View Full Version : OT/ Interesting Illusion

01-20-2006, 03:36 PM
This is an interesting site.


What makes it do that?


01-20-2006, 03:44 PM
wow, I dont know why but thats cool.

it realy works.

3 Phase Lightbulb
01-20-2006, 03:55 PM
Close one eye, and focus on the cross in the middle:


01-20-2006, 04:18 PM
3phase, I think it's in javascript, not just a gif, so all you who were too lazy to click on the link go ahead, it's a good one http://bbs.homeshopmachinist.net//biggrin.gif

01-20-2006, 04:21 PM
The reason is that the human eye gives us pretty crummy images, but the brain makes corrections so we don't know it. A famous example is the blind spot, which we never notice - the brain basically does a "cut-and-paste" from a good part of the image and sticks it in where it's not getting a real image.

In the present case, directly on-axis we can see three colors, and can make full-color images. But most of the off-axis areas of the retina see only two colors at best. So the visuals centers of the brain look at the center of the image, guess what the missing colors should be, and pastes 'em in. Evolution seems to have decided that if we think that whatever's going on over there is important, we'll look directly at it, and then our more capable on-axis retinal areas will give us a better picture. Illusions which tell you to look at one place (thus pre-empting the best part of the retina) and present a moving and/or colored target to a low-color-accuracy area (and a low-resolution area, too) take advantage of that. Think of it as an exploit of a software glitch in the brain.

[This message has been edited by sauer38h (edited 01-20-2006).]

01-20-2006, 04:49 PM
There are two other objects in the picture that blink. At the top of the three o'clock dot is a green triangle and at the inside bottom of the 10 o'clock dot is a red dash. Watch the triangle and see what happens. As you focus on different parts of the picture diffenent thing occur because your eyes can't consentrate on several things at the same time.


3 Phase Lightbulb
01-20-2006, 05:02 PM
<font face="Verdana, Arial" size="2">Originally posted by Scatterplot:

Yea I know. I thought it was more interesting watching all of the dots go away. I think the brain thinks they are defective optic nerves and blend in the background to fill in the missing information or something..

01-20-2006, 05:16 PM

OH CRAP, HERE ITNNNNNNOF DUUOD&DDYYD&*HU*)D)D*)H)))DF*Mf4tgjgpxzpmb89t07749849#$%^^

01-20-2006, 05:32 PM
Its a gif.

you can see the green when you load it into animation shop.

you can change the color or any other effect.

3 Phase Lightbulb
01-20-2006, 05:36 PM
I think it has to do with the level of difusion in the dots.. Try making them solid dots

01-20-2006, 05:48 PM
WJHartson, yes. Easy to see. But not until you pointed it out.

Most interesting. Part of the basis of subliminal whatever?

01-20-2006, 06:04 PM
What happens in that illusion takes place in the visual cortex of the brain, not the eye. The visual cortex is adapted to recognize motion and changes. It has special cells that are particularly sensitive to moving objects and tend to ignore stationary ones.

If an object stays in the same place in the visual field for a length of time it gradually fades away. This is particularly evident if you have floaters in your eye. To see them you need to move your eye so the floaters are slightly disturbed from their usual position and the image falls on a different part of the retina and therfore the visual cortex.

In the case of the purple dots when you fix on the center cross then the purple dots remain in the same place on the visual field and adaption takes place to a non-moving object. This happens in the neurons of the visual cortex. When the purple spots are momentarily switched off in sequence the response of the adapted neurons is to produce an opposite output which is interpreted as green since green is the opposite of magenta. There is no green in the image, just your brain.

If you follow the sequence around the circle the spots never stay in the same part of your visual field so no adaption takes place and no green signal is produced.

01-20-2006, 06:58 PM
<font face="Verdana, Arial" size="2">Originally posted by hoffman:


http://bbs.homeshopmachinist.net//biggrin.gif http://bbs.homeshopmachinist.net//biggrin.gif http://bbs.homeshopmachinist.net//biggrin.gif

thanks, hoffman. You made me spill on the keyboard again.

john hobdeclipe
01-20-2006, 07:48 PM
OK,so they have these flashing pink dots, and when you look at the + in the middle the dots turn green then disappear. So how do they know when I'm looking??? Is this some kind of big brother thing??? Are they gonna send somebody out to take away all the people whose dots disappear??

Lew Hartswick
01-20-2006, 08:42 PM
That is one of the best Optical "ilusions" / phenoma I have seen.
Very good. Thanks for the url.

