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    Thread: Visual Phenomena & Optical Illusions

    1. #1
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      Visual Phenomena & Optical Illusions

      I thought it might be nice to open a thread and start a collection of people´s favourite optical illusions and maybe related stuff.


      Here is something I find very impressive:



      The thing is - you back away from the screen - I had to go to the other side of the room, but I have good eyesight...
      And the faces swap expressions - the left one looks calm and the right one looks angry ..
      Go closer and it reverts back.

      Quote Originally Posted by grandillusions.com
      When we look at an object, we can normally see both fine detail and coarse detail. However when we are close, the fine detail will dominate, and when we are further away, we lose the fine detail, and see more of the coarse detail.
      Both of the faces you see above are hybrids - each face is actually a combination of two faces. The left hand face shows an angry man in fine detail, but within the picture there is also coarse detail of the calm face. Move away, and you lose the fine (angry) detail, and just see the coarse (calm) detail.
      The right hand face shows the calm face in fine detail, and the angry face in coarse detail.




      What made me think of this thread in the first place was an age-old thread about one of my favourites of all time.
      The Spinning Girl Illusion:

      The following is a mix of my own words and an edited quote from on here: neurologicablog.

      Take a look at the spinning girl above. Do you see her spinning clockwise or counter-clockwise? I first saw it spinning clockwise, and I had a hard time getting it to switch direction. Today it started counter-clockwise and tends back there.
      Give it a try!

      The visual system evolved to make certain assumptions that are almost always right (like, if something is smaller is it likely farther away). But these assumptions can be exploited to create a false visual construction, or an optical illusion.

      The image is not objectively “spinning” in one direction or the other. It is a two-dimensional image that is simply shifting back and forth.

      But our brains did not evolve to interpret two-dimensional representations of the world but the actual three-dimensional world. So our visual processing assumes we are looking at a 3-D image and it uses clues to interpret it as such. Or, without adequate clues it may just arbitrarily decide a best fit – spinning clockwise or counterclockwise. And once this fit is chosen, the illusion is complete – we see a 3-D spinning image.

      Tips:
      Look around the image, focus on the shadow or some other part in the picture -or what works best for me - read the text of the post while having the illusion in the peripheral field of vision too and switch attention.


      So you may force your visual system to reconstruct the image and it may choose the opposite direction, and suddenly the image will spin in the opposite direction.

      Since I can´t put text next to it - you could zoom out your screen-view to see her (partly).

      It is unfortunate that this illusion is sometimes put forth to support the myth about people being either more right-brained or left-brained.
      See the link above for arguments.



      By the way - I was a bit shy to open new threads and when stumbling over this pet illusion of mine and vigorously posting - I came to learn a new word!!
      I do realize now what "necroposting" means and that it is indeed not a good idea..
      Made me smile, this expression.

      Looking forward to seeing, what you find cool - I like going search-surfing for such things and will surely follow up!
      Oh - and - out of context - but I love this smiley and might put it as an end point again..



      Last edited by StephL; 10-25-2013 at 12:32 PM. Reason: mini-tweak..
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    2. #2
      Xei
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      Never seen the faces one before. It's amazing. And such a great demonstration of how the brain works. Thanks.
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      I like destruction and reality, and one invariably leads to the other.

      'Dreams are real while they last. Can we say more of life?'
      'We die to remember what we live to forget'

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      I've been seeing the dancer one so frequently the last few years it's getting boring. And yes, I can switch its direction over and over if I concentrate. This one remains my favourite. I used to have it as a desktop BG and would RC every time I saw it, leading to my first LD.



      Everyone's seen the dancer, but has everyone seen the spinning cat!? You can produce the effect with any silhouette. This one is a bit trickier to turn around because there's no shadow.
      EDIT: Wtf... what's weird about this one is, whenever I look away from it but keep it in the corner of my eye, I see it moving clockwise, but I can't look directly at it without seeing it counter-clockwise.

      Last edited by Dianeva; 10-26-2013 at 12:47 AM.

    5. #5
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      Quote Originally Posted by Xei View Post
      Never seen the faces one before. It's amazing. And such a great demonstration of how the brain works. Thanks.
      Thanks - they are really impressive - and I almost didn´t go away from the screen and tried it out when I first saw it.

      smile.gif

      Quote Originally Posted by GigaByte777 View Post
      Yepp!


