FoundationalConceptsNeuroscience

ceptor proteins are sensitive to low levels of light and have little or no
input into color perception. They operate at night or in other sources
of dim light. The experience of colors under conditions of low light is
not very strong. That is because the light is not bright enough to acti-
vate many cones and so the color perception system is not engaged.
In retinal achromatopsia, a genetic or developmental anomaly
results in loss of all functional cone cells. People with this condition
have no experience of color; they see the world in shades of black,
white, and gray. When comparing their visual experience with that
of individuals with normal color vision, retinal achromatopes some-
times report an appreciation of subtle gradations of contrast, shadow,
and texture that is more nuanced than someone with normal vision.
This may be akin to the idea that aspects of contrast, shading, and tex-
ture may be better represented in black-and-white photography and
cinematography than in the color versions.
In the human retina there are many more rods than there are cones:
about one hundred million rod cells and about five million cone cells.
Additionally, the rods and cones are differently distributed over the
retina (Fig. 14.3). Because the cones are concentrated at the fovea,
color perception is best when light from the object being viewed is fo-
cused there. This happen when we are looking directly at something.
We generally don’t realize that our color perception is sketchier in the
periphery of our vision, but if you carefully test for this you will find
that it is indeed the case.