THE ERROR-CONTROLLED REGULATOR 12/17 



to use this generality freely, so that often we shall not need to make 

 the distinction between determinate and Markovian. 



Another example of regulation by a Markovian system is worth 

 considering as it is so well known. Children play a game called 

 "Hot or Cold?" One player (call him Tom for T) is blindfolded. 

 The others then place some object in one of a variety of places, and 

 thus initiate the disturbance D. Tom can use his hands to find the 

 object, and tries to find it, but the outcome is apt to be failure. The 

 process is usually made regulatory by the partnership of Rob (for 

 R), who sees where the object is (input from D) and who can give 

 information to Tom. He does this with the convention that the 

 object is emitting heat, and he informs Tom of how this would be 

 felt by Tom: "You're freezing; still freezing; getting a little warmer; 

 no, you're getting cold again; . . .". And the children (if young) are 

 delighted to find that this process is actually regulatory, in that Tom 

 is always brought finally to the goal. 



Here, of course, it is Tom who is Markovian, for he wanders, at 

 each next step, somewhat at random. Rob's behaviour is more 

 determinate, for he aims at giving an accurate coding of the relative 

 position. 



Regulation that uses Markovian machinery can therefore now be 

 regarded as familiar and ordinary. 



DETERMINATE REGULATION 



12/17. Having treated the case in which T and R are embodied in 

 machines, and considered that in which the machinery is Markovian, 

 we can now take up again the thread dropped in S.12/7, and can 

 specialise further and consider the case in which the probabilities 

 have all become or 1 (S.12/8), so that the machinery is determinate. 

 We continue with the regulator that is error-controlled. In order, as 

 biologists, to explore thoroughly the more primitive forms of regula- 

 tion, let us consider the case in which the feedback has a variety of 

 only two states. 



An example of such a system occurs in the telephone exchange 

 when a selector starts to hunt for a disengaged line. The selector 

 tries each in turn, in a determinate order, gets from each in turn the 

 information "engaged" or "disengaged", and stops moving (arrives 

 at a state of equilibrium) at the first disengaged line. The set of 

 disturbances here is the set of possible distributions of "engaged" or 

 "disengaged" among the lines. The system is regulatory because, 

 whatever the disturbance, the outcome is always connexion with a 

 disengaged line. 



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