Modification by Experience 311 



increase. The power to discriminate appears to be better 

 in younger mice ; the power to associate better in oldet 

 ones. Thus the superiority of the younger animals is 

 rather in speed of sense perception and movement than in 

 real learning ability. 



Hubbert (345) has confirmed the |tatement that young 

 rats learn the maze more rapidly than older ones. More- 

 over, she finds that in the younger animals, the most rapid 

 stage of the learning occurs at an earlier point. 



(2) The sex of the learner may have some effect on the 

 learning, although no very definite differences have tJius far 

 appeared. Yerkes (821) reports that young male dancing 

 mice learn faster than females, and that females from four 

 to ten months of age learn faster than males. Hubbert 

 (345) states that except in the cases of very young and very 

 old rats, males learn more readily than females ; the absolute 

 time of running the maze is however shorter for females. 



(3) The number of trials a day affects the speed of the 

 learning. Yerkes (820) found that the dancing mouse 

 learned a white-black discrimination in fewer trials the 

 smaller the number of trials a day. Ulrich (738) has shown 

 that the white rat learns a puzzle-box habit or a maze 

 habit in fewer trials if one trial is given a day than it requires 

 if either three or five trials are given a day. Apparently 

 even better results are secured by one trial every third 

 day. The same principle appeared to hold when several 

 problems were being learned at once. This principle,^ 

 known as that of distributed repetitions, has long been 

 recognized in human memorizing, although we do not 

 know the explanation for it. But.learning is always more 

 economically secured if intervals of time- are allowed to 

 elapse between repetitions. 



(4) The learning of one habit may influence the later 



