12/2 AN INTRODUCTION TO CYBERNETICS 



and such that F blocks the flow of variety from D to E, so that E 

 stays within t]. 



T is usually given. It is the environment which the organism is 

 facing together with those parts of the organism that have to be 

 taken as given in the regulation. It cannot just be abolished, but 

 can usually be manipulated. The problem of regulation is then, 

 in general : 



Given E, 17, T, and D, to form the mechanism R so that R and T, 

 coupled, act to keep E within rj. 



From now to the end of the book we shall be studying how various 

 types of data (E, 7], T, and D) can specify the form of machine with 

 input (R) that will give regulation. We want to deduce the form 

 ofR. 



Were the situation always as simple as it was in Table 11/3/1, the 

 subject would soon be exhausted. As it is, many deviations from 

 that form are possible, so we shall proceed to examine various 

 deviations, as they put various difficulties in the way of the design 

 or specification of the regulator R. 



We can now assume, in discussing some particular regulation, that 

 full use has been made of the possibihties of redefining (S. 11/16) 

 so that the formulation is either like that of S.11/3, which gave 

 perfect regulation and control, or like those in S.11/4, in which such 

 perfection was impossible. The remainder of the book will be 

 concerned essentially with those cases in which perfect regulation 

 is not possible but in which we wish the regulation to be as good as 

 is possible in the conditions given. 



12/2. Sensory and motor restriction. A simple introduction to the 

 real difficulties is that given when i?'s capacity, as a channel for 

 transmitting variety or information from D to T, becomes insufficient, 

 according to the law of Requisite Variety, to reduce the variety in E 

 to that in rj. When this happens, the regulation is necessarily 

 imperfect. 



Examples of the phenomenon are myriad. First are all the cases 

 of sensory restriction, of deafness, of the driver who cannot see 

 clearly through a rain-obscured windscreen. There are the organ- 

 isms that cannot see ultra-violet light, and the tabetic who cannot 

 feel where his feet are. These are restrictions in the channel from 

 D to R. 



Then there are the restrictions in the channel from R to T, those 

 on the effector side of R. There is the man who has lost an arm, 

 the insect that cannot fly, the salivary gland that cannot secrete, and 

 the rudder that is stuck. 



220 



