# Fish; Why; feedforward; ballistic control

**URL:** <http://discourse.iapct.org/t/fish-why-feedforward-ballistic-control/4431>\
**Category:** CSG1993\
**Created:** [November 18, 1993, 4:16pm UTC](http://discourse.iapct.org/t/fish-why-feedforward-ballistic-control/4431 "1993-11-18T16:16:57Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![William\_T\_Powers2](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/w/c67d28/32.png) [@William\_T\_Powers2](http://discourse.iapct.org/u/William_T_Powers2)\
**Post date:** [November 18, 1993, 4:16pm UTC](http://discourse.iapct.org/t/fish-why-feedforward-ballistic-control/4431/1 "1993-11-18T16:16:57Z")

</div>

[From Bill Powers (931118.0630 MST)]

Bruce Nevin (931117.1545) --

> The problem attributed metaphorically to the fish is very  
> similar to the impossibility of recognizing a given perception  
> as such (or perceptions of a given level) unless you first go  
> up a level. Or, conversely, perceiving the world through nth-  
> level glasses: if you're a fish, all the world is watery.

The way I've always heard the aphorism, it was intended to show  
the impossibility of perceiving anything that pervades one's  
environment, like language customs. No "unlesses." Your second  
suggestion means almost the opposite: that you see the  
environment as containing the uibiquitous thing rather than  
seeing it as an interpretation of yours. In any case, I agree  
with your two interpretations, but I think you've modified the  
aphorism as "customarily" used.

> Since you understand the intended point -- and I believe you  
> when you say that you do -- perhaps you can suggest a metaphor  
> (and aphorism) free of the defect that troubles you.

The one I've always preferred, when an an aphoristic mood, is  
that of standing before a window and watching a baseball game  
being contested outside the house. If the game is engrossing, you  
may forget that you're looking through a window at it.

Another obvious possibility is watching a show on television. One  
of the greatest Star Trek: New Gen episodes involved the holodeck  
character Moriarty, who accidently achieved self-awareness,  
setting up a simulated holodeck that fooled Worf, an engineer  
whose name I forget, and Data into believing that Moriarty was  
able to leave the holodeck and survive. In that simulated  
Enterprise, Data and a simulated Geordi worked out a way to  
transport Moriarty's lady-love off the holodeck and into reality,  
but when they tried it the transporter log showed that nothing  
had happened. The crew on the real holodeck then created a  
simulation within the simulation to convince Moriarty that his  
lady friend had actually been successfully transported. All this  
was revealed only near the end, when Data said "computer, end  
program," and they were back in the original simulation, and then  
said "computer, end program" again, restoring them to the real  
Enterprise. At the end (why give it all away), the last character  
to appear looked uncomfortable, and muttered "computer, end  
program." When all remained as it was, the character looked  
satisfied and walked off the scene. The program (i.e., that  
episode) then ended. Wow.

All in all, the window metaphor is shorter.

