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.
Binocular Depth Cues
Properties of the visual system that facilitate depth perception by the nature of messages that are sent to the brain.
Binocular depth cues are based on the simple fact that a person’s eyes are located in different places. One cue, binocular disparity, refers to the fact that different optical images are produced on the retinas of both eyes when viewing an object. By processing information about the degree of disparity between the images it receives, the brain produces the impression of a single object that has depth in addition to height and width.
The second cue, called binocular convergence, is based on the fact that in order to project images on the retinas, the two eyes must rotate inward toward each other. The closer the perceived object is, the more they must rotate, so the brain uses the information it receives about the degree of rotation as a cue to interpret the distance of the perceived objects. Yet another cue to depth perception is called binocular accommodation, a term that refers to the fact that the lens of the eye changes shape when it brings an image into focus on the retina. The muscular activity necessary for this accommodation acts as a signal for the brain to generate perception of depth and distance.
Seeing with two eyes helps people to judge distances and to see in 3D, but even using one eye, there are many clues (often referred to as visual cues) to give people depth perception. Depth perception using computers is more difficult.
Binocular vision – seeing 3D with two eyes
There are two main binocular cues that help us to judge distance:
- Disparity – each eye see a slightly different image because they are about 6 cm apart (on average). Your brain puts the two images it receives together into a single three-dimensional image. Animals with greater eye separation, such as hammerhead sharks, can have a much greater depth perception (as long as the view from both eyes overlaps the same scene). This can be very useful when trying to catch fast-moving prey.
- Convergence – when looking at a close-up object, your eyes angle inwards towards each other (you become slightly cross-eyed). The extra effort used by the muscles on the outside of each eye gives a clue to the brain about how far away the object is. If you hold your finger 20 cm in front of your eyes, your muscles need to work a lot harder than when your finger is 50 cm away.
These binocular cues are most effective for objects up to 6 m away. After this, the amount of eye separation does not give a great enough difference in images to be useful.
3D movies make use of disparity by providing each eye with a different image. However, the brain does not receive any cues from convergence as it normally would. This may cause discomfort for some people.
Monocular cues – 3D information from a single eye
If you close one eye, your vision becomes much less three-dimensional, but there are still many clues that allow you to judge distances. You are still able to pick up a pen, move around without crashing into things and even catch a ball.
Some of these monocular cues are as follows:
– this is the change of
when you look at a close-up object. The ciliary muscles inside the eye need to work harder to change the shape of the lens inside your eye. The effort required provides the brain with information about distance.
or blurry – if two objects are at the same distance, they will both appear to be in
. Objects that are closer or further away will appear blurry.
- Motion parallax – if you move your head, objects that are close to you will appear to move more than those objects that are further away.
- Superposition – objects that appear to move in front of other objects must be closer (a little obvious perhaps, but very useful). You will often see some animals to move their heads from side to side or up and down. This gives important depth information both for motion parallax and for superposition. Try it out!
- Vividness of colours – distant objects often appear less bright and colourful. This is due to the scattering of light as it travels from that distant object. Having more of the atmosphere to travel through means that light will be scattered more, so the colours will not seem as bright.
- Definition and textures – close objects will have a lot of detail and definition apparent. More distant objects will not appear with as much detail. This is very noticeable when looking at a field of grass. Close up, the blades of grass will be noticeable. Further away, the grass is more of a sea of green.
- Relative size – if we already have an idea of the size of two people or objects in a photo, this can give a good clue as to how far apart they are.
Artists use some of these monocular cues to give a perception of distances in a two-dimensional picture.
Creating 3D for movies, robots and security cameras
Computers and robots do not have brains to process these cues from digital images and interpret 3D information. For them, there needs to be an entirely different technology.
The article Light – polarisation provides insight on how 3D glasses work.
In the activity, Pinhole cameras and eyes students make a pinhole camera and see images formed on an internal screen. They then use a lens and see brighter and sharper images. This models the human eye.