192 ROBERT M. YERKES AND CHARLES A. COBURN 



Problem 4. Middle Mechanism of the Series 



Setting Doors open No. of doors open No. of right door 



1 2.3.4 3 3 



2 5.6.7.8.9 5 7 



3 1.2.3.4.5.6.7 7 4 



4 7.8.9 3 8 



5 4.5.6.7.8 5 6 



6 1.2.3.4.5.6.7.8.9 9 5 



7 1.2.3 3 2 



8 2.3.4.5.6 5 4 



9 3.4.5.6.7.8.9 7 6 



10 6.7.8 3 7 



Total 50 



Both punishment and reward were used in these experiments. 

 The punishment consisted of confinement for a definite interval, 

 usually one minute, in each wrong box entered, while the reward 

 consisted of food which could be obtained in the trough of the 

 right box. 



EXPERIMENTAL PROCEDURE 



We shall now briefly enumerate, in order to supplement the 

 descriptions of apparatus and methods which have been given, 

 the steps in a regular series of observations. 



The experimenter having entered the enclosure with a supply 

 of food, record-book, stop-watch, etc., first raises each of the 

 nine exit doors and places in each section of the trough a quantity 

 of food (sour milk, shelled corn, vegetables). He then lowers 

 the exit doors, thus covering the food, and takes his position 

 on the observation bench. In case both pigs are in the shelter 

 yard, it is next necessary for him to drive one of them into the 

 other yard. This having been done, he may proceed to set 

 the entrance doors for the first trial. Let us suppose that the 

 problem to be presented is problem -1 and that setting 1 is first 

 to be used. In this case the experimenter raises entrance doors 

 1, 2, and 3. He is now ready to admit one of the pigs to the 

 reaction space B of figure 2. This he does by raising momentarily 

 the appropriate slide door between B and S. 



The instant the pig enters the reaction space, the experimenter 

 starts his stop-watch and begins to record the important features 

 of the behavior of the animal, noting especially its approach 

 to the several doors, its tendency to enter boxes and the actual 

 entrance and time of entrance into any one of the three acces- 



