Why can familiar objects help people recognize depth in a two-dimensional picture?

Familiar objects help people recognize depth in a two-dimensional picture because the perception of depth relies heavily on prior experience and knowledge of the true shape and size of objects.1

When viewing a two-dimensional representation, the brain interprets depth by comparing the projected image against the observer's internal knowledge of the object's actual characteristics. For example, if an observer sees a bicycle depicted at an angle where the wheels appear elliptical and vary in size, they recognize depth because they already know that the wheels are circular and of equal size in reality.1

This process is a form of monocular cue, where the brain integrates visual information—such as the relative sizes of familiar objects, light and shade, and the overlapping of contours—to infer a three-dimensional structure from a flat surface. Consequently, the ability to perceive depth in such patterns is not purely innate but is significantly shaped by an individual's learned experience regarding the physical world.12