Biology Reference
In-Depth Information
12
Mechanisms of chromatic rod
vision in scotopic illumination
12.1 All principle hues may be observed in
scotopic vision
A test of the prediction was carried out by Stabell and Stabell (
1965
).
The successive phases of the experiment were as follows: (1) Dark
adaptation for 30 min. (2) Pre-stimulation extrafoveally for 30 s using
one of several colour filters in front of the eye at an intensity 1 log
unit above the specific-hue threshold measured for the filter used.
(3) Dark adaptation for 30 s. (4) Test stimulation at scotopic intensity
levels in the pre-stimulated area using a green monochromatic test
light.
Pre-stimulation with a red colour filter produced a blue colour
upon the scotopic test stimulation, a yellow pre-stimulation filter
produced blue or blue-violet, a green filter, blue-violet or violet, while
blue and blue-green filters did not produce any chromatic effect upon
scotopic test stimulation.
The reason for the failure to produce red, yellow and green
scotopic contrast colours soon became apparent in a follow-up
study where it was found that by increasing the level of chromatic
adaptation (i.e. increasing the time of pre-stimulation, reducing the
time interval between pre- and test stimulation, and increasing the
size of the pre- and test-fields) scotopic red, orange and green colours
could be produced. Thus, pre-stimulation with a green-blue colour
produced a red colour upon test stimulation at scotopic intensi-
ties, a blue colour produced orange, and a purple colour produced
a blue-green colour. Furthermore, it was found that blue and green
scotopic contrast colours could be produced by simultaneous contrast
where the inducing field was illuminated by a deep-red light (see
Stabell,
1967
a).
