1/11 DESIGN FOR A BRAIN 



would, of course, involve a circular argument ; for our purpose 

 is to explain the origin of behaviour which appears to be teleo- 

 logically directed. 



It will be further assumed that the nervous system, living 

 matter, and the matter of the environment are all strictly deter- 

 minate : that if on two occasions they are brought to the same 

 state, the same behaviour will follow. Since at the atomic level 

 of size the assumption is known to be false, the assumption implies 

 that the functional units of the nervous system must be sufficiently 

 large to be immune to this source of variation. For this there is 

 some evidence, since recordings of nervous activity, even of single 

 impulses, show no evidence of appreciable thermal noise. But 

 we need not prejudge the question. The work to be described 

 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. 



Consciousness 



1/11. The previous section has demanded that we shall make no 

 use of the subjective elements of experience ; and I can antici- 

 pate by saying that in fact the book makes no such use. At 

 times its rigid adherence to the objective point of view may 

 jar on the reader and may expose me to the accusation that I am 

 ignoring an essential factor. A few words in explanation may 

 save misunderstanding. 



Throughout the book, consciousness and its related subjective 

 elements are not used for the simple reason that at no point have I 

 found their introduction necessary. This is not surprising, for the 

 book deals with only one of the aspects of the mind-body relation, 

 and with an aspect — learning — that has long been recognised to 

 have no necessary dependence on consciousness. Here is an 

 example to illustrate their independence. If a cyclist wishes to 

 turn to the left, his first action must be to turn the front wheel 

 to the right (otherwise he will fall outwards by centrifugal force). 

 Every practised cyclist makes this movement every time he 

 turns, yet many cyclists, even after they have made the move- 

 ment hundreds of times, are quite unconscious of making it. 

 The direct intervention of consciousness is evidently not necessary 

 for adaptive learning. 



10 



