# disturbing disturbances

**URL:** <http://discourse.iapct.org/t/disturbing-disturbances/13623>\
**Category:** CSG1998\
**Created:** [February 27, 1998, 3:46am UTC](http://discourse.iapct.org/t/disturbing-disturbances/13623 "1998-02-27T03:46:37Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![bnhpct](http://discourse.iapct.org/user_avatar/discourse.iapct.org/bnhpct/32/34_2.png) [@bnhpct](http://discourse.iapct.org/u/bnhpct)\
**Post date:** [February 27, 1998, 3:46am UTC](http://discourse.iapct.org/t/disturbing-disturbances/13623/1 "1998-02-27T03:46:37Z")

</div>

[From Bruce Nevin (980226.2200)]

Bruce Abbott (980224.1400 EST)--

This has probably been dealt with and I am just behind the times, but it  
has been bothering me. I have to ask why your diagram does not match your  
text. Here's your diagram:

> Hmmm. Change in d ---\> change in i -----\> change in p ----\>  
> change in e -----\> change in o (all simultaneously) and you say  
> that change in d has \_nothing to do\_ with change in o? Poppycock.

Simplifying:

&nbsp;&nbsp;delta d --\> delta i --\> delta p --\> delta e --\> delta o --\>

It doesn't matter if you say "all simultaneously" if you leave the loop out  
of the loop! It is the loop that enables all this to go on simultaneously!

Compare now Rick Marken (980223.1310):

> delta d --\>  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;+ delta i --\> delta p -\> delta e --\>  
> delta o --\> |  
> &nbsp;&nbsp;^ |  
> &nbsp;&nbsp;\> \>  
> &nbsp;&nbsp;----------------------------------------------

You said they were the same:

> This is the same arrangement I gave (except for substituting "delta" for  
> "change in." Read my post if you don't believe it!

You must have been referring to your text preceding your diagram:

> Let us assume (to simplify the argument) that r is constant. At time t, d  
> changes, inducing a change in i. The change in i causes p to change (via  
> the input function), thus altering r-p similarly. Now r-p = e, so e  
> changes, inducing a change in o (via the output function). The change in o  
> induces a change in i (via the environmental feedback function), which  
> exactly opposes the change in i induced by d. In this ideal control system,  
> all these changes are assumed to occur simultaneously around the loop. But  
> this leads to a paradox: the influence of d on i is opposed in the same time  
> instant in which it occurs. Because it is completely canceled, there can  
> have been \_no\_ change in i, \_no\_ change in p, \_no\_ change in o to oppose the  
> influence of d on i! It can't work!

The diagram described verbally here does indeed look like Rick's:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;PIF r-p  
delta d --\> delta i --\> delta p --\> delta e --\> delta o ---+  
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;^ |  
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\> \>  
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;+-----Environmental feedback function ------+

Why did you leave the loop out of your diagram? How could you have possibly  
done so if you were thinking about control of perceptual input? Whatever  
the reason, the result was to ignore the influence of delta o on delta i.

Assume change in d that does not overwhelm control. This means among other  
things that change between time t and time t+1 is continuous. Your sampling  
of values is discrete at two instants t and t+1 but the values in fact  
change continuously over that interval. Given these two assumptions  
(control and continuity), delta o is as much a contributor to delta i as  
delta d is. There is no moment at which delta d is an influence without  
delta o also being an influence. (Even before d changes, during a period  
when d was static, o may be changing slightly, maintaining control of p.)

Assume the point of view of the control system. The influences of delta o  
and delta d are indistinguishable from one another. It is only to an  
outside observer that d is identifiable as a distinct value. But it is  
precisely to overcome the limitations of a point of view outside the black  
box that we create, run, and analyze models. To understand a control system  
model, you must take a point of view inside the black box, you must take  
the point of view of the control system. To understand the organism being  
modelled, in order to model it, you have to take the point of view of the  
control system. The measurement of d and o is useful to verify the presence  
of control, they do not suffice for modelling or understanding control.

I suppose this is all water over the dam now. Rick said much the same:

> Note that the effect of d is irretrievably  
> mixed with that of o well before it enters the comparator (to  
> produce delta e). I guess it would have more appropriate for me  
> to say that d \_alone\_ has nothing to do with it. What I meant was  
> that, from the point of view of the control system, d is not  
> involved. The control system deals only with the variable  
> p which is, at any instant, a result of unknown contributions from  
> both d (or many d's) and o. Changes in o are not caused by changes  
> in d; they are caused by changes in \_both\_ d and o simultaneously.

But I was and am really puzzled why you would use a diagram that omitted  
the feedback through the environment, while talking about the control loop,  
making it look like a linear chain of causation. That was what created  
Zeno's chimaera for you.

&nbsp;&nbsp;Bruce Nevin