DESIGN FOR A BRAIN 1/15 



in their behaviour, and it is to these averages that our assumption 

 applies. 



The question whether the nervous system is composed of parts 

 that are determinate or stochastic has not yet been answered. 

 In this book we shall suppose that they are determinate. That 

 the brain is capable of behaving in a strikingly determinate way 

 has been demonstrated chiefly by feats of memory. Some of the 

 demonstrations depend on hypnosis, and are not quite sufficiently 

 clear in interpretation for quotation here. Skinner, however, has 

 produced some striking evidence by animal experiment that the 

 nervous system, if the surrounding conditions can be restored 

 accurately, may behave in a strictly reproducible way. By 

 differential reinforcement with food, Skinner trained twenty 

 young pigeons to peck at a translucent key when it was illuminated 

 with a complex visual pattern. They were then transferred to the 

 usual living quarters where they were used for no further experi- 

 ments but served simply as breeders. Small groups were tested 

 from time to time for retention of the habit. 



' The bird was fed in the dimly-lighted experimental apparatus 

 in the absence of the key for several days, during which 

 emotional responses to the apparatus disappeared. On the 

 day of the test the bird was placed in the darkened box. The 

 translucent key was present but not lighted. No responses 

 were made. When the pattern was projected upon the key, 

 all four birds responded quickly and extensively. . . . This 

 bird struck the key within two seconds after presentation of 

 a visual pattern that it had not seen for four years, and at 

 the precise spot upon which differential reinforcement had 

 previously been based.' 



The assumption that the parts are determinate is thus not un- 

 reasonable. But we need not pre-judge the issue; the book is an 

 attempt to follow the assumption of determinacy wherever it leads. 

 When it leads to obvious error will be time to question its validity. 



1/15. To be consistent with the assumptions already made, we 

 must suppose (and the author accepts) that a real solution of our 

 problem will enable an artificial system to be made that will be 

 able, like the living brain, to develop adaptation in its behaviour. 

 Thus the work, if successful, will contain (at least by implication) 

 a specification for building an artificial brain that will be similarly 

 self-co-ordinating. 



10 