> **···**
>
> ---------------------------------------------------------------  
> Bill Cunningham (931117.1700) --
> 
> > It has struck me that the WHY-HOW mismatch is at the heart of  
> > much of PCT's problems with the outside world. PCT is really a  
> > HOW theory. Sure it opposes other HOW theories, but it must  
> > really irritate the hell out of the WHY askers. That may be a  
> > simplistic assessment, but that's the way it comes across.  
> > And that's the source of PCT's weaknesses.
> 
> Only in some people's opinions. Those are the people who like to  
> see general principles behind specific processes; they aren't  
> satisfied with knowing HOW a system works, they want to put that  
> HOW in the context of a higher-level perception of principles.  
> When they succeed, it seems to them that they have found the WHY  
> of the system: why it HAS to be organized that way.
> 
> This gives the status of incontestible \_a priori\_ truth to the  
> principles, and makes it seem that the principles somehow have a  
> guiding influence on the lower-level processes, as if they were  
> purposive and forbad any other lower-level processes from  
> existing. They are purposive, but the purposes are those of the  
> person who wants those principles to apply. What is forgotten in  
> all this is that the principles were derived from observations of  
> the processes; only those principles that are consistent with the  
> observed processes are perceived. So the principles are dependent  
> on perceptions of processes, just as any higher-level perception  
> is a function of lower-level perceptions. If the processes  
> happened to work differently, different principles would be  
> perceived: a different WHY would be seen.
> 
> Hierarchical relationships between perceptions are confusing  
> because they are circular. The higher is derived from the lower,  
> yet once a higher perception is selected as a target, it serves  
> to guide the way the lower perceptions appear. Each seems to  
> explain the other. I see a ball BECAUSE there are certain  
> sensations of shading, curvature, and edges; yet it is BECAUSE I  
> want to see a ball that those shadings, curvatures, and edges  
> come into being in my experience.
> 
> A principle like conservation of energy (to pick a neutral  
> example) is not the explanation of why a pendulum works as it  
> does. It is a consequence of the way the pendulum works; it is a  
> more generalized way of perceiving the workings of a pendulum. It  
> is, of course, a very useful principle. But it has no causal  
> properties beyond those given to it by a purposive system.  
> --------------------------------------------------------------  
> Martin Taylor (931117.1745) --
> 
> > > Why don't those who use this old adage ask scoffingly if
> > 
> > people perceive the existence of air?
> 
> \<I thought of doing just that. Don't we perceive cold, wind,
> 
> > smells, and the like, rather than "air," just as the fish might  
> > be expected to perceive the proximity of other fish,  
> > turbulence, shearing currents and such stuff?
> 
> This is a matter of the level of perception. How do you perceive  
> a keyboard in front of you, if not through perceptions of colors,  
> edges, shadings, movements, and so forth? The higher perception  
> is a function of the lower. Air is a perception derived from a  
> collection of experiences at lower levels. If we were fish, water  
> would be a perception derived from collection of experiences at  
> lower levels.  
> -------------------------------  
> RE: feedforward
> 
> > I'll probably shut up about it soon, unless something does  
> > come up. How about Bernard Gibbs's J-curves as a possibility?
> 
> If EVERY ONE of Gibb's subjects showed the reversal for the 2nd  
> and 4th (or whatever) lights, I might try to model this  
> phenomenon. If not, how can I construct a model to be the right  
> explanation when it would be flatly incorrect a good part of the  
> time?  
> -------------------------------  
> RE: idea of recalibration
> 
> > In its favour, however, is a point made last year by Jeff  
> > Hunter and a couple of days ago by Tom Bourbon, that one can  
> > estimate a segregated effect by applying reference steps that  
> > can be correlated with effects on the CEV. No matter what the  
> > disturbance, the output-\>perception relational function can be  
> > estimated by this procedure in an analytic way, if the  
> > environment function is stable enough.
> 
> What do you mean, "one can estimate?" It's the behaving system  
> that must do the estimation, and to do it it must perceive  
> certain things and apply certain processes to the perceptions.  
> All those things and processes have to be put into the model and  
> it must be shown that they produce the effect we observe, every  
> time. I'm not doubting that this can be done (after all, Tom  
> reported its being done). But to model it is considerably beyond  
> our current capabilities. There are lots of things WE can do when  
> looking at a DIFFERENT system. The question is, how can a system  
> do these things for itself?  
> ------------------------------
> 
> > > Recalibration has its own problems: what's the standard?
> 
> > ... there is no standard; what has to be sensed is a  
> > relationship between output steps and perception changes.
> 
> Once that relationship has been sensed, what is the \_right\_  
> relationship? There must be a standard; otherwise the perceived  
> relationships is just whatever it is, and there is no reason to  
> change it toward any other relationship.  
> -----------------------------
> 
> > If it turns out that the accepted reorganization approach (an  
> > e-coli convergence to the appropriate function) does not work,  
> > then there is a problem. If it does work, a continuous  
> > updating of the model would fall out naturally.
> 
> # Not out of reorganization alone. There must be something sensed, and there must be a defined reference condition, in order for the e. coli method to work.
> 
> > We are still miscommunicating about getting to bed in the dark.  
> > I believe that the way you say it is done is essentially  
> > correct. But I have always thought that "control of  
> > perception" was taken to imply that the perception was of a CEV  
> > in the real world. If one cannot determine the state of that  
> > CEV through the senses, one cannot control it.
> 
> I have thought this was your conception since our early  
> discussions of the "mirror world." The CEV exists in the real  
> world; if we perceive it correctly (mirror it correctly in the  
> internal world), we can control it. Otherwise the CEV will remain  
> uncontrolled, or will be incorrectly controlled in some respect.  
> Other arguments have seemed more important, but now I guess we  
> must have it out.
> 
> The organism can know of CEVs only as perceptions. That goes for  
> you, too. You have a concept of a CEV, but that concept is in  
