Biology Reference
In-Depth Information
complementary colours. Assuming that rod signals may feed into
these cortical cells, the colour after-effect seen in scotopic illumina-
tion could be accounted for.
14.4 Contribution of S. Buck and co-workers
A more recent and systematic study of the effect of rod activity on
colour perception has been performed by Steven Buck and colleagues.
In a series of experiments, they attempted to single out multiple rod
influences on hue (Buck
et al
.,
1998;
Buck
et al
.,
2000
; Buck,
2001
;
Knight & Buck,
2002
). In the study, wavelength of a circular 8° test
field centred 7° extrafoveally was varied between 420 and 630 nm in
10-nm steps. For each wavelength tested, the observers described the
appearance of the test stimulus by using two of the four basic hues
(red, green, blue and yellow) assigning a percentage to the relative
strength of each component hue, so that the sum of the percentage
equalled 100% for each trial. Following the determination of the hue
percentages, the observers also assigned a percentage to the relative
strength of the
saturation
of the test stimulus.
In order to measure the influence of rod signals on colour
appearance, the colour scaling was obtained both in a completely
dark-adapted eye and during the cone-plateau period of the long-term
dark-adaptation curve, i.e. under conditions that, respectively,
maximized and minimized rod contribution. The test intensity was
mesopic, so that both rods and cones could be activated by the test
stimulus when in the dark-adapted state.
Also, they measured time-dependent changes in rod influence
on hue. A scotopic background field was flashed on for 2 or 6 s, while
a mesopic test flash of 30 ms was presented at 1 or 5 s after the onset
of the scotopic background flash (Knight & Buck,
2002
).
Most importantly, the experiments performed provided strong
evidence for a variety of different time patterns of rod influences on
hue. Evidence was obtained for a so-called 'fast' rod influence that
enhanced green relative to red and a so-called 'slow' rod influence
that enhanced short-wavelength red relative to green and also blue
relative to yellow.
