xvni 



Is the Brain a Calculating Machine? 



I have discussed at some length the various abihties of the remark- 

 able mass of cells which forms the human brain because it has fre- 

 quently been claimed in recent years that suitable models for brain 

 action are to be found in machines which really parallel only a very 

 small part of the whole performance. There is no doubt that many of 

 the simpler types of response of brains can be copied by machines. 

 The latter can be provided with sense organs, which detect and re- 

 spond to sounds and light and even to other physical agencies, such 

 as radio waves, for which we have no sense organ; they can also be 

 provided with a memory, since data can be put into the machine (often 

 in the form of punched cards) and stored away for future use; with 

 the power of recognition, in that the data supplied can be compared 

 with previously established standards (e.g. a slot machine, which can 

 recognize the proper coins and reject others; and finally with the 

 power of prediction, as when a gun predictor follows an aeroplane 

 and causes a gun to deliver a shell, not where the aeroplane was, but 

 where it will be when the shell arrives. Machines can also be provided 

 with controllers (feed-back) which maintain constant conditions, e.g. 

 of temperature or pressure or speed, and in this way resemble the 

 organism which maintains itself in the narrow range of conditions in 

 which it can function. 



This is an impressive list and could no doubt be extended. It might 

 suggest that the analogy between brains and machines is a very close 

 one. Attempts to develop these analogies have been encouraged very 

 much by the fact that the mode of operation of modern electronic 

 computors is not unlike what goes on in the brain, which, as we have 

 seen, consists of an enormous number of neurones, connected to- 

 gether into a very complex network by thread-like connections 

 (Fig. 26). The nerve fibres entering the grey matter of the brain are 



