Behavioral illusion, based on Powers (1978)

AM: I don’t see it. More examples of your definition of side effects, please.
RM: In the rubber band demo if you, as E, apply disturbances to the position of the knot so that S has to move her end of the rubber band in a way that traces out a perfect rendering of Botticelli’s Venus on the Half Shell , then that picture is a side effect of S controlling the position of the knot.

Ok, makes sense. Any properties of qo, the final trajectory are a side effect of keeping qi stable.

The problem is that this definition of side effects is in conflict with your definition of a behavioral illusion. If the contour of Venus look exactly like the template you wanted to get, this tells you something very important about the control system that made it. For one, it is a high-gain control system, at the speeds that you gave it. If the contour of Venus looks somewhat distorted, the gain was not so high, the errors were not well compensated.

AM: But in a way, I do agree with you, the power law does not tell you anything definite about the system until you find the controlled variables. It might be that it is an intended effect, it might be it is not. Proof and demonstration only by models and experiments.

RM: Amen.

No so fast.

The same thing goes for “a behavioral illusion” in your power law papers. If it turns out that the power law is the main effect, that the trajectory is the controlled variable, or the instantaneous affine velocity is the controlled variable, both of which you suggested might be controlled; then the power law is not a side effect, it is the main effect, intended and achieved.

On the other hand, if some other variable is controlled, then the power law is a side effect, but it does tell you something about the control system. The exact speeds where the power law appears tell you something about, for example, force production constraints of the organism, or something about the interaction of the body and the environment in the loop, things like friction, inertia. etc.

Either way, really, the definition of “a behavioral illusion” is not self consistent.

Hi Adam

AM: I don’t see it. More examples of your definition of side effects, please.
RM: In the rubber band demo if you, as E, apply disturbances to the position of the knot so that S has to move her end of the rubber band in a way that traces out a perfect rendering of Botticelli’s Venus on the Half Shell , then that picture is a side effect of S controlling the position of the knot.

AM: Ok, makes sense. Any properties of qo, the final trajectory are a side effect of keeping qi stable.

AM: The problem is that this definition of side effects is in conflict with your definition of a behavioral illusion. If the contour of Venus look exactly like the template you wanted to get, this tells you something very important about the control system that made it. For one, it is a high-gain control system, at the speeds that you gave it. If the contour of Venus looks somewhat distorted, the gain was not so high, the errors were not well compensated.

RM: Yes, but you know all that (or can know it, using modeling) because you know what the controlled variable is: the position of the knot. These are the kinds of things manual control theorists have been able to find out because they study control in situations where they know what the controlled variables are (or should be).

RM: What is unique about PCT Is that it posits that ALL behavior is the control of perceptual variables. This hypothesis is explicit in the hierarchical PCT model of purposive behavior. The hypothesis is that organisms control a hierarchy of different TYPES of perceptual variables. This hypothesis has been subjected to very little testing and yet it is treated as though it is a known fact. I’m trying to move PCT research in the direction of testing Powers’ hypothesis about the control hierarchy, a hypothesis (and a description of some of the evidence supporting it) that takes up at least 60% of B:CP.

AM: But in a way, I do agree with you, the power law does not tell you anything definite about the system until you find the controlled variables. It might be that it is an intended effect, it might be it is not. Proof and demonstration only by models and experiments.

RM: Amen.

AM: No so fast.

AM: The same thing goes for “a behavioral illusion” in your power law papers. If it turns out that the power law is the main effect, that the trajectory is the controlled variable, or the instantaneous affine velocity is the controlled variable, both of which you suggested might be controlled; then the power law is not a side effect, it is the main effect, intended and achieved.

RM: I agree. But I consider it very unlikely that the power law itself is a controlled variable; a person would have to be continuously perceiving whether the velocity and curvature of their movements had the appropriate power relationship. But if you could figure out a way to test that hypothesis (or the more plausible one about control of affine velicity) that would be great.

AM: On the other hand, if some other variable is controlled, then the power law is a side effect, but it does tell you something about the control system. The exact speeds where the power law appears tell you something about, for example, force production constraints of the organism, or something about the interaction of the body and the environment in the loop, things like friction, inertia. etc.

