Journal of Neurophysiology, Vol 54, Issue 2 293-303, Copyright © 1985 by APS
Mixing of color signals by turtle cone photoreceptors
R. A. Normann, I. Perlman and S. J. Daly
The direct mixing of red and green cone signals in the outer plexiform
layer of the turtle retina was studied by using intracellular recordings
from red cone photoreceptors. Cone photoresponses were a function of the
wavelength of the photons that stimulated them, even when small-diameter
stimuli were used. The intensity response curves measured with red and
green test flashes had different shapes. The kinetics of approximately
equal amplitude red and green responses also differed. To quantify the
short wavelength input onto red cones, differential chromatic adaptation
was used. The relative sensitivity of the red cone to red and green test
flashes was a function of the color and intensity of the background
illumination; red backgrounds decreased relative red sensitivity, and green
backgrounds increased relative red sensitivity. The spectral sensitivity of
the additional short wavelength input onto red cones was determined by
using differential chromatic adaptation, and was found to peak
approximately 550 nm. We conclude that red cones receive an additional
excitatory input from green cones (and possibly blue cones). A model of the
cone mosaic suggests that approximately 50% of the red cone response
(linear range) to a dim green test flash arises from neighboring green
cones.
