16/6 DESIGN FOR A BRAIN 



of all three parts will stop changing when, and only when, the 

 triple combination has a stable field. But we can go further 

 than that. If A, B and C should join intermittently in various 

 ways, sometimes joining as pairs, sometimes as a triple, and 

 sometimes remaining independent, then their step-functions will 

 stop changing when, and only when, they arrive at a set of 

 values which gives stability to all the arrangements. 



Clearly the same line of reasoning will apply no matter how 

 many subsystems interact or in what groups or patterns they 

 join. Always we can predict that their step-functions will stop 

 changing when, and only when, the combinations are all stable. 

 Ultrastable systems, whether isolated or joined in multistable 

 systems, act always selectively towards those step-function values 

 which provide stability ; for the fundamental interaction between 

 step-function and stability, the principle of ultrastability described 

 in S. 8/5, still rules the process. 



16/6. At the beginning of the preceding section it was assumed, 

 for simplicity, that the process of dispersion was suspended, for 

 we assumed that the two subsystems interacting remained the 

 same two during the whole process. What modifications must 

 be made when we allow for the fact that in the multistable system 

 the number and distribution of subsystems active at each moment 

 fluctuates ? 



It is readily seen that the principle of ultrastability holds equally 

 whether dispersion is absent or present ; for the proof of Chapter 8 

 was independent of special assumptions about the type of vari- 

 able. The chief effect of dispersion is to destroy the individuality 

 of the subsystems considered in the previous section. There 

 two subsystems were pictured as going through the complex 

 processes of ultrastability, their main variables being repeatedly 

 active while those of the surrounding subsystems remained 

 inactive. This permanence of individuality can hardly occur 

 when dispersion is restored. Thus, suppose that a multistable 

 system's field of all its main variables is stable, and that its repre- 

 sentative point is at a resting state R. If the representative point 

 is displaced to a point P, or to Q, the lines from these points will 

 lead it back to R. As the point travels back from P to R, sub- 

 systems will come into action, perhaps singly, perhaps in com- 

 bination, becoming active and inactive in kaleidoscopic variety 



176 



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