Biology Reference
In-Depth Information
of cone, and that two of the four primary mechanisms were served by
rods interacting with cones. Thus he presumed that:
1.
The primary 'red' mechanism was subserved by signals from cones
with maximum sensitivity at about 590 nm transmitted through Polyak's
midget bipolar cells.
2.
The primary 'green' mechanism was subserved by impulses
originating in the 'red' (590 nm) cones and in so-called 'day rods'.
These impulses were combined and transmitted through Polyak's
flat bipolar cells and determined a spectral sensitivity curve with
maximum sensitivity at about 535 nm. The 'day-rods' differed
from the ordinary dark-adapting rods in that they did not have the
ability to accumulate rhodopsin in any measurable quantity. Hence,
they could not increase their sensitivity during the second phase of
long-term dark adaptation.
3.
The primary 'blue' mechanism was subserved by impulses from the
dark-adapting rods being partially inhibited by the 'red' (590 nm) cones.
Due to this inhibition the spectral sensitivity of the rods was assumed to
change from that of rhodopsin (maximum sensitivity at about 500 nm)
to that of the primary 'blue' colour mechanism (maximum sensitivity
at about 450 nm) as test conditions changed from scotopic to photopic.
Thus, at variance with König's (
1894
) assumption that the bleaching
product of rhodopsin, 'visual yellow', was responsible for the primary
'blue' mechanism, Willmer presumed that it was an effect of cone-rod
interaction.
4.
Finally, the fourth mechanism was subserved by signals from the
ordinary dark-adapting rods.
As can be seen, the theory introduced by Willmer (
1946
)
involved only one type of cone and two types of rod receptor, while
the duplicity theory of von Kries (
1911
) operated with one rod receptor
type and three types of cone. Also, in sharp contrast to the basic
assumption of the duplicity theory that rods and cones functioned
independently of each other, Willmer (
1946
) made rod-cone
interaction a prerequisite for trichromatic colour vision. Thus, both
the 'blue' and 'green' primaries were served by rods interacting with
cones. Obviously, these radical, new ideas of rod-cone interaction
needed solid underpinning in order to gain general acceptance.
