I was enjoying a wall of public stereographs on my a walk today, I've always been pretty "good" at viewing them since I can control my focus distance fairly easily, and I noticed something...

The first time the first image came into stereo focus, it felt like becoming lucid in a dream! All of a sudden out of the vague haziness there was depth and clarity! It was a good stereograph: it gave you something concrete to focus on (a recognizable row of flowers) but at stereo focus hidden animals which were entirely invisible at normal focus in the background became visible. It was a total trip.

Maintaining the stereogram is like maintaining lucidity -- you must maintain the correct focus: lightly, not forcing it, but with some attention to the image you're viewing.

In fact I thought it was an interesting exercise, maintaining the stereo focus on the picture while bringing awareness of peripheral vision all around me at the same time.