DISCRIMINATION OF SIZE AND FORM IN THE RAT 



323 



The other rats were slower in learning and required from 600 

 to 800 trials. When they had learned the problem they were 

 given control series similar to those outlined in table VIII, but 

 in this case the results were quite different. Changes in the 

 relative brightness of the passages and forms did not affect the 

 accuracy of the reaction, while reduction of the difference in 

 size caused an increase in the per cent of error. In order to 

 make certain that the rats were not reacting to the movements 

 of the experimenter a test series was given by another person 

 and although the animals were excited by the change they still 

 made above 70 per cent of correct choices. 



TABLE IX 

 Discrimination of Size. Brightness Factor Eliminated 



EXPERIMENT 9 



As soon as definite evidence of size discrimination was ob- 

 tained an attempt was made to determine how small a differ- 



