68o "Journal of Comparative Neurology and Psychology. 



If the raccoons were discriminating the colored papers by bright- 

 ness differences alone these differences must have been very near 

 their difference threshold for brightness, for they learned very slowly 

 to make the discriminations. But the brightness difference between 

 some pairs of these papers was greater than that between other pairs, 

 since some of the colors were inexact matches for the gray. If, then, 

 we were not below their difference threshold with the exact matches, 

 but only near that threshold, the inexact matches should not have been 

 chosen at all, or at least, feioer mistakes should have been made on 

 inexact matches. As a fact almost an equal number was made on 

 each class, as shown by the following table. 



TABLE 24. 



The total averages for exact and inexact matches are practically 

 the same. This seems to be excellent evidence that we were below 

 the animal's difference threshold for brightness. If such was the 

 case, they must have been discriminating by color differences alone. 

 In this average are included all the colors, both dark and light, so 

 that the figures apply to the whole range of papers used. 



When Yerkes tested the dancing mouse by means of colored papers 

 the records showed at once that the dancer cannot distinguish green 

 from blue, nor violet from red.^^ As the raccoons have given no case 

 of failure to discriminate colored papers, it would seem from this 

 comparison that their vision is more nearly like that of human beings 

 than like that of the dancing mouse, or the common mouse. ^^ 



Table 25 gives the average number of the raccoons' errors on 

 each wrong color and the number of their errors on each gray. Of 

 course, records for Gray 5 which were made after we had used it 



^'Yerkes, R. M. The claucing mouse, pp. 147 and 149. 1907. 

 =^Waugh, K. T. The role of vision in the mental life of the mouse. Doctor's 

 thesis, Harvard University. 1907. (Unpublished.) 



