The Sense of Sight: Color Vision 169 



Throughout series 9 the brightness value of the left box re- 

 mained 3 candle meters, that of the right side 1800 candle 

 meters. Number 2 was so badly confused by this change 

 that his mistakes in this series numbered 12 ; No. 5 made 

 only 4 incorrect choices. Then series after series was given 

 under widely differing conditions of illumination. The ex- 

 pression "mixed values," which occurs in Table 26 in 

 connection with series 14 to 22 inclusive, means that the 

 brightnesses of the green and the red boxes were changed 

 from test to test in much the way indicated by the sample 

 series of Table 25. In view of the results of these 22 series, 

 320 tests for each of two mice, it is evident that the dancer 

 is able to discriminate visually by some other factor than 

 brightness. What this factor is I am not prepared to say. 

 It may be something akin to our color experience, it may be 

 distance effect. No other possibilities occur to me. 



Table 26 shows that discrimination was relatively easy for 

 Nos. 2 and 5 with green at 3 candle meters and red at 1800. 

 That their discrimination was made on the basis of the greater 

 brightness of the red, instead of on the basis of color, is in- 

 dicated by the results of the brightness check series 8a. 

 Increase in the brightness of the green rendered discrimina- 

 tion difficult for a time, but it soon improved, and by no 

 changes in the relative brightness of the two colors was it 

 possible to prevent correct choice. 



In addition to giving point to the statement that red ap- 

 pears darker to the dancer than to us, the above experiment 

 shows that the animals depend upon brightness when they 

 can, and that their ability to discriminate color differences is 

 extremely poor, so poor indeed that it is doubtful whether 

 their records are better than those of a totally color blind 

 person would be under similar conditions. Surely in view of 

 such results it is unsafe to claim that the dancer possesses 

 color vision similar to ours. 