      Quote Originally Posted by Dianeva View Post
      I've been seeing the dancer one so frequently the last few years it's getting boring. And yes, I can switch its direction over and over if I concentrate. This one remains my favourite. I used to have it as a desktop BG and would RC every time I saw it, leading to my first LD.



      Everyone's seen the dancer, but has everyone seen the spinning cat!? You can produce the effect with any silhouette. This one is a bit trickier to turn around because there's no shadow.
      EDIT: Wtf... what's weird about this one is, whenever I look away from it but keep it in the corner of my eye, I see it moving clockwise, but I can't look directly at it without seeing it counter-clockwise.

      I like these Kitaoka snakes as well - he made lots of anomalous motion and other illusions ..
      But how cool is that - you used it as RC and had your first LD with it!!



      And yeah - I should have looked for a less overused silhouette illusion - liking the cat!
      I can stabilize both directions so that they stay, whether I look directly at it, or more peripheral - also by changing where I have the cat in my field of vision.


      Made me laugh:



      This one is quite flashy:




      I´ve been doing the following as a kid - you people probably did too.
      It seems it got a name and a paper has been written on it in 1928 by one Sharp.
      Hopefully it´s not boring.
      What I find really fascinating is that you can do what you want - fingers 2 cm apart, fingers touching, back and forth - you will always have a sectioned sausage between the finger-tips - no normal merging when the focus is off.


      Quote Originally Posted by michaelbach.de
      The Notorious Frankfurter Illusion





      What to do & see

      If you have two roughly equivalent eyes you will see a ‘sausage’ floating in front of you in mid air, by following these steps:

      Hold your hands in front of you, at 20–30 cm distance from you, at eye level.

      Point your index fingers against each other, leaving about 2 cm distance between them.

      Now look “through” your fingers, into the distance behind them.

      The sausage should appear now, and you can change its length by varying the distance between the finger tips.

      For most observers, the sausage will look blurred, at least initially.

      If you try to look at the sausage, it will disappear, it is only present if you look at something more distant than your fingers.

      It helps if the background is rather homogenous and has a color very different from your fingers.


      Comment

      Basically, this ‘sausage’ is caused by two mechanisms, (1) physiological double images and (2) interocular rivalry and suppression.


      When you look at your fingers, the gaze direction of your two eyes is angled towards each other, so that their lines of sight meet at the target. When you then look into the distance, your eyes shift slightly outward, making their lines of sight nearly parallel. For close objects the image in the two eyes is consequently no longer at the right position, the images are no longer merged and can appear double for your “inner eye”. This is quite normal and occurs all the time, usually these double images are suppressed. So, if the two images overlap, why then doesn't the compound image look like the figure below?




      At the end of the image of each finger, there is a rivalry between the image from the two eyes when the brain tries to combine them. In one eye the finger ends, in the other it continues. So what does your brain do in such rivalry situations? If the two images are rather similar, the percept can oscillate between the alternatives. Here, however, we have a high contrast step in one eye, namely the end of the finger, where it is replaced by the background. In rivalry the eye with the higher contrast wins, at least locally; this is here meant by the term ‘suppression’. In the figure on the left this high contrast step is symbolised by the yellow halo.


      Last edited by StephL; 10-26-2013 at 10:49 PM. Reason: ongoing tinkering..
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    6. #6
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      This is maybe the most fascinating phenomenon I came across while looking for stuff for this thread - do click and play with it!!

      "Biological Motion" - it demonstrates how the brain and visual system can form a 'Gestalt' just from some moving dots:

      BioMotionLab

      One very compelling example of the visual system's ability to recover object information from sparse input is the phenomenon known as biological motion. Here the activity and identity of an animate creature are compellingly created using just a dozen or so "light points" strategically placed on the individual's body (Johansson 1973). With these animation sequences, no single dot conveys information about the object or event being depicted - individual dots merely undergo translational and/or elliptical motions. Perception of a biological organism engaged in an activity must entail global integration of these motion signals over space and time - perception of such animation sequences is literally the creation of motion information (in the same sense that perception of an object in a random-dot stereogram is the creation of binocular disparity information). When viewing point-light displays, observers can identify the gender of an actor (eg, Kozlowski & Cutting 1977; Mather & Murdoch 1994), the activity in which he/she is engaged (Johansson 1973) and, even, the emotional state of the actor (eg, Brownlow et al 1997). Human infants as young as 3 months of age can perceive biological motion (eg, Fox & McDaniel 1982), as can non-human mammals (Blake 1993).

