Feb 20, 2012
Is this yet another case where we assume a species is color blind simply because we haven't figured a way to ask it? I find it hard to believe.

This animal has an elaborate mechanism with which it can camouflage itself. It also uses color to communicate. And it does this with black-and-white vision??

At the very least, it would haven been prudent to explain why "we" think it is color blind.
Feb 20, 2012
What? You realize we understand the mechanics of vision very well right? Simply examining the eye of an organism will tell us what wavelengths of light are capable of being distinguished by it...

I find it is the case that most people's greatest challenge isn't their ignorance of specific information, it is instead their ignorance that the information even exists. The magnitude of what we (collectively, humanity) know and understand is severely underestimated by most laypersons. Don't even get me started on what we do to light in fiber optic communications with waveguides, wavelength division multiplexing, etc... Suffice to say we know a great deal about how light works, and also about how vision works. We could easily give sight to the blind if it were a matter of theory alone, the challenge is in the practical application of the knowledge, not the knowledge itself..
Feb 20, 2012
anyway, this statement "how it might look to a colourblind cuttlefish or octopus that see polarization angles but not colour" suggests to me not that they've determined that cuttlefish are colorblind, rather that in the context of this example, only the parameters of the cuttlefish's polarization perception was left in while any information regarding color was just plain left out - whether there is any or not.

I didn't really get the feel that they say cuttlefish are colorblind, rather that they left color perception out of the experiment.
Feb 20, 2012
Fascinating insights... re. chromaticism, i like G. C. Huth's geometric model http://www.ghuth.com/ and my own personal hunch is that most animals with colour sensitivity would have about an octave of bandwidth, just like us, likewise divided into seven distinct colours, but transposed up or down according to their specific habitats - so our 'green' may align with another species' red for example... suffice to say i base this on no objective evidence whatsoever, apart from a pet theory on the primacy of octave equivalence...
Feb 20, 2012
I suppose that the retinas of cuttlefish and octopuses have been examined and found to lack cone cells (color receptors).
Feb 20, 2012
To use camouflage, one needs to become the same color as the background. Unless this species can see color, it has to have some other method of exactly perceiving the color of the background. If this is the case, it really would have been correct to mention it.
Feb 20, 2012
The mechanism of octopus camouflage may be a much more tricky. Just try to imagine, how you would camouflage yourself, even if you would have a perfect color vision. And the lack of cone cells doesn't imply the absence of color vision, because the compound eyes of octopi developed independently for quite different light conditions. The differentiation of retina cells to rod and cones would be unnecessary under such a condition. The spiders can recognize colors well, yet they have no rods and cones.
Feb 20, 2012
Cuttlefish are remarkable and intelligent creatures. Staring at a large individual just inches from my face in an aquarium, while it stared right back at me with those eyes, I could not help but to feel that I was looking into the eyes of an alien intelligence. It was an amazing experience.
Feb 21, 2012
What techniques are used to measure the polarization in the prawn photo?

have they just aken a whole lot of photos with the filter set at different angles?
Feb 24, 2012
Hi to address some of your quesitons
Cuttlefish are colour blind.
Nearly all cephalopods have only one visual pigment and one type of photoreceptor, which means on a physiological level they have no basis for possessing colour vision. Behaviourally, octopus, cuttlefish and squid have been tested repeatedly and no evidence for colour vision has ever been found.

So you might ask, how can they be so good at camouflage...well it is simply really, while they are colour blind their predators are not, and so through selection (the main driving force of evolution) those cephalopods that could not match the background colour and texture well enough were removed from the population. So while they are colourblind, evolution is not.

As for the polarization imaging. You (Graeme) were exactly correct, we took three images at 0, 45 and 90 degrees and then use a custom program to calculate the angles of polarization.

Shelby Temple (author of the paper examined here)

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