Brought to you by Stuart Inglis
Most Stereogram pictures are usually generated so that if you look at (converge your eyes on) a position twice as far away as the picture, and focus on the picture, generally after a few minutes you see a surprising 3D image!
Most people find this extremely difficult for the first time. You have to focus on a point which is different from where you are looking. This is known as "de-coupling" your vision process. Instinctively people focus at the same point they are looking at, and this is the main obstacle in seeing images of this type.
This is why most stereogram posters come with a reflective surface such as glass or plastic covering them---if you try to look at your reflection you will be looking at a point twice as far away as the actual poster. It has been noted by almost everyone that while this sometimes helps beginners see the 3D effect for the first (and perhaps even the first few) times, experienced viewers to not need any help like this, and indeed the reflection is usually very distracting and decreases the quality of the 3D effect.
There are many ways to teach this de-coupling to either yourself or to others, including (in almost no particular order):
NOTE: If you wear glasses try with and without them on. Some near-sighted people can see them easier without their glasses on (if they get closer to the picture).
The pull-back
Hold the picture (or move your face) so your nose is touching the picture. Most people than can not possibly focus with something this close to their eyes, and they will be content with their inability to focus. With the picture up close, pretend that you are looking straight ahead, right through it. Now slowly pull the picture (or your face) away while keeping your eyes pointed straight ahead. If you do this slow enough, an image usually appears when the picture is at the correct distance.
The reflection
As mentioned above, with a reflective surface it is sometimes a lot easier to converge your eyes in the correct position. You simply focus on your nose or some central reflection in the picture, and wait until you focus on the image.
The drunk-eyes
This method is used to describe the feeling of the process of deconverging your eyes. It is very much like being drunk or having "staring-eyes". Your eyes don't look at the object, but rather through it. This state is common to some in the morning before the coffee caffine fix.
The wall, or the finger
Hold the picture so that it is half between you and a wall. Look *over* the top of the picture towards the wall, and focus on something such as a picture hook or mark. While keeping this "gaze" either slowly lift the picture or lower your eyes while keeping them converged on the wall.
A similar approach (but for cross-eyed viewing) is to stand arm's length away from the picture and put your finger on the picture. While slowly pulling your finger towards your face, keep looking at your finger, you will notice the picture becoming blurry, and at an intermediate position you will (eventually) see the 3D image.
And if you're still having difficulty, this comment by jhakkine@cc.Helsinki.FI (Jukka Hakkine),
may apply to you:
"Richards (1970; Experimental Brain Research 10, 380-388) did a
survey among 150 MIT students and noticed that "...about 4%
of the students are unable to use the cue offered by disparity, and
another 10% have great difficulty and incorrectly report the depth
of a Julesz figure relative to background." He further concludes that
inability to use stereopsis is an inherited defect and is related
to "three-pool"-hypothesis of binocular neurons."
But don't dispair, don't give up until you're tried for at least a month!
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