They move toward us and from us just as much as they move to the right and left.

We actually perceive the chairs or the rear wall of the room as further away from us than the persons in the foreground.

This is not surprising if we stop to think how we perceive the depth, for instance, of a real stage.

Let us fancy that we sit in the orchestra of a real theater and see before us the stage set as a room with furniture and persons in it.

We now see the different objects on the stage at different distances, some near, some far.