METHODS OF STUDYING VISION IN ANIMALS 31 



possibility of ready use in daylight, sunlight, or artificial light; 

 naturalness of colors. The latter would seem to be a very 

 important consideration, for colored objects in nature are seen 

 in white light as colored surfaces, as are colored papers when 

 used in daylight or sunlight. 



Defects: Inconstancy of qualities in successive sets of the 

 same manufacture; rapid fading under the influence of strong 

 light; impossibility of changing quality, except by the substitu- 

 tion of another paper; extreme difficulty and inaccuracy of 

 measuring either the w^ave-length or the intensity of the reflected 

 Hght; impossibiUty of getting any desired quality of light. 



As compared with spectral chromatic stimuli those obtained 

 from colored papers are unsatisfactory (a) because they can not 

 be well controlled with respect to color, saturation, and inten- 

 sity (the number of papers is finite) ; (b) because they are not 

 reliable either from day to day or from set to set, and (c) because 

 it is practically impossible to describe them accurately as to 

 color, saturation, and intensity. 



In view of this list of defects, it seems impossible that papers 

 should be extensively used in the future for quantitative inves- 

 tigations of color vision. They are invaluable for rough pre- 

 liminary tests, for class-experiments, demonstration experiments, 

 and, indeed, for all qualitative investigations which do not 

 demand complete control and accurate description of the chro- 

 matic stimuli employed. 



The characteristics of psychologically satisfactory colored 

 papers are enumerated by Titchener. > In the opinion of the 

 writers, spectral light is preferable even to the stimuli from 

 papers which fulfill all of Professor Titchener's requirements. 

 Our reasons for holding this opinion will appear in our descrip- 

 tion and discussion of the method which we recommend for the 

 quantitative investigation of color vision. 



A number of investigations of color vision in animals,' prom- 

 inent among which are those conducted under the direction of 



'Titchener, E. B. Experimental psycholofj^y, vol. I, part II, p. 14. 

 ^ Kinnaman, A. J. Mental life of two Macacus rhesus monkeys in captivity. 

 Amer. Jour. Psychol., 1902, vol. 13. p. 43. 



Cole, L. W. and Long, F. M. Visual discrimination in raccoons. Jour. Comp. 

 Neurol, and Psychol., 1909, vol. 19, p. 657. 



Samojioff, A. and Pheophilaktowa, A. Ueber die Farbenwahrnehmung beim 

 Hunde. Centralb. f. Physiol., 1907, Bd. 21, S. 133. 



