11/8 DESIGN FOR A BRAIN 



the pavement. Later, when he is more skilled, the act of changing 

 gear will have no effect on the direction of the car's travel. Adap- 

 tation thus demands not only the integration of related activities 

 but the independence of unrelated activities. 



We now, therefore, no longer maintain the restriction of S. 8/6 : 

 from now on the main variables may be of any type : full-, part-, 

 step-, or null-functions. This freedom makes possible new types 

 of ultrastable system, systems still ultrastable and still selective 

 for stable fields, but no longer necessarily fully inter-connected 

 internally. In particular, if many of the main variables are part- 

 functions, the system is able to avoid the earlier-mentioned diffi- 

 culty in getting adapted ; it does this by developing partial, 

 fluctuating, and temporary independencies within the whole 

 without losing its essential wholeness. The study of such systems 

 will occupy the remainder of the book. 



References 



Boyd, D. A., and Nie, L. W. Congenital universal indifference to pain. 



Archives of Neurology and Psychiatry, 61, 402 ; 1949. 

 Sherrington, C. S. The integrative action of the nervous system. New 



Haven, 1906. 



138 



