13/8 DESIGN FOR A BRAIN 



state in A will be destroyed ; but the first with resting state in B 

 will be retained. The displacement will then stop causing step- 

 function changes. So if we regard the application of the constant 

 displacement as • stimulus ', and the step-function and main- 

 variable changes as ' response ', then we shall find that the 

 response to the stimulus tends to diminish. 



13/8. This particular process cannot be shown on the homeostat, 

 for its resting state is always at the centre, but it will demon- 

 strate a related fact. If two fields (Figure 13/8/1) each have a 



B 



Figure 13/8/1. 



resting state at the centre and the line of one (A) from a constant 

 displacement returns by a long loop meeting critical states while 

 the return path of the other (B) is more direct, then the applica- 

 tion of the displacement will destroy A but not B. In other 

 words, a set of step-function values which gives a large ampli- 

 tude of main-variable movement after a constant displacement 

 is more likely to be replaced than a set which gives only a small 

 amplitude. 



The process is shown in Figure 13/8/2. Two units were joined 

 1 — > 2. The effect of 1 on 2 was determined by 2's uniselector, 

 which changed position if 2 exceeded its critical states. The 

 operator then repeatedly disturbed 2 by moving 1, at D. As 

 often as the uniselector transmitted a large effect to 2, so often 

 did 2 shift its uniselector. But as soon as the uniselector arrived 

 at a position that gave a transmission insufficient to bring 2 to its 

 critical states, that position was retained. So under constant 

 stimulation by D the amplitude of 2's response tended to diminish. 



The same process in a more complex form is shown in Figure 



148 



