# positive feedback and parties

**URL:** <http://discourse.iapct.org/t/positive-feedback-and-parties/14626>\
**Category:** CSG1995\
**Created:** [February 13, 1995, 2:54pm UTC](http://discourse.iapct.org/t/positive-feedback-and-parties/14626 "1995-02-13T14:54:01Z")\
**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:** [February 13, 1995, 2:54pm UTC](http://discourse.iapct.org/t/positive-feedback-and-parties/14626/1 "1995-02-13T14:54:01Z")

</div>

[From Bill Powers (950213.0600 MST)]

James Wilk (950209.1737 GMT)--

Nice to have you aboard, James, after meeting you in Wales last Spring  
and long ago in Northbrook, Illinois.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;I still can't figure out how to reply to posts so that they end up  
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;on CSG-net itself.

You just send your message as usual, but to the address

csg-l@vmd.cso.uiuc.edu

> **···**
>
> ---------------------------------------------------------------------  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;If two people look at a situation and one says, "There, \_that's\_ an  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;example of positive feedback!" and the other says, "But that's an  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;example of \_negative\_ feedback!" are they necessarily contradicting  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;one another?
> 
> Not if they're looking at different relationships among different  
> variables, so "that" refers to something different for each of them. The  
> \_same\_ relationship can't be both positive and negative feedback.
> 
> Your explorations of the logic of positive and negative feedback are  
> leading you in the right direction. There is, however, a limit to how  
> far you can go using only verbal logic and without some sort of  
> systematic analysis. Let's look at some of your examples.
> 
> The "practical joke," which is risky because it involves deception,  
> would probably not work as smoothly as it does in your imagination  
> unless you happened to pick people who are not inclined to reality-  
> testing. And even then, the existence of positive feedback is not  
> guaranteed -- both people could simply speak louder than usual. However,  
> at a party there might well be unexplained (to the victims) laughter  
> which is raising the noise level; presumably others are in on the joke,  
> since the whole point of a practical joke is to make the victims look  
> silly to others, thus showing the instigator's ability to control them.  
> It's hard to imagine a practical joker who never reveals the practical  
> joke to anyone but the victims (who, by definition of a practical joke,  
> must realize that they've been had, or there's no humiliation to enjoy).
> 
> But this leads nicely into your example of "social oscillations," the  
> explanation for the loudness of a party. Your analysis is mostly  
> correct, but needs to be more systematic.
> 
> Remember that feedback always involves a complete closed loop, which you  
> have to identify. People do not speak more loudly at a party just  
> because the noise level increases -- that's the S-R concept. They speak  
> more loudly in order to get an indication from someone else that they  
> are being heard, and to hear themselves clearly. So the variable they  
> must be controlling is the level of their own voice \_in relation to the  
> background noise\_. A person trying to speak to another person near a  
> waterfall or in a loud factory will increase the loudness of the voice  
> until it becomes distinguishable over the background noise, even if the  
> waterfall or factory doesn't become louder as a result. This is simply  
> negative feeback counteracting a disturbance: the efforts of speaking  
> are increased until the contrast of voice with background is acceptable.
> 
> We can work our way to the party example by starting with the waterfall.  
> Let's diagram the waterfall case:
> 
> &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;\> reference  
> &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;\> contrast  
> &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;v  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;-------\> Comparator -----\>  
> &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;\> perceived |  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\> contrast |  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;input func output func  
> &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;\> v  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;noise-voice \<------------ own voice  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;intensity  
> &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;waterfall
> 
> The perceived contrast is own-voice loudness minus waterfall-noise  
> loudness. An increase in noise loudness decreases contrast, and an  
> increase in own-voice loudness increases it. So the controlled variable  
> corresponding to the perceptual signal is noise minus own-voice  
> loudness, in decibels. If the perceived contrast is less than the  
> reference contrast, the own-voice loudness is increased to correct the  
> error.
> 
> Assuming this is a good control system, we predict that the controlled  
> variable will remain essentially constant. If the person talks while the  
> conversation is carried closer to the waterfall, the waterfall noise  
> intensity will increase, which alone would decrease the perceived  
> contrast. But we assume the perception (and hence the controlled  
> variable) to remain constant; therefore the sound intensity from the  
> voice must also increase, just enough to prevent the contrast from  
> decreasing. As the waterfall noise intensity increases, for whatever  
> reason, we will hear the voice intensity also increasing, just enough to  
> keep the perceived contrast the same. This is simply negative feedback  
> in the presence of a disturbance.
> 
> So we have established the PCT explanation for why and how much voice  
> sound intensity will increase as noise sound intensity increases. Let us  
> now do the same analysis for the party situation, where we assume each  
> person is trying to maintain a certain contrast of voice over noise, as  
> perceived.
> 
> I'll represent two individuals simply as boxes without internal  
> structure, the above diagram being understood for each one.
> 
> &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;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\> A | | B |  
> &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;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;/ \ x / \  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;ca + la ----------\>---- cb + lb  
