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RE: [KV] Colors (was Re: Movies)

From: Beth Fulton <beth.fulton@m...>
Date: Fri, 27 Jul 2001 10:17:15 +1000
Subject: RE: [KV] Colors (was Re: Movies)


 >I may very well be wrong here,
 >but humans see _colour_ with retinal
 >'cone' cells, that come in three
 >different types, which IIRC explains
 >the three primary colours - maybe
 >(anyone on the list know any more?)

We have cones and rods. The 120 million odd rods we have aren't colour 
sensitive, but pick up shapes, dim light and movement (they're
in the peripheral vision and absent from the centre of the retina so
why we see movement better off to the side). The cones are light and
sensitive and we have about 7 million in each ("healthy") eye and
concentrated in the centre of the retina and taper off to the sides.
are 3 types of cone and each is sensitive to a different set of 
wavelengths: short (430-440 nm), medium (535-540 nm) and long (560-565 
nm).  The light that we perceive to be "brightest" a greenish-yellow (is

555 nm).

 >Also IIRC, some bird species have 5
 >different types of cone cells, and so
 >probably see 5 different primary colours!

They definitely have 4 colour cones, they also have "double" cones which

maybe the 5th one you mention, but they're function is unknown (as yet).

For the 4 colour cone stuff they have the red, blue and green cones like
do (or cones sensitive to wavelengths close to what we are), but they
a 4th cone that is either violent or true UV depending on the type of
The bird set is actually more typical of early vertebrates (according
molecular biologists) whereas the human/primate set represents a
of the violet/UV cone to the blue spot, a loss of the "old blue cone"
and a 
slight shift in the "red" and "green" cones from the early (bird) 
wavelength peaks to our peaks. This probably also explains why some
can just see into the UV spectrum - they have a mutation so the "blue"
peak is not as shifted as in the rest of us (as its all based on 
biochemistry in the cones this is nothing too serious to achieve
Birds also have oil droplets in their eyes which help sharpen their 
discrimination along the spectra.

 >I remember seeing this on a BBC science series
 >'Supersense' about animal sensory capabilities -
 >worth watching if you want ideas for alien senses.

I caught some of that on the ABC down here, it was a GREAT show for 
broadening your horizons for weird alien ideas!! ;)

 >could well have only 2 cone cells, or 4 or more,

Or none, some aliens may well only have rods, but lots of them so
and shape detection is VERY sharp with no "weak spots" where cones would

dominate in us etc. Those with fewer types of cone would probably have a

restricted colour vision or a shifted vision... for instance bees (their

eyes don't have cones per se, but they could be a good guide to
effects) can see UV etc, but don't see red its just another blue to

 >if their eyes are sensitive to a wide spectrum, they probably see
 >a lot of primary colours.

Potentially they could also see polarised light.

 >OTOH, they may be colour blind (like cats).

Cats aren't strictly "colour blind" they do retain a few cones, though
sacrificed a lot for good movement and night vision. They probably
see in pale with the definition getting better the closer they get.



Elizabeth Fulton
CSIRO Division of Marine Research
GPO Box 1538
Phone (03) 6232 5018 International +61 3 6232 5018
Fax 03 6232 5053 International +61 3 6232 5053

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