Biology Reference
In-Depth Information
The theory that the human retina contains two basically different
types of photoreceptor (rods and cones) that function independently
of each other and operate under different conditions, giving rise to
qualitatively different colour sensations, brought about a paradigm shift
within vision research. Thus, the theory eventually became generally
accepted and introduced a fundamentally new understanding of visual
functioning. Schultze's theory also generated new fundamental questions
with regards to differences and similarities as well as possible interac-
tions between the information processing of the two receptor systems.
Obviously, answers to these questions presuppose knowledge of
the characteristics of both the rod and cone mechanisms. Knowledge
about basic characteristics of cones had long been accumulated within
the Newton-Young-Maxwell-Helmholtz tradition (in the following
referred to as the 'Newton tradition'), but little was known about
rod functioning at the time Schultze (
1866
) published his important
paper. The ignorance of the functioning of the rod receptor system is
clearly revealed in Helmholtz's 'Handbuch' (
1867
, p. 214). Actually,
at this developmental stage of research, he could find no conclusive
evidence of
any
rod contribution to vision. No wonder, then, that the
theory of Schultze did not gain immediate general acceptance.
In the following years, however, knowledge about basic rod
functions developed rapidly within the Schultze-Boll-Kühne-Parinaud-
König tradition (in the following termed the 'Schultze tradition')
and strong evidence supporting and extending Schultze's theory
emerged.
Early in the twentieth century, then, his theory had become
generally accepted. Von Kries, a leading authority on vision, was
its strongest defender and also coined the term 'Duplizitätstheorie'
(duplicity theory; see von Kries,
1929
). Perhaps his most important
contribution, though, was his attempt to integrate the evidence
accumulated within the Newton and Schultze traditions into a more
comprehensive duplicity theory (von Kries,
1911
).
Yet, the development of the duplicity theory was also profoundly
influenced by a third research tradition (in the following termed the
