Vision and the representation of visual space
As a graduate student I have conducted projects on the representation of visual space. When you move in the environement -- walk, move your head or your eyes -- the image projected on your retina undergoes a shift. The brain has to correct for this shift in order to perceive the physical object's motion independantly of artefactual motion on the retina. As an exemple, imagine that you are waiting for a friend to pick you up, while looking for him, you are looking at this car passing by:
The buildings in the background are, of course, stationnary. And the bike is moving a little slower than the car. But that's not what's happening on your retina! Rather, here is what image is projected:
Now the buildings are not stationnary but rather, they are moving, and so does the bike. Here we have a good illustration of why it is important that the brain compensates for this artefactual motion. If you want to cross the street after the car, you may want to know that the bike is actually coming towards you.