Biology Reference
In-Depth Information
an achromatic light in the same area, the achromatic light appears
greenish. In this case, the green colour observed was explained by
Hering in a straightforward manner by the assumption that the
sensitivity of the 'red' dissimilation process compared to that of
the 'green' assimilation process was reduced in the stimulated area
during the pre-stimulation period.
4.6 Contributions of Hering
It can be seen that Hering agreed with Goethe that opponency is a
fundamental characteristic of colour phenomena, but in addition he
also postulated an opponency of underlying material events. This
clearly opposes the suggestion of the Young-Helmholtz colour theory
(1896) that the nervous pathways, from receptor to brain, are like
isolated telegraph wires with no interaction between different neural
processes.
With hindsight, we can see that Hering pointed in the right
direction. Indeed, his ingenious ideas deserve to be ranked as
the fifth
major paradigm shift in vision research
. Yet, his phenomenological
approach has two serious weaknesses. Firstly, the phenomenological
report gives conclusive information only on the
relative
values of the
underlying material processes. In the case of the successive contrast
experiment, for instance, where the red pre-stimulation produced
a green after-effect upon test stimulation, Hering could reasonably
presume that the sensitivity for dissimilation relative to that of
assimilation was reduced in the red-green see-substance. But even
if this presumption is accepted, he was not in a position to decide
whether the sensitivity for assimilation in the test area increases or
remains constant. The sensitivity might even decrease, although less
so than for dissimilation (Hering,
1878
, p. 86).
Secondly, presupposing that the psychophysical maxim of
Mach (
1865
) is valid, one may draw legitimate conclusions about
material processes directly underlying consciousness, but not about
visual processes prior to the final material process. This limitation of
the approach is clearly revealed when the conditions are arranged so