> your head. It is part of your perceptions. You have no way of  
> knowing what actually corresponds to your perceptions. Nobody  
> does. All we have are the perceptions. The rest is hypothesis. It  
> is the external world that is the mirror of the perceived world.  
> The imagined mirror.
> 
> All that a control system needs to know about the environment is  
> that if it acts in certain ways, perceptions change in certain  
> ways. It does not need to know how those actions work to affect  
> the perceptions that change; the mechanisms linking action to  
> perception exist outside the organism, outside of you and me,  
> where we have no direct access to them. Perceptions can be  
> controlled without any knowledge of their external counterparts,  
> if any.
> 
> A CEV is the inverse perceptual function of a perceptual signal.  
> Normally, input functions have multiple inverses, so many  
> different conditions of the environment suffice to create a given  
> magnitude of a given perceptual signal. There is, therefore,  
> nothing external corresponding to "the" CEV. "The" CEV is a  
> ghost, a projection of internal perceptions onto an external  
> universe which is not experienced.
> 
> However an input function is organized, it creates a CEV: it  
> creates a perceptual signal that is seen as an entity in the  
> environment. Given that perceptual signal and one state of it  
> selected as a reference, a control system can be constructed that  
> will control the perceptual signal. The construction entails  
> choosing the signs of various output effects of the error signal  
> so that each loop is a negative feedback loop (or so that most of  
> them are). The choosing, we have shown in simple cases, can  
> result from a random reorganizing effect based on the error  
> signal itself, with the implicit goal of making the error signal  
> zero. No hypothesis about the external world is required for this  
> to work. If a particular output connection makes the error worse,  
> remove that connection. That is all that is required.
> 
> The resulting control does not imply that anything in the  
> environment is being brought to just one state. All that is  
> required is that the outputs bring the environment to one of the  
> states that is equivalent in terms of creating the same  
> perceptual signal. The "bellringers" analogy is worth repeating  
> briefly here:
> 
> "Of course if there are coordinates for which there are no ropes,  
> but which enter into the expression for the energy, then, if the  
> motion of these coordinates is periodic, there will be "adynamic  
> vibrations" communicated to the ropes, and by these the men below  
> will know that there is something peculiar going on above them.  
> But if they pull the ropes in proper time, they can either quiet  
> these adynamic vibrations or strengthen them, so that in this  
> case these coordinates cannot be ignored."
> 
> "If the machinery above has more degrees of freedom than there  
> are ropes, the coordinates which express those degrees of freedom  
> must be ignored. There is no help for it."
> 
> (paragraph order reversed)
> 
> Maxwell, J. C.: Thompson and Tait's Natural Philosophy. Nature,  
> Vol. XX, 1867. From Niven; The scientific papers of James Clerk  
> Maxwell, pp. 776-785. New York: Dover (1965).  
> ------------------------------  
> If you were blind ...
> 
> > Yes. Your control hierarchy would have to skip the on-line  
> > control of the relational perception you\<-\>bed.
> 
> No. Your control hierarchy would control that relationship in a  
> space defined kinesthetically instead of visually. A blind person  
> can put a cane down and then reach for it and pick it up. The  
> cane has a perceived location, and so does the reaching hand. The  
> coordinates of this space are simply not x, y, and radius as  
> visually defined.
> 
> Kinesthetic control is partially sample-and-hold control. Instead  
> of a continuous update of the visual model of the world, you get  
> only an intermittent update of a kinesthetic model. The bed is  
> where you last felt it to be until you can feel it again. The  
> cane, tapping inquistively around, is updating the model, moving  
> the chair or the sofa or the lamp a little, altering the position  
> of the dot that is you in this model. To control relationships  
> you alter the part of the relationship under your direct control.
> 
> All you're saying is that continuous control is more effective  
> than sampled control; that continuous perception works better  
> than intermittent perception in a control process. I would agree,  
> of course.  
> ---------------------------------
> 
> > I continue to believe that the output provided to the world by  
> > the relational perception ECS is open-loop when the lights go  
> > out, whether or not the ECS is, by that output, affecting a  
> > controlled imagined perception.
> 
> In the going-to-bed case, one perception in the relationship is  
> still under continuous control: the perception of where you are  
> on the map. Judging from joint angles you can alter your  
> perceived position according to number of strides and stride  
> length, and your perceived direction of movement by adding up  
> twists at the ankles and hips as you walk. It is not necessary  
> for BOTH inputs to a relational perceptual function to be real in  
> order for closed-loop control of a relationship perception to  
> exist. It is only necessary that they both be real if you want  
> the controlled variable to be veridical. The controlled variable  
> is ALWAYS a perception.
> 
> If you would stop thinking of relationships as exclusively visual  
> in nature, this problem would go away.  
> --------------------------------------------------------------  
> Bob Clark (931117.1700) --
> 
> Nice summary of points that have been made here and there on the  
> net.
> 
> In relation to ballistic types of control, one factor seldom  
> brought up is that the ball or projectile must be given a  
> specific vector velocity in order to reproduce a previous  
> trajectory accurately. This requires lower-level control systems  
> that control velocity very accurately up to the point of release.  
> Open-loop activation of muscles according to a stored program  
> would not be anywhere near accurate enough. Gary Cziko has a neat  
> demonstration of this lower-level control, in which he can apply  
> a substantial elastic restraint unexpectedly while a person is  
> tossing a ball underhanded toward a target. There is only a  
> slight disturbance of the trajectory, and the person throwing the  
> ball can feel the extra effort that suddenly appears, opposing  
> the effect of the restraint.  
> --------------------------------------------------------------  
> Chuck Tucker (direct communication)
> 
> Please post your demo of feedforward on the net. It's worth a  
> thousand abstract arguments.  
> -------------------------------------------------------------  
> Best to all,
> 
> Bill P.

