Depth perception cues psychology definition

How is Depth Perception Created?

Depth perception is created when the eyes and the brain work together in an effort to perceive the depth, or the length, width, and height, of the world around us. Humans have two eyes. Having two eyes to see through is called binocular vision. Binocular vision helps to create a stronger sense of depth perception than monocular vision or having one eye. This is because the brain can get a view from two different angles, thus seeing the same object or room from a slightly different length, width, and height, through both eyes. When the images are compiled within the brain and one image is produced for us to comprehend or ‘see’ then we can perceive depth. When looking at a small object, humans have the ability to turn both of their eyes in slightly. This effect is called convergence and it allows for a closer look at small objects, which allows the brain to better perceive the length, width, and height of the object within space. Depth perception examples include:

Knowing how close someone is when they are walking toward us.
Having a pencil and a mug on the desk and being able to tell which one is closer.
Seeing a dog running away and knowing how far away it is.

Seeing a dog running and knowing how close it is.

Binocular and Monocular Depth Cues

There are a variety of visual cues to help a person determine the depth of the world around them and have special awareness both in the monocular and binocular sense. Binocular depth cues are all of the ways that both eyes can help to perceive the world around us. Monocular depth cues are all the ways that just one eye can see the world around us and help us to perceive it. There are a few important terms to know when discussing depth cues.

Binocular depth cues include:

Retinal disparity which is the slightly different images a person’s two eyes send to the brain.
Fusion is where the brain combines two different images to make it into one.

Monocular depth cues include:

Shadow stereopsis refers to the perceptions of areas that are in the shadows and how they are perceived by people with normal binocular vision. These areas are perceived differently by the eyes because they do not have defined outlines, but instead have gradients.
Relative size of an object refers to the size that the object looks. Objects that are farther away look smaller to the eye, while objects that are closer up look larger.
Texture gradient is an example of linear perspective. Objects that are farther away or extend farter away from us such as a cornfield will appear to have a finer, smoother texture the farther out it is. The texture will be more defined with close-up objects.
Interposition is the perception that one object is covering another object because it is in front of it. It is a position cue.
Motion parallax refers to objects that appear to move faster if they are closer to a person, and objects appearing to move slower if they are farther away from a person. This is due to the perceived distance that the object is traveling.

Evolution of Depth Perception

Humans have good depth perception because their eyes are close together and face in front of them. This allows the vision that they see through binocular eyes to overlap. When the vision overlaps it improves the brain’s ability to perceive depth.

Many animals such as chickens, fish, and horses have eyes on the sides of their heads, this gives them a good panoramic view of the world, but it does not give them very good depth perception. Since their eyes have two different views of the world, and the images do not overlap, the brain is only processing each eye according to monocular depth cues, or one-eye depth.

Donkeys and chickens have less depth perception than cats or dogs.

Many of these discoveries were noted first by Charles Wheatstone in the Victorian era. He invented the stereoscope in the 1830s which allowed for the study of binocular vision to begin.

Wheatstone worked with retinal disparities to test the limits of the brain to see how different the images seen through each eye were. He also did experiments changing what each eye saw using the stereoscope to determine if the brain could process the images separately or together. He concluded that a person was able to view the different images easily. There are multiple theories on depth perception which include the Law of Newton-Muller-Gudden, and the Eye-Forelimb EF Hypothesis which will be discussed within this lesson.

The Law of Newton-Muller-Gudden

Isaac Newton first theorized that the side of the body the eye is on sends signals to the corresponding side of the brain, specifically the right and left hemispheres. The right eye would send signals to the right hemisphere. The left eye would send signals to the left hemisphere. The Law of Newton-Muller-Gudden involves the scientific principles that show how the structure of the brain, eyes, and nerves are interconnected. The Law of Newton-Muller-Gudden states that “the retinohypothalamic nerve, a neural input pathway, obeys the principle that the degree of optic fiber decussation in the eye cavity is inversely related to the front-facing portion of the optical axes of the eyes.” The term decussation means that what is seen if there is a flaw in the fibers on one side of the eye will have an effect on the other side of the body.

