Shooting with both eyes open
I trained myself to shoot with both eyes open over a period of a couple of weeks by dry practicing a little bit every day. I'm right-handed and right eye dominant. When I would focus on the front sight I'd see two images. The one I wanted to use was on the left. After a while my brain started to ignore the wrong one. It's still there, but now I have to intentionally try to see it.
I remember hearing of an experiment many years ago where a group of subjects were fitted with glasses that inverted the image they saw. After a period of adjustment (days or weeks, I don't know) they began to see the world right side up again. Their brains had made the correction. Of course when they took the glasses off at the end of the experiment they had to go through the same transition in reverse.
I suspect the ability to shoot with both eyes open will have to be relearned if it's not practiced with some regularity - use it or lose it.