There's a damn good reason stereoscopic imagery is so painful for many people: we evolved (in all likelihood) from something that survived because it was capable of noticing the twitching tail of that tiger, and very quickly tracking it and focussing on it to decide whether it's going to bite us or not.
Until the 3-d directors (I'm looking at you, Cameron) can provide an image which is in focus at all depths, we're going to be stuck with moving elements on which the eye tries to track and focus and *can't*.
Eye tracking angle is only one of a list of cues the brain uses to position objects in space, and I'm not convinced it's even the most important one:
- relative size (this cow is small, but that cow is far away)
- absolute size (people are much the same size, so that smaller one must be further away; mountains are *huge* so if you can see it all it must be distant)
- relative colour (blue atmospheric haze, for example)
- occlusion (near objects hide far objects)
- similarity of view (seeing slightly different views of an object, and how different they are)
and of these it's probably focus that causes (literally) the most headaches. Stereoscopic projection requires that the eyes focus on the screen - effectively close to infinity, or at least the hyperfocal distance) while the tracking information insists that the object is nearer. Which is why it's less of a problem when the stereo field is beyond the screen, and why Cameron's floating thingies irritated all the way through the film.
In the 1890s, the 'American Pattern' stereograms were very popular, and they're still effective - largely I believe because the contact prints used had very good resolution. The image is at infinity (tilted lenses in the viewer) so every detail is sharp, wherever the viewer looks - and the main cue is the differing *view* rather than the eye tracking position.
But films have a grammar all of their own, and the directors pull the focus to guide the viewer's attention... and until that goes, we'll never get decent 3-d film.
The technology is fascinating, but the sooner this fad disappears for another twenty or thirty years, the better.
(http://stereo.nailed-barnacle.co.uk/#!album-10 for Victorian 3-d technology explained; http://stereo.nailed-barnacle.co.uk/#!album-0 for some American Pattern scanned images; http://stereo.nailed-barnacle.co.uk/#!album-9 for the same images a red-cyan anaglyphs.)