Regarding the latter part of your question, how our human vision and its "quirks" affect how we use a camera and how we photograph the world around us. I think the single most valuable piece of advice I have found regarding photography was from an article on Luminous Landscape, part of the series "Aesthetics and Photography" by Alain Briot titled:
"How to See Photographically"
What I am talking about here is seeing
photographically, or seeing like a
camera. How to learn how to see like a
camera is the purpose of this essay.
Creating photographs is all about
seeing and in this sense it is no
different from other two dimensional
arts such as painting and drawing.
Creating photographs is really about
studying and practicing "the art of
The art of seeing, while it may seem mediocre and obvious, is not as easy as it sounds. As mentioned by the other answers here, the human eye and the brainpower behind our "vision" is a subjective engine, constantly and automatically working to make sure we see most clearly what we need and want to see, and pushing all the other "noise" in a scene to the background.
When we look at a beautiful mountain vista with our own eyes, we see only the key things we want to see, or what we are drawn to see. The mechanics of our vision take care of "eliminating" the distracting and useless elements, and impose a vision of astounding beauty. The moment we take a photograph of the same scene and chimp it on site, were immediately confused at how boring and commonplace it looks.
A simple analogy I've come up with since reading Alain's article is this:
The art of seeing is the seeing of
It is not enough to see a beautiful scene with our minds eye, and capture it the same way. You must also "see" with the camera's eye, and purposefully, explicitly compose the scene you originally envisioned with your minds eye. The latter is where artistic vision comes into play. This is the process of taking direct control of our vision center, seeing everything, and subtracting until our "camera eye" and "minds eye" match.
I think a key distinction between the technological eye in our hands and the biological eye in our heads is that the former operates under a fixed set of algorithms, while the latter is adaptive and under the control of conscious thought. We can change aperture, focal length, and sensitivity with our camera, but we can literally change the vision of our mind to suit our needs. All thats needed to achieve that is training and practice.
A few of the key factors in seeing photographically, the factors that help you change modes from "human sight" to "camera sight", include the following:
These aspects can be followed explicitly, in order as a sequence of steps, as a form of training. Approaching each scene this way can help you develop your own mode of "camera vision" to complement your normal vision, and bring a whole new level of seeing photographically to your work.
Before you can work a scene, you must first see it. Not seeing like a human, but seeing like a camera. Looking at a scene, and reversing the automatic simplification your mind does to help you abstract a scene and focus on the important parts. Expand your vision and observe everything that is.
Once you see everything before you, you need to begin reconstructing what your minds eye saw originally. You need to abstract your expansive vision, separate the different elements, identify what is necessary, what isn't, what is primary, what is secondary. At the same time, recognize the non-visual elements of what you are experiencing...your sense of emotion, the physical feel of the scene, the sounds that are present. Even though they are not visual elements, they are factors of what you are "seeing", elements of emotion that can still be portrayed via artistic license as you compose and eventually process the final image.
Now that you have identified the elements of the scene before you, its time to contract, to zero in on the important aspects...to focus your vision on what matters and what draws your attention. Localize the abstracted elements of the scene that you wish to keep, and those that you wish to discard: What is interesting, and what isn't? What's important, and what is irrelevant "noise"? What can be done to interweave some sense of emotion into the scene?
Now that you know which elements of a scene you intend to capture, you can finally begin to compose. Composition is framing the focus of your scene while discarding the rest. Composition is involving depth, perspective, and placement of key elements according to natural rules such as thirds or the golden ratio. Composition is the technological equivalent of everything your brain did automatically, in an instant, when your eye first caught a glimpse of that beautiful thing your now trying to photograph. You're now seeing photographically, artistically seeing the art before you.
The "eye" may be simple in the grand scheme of optical systems, it may be small, it may be rather mediocre by our considerably advanced technological standards...but it is still a truly, uncompromisingly amazing device that sees, abstracts, focuses, and composes a thousand times a second. It will let you make the decisions when told, see what you want to see. It is the best tutor your artistic side could ever ask for.