Biology Reference
In-Depth Information
Yet, important contributions to the development of the theory
were also made by workers who focused on more limited aspects
of the theory. The most important contributions were provided by
research workers who made penetrating and thorough studies to
uncover the underlying mechanisms of the most basic assumption of
the duplicity theory, namely that rods alone operated in night vision
and cones in day vision.
Schultze (
1866
) could not provide any explanation of this differ-
ence in rod and cone sensitivity, either in photochemical, anatomical
or physiological terms. Following Boll's (
1877
) discovery of the
bleaching and regeneration of rhodopsin, however, important insights
into the sensitivity regulation mechanisms were provided by Kühne
in the nineteenth century and by Hecht, Wald, Rushton, Barlow and
Lamb in the twentieth century. In fact, their contributions may be
seen as a mainthread in the developmental history of the duplicity
theory.
Yet, contributions were also provided by research workers who
presented evidence opposing Schultze's (
1866
) second major assump-
tion that rods mediated achromatic vision only. Indeed, the evidence
offered strongly suggested that the rod system was an important
contributor to chromatic colour vision and that rod signals served
achromatic vision only under scotopic conditions when the eye was
in a dark-adapted and chromatically neutral state of adaptation.
Thus, it was found that (1) rod signals of the primate retina were
transferred to ganglion cells via cone pathways (
Fig. 10.1
) and fed
both spectrally opponent and non-opponent colour cells (De Valois,
1965
; Wiesel & Hubel,
1966
; Daw
et al
.,
1990
; Lennie & Fairchild,
1994
; Wässle
et al
., 1995); and (2) rod signals could give rise to all
sorts of hue sensations when interacting with cone activity (Stabell,
1967a; Stabell & Stabell, 1973a,
1994
; McCann & Benton,
1969
;
Stromeyer, 1974a, b; Buck,
1997
). Obviously, a major reformulation
of the duplicity theory was called for.
In the following part we will describe how our knowledge of
the sensitivity regulation mechanisms of rods and cones and of the
