impression I always had was that  
much lower levels of perception were being investigated. But from your  
descriptions, I can see that you're right.

> > Unfortunately, the degree of the experimenter's satisfaction is a second  
> > perception with its own unknown relation between actual and perceived  
> > satisfaction.
> 
> That hardly matters, since it is the subject's perception of the  
> experimenter's satisfaction that is being compared with the subject's  
> reference for the exdperimenter's satisfaction--as with any other  
> perceptual control. If "behaving well" in the experiment brings the  
> subject's perception of the experimenter's satisfaction closer to its  
> reference, the mechanism has served its purpose in controlling the  
> relevant perception.

I should think that if the subject can tell how well the experimenter is  
satisfied by the subject's performance, a great possibility would exist for  
the subject to provide the experimenter with the results that are wanted or  
expected -- in other words, for the experimenter to control the results  
simply by withholding or expressing satisfaction. The "Clever Hans" effect.

> > This has been the problem with psychophysical experiments all  
> > along. We can estimate the scaling of one perception relative to another,  
> > but there is no absolute scale.
> 
> That's another question entirely, and one that has been of concern since  
> at least my summer student days in the late 50's. I tried to work around  
> it in a series of experiments in which I looked for "anchoring effects"  
> in different perceptual continua--time, grey-scale, colour along an arc  
> in colour space, location of a dot along a line, location of a nonsense  
> syllable in an incompletely learned list, and even cardinal number. Some  
> of these continua were open at one end, some closed at both ends (and as  
> you may have observed, some even had discrete stimulus possibilities, yet  
> acted as if the perceptual space was continuous--the opposite of what  
> you sat Stevens thought).

In his Power-Law work, Stevens was investigating a continuum. The stepwise  
JND work was something else, and I believe, later.

> The basis of my experiment was the idea that you propose later in your  
> message:
> 
> > Breaking the loop works fine for an artificial nonadaptive control  
> > organization. It is much harder to use with a living control system,  
> > because breaking the loop means loss of control, and loss of control  
> > usually leads to an immediate switch to a different mode of control. So  
> > when you think you're measuring the same system open-loop, you're probably  
> > looking at a different system.
> 
> My idea was that when the subject had control of a stimulus it would look  
> different from when the stimulus was just "presented" by an experimenter.  
> What I did was to use one of the continua as "stimulus" and another as  
> "response". In the classic Stevens magnitude estimation, a number would  
> be the response. I might instead use a number as the stimulus, and ask  
> the person to make a grey that matched the number. Or to make the  
> angle of a pointer in a quadrant match the timing of a light flash between  
> two others. Anyway, the result was clearly that the perception \_was\_  
> different when the subject controlled it as compared to when the  
> experimenter controlled it (though, of course I was not thinking in PCT  
> terms).

I think that in PCT terms we have to assume that a subject can never just  
"produce a response," open-loop. When one continuum is used as the response  
measure and another as the stimulus measure, the subject must be  
controlling a relationship between the two continua. The controlled  
perception is a function of both continua, but the subject can affect only  
one of the two contributing lower-level perceptions. If a perception in  
continuum 1 is varied by the experimener, the relationship is disturbed and  
is corrected by actions that alter the perception from continuum 2.

The behavioral illusion is that the manipulated perception is a stimulus,  
and the action that alters the other perception is a response. The actual  
controlled variable is something that is a function of both the stimulus  
and the response; here, the relationship between the two (lower-level)  
perceptions (the simplest relationship is equality).

When a number is used as the response, it is really (according to PCT) a  
perception of magnitude (elicited by the numeral or spoken word) that is  
under control at the lower level. Hence my question yesterday: "How big is  
'2'"? Between hearing or seeing the number-symbol and getting a sense of  
analog magnitude there is a perceptual transformation. The subject utters  
the name of a number such that the resulting sense of magnitude seems equal  
to the sense of magnitude of some other perception. We are therefore still  
comparing two perceptual transformations, with any properties common to  
both of them being invisible.

> For magnitude estimation studies, then, your comments are clearly justified.

Good. I'm glad that we agree that this is a case where re-examination of an  
older experiment leads to a different interpretation. The observations  
themselves are not altered in this case, but the conclusions are definitely  
altered by PCT analysis.

> And they might even be justified for the more usual type of psychophysical  
> studies in which the ability to discriminate is what is tested. However,  
> whether or not that is in fact so, any study, by any method, that shows  
> a subject \_can\_ discriminate A from B also shows that the difference  
> between A and B could correspond to a controllable attribute of perception.  
> It provides at least an upper bound on the least ability to distinguish,  
> and the ability to distibguish is fundamental to the ability to control.  
> That is why I think that such studies remain useful. And despite what I  
> say in the next paragraph, I don't think that there is much likelihood  
> of large discrepancies in the measured ability of people to discriminate,  
> regardless of the method.

The experiments as you describe them, which involve comparing two different  
perceptions, would seem to be tests of relationship perceptions, rather  
than basic abilities to discriminate, say, intensity changes in a single  
level-one perception. To test the ability to discriminate small changes in  
intensity, all we need to do is give the person control over a single  
intensity perception and determine the smallest disturbance that will  
produce a corrective action. The concept of a hierarchy of perceptions  
suggests that this kind of discrimination is quite different from the kind  
in which a person tries so say whether, for example, a light intensity is  
greater than a sound intensity, or a sound intensity is greater than the  
rate of rotation of something.

I think this discussion gives us an idea of just how PCT is likely to alter  
our view of previous experimental results. There are many traditional  
categories, like "discrimination," which lump together a wide range of  
phenomena that are seen as different in PCT. As soon as we introduce the  
idea of a hierarchy of perceptions, we can no longer say that  
discrimination is discrimination is discrimination. We might expect JNDs  
for intensity perception to be quite different from JNDs for relationship  
or logical perceptions, even though the same input stimuli are involved.

> Now, why I think it possible that direct control studies \_might\_ give  
> a different result even in discrimination experiments: Experimental  
> techniques known as "adaptive threshold" methods, especially one called  
> PEST that I developed (with Doug Creelman), give results that seem to show  
> subjects to be a bit more sensitive to delicate discriminations than the  
> results of fixed level studies. ...

This falls into the category of experimental results that you have obtained  
or have accepted, so by my modest proposal it is exempt from the need for  
re-evaluation by you. Your expectation is that a PCT experiment would not  
make any material difference in the facts you found, so there is no need  
for you to do the experiments, and you can continue to accept those facts.

This may not be true of others thinking about the same experiments and  
facts, but you are relieved of responsibility for doing any re-evaluation.  
If somebody else becomes interested, they can do the required work.

> ----------------
> 
> > Breaking the loop works fine for an artificial nonadaptive control  
> > organization. It is much harder to use with a living control system,  
> > because breaking the loop means loss of control, and loss of control  
> > usually leads to an immediate switch to a different mode of control. So  
> > when you think you're measuring the same system open-loop, you're probably  
> > looking at a different system.
> 
> Yes. That's what happens when the person is actually trying to control  
> the perception in question. But if control is not intended (reference  
> level zero, as you discussed in another message yesterday), asking the  
> subject to provide output relating to the stimulus is not \_necessarily\_  
> going to provide a different result than would be the case on another  
> (non-experimental) occasion when the subject is controlling the perception  
> corresponding to that stimulus.

The question is not whether, in general, a person \_might\_ produce the same  
output with and without control, but whether in a given case the person  
\_does\_ produce the same output. It's not enough to say that your open-loop  
results aren't \_necessarily\_ different from corresponding closed-loop  
results -- that doesn't warrant concluding that they would in fact be the  
same in any particular case.

And don't forget that the subject can't really "provide output" open-loop.  
I showed above how such situations need to be analyzed in terms of PCT, as  
controlling a relationship between a perception you can control and one  
that is arbitrarily varied. The result is not the same as simply breaking a  
loop that was formerly closed. The organization of the system becomes  
different.

> > Yes. But it's not only the input function you have to worry about.
> 
> Sure. But if you are trying to study the input function, it is what you  
> are worrying about at that moment.

I was speaking of confounding factors. If the output function changes, you  
may only be concerned with the input function, but that will lead you to  
attribute any changes to changes in the input function. In dealing with  
living control systems, there is no way for an experimenter to isolate the  
input function by breaking the loop. When you eliminate the environmental  
feedback function, what is left is the path through the organism consisting  
of input function, comparator, and output function. And in a hierarchical  
system, you may or may not eliminate feedback at all levels. You might  
find, in fact, that eliminating what you see as the EFF for a given control  
system has no discernible effect on control -- you have not eliminated ALL  
EFFs. The only way to do that would be to immobilize the person or cut all  
afferent pathways.