J. Randall
01-20-2006, 09:48 PM
Unless I really focus on the center, I always see the pink dots along with a rotating green dot. I also easily see the red dash and green triangle. I think my eyes work differently than most because my neck is completly fused from arthritis and bent forward at about 45 degrees. I move my eyes a lot more than most people and I think my brain has compensated for that reason. James

J Tiers
01-20-2006, 10:56 PM
I thought the lime colored twinklies were pretty cool, until they started making the trees melt.

Those darn things keep following me around..... I wonder, will they make YOU melt too?

01-21-2006, 12:09 AM
This phenomenon is related to, although not strictly dictated by, the chemistry of the human retinae. The "cones" of the retinae, highly specialized ciliary cells that allow us to see color (the "rods" allow us to distinguish black/white gray etc), can only detect three distinct wavelengths. These wavelenghts are the primary colors of light, red, green and blue. The are red green and blue, not the primary colors we learned in preschool, red yellow and blue. Anyway, the combination of frequencies is what allows us to see all the different shades and colors.

Now it gets interesting and hopefully applicable to this illusion http://bbs.homeshopmachinist.net//wink.gif The tip of the cillary cell (the cone) has a very very important molecule called rhodopsin, i.e. a protein based compound containg retinal and opsin. With out actually getting into the chemistry of it too too much, there is a double bond between to carbon atoms in the molecule. Double bonds are stiff and require energy to be broken. If a photon (particle of light) of correct energy (i.e. color) hits the rhodopsin, the Pi bond is broken and the molecule twists. The twisting causes the retinal to seperate from the opsin and triggering a furhter and more complex reaction to produce an impulse. The rhodopsin slowly reverts to its original shape. This slowness, however, accounts for differences in color perception. For instance, after being outside on a very bright day, you may walk into your fairly dark shop and everything seems a green color. Conversely walking back outside everything looks pink or magenta. (Hey those are the colors of the dots...hmmm maybe we're onto something) As the initial pulse of magenta light fades, it requires time for the retinal to reattach to the opsin. In the process it hits a distinct orientation angle synthesize green light. The "green" dot appears as an after image burned into your sight as the rhodopsin slowly recovers to its original position, much like the after image of a welding arc or a glimpse of the sun, except those after images undergo several distinct orientations. Welding arc after image generally fades to a magenta color and then to green. (hmm whaddya know, they undergo distinct color changes because they have distinct orientation geometry, thus, due to the fact that only certain orientations produce a signal, only three freuquencies of the balmer series are detected. Based on how many of the 3 million cones detect the three individual photons, the brain can guess about what color is actually being refelcted. wow bet you didn't know that we only see three colors...just think almost every color we see is being faked by our brains...) (i wonder if anyone actually read all of this enormous post...?)

01-21-2006, 12:42 AM

It's much too quick a process for the retinal cells to "burn in". This illusion has nothing to do with the visual pigments. It is strictly in the visual cortex. That is why the illusion is nearly immediately visible.

The specialized cells that detect movement are intended to quickly ignore non-changing objects in the field of view. They react in milleseconds to changes and stop or start firing accordingly. If no changes occur then they quickly stop firing which is why the spots fade from view.

The eye normally makes small jerky motions all the time. They are called saccades. If the eye did not do this the visual cortex would quickly begin to ignore what is stationary in the field of vision.

The cells responsible for this action in the visual cortex are called "simple cells". They are far from simple and feed their signals to the "complex cells".

These cells are not only specialized to detect types of movement but also specific colors. The cells that fire for red, green and blue are generating signals that are summed in other parts of the visual cortex to produce the appearance of color.

If one color is brighter than the others, in this case red plus blue which makes magenta, then the signal from the red and blue sensitive cells outweighs the signals from the green cells. The green cells are also firing because the gray background contains equal amounts of red, green and blue.

After a short time the red and blue sensitive cells begin to desensitize and the output of thoses cells becomes equal to the output of the green cells. The magneta spots then seem to vanish.

The moment a magenta spot is turned off an imbalance occurs for a split second. The red and blue cells have a reduced output now compared to the green cells because the red and blue cells are desensitized from seeing the magenta. The green cell outputs suddenly increase when gray replaces magenta and the effect is for the green signal to outweigh the red and blue. This means the green output dominates for a moment and gives the appearance of green where the magenta was.

Again, the cells responsible for this are not in the eye but in the visual cortex of the brain.

[This message has been edited by Evan (edited 01-21-2006).]

01-21-2006, 12:51 AM
Just a note: When I worked for Xerox I was extensively trained on various color copiers and printers. I first worked on a color copier in the 1970s and saw the first color laser printer in 1979 at PARC. They gave us extensive training on how color works including a lot about how the eye and brain perceives color.