RM: I don’t think so but if you do figure out a way to test for the variables being controlled when organisms move their limbs then that in itself would be a wonderful discovery, from my perspective anyway.

RM: Perhaps now is the appropriate time for me to confess that I don’t consider myself to be a PCT research maven. I’m pushing research based on testing for controlled variables because I know that’s the right way to study the behavior of living control systems and I know that’s the kind of research Bill Powers was hoping researchers would start doing. I haven’t done a lot of this kind of research myself but I have some some (the best example, I think, is my object interception research where the test for controlled variable was used to choose the best of three different hypotheses about the variable controlled when intercepting moving objects).

RM: I’m mainly pushing testing for controlled variables because I would like some help doing this kind of research from people, like you Adam, are a lot smarter than I am. This is a very new approach to studying the behavior of living systems and it will take some ingenuity to figure out how to do it properly since it has never really been done before.

Best

Rick

I feel like you’ve missed my main point: side effects, as you define them, do tell you something about the system you’re testing. If you define a behavioral illusion as taking the side effects to tell you something about the system you’re testing, then that definition is wrong. It is not an illusion, side effects CAN tell you something about the organism or the control loop in general, after you find the controlled variable.

M&S: " …a behavioral illusion occurs when an observed relationship between variables is seen as revealing something about the mechanisms that produce a behavior when, in fact, it does not"

RM: In the rubber band demo if you, as E, apply disturbances to the position of the knot so that S has to move her end of the rubber band in a way that traces out a perfect rendering of Botticelli’s Venus on the Half Shell , then that picture is a side effect of S controlling the position of the knot.

AM: The problem is that this definition of side effects is in conflict with your definition of a behavioral illusion. If the contour of Venus look exactly like the template you wanted to get, this tells you something very important about the control system that made it. For one, it is a high-gain control system, at the speeds that you gave it. If the contour of Venus looks somewhat distorted, the gain was not so high, the errors were not well compensated.

RM: You can only have found – let alone even known about the existence of – the controlled variable if you had approached understanding the behavior from a PCT perspective. And in that case you would know which aspects of the behavior are side-effects (which are irrelevant to understanding the behavior) and which are not (which are relevant to understanding the behavior.

M&S: " …a behavioral illusion occurs when an observed relationship between variables is seen as revealing something about the mechanisms that produce a behavior when, in fact, it does not"

RM: In the rubber band demo if you, as E, apply disturbances to the position of the knot so that S has to move her end of the rubber band in a way that traces out a perfect rendering of Botticelli’s Venus on the Half Shell , then that picture is a side effect of S controlling the position of the knot.

AM: The problem is that this definition of side effects is in conflict with your definition of a behavioral illusion. If the contour of Venus look exactly like the template you wanted to get, this tells you something very important about the control system that made it. For one, it is a high-gain control system, at the speeds that you gave it. If the contour of Venus looks somewhat distorted, the gain was not so high, the errors were not well compensated.

RM: The side-effect is the observation that S is drawing a perfect rendering of Venus on the Half Shell. That observation tells you nothing about the mechanism that produced that behavior. But once you know that S is controlling the position of the knot (the controlled variable) then you know that how closely S’s drawing motions mirror the disturbance produced by E tells you something about the mechanism that produced that behavior; how closely S’s drawing motions mirror the disturbance produced by E is not a side-effect of control; it is a characteristic of control. But you can only know that once you know what S is controlling and, thus, that E’s movements are a disturbance to that variable.

Best

Rick

RM: You can only have found – let alone even known about the existence of – the controlled variable if you had approached understanding the behavior from a PCT perspective. And in that case you would know which aspects of the behavior are side-effects (which are irrelevant to understanding the behavior) and which are not (which are relevant to understanding the behavior.

A “controlled variable” is standard jargon of control theory, including perceptual control theory.

And yes - when you find the controlled variable, you know that maintaining the controlled variable is the main effect of the control system. All other effects are side effects. You cannot know what is a side effect and what is a controlled variable without at least a few TCVs.

You don’t know what is the main effect or what is the side effect until you find the controlled variable.

And here we come back to “a behavioral illusion”. You cannot claim something is a side effect if you haven’t found the controlled variable.

