Biology Reference
In-Depth Information
(
1977
) concluded that rods may share the colour channels with both
the middle- and short-wave cones.
14.2 Contribution of P. W. Trezona
Another early contribution to the idea of chromatic rod vision was
provided by Trezona (
1960
,
1970
). Her starting point was an explor-
ation of colour after-effects observed following stimulation with a
'white' stimulus (illuminant S
A
). Retinal illumination, field size,
time of exposure and the part of the retina stimulated were varied,
and the subject, sitting in the dark, simply reported on the colour
after-effects seen (Trezona,
1960
).
The most significant after-effect observed was the so-called
'after-blueness' - a blue sensation that lasted only a few seconds. This
'after-blueness' was observable only when the 'white' pre-stimula-
tion light had activated receptors outside the rod-free region. Hence,
she concluded that it might be triggered by rods.
She found supporting evidence by reviewing previous studies
where she, just like Willmer (
1961
), could point to observations that
showed rod activity was associated with blue colour sensations under
a variety of conditions. For instance, it had been found that when rod
activity was added to a test field that matched the colour of a compar-
ison field, a blue component had to be added to the comparison field
in order to restore the match.
As mentioned above, König (
1894
) did not make any serious
attempt to explain the change-over from achromatic to blue rod vision
as intensity increased from scotopic to photopic levels. Trezona (
1970
),
on the other hand, attempted to explain this shift in rod colour based on
the assumption that rod signals had access to the spectrally opponent
yellow-blue cells (the y-b unit), and that they would generate a blue
colour sensation only when they reached above the threshold level
of the (y-b) unit. Yet, she held that the 'blue'cones tended to inhibit
rod activity and that, as a consequence, the blue-related rod activity
would be increasingly inhibited as the intensity increased within the
mesopic intensity interval when 'blue' test lights were employed.
