224 
PSYCHOLOGY: A. C. HARDY 
Proc. N. a. S. 
For red light (6776 A°) the persistence of vision in the fovea was 0.0209 
second. The persistence for points lying at equal distances from the 
fovea was found to be very nearly the same. That is, if lines are drawn 
showing equal values of the persistence of vision, they appear to approxi- 
mate circles with the fovea at the center. The deviation from the circle 
is enough to make them resemble the limits of the color fields for the retina. 
The circles are in every case flattened so that the major axis of the re- 
sulting ellipse is horizontal. The persistence is less for the fovea than for 
any other part of the retina, and there is a steady increase in the per- 
sistence nearly proportional to the distance from the fovea. The maxi- 
mum value observed occurs on the nasal side of the retina at about 38° 
from the fovea. The persistence is slightly greater on the nasal side than 
on the temporal. The maximum value is 0.109 second. 
For the yellow-green (5310 A°) very similar results were obtained. 
The persistence of vision for the fovea is 0.0179 second and is less than 
any other portion of the retina. The lines of equal values of the per- 
sistence are ellipses with the major axes horizontal. The persistence 
is still slightly greater on the nasal side. The maximum value is observed 
to occur for the same region as for the red light but the maximum in this 
case is 0.0339 second showing that the persistence is more nearly constant 
over the whole retina. 
For the blue-violet (4631 A°) the persistence of the fovea is 0.0346 
second. There is little change in the persistence for different portions 
of the retina. The region which gave a maximum value for the red and 
the yellow-green, now gives a value of 0.0339 second or slightly less than 
the fovea. The maximum occurs about 7° from the fovea on the nasal 
side and is 0.0401 second. The minimum of 0.0305 second occurs on 
the temporal side at an angle of 35° from the fovea. The change between 
the maximum and minimum amounts only to the difference between 
V25 second and V35 second. For the blue-violet light used, the persistence 
is very nearly constant over the whole retina. 
It will be noticed that these values for the persistence are smaller than 
those which are sometimes quoted. The values given here represent the 
time required for the impression on the retina to fade sufficiently to be 
noticed when compared to a fresh stimulus. They do not represent the 
time for the total extinction of the retinal image. 
The above results were obtained at the laboratories of the Department of 
Physics at the University of California. 
' Physic. Rev., 28, 1909 (48). 
2 Sir William Abney, Researches in Color Vision, p. 190, et. seq. 
^ See Abney, loc. cit., p. 181. 
