Hence the reason we have two eyes... triangulation. The three points of the triangle being our two eyes, and the object. The intersecting point of the lines of site from each eye determines the depth/distance of the object. Of course this works in combination with other perceptions, relative sizes of objects etc... When we remove one eye, the brain is left without true depth perception, but only relies on the other information available - ie. the information you already know: for instance, a house is bigger than a car, so if they appear to be the same size, than the car must be much closer in proximity than the house. This effect is probably emphasized by TV, as it actually is a 2D medium, whereas the images within contain quite accurate depth information. So the brain, left with only one eye, and looking only at the TV screen, will re-contruct the scene in 3D. I think that's clear, no?