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Wheel illusion

  1. Apr 22, 2010 #1
    I'm sure this is a dumb question, hence why I ask people of da netz.
    So, when a car wheel spins slow/medium speed, you can see it make revolutions. But then it goes faster, you cannot see it make individual rotations.
    Duh.
    I get that...but why does it appear to spin slowly BACKWARDS? I understand our eyes can't see it spin well, but why backwards?
     
  2. jcsd
  3. Apr 23, 2010 #2
  4. Apr 23, 2010 #3

    HallsofIvy

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    Also please not that you will NOT see a wheel appear to be moving backwards in "real life". That illusion is produced when you watch a motion picture and is produced by the timing of the individual frames of the picture.
     
  5. Apr 23, 2010 #4
    I've never thought about that until you mention it, the frame rate or Hz of the 'picture' does indeed create that. however I've seen the same effect in the 'real world', I think it has to do with the brains ability to process the information from the visual cortex and the 'expected' image, from what I recall the visual cortex can only supply so much information and the brain then has to provide an image and a memory of the image to keep a continual 'smooth' moving picture. In some instances if your field of vision moves to fast the time rate is off and you'll get odd illusions.

    example, watching the second hand on an anolog clock and quickly looking away then back will make the hand appear to move backwords and repeat time, it's the brain going off memory that is fooling you into seeing whats not there.

    I'll see if I can dig up the article on it, it was in a neurobiology paper awhile back.
     
  6. Apr 23, 2010 #5
    quick addition, another reason why having instruments record data is far superior to just 'our' observational recording. the parietal lobe, basal ganglia and dopamine control the 'time sense' and as we age or have problems with dopamine levels the sense of time and the rate at which your brain perceives time changes. This would lead to miss-matched observations when trying to correlate them between observers.
     
  7. Apr 23, 2010 #6

    SpectraCat

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    No, I really don't think this is correct ... I have seen this effect in real life (in outdoor ambient light) many times. I think madhatter's hypothesis about the intrinsic frame-rate of our eyes/brains sounds very plausible.
     
  8. Apr 23, 2010 #7
    if you want some good reading, look up frames of reference for perception and action. there is two distinct pathways in the cerebral cortex for these, so that visual illusions do not alter physical movement, in other words, what we think we see is not always what guides our actions.

    here's a start...
    http://www.mitpressjournals.org/doi/abs/10.1162/089892998563824
     
  9. Apr 23, 2010 #8
    Yes sir... You must have seen the same effect in the real life too.... Though you must mention the place too, where you have seen the effect.... At night or in the broad day light?
     
  10. Apr 23, 2010 #9
    It's usually been indoors, the Hz of the lighting is going to create this. fluorescent bulbs being the primary light source indoors and in the workshop.
     
  11. Apr 23, 2010 #10
    That's a really weird illusion.
    And I do see that in real life. It's trippy. o_O
     
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