DESIGN FOR A BRAIN 



17/5 



affected, in part at least, by the position of the ball in the air. 

 Thus the server at tennis normally co-ordinates his left and right 

 arms' movements by the method: Left arm throws up the ball 

 with imperfect accuracy, then the position of the ball in the air 

 (through vision) guides the right arm. The diagram of immediate 

 effects is (to show the correspondence with Figure 16/6/1) as 

 shown in Figure 17/4/1. 



Thus, within the assumptions bounding this example, co- 

 ordination between parts can take place through the environment; 

 communication within the nervous system is not always necessary. 



17/5. After these observations, one may begin to wonder why 

 the brain should have connexions between its parts at all. There 

 are at least two reasons. 



The first comes from the fact that, in the organism's life-long 

 struggle to defend its essential variables against disturbance, there 

 is a fundamental advantage in getting information about the 

 disturbance early. (The fact can either be accepted as obvious, 

 or proved more formally, as in /. to C, S. 12/5.) Now while 

 many of the disturbances that threaten an essential variable come 

 ultimately from the environment, some of them may come from 

 other parts of the same organism. Thus every child that is 

 learning to feed itself discovers that its lip may be hurt both by 

 environmental objects and also by its own attempt to pass a 

 spoonful of food into its closed mouth. If the lip is not to be 

 struck, the mouth must be opened in advance of the spoon's 

 arrival ; for this to be possible, information that the spoon is 

 approaching must get to the ' mouth centre ' before the spoon 

 arrives. Sometimes the information may come through the 

 environment (by the child watching the spoon), with the diagram 

 of immediate effects: 



Centre for 



hand 

 movements 



Centre for 



mouth 

 movements 



Muscles 



of 

 mouth 



But if, for whatever reason, communication from hand to mouth 

 is not possible through the environment, then communication 

 within the brain, from hand-centre to mouth-centre, is necessary 

 if the mouth is to be opened before the spoon arrives. Thus 



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