Why does our brain invert the image received from our eyes?

  1. There's really no such thing as "upside down" in an absolute sense, only relative to what we're used to. Why then does our brain invert the image? What's wrong with leaving it the way it is?
     
  2. jcsd
  3. How do you figure? If my perceptions changed would the trees, rocks and objects in my surroundings conform to my changed perception? Most would say no. Our vision needs to correlate to our surroundings otherwise it would be of no use at all.
     
  4. Evo

    Staff: Mentor

    Apparently it allows us to see a larger image.
    http://retinaeyedoctor.com/2010/03/eye-images-reversed-on-retina/ In answer to "why not leave the image upside down" Our brain flips it back so that what we see matches our physical experience.
     
  5. They wouldn't need to change, I don't see your point. The world doesn't "look like" anything independently of how our brains choose to model it. I don't see how it is any less correlated before it's inverted - it's just that we're used to it this way.

    And to Evo: I'm not sure what you mean "match our physical experience". If it was upside down (compared to the way it is now), then that would be our physical experience.

    The part about having a larger field of vision is very interesting.

    Edit: Although it seems the larger field of vision only comes from the pinhole aspect and not the actual reversing at the end, although I may have misunderstood.
     
  6. Perception is not reality. If I perceive a rock flying in at the top of my field of vision then I duck. If I perceived that correctly I live, otherwise I die. The brain flips the image around so that when rocks actually fly at us we know to duck rather than jump. Why does the brain do that? Presumably because of natural selection.
     
  7. Evo

    Staff: Mentor

    No, it would only be your visual experience.

    Great example Academic.
     
  8. Pythagorean

    Pythagorean 4,632
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    That doesn't quite settle it though. The point I think is being made in the OP is that if the image were upside down, we'd just learn to jump when a projectile is up high and to duck when it's low, and our generalized model of up and down would be flipped from what it is now.

    I'm curious whether a system like the brain will always eventually correlate information in a way that reduces computational stress, so even if we wired ourselves so that we saw the image upside down, it would eventually correct itself if plasticity allowed.
     

  9. The image is upside down on the retina, and we have learned to jump with a projectile is high and duck when it is low. This is what 'brain inverting the image' means, it means that the brain knows when to jump and when to duck based off of the inverted image projected on the retina.
     
  10. Evo

    Staff: Mentor

    It does, apparently. I'm trying to find something about this study mentioned, I have found a different study for a longer duration.

    http://www.physlink.com/education/askexperts/ae353.cfm
     
  11. Monique

    Monique 4,699
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    Not exactly, the inverting is a plastic process. When you wear special glasses that turn the world up-side-down, the image will invert after some time. When you take the glasses off, the brain adjusts again.

    I think it is a really interesting concept, why do we all see our feet as "down", how does our brain learn to interpret the world. What happens if someone grows up in 0 gravity and comes to our world, would they have a concept of up and down and how would their brain adjust?
     
    Last edited: Jul 8, 2010
  12. Sure, the inverting process is plastic. That is completely consistent with my quote, isnt it?

    The brain figuring when to jump and when to duck is the brain inverting the image.
     
  13. I believe you may be getting tangled up in the statement "the brain inverts [the] image". It is really more precisely stated as "the brain interprets the image as inverted". And that is simply because our brain has learned that a positive lens creates an inverted real image of an object.

    In other words, your brain interprets direction on the retina to be inverted compared to an object in space. It does this because the optics of your eye (cornea/pupil/lens) have formed an image on your retina that is inverted compared to the object in focus. E.g., your brain has learned that when the image of your hand on your retina moves 'up' (towards the top of your head), your hand in front of your face is actually moving 'down' (towards your feet).

    Hopefully I've understood your question well enough to clear it up for you.
     
  14. Monique

    Monique 4,699
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    This is not true, since if you project the image the right side up, your brain adjusts as well. Academic, that's what I addressed in your quote, you start off by saying "The image is upside down on the retina", but in essence that has nothing to do with it.

