VISION IN THE MOUSE 565 



The order of preference is obtained by comparing the numbers 

 which represent the preference-value of each color. Such a number 

 may be obtained by adding together the number of times a 

 color is chosen first X 4, the times it is chosen second X 3, the times 

 chosen third X 2 and the number of times chosen last. Thus for 

 K, the preference value of blue is: 6x4+3x3 + 10x2 + 5 = 



58. In the same way the preference value of red is found to be 

 67, of yellow 66, and of green 49. For X the values are: blue 



59, red 67, yellow 70, and green 44. 



This preference-value is useful in showing the const ancy through - 

 out the series. Thus the whole set of results for X was divided into 

 halves and the preference values for each half were as follows: 



Conclusions: The mouse can learn to associate food or elec- 

 tric shock with red or blue objects. The connections thus formed 

 may be disassociated and an association formed with another 

 color. 



In albino mice, color discrimination is poor. 



Red and yellow are preferred to blue and green, and of the latter 

 two, blue is preferred to green. 



Whether the discrimination involved is true color discrimina- 

 tion, after the fashion of that in human beings, can not be dis- 

 covered, but we may call it color discrimination so long as it 

 answers the practical purposes of the mouse in distinguishing 

 between such objects as it is likely to meet with in its habitat. 



If it be claimed that colors of the red end of the spectrum are 

 preferred by the black mice because they seem to them the darker, 

 we would suggest a correlation with the results obtained in the 

 matter of the preference for gray yarns (see pp. 556). The same 

 mouse, X, appeared in the two experiments. White and black 

 were both preferred to either of the intermediate grays. 



THE JOURNAL OF COMPARATIVE NEUROLOGY AND PSYCHOLOGY. VOL. 20, NO. 6. 



