T/ie Sense of Sight: Brightness Vision 95 



secondary coil of a Porter inductorium whose primary coil 

 was in circuit with a No. 6 Columbia dry battery. In the 

 light of preliminary experiments, made in preparation for 

 the tests 'of vision, the strength of the induced current re- 

 ceived by the mouse was so regulated, by changing the posi- 

 tion of the secondary coil with reference to the primary, that 

 it was disagreeable but not injurious to the animal. What 

 part the disagreeable shock played in the test of brightness 

 vision will now be explained. 



An opportunity for visual discrimination by brightness 

 difference was provided by placing dead black cardboard at 

 the entrance and on the inside of one of the electric-boxes, 

 as shown in Figure 14, B, and white cardboard similarly in 

 the other box. These cardboards were movable and could 

 be changed from one box to the other at the will of the experi- 

 menter. The test consisted in requiring the mouse to choose 

 a certain brightness, for example, the white cardboard side, 

 in order to return to the nest- box without receiving an 

 electric shock. The question which the experimenter asked 

 in connection with this test really is, Can a dancer learn to 

 go to the white box and thus avoid discomfort? If we 

 assume its ability to profit by experience within the limits of 

 the number of experiences which it was given, such a modi- 

 fication of behavior would indicate discrimination of bright- 

 ness. Can the dancer distinguish white from black; light 

 gray from dark gray; two grays which are almost of the 

 same brightness ? The results which make up the remainder 

 of this and the following chapter furnish a definite answer to 

 these questions. 



To return to the experimental procedure, the mouse 

 which is being tested is placed by the experimenter in the 

 nest- box, where frequently in the early tests food and a 

 comfortable nest were attractions. If it does not of its own 