> > ------------------------------------  
> > To whom it may concern:
> > 
> > I don't think that my real message is getting across here. Some people are  
> > acting as if I said that all psychological facts discovered through  
> > traditional methods are wrong. That's not my point at all. What I'm saying  
> > is that because control-system considerations were not taken into account  
> > when those experiments were done, WE DON'T KNOW WHICH RESULTS ARE RIGHT AND  
> > WHICH ARE WRONG. There might be selected cases in which we could review the  
> > methodology and look at the data and conclude that a control-system  
> > experiment was in fact (unwittingly) done, or that if the loop were closed  
> > we could reasonably expect that the results would be the same. But even to  
> > do that requires that we review everything.
> 
> I can go along with this as stated. But you usually come across a bit  
> stronger.

I have never said anything in this regard but that all psychological facts  
need to be re-examined in the light of control theory.

In other contexts, I have also said that facts which have a low probability  
of being true in any given case (whatever theory they come from) are not  
sufficient for building a science. I think this seive needs to be applied  
to all facts, even facts from PCT, first. This would greatly reduce the  
workload in reviewing past findings.

> I think that we can make a fairly easy triage, separating  
> results/observations into a class that we are reasonably safe to accept,  
> a class that is obviously untrustworthy or makes no sense in the PCT  
> way of looking at things, and a class that needs to be examined closely  
> to see whether the results might be worth rechecking. How large those  
> three classes are might be a topic of some controversy, given the recent  
> Marken-Abbott interchange:-) I'd start by putting most results from  
> discriminative psychophysics into the "safe to accept" category.

Perhaps my comments above might suggest a different conclusion. But as I  
say, this is not your responsibility, since you are speaking of results  
obtained by you, or that you have accepted and used as factual. It would be  
helpful if you were to review work in \_other\_ fields in the way you  
suggest. The more classes of results that we can eliminate by consensus,  
the less labor will be involved in dealing with the rest.

I trust that we would also agree that where there are disputes over whether  
or not to re-examine some kind of result, that would be sufficient reason  
to re-examine it, although the person who thinks it unnecessary would not  
have any obligation to do the work. Sort of on the principle that we all  
have the right not to incriminate ourselves.

Best,

Bill P.

> **···**
>
> At 02:19 AM 1/2/98 -0500, you wrote:

---

<div class="post-metadata">

**Author:** ![Bill\_Powers1](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/b/8e7dd6/32.png) [@Bill\_Powers1](http://discourse.iapct.org/u/Bill_Powers1)\
**Post date:** [January 2, 1998, 7:39pm UTC](http://discourse.iapct.org/t/bridges/1961/7 "1998-01-02T19:39:54Z")

</div>

[From Bill Powers (980102.1237 MST)]

i.kurtzer (980102.0300)

> 

(replying to Martin Taylor):

> This effectively rewrites every concievable experiment in the history of  
> psychology as control-system experiments.  
> Is this the bridge?  
> Is an experiment a control-system experiment if the authors acted as if it  
> wasn't? If so, then that's replacing ontology with methodology and makes

it \>an apologist to all theories thereafter as being anticipating, but

> misunderstood.

Well said, Isaac. If the goal is to show that PCT is simply an extension of  
existing psychology, this is certainly a good way to get there.

Best,

Bill P.

---

<div class="post-metadata">

**Author:** ![Martin\_Taylor4](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/m/71c47a/32.png) [@Martin\_Taylor4](http://discourse.iapct.org/u/Martin_Taylor4)\
**Post date:** [January 3, 1998, 3:53am UTC](http://discourse.iapct.org/t/bridges/1961/8 "1998-01-03T03:53:18Z")

</div>

[Martin Taylor 980102 21:30]

> Bill Powers 980102
> 
> > [Martin Taylor 990102 01:35]

> > Most psychophysics is  
> > concerned with the conditions under which people can tell whether A is  
> > different from B. Is the area of that triangle bigger than of this disk;  
> > was there a beep in that time interval or not; is this colour redder  
> > than that one or not...

> So most psychophysics experiments are really concerned with perception of  
> relationships? That's interesting; the impression I always had was that  
> much lower levels of perception were being investigated. But from your  
> descriptions, I can see that you're right.

I suppose you could see it as perception of relationship. But it's a  
funny kind of relationship, since it could be a relationship between  
variables at any level of the hierarchy: is the tone in this interval  
louder than the tone in that? Is the first sequence the same as the second?  
Is that chord in tune? Is this noise a /p/ or a /b/? Is the line bent  
upward or downward?

> I should think that if the subject can tell how well the experimenter is  
> satisfied by the subject's performance, a great possibility would exist for  
> the subject to provide the experimenter with the results that are wanted or  
> expected -- in other words, for the experimenter to control the results  
> simply by withholding or expressing satisfaction. The "Clever Hans" effect.

I don't know how long experimenters have been aware of this possibility,  
but it was drilled into us in my first introduction to experimental  
psychology that we had to use methods that made it nearly impossible  
for the subject to do this. I imagine that the techniques for making it  
hard for the subject to cheat in this way were developed a few decades  
earlier than that. As for the "clever Hans" effect, most psychophysical  
experiments use machines to present the stimuli, and the subject is isolated  
from the experimenter, who doesn't know the correct answer for a particular  
presentation, anyway. Maybe it was Clever Hans who made psychophysicists  
aware of the problem and started them devising methods to counter it.

> I think that in PCT terms we have to assume that a subject can never just  
> "produce a response," open-loop. When one continuum is used as the response  
> measure and another as the stimulus measure, the subject must be  
> controlling a relationship between the two continua.

I'm not clear how you mean this. Surely every action a person does is  
(part of) the output action that controls some perception(s). So in that  
sense it cannot be "open loop." But I don't think that's what you mean,  
is it?

The prototypical trial cycle in a psychophysical experiment is like  
this: The experimenter presents something for the subject to see (or  
hear, or taste, or...), and the subject says "Yes" or "No", or identifies  
the presentation as belonging to a prespecified category. Alternatively,  
the experimenter presents two things, one of which contains the item  
of interest, and the subject says "Number 1" or "Number 2". (Actually,  
in all these cases, the subject is much more likely to push a button  
than to say anything, and in some experiments a "magnitude estimation"  
element is added, in that the subject may give a number of move a slider  
to indicate how sure the answer is; but that's by the way). In no case  
can the subject affect what has been presented, or what will be the  
"correct" answer on the next trial. I'd call that open loop. Isaac,  
in a message I find hard to comprehend (i.kurtzer (980102.0300)), calls  
it "S-R to its core." You say it is not open loop. I guess I'm in the  
middle between you and Isaac. I say it is a mechanism forming part of  
the output path of a control loop.

> When a number is used as the response, it is really (according to PCT) a  
> perception of magnitude (elicited by the numeral or spoken word) that is  
> under control at the lower level.

I don't see how this applies in the usual psychophysical experiment. "One"  
is not bigger than "two" when they are identifiers for the first or second  
time interval of a trial--and in any case, the response is usually a choice  
of which button to push, since it is hard for the machine (at least until  
recent years) to recognize what the subject says.

> The experiments as you describe them, which involve comparing two different  
> perceptions, would seem to be tests of relationship perceptions, rather  
> than basic abilities to discriminate, say, intensity changes in a single  
> level-one perception.

I don't understand why you say "rather than" instead of "which depend on"  
at least in the case where it is the intensity of a sound or light that  
is being compared.

> To test the ability to discriminate small changes in  
> intensity, all we need to do is give the person control over a single  
> intensity perception and determine the smallest disturbance that will  
> produce a corrective action.

I dispute that. It depends totally on having a control function that is  
linear through zero. There are two places in the loop that might put a  
lower bound on the smallest disturbance to produce a corrective action:  
the discriminative ability of the input function, and the shape of the  
output function. It is surely better to dissociate them if you are trying  
to examine one of them.

> The concept of a hierarchy of perceptions  
> suggests that this kind of discrimination is quite different from the kind  
> in which a person tries so say whether, for example, a light intensity is  
> greater than a sound intensity, or a sound intensity is greater than the  
> rate of rotation of something.

