What Is Depth Perception?
Wondering how to define depth perception? It refers to the ability to see objects in three dimensions, i.e., length, width, depth, and to judge how far away an object is. This also includes the ability to judge the distance between two objects.
To be able to perceive depth accurately, we generally need to have a binocular stereoscopic vision (vision in both eyes). In a process known as convergence or stereopsis, the brain collates the 2 sets of information based on the different angles of sight from our two eyes to form a unified 3D image.
Depth perception is an innate mechanism, strengthened by visual experience. Over time, the brain is able to speed up the computation of objects in our sight. Depth perception examples take place multiple times a day without even realizing it.
When both eyes see clearly and the brain is able to process a single image effectively, it is known as stereopsis. This is the concept that makes you feel like you’re able to perceive depth when watching a 3D movie.
Monocular cues provide depth information when relying on one eye to see objects. Those with monocular vision may face depth perception inaccuracy since they have to rely on other visual cues to gauge depth.
Why is depth perception important?
What are depth cues?
Depth cues are the different tools that our eyes use to interpret depth in sensed images. These depth cues can either be physiological and psychological.
Physiological depth cues
Accommodation: This is the process by which your eyes bring objects into focus at different distances. It ensures that light entering the eye focuses on the retina. The process involves contracting and relaxing the eye muscle to change the focal length of the lens.
Convergence: This refers to the change in eye direction that occurs when watching an object that is close to us. Our eyes point slightly inward. This cue can work effectively at a distance of fewer than 10 meters.
Binocular Parallax: Since our eyes are roughly 2 inches apart, the images received from each of our eyes are slightly different. The difference between the two images is called binocular parallax which is the most crucial depth cue when we see objects at a medium distance.
Our eyes can still calculate depth using binocular parallax even when all other cues are removed. However, this method only works well when the object is close up. When objects are far away, the 2 images our eyes receive seem more similar.
Monocular Motion Parallax: When we close one eye, a sense of depth can still be achieved if we move our head from side to side. While closer objects move in the opposite direction of the head movement, further objects move in the same direction.
Furthermore, the closer object moves quickly across your retina while objects that are further away don’t move as much or do not move at all.
Psychological depth cues
Retinal Image size: Our brain calculates the sensed size of objects by comparing it to their known size to then perceive the distance.
Linear Perspective: Known objects are thought to be moving further away if they become smaller and smaller.
Texture Gradient: The further away the object is, the less of its surface texture we can see and the smoother it appears. On the other hand, when we can see more detail of an object’s surface texture, it can be calculated as being closer.
Overlapping: We can understand if an object is closer to us when it blocks other objects from our sight. This closer object will have a more continuous borderline.
Aerial Perspective: Depth can also be interpreted based on the relative colour and contrast of objects. An object is considered as being further away when it is blurry.
Shades and Shadows: When an object casts shades and shadows on other objects, we understand that this object is closer to the light source.
Of all the above cues, only convergence and binocular parallax are binocular (require both eyes to be open) while the rest are monocular (require only one eye to be open).
What causes depth perception problems?
Depth perception problems usually result from the following common conditions:
Blurred vision: A lack of sharpness of vision which reduces the ability of our eyes to see fine details.
Strabismus: Eyes are misaligned (cross eye syndrome) so the eyes cannot see clearly or work together effectively.
Anophthalmia: A rare congenital situation where there is an absence of one or both eyes due to many reasons such as genetic mutations, infections, etc.
Amblyopia (lazy eye): A sight disorder that is typical in children. When children encounter double vision, their brain tends to suppress the input from one eye, and over time, it favors the other eye. Read our post on dominant eyes for more information.
Optic nerve hypoplasia: A condition where the optic nerve, which sends visual signals from your eyes to your brain, has incomplete development before birth. It can result in partial or complete vision loss in children.
Macular degeneration leads to a loss in the center part of one’s vision, hence leading to declining depth perception.
DID YOU KNOW?
You can easily test your own depth perception at home and also improve it by doing some simple exercises.