312 K. S. LASH LEY 



sists, essentially, of a starting-room, a, leading by a door into 

 the discrimination compartment, c, in which the choice of two 

 passages is offered to the animal. The forms to be discrim- 

 inated are placed at the ends of the passages so that the animals 

 must go directly toward them in order to reach the doors lead- 

 ing to the food compartments, g, g. The forms consist of metal 

 plates, pierced by suitable openings and backed by opal flashed 

 glass. They are fastened in a wooden frame, h, which may be 

 lifted out of the box and inverted in order to transpose the 

 stimuli. Sixteen candle power, carbon filament lamps, placed 

 in a compartment, f, behind this frame, illuminate the forms 

 brightly. The passages, d, d, are wired with an electric grill 

 by which punishment may be administered. 



Food, given in the compartments g, g, after a correct choice, 

 and punishment, given in the passages after an incorrect one, 

 were used as motives for discrimination. The rats were allowed 

 to run from the starting box to the food compartment and were 

 then lifted back to the starting box. In the first experiments 

 punishment did not seem to give good results and it has been 

 used as a motive only where indicated in the descriptions of 

 experiments. 



Since none of the work was quantitative, no regular system 

 was followed in reversing the stimuli, but care was taken that 

 the number of times that the positive stimulus was exposed 

 in each passage should be equal in any given series of trials. 

 In spite of this the animals, especially those which were pun- 

 ished, showed a. strong tendency to form position associations, 

 going again and again through one of the passages even when 

 severely punished. 



At different times during the experiment some of the rats 

 learned to react to the noise made in reversing the forms, to 

 the position of the experimenter during the trials, and possibly 

 to variations in the time between successive trials. They usu- 

 ally tended to avoid the passage in which they had last been 

 punished, and learned readily to follow simple rhythms of 

 alternation. In experiments with Rat No. 6 it was customary 

 to electrify the punishment grill before admitting the animal to 

 the discrimination compartment, and there is some evidence 

 that she learned to test the grill with her vibrissae before ven- 

 turing over it. 



