DISCRIMINATION OF SIZE AND FORM IN THE RAT 



321 



used as stimuli is equal per unit area, but since the flashed 

 glass forms a total diffusing surface it acts as a direct source 

 of illumination for the two passages. Consequently the bright- 

 ness of the passages differed appreciably, being directly propor- 

 tional to the areas of the circular openings. For the experi- 

 menter the difference in size between the stimuli was so much 

 more evident than the difference in brightness that this latter 

 was not considered at the beginning of the experiment. 



Rats Nos. 4, 5 and 6 were used, with food, punishment, and 

 food and punishment as motives. After 200 trials all began 

 to show evidence of discrimination, but it required more than 

 500 trials to establish the association thoroughly. Even after 

 700 trials No. 5 was very uncertain in her reactions. Table VII 

 shows the daily percentages of error in this experiment. 



TABLE VII 



Under the conditions of the experiment it was uncertain 

 whether the animals were reacting to the difference in size of 



