DESIGN FOR A BRAIN 8/5 



comparison of the effect of D 3 on 1 with that of D 2 shows that 

 compensation has occurred again. 



If the two phenomena are to be brought into correspondence, 

 we must notice, as in S. 3/12, that the anatomical criterion for 

 dividing the system into ' animal ' and i environment ' is not 

 the only possible: a functional criterion is also possible. Suppose 

 a monkey, to get food from a box, has to pull a lever towards 

 itself; if we sever the flexor and extensor muscles of the arm 

 and re-attach them in crossed position then, so far as the cerebral 

 cortex is concerned, the change is not essentially different from 

 that of dismantling the box and re-assembling it so that the 

 lever has to be pushed instead of pulled. Spinal cord, peripheral 

 nerves, muscles, bones, lever, and box — all are ' environment ' 

 to the cerebral cortex. A reversal in the cerebral cortex will 

 compensate for a reversal in its environment whether in spinal 

 cord, muscles, or lever. It seems reasonable, therefore, to expect 

 that the cerebral cortex will use the same compensatory process 

 whatever the site of reversal. 



To apply the principle of ultrastability we must add an assump- 

 tion that i binocular vision ' and ' normal progression ' have 

 neural correlates such that deviations from binocular vision or 

 from normal progression cause an excitation sufficient to cause 

 changes of step-function form in those cerebral mechanisms that 

 determine the actions. (The plausibility of this assumption will 

 be discussed in S. 9/4.) Ultrastability will then automatically 

 lead to the emergence of behaviour which produces binocular 

 vision or normal progression. 



8/5. A more complex example is shown in Figure 8/5/1. The 

 machine was arranged so that its diagram of immediate effects 

 was 



>3 



The effect 3 — > 1 was set permanently so that a movement of 

 3 made 1 move in the opposite direction. The action 1 — > 2 

 was uniselector-controlled, and 2 — >► 3 hand-controlled. When 

 the tracing commenced, the actions 1 — >• 2 and 2 — > 3 were 

 demonstrated by the downward movement, forced by the operator, 

 of 1 at S^. 2 followed 1 downward (similar movement), and 3 



106 