Oh, quite different. I don't see much sense in these comparisons as absolute  
statements. I do see some sense in asking whether, if sound A is perceived  
as being as strong as light B, then is sound 2\*A greater or less than light  
2\*B. I don't find this latter question interesting, but at least it seems  
to have some possible internal consistency.

> I think this discussion gives us an idea of just how PCT is likely to alter  
> our view of previous experimental results. There are many traditional  
> categories, like "discrimination," which lump together a wide range of  
> phenomena that are seen as different in PCT. As soon as we introduce the  
> idea of a hierarchy of perceptions, we can no longer say that  
> discrimination is discrimination is discrimination. We might expect JNDs  
> for intensity perception to be quite different from JNDs for relationship  
> or logical perceptions, even though the same input stimuli are involved.

I don't think most traditional psychophysicists would disagree, and there  
have indeed been studies in the area of phonemic/phonetic discrimination  
that show you to be correct in principle. But not using the idea of "JND",  
please:-)

But correct or not, I fail to see the relevance of the comment.

> > Now, why I think it possible that direct control studies \_might\_ give  
> > a different result even in discrimination experiments: Experimental  
> > techniques known as "adaptive threshold" methods, especially one called  
> > PEST that I developed (with Doug Creelman), give results that seem to show  
> > subjects to be a bit more sensitive to delicate discriminations than the  
> > results of fixed level studies. ...
> 
> This falls into the category of experimental results that you have obtained  
> or have accepted, so by my modest proposal it is exempt from the need for  
> re-evaluation by you. Your expectation is that a PCT experiment would not  
> make any material difference in the facts you found, so there is no need  
> for you to do the experiments, and you can continue to accept those facts.

No. You didn't quote my reason, which is that in many of those cases there  
is only about 4 or 5 dB further \_possible\_ improvement. Since the question  
of interest in analyzing the control system's input function is how  
discriminating (sensitive) it can be, experiments that show poorer  
sensitivity are of no interest, and no experiment could show much greater  
sensitivity. Therefore the results can be treated as useful.

And in any case, you quoted my introduction to the reasons why a PCT  
experiment might indeed make a difference, even though that difference  
\_could not be\_ large, at least not in the direction of demonstrating greater  
sensitivity than is found in a non-control study.

> **···**
>
> ---------------------------
> 
> > And don't forget that the subject can't really "provide output" open-loop.  
> > I showed above how such situations need to be analyzed in terms of PCT,
> 
> I think you should show it again, in a way relevant to the way the  
> experiments are ordinarily done. As I see it, the experiment is quite  
> simply open loop from the subject's point of view. What is not open-loop  
> is the subject's control of the perception of the experimenter's satisfaction.
> 
> > I trust that we would also agree that where there are disputes over whether  
> > or not to re-examine some kind of result, that would be sufficient reason  
> > to re-examine it,
> 
> Yes, we can agree on that.
> 
> -------------------  
> I'm a bit puzzled both by your message and (more so) by Isaac's. I'm  
> perceiving a subtext that seems to say that a person cannot choose to act  
> in a way coordinated with a perception that is not being controlled. If that  
> were so, one could not beat time to an orchestral recording any more than  
> one could say "Yes, there was a tone in the first time interval." But  
> people can and do do both. Where's the problem in that? If we wanted to  
> know how accurately people could perceive the timing of the orchestral  
> beat, we could put an upper bound on that capability by measuring the  
> discrepancy between the visible hand-waving and the acoustic beat. Likewise,  
> if we want to know how well a person can hear a tone, we can put an upper  
> bound on that ability by measuring how reliably the subject says "Yes"  
> when the machine actually presented a tone.
> 
> What's the problem?
> 
> Other than the issue that I raised in my first message on the topic.
> 
> +Martin Taylor 971231 17:45  
> +The question arises as to whether the perceptual input functions operate  
> +the same way when the resulting perception is being controlled as when it  
> +isn't. This issue is not ordinarily considered within HPCT, since normally  
> +the perceptual input function is taken to be whatever it is, and only the  
> +magnitude of its output is controlled. But it is an issue, one that might  
> +invalidate the uncritical use of the results of psychophysical studies  
> +to assess the elements of related control loops.
> 
> ----------------------------
> 
> \<i.kurtzer (980102.0300)  
> \<\>Psychophysical experiments \_are\_ control system experiments, though not in  
> \<\>the sense you intend.  
> \<  
> \<What up, Martin? You knew someone was going to freak on this one. So this  
> \<must be some weirdo intro thread, but to what?
> 
> I'm sorry, Isaac. I'm afraid I understand only small portions of your  
> message. This part, I think I do understand. The answer is that "freak"  
> is a response to a stimulus, isn't it? And we have only one person  
> on CSGnet who acts like an S-R system. I didn't control the perception  
> (in imagination) of someone freaking.
> 
> I said that psychophysical experiments are control system experiments  
> inasmuch as the subject actually has to be controlling some perception  
> in order for the experiment to function in its intended manner. But I  
> said the overt experiment is S-R, and you agreed.
> 
> What I did was control not for a perception of someone freaking, but against  
> a disturbance to my perception that psychophysical studies, by and large,  
> are useful and provide data that can be helpful in the analysis of  
> control systems. From time to time comments are made that they can't  
> be useful because they are not done using control methodology. I do  
> have a dead-band in my control against this disturbance, but my  
> output system is at least partly an integrator, and when the comments  
> are repeated often enough, I provide a countering output (message).
> 
> I'm afraid I'm at a loss to respond to your other comments. For example,
> 
> \<\>In a psychophysical experiment (other than one using  
> \<\>the method of adjustment) the subject is unable to influence what the  
> \<\>experimenter thinks of as the "stimulus," but is able to control an  
> \<\>important perception--the perception of the experimenter's satisfaction  
> \<\>with the subject's performance.  
> \<  
> \<Who knows how important?
> 
> The subject does. I'm afraid that was self-evident in the original, so I'm  
> sure it doesn't answer your comment, but I can't guess what would.
> 
> Likewise with:
> 
> \<\>There are real problems with a lot of psychophysical studies, but not being  
> \<\>control system experiments is not among them  
> \<  
> \<This effectively rewrites every concievable experiment in the history of  
> \<psychology as control-system experiments.
> 
> What, precisely, does this mean? I think I said that the overt psychophysical  
> experiment was not a control-system experiment, and I think you agreed.  
> I said that this was not among the real problems of the studies, and  
> somehow this means rewriting every conceivable experiment in the history  
> of psychology as a control system experiment. Does this \_really\_ make sense  
> to you? It doesn't, to me.
> 
> Perhaps I might be able to respond more satisfactorily if you were to  
> restate what you see as issues. Sorry not to be more helpful.
> 
> Martin

---

<div class="post-metadata">

**Author:** ![R\_Marken](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/r/8797f3/32.png) [@R\_Marken](http://discourse.iapct.org/u/R_Marken)\
**Post date:** [January 3, 1998, 7:10am UTC](http://discourse.iapct.org/t/bridges/1961/9 "1998-01-03T07:10:33Z")

</div>

[From Rick Marken (980102.2310)]

Martin Taylor says:

> Psychophysical experiments \_are\_ control system experiments,  
> though not in the sense you intend.

I already explained why this is not even close. It's because  
psychophysical experiments \_never\_ involve a test for the  
controlled variable. However, i.kurtzer (980102.0300) says:

> What up, Martin? You knew someone was going to freak on this one.

Martin Taylor (980102 21:30) replies:

> I'm sorry, Isaac. I'm afraid I understand only small portions  
> of your message.

I think that's the problem, Martin.

Martin repeats the fiction:

> There are real problems with a lot of psychophysical studies,  
> but not being control system experiments is not among them

isaac astutely replies:

> This effectively rewrites every concievable experiment in the  
> history of psychology as control-system experiments.

And Martin says:

> What, precisely, does this mean?

Martin, do you know the difference between a control system  
experiment and a conventional psychology experiment (hint:  
read my "Dancer..." paper)? Do you know the difference between  
a psychophysical study and a conventional experiment (hint: none)?  
Do you know the kind of experiments that have been done throughout  
the history of psychology (hint: conventional psychology  
experiments)? Now do you understand preciely what isaac's  
comment means?

