Octopus sight

Nancy

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Thanks, John, very interesting!

Just one note - some octos live close to the shore in shallower water where more light would penetrate. I wonder whether these species would have more use for color perception.

Nancy
 

Jean

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Light filters out very quickly particularly the short wavelengths such as red....which is why many critters are red/orange. Below about 10m they look black and are much harder to see. In fact most photos of coral reefs you see would be blue if the photographer hadn't used a white strobe! So it would be an advantage to see "more" than just colour; hue, saturation, polarisation etc would be more useful visual tools than just colour.

J
 
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Jean said:
Light filters out very quickly particularly the short wavelengths such as red.... So it would be an advantage to see "more" than just colour; hue, saturation, polarisation etc would be more useful visual tools than just colour.

J

True enough, but I think that what we're looking at from an evolutionary perspective is something building on the original molluscan bauplan. If the eyes of the ancestral forms weren't originally color-sensing, then the derived forms might have the same issues to this day unless acted upon by the right mutations and selective pressures. Think of it as a Newton's Law of Evolution, except without the apples.

Well, maybe Watasenia is one such individual.

John
 

monty

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color vision

Cephalopods notwithstanding, color vision is not nearly as important a factor in most animals than it is in humans. We are strongly biased in our ideas of how other animals see the world by the way we see the world. Some theorists believe that the reason we have the type of color vision that we do is because our monkey ancestors needed to identify different fruits and their levels of ripeness, so our lifestyle of eating fruit in bright sunshine (I wish I actually spent more time eating fruit in the bright sunshine :wink:) really explain our style of vision. Noctournal predators like cats generally are more optimized for seeing movement in very low light levels. I assume deer are color blind and sensitive to movement as well, since hunters can wear colorful vests to not be shot by other hunters and yet can still sneak up on deer. Of course, insects that need to find flowers can gain from color vision, and I understand some stomatopods have 11 or so different visual pigments, so presumably they get some information about spectrum from that.
My point is that it's not even clear what color would mean to most of these animals; certainly it's not the same thing that we see.

I've studied a lot about color in the context of computer graphics and visual psychophysics, and generally find that almost nobody has a good understanding of what color "is"-- there are different aspects of color in many fields. A friend of mine believes that the chemists are the ones who understand color the best, since they use spectroscopy to examine different materials, so they're heavily invested in what the actual spectrum of light is. There are a large number of color models used by the art, print, materials, video, lighting and film fields, all of which have a lot of value in some areas but less so in others-- some concentrate on the pigment properties, some on the spectrum of light, some on human perceptions. There was an attempt to clarify this sort of thing in the creation of the CIE color space, which describes a basis for representing the gamut of colors that the human eye can perceive... it's interesting how much of that falls outside what can be represented with the red+green+blue phosphors of video screens.

My bottom line is that it's quite clear to me, just because of the differences in nervous systems, that any color vision cephalopods may possess is likely to be very different than human color perception. As was pointed out, the spectrum of light in the ocean tends to be quite different than what we get on land. Someone (John, maybe) posted a reference to a fascinating paper a few months ago which discussed a whole bunch of aspects of deep-sea vision, lighting, and color issues-- it's quite interesting... I'll look for the thread when I have a bit more time.

I'm not sure what Jean is getting at by mentioning "hue" as distinct from color-- in my experience, hue is defined as the "normalized" color, in systems like HLS and HSV that try to separate out color from "intensity"/"lightness"/"brightness" and "saturation," so I don't understand how an animal could make sense of "hue" without color vision.

I think the prevailing assumption is that since most cephs seem to only have one visual pigment in their retinas, that they don't have any way to distinguish frequencies-- humans do that by comparing the responses of 3 different pigments, roughly corresponding to red, green, and blue. If there is any alternately proposed mechanism, I've never heard of it.

:rainbow:
 

Jean

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monty said:
I'm not sure what Jean is getting at by mentioning "hue" as distinct from color-- in my experience, hue is defined as the "normalized" color, in systems like HLS and HSV that try to separate out color from "intensity"/"lightness"/"brightness" and "saturation," so I don't understand how an animal could make sense of "hue" without color vision.

I think I was thinking more of tone and/or shade. I'm a little colour blind (due to retinal damage! not true colour blindness) and I have great difficulty with greens, yellows and strangely grey. This is because I see some greens and yellows as grey :bugout: For example Lime green, lemon yellow and a kind of palish grey all look the same to me. Made it rather difficult when I worked in a department store's dress making area and had to match thread to fabric in these colours. Eventually we organised the thread display and separated these shades and wrote the colour on the fabric bolt BUT my point is if I knew that the fabric was lemon yellow I could go to the thread and pick out EXACTLY the right shade of thread to match but I wasn't using colour I was matching the shade of the grey that I see. I do the same now with my bead work. I think I do use some of the saturation as well, but it's kinda hard to explain to people with normal colour vision! (just as hard to explain "green" or "yellow" to me!!!)

Used to have a lot of "fun" matching pH colours :roll: now I use a digital pH meter!

