THE PROBLEM 1/8 



so that the correctness is determined not by the process itself but 

 by the relations which it bears to the other processes. 



This dependence of the ' correctness ' of what is happening at 

 one point in the nervous system on what is happening at other 

 points would be shown if the engine-driver were to move over to 

 the other side of the cab. For if previously a flexion of the elbow 

 had closed the throttle, the same action will now open it ; and 

 what was the correct pairing of red and green to push and pull 

 must now be reversed. So the local action in the nervous system 

 can no longer be regarded as 4 correct ' or ' incorrect ', and the 

 first simple solution breaks down. 



Another example is given by the activity of chewing in so 

 far as it involves the tongue and teeth in movements which must 

 be related so that the teeth do not bite the tongue. No move- 

 ment of the tongue can by itself be regarded as wholly wrong, for 

 a movement which may be wrong when the teeth are just meeting 

 may be right when they are parting and food is to be driven on 

 to their line. Consequently the activities in the neurons which 

 control the movement of the tongue cannot be described as either 

 4 correct ' or ' incorrect ' : only when these activities are related to 

 those of the neurons which control the jaw movements can a cor- 

 rectness be determined ; and this property now belongs, not to either 

 separately, but only to the activity of the two in combination. 



These considerations reveal the main peculiarity of the problem. 

 When the nervous system learns, it undergoes changes which 

 result in its behaviour becoming better adapted to the environ- 

 ment. The behaviour depends on the activities of the various 

 parts whose individual actions compound for better or worse into 

 the whole action. Why, in the living brain, do they always 

 compound for the better ? 



If we wish to build an artificial brain the parts must be specified 

 in their nature and properties. But how can we specify the 

 4 correct ' properties for each part if the correctness depends not 

 on the behaviour of each part but on its relations to the other 

 parts ? Our problem is to get the parts properly co-ordinated. 

 The brain does this automatically. What sort of a machine can 

 be ^//-co-ordinating ? 



This is our problem. It will be stated with more precision in 

 S. 1/12. But before this statement is reached, some minor topics 

 must be discussed. 



7 