Best

Rick

> **···**
>
> --
> 
> Richard S. Marken Phone or Fax: 310 474-0313  
> Life Learning Associates e-mail: rmarken@earthlink.net  
> [http://home.earthlink.net/~rmarken/](http://home.earthlink.net/~rmarken/)

---

<div class="post-metadata">

**Author:** ![Bill\_Powers1](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/b/8e7dd6/32.png) [@Bill\_Powers1](http://discourse.iapct.org/u/Bill_Powers1)\
**Post date:** [January 3, 1998, 12:44pm UTC](http://discourse.iapct.org/t/bridges/1961/10 "1998-01-03T12:44:44Z")

</div>

[From Bill Powers (980103.0418 MST)]

Martin Taylor 980102 21:30--

> > So most psychophysics experiments are really concerned with perception of  
> > relationships? That's interesting; the impression I always had was that  
> > much lower levels of perception were being investigated. But from your  
> > descriptions, I can see that you're right.
> 
> I suppose you could see it as perception of relationship. But it's a  
> funny kind of relationship, since it could be a relationship between  
> variables at any level of the hierarchy: is the tone in this interval  
> louder than the tone in that? Is the first sequence the same as the second?  
> Is that chord in tune? Is this noise a /p/ or a /b/? Is the line bent  
> upward or downward?

I'm sure you know that in HPCT, a perception at any level can be a function  
of perceptions from any lower levels, at least as the model stands now. In  
this latest batch of examples, however, you've picked some new cases. For  
the tone and the sequence, you present a perception (which is presumably  
remembered) and then ask if a new example of it matches the first example.  
This could correspond to setting up the first perception as a reference  
condition and stating whether the second occurrance of the same perception  
creates an error. Since we don't postulate that error signals can be  
perceived consciously, a better interpretation might be that a remembered  
perceptual signal is perceived along with a present-time one, and the  
person is judging the two signals in terms of a relationship of equality or  
of inequality (higher or lower than, in pitch).

That's different from judging the curvature of a line; curvature can be  
understood as a single perception with a variable state. Now the person is  
being asked to judge whether curvature is zero, positive, or negative. A  
threshold can be detected in this way, but not the relation of the sense of  
curvature to the actual magnitude of curvature.

As to relationships between sequences, the levels I have proposed have a  
problem with this, because sequences are supposedly of a higher level than  
relationships. One possible answer is that the actual perception being  
judged is at the event level, rather than the level concerned with ordering  
per se. But without some specific experimental evidence on this, I'd just  
have to admit ignorance.

As you can see, the PCT analysis of these situations would get us into many  
questions that don't have any counterparts in the traditional way of  
slicing the pie. Experiments that look the same in traditional terms can be  
very different in PCT terms.

> > I should think that if the subject can tell how well the experimenter is  
> > satisfied by the subject's performance, a great possibility would exist for  
> > the subject to provide the experimenter with the results that are wanted or  
> > expected -- in other words, for the experimenter to control the results  
> > simply by withholding or expressing satisfaction. The "Clever Hans" effect.
> 
> I don't know how long experimenters have been aware of this possibility,  
> but it was drilled into us in my first introduction to experimental  
> psychology that we had to use methods that made it nearly impossible  
> for the subject to do this. I imagine that the techniques for making it  
> hard for the subject to cheat in this way were developed a few decades  
> earlier than that. As for the "clever Hans" effect, most psychophysical  
> experiments use machines to present the stimuli, and the subject is isolated  
> from the experimenter, who doesn't know the correct answer for a particular  
> presentation, anyway. Maybe it was Clever Hans who made psychophysicists  
> aware of the problem and started them devising methods to counter it.

Do I take it, then, that you are retracting the explanation that involves  
the subject's controlling for the experimenter's being satisfied by the  
results? According to the above, experimenters are very careful to prevent  
the subject from being able to perceive the experimenter's satisfaction, so  
obviously this can't be a controlled variable.

You do point out a basic problem with experimenters being their own subjects.

> > I think that in PCT terms we have to assume that a subject can never just  
> > "produce a response," open-loop. When one continuum is used as the response  
> > measure and another as the stimulus measure, the subject must be  
> > controlling a relationship between the two continua.
> 
> I'm not clear how you mean this. Surely every action a person does is  
> (part of) the output action that controls some perception(s). So in that  
> sense it cannot be "open loop." But I don't think that's what you mean,  
> is it?

What I mean is that saying "yes" or "no" (as in your following paragraph)  
is not just an open-loop version of a control action by which the subject  
might control the perception in question. Saying yes or no is controlling  
the perception of hearing oneself say yes or no, in the relationship to the  
perception that is specified in the instructions. The perceptual condition  
under control is something like "sound implies yes, no sound inplies no."

> In no case  
> can the subject affect what has been presented, or what will be the  
> "correct" answer on the next trial. I'd call that open loop.

What is being controlled is a function of a perception of the required  
action and the perception being manipulated. So a different perception is  
being controlled than when the subject has some means of altering the  
perception now being manipulated by the experimenter. In the situation you  
describe, a higher-level perception is being controlled (since the  
lower-level perception can't be controlled). Some of the characteristics of  
what you measure will be those of the higher-level system. Are we measuring  
the threshold of intensity-perception or sensation-perception, or of the  
system that senses the satisfaction of a logical condition?

When differences are involved, what you may be measuring is the transition  
level of perception, rather than the sensation level. Of course these  
distinctions didn't exist in the old psychophysics; it was assumed that if  
you present one tone, then another tone, all that is being judged is  
magnitude.

> Isaac,  
> in a message I find hard to comprehend (i.kurtzer (980102.0300)), calls  
> it "S-R to its core." You say it is not open loop. I guess I'm in the  
> middle between you and Isaac. I say it is a mechanism forming part of  
> the output path of a control loop.

But the "reponse" to which you refer does not affect the "stimulus" -- you  
aren't just opening the loop of an existing control system to check its  
open-loop behavior. You're setting up a \_different\_ control system that  
uses -- you hope -- the same input function. It certainly doesn't use the  
same output function.

Anyway, all you measure in the way described above is the lower threshold  
of the perceptual function, distinguishing the smallest detectable amount  
of signal from no signal. This gives no information about the relation of  
signal to stimulus for above-threshold stimuli, which is the sort of thing  
that the power law or the logarithmic law is about.

> > When a number is used as the response, it is really (according to PCT) a  
> > perception of magnitude (elicited by the numeral or spoken word) that is  
> > under control at the lower level.
> 
> I don't see how this applies in the usual psychophysical experiment. "One"  
> is not bigger than "two" when they are identifiers for the first or second  
> time interval of a trial--and in any case, the response is usually a choice  
> of which button to push, since it is hard for the machine (at least until  
> recent years) to recognize what the subject says.

No, but as magnitude estimates, numbers satisfy the example I gave. You're  
bringing up, de novo, the use of numbers as cardinal numbers, which is a  
different subject. In that application, 1 and 2 are no different from A and  
B. They aren't numbers, they're just arbitrary symbols.

> > The experiments as you describe them, which involve comparing two different  
> > perceptions, would seem to be tests of relationship perceptions, rather  
> > than basic abilities to discriminate, say, intensity changes in a single  
> > level-one perception.
> 
> I don't understand why you say "rather than" instead of "which depend on"  
> at least in the case where it is the intensity of a sound or light that  
> is being compared.

Because I am assuming HPCT, in which there are different levels of  
perception, each level having its own characteristics. In addition to the  
ability to detect intensitites, we have the ability to detect intensity  
transitions (which occurs at a different level), and at still higher levels  
the ability to detect relationships between intensities, which introduces  
still different characteristics. As far as I know, psychophysics has never  
dealt with levels of perception, so even when thresholds are measured, we  
don't know which level of perception is associated with the threshold. It's  
possible that when we look at thresholds for relationship perceptions, we  
are seing higher thresholds than exist at the level of intensity  
perception. It's not hard to think of examples in which a higher-level  
perception isn't altered until a lower-level perception has undergone a  
considerable and easily-detected change.

To find out whether this effect has been occurring in psychophysical  
experiments, we'd just have to do them again.

> > To test the ability to discriminate small changes in  
> > intensity, all we need to do is give the person control over a single  
> > intensity perception and determine the smallest disturbance that will  
> > produce a corrective action.
> 
> I dispute that. It depends totally on having a control function that is  
> linear through zero.

