Biology Reference
In-Depth Information
B
=
R
− K (
C
−
C
0
)
where
B
is the effective response from rods that generates the
spectral sensitivity of the 'blue' primary,
R
and
C
the immediate
responses from, respectively, rods and cones,
C
0
the threshold response
at which the cones begin to inhibit the rods, and K a constant equal
to 1.75.
It should be noted that the primary 'blue' mechanism was
assumed to consist of two underlying mechanisms. Thus, presuming
that the primary 'red' and 'green' cone receptor systems may inhibit
the rod receptor system somewhat differently, Willmer (
1961
) derived
two 'blue' mechanisms with spectral sensitivities that closely
matched the 'blue' π
1
and π
3
mechanisms obtained by Stiles with his
well-known two-colour threshold technique (see Stiles,
1978
).
Having determined the spectral sensitivities of four colour
mechanisms operating in photopic vision, Willmer (
1961
) attempted
to increase the explanatory power of his theory by incorporating new
assumptions to account for the opponent characteristics of colour
vision that Hering (
1878
) had called attention to. Thus, the 'red' and
'green' cone receptors were assumed to activate 'red-green' opponent
cells where the 'red' cones generated a red colour by increasing the
positive potential of the cells, while the 'green' cones generated a
blue-green colour by increasing the negative potential of the cells.
The 'red' and 'green' cones were also assumed to activate
'yellow-blue' opponent cells, generating a yellow colour by increasing
the positive potential of the cells, while the photopic rod activity
was assumed to generate a bluish (indigo) colour by increasing the
negative potential of these cells.
9.1.4 Evidence supporting rods as 'blue' primaries
The formula
B
=
R
- K (
C
-
C
0
) represented the most basic and original
assumption of the second version of Willmer's (
1961
) theory, and he
made a thorough attempt to underpin it. Firstly, he presented a long
list of circumstantial evidence where he showed the characteristics of
the 'blue' mechanism to differ from the 'red' and 'green' mechanisms
