Biology Reference
In-Depth Information
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Fig. 12.1 Spectral threshold curves of scotopic contrast hues subsequent
to pre-stimulation with 670 nm for 10 s at a retinal illumination of
3 photopic troland (Δ) together with absolute spectral threshold curve of
rods measured in a completely dark-adapted eye (● ). Both the test- and
pre-stimulation fields were applied 6° temporally to the fovea. The size
of the pre- and test- stimulation fields was 1 × 1° and the test flash was
exposed for 0.5 s.
12.2 Scotopic contrast colours are
triggered by rod signals
The discovery that selective chromatic adaptation may generate
a variety of different colour sensations upon test stimulation at
scotopic intensity levels seemed to imply that at least one of the
basic assumptions of the duplicity theory was wrong.
Clearly, if one presumes that the scotopic contrast hues were
triggered by cone impulses activated by the test light, one would be
forced to accept that cone receptors may function at intensity levels
down to the absolute threshold of the dark-adapted eye - this, of
course, is in violation of the basic assumption that cones are less
sensitive than rods.
On the other hand, if one presumes that the scotopic contrast
hues were triggered by rod impulses, this would contradict the