RM: The side-effect is the observation that S is drawing a perfect rendering of Venus on the Half Shell *. That observation tells you nothing about the mechanism that produced that behavior. But once you know that S is controlling the position of the knot (the controlled variable) then you know that how closely S’s drawing motions mirror the disturbance produced by E tells you something about the mechanism that produced that behavior; how closely S’s drawing motions mirror the disturbance produced by E is not a side-effect of control; it is a characteristic of control. But you can only know that once you know what S is controlling and, thus, that E’s movements are a disturbance to that variable.

Bold is demonstrably wrong. If the drawing is a perfect rendering of the Venus, this tells you that the mechanism is a high gain control system. That is the property of the mechanism, a characteristic of control.

Now, you claim that the power law is an example of a behavioral illusion, but you haven’t done a single test for the controlled variable. You don’t know what is the main effect and what is a side effect.

AM: when you find the controlled variable, you know that maintaining the controlled variable is the main effect of the control system. All other effects are side effects.

RM: Not true. For example,the effects of output and disturbances on the controlled variable are not side effects.

AM: And here we come back to “a behavioral illusion”. You cannot claim something is a side effect if you haven’t found the controlled variable.

RM: True, you have to have demonstrated that the observed behavior could be a side-effect of controlling some variable. And I have.

RM: The side-effect is the observation that S is drawing a perfect rendering of Venus on the Half Shell *. That observation tells you nothing about the mechanism that produced that behavior. …

AM: Bold is demonstrably wrong. If the drawing is a perfect rendering of the Venus, this tells you that the mechanism is a high gain control system. That is the property of the mechanism, a characteristic of control.

RM: As I said before, that is true only if you know that E’s disturbance movements were a mirror image of the Venus – so that S’s compensatory movements would be the non-mirror image of the Venus. The perfect rendering of the Venus in itself tells you nothing about the mechanism that produced S’s behavior.

AM: Now, you claim that the power law is an example of a behavioral illusion, but you haven’t done a single test for the controlled variable. You don’t know what is the main effect and what is a side effect.

RM: I have done such a test and I know that the power law could definitely be a side-effect of control. I described this test in my reply to your reply to my power law paper and in a previous post. But here it is again. Here are the data that demonstrate that the power law can be a side effect of controlling cursor position:

image

RM: Here are cursor movements made with a mouse.The controlled variable is the position of the cursor. It is controlled relative to a variable reference while it is also being disturbed by the computer. The cursor movements follow the power law; the mouse movements that produced the cursor movements don’t. The power coefficient for cursor movement is .3 (for R versus V) and .7 (for C versus A). The power coefficient for mouse movement is .05 (for R versus V) and .98 (for C versus A). The controlled result of mouse movement follows a power law but the mouse movements that produce that result don’t. So the power law fits a movement that was not the movement the subject was making (the mouse movement) but the one the subject was intending.

RM: The power law that characterizes cursor movement is a side effect of a control process that had nothing to do with producing a power law, as evidenced by the completely non-power law mouse movements that produced those cursor movements. The power law seen here is, therefore, a side effect of the operation of a control system that is intending to produce a particular cursor movement trajectory.

Best regards

Rick

AM: And here we come back to “a behavioral illusion”. You cannot claim something is a side effect if you haven’t found the controlled variable.

RM: True, you have to have demonstrated that the observed behavior could be a side-effect of controlling some variable.

Could be? That is not enough. The power law can be observed in pure noise. It also is perfectly possible to not get a power law when controlling position for slow targets. On the other hand, it is not possible for humans to make a non-power law trajectory when they are drawing ellipses fast. After some speed, all the exponents are 2/3.

For that behavior, fast drawing, relevant for the phenomenon of the power law, you did not do a test for the controlled variable. Position control fails for high speeds, you need to control a different variable.

To show that the power law is a side effect of controlling some variable, you need to find - well, I need to find - one variable or a set of variables that are stable when a person draws fast ellipses (or other shapes) despite disturbances to those variables; and a model that controls those variables and shows the power law in the same situations as the person - and does not show the power law in the same situations as the person.

But this is a topic on the behavioral illusion, and we already agreed that the power law is not an example of the behavioral illusion.