> &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;\> 1 1 |  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\ y /  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;--------\<------------------------
> 
> Contrast perceived by A is ca, voice loudness of A is la, and ditto for  
> cb and lb for person B.
> 
> We assume these people are talking not to each other but to different  
> people not shown, so they are talking simultaneously. If you look just  
> at person A, you will see the same thing as in the first diagram: the  
> perceived contrast is increased by the loudness of A's own voice and  
> decreased by "noise" (the loudness of B's voice). So if B talks more  
> loudly, A will necessarily talk more loudly in order to maintain a  
> constant perceived contrast, ca. The plus and minus signs indicate the  
> effects on perceived contrast.
> 
> We also find that if A talks more loudly, B will also maintain a  
> constant perceived contrast by talking more loudly.
> 
> You have correctly deduced that A and B are in a positive-feedback  
> relationship, unwittingly. But we do not yet have a runaway situation.
> 
> In the diagram, a "1" is shown on the path from each person's output to  
> that person's input contrast (assumed to be perceived contrast). This  
> means that a 1-unit change in the voice output will always produce a 1-  
> unit cbange in perceived contrast for that person.
> 
> A corresponding factor is indicated on the line from A's output to B's  
> input (x) and from B's output to A's input (y). Suppose that both x and  
> y are 1. Because control is assumed perfect and the perceived contrast  
> in both cases is assumed to remain constant, this means that a 1-unit  
> increase in B's output loudness lb will result in a 1-unit increase in  
> A's output loudness la. But a 1-unit increase in la will result, for the  
> same reason, in a 1-unit increase in lb.
> 
> We can now trace the effect of A's output loudness on A's perceived  
> contrast via two pathways, one local and direct, the other remote, via  
> B's response to A. The local effect has a magnitude of 1 unit of effect  
> per unit of cause. If you trace the remote effect from A's output,  
> through B, back to A, and remember that B's output \_decreases\_ contrast,  
> you find that A's effect on A's perceived contrast by that path has an  
> effectiveness of -xy or -1 unit of contrast ca per unit of increase in  
> output loudness la.
> 
> So the NET effect of A's output loudness la on A's own perceived  
> contrast ca is ZERO! The local negative feedback is just cancelled by  
> the remote positive feedback, and the net feedback strength is zero.
> 
> We can now imagine A having a strolling conversation with A's partner  
> (not shown), and B doing likewise with B's partner (also not shown).  
> Recalling the physical principle that sound intensity falls off as the  
> square of distance d, we can see that x and y both vary as 1/(d^2).  
> Also, if you hadn't noticed, the total positive feedback effect is x  
> times y, because both multipliers appear in the remote feedback path. So  
> the total positive feedback goes as the inverse \_fourth\_ power of  
> distance.
> 
> When the strolling couples are far apart, x and y are much less than 1,  
> so local feedback predominates. There is a slight positive feedback  
> effect which results in slightly elevated voice levels, but only  
> slightly.
> 
> As the couples approach to pass very near each other, x and y will begin  
> to increase rapidly. As they do, the voice levels on both sides will  
> increase. As x and y approach 1, the voice levels will get louder and  
> louder. At x = y = 1, the speakers will be speaking quite loudly, and  
> even though they don't realize it, they have both lost control of  
> perceived contrast. As the approach becomes even closer, x and y  
> approach 1.414, so the total positive feedback is 1.414 x 1.414 or 2,  
> and the net magnitude of positive feedback approaches (2 - 1) or unity.  
> At this point the process is on the verge of running away. Any further  
> approach will result in a net positive feedback factor greater than 1,  
> and both speakers will quickly escalate to screaming as loudly as they  
> can, at the limit of output.
> 
> Of course this is an unlikely scenario, because we're forgetting about  
> higher-level systems. Suppose that David, "A", is saying to Felicia, "I  
> think Nigel is trying to get into Andrea's pants," while Andrea ("B") is  
> saying to Nigel "I think David is two-timing Felicia." Both of them, of  
> course, are shouting. If the speakers themselves don't realize that the  
> objects of their discussion are one foot away, their silent partners  
> very well might; anyway, it is unlikely that such subject-matter would  
> actually be discussed at the top of one's voice. The couples would  
> simply avoid a close approach: they would stay far enough apart so they  
> could maintain net negative feedback while speaking near a whisper.
> 
> So that is the basic analysis. Now let's extend it to N persons at a  
> party.
> 
> Let's consider A the person in question. B is now a large collection of  
> other people all talking at once (if there are N people at the party,  
> presumably the number of other people talking is about (N-1)/2). These  
> people are relatively far from A, so the value of x is smaller than 1  
> between any one other person and A. But the total positive feedback for  
> A is x (the outgoing path to the average other person) times y(N-1)/2  
> (the average return path from \_all\_ the others who are talking), or  
> xy(N-1)/2. The dimensions of the room, its acoustics, and the number of  
> other people will determine the net positive feedback. When N gets too  
> large for the room, everyone ends up screaming into the nearest person's  
> ear.
> 
> After the first few people have arrived at the party, we will thus see a  
> few conversations being held here and there in the room. As more people  
> arrive, the conversations will spread apart to maintain maximum  
> distance, and when N reaches a large number, people will be huddled  
> together into little groups shouting to be heard over the din. By "over  
> the din" we now indicate the phenomenon of "maintaining contrast".  
> ----------------------------------  
> Don't be fooled by Tom Bourbon's heuristic tricks. He knows what  
> positive feedback is, and how it shows up in two-person control  
> experiments when the cross-connection is too strong. He just wanted  
> someone to come up with a detailed analysis proving that positive  
> feedback exists. My own style is more to reveal the secret first and  
> show how an analysis can be done, and THEN see if others can apply it in  
> other situations.  
> ------------------------------------------------------------------------  
> Best to all,
> 
> Bill P.

