DESIGN FOR A BRAIN 



10/10 



must be some gating mechanism r to determine which set shall 

 be on the feedback circuit, and the gating mechanism r must be 

 controlled (usually through R, as this is the organism's structure) 

 by the value of P. 



Envt 



Figure 10/9/1. 



Figure 10/9/1 presents the diagram of immediate effects, but 

 the Figure is best thought of as a mere mnemonic for the functional 

 relations, lest it suggest some anatomical form too strongly. The 

 parameter P can be set at various values, P lt P 2 , . . . The step- 

 mechanisms are divided into sets, and there is a gating mechanism 

 r, controlled by P through the environment and the reacting 

 part R, that determines which of the sets shall be effective in 

 the second feedback via the essential variables. 



10/10. The diagram of Figure 10/9/1 and the behaviour of the 

 gating mechanism may seem somewhat complex, but we must 

 beware of seeing into it more complexity than is necessary. All 

 that is necessary is that the step-mechanisms involved in any 

 particular problem P { be distinct from those involved in the 

 others, that if S { be affected by the essential variables then S t shall 

 be the mechanisms that affect R, and that there shall be a corre- 

 spondence between the problems and the sets of step-mechanisms. 

 This latter correspondence need not be orderly or ' rational ' ; it 

 may be perfectly well set up at random (i.e. determined by factors 



144 



