COLOR BLINDNESS OF CATS 137 



flicker value differs slightly from yellow the presence of green 

 enables discrimination. Add a "tint" and confusion takes place. 

 Brighten the color to the next brighter tint and the result is 

 still confusion. Thus, 



Here the effect of the tints overbalances the effect of the 

 green and produces confusion. Elsewhere the darkening effect 

 of the colors is so enormous that the tints and shades have 

 relatively slight effect on the cat. This was to be expected, of 

 course, if the curve derived ' from experiments with grays is 

 approximately correct. Altogether the results derived from 

 experiments with grays and with colors are surprisingly consistent. 



USEFULNESS OF FLICKER EQUIVALENTS 



The great drawback of our experiments was the time they 

 consumed in trying so long a list of colors. Could this, by any 

 means have been shortened ? In our work with colors had we 

 tested for yellow only those of its flicker equivalent, we should 

 have discovered five of the twelve confusions. Had we explored 

 one-half of a flicker unit on each side the yellow, we should have 

 discovered five more confusions, and had we explored for two 

 and one-half units on either side, we should have found them all. 

 To have done the same thing with blue we should have had to 

 explore a range of fourteen units, but using only the exact flicker 

 equivalent would have found for us one of the four confusions 

 with blue. 



Exploring a range of three flicker units on either side the green 

 would have discovered all the confusions. Using the exact flicker 

 value of the green would have revealed one confusion. Using 

 the exact flicker-equivalent of red would not have yielded any 

 one of the confusions, (It is true only of red.) but using one half 

 of a flicker unit on either side of the red would have brought 

 out one confusion. Two flicker units would have shown three 

 of the nine confusions, five units would have shown six, fifteen 

 flicker units would have shown them all. 



Even exploring a range of fifteen flicker units on each side of 



