# Highest level; the Test; misc

**URL:** <http://discourse.iapct.org/t/highest-level-the-test-misc/5259>\
**Category:** CSG1996\
**Created:** [February 15, 1996, 6:21am UTC](http://discourse.iapct.org/t/highest-level-the-test-misc/5259 "1996-02-15T06:21:05Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![William\_T\_Powers4](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/w/977dab/32.png) [@William\_T\_Powers4](http://discourse.iapct.org/u/William_T_Powers4)\
**Post date:** [February 15, 1996, 6:21am UTC](http://discourse.iapct.org/t/highest-level-the-test-misc/5259/1 "1996-02-15T06:21:05Z")

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[From Bill Powers (960214.1800 MST)]

Hans Blom, 960214c --

I said:

> > This is one reason I don't place the reorganizing system at the  
> > top of the hierarchy, or anywhere else in the hierarchy.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;I don't see the connection between my remark and yours.

I was a bit cryptic. I assume that the process of reorganization (E.  
coli style) is driven by errors in systems that monitor critical  
variables having to do with the life support systems.

> **···**
>
> -----------------------------  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;We have a real problem here, I think. Maybe these two types of  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;uncertainty reduce to one fundamental process. How can there be an  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"underlying" perceptual variable y if there is no corresponding  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"real world" variable x?
> 
> Easily. Think of a relative humidity detector, which receives a wet-bulb  
> and a dry-bulb temperature and emits a signal proportional to relative  
> humidity. That signal does not correspond to any one variable in the  
> environment; it is constructed from two observable variables, but does  
> not correspond to either of them.
> 
> Many human perceptions are of this nature: they are constructed from  
> sensory input signals, but do not correspond to any one input. In many  
> cases (color, smell, beauty) they do not have direct physical  
> counterparts.
> 
> On a loftier plane, we are talking about the basic problem of  
> espistemology: we experience perceptions of a world, but we have no  
> direct way to check to see if those perceptions have one-to-one  
> correspondence with entities in the world. That's the kind of  
> uncertainty I was talking about.  
> -------------------------------------
> 
> > > Rick suggested that you apply a disturbance and see if this  
> > > system resists its effects on progress up the gradient. It would  
> > > be interesting to know how effective the control is.
> 
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;See my answer to Rick. What kind of disturbance would satisfy you?  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;And what kind of outcome ought to occur before you pronounce the  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;verdict "control"?
> 
> I should think that a constant applied force would be an acceptable kind  
> of disturbance. You could compare the effect of the disturbance on mean  
> velocity with and without the change-of-size term that you use to create  
> control. We can judge the degree of control by seeing how much the  
> effect of the disturbance on the velocity is reduced when the control is  
> turned on. You can use small disturbances so as not to exceed the  
> capacities of the putative control system.
> 
> This is a quantitative question. I'm not disputing that control may  
> exist in your simulation. If the effect of the disturbance is reduced by  
> any amount, then control technically exists. However, if the effect of  
> the disturbance is reduced only by, say, 0.1%, I don't think we would  
> consider this a very useful kind of control system.
> 
> This is why I asked you to compare the mean velocity with the up-  
> gradient component of velocity. In E. coli, the up-gradient component  
> averages 50% to 70% of the swimming speed, so while the control is not  
> spectacularly good, it is quite detectable. In the Brownian movement  
> simulation, you should be able to compute the mean speed of the particle  
> and the component of that speed up the gradient, and come up with a  
> relevant number.  
> ----------------------------------  
> P.S. Hans, when you reply to one of my posts, I get two copies: one sent  
> directly to my e-mail address, and the other via CSGnet.  
> -----------------------------------------------------------------------  
> Only brief replies today. I'm happily exhausted from getting the  
> observing platform joists in place.  
> -----------------------------------------------------------------------  
> Best,
> 
> Bill P.