I don't see why. If the function is nonlinear near zero, we will find that  
a larger disturbance is required to produce a corrective action at low  
values of the controlled variable than at high values. In fact, by using  
small oscillating disturbances at different mean values of the controlled  
variable, you could map out the static input-output curve and also measure  
the system noise at each input level, as well as getting the noise  
spectrum. Of course this map would include both the input and output  
functions of the control system; there's no way to separate them that I can  
see at the moment (outside neural measurements). Perhaps the different  
reference levels that would be involved would permit the separation.

> There are two places in the loop that might put a  
> lower bound on the smallest disturbance to produce a corrective action:  
> the discriminative ability of the input function, and the shape of the  
> output function. It is surely better to dissociate them if you are trying  
> to examine one of them.

I agree, but I don't see how to do that right now in a behavioral  
experiment. We also have the question of thresholds at the comparator.

> > The concept of a hierarchy of perceptions  
> > suggests that this kind of discrimination is quite different from the kind  
> > in which a person tries so say whether, for example, a light intensity is  
> > greater than a sound intensity, or a sound intensity is greater than the  
> > rate of rotation of something.
> 
> Oh, quite different. I don't see much sense in these comparisons as absolute  
> statements. I do see some sense in asking whether, if sound A is perceived  
> as being as strong as light B, then is sound 2\*A greater or less than light  
> 2\*B. I don't find this latter question interesting, but at least it seems  
> to have some possible internal consistency.

But this is basically what all psychophysical estimates of magnitude are  
doing. Is perception A greater or less than perception B? There is no way  
to get an absolute scale.

> I don't think most traditional psychophysicists would disagree, and there  
> have indeed been studies in the area of phonemic/phonetic discrimination  
> that show you to be correct in principle. But not using the idea of "JND",  
> please:-)

All right. No more JNDs. I'm not interested in them, anyway.

> > > Now, why I think it possible that direct control studies \_might\_ give  
> > > a different result even in discrimination experiments: Experimental  
> > > techniques known as "adaptive threshold" methods, especially one called  
> > > PEST that I developed (with Doug Creelman), give results that seem to show  
> > > subjects to be a bit more sensitive to delicate discriminations than the  
> > > results of fixed level studies. ...
> > 
> > This falls into the category of experimental results that you have obtained  
> > or have accepted, so by my modest proposal it is exempt from the need for  
> > re-evaluation by you. Your expectation is that a PCT experiment would not  
> > make any material difference in the facts you found, so there is no need  
> > for you to do the experiments, and you can continue to accept those facts.
> 
> No. You didn't quote my reason, which is that in many of those cases there  
> is only about 4 or 5 dB further \_possible\_ improvement.

Of course not. I gave \_my\_ reason. You accept the facts you cite as true,  
and you yourself have done many experiments of this kind. So you have no  
responsibility, under my modest proposal, for applying PCT to them to see  
if anything needs to be re-evaluated. Under the rules I propose, you're not  
only exempt from the requirement of re-evaluation, you're disqualified.

> Since the question  
> of interest in analyzing the control system's input function is how  
> discriminating (sensitive) it can be, experiments that show poorer  
> sensitivity are of no interest, and no experiment could show much greater  
> sensitivity. Therefore the results can be treated as useful.

So you agree with me. You see no reason actually to re-do the experiments  
because you consider them to have been done so perfectly, in technique and  
conception, that PCT could not possibly make any material difference in the  
results. You may be quite right, for all I know. But because of your belief  
in these results, you are not the right person to do the re-evaluation. If  
anyone wants to do one.

> ---------------------------
> 
> > I trust that we would also agree that where there are disputes over whether  
> > or not to re-examine some kind of result, that would be sufficient reason  
> > to re-examine it,
> 
> Yes, we can agree on that.

Good. That will save a lot of arguments.

> -------------------  
> I'm a bit puzzled both by your message and (more so) by Isaac's. I'm  
> perceiving a subtext that seems to say that a person cannot choose to act  
> in a way coordinated with a perception that is not being controlled.

Not at all. But "coordination" is a different kind of controlled variable.  
It involves higher levels of perception.

> If that  
> were so, one could not beat time to an orchestral recording any more than  
> one could say "Yes, there was a tone in the first time interval." But  
> people can and do do both. Where's the problem in that?

No problem. Both involve higher levels of perception and control than those  
associated with the individual elements of the controlled perceptions. I  
assume that the higher level perceptual systems will introduced new  
characteristics, including perhaps different threholds and sensitivities.  
Perhaps not, but we can't settle that without experiments.

> +Martin Taylor 971231 17:45  
> +The question arises as to whether the perceptual input functions operate  
> +the same way when the resulting perception is being controlled as when it  
> +isn't. This issue is not ordinarily considered within HPCT, since normally  
> +the perceptual input function is taken to be whatever it is, and only the  
> +magnitude of its output is controlled. But it is an issue, one that might  
> +invalidate the uncritical use of the results of psychophysical studies  
> +to assess the elements of related control loops.

To this, I add the fact that in the so-called "open loop" situations, we  
actually are studying different control systems, not the same control  
system with its EFF removed.

Best,

Bill P.

---

<div class="post-metadata">

**Author:** ![Martin\_Taylor4](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/m/71c47a/32.png) [@Martin\_Taylor4](http://discourse.iapct.org/u/Martin_Taylor4)\
**Post date:** [January 3, 1998, 4:57pm UTC](http://discourse.iapct.org/t/bridges/1961/11 "1998-01-03T16:57:27Z")

</div>

[Martin Taylor 980103 11:45] following up

> [Martin Taylor 980102 21:30] to Bill Powers 980102

> > To test the ability to discriminate small changes in  
> > intensity, all we need to do is give the person control over a single  
> > intensity perception and determine the smallest disturbance that will  
> > produce a corrective action.
> 
> I dispute that. It depends totally on having a control function that is  
> linear through zero. There are two places in the loop that might put a  
> lower bound on the smallest disturbance to produce a corrective action:  
> the discriminative ability of the input function, and the shape of the  
> output function. It is surely better to dissociate them if you are trying  
> to examine one of them.

When I awaoke this morning I remembered the very first study I was exposed  
to in my transition from being an engineer into becoming a psychologist.  
It was a study of the rangefinder of some kind of gun. I think it was a  
stereo view that was adjusted through a gear train, though it might have  
been a vernier view. Part of the experiment involved seeing what effect  
the gear ratio might have. The subject adjusted the sight as accurately  
as he could, and we determined the variability at different ranges, with  
different gear ratios. It was, in fact, exactly the kind of study you  
propose, since the subject was adjusting a perception of stereo or vernier  
disparity to a reference value of zero, as accurately as possible, and  
we were measuring the smallest disturbance that would produce a corrective  
action.

What we found was that the setting accuracy depended strongly on the gear  
ratio, with an optimum that was neither too high (moving the image too  
quickly) or too low (moving it too slowly). The setting accuracy was  
therefore clearly not limited by the ability of the person to perceive  
the disparity, at least not for most gear ratios and perhaps for none.  
Changing the environmental feedback function should not affect the  
perceptual input function--the ability to discriminate small changes--but  
it does affect the result of the experiment when it is performed as a  
control system experiment.

Separately from that, I have a personal (anecdotal) comment, based on my  
experience in setting up the tracking for the sleep study. With the  
square-wave disturbances, I found that I very frequently would not  
correct a 1 or 2 pixel error that was clearly perceptible, the conscious  
reason being that a new disturbance would come along soon enough and it  
wasn't "worth" fixing such a small error. If this happened to me, who  
had a strong motivation to get the best results I could, I think it  
quite probable that it would happen to at least some of the experimental  
subjects (which is why I tried using a dead-band parameter in some of  
the model fits for the study).

If you want to study input functions, it seems important not to obtain  
results that are depend strongly on the environment or the output function.

Martin

---

<div class="post-metadata">

**Author:** ![Martin\_Taylor4](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/m/71c47a/32.png) [@Martin\_Taylor4](http://discourse.iapct.org/u/Martin_Taylor4)\
**Post date:** [January 3, 1998, 5:10pm UTC](http://discourse.iapct.org/t/bridges/1961/12 "1998-01-03T17:10:16Z")

</div>

[Martin Taylor 9801013 11:55]

> [From Rick Marken (980102.2310)]
> 
> Martin Taylor says:
> 
> > Psychophysical experiments \_are\_ control system experiments,  
> > though not in the sense you intend.
> 
> I already explained why this is not even close. It's because  
> psychophysical experiments \_never\_ involve a test for the  
> controlled variable.

