Rods or Cones?

et_al at et_al at
Sun Nov 19 02:28:21 EST 2000

On Sat, 18 Nov 2000 20:17:38 -0600, mike-anderson at (mike)

>In article <8v77b1$qlb$1 at>, "JKH" <sorry at> wrote:
>> After checking the literature, I found some information which might be
>> interesting to the discussion here:
>> 1. Birds have photoreceptors which can detect wavelength in ultraviolet
>> range; it means they have even wider range of color perception than mammals.
>> 2. Most vertebrates, including the "living fossil" ancient fish, have both
>> cone-type and rod-type photo pigments which are sensitive to different
>> wavelength of light.
>> 3. From some phylogenetic evidence, cones actually appeared earlier in the
>> evolution than rods.
>> However, the presence of multiple photo pigments or cones in retina is only
>> necessary but not sufficient for color vision; there is a "knock-in" study
>> in mice that the engineered mice expressed human photo pigment in their
>> cones, which is necessary for trichromacy of color vision. These
>> artificially added photoreceptors are functional, expanding the range of
>> light sensitivity in these transgenic mice shown by electroretinogram, but
>> behavioral tests failed to show that this capacity is realized to their
>> ability of trichromacy. It is concluded that the wiring of photoreceptors is
>> important as well.
>Interesting, it sounds like it could also be a failure of the brain to be
>able to comprehend the information it is being sent.

As much of what we "see' is actually a construct of the brain
filling in the gaps, this would make sense.


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