myself i learnt to see double with this kind of images, couldnt at all before:
if you think about it evry artificial 3d you cross the eyes
so maybe thats the method to see 3d(like a 3d movie) in real life
edit:
basically the training which got me to see auras and see sometimes stereovision as to discover tv is actually stereovision is this, oh also its healing my shortsigthtedness:
i look very slightly double as to let my brain do the overimposition
this is very tyring though
edit:
basically i believe people look wrong:
one should converge the rays of the eyes not in the object youre looking at but at midle disctance to the the object
my biggest success so far is not seeing auras or in stereo but i have manage for moments to see perfect without glasses when i have 8 dioptries of shortsightedness
