Chapter 8 



TRANSMISSION OF VARIETY 



8/1. The previous chapter has introduced the concept of "variety", 

 a concept inseparable from that of "information", and we have 

 seen how important it is, in some problems, to recognise that we are 

 dealing with a set of possibihties. 



In the present chapter we shall study how such possibilities are 

 transmitted through a machine, in the sense of studying the relation 

 that exists between the set that occurs at the input and the consequent 

 set that occurs, usually in somewhat coded form, at the output. 

 We shall see that the transmission is, if the machine is determinate, 

 perfectly orderly and capable of rigorous treatment. Our aim will 

 be to work towards an understanding good enough to serve as a 

 basis for considering the extremely complex codings used by the 

 brain. 



8/2. Ubiquity of coding. To get a picture of the amount of coding 

 that goes on during the ordinary interaction between organism 

 and environment, let us consider, in some detail, the comparatively 

 simple sequence of events that occurs when a "Gale warning" is 

 broadcast. It starts as some patterned process in the nerve cells 

 of the meteorologist, and then becomes a pattern of muscle-move- 

 ments as he writes or types it, thereby making it a pattern of ink 

 marks on paper. From here it becomes a pattern of light and dark 

 on the announcer's retina, then a pattern of retinal excitation, then 

 a pattern of nerve impulses in the optic nerve, and so on through 

 his nervous system. It emerges, while he is reading the warning, 

 as a pattern of lip and tongue movements, and then travels as a 

 pattern of waves in the air. Reaching the microphone it becomes 

 a pattern of variations of electrical potential, and then goes through 

 further changes as it is amplified, modulated, and broadcast. Now 

 it is a pattern of waves in the ether, and next a pattern in the receiving 

 set. Back again to the pattern of waves in the air, it then becomes a 

 pattern of vibrations traversing the listener's ear-drums, ossicles, 

 cochlea, and then becomes a pattern of nerve-impulses moving up 

 the auditory nerve. Here we can leave it, merely noticing that this 



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