11/11 



AN INTRODUCTION TO CYBERNETICS 



We can now show these relations by the diagram of immediate 

 effects : 



T 



D 



R 



The arrows represent actual channels of communication. For the 

 variety in D determines the variety in R\ and that in Tis determined 

 by that in both D and R. If R and T are in fact actual machines, 

 then R has an input from D, and Thas two inputs. 



(When R and T are embodied in actual machines, care must be 

 taken that we are clear about what we are referring to. If some 

 machine is providing the basis for T, it will have (by S.4/1) a set of 

 states that occur step by step. These states, and these steps, are 

 essentially independent of the discrete steps that we have considered 

 to be taken by D, R, and T in this chapter. Thus, T gives the out- 

 come, and any particular outcome may be compared with another, 

 as unit with unit. Each individual outcome may, however, in 

 another context, be analysed more finely. Thus a thirsty organism 

 may follow trajectory 1 and get relief, or trajectory 2 and die of thirst. 

 For some purposes the two outcomes can be treated as units, 

 particularly if they are to be contrasted. If however we want to 

 investigate the behaviour in more detail, we can regard trajectory 1 

 as composed of a sequence of states, separated by steps in time that 

 are of quite a different order of size from those between successive 

 regulatory acts to successive disturbances.) 



We can now interpret the general phenomenon of regulation in 

 terms of communication. If R does nothing, i.e. keeps to one value, 

 then the variety in D threatens to go through T to E, contrary to 

 what is wanted. It may happen that T, without change by R, will 

 block some of the variety (S.11/9), and occasionally this blocking 

 may give sufficient constancy at E for survival. More commonly, a 

 further suppression at £■ is necessary; it can be achieved, as we saw 

 in S.11/6, only by further variety at R. 



We can now select a portion of the diagram, and focus attention 

 on i? as a transmitter : 



D 



R 



210 



