ULTRASTABILITY IN THE LIVING ORGANISM 9/5 



This type of experiment reveals its essential dynamic structure 

 more clearly if contrasted with elementary Pavlovian condition- 

 ing. In the experiments of Grindley and Pavlov, both use the 

 sequences ' . . . buzzer, animal's response, food . . .' In Grindley's 

 experiment, the value of the variable 4 food ' depended on the 

 animal's response : if the head turned to the left, ' food ' was 

 ' no carrot ', while if the head turned to the right, ' food ' was 

 4 carrot given \ But in Pavlov's experiments the nature of 

 every stimulus throughout the session was already determined 

 before the session commenced. The Pavlovian experiment, there- 

 fore, allows no effect from the variable 4 animal's behaviour ' to 

 4 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 4 conditioning ' and 

 4 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. 

 Culler et al. performed an experiment in which feedback, at first 

 absent, was added at an intermediate stage : as a result, the 

 dog's behaviour changed. They gave the dog a shock to the 

 leg and sounded a tone. The reaction to the shock was one of 

 generalised struggling movements of the body and retraction of 

 the leg. After a few sessions the tone produced generalised 

 struggling and retraction of the leg. So far there had been no 

 feedback ; but now the conditions were changed : the shock was 

 given at the tone only if the foot was not raised. As a result 

 the dog's behaviour changed : the response rapidly narrowed to 

 a simple and precise flexion of the leg. 



It will be seen, therefore, that the 4 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-functions 

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

 because the human trainer may be replaced in some experiments 



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