Biology Reference
In-Depth Information
The systematic evaluation of the duplicity theory by Saugstad and
Saugstad could leave little doubt that there was ample room for improve-
ment and further development of the duplicity theory. In particular,
they stressed the lack of knowledge with regard to rod-cone interaction
under mesopic conditions. The available evidence strongly suggested
that rod and cone impulses interacted and produced a combined effect
under a variety of mesopic test conditions, but the essential character-
istics of the interaction processes were still largely unknown.
9.3
Ivar Lie: interactions between rod
and cone functions at mesopic
intensity
9.3.1 Psychophysical experiments
Only a few years later, however, the question of how rods and cones
interact under mesopic conditions was successfully addressed by Lie
(
1963
). In an extensive psychophysical, empirical investigation, using
a Hecth & Schlaer adaptometer (Hecth & Schlaer, 1938) he provided
conclusive evidence that the achromatic rod and the chromatic cone
components may interact in a kind of colour-mixing process.
In his investigation, Lie took advantage of the generally accepted
assumption that cones dark adapt much faster than rods. Thus, it had
long been known that following substantial bleaches, cones reach
their maximum sensitivity after a few minutes of dark adaptation,
while the rods may need more than 40 minutes to approach their
final level. Hence, the effect of rod activity upon cone functions may
be measured at mesopic intensity levels after the cones have reached
their dark-adapted state and the rods still increase their sensitivity.
Loeser (
1904
) appears to be the first to utilize this ideal method
under adequately controlled conditions. In this study he investigated
how rod signals affected cone-mediated colour sensation when they
intruded during long-term dark adaptation. During the first phase of
the dark adaptation period, he found the absolute and the specific-hue
thresholds (i.e. the intensity levels where the subject first becomes
