DISTURBED SYSTEMS AND HABITUATION 13/10 



two such systems (C and D) with circuits such as arc shown in 

 Figure 13/9/3. We can predict (by S. 13/4) that a system of 

 type D, with a short and central circuit, will have a higher 

 immunity to random disturbance than a system of type C. 

 Maximal immunity will be shown by systems in which a and ft 

 coalesce at the centre of the region. 



<& 



D 



Figure 13/9/3. 



If there are many systems like C and D, the probabilities become 

 actual frequencies. As the less resistant fields are destroyed while 

 the more resistant remain, the average movement of the repre- 

 sentative point, as the parameter is alternated between p' and 

 p", will change from a large circuit like C towards a small central 

 circuit like D. So both the number of step-function changes and 

 the range of movement evoked by the stimulus p will diminish. 



Habituation 



13/10. Some uniformity is now discernible in the responses of an 

 ultrastable system to repeated stimuli. There is a tendency for 

 the response, whether measured by the number of step-functions 

 changing or by the range of movement of the main variables, 

 to diminish. The diminution is not due to any triviality of 

 definition or to any peculiarity of the homeostat : it follows from 

 the basic fact, inseparable from any delicate or ultrastable system, 

 that large responses tend, if there is feedback, to destroy the 



151 



