Biology Reference
In-Depth Information
to the material processes underlying, respectively, green, blue and
black (Hering,
1878
, pp. 70-126). Accordingly, he presumed that
there were three pairs of opponent material processes: a 'red-green', a
'yellow-blue' and a 'white-black' pair, and that each pair had opposing
metabolic dissimilation and assimilation processes in a 'see-sub-
stance' ('Sehsubstanz'). The red, yellow and white sensations were
correlated with dissimilation processes that reduced the amount of
the see-substance, while the green, blue and black sensations were
correlated with assimilation processes that increased the amount
of the see-substance. In the simplest version, the see-substance was
assumed to consist of three different substances: a 'red-green', a
'yellow-blue' and a 'white-black' see-substance, where each could
generate opposing dissimilation-assimilation processes independ-
ently of the activity of the other two. Hering did not locate these
see-substances in the visual pathway. He simply suggested that waves
of light in the ether generated chemical changes in the retina and that
these changes triggered chemical processes in the optic nerve that
eventually gave rise to chemical changes in the brain. Whether the
see-substance was located only in the brain or also in the optic nerve
and retina, he left undecided (Hering,
1878
, pp. 70-75).
The 'red-green' see-substance could be activated by lights of all
wavelengths, with the exception of pure yellow and pure blue, where
the dissimilation and assimilation processes in the see-substance
were assumed to be of equal magnitude, preventing any change in
amount of substance. The same considerations also applied to the
'yellow-blue' see-substance, except that dissimilation and assimila-
tion in this substance were assumed to be of equal magnitude for
pure red and pure green light.
The 'white-black' see-substance, on the other hand, was
assumed to differ from the two chromatic-related see-substances
in two important respects: (1) the dissimilation and assimilation
processes going on in this substance in darkness were assumed to be
relatively large, and (2) light from the spectrum was assumed to only
produce dissimilation in the stimulated area.