AM: And here we come back to “a behavioral illusion”. You cannot claim something is a side effect if you haven’t found the controlled variable.

RM: True, you have to have demonstrated that the observed behavior could be a side-effect of controlling some variable.

AM: Could be? That is not enough.

RM: I said “could be” in order to leave the door open to the very slight possibility that the power law is a controlled variable. But there is considerable evidence against that possibility: 1) the variability of the power law coefficient is more than what would be expected if it were controlled 2) most randomly generated movements correspond to a 2/3 power law coefficient, varying around it by about the same amount as organism-produced limb movements and 3) if none-power law movements are required to compensate for disturbances to a controlled variable – as was the case for the mouse movements in the tracking task I described in the previous post – then those non-power law movements will made; no problem. So I believe it has been conclusively demonstrated that the power law IS a side effect of control.

AM: For that behavior, fast drawing, relevant for the phenomenon of the power law, you did not do a test for the controlled variable. Position control fails for high speeds, you need to control a different variable.

RM: Perhaps. But I think it has been shown pretty clearly that the power law is a side effect of control, whatever variable(s) is (are) being controlled.

AM: To show that the power law is a side effect of controlling some variable, you need to find - well, I need to find - one variable or a set of variables that are stable when a person draws fast ellipses (or other shapes) despite disturbances to those variables; and a model that controls those variables and shows the power law in the same situations as the person - and does not show the power law in the same situations as the person.

RM: Why waste your time on showing that the power law is a side effect of control? I only did it to encourage those who are studying how people produce movements to stop wasting time studying this behavior from the mainstream perspective and start studying it from a control theory – specifically perceptual control theory – perspective. In other words, why not start figuring out the variables organisms control when they move their limbs.

AM: But this is a topic on the behavioral illusion, and we already agreed that the power law is not an example of the behavioral illusion.

RM: I suppose we agreed that it is not an example of “the” S-R illusion described in Powers 1978. But since it is an irrelevant side effect of control, having nothing to do with how movement is produced, it is certainly “a” behavioral illusion.

Best

Rick

RM: Why waste your time on showing that the power law is a side effect of control? I only did it to encourage those who are studying how people produce movements to stop wasting time studying this behavior from the mainstream perspective and start studying it from a control theory – specifically perceptual control theory – perspective. In other words, why not start figuring out the variables organisms control when they move their limbs.

The problem always was - and still is - how do people move their limbs. Any side effect - properties of the action that appear in human behavior - MUST appear in the behavior of the model doing the same task in the same conditions, if we are to consider the model explaining the behavior.

Hi Adam

RM: Why waste your time on showing that the power law is a side effect of control? I only did it to encourage those who are studying how people produce movements to stop wasting time studying this behavior from the mainstream perspective and start studying it from a control theory – specifically perceptual control theory – perspective. In other words, why not start figuring out the variables organisms control when they move their limbs.

AM: The problem always was - and still is - how do people move their limbs. Any side effect - properties of the action that appear in human behavior - MUST appear in the behavior of the model doing the same task in the same conditions, if we are to consider the model explaining the behavior.

RM: You know that they are side effects only if you have already got the correct model of the behavior. A correct model of the behavior will be organized around the control of the perceptual variables that are the ones controlled by the organism being modeled. This model will automatically produce the same “side effects” as does the organism in the same circumstances.

RM: The goal of modeling behavior from a PCT perspective isn’t to develop a model that produces the same side-effects of control; it’s to develop a model that accounts for the observed controlling that is being done by the organism. Side effects are simply the aspects of behavior that behavioral scientists pay attention to when they don’t know that behavior is control. Behavioral scientists want to account for these side effects because they are consistent with their mainstream view of how behavior “works”. Side effects of control are the “red herring” you hear tell of in Bill’s 1978 paper. If you don’t know that behavior is control then you really have no need for PCT, which is a theory of control, not of irrelevant side effect of control.

RM: With PCT it’s phenomena phirst. If you don’t know that the phenomenon you are dealing with is control – the production of consistent results in a disturbance prone environment – then applying PCT to behavior is putting the cart way before the horse.

