DESIGN FOR A BRAIN 16/8 



field. Its behaviour will not be essentially different from that 

 recorded in Figure 8/4/1. If, however, we regard the same 

 series of events as occurring, not within one ultrastable whole, 

 but as interactions between a minor environment and a minor 

 organism, each of two subsystems, then we shall observe 

 behaviours homologous with those observed when interaction 

 occurs between 4 organism ' and ' environment '. In other words, 

 within a multistable system, subsystem adapts to subsystem in exactly 

 the same way as animal adapts to environment. Trial and error 

 will appear to be used; and, when the process is completed, the 

 activities of the two parts will show co-ordination to the common 

 end of maintaining the essential variables of the double system 

 within their proper limits. 



Exactly the same principle governs the interactions between three 

 subsystems. If the three are in continuous interaction, they form 

 a single ultrastable system which will have the usual properties. 



As illustration we can take the interesting case in which two 

 of them, A and C say, while having no immediate connexion 

 with each other, are joined to an intervening system B, inter- 

 mittently but not simultaneously. Suppose B interacts first with 

 A: by their ultrastability they will arrive at a terminal field. 

 Next let B and C interact. If B's step-mechanisms, together with 

 those of C, give a stable field to the main variables of B and C, 

 then that set of B's step-mechanism values will persist indefinitely; 

 for when B rejoins A the original stable field will be re-formed. 

 But if B's set with C's does not give stability, then it will be 

 changed to another set. It follows that 2?'s step-mechanisms will 

 stop changing when, and only when, they have a set of values 

 which forms fields stable with both A and C. (The identity in 

 principle with the process described in S. 8/10 should be noted.) 



16/8. The process can be illustrated on the Homeostat. Three 

 units were connected so that the diagram of immediate effects was 

 2 ^± 1 ^± 3 (corresponding to A, B, and C respectively). To 

 separate the effects of 2 and 3 on 1, bars were placed across the 

 potentiometer dishes (Figure 8/2/2) of 2 and 3 so that they could 

 move only in the direction recorded as downwards in Figure 

 16/8/1, while 1 could move either upwards or downwards. If 

 1 was above the central line (shown broken), 1 and 2 interacted, 

 and 3 was independent; but if 1 was below the central line, then 



210 