---

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**Author:** ![\_Martin\_Taylor](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/_/a9adbd/32.png) [@\_Martin\_Taylor](http://discourse.iapct.org/u/_Martin_Taylor)\
**Post date:** [November 18, 1993, 10:14pm UTC](http://discourse.iapct.org/t/fish-why-feedforward-ballistic-control/4431/2 "1993-11-18T22:14:11Z")

</div>

[Martin Taylor 931118 14:40]  
(Bill Powers 931118.0630)

> RE: feedforward
> 
> > I'll probably shut up about it soon, unless something does  
> > come up. How about Bernard Gibbs's J-curves as a possibility?
> 
> If EVERY ONE of Gibb's subjects showed the reversal for the 2nd  
> and 4th (or whatever) lights, I might try to model this  
> phenomenon. If not, how can I construct a model to be the right  
> explanation when it would be flatly incorrect a good part of the  
> time?

I've tried to find Gibbs' papers, to refresh my memory on this, but I  
assume that even if I did, he wouldn't report on every subject. I did  
find one paper that seems to be a precursor of his alcohol studies  
(British J. Psychol, 1965, 56, 233-242). It uses the same kind of task  
and shows examples of the J-curve, but that wasn't the main interest  
in the paper. You might like, however, a few words from the summary:  
"The essence of inflow theory is that patterns of proprioceptive sensations,  
rather than motor impulses, form the content of learning. Notions of  
motor reinforcement are, at best, redundant, and have nothing to commend  
them except respectable antiquity."

And from the introduction: "A hypothetical function of proprioception is  
to provide negative feedback which ensures that a movement initiated by  
an error-stimulus reduces that error."

The paper argues that negative feedback control loops bring the pointer to  
the right place, but that the first movement is based on outflow that is  
conditioned by the probable direction of the movement required. The  
experiment itself (in this paper) seems inadequate, in that there was  
no real time pressure on the subjects. One of the lights came on for  
one second, and then another after a one-second gap. The subjects were  
just asked to respond "as rapidly and accurately as possible." He did  
impose a stress by reversing the normal control-display relationship  
in this study, but I don't think he did that later on.

It seems to me that it would be worthwhile to try to gather data akin  
to Gibbs, and see how consistent the J-curve effect might be, and  
to model it if it is consistent enough.

