As I read this sort of thing and try to apply it to my own shooting practice and theory (thinking about the worst case scenario) I remember a real lesson from a point-shooting lesson I received last fall. During these exercises, I actually had a hard time focusing on the target, my vision just automatically went to my sights - including all the relatively complex details that make up the OAK Vision that I practice. (
See here if you don't know about OAK Vision.) It took quite a few drills before I was able to force myself to keep my eyes focused on the threat even
some of the time, and I was never able to override the habit 100% of the time.
I'm very glad I took that class, because I learned a lot about
my accuracy envelope when I'm not looking at the sights (though they were certainly in my field of view.) But it also reinforced the idea in my mind, rightly or wrongly, that if I keep being disciplined about my vision during practice, I'll be disciplined about my vision at other times as well. Extrapolation from personal experience is dangerous, but I'll do it here anyway, just for curious speculation: for folks who practice shooting fairly regularly, yet "instinctively" focus on the threat during a shooting, how disciplined are they about their vision during practice? My personal anecdata suggests one answer.
And another navel-gazing type question: does my vision practice, with its distinct "feeling" in the eyes of separating accomodation and convergence, make it easier to subconsciously perform it under stress? There's certainly a very distinct "I'm shooting now" feeling in my eyes when I do it, so maybe subconsciously tying that distinct feeling makes it more likely for my subconscious mind to tightly couple that "shooting eyes" feeling when I flip the switch into shooting mode?
Much of the vision discussion I've read is fairly narrow-minded, in the sense that it assumes one single way of "using" your sights. For most of those discussions, it seems they break down into a restatement of a special case, once you add in the consideration that "using your sights" is a spectrum (i.e., seeing what you need to see,) and the idea that there's a whole matrix of combinations for what, exactly, you're converged on and focused on while shooting.