Biology Reference
In-Depth Information
13
Rod-cone interactions in
mesopic vision
13.1 R o d - c o n e i n t e r ac t i o n s u n d e r m e s o p i c
conditions in a chromatically
neutral state of adaptation
In the period from Schultze (
1866
) to Lie (
1963
) it had been generally
agreed that rods and cones interacted in a kind of colour-mixture
process in mesopic vision. Rods and cones were assumed to
contribute an achromatic and a chromatic component, respectively.
The most advanced attempt to further characterize the rod-cone
interaction under mesopic conditions had been made by Granit
(
1938
,
1947
) and Lie (1963). They both suggested that rod and cone
activities antagonized each other at the retinal level in that the most
sensitive receptor system tended to suppress the other. The rise of the
specific-hue threshold obtained when rods intruded during long-term
dark adaptation was compelling evidence in favour of this antagonistic
interaction. There could be little doubt that rod signals completely
suppressed the chromatic cone signals within the intensity interval
between the cone-plateau level and the specific-hue threshold.
Yet, in apparent opposition to the psychophysical data and
the hypothesis of rod-cone antagonism proposed by Lie (
1963
), the
histological and electrophysiological evidence obtained in the late
1980s and early 1990s indicated that rods and cones
added
their
responses of the same polarity both at the receptor and bipolar cell
levels (Daw
et al
.,
1990
; Schneeweis & Schnapf,
1995
).
Fortunately, this apparent conflict between the psychophysical
and the electrophysiological data could easily be resolved. Thus, the
desaturation effect of the rods could be explained simply by suggesting
that rod signals in a dark-adapted and chromatically neutral state of
adaptation activated the different types of spectrally opponent cell
