RESPONSES TO MONOCHROMATIC LIGHT 3 



While there is nothing wonderful in the formation of this 

 discrimination habit, it does become significant when we con- 

 trast it with our failure to get such a habit set up with the 

 yellow and blue (see page 7). If modern color theories have 

 any phylogenetic reference at all we would expect the formation 

 of the red-green habit to be much slower than that of the yellow-' 

 blue. Taken at their face value the records invite three possibil- 

 ities of interpretation : — 



1st, the animals are discriminating upon the basis of differ- 

 ence in wave length; 



2nd, upon the difference in intensity between the two lights; 



jrd, only one stimulus is effective (for whatever reason) and 

 no real discrimination is involved. It is possible that the red 

 chosen lies outside the spectrum of one or both animals. On 

 this hypothesis the habit might be formed easily. Yerkes, 1 

 Washburn, 2 Hess, 3 and Watson, 4 have all remarked upon the 

 apparent low stimulating power of red light. Another fact 

 which must be taken into consideration in connection with the 

 two stimuli discrimination method, which may have some bear- 

 ing upon the present work, is the one discussed by Dr. Clara 

 Jean Weidensall. Her results were reported at the Washington 

 meeting of the American Psychological Association (December, 

 191 1). In her work on the discrimination of two grays differ- 

 ing greatly in intensity it was shown that, usually, only one 

 stimulus is effective. In other words it is possible to get appar- 

 ent discrimination between two stimuli where no real discrim- 

 ination is involved. A further discussion of this point will be 

 given upon page 6. 



These three possibilities of interpretation were not clearly 

 foreseen in the early stages of the experiments. Two things 

 lead us to a favorable consideration of the view that the red 

 lay outside the animals' spectrum. (1) The fact that, in the 

 control experiments (to be cited below), the complete elimina- 

 tion of red failed to change the responses of the animals, and 



1 Yerkes, Robert M. The Dancing Mouse, New York, 1907. 



2 Washburn, M. F. and Abbott, E. Experiments on the Brightness Value of 

 Red for the Light Adapted Eye of the Rabbit. Jour. Animal Behavior. 1912 , 

 vol. 2, pp. 145-180. 



3 Hess, C. Experimentelle Untersuchungen zur vergleichenden Physiologie des 

 Gesichtssinnes. Arch. f. d. ges. Physiol. 1911, Bd. 142, S. 405-446. 



4 Watson, J; B. Some Experiments Bearing Upon Color Vision in Monkeys. 

 Jour. Comp. Neurol, and Psychol. 1909, 1, vol. 19, pp. 1-28. 