> **···**
>
> =================================
> 
> > RE: idea of recalibration
> > 
> > > In its favour, however, is a point made last year by Jeff  
> > > Hunter and a couple of days ago by Tom Bourbon, that one can  
> > > estimate a segregated effect by applying reference steps that  
> > > can be correlated with effects on the CEV.
> 
> > What do you mean, "one can estimate?" It's the behaving system  
> > that must do the estimation, and to do it it must perceive  
> > certain things and apply certain processes to the perceptions.
> 
> By "one can estimate" I mean that there is sufficient information  
> available that estimation is possible.
> 
> > I'm not doubting that this can be done (after all, Tom  
> > reported its being done). But to model it is considerably beyond  
> > our current capabilities. There are lots of things WE can do when  
> > looking at a DIFFERENT system. The question is, how can a system  
> > do these things for itself?
> 
> In reorganization, it isn't the behaving system that lloks at its own  
> behaviour--it looks at its CEV and only at that. It is some other  
> system that has as its "CEV" the behaviour of the system to be reorganized.  
> This "CEV" may be some global function of errors in the whole hierarchy,  
> or some more local phenomenon ivolving the behaviour of only one ECS.  
> But it is not the ECS itself that both behaves and perceives its own  
> behaviour.
> 
> I have been assuming that some function akin to reorganization will  
> shape the function that needs calibrating, just as it can shape the  
> perceptual input function. As I agreed before, it has not been shown  
> that such a recalibration system can exist with less than an engineer's  
> intelligence, and before we argue too much about it, experiments are  
> required to show feasibility.
> 
> > > > Recalibration has its own problems: what's the standard?
> > 
> > > ... there is no standard; what has to be sensed is a  
> > > relationship between output steps and perception changes.
> > 
> > Once that relationship has been sensed, what is the \_right\_  
> > relationship? There must be a standard; otherwise the perceived  
> > relationships is just whatever it is, and there is no reason to  
> > change it toward any other relationship.
> 
> > From that point of view, the standard is the same as for classical
> 
> reorganization--minimization of error in the ECS. I meant that  
> there is no standard for the function that describes the output-\>  
> perception relationship.
> 
> > > If it turns out that the accepted reorganization approach (an  
> > > e-coli convergence to the appropriate function) does not work,  
> > > then there is a problem. If it does work, a continuous  
> > > updating of the model would fall out naturally.
> > 
> > Not out of reorganization alone. There must be something sensed,  
> > and there must be a defined reference condition, in order for the  
> > e. coli method to work.
> 
> # OK. See immediately above.
> 
> On CEVs and perceptual signals, I must be suffering from some mental  
> blind spot, because I really can't see what we are arguing about. What  
> you write rings absolutely true with me. It generates no error signals.  
> I just wish I could have written it as clearly as you do. And yet you  
> have some strong disagreement with me. I can't find where it is.
> 
> I have long accepted your view that a CEV can be any function whatever  
> of variables in an outer world that we presume to exist. Perceptual  
> Input Functions (PIFs) are functions of variables in that outer world,  
> so they define CEVs. Is part of the difficulty that you disallow CEVs  
> that are defined by functions other than PIFs, whereas I take Complex  
> Environmental Variable to be any function whatever?
> 
> I have long accepted that no organism (myself included) can perceive any  
> CEV other than those instantiated in the PIFs of that organism, that we  
> cannot know what the real state of those outer world variables might be.  
> And that no PIFs has an inverse because each defines a one-dimensional  
> subspace of its multidimensional input. But I do insist that our whole  
> structure of perceptual control cannot work unless there exists an outer  
> world -- a Boss Reality. Its existence, not its content, is all we need  
> for the rest of the structure to develop. I don't think you disagree?
> 
> > However an input function is organized, it creates a CEV: it  
> > creates a perceptual signal that is seen as an entity in the  
> > environment. Given that perceptual signal and one state of it  
> > selected as a reference, a control system can be constructed that  
> > will control the perceptual signal.
> 
> Precisely so. If the PIF that defines a particular CEV does not admit  
> of actions that affect the output of that PIF (the perceptual signal),  
> reorganization will tend to change the PIF, as well as the output link  
> structure. Reorganization doesn't care what perception is controlled,  
> so long as the intrinsic variables are, and when a PIF and an output  
> function are linked through the world so that changes in the output  
> magnitude have largely predictable and correct directions of effect  
> on the output of the PIF, reorganization will stop. What is then  
> perceived (i.e. the precise form of the PIF) is unpredictable a priori.  
> But it is controllable, and has some relation to maintenance of intrinsic  
> variables near their reference states. Whatever it is, it defines a CEV.
> 
