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27 November 2010 / Liz Johns

Do You See What I See? I Guess It Depends Where Your Eyes Are.

We know the chicken crossed the road to get to other side, but how did he do it safely? Easy, by looking left and right at the same time. No left-right-and-left-again rule for this chicken. Anatomically designed with eyes on the side of his head, he was able to see panoramically, which in this case means that he could see to the left and to the right at the same time without moving his head.

Like Having Eyes in the Back of your Head

I always wondered what it would be like to have the vision of an animal with eyes on the side of its head. To be able to see in different directions at the same time. Only being able to look forward is rather limiting at times. I’ve seen my parrot tilt his head and stare intently at something on the grass, but then thought, how do I know that he’s focusing on the ground, maybe something way up in the sky has caught his attention instead? Maybe there’s something in the grass and something flying up high and he’s watching both. I’ve tried to imagine what this ability is like and noticed that if you try to see what’s to your left and to your right at the same time (without moving your head), that your brain gets so lost in this impossible task that it stops its mindless chatter for a brief moment and you think of nothing. A useful aid in meditation don’t you think?

Why are cameleons good at meditation? Because they have a third eye. It’s situated in the middle of their foreheads and is sensitive to blue and violet light, but cannot form images.

Binocular v Monocular Vision

Having sideways facing eyes means that an animal has monocular vision (seeing out of one eye), but this is compensated with an almost 360° panoramic vision. Us, with our two forward facing eyes have a much smaller field of sight, but having eyes pointing in the same direction gives us binocular vision and the ability to judge depth. As the diagram shows, the location of the eyes changes the monocular to binocular ratio of vision.

The chameleon deserves a special mention at this juncture. With its eyes-on-stalks, it takes advantage of both panoramic vision (each eye can swivel 180°) and depth perception. Once it spots something (probably dinner) with one eye, it can swivel its other eye around, thus allowing it to see a single image of its target in stereoscopic vision and can measure the distance between itself and the unfortunate prey. All without moving its head. Clever huh?

Why has nature given different creatures different visual experiences?

The most obvious reason is that predator animals need to focus on their prey and be able to measure the distance between themselves and their prey so they can pounce effectively. Prey, in contrast, need to be aware of any predators so their panoramic vision means that it’s much harder to sneak up on them. (Sneaking up on a human predator from behind and shouting ‘boo’ has long been held an amusing pastime.)

But this cannot be the sole reason as there are a number of predator animals with eyes at the side, such as killer whales, hammer head sharks, mongooses, and there are some prey animals with front-facing eyes, e.g. fruit bats.

Considering this point, another reason has been put forward for the eye placement in animals from a study done by Rensselaer Polytechnic Institute in New York and the California Institute of Technology (Caltech), which has considered the importance of the habitat of the creature. Animals that largely live in cluttered enviroments e.g. forests, have developed forward facing eyes and binocular vision so that they can see through objects in front of them, such as leaves or small branches, which enables them to keep sight of their prey.

To prove this, try this experiment – Hold your finger in front of your eyes. Look at it with one eye only, the other closed and it appears a solid object. When you look at it with both eyes and focus on something beyond your finger, you can see through it. This only works with objects no wider than the width of your eyes.

Animals that live in non-cluttered environments (horses, birds etc) are better off taking advantage of greater field of vision. Obviously this theory doesn’t preclude the prey/predator one, but the research shows there does seem to be more than one simple reason for eye positioning.

I’ll never get to see through the eyes of a side-eyed creature, but it’ll never stop me from wondering how they see the world.

Today’s post was brought to you by a forward-facing eyed vegetarian.

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7 Comments

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  1. Julie Helms / Nov 28 2010 5:15 pm

    LOL! We have a problem with our chickens crossing the road this time of year because the field across the street was recently harvested leaving an abundance of corn kernels behind. Just this afternoon I was lamenting that my chickens were not looking both ways before crossing–now, thank you, I no longer need to feel that way! Of course, oncoming traffic doesn’t stop them from walking into the road. So far people have been gracious and stopped and waited…. Great article!

    Like

    • Liz Johns / Dec 5 2010 12:56 pm

      How spooky. We must have been on the same wavelength at that moment, thinking about chickens crossing road. Their panoramic vision doesn’t stop them from going half way, turning round, going back, turning round again, then dashing across the road, though does it?

      Like

      • Julie Helms / Dec 5 2010 1:09 pm

        Well, since my above post one driver was not so gracious and we saw the shower of feathers .
        But I want to thank you Liz, after looking at your blog and a few others I was motivated to start my own. It isn’t smart and scientific like this— just day to day stuff on the farm. If you feel like looking at some non-feathered companions too, please come visit! 🙂
        http://woolyacres.wordpress.com/

        Julie

        Like

  2. Cymbria / Dec 1 2010 6:22 am

    Humans sure need to pay attention to their own habitats before trying out cool visual experiments like the one above lol I just gave it a whirl while sitting at the receptionist’s desk (covering her coffee break) in the middle of my office. True, the pen was transluscent. Also True, I must have looked like a total wacko. All in the name of science… sigh. Excellent post!

    Like

    • Liz Johns / Dec 5 2010 12:54 pm

      Ha – I’d love to have seen you looking cross-eyed at a pen. All in the name of science, eh?

      Like

  3. creatively put / Dec 5 2010 5:15 pm

    I LOVE your article! It definitely is hard to imagine what a bird or other side eyed animals would be looking at or focusing on. I’ve often wondered this when fraternizing with Macaws. Its something very hard to wrap your mind around, and once you do, then it doesn’t make sense again…at least from my perspective! Very cool. 🙂

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    • Liz Johns / Dec 5 2010 5:39 pm

      Thanks for your kind words. It is ultimately impossible to imagine how a bird sees the world. It must be so much bigger for them.
      Where do you get to fraternise with Macaws? Magnificent birds that they are.

      Like

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