Biology Reference
In-Depth Information
had made another important contribution by attempting to integrate
evidence accumulated within the Newton and Schultze traditions
into a unified theory (von Kries,
1911
). In this endeavour he encoun-
tered a serious problem: no existing theory could adequately account
for achromatic colour sensation. The explanation provided by the
Young-Helmholtz colour theory had long been outdated. Clearly, the
presumption that white sensation was generated by the three primary
cone receptor types activated to about the same degree was challenged
by the fact that the rod receptors also mediated achromatic sensation.
Furthermore, it had been found that
monochromatic
spectral lights
could give rise to colourless sensations under daylight conditions
when the size of the test field was very small, and also when the test
stimulus was exposed in the far peripheral retina (von Kries,
1911
,
pp. 430-432). Hence, a more comprehensive theory was called for.
In his attempt to provide a more adequate explanation of
achromatic colour sensation, von Kries (
1911
) presumed that the white-
related process could be provoked by two different
centrally
located
mechanisms operating more or less independently of each other: the
cone-related mechanism, with a tripartite structure, generating both
chromatic and achromatic sensations; and the rod-related mechanism,
with a unitary structure, reacting to different wavelengths in a
qualitatively homogeneous manner, giving rise to achromatic vision
only. Thus, day and night vision were thought to be special modes
of vision based on separate and distinct parts of the visual organ as a
whole (see von Kries,
1911
, p. 395).
As revealed by the following quotation, however, von Kries
was keenly aware of the fact that important problems remained to be
solved, particularly with regard to the complex cone mechanism:
… it may be considered as extremely probable that the organisa-
tion in three components assumed in the Helmholtz theory does
not apply to the organ of vision as a whole, but only to those parts
that are directly exposed to the action of light and a more or less
extended series of parts connected with them; and that, on the other
