How to See Stereograms
There are several techniques that help in seeing stereograms, or SIRDS (single image random dot stereo) as they are sometimes called.
The techniques listed here are helpful for converged viewing, where you look through and past the image as opposed to cross-eyed images. Converged images are much more popular in general, however, the cross-eyed technique has one major benefit. They can be used with very large images, the size of billboard, or larger. The cross-eyed technique can also be easier to see, since you can simply look at a pencil tip between you and the image to create the correct focus.
Be relaxed and give it some time.
First, a few hints to make viewing stereograms easier:
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In general, you want bright lighting when you are learning to view 3D illusions.
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Some people who wear glasses will find it easier to if they take them off as long as they can move close enough to the image to see it clearly.
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Look straight on, don't twist your head. The 3D illusion is most apparent with your head level.
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Be relaxed and give it some time.
De-Coupling
The main trick to seeing stereograms is learning to de-couple your focus and eye positioning. You will need to position your eyes as though you were looking at an object about twice as far away, while focusing on the image. Instinctively you focus on the object you are looking at... with our free 3D illusions, you will have to LOOK at an imaginary object twice as far away while FOCUSING on the image.
Sound tricky? Well, it is a little tricky until you get the hang of it. With practice, it will become easy, and we've got a few ideas that you can try.
Look at the Reflection
As we said above, you'll need to LOOK at something about twice the distance of the image. It turns out we have something that is almost always available that is the exact distance... your reflection. By looking at your reflection on your computer monitor, or if you are looking at a book of stereograms, SIRDS, or 3D optical illusions, you will notice they often come with glossy coatings that are shiny enough to let you see your reflection.
After looking at your eye, simply stop focusing on your eye, and try to see the image. Repeat, switching your focus from your eye to the image, and your reflection... and suddenly you will get it.
The Pullback
Get very close to the stereogram, and very, very slowly pull it away (or move away from it). At first you won't even be able to focus on the image... However, keep moving the image in and out, relaxing, and it will appear.
The Transparency
If possible, copy some of the simple SIRDS images onto a transparency. Next, hold it out in front of you halfway between your eyes and a wall. Now change your focus from the image to the wall and back again repeatedly. If you do not see the effect immediately, you can move the image in and out while continuing to change your focus back and forth.
Good Luck, and Enjoy!
Source : https://www.focusillusion.com/Instructions/
Why Some People Cannot See Hidden Stereogram Images
by Jason Weekley A.B.O.C., L.D.O.
The basic principle behind a stereogram depends on the ability for a person to merge multiple objects into one. There are many factors that could inhibit a person's ability to see the object hidden beneath the initial surface. As an example....place your thumbs and index fingers together in the shape of a triangle, and find an object in the distance to look at through the triangle. It must be a distant object! independently close one eye, then the other....you will notice that you were only able to see the complete object through one eye without moving the triangle. This concept is called eye dominance. Sometimes the brain will shut off one eye, and rely on the dominant eye, if the object to be viewed doesn't come in focus. There are many people who need corrected vision that don't realize it because of the human ability to adapt.
Another possible cause is convergence. At close range (12-18 inches), your eyes converge an average of 3mm...but this is not so for everyone. Just as you have a dominant eye for distance, you will also have a dominant eye for near. After years of depending on one eye to do the majority of the work, you can depend less on convergence and adaptability. By allowing your eyes to relax, and blur....you attempt to overide your brain's intent, and allow both eyes to be equally dysfunctional. Thus, images begin to overlap and the muscles that control your eyes are less likely to fix at the same point that they normally would. The same people that have problems crossing their eyes...even a little...will have the greatest frustration when attempting to view stereograms.
Other conditions such as esophoria and esotropia can cause the eye to move inwards...(commonly called a lazy eye), and exophoria and exotropia (a tendency for an eye to shift toward the temple), will have an impact. I would suggest that people could adjust their distance from the stereogram and have a greater rate of success. A distance that works for the majority, doesn't always work for everyone. And last but not least...I would enjoy the statistics relating the ability of a person to see stereograms with regard to their profession. Analytical/Artistic mindset?
©1998, Jason Weekley
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