J
 

Feelers

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monty said:
I'm not sure what Jean is getting at by mentioning "hue" as distinct from color-- in my experience, hue is defined as the "normalized" color, in systems like HLS and HSV that try to separate out color from "intensity"/"lightness"/"brightness" and "saturation," so I don't understand how an animal could make sense of "hue" without color vision.

I think the prevailing assumption is that since most cephs seem to only have one visual pigment in their retinas, that they don't have any way to distinguish frequencies-- humans do that by comparing the responses of 3 different pigments, roughly corresponding to red, green, and blue. If there is any alternately proposed mechanism, I've never heard of it.



I thought this meant that they distinguish the different frequencies in the hue, ie different shades of grey correspond to a pre-programmed uncontious memory of chromotophore "positions".

For example the octo sees a "very dark grey", and attempts to match this with its "very dark grey response", trying to make them match (in hue).
To us this might be dark red, but if you use different a colour of the same hue the octo would apply the exact same response.

Perhaps there is a more limited vocabulary of hues in the marine environment allowing the octopus to match effectivly most of the time. ie a "very dark grey" is nearly always a dark red , and evolution has picked the most common response out of all the colour candidates.

This would explain why they can change so easily, and also how they can take a pattern - mixes of hues, and can replicate these too.

I would assume they have a higher ability to detect minmal differences in hue than us, allowing them to be even more specific.



However this would all be incorrect if a blind octo can match its surroundings , can anyone confirm this? I know it is a common "fact", it appears that it isnt true.
 

Feelers

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I think monty is correct about "hue", I dont think it's the word we should be using, all the definitions I find are about different shades of colour.

"Color value or saturation, as opposed to brightness or intensity. (2) Tint control. Hue is the parameter of color that allows us to distinguish between colors. The hue, or tint control adjusts the amount of color displayed."

Is there a more appropriot term to use? (I wouldnt have a clue)
 
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Hmmm forgive my ignorance (I beg of you, as I am very ignorant when it comes to Marine Biology) as regards Octo Prey or predators, are they colour blind too? I'm guessing fish can see in colour.
 

monty

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Feelers said:
However this would all be incorrect if a blind octo can match its surroundings , can anyone confirm this? I know it is a common "fact", it appears that it isnt true.

Well, I don't have a specific reference for octopus, but I was told by a cuttlefish chromataphore researcher that blind sepia officionalis lose their camouflage abilities.
 

monty

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Feelers said:
I think monty is correct about "hue", I dont think it's the word we should be using, all the definitions I find are about different shades of colour.

"Color value or saturation, as opposed to brightness or intensity. (2) Tint control. Hue is the parameter of color that allows us to distinguish between colors. The hue, or tint control adjusts the amount of color displayed."

Is there a more appropriot term to use? (I wouldnt have a clue)

I'm not sure of a better word; maybe "tone," but I'm not sure that has a well-defined definition in any of the color science fields.

I did get a chance to look up something this discussion has reminded me of-- there was a paper at the SIGGRAPH computer graphics conference this year about ways of looking at turning a color image into shades of gray that preserves as much of the color detail as possible while not making the intensities look "wrong". It's available online at http://www.color2gray.info
 

Neogonodactylus

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Let me strongly recommend "The Octopus's Garden: The visual world of Cephalopods" by G. Gleadall and Nadav Shashar in "Complex Worlds from Simpler Nervous Systems" edited by F. R. Prete, MIT Press, 2004. It has an excellent discussion of vision in cephalopods. And while you are threre, check out the chapter on Stomatopod vision by Cronin and Marshall that describes the most complicated eye in the animal kingdom. It can contain 16 visual pigments, 4 color filters, and the ability to see polarized light in three different e-vectors. The eye has the ability to adjusted the spectral qualities of the filters depending on ambient lighting and stomatopods have as many visual pigments in the UV (3) as we have devoted to color in the entire visible light spectrum.

Roy
 
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i dont know if this has anything to do with this, but i just made an obseveration. i looked at diffrent colors under red light (only red lightbulbs in a room) and to me blue in normal light looked gray, green also looked gray, a slightly diffrent shade, but still gray. yello looked more like a white, and purple looked like black. So i think the actual color that we see is not real or should i say is subjective to the wavelenght of light we are seeing it, so possibly octo's are color blind under our light spectrum, but not or at least are able to distinguish between colors under the light spectrums that are present in there natural habitat.
 
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Architeuthoceras said:
And then there are the colors you think you see.

OMG! Sorry to take the discussion away a little (cause I think this is a really fascinating topic) but that green dot thing is the coolest ever! It took like 4 second for me to see the green dot, and then slowly the purple dots disappear as well. Its funny cause they don't all just go, one goes here, then a few there, one last one over there, and then they're all gone. Definitely worth a look.

Cheers!

PS: Interesting note, you can cycle through different colours by hitting the "Colour ±" button. One of the last colours is red, with a rotating blue dot. After watching this for a while, when you cycle through the colours again it appears that all of the reciprocal colours have changed to blue! It takes a few more cycles before your eyes adjust to the new reciprocal colour! Wierd!
 
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