Biology Reference
In-Depth Information
The hypotheses of Polyak, Granit, Willmer, Saugstad and
Saugstad and Lie represented a radical break with the previous,
long-held assumptions of separation and independence between the
rod and cone functions. Together they made a strong case for the idea
of rod-cone interactions at the retinal level.
9.1 The duplicity theory of Willmer
The new version of the duplicity theory put forward by Willmer
( 1946 ) was intended to stimulate research and promote new experi-
mental investigations. Yet, he admitted that his theory was both
speculative, provocative and not able to account for all important
colour phenomena.
As a basic premise, he held that there were four primary
mechanisms in the human retina. This had been proved by
previous research work. Thus, Maxwell ( 1855 , 1860 ) had shown
that the retinal colour response to spectral lights involved a
triplex mechanism, and König ( 1894 ) had shown that a separate
rod receptor mechanism functioned in scotopic vision. Also, König
and Dieterici ( 1893 ), in a very comprehensive study on colour
vision and spectral sensitivity in monochromats, dichromats,
and normal and anomalous trichromats, had demonstrated that
a minimum of four primary processes (Grundempfindungen) were
needed to explain their results.
Yet, there was no agreement on the anatomical substrate of the
four primary mechanisms. Indeed, Schultze ( 1866 ) and Polyak (1941)
had found that only two different types of receptor, rods and cones,
could be differentiated in the human retina by histological examina-
tion. Hence, the question naturally arose of how these two receptor
types could account for the four primary mechanisms.
9.1.1 C of l of u r v i s i of n e x p l a i n e d b y t w of t y p e s of f r of d
and one type of cone
Willmer ( 1946 ) attempted to solve this problem by suggesting that
the human retina contained two different types of rod and one type
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