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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