There are several cues that we use to perceive depth in our environment. These cues can be grouped into two main categories: monocular cues and binocular cues.
Monocular cues are depth cues that can be perceived with just one eye. Examples of monocular cues include:
Perspective: When we look at objects that are further away, they appear smaller than objects that are closer to us. This is due to the fact that the objects are farther away and therefore, more of the space between us and the objects is visible.
Interposition: If one object occludes another, we perceive the occluded object as being closer.
Shadows: Shadows can provide information about the shape and position of an object, and can also give us a sense of its distance from other objects.
-Texture gradient: When we look at a texture, such as a field of grass or a brick wall, the texture appears to get smaller as it extends away from us. This is known as texture gradient and it provides a cue to depth.
Relative size: If we know the size of an object, we can use that information to judge its distance. For example, if we see a small car on the side of the road, we know that it is probably farther away than a large truck that is closer to us.
Binocular cues are depth cues that require the use of both eyes. Examples of binocular cues include:
Stereopsis: When we look at an object, each eye sees a slightly different view of it. The brain combines these two views to create a single, 3D image. This is known as stereopsis.
Convergence: When we look at an object that is close to us, our eyes converge or turn inward. This provides a cue to the brain about the distance of the object.
Accommodation: When we look at an object, the muscles in our eyes adjust the shape of the lens to focus on the object. This is known as accommodation. The amount of accommodation required can provide a cue to the distance of the object.