PSYCHOLOGY: R. M. YERKES 
117 
Such a formula would indicate to the examiner that X is especially 
deficient or peculiar in affective characteristics. 
6. The measuring scale shall be arranged on four pages, those measure- 
ments deaHng with one of the four categories of mentaHty occupying 
a page. On each sheet, the several measurements shall be arranged 
in order of increasing difficulty, and the same shall hold of the order 
of arrangement within any given part of the series, that is, any one of 
the twenty types of measurement. 
7. The measurements shall be chosen, so far as possible, with a view 
to simplicity of materials and ease and uniformity of observation. 
8. The scale shall be dependent for its value upon safely determined 
norms. 
COLOR VISION IN THE RING-DOVE (Tutur risorius) 
By Robert M. Yerkes 
PSYCHOLOGICAL LABORATORY. HARVARD UNIVERSITY 
Presented to the Academy, December 4, 1914 
The psychophysiological literature, both naturalistic and experiental, 
on color vision in infra-human animals, is surprisingly extensive. But 
even more surprising is the extreme uncriticalness of the methods which 
have been employed. A realization of this condition of affairs within 
the past decade led simultaneously to the development, by C. Hess, in 
Europe, and by R. M. Yerkes in association with J. B. Watson, and 
more recently by G. H. Parker, in America, of spectral methods for the 
comparative study of color vision. These methods enable the experi- 
menter to measure and control his stimuH in their various aspects and 
to observe with reasonable accuracy organic response to specific stimuli. 
The method now in use in this country, developed by Watson and me, 
may be named from the nature of the stimulus and the form of reaction 
demanded ^the method of discriminating spectral stimuli.' It involves 
the use of a special form of prism spectrometer with devices for selecting, 
spacing, reversing, and displaying any two portions of the spectrum, 
with means of controlling the selected stimuH quahtatively and inten- 
sively, of measuring them in photometric and energy units, and of so 
presenting them to the reacting animal that it may, if capable of so 
doing, recognize them and react appropriately.^ 
Until very recently, it has been the prevalent opinion even among 
scientific persons that many, if not most of the vertebrates, possess 
fairly highly developed color vision, which in many instances is closely 
