Biology Reference
In-Depth Information
somewhat displaced towards shorter wavelengths in the 700-573 nm
region and towards longer wavelengths in the 478-440 nm region.
Clearly, in order to account for the scotopic contrast hues
obtained, the opponent colour theory of Hering would have to be
modified, presuming that the points of equilibrium of the red-green
substance (where no disposition for red and green is produced by
pre-stimulation) were displaced towards wavelengths that had a red
valence, while the points of equilibrium of the yellow-blue substance
(where no disposition for yellow and blue is produced by pre-stimu-
lation) were displaced towards wavelengths that had a blue valence
(Stabell & Stabell,
1973
a).
A similar criticism of Hering's colour theory had previously
been presented by G. E. Müller (
1930
) who had suggested that
'Urfarben' may involve complex retinal processing (see
section 5.2.8
and
Fig. 4.1
).
Hering's (
1878
) opponent colour theory also failed in another
important respect. Thus, as noted above, Hering could not distin-
guish between achromatic scotopic and achromatic photopic colours.
Hence, according to his opponent colour theory, one would expect
scotopic and photopic contrast colours to be identical provided that
(1) the pre-stimulation of cones was identical, and (2) the scotopic and
photopic test-stimulations generated identical achromatic colours in
a chromatically neutral state of adaptation.
This prediction was tested but not confirmed. Thus, the scotopic
contrast colours, as compared with the photopic ones, were generally found
to be somewhat displaced towards blue. This displacement was explained
by the suggestion that short-wave opponent cells relative to long-wave
opponent cells were generally somewhat more excited when rods, compared
to cones, were test-stimulated (see Stabell & Stabell,
1994
).
