Biology Reference
In-Depth Information
the rod signals and cut them off completely. Gouras and Link (
1966
)
pointed out that the transitory inhibition they had found would tend
to prevent rods and cones from acting in the same place simultan-
eously and, therefore, might play an important role in the apparent
independence of the two receptor systems obtained when tested at
threshold levels (see Stiles,
1978
).
Yet, the investigation of Gouras and Link (
1966
) was followed
by a long series of psychophysical investigations that established
beyond doubt that the two receptor systems also interacted at
absolute threshold level. A pioneer study was performed by Frumkes
et al
. (
1972
). After dark adapting the eye for 25 min, they presented an
adapting flash and a test flash concentrically at 7ยบ in the extrafoveal
retina against a continuously exposed scotopic background. The
wavelength of the adapting and test flash could both be fixed at
either 420 nm (to stimulate rods) or 680 nm (to stimulate cones).
In a different experimental series, the time interval between the
adapting and test flash was varied.
In opposition to the generally held idea of rod-cone independ-
ence at threshold level, they found that there was a marked reciprocal
antagonistic interaction between the two systems in that the threshold
level of cones was markedly raised by rod activity and vice versa.
Indeed, in accord with the relatively long latency of the rod system,
they found that the rod adapting flash increased the cone-threshold
test-flash intensity level later in time than the cone adapting flash
increased the rod-threshold test-flash level.
A series of psychophysical studies on cone-rod and rod-cone
interactions with regard to sensitivity followed shortly. Inhibition,
facilitation, sustained and transient effects were found and explored
(see Frumkes
et al
.,
1973
; Makous & Booth,
1974
; Ingling
et al
.,
1977
;
Latch & Lennie,
1977
; Temme & Frumkes,
1977
; Frumkes & Temme,
1977
; Blick & MacLeod,
1978
; Buck
et al
.,
1979
; Buck & Makous,
1981
; Buck
et al
.,
1984
; Buck,
1985
). Surely, the 1970s and early
1980s witnessed the final blow to the long-held idea of independence
between the rod and cone sensitivity regulation mechanisms.