That's why I said "Not in the sense you intend". I suppose you didn't read  
that bit. I also pointed out that the overt experiment is S-R, which  
the "astute" isaac agreed with. I'm not clear why you need to explain  
that to me. Could you elucidate?

> However, i.kurtzer (980102.0300) says:
> 
> > What up, Martin? You knew someone was going to freak on this one.
> 
> Martin Taylor (980102 21:30) replies:
> 
> > I'm sorry, Isaac. I'm afraid I understand only small portions  
> > of your message.

Actually, I answered that I was not concerned whether our resident S-R  
system would emit the "freak" response to my stimulus. It was not a  
perception for which I was controlling. You quoted my answer to the  
message as a whole, rather than to the bit you quoted. But that's normal:-)

> Martin repeats the fiction:
> 
> > There are real problems with a lot of psychophysical studies,  
> > but not being control system experiments is not among them

I'm not clear which is the fiction--whether there are problems with  
a lot of psychophysical studies, or whether the fact that they are not  
control studies is not the problem.

> isaac astutely replies:
> 
> > This effectively rewrites every concievable experiment in the  
> > history of psychology as control-system experiments.
> 
> And Martin says:
> 
> > What, precisely, does this mean?
> 
> Martin, do you know the difference between a control system  
> experiment and a conventional psychology experiment

Yes. Since I pointed out that the overt psychophysical experiment is  
pure S-R, I think I showed that at least I knew that there just tiddly  
might be a teensy difference.

hint:

> ... Now do you understand preciely what isaac's  
> comment means?

No. It remains incomprehensible.

Neither do I understand why you think I need lecturing on the difference  
between studies of controlled variables and studies of the individual  
(input-output) components of control systems using S-R methods.

The issue isn't there at all. The issue is whether the components of  
the control systems perform the same way when the relevant perception  
is actively under control as when it isn't. I pointed that out in my  
original message, noting that there seems to be some neurological  
evidence that they may not. It is this, not the question of experimental  
method, that may determine whether the results of psychophysical studies  
are useful in teasing apart the functions of individual loop components.

Martin

---

<div class="post-metadata">

**Author:** ![Bill\_Powers1](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/b/8e7dd6/32.png) [@Bill\_Powers1](http://discourse.iapct.org/u/Bill_Powers1)\
**Post date:** [January 3, 1998, 6:16pm UTC](http://discourse.iapct.org/t/bridges/1961/13 "1998-01-03T18:16:33Z")

</div>

[From Bill Powers (980103.1101 MST)]

Martin Taylor 980103 11:45] --

> When I awaoke this morning I remembered the very first study I was exposed  
> to in my transition from being an engineer into becoming a psychologist.  
> It was a study of the rangefinder of some kind of gun. I think it was a  
> stereo view that was adjusted through a gear train, though it might have  
> been a vernier view. Part of the experiment involved seeing what effect  
> the gear ratio might have. The subject adjusted the sight as accurately  
> as he could, and we determined the variability at different ranges, with  
> different gear ratios. It was, in fact, exactly the kind of study you  
> propose, since the subject was adjusting a perception of stereo or vernier  
> disparity to a reference value of zero, as accurately as possible, and  
> we were measuring the smallest disturbance that would produce a corrective  
> action.

Nice find. It would be interesting to do the same experiment with  
instructions to maintain different nonzero distances between the crosshairs  
and the target (or whatever). This would explore the control function for  
values of input different from zero.

> What we found was that the setting accuracy depended strongly on the gear  
> ratio, with an optimum that was neither too high (moving the image too  
> quickly) or too low (moving it too slowly). The setting accuracy was  
> therefore clearly not limited by the ability of the person to perceive  
> the disparity, at least not for most gear ratios and perhaps for none.  
> Changing the environmental feedback function should not affect the  
> perceptual input function--the ability to discriminate small changes--but  
> it does affect the result of the experiment when it is performed as a  
> control system experiment.

The performance of the whole loop depends on the properties of the whole  
loop. When you increase the gear ratio (give the control knob less effect  
on the controlled variable), the loop gain decreases by the same factor. In  
a leaky-integrator system, which behaves like a proportional system for  
slow changes, there can still be error at the point where the output ceases  
to change. Only in a pure integrator will the output keep changing until no  
error remains. As for decreasing the gear ratio, the effect is to increase  
loop gain, and since you start out doing the best you can, the immediate  
effect is likely to be instability and a longer time to reach zero error.

> Separately from that, I have a personal (anecdotal) comment, based on my  
> experience in setting up the tracking for the sleep study. With the  
> square-wave disturbances, I found that I very frequently would not  
> correct a 1 or 2 pixel error that was clearly perceptible, the conscious  
> reason being that a new disturbance would come along soon enough and it  
> wasn't "worth" fixing such a small error.

I'm glad you said "conscious reason." I've had the same experiences, and  
have come up with the same rationalization. Fitting models is a much more  
trustworthy way of characterizing what's happening. When a simulation fit  
to the same data shows the same uncorrected small errors, one becomes  
rather suspicious of "reasons." There are no "reasons" in the model!

I think that in these low-order tracking tasks, the higher-level systems  
keep themselves busy by thinking up explanations for what's going on, but  
that these explanations have little to do with what is actually happening.

Best,

Bill P.

---

<div class="post-metadata">

**Author:** ![Bill\_Powers1](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/b/8e7dd6/32.png) [@Bill\_Powers1](http://discourse.iapct.org/u/Bill_Powers1)\
**Post date:** [January 3, 1998, 6:38pm UTC](http://discourse.iapct.org/t/bridges/1961/14 "1998-01-03T18:38:28Z")

</div>

[From Bill Powers (980103.1136 MST)]

Martin Taylor 9801013 11:55--

> > [From Rick Marken (980102.2310)]

&nbsp;&nbsp;[Also replying to i. kurtzer]

I think that all you guys might be missing the point that if PCT is  
correct, there is no such thing as an open-loop experiment because there is  
no such thing as open-loop behavior.

Best,

Bill P.

---

<div class="post-metadata">

**Author:** ![Martin\_Taylor4](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/m/71c47a/32.png) [@Martin\_Taylor4](http://discourse.iapct.org/u/Martin_Taylor4)\
**Post date:** [January 4, 1998, 6:19am UTC](http://discourse.iapct.org/t/bridges/1961/15 "1998-01-04T06:19:55Z")

</div>

[Martin Taylor 980104 01:20]

> Bill Powers (980103.1136 MST)
> 
> Martin Taylor 9801013 11:55--
> 
> > > [From Rick Marken (980102.2310)]
> 
> [Also replying to i. kurtzer]
> 
> I think that all you guys might be missing the point that if PCT is  
> correct, there is no such thing as an open-loop experiment because there is  
> no such thing as open-loop behavior.

Actually, it was saying that that got me into trouble with Isaac. At  
least I think it was, since I still have trouble understanding Isaac's  
message, despite Rick's "helpful" intervention.

I hope it doesn't get you into trouble with Isaac as well.

Martin

---

<div class="post-metadata">

**Author:** ![R\_Marken](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/r/8797f3/32.png) [@R\_Marken](http://discourse.iapct.org/u/R_Marken)\
**Post date:** [January 4, 1998, 7:48am UTC](http://discourse.iapct.org/t/bridges/1961/16 "1998-01-04T07:48:42Z")

</div>

[From Rick Marken (980103.2350)]

Bill Powers (980103.1136 MST) --

> I think that all you guys might be missing the point that if  
> PCT is correct, there is no such thing as an open-loop experiment  
> because there is no such thing as open-loop behavior.

Martin Taylor (980104 01:20) --

> Actually, it was saying that that got me into trouble with Isaac.  
> At least I think it was, since I still have trouble understanding  
> Isaac's message, despite Rick's "helpful" intervention.

What got you into trouble with isaac (and me -- and Bill for that  
matter) for was your claim that:

> Psychophysical experiments \_are\_ control system experiments,  
> though not in the sense you intend.

isaac and I (and I think Bill too) thought you were saying that  
psychophysical experiments are control system experiments in  
the sense that they are appropriate tests of control system  
behavior. We thought this because you went on to claim that  
the results of psychophysical experiments, because they are  
"control system experiments", can be retained as part of the  
PCT canon.

