8/6 DESIGN FOR A BRAIN 



chapters have been working towards it : the later chapters will 

 develop it. 



8/6. In the previous sections, the critical states of the step- 

 functions were unrestricted in position ; but such freedom does 

 not correspond with what is found in biological systems (S. 9/8), 

 so we will examine the behaviour of an ultrastable system whose 

 critical states are so sited that they surround a definite region 

 in the main-variables' phase-space. (At first we shall assume 

 that the main variables are all full-functions, though the defini- 

 tion makes no such restriction. Later (S. 11/8) we shall examine 

 other possibilities.) 



8/7. The simplest way to demonstrate the properties of this 

 system is by an example. Suppose there are only two main 

 variables, A and B, and the critical states of all the step-functions 



HI 



Figure 8/7/1 



Changes of field in an ultrastable system. The critical 

 states are dotted. 



are distributed as the dots in Figure 8/7/1. Suppose the first 

 field is that of Figure 8/7/1 (I), and that the system is started 

 with the representative point at X. The line of behaviour from 



92 