Best

Rick

RM: You know that they are side effects only if you have already got the correct model of the behavior. A correct model of the behavior will be organized around the control of the perceptual variables that are the ones controlled by the organism being modeled. This model will automatically produce the same “side effects” as does the organism in the same circumstances.

Nope. Demonstrably false.

In the tracking task, the controlled variable is the cursor-target distance. When you make a model with the correct controlled variable, you have to fit the model to each individual subject. Only then will you get a lot of the properties of subject behavior reproduced in the model.
The subject in a tracking task does not intent to have any particular accuracy, or any particular speed, for example. Simply using the correct controlled variable is the first step, but only when you tune the gains, delays, etc, the behavior of the model, will you get the model reproducing subject behavior for many different disturbances. Same speeds, same accuracy, same delays…

RM: The goal of modeling behavior from a PCT perspective isn’t to develop a model that produces the same side-effects of control; it’s to develop a model that accounts for the observed controlling that is being done by the organism. Side effects are simply the aspects of behavior that behavioral scientists pay attention to when they don’t know that behavior is control.

Again, demonstrably incorrect.

Look at Bill’s paper on arm control - he reproduced bell-shaped velocity curves and acceleration curves in arm movement, at the same time claiming that they are side effects of control of position and the properties of muscles and really the whole control hierarchy.

RM: Behavioral scientists want to account for these side effects because they are consistent with their mainstream view of how behavior “works”. Side effects of control are the “red herring” you hear tell of in Bill’s 1978 paper. If you don’t know that behavior is control then you really have no need for PCT, which is a theory of control, not of irrelevant side effect of control.

No, not at all. Behavioral scientists have observed some invariants and laws in behavior, and a correct model of behavior in question must reproduce those side effects.

The red herring (not in 1978 paper, I think) is simply assuming that the invariants and laws themselves are the controlled variable, the intended result. If there is a bell-shaped velocity, the red herring is assuming that the subject intended to produce the bell-shaped velocity, and then creating an elaborate control architecture that can produce such a velocity profile.

In the power law business, the produced trajectory has specific speed-curvature relationships. The red herring is assuming that the trajectory itself is intended and controlled.

RM: With PCT it’s phenomena phirst. If you don’t know that the phenomenon you are dealing with is control – the production of consistent results in a disturbance prone environment – then applying PCT to behavior is putting the cart way before the horse.

Yeah, ok, that doesn’t sound so bad.

I like these paragraphs on modelling from LCS:

RM: You know that they are side effects only if you have already got the correct model of the behavior. A correct model of the behavior will be organized around the control of the perceptual variables that are the ones controlled by the organism being modeled. This model will automatically produce the same “side effects” as does the organism in the same circumstances.

AM: Nope. Demonstrably false.

RM: I’d say it demonstrably took too much for granted so you got your signals crossed.

AM: In the tracking task, the controlled variable is the cursor-target distance. When you make a model with the correct controlled variable, you have to fit the model to each individual subject.

RM: Of course. I took that for granted. But I accept your correction. I should have said: A model controlling the correct variables with the appropriately selected control parameters will automatically produce the same “side effects” as does the organism in the same circumstances. How’s that?

RM: The goal of modeling behavior from a PCT perspective isn’t to develop a model that produces the same side-effects of control; it’s to develop a model that accounts for the observed controlling that is being done by the organism. Side effects are simply the aspects of behavior that behavioral scientists pay attention to when they don’t know that behavior is control.

AM: Again, demonstrably incorrect.

RM: Well, to quote a politician a dearly dislike: There you go again;-) In fact, it’s exactly right. And I"ll say it again to prove it: The goal of modeling behavior from a PCT perspective isn’t to develop a model that produces the same side-effects of control.

AM: Look at Bill’s paper on arm control - he reproduced bell-shaped velocity curves and acceleration curves in arm movement, at the same time claiming that they are side effects of control of position and the properties of muscles and really the whole control hierarchy.

RM: Oy vey! He didn’t do this to show how PCT research is done! He did it to show why mainstream research is bankrupt. That is, he did it for the same reason I produced my control model of movement control: to show that the folks who are studying invariant movement trajectories and power laws of movement are completely off base in their research; they are studying irrelevant side effects of control thinking they things tell them something important about behavior when they don’t.