> To paraphrase you some time ago, one could have a CEV that was blueness  
> squared plus the distance to Moscow divided by the height of your daughter.  
> But a PIF that constructed such a CEV would not yield a controllable  
> perceptual signal, at least not through normal e-coli processes, I should  
> think.
> 
> PIFs that yield perceptual signals for which the actions required for control  
> do not exist are likely to be reorganized away. In the end, we will  
> be perceiving only what we have reorganized the output link strructure  
> to control. Both PIFs and outputs reorganize. So this is correct:
> 
> > No hypothesis about the external world is required for this  
> > to work. If a particular output connection makes the error worse,  
> > remove that connection. That is all that is required.
> 
> But this is false:
> 
> > The resulting control does not imply that anything in the  
> > environment is being brought to just one state.
> 
> It should read "that any of the inputs to the PIF is being brought".  
> Yes, something in the environment IS being brought to just one state.  
> What is brought to one state is the output of a single-valued function,  
> not the arguments of that function, as you seem to want to read me as  
> claiming. It is the complex function of states that is defined by the PIF.  
> (Taking "one state" with the grain of salt demanded by the information  
> limitations of the sensory inputs and intervening functions).
> 
> On getting to bed:
> 
> > If you would stop thinking of relationships as exclusively visual  
> > in nature, this problem would go away.
> 
> Never have. And it hasn't. Relationships are abstractions far above  
> a level at which one can talk about "visual." And the problem remains.
> 
> I don't know what either of us can add to previous communications that  
> would not be further repetition. But I'll try.
> 
> All I have been trying to say is that there was a question as to whether  
> some particular output TO THE WORLD was affecting a controlled CEV--one  
> for which there was a perception that was being stabilized at its  
> reference value. You answer that there is a perception being controlled.  
> It is being controlled in imagination, though one of the necessary two  
> sensory inputs is being provided from the world. There is a mismatch  
> between the things we two are talking about.
> 
> > It is not necessary  
> > for BOTH inputs to a relational perceptual function to be real in  
> > order for closed-loop control of a relationship perception to  
> > exist.
> 
> In imagination, but it is necessary for them both to be real for control  
> of a perception of the real-world CEV.
> 
> > It is only necessary that they both be real if you want  
> > the controlled variable to be veridical.
> 
> That is also another red herring being drawn across the path of true  
> discourse, a conflation of "veridical" with "controlled." For a perception  
> to be asserted as "veridical" one would have to know the real-world state,  
> and we can't do that. For a perception to be controlled, actions  
> must be able to bring the perception to a desired state. In that  
> sense, we can control imaginary perceptions much more readily than we  
> can control perceptions based on the world (remember our Durango discussion  
> of "Nobody, Nowhere"; the autist seems to control in imagination as a  
> substitute for inability to control through the real world). But to  
> survive, we must control perceptions by our actions in the real world,  
> controlling perceptions derived from current sensory input from the world.
> 
> In my mind, the one and only question in the discussion was whether the  
> actions of walking in a way that controlled the imagined relation of  
> you\<-\>bed were actually controlling the perception of the current state  
> of the real world CEV you\<-\>bed. I concluded (and still conclude) that  
> they don't, even though they do result (usually) in success in bringing  
> the CEV to the desired state. Those actions on the world are reasonably  
> accurate because of lower-level control, but the output of the relation  
> ECS still seems open-loop to me.
> 
> How could one know that the CEV had been brought to its desired state?  
> Because the reference level for its perceptual signal is zero, and when  
> the CEV is as desired, senses other than vision can be used in creating  
> the perception. The desired result CAN be achieved only because the world  
> is stable enough that the model within which you are performing imaginary  
> perceptual control remains reasonably valid for the period of interest.  
> If the model were not valid, you could execute 2-D random walks until  
> you could use non-visual senses to create the relation perception (by  
> bumping into the bed). You could still succeed, but it would be hard  
> to say that you were controlling the relation perception.
> 
> I do acknowledge that there is a strong relation between this situation  
> and sampled control. In both cases it is important that the world  
> be stable enough that calibration developed in one sample remains  
> reasonably close at the next. One could not shoot accurately if  
> the sights were realigned at random moments averaging several realigments  
> between consecutive shots, or if one was shooting lightweight pithballs  
> in a strong variably gusting wind. One can do it with fixed sights in  
> a steady wind (given that it is not so strong as to prevent the pithballs  
> from reaching the target at all).
> 
> Martin

