Depth perception – or why pigeons bob their heads

Written by: Captain Skellett // September 22nd, 2010 // How Things Work, Science Communication, Science in the Movies

I’ve been doing some science tricks lately that show the difference between both eyes. Simple one, close your left eye and line your two pointer fingers up with one 10cm behind the other. Get them so they are exactly in line and you can only see one finger. Now open your left eye and close your right eye. Not so in line anymore.

So we have two eyes on the front of our face, and they both see slightly different images of our world. Our smarty pants brain puts the images together, but it also notices the difference between the pictures and uses it for depth perception.

The same thing is used in 3D cinema, which you can see when you take off the glasses. There’s two pictures, and when an object is supposed to look closer the two pictures are further apart from each other (winces and waits for SexyMan to correct me.)

That’s why most predators have eyes on the front of their heads, so they can gauge the depth from prey. Prey animals usually have eyes on the sides, so they have a bigger range of vision and can see danger coming.

But when I was doing the hole-in-the-hand trick, it just didn’t work for me. I get a hole on the side, like a someone has taken a nibble out of my hand, but not through the middle like everyone else. Is their something wrong with my depth perception? Am I missing out on a 3D world that everyone else in enjoying in full spectroscopic vision?

My saving grace is those stereogram books, where a 3D picture is hidden inside a pattern and you have to go semi-crosseyed to see it. I rock at those books. Oh yeah. I can see the rabbit, or at least a 3D blob that could be a rabbit.

So I’m hoping I have 3D vision. But I wiki’d depth perception anyway, and it turns out there are lots of ways you can check depth besides having two forward facing eyes. Pigeons bob their heads to do it. By moving their heads a little they can see how objects around them move. Objects which are close to them move a lot, and objects that are far away stay stationary. Try it at home!

Captain Skellett

I be Captain Skellett. Me blog started in April 2009 when I was working full time and didn’t get a chance to talk science. Now I have changed jobs and talk science all the time, but that doesn’t stop me blogging. More About Captain Skellett   Google


One Response to “Depth perception – or why pigeons bob their heads”

  1. […] The electroreceptors are located in rows on the bill, which might help the platypus find the direction of the prey by noticing which receptors pick up the electricity first. We do the same thing with our ears, hearing sounds at slightly different times to tell us the direction of the sound. It hunts by moving its bill side to side, possibly to reveal how far away the prey is. It’s similar to how pigeons bob their head for depth perception. […]

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