This Law has been disputed as recently as 2016 by a variety of scientists who have studied 23 species types from 11 different orders to discover that the opposite could be true. This theory is heavily debated in ocular science.

The Eye-Forelimb EF Hypothesis

Another theory on depth perception is the Eye-Forelimb EF Hypothesis, which suggests that the development of depth perception and make up of visual structures needed for depth perception stemmed from a need to better control forelimbs.

E.J. Gibson and R.D. Walk developed an experiment to test when depth perception develops in babies and animals. They discovered that it was developed around the time a baby could craw, or when a baby needs better control of his or her limbs. The experiment was called the visual cliff test. Plexiglass was placed over a drop-off. The babies were placed on one side, and the caregiver on the other side. Walk and Gibson hypothesized that if depth perception had already developed then the babies would be hesitant to cross over the plexiglass. They were proven correct.

Poor Depth Perception

People and other living organisms experience problems with poor depth perception. Some animals, like pigeons, use head movement to compensate for issues related to poor depth perception. There is a potential danger when humans have bad depth perception. Humans are supposed to have good depth perception to navigate the world around them. Poor depth perception can cause problems when driving, working, or just walking around the world.

Testing Depth Perception

One way to test depth perception is to put a photo of a golf ball on your wall about 6 inches in front of your eyes. Then, using your finger, hover it in front of the golf ball.

Then, focus on the golf ball and you will see the ball clearly, but you will also see two slightly blurry images of your finger on either side of the tennis ball.

After you are finished, then focus on your finger, and the ball should appear to be cut in half.

Golf ball for testing depth perception.

Disorders and Causes

There are several disorders that can cause a person to have depth perception issues, and these include:

Strabismus: both eyes do not line up in the same direction, also known as cross-eyed.
Amblyopia: a lazy eye

These disorders cause poor depth perception because they change the view that is coming from one or both eyes. When the view is not overlapping correctly, to give the brain two similar images that it can process, then the resulting image the person comprehends will lack depth perception.

Blindness in one eye or the loss of an eye can also create poor depth perception because it leaves a person to rely only on monocular depth cues. Though there is no cure for blindness, there are some common treatments for the disorders listed above. For strabismus, the treatments include one of the following:

Eyeglasses
Vision therapy
Muscle surgery

For Amblyopia, the treatment includes an eye patch over the afflicted eye until it is corrected.

Lesson Summary

In summary, depth perception is created by the brain working closely with the eyes. There are two different types of depth perception cues which include:

Binocular depth perception cues
Monocular depth perception cues

Depth perception has been studied for many years, and tests for depth perception were used as of the 1930s when the stereoscope was invented. Depth perception occurs in babies around the time they learn to crawl, as it helps babies to perceive their environment. Poor depth perception can be caused by a few disorders which include a lazy eye and issues with crossed eyes. Some of these issues can be corrected with the appropriate therapies.

Depth Cues in the Human Visual System

Author: Marko Teittinen

The human visual system interprets depth in sensed images using bothphysiological and psychological cues. Some physiological cues requireboth eyes to be open (binocular), others are available also whenlooking at images with only one open eye (monocular). Allpsychological cues are monocular. In the real world the human visualsystem automatically uses all available depth cues to determinedistances between objects. To have all these depth cues available ina VR system some kind of a stereo display is required to takeadvantage of the binocular depth cues. Monocular depth cues can beused also without stereo display.

The physiological depth cues are accommodation, convergence,binocular parallax, and monocular movement parallax. Convergenceand binocular parallax are the only binocular depth cues, all othersare monocular. The psychological depth cues are retinal image size,linear perspective, texture gradient, overlapping, aerialperspective, and shades and shadows.

Accomodation

Accommodation is the tension of the muscle that changes the focallength of the lens of eye. Thus it brings into focus objects atdifferent distances. This depth cue is quite weak, and it iseffective only at short viewing distances (less than 2 meters) andwith other cues.

Convergence

When watching an object close to us, our eyes point slightly inward.This difference in the direction of the eyes is called convergence.This depth cue is effective only on short distances (less than 10meters).