RM: Behavioral scientists want to account for these side effects because they are consistent with their mainstream view of how behavior “works”. Side effects of control are the “red herring” you hear tell of in Bill’s 1978 paper. If you don’t know that behavior is control then you really have no need for PCT, which is a theory of control, not of irrelevant side effect of control.

AM: No, not at all. Behavioral scientists have observed some invariants and laws in behavior, and a correct model of behavior in question must reproduce those side effects.

RM: That’s your conclusion. It’s certainly not mine or Bill’s. Indeed, it’s precisely the opposite of what one would conclude based on an understanding of PCT. What behavioral scientists who understand PCT should do is ignore these things!! They are red herrings, sirens calling you from the rocks of ignorance. Just drop it and start doing research based on an understanding of organisms as perceptual control systems.

AM: The red herring (not in 1978 paper, I think) is simply assuming that the invariants and laws themselves are the controlled variable, the intended result.

RM: “… if one’s purposes [in doing behavioral research]concern objectivized side effects of control behavior, the man-machine blunder amounts to nothing worse than a few mislabelings having no practical consequences. If one’s interest is in the properties of persons, however, the man-machine blunder pulls a red herring across the path of progress” (Powers, 1978).

RM: It doesn’t sound to me like Bill was saying what you take him to be saying. The power law, invariant trajectory profiles, etc are objectivized side effects of control behavior. They are red herrings because they are irrelevant to understanding the behavior of living control systems.

RM: The only way you could know that the power law, invariant trajectory profiles, etc are objectivized side effects of control behavior is because you know what the actor is controlling. So you’ve already explained these side effects once you have explained the behavior in terms of the variables under control.

AM: If there is a bell-shaped velocity, the red herring is assuming that the subject intended to produce the bell-shaped velocity, and then creating an elaborate control architecture that can produce such a velocity profile.

AM: In the power law business, the produced trajectory has specific speed-curvature relationships. The red herring is assuming that the trajectory itself is intended and controlled.

RM: If a researcher assumed that the subject intended (in the PCT sense) to produce the invariant velocity profile or power law then that researcher would know that these are hypotheses about the variables the actor is controlling. So this researcher would would test to see whether the invariant velocity profile or power law are, indeed, controlled variables. And she would find that they are not and would move on to other hypotheses about the variables controlled when people make movements in space.

RM: In fact, the researcher who study these things are mistakenly taking them for intended results. They can’t tell an intended from an unintended result because they are looking at organisms are output generators. What is going on with research on what we know (but the researchers don’t know) are objectivized side effects of control is that researchers think these invariants reveal something important about how people work. So they will keep chasing these red herrings by doing experiments to see how variables affect them in the vague hope that this will reveal something about the mechanisms that produced these phenomena – and they won’t find what they are looking for because the actual explanation is just not what they want to hear: that these are irrelevant side effects of control – boy do they not want to hear that!

RM: Once you understand that organisms are control systems you no longer get seduced by randomly noticed characteristics of behavior – such as velocity profiles or power laws – no matter how invariant or mathematically attractive they are. You just ignore them and start looking for the variables around which the behavior of interest is organized.

RM: With PCT it’s phenomena phirst. If you don’t know that the phenomenon you are dealing with is control – the production of consistent results in a disturbance prone environment – then applying PCT to behavior is putting the cart way before the horse.

AM: Yeah, ok, that doesn’t sound so bad.

RM: Good.

Best

Rick

RM: Me too!

RM I should have said: A model controlling the correct variables with the appropriately selected control parameters will automatically produce the same “side effects” as does the organism in the same circumstances. How’s that?

That is good. The point of it being - the side effects of control of position in the tracking task are also side effects of the control parameters, including properties of the organism - input gain, output gain, etc.

If side effects depend on the parameters, that means you can learn a lot about the system just from the side effect (again with the disclaimer that you know the controlled variable).

RM: The goal of modeling behavior from a PCT perspective isn’t to develop a model that produces the same side-effects of control .

Nonsense.

If the model does not reproduce behavior of the subject, it does not deserve to be called a model of the behavior of the subject. Behavior of the subject includes all the main effects and side effects.

