6/5 PARAMETERS 



When later the animal was not under its influence, the conditioned 

 response could not be elicited. But when the dog was again put 

 under its influence, the conditioned response returned. Thus 



(£ 100 200 100 200 300 



BLOOD GLUCOSE (mg. per 100 ml J 



Figure 6/4/2 : Fields of the two lines of behaviour, A and B from 

 Figure 6/4/1. Cross-strokes mark each quarter-hour. 



two characteristic lines of behaviour (two responses to the stimulus) 

 existed, and one line of behaviour was shown when the parameter 

 * concentration of curare in the tissues ' had a high value, and 

 the other when the parameter had a low value. 



Stimuli 



6/5. Many stimuli may be represented adequately as a change 

 of parameter- value, so it is convenient here to relate the physio- 

 logical and psychological concept of a ' stimulus ' to our methods. 



In all cases the diagram of immediate effects is 



(experimenter) — - > stimulator — ► animal — > recorders. 



In some cases the animal, at some state of equilibrium, is 

 subjected to a sudden change in the value of the stimulator, and 

 the second value is sustained throughout the observation. Thus, 

 the pupillary reaction to light is demonstrated by first accustoming 

 the eye to a low intensity of illumination, and then suddenly 

 raising the illumination to a high level which is maintained while 

 the reaction proceeds. In such cases the stimulator is parameter 

 to the system ' animal and recorders ' ; and the physiologist's 

 comparison of the previous control-behaviour with the behaviour 

 after stimulation is equivalent, in our method, to a comparison of 

 the two lines of behaviour that, starting from the same initial 

 state, run in the two fields provided by the two values of the 

 stimulator. In this type, the stimulator behaves as a step- 

 function (S. 7/13). 



75 