---

<div class="post-metadata">

**Author:** ![Tom\_BOURBON3](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/t/85e7bf/32.png) [@Tom\_BOURBON3](http://discourse.iapct.org/u/Tom_BOURBON3)\
**Post date:** [November 17, 1993, 5:39pm UTC](http://discourse.iapct.org/t/fish-why-feedforward-ballistic-control/4431/3 "1993-11-17T17:39:34Z")

</div>

> From Tom Bourbon [931119.1046]

> [Martin Taylor 931118 14:40]  
> (Bill Powers 931118.0630)

. . .  
Martin:

> On getting to bed:

. . .

> In my mind, the one and only question in the discussion was whether the  
> actions of walking in a way that controlled the imagined relation of  
> you\<-\>bed were actually controlling the perception of the current state  
> of the real world CEV you\<-\>bed. I concluded (and still conclude) that  
> they don't, even though they do result (usually) in success in bringing  
> the CEV to the desired state. Those actions on the world are reasonably  
> accurate because of lower-level control, but the output of the relation  
> ECS still seems open-loop to me.

As Bill and Rick (and others? I?) have said in previous posts on this topic,  
the impression that the relation ECS is operating open-loop is probabnly  
just that, an impression, but not necessarily a correct one. Consider this  
change in the "getting to bed" example: The lights are on and the person is  
at point P, in a room other than the one containing the bed, which is at  
point B in the bedroom. To make the example more specific, point P is in a  
room down the hall from the bedroom and around a corner to the left. With  
the lights on, when the person walks from P to B and climbs into the bed, at  
which point(s), if any, is the person's relation control system operating  
"open-loop?"

> How could one know that the CEV had been brought to its desired state?  
> Because the reference level for its perceptual signal is zero, and when  
> the CEV is as desired, senses other than vision can be used in creating  
> the perception. The desired result CAN be achieved only because the world  
> is stable enough that the model within which you are performing imaginary  
> perceptual control remains reasonably valid for the period of interest.  
> If the model were not valid, you could execute 2-D random walks until  
> you could use non-visual senses to create the relation perception (by  
> bumping into the bed). You could still succeed, but it would be hard  
> to say that you were controlling the relation perception.

Would you want to change any of these comments and questions after you  
interpreted the revised scenario I described above, or would you leave this  
paragraph as it is?

Still in the dark,

Tom

---

<div class="post-metadata">

**Author:** ![\_Martin\_Taylor](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/_/a9adbd/32.png) [@\_Martin\_Taylor](http://discourse.iapct.org/u/_Martin_Taylor)\
**Post date:** [November 22, 1993, 4:58pm UTC](http://discourse.iapct.org/t/fish-why-feedforward-ballistic-control/4431/4 "1993-11-22T16:58:02Z")

</div>

[Martin Taylor 931122 11:50]  
(Tom Bourbon 931119.1046)

> To make the example more specific, point P is in a  
> room down the hall from the bedroom and around a corner to the left. With  
> the lights on, when the person walks from P to B and climbs into the bed, at  
> which point(s), if any, is the person's relation control system operating  
> "open-loop?"

At all points where the person cannot see the bed. When all required elements  
of the relation perception can be derived from current sensory data,  
real-world perceptual control is possible. If they can't, then the effect  
of output on the real CEV cannot be perceived. What can't be perceived  
can't be controlled. Outputs that have effects that can't be perceived  
are open-loop, in my understanding of the term.

> > How could one know that the CEV had been brought to its desired state?  
> > Because the reference level for its perceptual signal is zero, and when  
> > the CEV is as desired, senses other than vision can be used in creating  
> > the perception. The desired result CAN be achieved only because the world  
> > is stable enough that the model within which you are performing imaginary  
> > perceptual control remains reasonably valid for the period of interest.  
> > If the model were not valid, you could execute 2-D random walks until  
> > you could use non-visual senses to create the relation perception (by  
> > bumping into the bed). You could still succeed, but it would be hard  
> > to say that you were controlling the relation perception.
> 
> Would you want to change any of these comments and questions after you  
> interpreted the revised scenario I described above, or would you leave this  
> paragraph as it is?

I can't see where you might imagine I might change it. And I can't see  
where I would change it, except to wish for the gift of greater literary  
clarity.

Martin