SERIAL ADAPTATION 17/5 



brain, step-functions that were once labile may become fixed. 

 Duncan, for instance, let rats run through a maze, and at various 

 times after the run gave them a convulsion by giving an electric 

 shock to the brain. He found that if the shock was given within 

 about half an hour of the run, all memory of the maze seemed to 

 be lost ; but if the shock was given later, the memory was retained. 

 In his words : ' It is suggested that newly learned material under- 

 goes a period of consolidation or perseveration. Early in this 

 period a cerebral electroshock may practically wipe out the effect 

 of learning. The material becomes more resistant to such disrup- 

 tion ; at the end of an hour no retroactive effect was found.' 

 Such a consolidation could easily occur in the animal brain : 

 many proteins, for instance, if kept in unusual ionic conditions 

 undergo irreversible changes. But with the details we are hardly 

 concerned : we simply assume the possibility. 



If, then, the first learned reaction is unbreakable, the whole 

 system becomes simple, at least in principle, for as it is an ultra- 

 stable system adapting to a system not subject to step-function 

 change (i.e. to the complex of environment and first reaction- 

 system acting together), the situation is homologous with that 

 already treated in Chapter 9 — the adaptation and ' training ' of 

 an ultrastable system by an environment. It is therefore not 

 playing with words, but expressing a fundamental parallelism to 

 say that, in serial learning, the first reaction-system and the 

 environment together i train ' the second. They train it by not 

 allowing the second to follow lines of behaviour incompatible 

 with their own requirements. 



To see the process in more detail, consider the following example. 

 A young animal has already learned how to move about the world 

 without colliding with objects. (Though this learning is itself 

 complex, it will serve for illustration, and has the advantage of 

 making the example more vivid.) This learning process was due 

 to ultrastability : it has established a set of step-function values 

 which give a field such that the system composed of eyes, muscles, 

 skin-receptors, some parts of the brain, and hard external objects 

 is stable and always acts so as to keep within limits the mechanical 

 stresses and pressures caused by objects in contact with the skin- 

 receptors (S. 5/4). The diagram of immediate effects will therefore 

 resemble Figure 17/5/1. This system will be referred to as part A, 

 the c avoiding ' system. 



187 