I think your current position, however, is that psychophysical  
experiments \_are\_ control system experiments in the sense  
that they are experiments carried out on control systems. My  
"helpful" intervention was aimed at pointing out that (as Bill  
notes) if PCT is right, then every experiment that has ever been  
done in psychology is a "control system experiment" in this sense  
because organisms are control systems. But this would not make  
these experiments "control system experiments" in the sense that  
they are \_appropriate\_ tests of control system behavior since  
all these experiments were done with no understanding of the  
\_nature\_ of control and no awareness of the possibility that  
the subjects in these experiments were busy controlling various  
perceptual input variables; simply put, these experiments include  
no tests for controlled variables.

Yes, if PCT is correct then there is no such thing as an open-  
loop experiment in the sense that there is no experiment in  
which the subject's can behave "open loop". But there are  
experiments (like psychophysical experiments and all other  
conventional psychology experiments) that \_ignore\_ the  
possibility that the subjects are closed-loop control systems.  
So even if subjects are closed-loop systems (as per PCT)  
psychophysical and other conventional experiments tell us  
virtually nothing about the behavior of these systems because  
these experiments tell us nothing about the perceptual variables  
that these systems are controlling.

I presume that you agree with all this, now that I understand  
what you really meant to say.

Best

Rick

> **···**
>
> --
> 
> Richard S. Marken Phone or Fax: 310 474-0313  
> Life Learning Associates e-mail: rmarken@earthlink.net  
> [http://home.earthlink.net/~rmarken/](http://home.earthlink.net/~rmarken/)

---

<div class="post-metadata">

**Author:** ![Myrexsw](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/m/858c86/32.png) [@Myrexsw](http://discourse.iapct.org/u/Myrexsw)\
**Post date:** [January 4, 1998, 8:25am UTC](http://discourse.iapct.org/t/bridges/1961/17 "1998-01-04T08:25:58Z")

</div>

i.kurtzer (980104.0200)

night-owling into the new year!

> I'm a bit puzzled both by your message and (more so) by Isaac's. I'm  
> perceiving a subtext that seems to say that a person cannot choose to act  
> in a way coordinated with a perception that is not being controlled.

That makes us one to one, I suppose; could you say this differently?

> \<i.kurtzer (980102.0300)  
> \<\>Psychophysical experiments \_are\_ control system experiments, though not in  
> \<\>the sense you intend.  
> \<  
> \<What up, Martin? You knew someone was going to freak on this one. So this  
> \<must be some weirdo intro thread, but to what?
> 
> I'm sorry, Isaac. I'm afraid I understand only small portions of your  
> message. This part, I think I do understand. The answer is that "freak"  
> is a response to a stimulus, isn't it? And we have only one person  
> on CSGnet who acts like an S-R system. I didn't control the perception  
> (in imagination) of someone freaking.

Who is that person?

> I said that psychophysical experiments are control system experiments  
> inasmuch as the subject actually has to be controlling some perception  
> in order for the experiment to function in its intended manner. But I  
> said the overt experiment is S-R, and you agreed.

And i would say further that this "overt" experiment means simply the type of  
experiment. To rewrite the experiment to account for how \_we\_ concieve of the  
scenario and say \_that\_ is the experiment is confuse methodology with  
theory--or if the theory is true then with ontology.

Methods and theories go hand in hand, right? These experiments were cast in a  
specific way consistent with their notions of how we tick, right? That the  
implicit basis of their methods was wrong does not mean they were studying what  
we focus to. That would be like calling Decartes a neurophysiologist.  
In fact, the leap might be even greater.

\>\<\>In a psychophysical experiment (other than one using

> \<\>the method of adjustment) the subject is unable to influence what the  
> \<\>experimenter thinks of as the "stimulus," but is able to control an  
> \<\>important perception--the perception of the experimenter's satisfaction  
> \<\>with the subject's performance.  
> \<  
> \<Who knows how important?
> 
> The subject does. I'm afraid that was self-evident in the original, so I'm  
> sure it doesn't answer your comment, but I can't guess what would.

Well, since that was introduced I assumed that it might stand that "importance"  
would be something the tester would want independent verification of; thereby  
the tester might find \_independent\_ reasons for discarding or keeping the data  
other than confirmation with his ideas. We could assume the 'importance" might  
function such that the gain would be tighter in such cases, and since we would  
want that very much, we should confirm or disconfirm the state of "importance".  
But this is again obviated by the Test. Its requirements of "instructional"  
protocal are of a far different sort, ones that side-step the  
"interpretational". We simply ask the person, for example, to keep something  
the same size. This is their size, not the tester's foisting of "size  
protocals" which are known to be extremely flexible. I know for a fact that  
this situation pervades vowel studies. Make the protocal with two choices or  
self-genrated, or embedded in a common word, or a set of orthographic  
symbols....and what we find is unaccpetable variations to the \_same\_  
presentation. Taken literally one might suspect that persons really heard  
something different \_because\_ of the scenario.  
i believe this is false.  
i believe instead that the individual acted differently to cooincide with the  
different instructions.  
This is a major problem with these and all such studies.

&nbsp;&nbsp;&nbsp;\>Perhaps I might be able to respond more satisfactorily if you were to

> restate what you see as issues.

did this help?

---

<div class="post-metadata">

**Author:** ![Martin\_Taylor4](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/m/71c47a/32.png) [@Martin\_Taylor4](http://discourse.iapct.org/u/Martin_Taylor4)\
**Post date:** [January 4, 1998, 6:29pm UTC](http://discourse.iapct.org/t/bridges/1961/18 "1998-01-04T18:29:16Z")

</div>

[Martin Taylor 980104 12:40]

> i.kurtzer (980104.0200)

Thanks. Isaac, for a rather clearer message. I think I can respond to  
most of it.

> > I'm a bit puzzled both by your message and (more so) by Isaac's. I'm  
> > perceiving a subtext that seems to say that a person cannot choose to act  
> > in a way coordinated with a perception that is not being controlled.
> 
> That makes us one to one, I suppose; could you say this differently?

I read you and Bill as saying that it was not possible for a person to  
say "Yes" when she heard a tone and "No" when she didn't, and for those  
statements to be used as evidence for or against the person's ability  
to hear the tone at that intensity.

> Methods and theories go hand in hand, right?

Right. But different theories can accept the same methods. If that were not  
so, there would be no possibility of believing in the unity of science.  
I happen to believe (purely on faith) that there is a real world out there,  
and that there are various ways of observing it, some more useful than  
others, to be sure. But if every method of observation used because the  
observer had a particular notion of the real world gave results that were  
automatically invalid in any other view of the real world, we would have  
no possibility whatever of deeming one view more reasonable than another.  
I prefer to look at methods and see whether they seem to provide sensible  
(i.e. interpretable) results, whatever the viewpoint of the user of the  
method, because I believe there is only one "real world" out there.

> These experiments were cast in a  
> specific way consistent with their notions of how we tick, right? That the  
> implicit basis of their methods was wrong does not mean they were studying  
> what  
> we focus to. That would be like calling Decartes a neurophysiologist.

Who cares whether Descartes was or called himself a neurophysiologist  
(I think Goethe would have been a better example)? What we should care  
about is whether what he said or observed is or might be valid in other  
contexts.

> \>\<\>In a psychophysical experiment (other than one using
> 
> > \<\>the method of adjustment) the subject is unable to influence what the  
> > \<\>experimenter thinks of as the "stimulus," but is able to control an  
> > \<\>important perception--the perception of the experimenter's satisfaction  
> > \<\>with the subject's performance.  
> > \<  
> > \<Who knows how important?
> > 
> > The subject does. I'm afraid that was self-evident in the original, so I'm  
> > sure it doesn't answer your comment, but I can't guess what would.
> 
> Well, since that was introduced I assumed that it might stand that  
> "importance"  
> would be something the tester would want independent verification of; thereby  
> the tester might find \_independent\_ reasons for discarding or keeping the data  
> other than confirmation with his ideas.

Huh? Now I am confused as to what you mean. Are you suggesting that the  
honest experimenter would discard data because it didn't conform to his  
theory? Or are you saying that the subject would be controlling for some  
perception that was not "important" to her? I define "important" in this  
context as "being worth controlling," which I would have thought clear.

"Experimenter satisfaction" in my book comes with consistency of  
subject performance, helping the experimenter to discover how the world  
works. Anyway, I used "experimenter satisfaction" as an example of what  
the subject might be controlling for in order that he might act in the  
experiment. There could be, and probably are, other higher-level perceptions  
using the same mechanism.

