Single image random dot stereogram: principles and clinical implications.

The single image random dot stereogram is different from traditional stereograms in that it does not require a stereoscope or stereo glasses for viewing. There is an artistic variation of these stereograms in which the random dots have been replaced with colorful geometric patterns. An observer needs to view them according to specific instructions. While most observers can see the hidden stereo images after a few trials, some are not able to perceive the effect even after numerous attempts.This paper explains the underlying principles by which these stereograms are constructed and describes the reasons why some individuals are not able to appreciate this stereo effect. A unique requirement for the successful viewing of these stereograms is divergence of the eyes from the plane of the stereogram. This unusual divergence may be the reason for unsuccessful viewing. By converting a single image random dot stereogram to a Brewster stereogram, an observer can view the same stereogram with a stereoscope, thus eliminating the divergence requirement.Using this modified viewing method, some previously unsuccessful observers were able to see the stereo effect.The main reason for unsuccessful viewing by a person with normal stereo vision is an inability to initiate or maintain the proper amount of divergence.