Cephalopod Eyes-- Sight in 3 Dimensions?

Discussion in 'Physiology and Biology' started by katiefa, Sep 5, 2008.

  1. katiefa

    katiefa Larval Mass Registered

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    I assume, given the hunting mechanisms and/or spatial problem-solving abilities of many cephalopods, that they can see in three dimensions. My physics is pretty poor, but I know that human beings perceive depth and distance primarily through the minute differences in sight between our two eyes. Does anyone know what adaptations cephalopods have developed which enable them to see in three dimensions with only one eye?

    Thanks!
     
  2. monty

    monty Colossal Squid Staff Member Supporter

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    :welcome:

    Most squids and cuttles use both eyes for hunting, just as mammals do. I'm less sure about octos, but they tend to do the pounce more by feel/touch than visually, so they probably don't need such precise aim.

    Weird squids like Histioteuthis I'm not sure about.

    There is at least one animal that has single-eye depth perception, stomatopods (mantis shrimps) have eyes that point 3 different sets of their compound eyes at a target, in an arrangement where which part of the eye sees the target gives an indication of the range to it. Their eyes are more compound eye style, like insects, rather than camera eyes, like us humans and all cephalopods, though.

    There are some interesting aspects to cuttle eyes, in that the W-shaped pupils may form 2 images on the retina. I remember reading someone's idea of how that is used, but I don't remember if it has anything to do with depth (although I believe it is used for looking forward for hunting, but cuttles can usually see prey directly in front of them with both eyes.)
     
  3. chrono_war01

    chrono_war01 Colossal Squid Supporter

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    Perhaps the "2 images on the retina" part is similar to how 3d glasses work, using 2d images to form a sharper 3d one.
     
  4. cuttlegirl

    cuttlegirl Colossal Squid Supporter Registered

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    Cephalopods have two eyes.
     
  5. gholland

    gholland Haliphron Atlanticus Supporter

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    Mercs may be an exception to this as mine regularly pounce on fiddlers (or sometimes at each other) from up to 8 inches away (keeping in mind that their mantles are only ~1" at this point).

    I think maybe there was an assumption that octos don't have binocular vision because of the placement of the eyes on opposite sides of the mantle. Do octos have binocular vision?
     
  6. cuttlegirl

    cuttlegirl Colossal Squid Supporter Registered

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  7. gholland

    gholland Haliphron Atlanticus Supporter

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    Ah! I had read the comments, but not the original link. Now it makes sense.

    Hanlon and Messenger are unclear on the issue of binocular vision in octopuses, stating: "In some cephalopods there are convergent eye movements that are probably used for depth perception..." Unfortunately, that statement is referenced to an article on cuttles and I don't see a statement specifically attributable to octopuses.
     
  8. katiefa

    katiefa Larval Mass Registered

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    Whoops, sorry!

    After re-reading my post, I realized I hadn't really specified "one eye on each side." Sorry! Still, the question still remains-- how do they perceive depth without binocular vision? Thanks for all the responses so far!
     
  9. OB

    OB Colossal Squid Staff Member Moderator

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    Urrr... they have binocular vision, for the most part, as stated in monty's initial response :wink: A fine example is Mesonychoteuthis, or Teuthowenia, as illustrated here:

    [​IMG]
     
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  10. monty

    monty Colossal Squid Staff Member Supporter

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    At least some species do have binocular vision in the direction they attack:

    [​IMG]

    I also realized after my last post that many octopuses have their eyes "stick up" enough in their usual postures that I wouldn't rule out binocular vision there, although I still think octos are less reliant on precision for their strikes than cuttles or squids.

    Still, a lot of cephs do seem to have eyes that aren't well-suited to binocular vision. I suspect that's more due to their lifestyles not needing accurate depth perception for hunting, and benefiting more from a wide field of view to see incoming predators. Looking at whales as an example, they largely hunt with sonar, so they don't really have eyes positioned for good binocular vision.

    I also think that binocular vision is somewhat overrated, but maybe I'm biased-- I tend not to like 3-d movies, and I can't see those single-image-stereogram pictures, so I seem to rely less on binocular vision and more on paralax, depth of field, occlusion, and the assortment of other cues for that. Really, the only time binocular vision is useful is for things relatively close compared to the distance between the eyes. Try covering one eye and doing tasks-- it's usually not a problem to walk around the house, drive a car, pick up a glass off the table, and such; it's more of a problem for close-in tasks, or rapid response, like if someone throws a ball at your face.

    Still, animals like squids and chameleons that shoot out tentacles or tongues to grab food do have a very big need for precise range estimates, and so most of them to have the ability to look at the target with both eyes. Some squid species, like the colossal Mesonychoteuthis that's been in the news lately, have eyes that protrude a bit to see around the arms and tentacles. In this picture of Dosidicus gigas their eyes, which give the appearance of looking sideways, are positioned so that they can see forwards when the arms are bunched together in hunting posture:

    [​IMG]

    Many squids and cuttles (I don't know about Dosidicus but I strongly suspect it) have retinas positioned so that their best acuity is for light coming in from the front (and sometimes back) direction, and even though the eyes look like they primarily see sideways, the internal geometry of the eyes is best at looking forward with both eyes, with the retina tuned to the hunting task on the mantle side of the eyes rather than in the back of the eyes opposite the pupil.
     
  11. gholland

    gholland Haliphron Atlanticus Supporter

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    I had always assumed binocular vision was the norm in octos (based on photos of my own), but something about the line of questioning made me wonder if I had made a mistake... the mistake of course was looking for a generalized statement that was true for all cephs! :wink:
     
  12. Neogonodactylus

    Neogonodactylus Haliphron Atlanticus Staff Member Moderator

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    One of the most common ways that octopus judge distance is by bobbing their heads up and down.

    Roy
     
  13. gholland

    gholland Haliphron Atlanticus Supporter

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    :banghead: I guess that would explain why they do the head bobbing when they see prey... I never associated a vertical movement with parallax (probably because I'm just used to thinking of eyes being spaced horizontally), but it makes perfect sense. I always thought that was just "eagerness" the way a cat wiggles its hind-quarters before pouncing.

    This is why I love this place... the expansion of my mind! Thanks.
     
  14. DWhatley

    DWhatley Cthulhu Staff Member Moderator

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    Thanks Roy! Bobbing has been mentioned by many but with no explanation. I have thought about bobbing back but had not since I could not tell if it was an aggressive or assertive behavior. I have been responding by moving my head side ways in response to acknowledge but hopefully not challenge (and it seems to be a motion they cannot emulate but does seem to be a common query expression). If it is only an action to judge size or distance, I guess my octos may have found me peculiar :smile:
     

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