    The original report: Some preliminary experiments on vision without inversion of the retinal image.
     
    Last edited: Jul 8, 2010
  15. Has nothing to do with what? I thought thats what this post was about, the image being projected upside down on the retina.

    So you can change that with lenses and make the image right side up on the retina. In that case the brain then inverts the image again to make it consistent with reality. It re-calibrates your motor movements to properly correlate with your visual observations The question is why does it do that, and the answer is so that it can cope with its surroundings. (that is, so it can jump or duck in the right situation)


    edit - After re-reading this thread I think an issue is the perceived difference between the brain inverting the image and its calibration with your body to move correctly. Its almost like the question is why does the brain invert the image rather than recalibrating motor movements. My answer would be, those are the same thing.
     
  16. Monique, your statement quoted above is, well, annoying. It is annoying because it is carelessly vague. You say "this is not true". WHAT is not true? My whole post? The statement that a positive lens creates a real inverted image? I tried very hard to be precise and clear and define my terms and the problem I was solving, like a good physicist. You throw around pronouns like a 5-year-old.

    You then follow that four word opacity with the non sequitur "since if you project the image the [sic] right side up, your brain adjusts as well." Hmmm, it may be true that your brain adjusts, but that invalidates NONE of my post. When your retina receives an inverted image, your brain interprets the image as inverted. What your brain would do with an upright image, I remained silent on.

    Your final sentence is the kicker: "... IN ESSENCE has nothing to do with IT." (my capitals). What is it? Again, a pronoun that brings no clarity, only mud. And "in essence"? What essentiel element do you think you're distilling here?

    I'm new to this forum, but what I'm reading here on this thread and on other threads erodes my eagerness to participate-- rather than people asking physics questions and getting straightforward, simple-to-understand physics answers, I'm seeing vagueness, confusion, lack of definitions, grand leaps into metaphysical speculation, and nonsense like "0 gravity". Is this a forum for chit-chat and casual conversation about aliens, or are we trying to help people understand the physical world around them?
     
  17. Monique

    Monique 4,699
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    In this forum we treat other members with respect, I suggest you adjust your attitude.
     
  18. Andy Resnick

    Andy Resnick 6,010
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    I think you are confusing the retinal image with 'visual perception'. Yes, the image on the retina is inverted. By the time the nerve impulses have passed the optic chiasm, the lateral geniculate nucleus, into V1 and then back out to the extrastriate cortex, so much processing has occurred that it hardly makes sense to even reference back to the retinal image.

    For example, an elementary unit of visual perception is an oriented bar, not a point. We do not yet know how we extract information (beginning with 'up' and 'down' all the way through object recognition) from the retinal image.

    At this point in time 'why?' is not a good question to ask. Better to ask 'How?'.
     
  19. Pythagorean

    Pythagorean 4,632
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    Yes, but we're talking about the perceived image. As Monique is saying, the retina has nothing to do with it, it was merely the spark that triggered the OP's question. The question itself pertains to the image as processed by the occipital and parietal lobes (at the least).

    So to restate my post, if the image were perceived were upside down, we'd have learned how to adapt to it with muscle control. But I assume (and em encouraged by responses in this thread) that this would be computationally expensive to navigate through the world like this, so the brain (or the genetic basis of it) already long ago decided it was computationally cheaper to align the map with the terrain (as we prefer to do when using GPS).
     
  20. Whats the difference between 'adapting to it with muscle control' and 'aligning the map with the terrain'? Those are the same thing. They are each essentially setting 'y' to '-y'.
     
    Last edited: Jul 8, 2010
  21. Pythagorean

    Pythagorean 4,632
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    Not quite. Vision processing is handled largely by the occipital lobe and then integrated into our spatial world model in the parietal lobe.

    The motor cortex, and other parts of the brain that handle coordinated output are different (both in terms of location and in terms of information processing).

    Some automated muscle movements like reflexes don't even require information from visual input. They're based mostly off mechanoreceptors and the network topology.
     
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