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      Illusionary Light-"Emittence":





      Happy Reflections:





      Now something delicious - if only they had used a high-speed camera for this..

      Quote Originally Posted by guyism
      What do you get when you combine a spinning chocolate sculpture and a perfectly timed strobe light? A mind-blowing optical illusion.
      This is an exhibit at Melbourne’s Phillip Island Chocolate Factory, not to be confused with R. Kelly’s Chocolate Facotry. If you look closely as the sculpture starts to spin, it’s obvious how it works, but that isn’t the point. It looks awesome. I didn’t quite have the same emotional experience as the guy who said, “Now I’ve seen it all!” though.
      If this can be called a phenakistoscope, like somebody suggested, I have only ever seen the two-dimensional versions, like the one from Wikipedia below.




      Quote Originally Posted by Wikipedia
      The phenakistoscope (also spelled phenakistiscope or phenakitiscope) was an early animation device that used the persistence of vision principle to create an illusion of motion.

      Although the principle behind the phenakistoscope had been recognized by the Greek mathematician Euclid and later in experiments by Newton, it was not until 1829 that this idea became firmly established by Belgian Joseph Plateau. Plateau planned it in 1839 and invented it in 1841. Later the same year the Austrian Simon von Stampfer invented the stroboscopic disk, a similar machine. A contemporary edition of Britannica says "The phenakistoscope or magic disc...was originally invented by Dr. Roget, and improved by M. Plateau, at Brussels, and Dr. Faraday."

      Technology

      The phenakistoscope used a spinning disc attached vertically to a handle. Arrayed around the disc's center were a series of drawings showing phases of the animation, and cut through it were a series of equally spaced radial slits. The user would spin the disc and look through the moving slits at the disc's reflection in a mirror. The scanning of the slits across the reflected images kept them from simply blurring together, so that the user would see a rapid succession of images that appeared to be a single moving picture.

      A variant of it had two discs, one with slits and one with pictures; this was slightly more unwieldy but needed no mirror. Unlike the zoetrope and its successors, the phenakistoscope could only practically be used by one person at a time.

      Etymology

      The first part of the term 'phenakistoscope' comes from Greek φενακίζειν (phenakizein), meaning "to deceive, to cheat", as it deceives the eye by making the objects in the pictures appear to move.

      Alternate names

      Online sources sometimes refer to this invention as the Phantasmascope or the Phantascope. However, Phantascope is also the name given to two different, later, projection-based moving picture devices by John Arthur Roebuck Rudge.

      Today

      The Special Honorary Joseph Plateau Award, a replica of Plateau's original phenakistiscope, is presented every year to a special guest of the Flanders International Film Festival whose achievements have earned a special and distinct place in the history of international film making.



      Link To Video - Disk in Action*

      *too big for here.. hm... maybe for youtube as well..

      Last edited by StephL; 11-02-2013 at 06:50 PM. Reason: little corrections..
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    8. #8
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      To get the spinning woman to switch directions all I have to do is close my eyes and visualize her spinning in the opposite direction, or if that doesn't work (which it occasionally doesn't) I focus my attention on the foots reflection and then switch back and forth looking at the foot and its reflection while imagining her spinning the opposite direction. Almost always works for me.

      [edit]
      The cat is easier to switch. Once you realize the illusion is in that the cat is actually spinning at all, you imagine it going the opposite way when it's facing "backwards" and since there are less frames it switches more easily.

      The face one makes sense how it works. The finer detail is visible only from close up, but the shadow and lighting detail becomes apparent as the finer detail is lost due to distance. It looks like they took two pictures of two different expressions, took them in photoshop, made a high pass filter of both and copied and pasted the opposite face and overlayed them onto each other, while mildly blurring the original background image. That one makes much more sense than the spinning cat and woman imo.

