232 The Dancing Mouse 



series, it descends to 5.8 for the second series, and thence 

 abruptly to 5.05 for the first training series. This series of 

 ten tests therefore served to reduce the black preference very 

 considerably. The curve continues to descend constantly 

 until the tenth series, for which the number of errors was the 

 same as for the preceding series, .65. This irregularity in 

 the curve, indicative, as it would appear, of a sudden cessation 

 in the learning process, demands an explanation. My first 

 thought was that an error in computation on my part might 

 account for the shape of the curve. The error did not exist, 

 but in my search for it I discovered what I now believe to 

 be the cause of the interruption in the fall of the error curve. 

 In all of the training series up to the tenth the white card- 

 board had been on the right and the left alternately or on 

 one side two or three times in succession, whereas in the tenth 

 series, as may be seen by referring to Table 12 (p. in), it was 

 on the left for the first four tests, then on the right four times, 

 and, finally, on the left for the ninth test and on the right for 

 the tenth. This series was therefore a decidedly more severe 

 test of the animal's ability to discriminate white from black 

 and to choose the white box without error than were any that 

 had preceded it. If my interpretation of the results is correct, 

 it was so much more severe than the ninth series that the 

 process of habit formation was obscured. It would not be 

 fair to say that the mouse temporarily ceased to profit by 

 its experience; instead it profited even more than usually, 

 in all probability, but the unavoidably abrupt increase in 

 the difficultness of the tests was just sufficient to hide the 

 improvement. 



As I have suggested, the plan of experimentation may 

 be criticised adversely in the light of this irregularity in the 

 error curve. Had the conditions been perfectly satisfactory 

 the curve would not have taken this form. I admit this, but 



