82 CHARLES A. COBURN AND ROBERT M. YERKES 



of his subject. At no time during the investigation did the 

 crows give evidence of noticing the experimenter when they 

 were reacting. 



The remaining features of the apparatus will be mentioned 

 in connection with the following brief description of the exper- 

 imental procedure. In preparation for a series of trials, the 

 experimenter opens each of the exit doors and places in each 

 food container a small bit of milk-soaked bread. He then closes 

 the exit doors, thus covering the food, and takes his place at K. 

 He next opens a group of entrance doors. Let us suppose, as 

 is shown in figure 1 E, that the doors numbered 1 to 6 are opened, 

 and, further, that the compartment which may be designated 

 as the correct one is the first at the subject's left, that is number 

 1. Having made these preparations, the experimenter, by means 

 of the proper cord, opens the main entrance door F, and the 

 bird, either by walking up the approach board I or by alighting 

 on the approach board L, on a level with the entrance door, 

 is immediately able to enter the reaction chamber H, by way 

 of the alley R. By two wire partitions which appear as dotted 

 lines in figure 2, it is forced to walk straight ahead until it reaches 

 the center of compartment H. It may then face and, if it so 

 chooses, directly approach the central compartment of the mul- 

 tiple choice box. But under the circumstances, with entrance 

 doors 1 to 6 open, it would naturally swerve toward the left. 



In case it enters compartment 1, the experimenter quickly 

 and noiselessly closes the entrance door after it, by releasing 

 the appropriate cord, and immediately thereafter, opens the exit 

 door of the compartment by pulling on the appropriate cord. He, 

 thus, with one hand prevents the retreat of the bird from the 

 compartment and with the other uncovers the food, so that the 

 bird may obtain the reward for a correct reaction. As soon as 

 the food has been swallowed, the crow steps out of the compart- 

 ment, the exit door is closed by the experimenter, and the bird 

 either immediately, or at the experimenter's pleasure, is allowed 

 to return to the fly C by way of the main exit door G. 



If, instead of choosing the right compartment, the crow enters 

 some other one, the procedure is different. Immediately upon 

 its entrance, the experimenter closes the entrance door. He 

 then, with a stop-watch, measures a definite period during which 

 the bird is confined in the compartment. This period was varied 