Take the tracking task - it reproduces all the main effects and most of the side effects of controlling position in a situation with a random disturbance.

RM: Oy vey! He didn’t do this to show how PCT research is done! He did it to show why mainstream research is bankrupt. That is, he did it for the same reason I produced my control model of movement control: to show that the folks who are studying invariant movement trajectories and power laws of movement are completely off base in their research; they are studying irrelevant side effects of control thinking they things tell them something important about behavior when they don’t.

He built a model of human arm control. He showed how the velocity profiles emerge from the properties of the system and control of position, without explicit trajectory control. Sure, there are other reasons for building the model, but the model DID reproduce the laws found in human behavior.

RM: That’s your conclusion. It’s certainly not mine or Bill’s. Indeed, it’s precisely the opposite of what one would conclude based on an understanding of PCT. What behavioral scientists who understand PCT should do is ignore these things!! They are red herrings, sirens calling you from the rocks of ignorance. Just drop it and start doing research based on an understanding of organisms as perceptual control systems.

Nonsense. Why did Bill show velocity profiles of the arm? He certainly did not ignore them.

RM: Once you understand that organisms are control systems you no longer get seduced by randomly noticed characteristics of behavior – such as velocity profiles or power laws – no matter how invariant or mathematically attractive they are. You just ignore them and start looking for the variables around which the behavior of interest is organized.

Let’s just focus on this part. Bill certainly did not ignore the velocity profiles. If his arm produced trapezoidal profiles, it would have to go back to the drawing table.

Side effects of control are ALSO side effects of organism properties and also side effects of disturbance properties and so on. If there are regular side effects, they must be explained by the model.

A PCT model of behavior must first identify the controlled variable, and second, all the properties of behavior must be reproduced, including any laws and mathematical regularities (if they are indeed regularities and not illusions), in the same conditions that they appear in experiments in humans.

RM: Me too!

So what does this mean to you: "To understand a system, we must be able to see that it must, because of its inner nature, behave as we see it behaving. Its properties must grow out out its inner organisation; its behavior must arise from its properties" ?

If human behavior shows the power law in some conditions, and does not show it in other conditions; if the exponent depends on the shapes drawn, on the medium of movement, on the speed of movement, etc, how can an explanatory model ignore this regularity?

AM: If side effects depend on the parameters, that means you can learn a lot about the system just from the side effect (again with the disclaimer that you know the controlled variable).

RM: Again, you don’t even know if something is a side effect until you have developed a successful control model of the behavior of which that something happens to be is a side effect. I actually did this in our “Control Blindness” paper ( Willett, A. B. S., Marken, R. S., Parker, M. G. & Mansell, W. (2017) Control Blindness: Why People Can Make Incorrect Inferences about the Intentions of Others, Attention, Perception & Performance , doi:10.3758/s13414-016-1268-3). See the section on the computer model. That little exercise shows that once you get the control model right every possible side-effect falls out naturally. You learn about the parameters of control from building the model, not from trying to get the model to reproduce some eye-catching side effect.

RM: The goal of modeling behavior from a PCT perspective isn’t to develop a model that produces the same side-effects of control .

AM: Nonsense.

RM: Well, at least it’s not BS;-)

AM: If the model does not reproduce behavior of the subject, it does not deserve to be called a model of the behavior of the subject. Behavior of the subject includes all the main effects and side effects.

RM: That’s true. But you don’t build the model to match the side effects. You build the model to match the controlling that you observe. If you get that right – if the model’s controlling matches that of the real system – then you know that ALL possible side effect of that controlling – and there are an infinite number of them – are captured as well.

AM: Take the tracking task - it reproduces all the main effects and most of the side effects of controlling position in a situation with a random disturbance.

RM: Exactly!! But it is a model that is build only to account for the controlling that is the tracking. Once you get the model to mimic that then Bob’s your Uncle, as far as side effects go.

RM: Oy vey! He [Bill Powers] didn’t do this to show how PCT research is done! He did it to show why mainstream research is bankrupt.

AM: He built a model of human arm control. He showed how the velocity profiles emerge from the properties of the system and control of position, without explicit trajectory control. Sure, there are other reasons for building the model, but the model DID reproduce the laws found in human behavior.

