8 INDIVIDUAL DIFFEEENCES AND FAMILY RESEMBLANCES 



described, the red one being the only one which could be pushed 

 open, and through it the mouse could enter the second compartment. 

 If the mouse attempted to pass through one of the blue doors it re- 

 ceived a slight electric shock from the punishment pad "P," which 

 was on the floor of the maze directly in front of the door. The posi- 

 tion of the red gate was changed every day, being now in one place 

 and now in another, following a program which had previously been 

 made out. After making the successful choice, the mouse entered 

 the second compartment where he was free to go directly into its 

 nest cage by means of one of the exit doors, where the usual reward 

 was given. Twenty-five trials were made with each individual, and, 

 as in the previous maze, the trials were divided into three somewhat 

 homogeneous groups. The first group, irregular on account of the 

 great play of chance, includes the first two trials ; the second group, 

 including the next five trials, marks the period of rapid learning, and 

 the third group of eighteen trials represents the period when the 

 learning was practically completed. It has been found, as will be 

 discussed later on, that the last period of trials was longer than 

 necessary; in fact, the mice showed very little improvement during 

 this period. The day after completing the trials in the multiple 

 choice test the animals were given a series of trials in the maze test 

 first considered. This was a retention test, designed to give a measure 

 of the permanence of association for the previously learned task. In 

 this case ten trials were given, and the gates were opened in the same 

 order as during the last ten trials of the interference test. 



