NOTES 



THE DISCRIMINATION METHOD 



The discrimination method, as described by me in the " Dancing Mouse " ' 

 :iii<l in greater detail in my report with Watson on " Methods of Studying Vision 

 in Animals," 2 demands, in the light of results which have thus far been obtained 

 with it, certain criticisms. What I have to say at present in connection with the 

 method is intended for the guidance of investigators who may wish to employ it 

 in the study of sensory discrimination or other forms of organic reaction. 



The method, as described in both references, consists, essentially, in the presen- 

 tation to an animal of two objects which differ with respect to one or more char- 

 acteristics on the basis of which the organism may select the one and reject the 

 other. In one form, the method consists in the presentation of two visual areas 

 of like size, form, and brightness whose discriminable difference is color. In 

 another form, it consists in the presentation of visual areas which differ only in 

 brightness, in size, or in form. 



The conditions of discrimination, as thus presented to an animal, are somewhat 

 unnatural, first, because the method is, as a rule, employed in a dark-room, and, 

 second, because the objects to be discriminated differ in fewer respects than do 

 objects which are usually dealt with in nature. Both of these possible objections 

 to the method may be met satisfactorily by the experimenter, for the method 

 may be employed advantageously under widely differing conditions of general 

 illumination, and the objects to be discriminated may be varied in complexity as 

 seems to the experimenter desirable. 



In certain recent investigations with birds and mammals, the method has yielded 

 negative results even after extremely long periods of training. I wish to point 

 out that in some of these investigations the experimenters probably have wasted 

 a considerable amount of time and energy by presenting to their animals visual 

 objects which differ in only one respect: for example, in color, in brightness, in 

 size, or in form. 



It seems fairly certain that in our experiments we should not aim directly at our 

 goal but, instead, begin with conditions which are rather more natural than those 

 demanded for the accurate testing and measuring of any particular kind of visual 

 discrimination by either the "brightness apparatus" or the "color apparatus." 

 In an investigation of the perception of size, for example, it would seem safer to 

 begin by using objects which differ in several respects. Thus the animal may 

 more quickly be brought to attend to the proper objects and be trained to react 

 appropriately. 



Let us suppose that the initial condition of the experiment involved the use of 

 objects which differed in brightness and form as well as in size. Then, just as 



1 Yerkes, Robert M. The Dancing Mouse. New York: The Macmillan Com- 

 pany. 1907. 



2 Yerkes, Robert M. and Watson, John B. Methods of Studying Vision in 

 Animals. The Behavior Monographs. 1911. vol. 1, no. 2. 



142 