RM: Actually, the model he used was the “Little Man” which he developed to show how a control model could account for the behavior of pointing to a moving target in three space. That model was developed well before he was told about invariant velocity profiles and he just wanted to see if the little man model would produce those profiles when it did what the subjects in the velocity profile study did. And it did. He actually didn’t derive the velocity profiles; he compared the model to another aspect of the Atkeson, Hollerbach (A-H) data. But I am preparing a paper showing that the Little Man model does produce exactly the velocity profiles found by A-H.

RM: The fact that the Little Man model reproduces the velocity profiles doesn’t mean that PCT modeling should be aimed at accounting for side effects. Indeed, Bill only suspected that the profiles were possible side effects because they were made by people doing what the Little Man was built to do. Bill stated what he wanted to show by matching the Little Man model to the velocity profiles iin his post describing his results:

BP: The path which Atkeson, Hollerbach (and many others at MIT and elsewhere) are treading is a blind alley, because no matter how the observations are made and the invariances are calculated, there will be no hint of the control-system organization, the SIMPLE control-system organization, that (I claim) is actually creating the observed trajectories.

RM: I leave it as an exercise for you to determine who the “many others at MIT and elsewhere” are that Bill is referring to. But I’ll give you a hint: The blind alley he is talking about is paved with the side effects of control, such as invariant velocity profiles.

RM: That’s your conclusion. It’s certainly not mine or Bill’s. Indeed, it’s precisely the opposite of what one would conclude based on an understanding of PCT. What behavioral scientists who understand PCT should do is ignore these things!! They are red herrings, sirens calling you from the rocks of ignorance. Just drop it and start doing research based on an understanding of organisms as perceptual control systems.

AM: Nonsense.

RM: I don’t think that word means what you think it means;-)

AM: Why did Bill show velocity profiles of the arm? He certainly did not ignore them.

RM: See Powers’ quote above. He did it to show that studying the irrelevant side effects of control – such as velocity profiles and power functions – is a blind alley.

RM: Once you understand that organisms are control systems you no longer get seduced by randomly noticed characteristics of behavior – such as velocity profiles or power laws – no matter how invariant or mathematically attractive they are. You just ignore them and start looking for the variables around which the behavior of interest is organized.

AM: Let’s just focus on this part. Bill certainly did not ignore the velocity profiles.If his arm produced trapezoidal profiles, it would have to go back to the drawing table.

RM: No, it would most likely have meant that either there was something the subjects were instructed to do that was not captured by the model or that there were characteristics of the environmental situation that were not captured in the simulation. But I think it was pretty clear that the Little Man model would produce results very much like those of A-H; just looking at it you could see that the little man moved very much like a real person.

AM: A PCT model of behavior must first identify the controlled variable, and second, all the properties of behavior must be reproduced, including any laws and mathematical regularities (if they are indeed regularities and not illusions), in the same conditions that they appear in experiments in humans.

RM: If you actually do that first part then you can study all the irrelevant side effects of control that you want to because you will still have done valuable PCT research.

Best

Rick

It comes down to the fact that PCT research cannot ignore the side effects of control. If there are regularities in behavior that are not the controlled variabe itself, a model must reproduce those regularities, and by definition, they are side effects.

The side effects will fall out of a model that has the correct controlled variable and the correct parameters, and is in an identical situation as the human subject.

If the regularities don’t fall out, well, then the model is not correct, regardless of why the model was developed, or what was the aim during development.

There is more in the archives on the Atkeson and Hollerbach paper. Look at BP (920330.0800), for a list of needed changes that would make the arm model trajectories conform to those observed in human behavior, as reported in A&H. Bill talks about a adding a possible path control level, and about adding a remapping between visual and kinestethic space, and about problems with raping movements.

RM: Thanks for that! I just scanned it quickly but i see that Bill was suggesting the addition of another, higher level perception to control. The recent research we have done on this – that will be part of the paper I’m writing that is inspired by this wonderful dialog – shows that the Little man model, as it existed when Bill built it, will produce invariant trajectory profiles that match the A-H profiles perfectly, which no need for a new level. But this post fro Bill is certainly worth thinking about.

Thanks again.

Best

Rick