302 ALDA GRACE BARBER 



was a signal for response. The third stage of the learning was 

 one in which hesitancy was manifested when the stimulus came. 

 The rat would turn his head in all direct ons before deciding 

 in which direction to go. During the rest of the reactions 

 (embracing the fourth division of the learning of the association) 

 the attention was placed predominately upon the proper stimulus. 

 The progress during this stage was an increase in accuracy. 

 B. Control period — Now that the first question of the problem 

 has been answered, i. e., can the white rat localize noise, the 

 other two questions arise: (1) Is this an auditory reaction ? 

 (2) What factors determine accuracy of response ? Twelve 

 different control tests were put in to investigate these points. 



a. Visual controls — To eliminate visual cues which might 

 have been gotten from the operator, a screen of black cloth was 

 fastened around the table, as has been indicated. Furthermore, 

 the operator constantly stood so that the angle from the section 

 tapped varied from trial to trial. A conclusive proof that the 



' rat was not using the operator as a guide occurred elsewhere, 

 e. g., in control III. when the sound of a vibrating tuning fork 

 was used as a stimulus. Here the rat broke down entirely. 

 If the rat had been reacting to a visual cue or even to any type 

 of cue from the experimenter, the response w T ould have been 

 as accurate as before. 



b. Olfactory control (I) — As the rats frequently stood up and 

 sniffed in all directions before responding, odor was considered 

 a possible cue in that food was always held in the experimenter's 

 hand. Accordingly, small pieces of bread soaked with milk 

 (the food used as the reward) were laid along the edges of the 

 box in order to distribute the odor uniformly. The reaction 

 remained normal. The odor appeared possibly to stimulate the 

 rats in quickness of response, but no confusion arose. To serve 

 as a further check, throughout the experiment the food was 

 held at different angles to the point of stimulation. Final proofs 

 were : ( 1 ) that the rat would respond accurately when the ex- 

 perimenter had no food in his hand; and (2) that the reaction 

 broke down when the auditory stimulus suffered certain changes 

 as recorded below. 



c. Kinaesthetic-tactual control (II) — Another possible guiding 

 cue was the kinaesthetic-tactual sensation gotten from the 

 vibrations in the floor of the apparatus box when the stimulus 