---

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**Author:** ![Lars-Christian\_SMITH](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/l/779978/32.png) [@Lars-Christian\_SMITH](http://discourse.iapct.org/u/Lars-Christian_SMITH)\
**Post date:** [February 14, 1995, 6:58pm UTC](http://discourse.iapct.org/t/positive-feedback-and-parties/14626/2 "1995-02-14T18:58:00Z")

</div>

[Lars Christian Smith (950214 16700 CET)]

Re: Control leading to positive feedback in non-controlled variables

I don't have a copy of \_The Fifth Discipline\_ here, but didn't Peter  
Senge have a set of diagrams defining various "archetypes" of systemic  
interactions leading to positive feedback?

Presumably this could be useful as a diagnostic, i.e. on could say that  
a process is of "type X".

Whose work is it anyway? I presume it is not Senge's. Is it useful?

Best,  
Lars

> **···**
>
> To: James Wilk (950209.1737), Dag Forssell

---

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**Author:** ![Marc\_Abrams5](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/m/f08c70/32.png) [@Marc\_Abrams5](http://discourse.iapct.org/u/Marc_Abrams5)\
**Post date:** [February 15, 1995, 2:45am UTC](http://discourse.iapct.org/t/positive-feedback-and-parties/14626/3 "1995-02-15T02:45:58Z")

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> **···**
>
> Date: Tue, 14 Feb 1995 19:58:00 MET  
> From: Lars-Christian SMITH +352 67287 \<LCSMITH@RESTENA.LU\>  
> Subject: Re: positive feedback and parties  
> Lines: 19
> 
> From: [Marc S. Abrams (950214.1900)]
> 
> X-To:  
> [Lars Christian Smith (950214 16700 CET)]
> 
> To: James Wilk (950209.1737), Dag Forssell
> 
> Re: Control leading to positive feedback in non-controlled variables
> 
> Lars Asked:  
> I don't have a copy of \_The Fifth Discipline\_ here, but didn't Peter  
> Senge have a set of diagrams defining various "archetypes" of
> 
> systemic interactions leading to positive feedback?
> 
> Marc said:  
> Yes he did, both in \_The Fifth Discipline\_ and the subsequent  
> \_Field Book\_.
> 
> Lars Stated:  
> Presumably this could be useful as a diagnostic, i.e. on could say
> 
> that a process is of "type X".
> 
> Marc Responded:  
> The original intention of the diagrams was to help teach \_System
> 
> Dynamics\_ at MIT. Dan Kim (publisher of \_The Systems Thinker)  
> expanded upon the original concept and utilized the diagrams as a  
> diagnostic tool. The jury is still out. The main critisism of the  
> archetypes is that people try to "shoe horn" the problem to fit  
> the model.
> 
> Lars Asked:  
> Whose work is it anyway? I presume it is not Senge's. Is it useful?
> 
> Marc Answer:  
> See above. I personally believe that systems thinking is a very  
> useful set of skills, especially within the framework of PCT.  
> Unfortunately, all of those systems thinkers out there are  
> generally unaware of the existence of PCT. Maybe we can help  
> change that. I know I am going to give it a shot.
> 
> Lars, or anyone else, if you want more info on this stuff, zip me a  
> line and I'll get off some references and ftp sites.
> 
> Marc
> 
> Best,  
> Lars

---

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**Author:** ![Lars-Christian\_SMITH](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/l/779978/32.png) [@Lars-Christian\_SMITH](http://discourse.iapct.org/u/Lars-Christian_SMITH)\
**Post date:** [February 15, 1995, 6:45pm UTC](http://discourse.iapct.org/t/positive-feedback-and-parties/14626/4 "1995-02-15T18:45:00Z")

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[Lars Christian Smith (950215 19:40)]

To; Marc S. Abrams (950214.1900)

Re: Systems Thinking

I don't know Dan Kim's \_The Systems Thinker\_, and I tried to look it up  
on a list of books in print, but I couldn't find it. Who it the publisher?  
ISBN number? Is it any good? Any reviews of it anywhere?

Best,  
Lars