Ronn!Blankenship <[EMAIL PROTECTED]> wrote
... some types of birds have five types of cone cells, suggesting that they can see colors we can't.
Can you tell us more? This is deep.
As far as I know, humans see by comparing the total and differential inputs from three types of cell, each with a different frequency response. Am I right about this? I know little about biosystems.
>From what you said, one possibility is that birds see further into the infrared and ultraviolet than humans; another is that birds see within the same frequency range (colors) as humans, but distinguish more colors. Which is it?
If it is a combination of the two, what are the wavelength/frequency/color ranges of the five types, and what does that imply for humans?
From <<http://www.bio.bris.ac.uk/research/vision/4d.htm>>:
"Bird colour vision differs from that of humans in two main ways. First, birds can see ultraviolet light. It appears that UV vision is a general property of diurnal birds, having been found in over 35 species using a combination of microspectrophotometry, electrophysiology, and behavioural methods. So, are birds like bees? Bees, like humans, have three receptor types, although unlike humans they are sensitive to ultraviolet light, with loss of sensitivity at the red end of the spectrum. This spectral range is achieved by having a cone type that is sensitive to UV wavelengths, and two that are sensitive to "human visible" wavelengths. Remember, because 'colour' is the result of differences in output of receptor types, this means that bees do not simply see additional 'UV colours', they will perceive even human-visible spectra in different hues to those which humans experience. Fortunately, as any nature film crew knows, we can gain an insight to the bee colour world by converting the blue, red and green channels of a video camera into UV, blue and green channels. Bees are trichromatic, like humans, so the three dimensions of bee colour can be mapped onto the three dimensions of human colour. With birds, and indeed many other non-mammalian vertebrates, life is not so simple. As well as seeing very well in the ultraviolet, all bird species that have been studied have at least four types of cone. They have four, not three, dimensional colour vision. Recent studies have confirmed tetra-chromacy in some fish and turtles, so perhaps we should not be surprised about this. It is mammals, including humans, that have poor colour vision! Whilst UV reception increases the range of wavelengths over which birds can see, increased dimensionality produces a qualitative change in the nature of colour perception that probably cannot be translated into human experience. Bird colours are not simply refinements of the hues that humans, or bees, see, these are hues unknown to any trichromat."
From <<http://home.pacifier.com/~ppenn/animals.html#birds>>:
"Birds see "higher dimension" color than do humans. Human color is three-dimensional. Bird color is four, five, or six dimensional. Full color is potentially infinite dimensional: this is the wavelength discrimination a spectroscope gives us. That "infinity-space" color is one of the things it took humans a long time to discover, and it remains today one of the more difficult concepts for us to understand."
From <<http://www.backyardnature.net/birdeyes.htm>>:
"A bird's retina actually has three types of photoreceptors that "translate" light into nervous impulses:
rods - black & white vision in dim light cones - color vision in bright light double cones - color vision
The interesting thing here is that humans only have two types of photoreceptors, rods and cones. Thus birds may see more colors than humans. In fact they may be able to perceive ultraviolet or near-ultraviolet light, which humans cannot. Moreover, bird retinas, in contrast to human retinas, contain no blood vessels. This prevents shadows and light scattering, which cut down on human vision."
Graphs and stuff: <<http://www.biology.eku.edu/RITCHISO/birdbrain2.html>>.
I have read that an owl's eyes are around 100 times as sensitive to light as the average human's (a cat's are 6 times as sensitive), so I made up a series of charts of the area around the constellation Orion showing what it would look like to each of those (based only on the sensitivity) Since I can't reproduce them here, let me just say that while there are about 6,000 stars over the entire celestial sphere which are visible to the average human, with a cat's sensitivity it could see over 40,000 stars, and an owl should be able to see in excess of 1 million stars.
Another statement I came across from somewhere is that a rabbit's eyes are so sensitive to movement that she could actually see the Sun moving across the sky. Again, though, I haven't been able to trace that back to its original source.
-- Ronn! :)
"Earth is the cradle of humanity, but one cannot remain in the cradle forever." -- Konstantin E. Tsiolkovskiy
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