The ability to see a three dimensional world which consists of plastic objects is one of the most amazing characteristics of sight. The
retina
registers two-dimensional images comprised of lines, contours, patches of color, varying brightness and shadows, all of which are interpreted as three dimensional solutions. The ability to grasp depth is so well developed that a person with normal eyesight can identify depth not only in objects that are at a relatively close distance of a few dozen meters such as scenery or actors on the stage, but also in extremely distant objects.
In order to expand our comprehension of viewed events, we need to know not only what it is that we are perceiving but also the orientation of each object, the direction of its movement, where other objects are located in relation to it, and where we are located in relation to them. This is known as spatial perception.
