Octopus sight

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Feelers said:
And this doesnt explain how a blind octopus can match its surroundings. Also I was under the impression that a severed arm would also match its' surroundings, not sure on either of these facts,(I read them somewhere) can anyone confirm if they are true?

Octopuses aren't blind. But if you meant..how an octo going blind or supposadely IS blind as a result of injury, I wouldn't know the answer to that other than the fact that their color-reflective cells aid them in camoulflage.

Nancy, for the green color, I watched a cuttlefish on a video camoulflage itself to try and take on the shades of a rocky bottom filled with blues and greens. The camoulflage failed, however...to the cuttelfish, all the green and blue rocks were all the same shade of grey. And they remained no different from one another to the cuttlefishes eye. To our eyes, the rocks were green and blue...two different shades. So the cuttle took no pattern at all and simply turned into a very, very light greyish color. This probably works for octo's and squids as well.
 

Jean

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From what I understand, although most cephs can't see colour, they can discriminate (to a very fine degree) the differences between hue and colour intensity (and patterns but that's another story!). I watched a Discovery doco which had John Forsythe demonstrating that a cuttle can match patterns based on colours of different intensity BUT when he put the cuttle in a tank with a substrate of yellow tiles and green pebbles which had the same intensity the cuttle didn't change. The other was put in a tank with (I think) red tiles and blue pebbles and the cuttle opted for a checkerboard pattern. The tanks were then filmed in black and white and to our eyes (well mine anyway!) the red and blue were different shades of grey and the yellow and green were all one shade of grey! So cephs may have a better ability to match based on tone, hue and intensity.
Just my :twocents:

J
 

Feelers

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Oh, yeah I meant an octo that has become blind/ possibly has its eyes covered for an experiment? Just remember reading that somewhere
 
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Jean said:
From what I understand, although most cephs can't see colour, they can discriminate (to a very fine degree) the differences between hue and colour intensity (and patterns but that's another story!). I watched a Discovery doco which had John Forsythe demonstrating that a cuttle can match patterns based on colours of different intensity BUT when he put the cuttle in a tank with a substrate of yellow tiles and green pebbles which had the same intensity the cuttle didn't change. The other was put in a tank with (I think) red tiles and blue pebbles and the cuttle opted for a checkerboard pattern. The tanks were then filmed in black and white and to our eyes (well mine anyway!) the red and blue were different shades of grey and the yellow and green were all one shade of grey! So cephs may have a better ability to match based on tone, hue and intensity.
Just my :twocents:

J

Yea, thats exactly what I saw on discovery also. I meant yellow and green...not blue and green, sorry Nancy, lol. It explained very well how they can blend in though. I own that tape with that video clip...and its "The Ultimate Guide: Octopus" which I ordered on TV after it aired for 19.99. Im planning on purchasing "Incredible Suckers" and "The Octopus Show" both on The Nature Show website.
 
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Well, these are all good answers. I would also think that this topic also deals with several major factors of octopus sight including sensation and perception, the evolutionary morphology of the cephalopod eye, and properties of light in the ocean.

People always remark about how similar the Cephalopod eye is to the human eye. I prefer to look at the morphological differences and remark about the similarity in function. If you really study the ceph eye, you see it’s more of a highly derived version of the basic mollusc eye, itself a modified pigment cup ocellus similar to those of the flatworms.

Another interesting thought is the idea of the use of the Cephalopod visual pigments like rhodopsin and retinochrome. The rhabodmeres (or cell units of the cephalopod eye – analogous to our rods and cones), house these pigments, which actually move in response to light, unlike our own. This could affect what they perceive as “color” versus what we perceive and see in our own non-aquatic world.

Also, the cephalopod optic lobe is nearly half of the brain, which is a far higher ratio of optic nerve tissue to brain weight than ours. There would have to take a lot of processing power for sight in the Cephalopod eye, which means their visual acuity may be greater than we think.

Color vision isn’t really a necessity in the ocean, though I can see where in certain animals this might be an advantage. Light has weird properties in the ocean, and certain wavelengths (colors) will simply not penetrate far down. You’d be better off collecting light than dedicating your resources toward color vision.

I just can’t shake the feeling that, given that our sight is the sum total of a lot of different factors, the “color vision” of a cephalopod is not that straightforward. There are probably numerous factors that we aren’t seeing at the present time.

John
 

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:
 

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