PSYCHOLOGY: R. M. YERKES 
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nation and habit formation, has proved remarkably satisfactory and 
has yielded valuable results in numerous investigations. 
It has thus far been demonstrated that the ring-dove may be trained, 
although rather laboriously, to appropriate forms of achromatic dis- 
crimination, and that similarly it may be used by the sensory habit 
method for studies of chromatic discrimination. Experiments with two 
individuals demonstrate the existence of the Purkinje phenomenon in 
this organism. This was done by use of a red of 630 fxfi and green of 
505 fjLiJ,, approximately equal in energy. In general illumination, the 
two stimuli seemed to be of approximately equal stimulating value for 
the female, whereas for the male, the red was the more stimulating. 
A moderate degree of adaptation to darkness reversed this relation, 
the green then being much more stimulating than the red for the female, 
whereas the two were approximately equal for the male. 
This observation indicates at once changing sensitiveness with adap- 
tation and an individual, or more likely, a sex, difference in the stimu- 
lating value of the colors in question. Apparently the male ring-dove 
is markedly more sensitive to red than is the female. 
This report of work which is still in progress may be concluded with 
a word concerning the significance of temperamental differences. In the 
doves in question, these were very striking indeed and are responsible 
for certain important features of the results obtained. The female was 
tame and timid; the male, on the contrary, somewhat wild and bold. 
In view of these facts, it is not surprising that the male proved an 
excellent subject for the sensory habit method, whereas the female was 
much less satisfactory. The suggestion from the work is that tempera- 
ment should be analyzed by the student of animal behavior and its 
various important components separately studied and accurately meas- 
ured so that our animal subjects may be described with respect to the 
same, even although the investigation especially in point be one on 
color vision or some other aspect of reaction or experience which might 
at first seem unrelated to 'temperament.' 
1 See Yerkes, Robert M. and Watson, John B, Methods of studying vision in animals. 
Behavior Monographs, vol. 1, no. 2. (1911). 
2 Robert M. Yerkes. The dancing mouse. New York, 1907. 
3 This work was made possible by a grant from the Bache Fund of the National Academy, 
for which the writer takes this opportunity to express his hearty thanks. 