      [edit 2]
      That's what I get for just looking at illusion and not reading the post--didn't realize the face one was already explained.
      Last edited by snoop; 11-02-2013 at 07:46 PM.
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      Quote Originally Posted by StephL View Post
      Illusionary Light-"Emittence":

      That's an interesting one I've never seen before, thanks for posting. I looked at it for a bit, not understanding what the illusion was. Of course I couldn't stare at it for more than a second before the light felt too bright and I kept scrolling down. Then I realized way embarrassingly late - that was it! Bright light can't emit from a computer screen.
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      Quote Originally Posted by snoop View Post
      To get the spinning woman to switch directions all I have to do is close my eyes and visualize her spinning in the opposite direction, or if that doesn't work (which it occasionally doesn't) I focus my attention on the foots reflection and then switch back and forth looking at the foot and its reflection while imagining her spinning the opposite direction. Almost always works for me.

      [edit]
      The cat is easier to switch. Once you realize the illusion is in that the cat is actually spinning at all, you imagine it going the opposite way when it's facing "backwards" and since there are less frames it switches more easily.

      The face one makes sense how it works. The finer detail is visible only from close up, but the shadow and lighting detail becomes apparent as the finer detail is lost due to distance. It looks like they took two pictures of two different expressions, took them in photoshop, made a high pass filter of both and copied and pasted the opposite face and overlayed them onto each other, while mildly blurring the original background image. That one makes much more sense than the spinning cat and woman imo.

      [edit 2]
      That's what I get for just looking at illusion and not reading the post--didn't realize the face one was already explained.

      Wow - great tips!
      Cool.gif



      Quote Originally Posted by Dianeva View Post
      That's an interesting one I've never seen before, thanks for posting. I looked at it for a bit, not understanding what the illusion was. Of course I couldn't stare at it for more than a second before the light felt too bright and I kept scrolling down. Then I realized way embarrassingly late - that was it! Bright light can't emit from a computer screen.
      It even seems to be emitted by plain paper - first I thought, it was too simple to post it - but it´s funny, how you can almost not trick yourself out of the avoidance of stuff that gives you blinding sensations.
      It does take a while of looking at it to realize this.


      One more:



      Not really something nobody saw before - but stunning non the less I find - and you don´t have to look it up - I can directly post the thing.

      Watch the X in the middle very closely. You should start to see a green dot that rotates around the circle - this dot is an illusion; then you should see see the purple dots disappear.... but they haven't really gone. It is an after image effect, sometimes called a 'negative retinal afterimage' - move your head slightly, and the dots will reappear...
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      Described first in 1998 it fits fantastically with modern neuroscience - and I have the nagging feeling, this has a lot to do with forming a dream-body as well.

      It is described as a process of fusing perceptions together here.
      Another related term is binding - maybe I will put something up on that as well.

      There have even been experiments with whole body illusions in the waking state - but I want to search for the best stuff.
      That might take a while.
      These are the basics - enjoy!

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      Quote Originally Posted by ??
      The Margaret Thatcher Effect:The demonstration above is called the "Margaret Thatcher Effect" (named after the former Prime Minister of England - (all Britain actually) whose face is depicted). Look at the face on the left. The eyes and mouth of Margaret Thatcher have been inverted relative to the rest of her face. It's interesting that these distortions are much easier to notice when the face is upright than when it is upside-down.
      Found this sort of nice..
      It's the original thing, these pictures - I saw it on Qi (Quite interesting) and they did it newly with better photos - it's actually much more striking there: http://www.youtube.com/watch?v=T2amZ...730E0F313A9B16 from 24:50 min. - don't complain, if you get amused pretty dirtily further on, though..
      Last edited by StephL; 03-03-2014 at 04:31 PM. Reason: Open to suggestions..

    13. #13
      Xei
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      Prime Minister of Britain.
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      Yeah - and she doesn't look a nice person - in both versions.
      I've failed to make visible the fact that I copy-pasted part one of the text - didn't notice the omission.
      And usually I do use the quote function for external quotes ..
      Caught myself a lapsus - it's corrected now!
      Which part of Britain are you from, by the way? Just wondering, why your emoticon has such red a colouring..tongue.gif

    15. #15
      Xei
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      England.
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