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Medical Eyes and Vision

  1. Jun 30, 2011 #1
    Hey all,
    I am curious. I was discussing magic tricks earlier today and how the "hand is faster than the eye." It got me thinking. How exactly do we perceive the world around us? Does the brain take frames from each eye and amalgamate them to produce a 3d model of the world around us like a video camera in a sense or is it a continuous image with no gaps?

    Reason i ask is that the claim was made that its easier to fool a camera than the eye, which I disagreed with. But didn't have a good reason for holding that position as i don't know exactly how we see things. I would like to know why i am right/wrong.

  2. jcsd
  3. Jun 30, 2011 #2

    I like Serena

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    As I understand it, it takes the eye about 200 ms to respond to an unexpected stimulus and then still another 20-200 ms to take in what's there.

    There's more info for instance on wiki: http://en.wikipedia.org/wiki/Saccade
  4. Jul 1, 2011 #3


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    The eye doesn't take "frames" as such, when a camera takes a picture it is a snapshot of what all the receptors are sensing at one time. With the eye your http://en.wikipedia.org/wiki/Rod_cell" [Broken] are constantly firing and not all as a group.

    The brain takes all of these images and builds a picture. However this picture is not a faithful one, the brain is constantly trying to match what it sees to what it knows (ever thought you've seen a person out of the corner of your eye but when your head turns it's a coat?), this is demonstrated by the http://en.wikipedia.org/wiki/Blind_spot_(vision)" [Broken] our optic nerve has to tunnel through our photoreceptors, consequently our brain "fills in" what it thinks is in this blind spot.

    With regards to magic tricks it is not often that the trick involves the hand moving fast, normally it also involves showmanship, misdirection and illusion. For an example of how much faster your hand can go compared to your brains ability to build a composite picture just shake your hand really fast in front of your eye.
    Last edited by a moderator: May 5, 2017
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