Binocular Parallax

As our eyes see the world from slightly different locations, theimages sensed by the eyes are slightly different. This difference inthe sensed images is called binocular parallax. Human visual systemis very sensitive to these differences, and binocular parallax is themost important depth cue for medium viewing distances. The sense ofdepth can be achieved using binocular parallax even if all other depthcues are removed.

Monocular Movement Parallax

If we close one of our eyes, we can perceive depth by moving our head.This happens because human visual system can extract depth informationin two similar images sensed after each other, in the same way it cancombine two images from different eyes.

Retinal Image Size

When the real size of the object is known, our brain compares thesensed size of the object to this real size, and thus acquiresinformation about the distance of the object.

Linear Perspective

When looking down a straight level road we see the parallel sides ofthe road meet in the horizon. This effect is often visible in photosand it is an important depth cue. It is called linear perspective.

Texture Gradient

The closer we are to an object the more detail we can see of itssurface texture. So objects with smooth textures are usuallyinterpreted being farther away. This is especially true if thesurface texture spans all the distance from near to far.

Overlapping

When objects block each other out of our sight, we know that theobject that blocks the other one is closer to us. The object whoseoutline pattern looks more continuous is felt to lie closer.

Aerial Perspective

The mountains in the horizon look always slightly bluish or hazy. Thereason for this are small water and dust particles in the air betweenthe eye and the mountains. The farther the mountains, the hazier theylook.

Shades and Shadows

When we know the location of a light source and see objects castingshadows on other objects, we learn that the object shadowing the otheris closer to the light source. As most illumination comes downward wetend to resolve ambiguities using this information. The threedimensional looking computer user interfaces are a nice example onthis. Also, bright objects seem to be closer to the observer thandark ones.

Further Information

Okoshi, T., Three-Dimensional Imaging Techniques, Academic Press, NewYork, 1976.

Human Interface Technology Laboratory

Learn about the binocular cues for depth perception, and understand the meaning of binocular rivalry and retinal disparity through the binocular cues examples. Updated: 03/09/2022

Shannon has a Ed.D in curriculum and instruction from Oakland City University. She earned her Masters in building level administration from Oakland City University and her Bachelors of Science in biology from Marian University. Shannon transitioned to teaching over 11 years ago. She has experience teaching 6th-12th grade in the areas of general science, biology, and advanced biology.

What are the Binocular Cues for Depth Perception?

When one uses two eyes to see it is called binocular vision. With binocular vision, one can sense the depth of objects. Depth perception, or stereopsis, provides a relationship between the things one sees in their visual field, near or far. Each eye produces an image that is put together in the brain to create a three-dimensional image. These objects appear three-dimensional due to binocular depth cues.

When one looks at the image, they see the depth of the hearts toward the center of the image.

There are two types of binocular depth cues: convergence and retinal disparity. Convergence uses both eyes to focus on the same object. As an object moves close, the eyes come closer together to focus. As the eye look at an object further away, the eyes move further apart to focus. Retinal disparity creates an overlapping image. Each eye produces an image; however, the angle of each eye is different, making the images different from each eye.

What is Binocular Convergence?

Proprioceptive senses rely on the five senses: touch, taste, smell, sight, and hearing. Proprioceptive senses are receptors in the body that help one experience the world around them. In the case of sight, it is binocular convergence.

Binocular convergence is when both eyes rotate inward at different angles to focus on an object. The degree to which the eyes turn is sent to the brain to determine how far away an object may be. Binocular convergence creates a three-dimensional image that helps with depth perception and the location of objects.

Retinal Disparity (Binocular Parallax)

Retinal disparity, or binocular parallax, is one’s sense of depth perception. Depth perception is possible due to each eye seeing at different angles. The eyes are approximately 6.3 centimeters apart, providing two different views of the same object and the environment. Retinal disparity exists in organisms with two eyes that are directed toward the front.

To observe retinal disparity, cover one eye and look at an object, observe the location of the object. Cover the other eye and view the same object, paying attention again to the location of the object. The two different eyes view the same object to exist in different places.