8/9 THE HOMEOSTAT 



effect from the variable ' animal's behaviour ' to ' quantity of 

 food given ' ; there is no functional circuit and no feedback. 



It may be thought that the distinction (which corresponds to 

 that made by Hilgard and Marquis between ' conditioning ' and 

 ' instrumental learning ') is purely verbal. This is not so, for 

 the description given above shows that the distinction may be 

 made objectively by examining the structure of the experiment. 



It will be seen, therefore, that the ' training ' situation neces- 

 sarily implies that the trainer, or some similar device, is an 

 integral part of the whole system, which has feedback: 



We shall now suppose this system to be ultrastable, and we 

 shall trace its behaviour on this supposition. The step-mechanisms 

 are, of course, assumed to be confined to the animal; both because 

 the human trainer may be replaced in some experiments by a 

 device as simple as a sheet of glass (in the example of the pike); 

 and because the rules of the training are to be decided in advance 

 (as when we decide to punish a house-dog whenever he jumps 

 into a chair), and therefore to be invariant throughout the process. 

 Suppose then that jumping into a chair always results in the 

 dog's sensory receptors being excessively stimulated. As an 

 ultrastable system, step-function values which lead to jumps into 

 chairs will be followed by stimulations likely to cause them to 

 change value. But on the occurrence of a set of step-function 

 values leading to a remaining on the ground, excessive stimula- 

 tion will not occur, and the values will remain. (The cessation 

 of punishment when the right action occurs is no less important 

 in training than its administration after the wrong action.) 



8/9. The process can be shown on the Homeostat. Figure 8/9/1 

 provides an example. Three units were joined: 



>2 



3 



and to this system was joined a ' trainer ', actually myself, which 

 acted on the rule that if the Homeostat did not respond to a 



113 



