Biology Reference
In-Depth Information
illustrated by G. E. Müller's model for the r-process in the red-green
substance presented in the following simplified diagram:
Red ligh� → photon-absorption process P1 → A → r → g
As can be seen, red light activates P1 that increases the turnover
of the base substance A to a substance r. As the amount of this
second substance increases, it is transformed into a third substance
g. The change from r to g generates the r-process, while the g-process
is generated when the process goes in the opposite direction, from
substance g to substance r. The r substance may then be transformed
back to A.
This complex and highly speculative colour theory of the rod and
cone systems may be seen as an attempt to cover all the major facts of
colour vision available. The theory deviates markedly from both the
Young-Helmholtz and the Hering colour theories. At variance with the
Young-Helmholtz theory, it involves both opponent colour processing
and rod activity, while in opposition to Hering's theory, it involves rod
activity and operates with a triplex photochemical cone mechanism.
Moreover, in contrast to Hering, who assumed the so-called 'Urfarben'
(pure red, pure yellow, pure green and pure blue) to be correlated with
homogenous, uncompounded material processes, G. E. Müller (
1930
)
assumed that these colours were determined by complex processes in
the outer segments of the cones. A
pure yellow colour
of the Hering
type, for example, would be determined by both P1 and P2 and, hence,
by r-, y- and g-processes in the outer segment of the cone receptors.
5.3 E va l uat i of n of f G . E . M ü l l e r ' s c of l of u r
theory
With hindsight, it seems clear that G. E. Müller's broad speculation
on the actual colour-related processes in the visual pathways, based
on insufficient evidence, did not entail a new, deeper understanding
of rod and cone functions. Indeed, alternative theories that explained
the same colour phenomena equally well were developed. An
interesting example is the colour theory presented by Schjelderup
