# Martin's Thought Experiment

**URL:** <http://discourse.iapct.org/t/martins-thought-experiment/6780>\
**Category:** CSG1993\
**Created:** [March 31, 1993, 5:15pm UTC](http://discourse.iapct.org/t/martins-thought-experiment/6780 "1993-03-31T17:15:59Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Marken\_Richard\_S1](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/m/977dab/32.png) [@Marken\_Richard\_S1](http://discourse.iapct.org/u/Marken_Richard_S1)\
**Post date:** [March 31, 1993, 5:15pm UTC](http://discourse.iapct.org/t/martins-thought-experiment/6780/1 "1993-03-31T17:15:59Z")

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[From Rick Marken (930331.0800)]

Martin Taylor (930330 11:20) --

> Let's consider a thought experiment to test this.

EXCELLENT THOUGHT EXPERIMENT! Now let's do it as a simulation,  
shall we?

> If I understand the  
> claim, oft repeated, Rick means that no function that takes as input  
> (a) the perceptual signal and (b) any other signal that is agreed to have no  
> information about the disturbance can reconstruct the disturbance, but  
> that nevertheless the disturbance is mirrored in the output.

I'll buy it.

> I'll leave the logical problem with the "mirroring" unaddressed, and  
> assume that Rick accepts as correct what he says, that the output  
> mirrors the disturbance.

What's the "logical" problem with the "mirroring"? You can look at  
the data from our tracking experiments and see that o = -d to within  
a few pixals throughout an experimental run. When both o and d are  
measured in screen units, the time traces of these two variables will  
be symmetrical about a line corresponding to the fixed screen position  
of the target. I call this characteristic of the graph "mirroring".

> In my thought experiment, I will take the ECS, and add a simple function  
> that takes as its input the reference signal to the ECS (which I think we  
> can agree has no information about the disturbance) and the perceptual  
> signal, which Rick CAPITALIZES as having no information abou the disturbance.

Excellent! For simplicity, let's make the reference signal a constant  
when we simulate your model. But a variable r will work too -- just  
trying to keep it simple.

> Let us see whether a function can be constructed that takes these two  
> inputs and produces a signal that matches the disturbance. If so, I  
> would consider it conclusive evidence that information about the disturbance  
> is to be found in the perceptual signal.

OK!

> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;------------\> Signal X (which should match the disturbance)  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\>  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;mystery function M(r, p)  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;^ ^  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\> \>  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\> \> V (reference signal R(t) into ECS)  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\> \> \>  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\> \<-------|  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\> V  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\>----------\>comparator------- error = P-R  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\> \>  
> &nbsp;&nbsp;&nbsp;perceptual output  
> &nbsp;&nbsp;&nbsp;&nbsp;signal P(t) function O(error)  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;^ |  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\> V  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\> output signal  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\> (accepted as mirroring the disturbance)
> 
> -------------------------------------------------------------------
> 
> If Signal X matches the disturbance, the perceptual signal must be the  
> route from which the mystery function M(r, p) gets the information about  
> the disturbance. Right?

Right!! I completely agree with your proposal as diagrammed above.  
I think a good first candidate for M(r,p) would be the function  
O(r,p), right? Ah, I see you think so too:

> Now let the function M be indentical to O(R-P). Signal X will then be the  
> negative of the output signal, which is the disturbance.

It is at this point that experience will triumph over the "obvious"  
conclusions of your thought experiment. I think it's time to fire up  
the simulator; really!

> The only question  
> here is whether O(error) is a function or a magical mystery tourgoodie.

Your magical mystery tour will really begin when you run the simulation!

> I  
> prefer to think we are dealing with physical systems, and that O is a

function.

> Therefore, information about the disturbance is in the perceptual signal,  
> and moreover, it is there in extractable form.

> QED.

And a right excellent proof i'tis. Now try the simulation.

Best

Rick "There is no information about the disturbance in controlled  
perception" Marken

---

<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:** [March 31, 1993, 11:16pm UTC](http://discourse.iapct.org/t/martins-thought-experiment/6780/2 "1993-03-31T23:16:52Z")

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[Martin Taylor 930331 18:15]  
(Rick Marken 930331.0800)

Rick accepts my thought experiment, and suggests doing a simulation, which  
he suggests will not turn out as I claim. Seems reasonable, though I  
am not clear how they could come out different.

> **···**
>
> ----------
> 
> > > I'll leave the logical problem with the "mirroring" unaddressed, and  
> > > assume that Rick accepts as correct what he says, that the output  
> > > mirrors the disturbance.
> > 
> > What's the "logical" problem with the "mirroring"? You can look at  
> > the data from our tracking experiments and see that o = -d to within  
> > a few pixals throughout an experimental run.
> 
> The logical problem is that the output of the ECS, like the perceptual  
> signal, is a neural current, whereas the disturbance is something in the  
> world. The output being modelled by the function M(r,p) in my proposal  
> is a neural current. The output one sees on the screen (Rick's "o") is  
> related to that neural current, but may be affected also by the actions  
> of other control systems, so there is no one-to-one relation between the  
> output and the effect on the screen. There IS a correspondence between  
> the output and the error, so this lack of a one-to-one relationship does  
> not cause a problem for control (as it would if we were dealing with  
> inverse kinematics). It does mean that the signal X in my model does  
> not replicate the disturbance. It mirrors the output.
> 
> Martin