I think it's remarkably simple, and individually pretty complex.
I think we photograph what we see. And we all go through the world, camera in hand or not, seeing some things and not other things. Some men see blondes more than redheads. Joel Witkin sees fascination in the mechanics and form of human parts. Ansel Adams saw more linearly and symmedtrically, which kind of goes with seeing photography as much of a science as it is an art.
Aggie is having a hard time seeing how a rangefinder camera works at the moment, so I'd bet her photographs of one at the moment would be pretty elementary. But I'll bet there's a patch of someone's yard where she walks every day in her foggy Bay Area that she sees extremely well, and from it she could produce photographs of things that rest of us would swear were not there.
A few years ago I was in a bit of a depression, and all of my portraits looked a little sadder and a little more hopeless. It's because of what I was seeing...recognizing, probably...at the instant I pushed the shutter. I wonder what AA was going through during that period in which he printed everything dark? He said it was a reflection of how he saw the world in those years.
So what we communicate is what we have the ability to see clearly enough to turn around and show, whether we are doing so consciously or not.