Biology Reference
In-Depth Information
impulses. Nerve fibres connected solely to cones, on the other hand,
become occupied with cone activity. However, the achromatic rod
component in the colour-mixture process will be dominant so that the
subject will not detect the small chromatic component involved.
As the test intensity increases further, the relative strength
of the cone impulses gradually increases resulting in an increasing
number of cone-occupied nerve fibres. Eventually, the subject will
detect the so-called 'correct' hue of the test light. It should be noted
that the change-over from rod to cone occupied nerve fibres was
assumed to take place at different intensity levels for different fibres,
depending on the sensitivity of the individual receptors and the
number of cones relative to rods connected to each fibre.
When the test intensity increases above the specific-hue
threshold level, the saturation of the test colour will increase as the
number of cone-occupied nerve fibres increases.
At the highest intensity levels only fibres connected exclusively
to rods will be occupied with rod activity. However, as indicated by his
results obtained with the green test light (Experiment 7), the subjects
would not be able to detect this small achromatic rod component in
the colour-mixture process.
Although both his theoretical models could explain the data
reasonably well, Lie (
1963
) pointed out that several important
questions remained, and that his investigation should be expanded.
In particular, he found it of interest to explore how the specific-hue
threshold level changed with
light adaptation
. He predicted that
if the mechanisms of light and dark adaptation were the same, the
specific-hue threshold should be obtained at the same intensity level
under mesopic test conditions when the absolute rod thresholds for
dark and light adaptation under scotopic test conditions were the
same. He held that this prediction should be subjected to an empirical
test, but never engaged in such an investigation.
Lie (
1963
) also pointed out the lack of knowledge with regard to
variation in the relative strength of the achromatic rod and chromatic
cone component with test parameters.