Biology Reference
In-Depth Information
activity rates of the opponent cells, giving rise to a hue approximately
opponent to the hue of pre-stimulation.
The scotopic hue of simultaneous contrast was explained on
the same principle. Thus, selectively chromatic stimulation of the
three types of cone of the inducing field was thought to change the
relative sensitivity of the opponent cells associated with the test area,
producing a disposition for scotopic hue, triggered by test stimulation
of rods (Stabell & Stabell,
1971
c,
1973
a).
12.5 M of d i f i c at i of n s of f H e r i n g ' s of p p of n e n t
colour theory
As can be seen, this explanation of the scotopic contrast colours is
in close agreement with Hering's opponent colour theory. However,
when more specific tests of the theory were applied, predictions failed
in several important respects, as clearly revealed in a series of investi-
gations carried out in the early 1970s where wavelength, intensity
and exposure time of pre-stimulation; wavelength and intensity of
test stimulation; time between pre and test-stimulation; as well as
retinal location of pre- and test-stimulation, were varied (see Stabell
& Stabell,
1973
a). Most importantly, pre-stimulation with primary
yellow and primary blue colours produced, respectively, violet-blue
and orange scotopic contrast hues instead of pure blue and pure
yellow, as would be expected from Hering's theory, and pre-stim-
ulation with primary red (obtained by mixing 700 nm and 470 nm
lights) and primary green produced, respectively, scotopic green-blue
and purple, instead of pure green and pure red. Presuming, in accord
with the opponent colour theory of Hering (
1878
), that an interme-
diate hue sensation involved both pairs of the chromatic opponent
processes and not just one pair, these results indicated that pre-stim-
ulation with a primary hue generated adaptation effects in both the
red-green and yellow-blue substances.
Also, the results showed that the scotopic contrast hue, although
closely similar to the additive opponent hue of the pre-stimulation, was
