DISCRIMINATION OF SIZE AND FORM IN THE RAT 315 



The average percentage of error is slightly below 50 and this 

 may be explained by the training method employed, which fre- 

 quently allowed the animals to make several correct trials be- 

 fore the stimuli were transposed. The effect of this method 

 appears in the first 500 trials (46.8%) but disappears in the 

 last 500 (49.8%), in which an effort was made to eliminate all 

 secondary criteria by which the animals might regulate their 

 reactions. 



Since the rats learned to react to sound and to other acci- 

 dental stimuli it is certain that they were not indifferent to the 

 motives provided and that their failure to respond to the visual 

 stimuli was not due primarily to a fault in the technique of 

 experimentation. The cause of their failure is to be sought in 

 the nature of the visual stimuli, or in some defect in their visual 

 apparatus. After a few hundred trials the animals became 

 almost machine-like in their actions, the choice of the passage 

 taken usually having a definite relation to the success or failure 

 of the preceding trial. They rarely paused in the discrimination 

 compartment or passages and did not seem to attend to the 

 stimuli. It seemed, then, that the failure might be explained 

 by this inattention and a second experiment was therefore un- 

 dertaken in the hope of training the rats to attend to the illumi- 

 nated areas. 



EXPERIMENT 2. MOVING STIMULUS 



Apparatus: The discrimination box with the forms as in 

 experiment 1. A revolving sector was introduced into one of 

 the light compartments (figure 1, f) between the light and the 

 metal form. The sector was composed of two vanes, each of 

 45 degrees, and was turned by a small motor at a speed of five 

 revolutions per second, thus interrupting the light 10 times per 

 second and producing a regular flickering. It was expected 

 that this flickering light, simulating movement, would hold the 

 animal's attention, and that, by decreasing the size of the sector 

 and increasing its speed, the factor of movement might be 

 gradually eliminated and the attention transferred to the differ- 

 ence in form. The square and circle were retained as stimuli 

 and the sector was kept constantly behind the square, the forms 

 being reversed as usual. 



In the first series of trials given after the introduction of the 

 sector all the rats showed evidences of fear, refusing to go toward 