> We could assume the 'importance" might  
> function such that the gain would be tighter in such cases, and since we would  
> want that very much, we should confirm or disconfirm the state of  
> "importance".

Why would that matter, so long as the subject tries to do the experiment  
as best she can?

> But this is again obviated by the Test. Its requirements of "instructional"  
> protocal are of a far different sort, ones that side-step the  
> "interpretational". We simply ask the person, for example, to keep something  
> the same size. This is their size, not the tester's foisting of "size  
> protocals" which are known to be extremely flexible.

Again you confuse me. If you ask the subject "did you see it," is it not the  
subject's decision as to whether he did see it? It's clearly not the  
experimenter's, for if it were, why bother with the subject at all?

> I know for a fact that  
> this situation pervades vowel studies. Make the protocal with two choices or  
> self-genrated, or embedded in a common word, or a set of orthographic  
> symbols....and what we find is unaccpetable variations to the \_same\_  
> presentation. Taken literally one might suspect that persons really heard  
> something different \_because\_ of the scenario.

And can you say that they don't? You are into tricky stuff here:  
"unacceptable" implies a purpose for which the vowel might be acceptable;  
change the scenario and you change the dead zone for the controlled  
perception(s).

> i believe this [that they heard something different] is false.

On what ground?

You and Bill appear to be parting company here. Bill asserts equally  
baldly that people \_do\_ perceive the same thing differently at different  
hierarchic levels, and perhaps even discriminate differently at different  
levels. I go along with him on this.

> i believe instead that the individual acted differently to cooincide with the  
> different instructions.

Yes...but. Did they also perceive differently, and is this why they acted  
differently?

I once did a study that might be relevant to this (with G.B. Henning,  
reported in the Canadian Journal of Psychology around 1963-65 sometime).  
We asked people to listen to repeated short tape loops of English words.  
When people listen to such stuff, they start hearing different words after  
a while. We found that we could affect how many different words and  
what kind of words they heard by altering the instructions. We told  
some people that the words would change and that all the changes would  
be into other English words, whereas other people were told that the  
changes might be into nonsense syllables as well as into English words.  
Lo and behold, the subjects told they would hear only English reported  
only English, and the subjects told that there might be nonsense reported  
both English and nonsense. Surprise, surprise:-)

Now, the question. Were the "English-only" subjects hearing the nonsense  
words but suppressing the report, or were they not perceiving the  
nonsense words that they might otherwise have perceived if they had had  
the other instructions? How could anyone tell? The natural presumption is  
that they were just following instructions in what they reported, and  
the groups all heard the same kinds of things.

Luckily, there is a way to distinguish the "perceived differently" and  
"acted differently" hypotheses.

We asked each subject to report what they heard every time it changed.

> From these reports we could plot the number of changes against the

number of different things they reported. In every case, the plot formed  
a perfect fit (within the width of the plotting line, almost) to the  
function N\_changes = k\*(N\_forms\*(N\_forms-1). This is the function that  
would occur if the subject from time to time generated a new form to  
perceive and thereafter changed randomly among the forms so far generated.  
We had found the same function for the analogous task in many different  
perceptual domains.

Now suppose that the subject had actually perceived a nonsense form, but  
had suppressed its report because of the instruction that all the changes  
would be to English words. Let's say A and B were English word forms, and  
X was a nonsense form. Then there should have been transitions A-X-B,  
reported as such by a "nonsense-permitted" subject (2 transitions),  
but as A-B by the "English-only" group. The form of the function would  
have been quite different, especially as the numbers of forms increased  
over time. It wasn't. The function for the "English-only" people tracked  
as exactly as can be plotted with the function for the "nonsense-permitted"  
people. (For each subject, in case that needs emphasizing). The conclusion  
is that it is highly unlikely that the instructions were affecting the  
reports, and highly probable that they were affecting the perceptions.

I think this is true much more generally in life. We perceived what we have  
been "instructed" (by experience) to perceive. We have, in other words,  
reorganized our perceptual input functions so that our controlling our  
various perceptions don't lead to too much conflict--and those of us for  
whom this is false may seek therapy or jail. In other words, instructions  
may well change what we perceive in any particular situation.

> did this help?

Oh, yes, thank you. Did my response?

Martin

---

<div class="post-metadata">

**Author:** ![Martin\_Taylor4](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/m/71c47a/32.png) [@Martin\_Taylor4](http://discourse.iapct.org/u/Martin_Taylor4)\
**Post date:** [January 4, 1998, 6:29pm UTC](http://discourse.iapct.org/t/bridges/1961/19 "1998-01-04T18:29:25Z")

</div>

[Martin Taylor 980104 12:20]

> Rick Marken (980103.2350)]

> What got you into trouble with isaac (and me -- and Bill for that  
> matter) for was your claim that:
> 
> > Psychophysical experiments \_are\_ control system experiments,  
> > though not in the sense you intend.

> I think your current position, however, is that psychophysical  
> experiments \_are\_ control system experiments in the sense  
> that they are experiments carried out on control systems.

That was always my position. The statement that seems to have caused you  
a problem was made because, even on CSGnet, it is too often claimed that  
they are not, which to me is ridiculous. When this claim is restated  
often enough in a short enough time, my integrating output function, for  
a perception that we should deal in common sense, produces action in  
the form of a message. People act in a psychophysical experiment because  
they are controlling some perception, just as they do in any other  
situation (including other experiments).

However, I can see how the three of you misconstrued my statement as  
coming from the other side and therefore misread the whole of the  
rest of what I had to say, which was a pity. Perhaps if you were to  
take such statements in the context of all my other writings, you would  
be able to understand better what I was getting at.

> Yes, if PCT is correct then there is no such thing as an open-  
> loop experiment in the sense that there is no experiment in  
> which the subject's can behave "open loop". But there are  
> experiments (like psychophysical experiments and all other  
> conventional psychology experiments) that \_ignore\_ the  
> possibility that the subjects are closed-loop control systems.

I agree with this.

> So even if subjects are closed-loop systems (as per PCT)  
> psychophysical and other conventional experiments tell us  
> virtually nothing about the behavior of these systems

And it is this that I dispute.

> because  
> these experiments tell us nothing about the perceptual variables  
> that these systems are controlling.

What they tell us is about limits on the ability of people to control those  
perceptual variables they choose to control.

When you are trying to examine a piece of machinery, you can do it in  
at least two ways. One is to treat it as a black box and push and pull  
it in various ways. The other is to tease apart its components and see  
what each does, and how that component relates to the behaviour you  
see when you push and pull. You can't do without the push-pull examination,  
but its power is much enhanced if you can also see the function of the  
components individually. If you look only at the components, you will  
find it hard to discover what the machine is doing, but once you know  
that, knowledge of the components is very helpful.

That's the position I think psychophysics has. It matters not a whit that  
most psychophysicists haven't a clue about living control systems. They  
measure a gear ratio in a machine whose function is obscure. But it is  
still a valid gear ratio, useful to those who understand what the machine  
is doing.

Martin

---

<div class="post-metadata">

**Author:** ![Myrexsw](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/m/858c86/32.png) [@Myrexsw](http://discourse.iapct.org/u/Myrexsw)\
**Post date:** [January 4, 1998, 8:10pm UTC](http://discourse.iapct.org/t/bridges/1961/20 "1998-01-04T20:10:26Z")

</div>

i.kurtzer (980104.1400)

> [From Bill Powers (980103.1136 MST)]
> 
> Martin Taylor 9801013 11:55--
> 
> > > [From Rick Marken (980102.2310)]
> 
> [Also replying to i. kurtzer]
> 
> I think that all you guys might be missing the point that if PCT is  
> correct, there is no such thing as an open-loop experiment because there is  
> no such thing as open-loop behavior.

i agree, but only partly. There is a differnce between methods appropriate to  
one theory vs another theory. The arrival of another theory does not render  
the previous methodologies "poor realizations" of the newly inspired  
methodology, no more than the previous theories are poor realizations of the  
new theory. For theories this is a tricky issue, i'll leave for now. But for  
methods it is straight-forward. Methods are different as they are carried out  
differently. "Overt" method is method. To re-intrepret is one thing. But to  
re-write is another. I agree with your re-interpreting and also with Martin if  
that is what he is positing. But not with the latter.

i.

[Next page](http://discourse.iapct.org/t/bridges/1961.md?page=2)