Monocular Cues

Monocular cues are depth clues available to either eye alone.  Linear perspective and Interposition are the two common cues associated with monocular cues.

Linear perspective are parallel lines, such as railroad tracks, that appear to get closer together or converge with distance. Linear perspective can contribute to rail-crossing accidents by leading people to overestimate a train's distance.

Example.
















As you can see, the father you look in the distance, the closer the road seems to converge.

Interposition occurs when one object partially blocks our view of another, so we perceive it to be closer.

Example:

The green triangle appears to be closer, and the red triangle appears father away, but in reality they are both the same distance from you as measured between your eyes and the screen. This happens because the green triangle partially blocked our view of the red one.