Biology Reference
In-Depth Information
The results of the experiments indicated that rod activity
under mesopic test conditions may contribute with all kinds of
colour, and that the relative contributions of rods and cones in the
colour-mixture process may change with test intensity, in that rods
dominate at low and cones at high levels. Although this change in
relative contribution was found regardless of colour quality of the
rod and cone components, it could most simply be demonstrated
when the rod and cone components represented a pair of opponent
colours. For instance, when a blue rod and a yellow cone component
were mixed and the intensity of the test field gradually increased
within the mesopic intensity interval, the saturation of the blue rod
component was seen to decrease gradually until only the achromatic
component remained. Thereafter, the yellow cone component
emerged with increasing saturation. Apparently, the rod and cone
opponent colour processes antagonized each other to the extent that
only the chromatic rod component could be observed at low and the
chromatic cone component at high mesopic intensity levels. The
inhibition of rods was completed when the test intensity reached
photopic levels, where no trace of the rod component could be
observed.
It should be noted that this inhibition of the rod influence has
an obvious survival value. Thus, by taking over the control of the
relative activity rate of the spectrally opponent cells at high mesopic
intensities, cones may prevent rods from confusing the coded
information about hue (Stabell & Stabell,
1973
b).
Another fundamental difference between cone-cone and
rod-cone mixture data was also revealed by experimental investigation.
Thus, in sharp contrast to the cone-cone colour-mixture data, gross
failures of the additive colour-mixture law were found when rod and
cone colours were mixed. The extent of the deviation was found to
vary both with colour quality of the rod and cone components, and
also with test intensity (Stabell & Stabell, 1998).
