Part of depth-perception is the ability to perceive the distance of an object. There are a variety of things that we use to judge how far away an object is. Some of these cues can be processed by just one eye, which is why they are referred to as monocular cues.
The following are some of the most common monocular cues:
- Relative Size:
If two objects are roughly the same size, the object that looks the largest will be judged as being the closest to the observer.
- Texture Gradient:
When you are looking at an object that extends into the distance, such as a grassy field, the texture becomes less and less apparent the farther it goes into the distance.
- Motion Parallax:
As you are moving, objects that are closer seem to zoom by faster than do objects in the distance. When you are riding in a car for example, the nearby telephone poles rush by much faster than the trees in the distance.
- Aerial Perspective:
Objects that are farther away seem to be blurred or slightly hazy due to atmosphere.
- Linear Perspective:
Parallel lines appear to meet as they travel into the distance. For example, the outer edges of a road seem to grow closer and closer until they appear to meet. The closer together the two lines are, the greater the distance will seem.
- Overlap (or Interposition):
When one object overlaps another, the object that is partially obscured is perceived as being farther away.