Depth perception activities | How to explain depth perception?


Depth Perception

The ability to see the world in three dimensions is known as depth perception. It develops in infants at a very young age. Without depth perception, it would have been very difficult for people to judge how far away objects are. Both human beings and animals use depth perception to move accurately or to give a consistent response. There are various cues that help to perceive depth in the world. Some of them use the vision of only one eye, while others use the field of vision of both the eyes.

Perception Definition

Perception refers to the ability to take all the sensations people experience around them at a given moment and interpret them in their own meaningful way. It can differ from one person to another. Two people might be looking at a cloud – while one of them thinks it is shaped like a dinosaur, the other one think it looks like a dragon. They both are seeing the same cloud at the same time but their way of perception and interpretation is absolutely different from one another.  Depth perception depends on various perspectives and variables.

One of the best examples to illustrate perception is using the optical illusion of Rubin’s vase. Some people see it as a vase because they pay more attention to the black area. While others see two faces because of the white area. Most people can see both, but only one at a time.

Perceptual Constancy

Perceptual constancy is the tendency to perceive a familiar object as having a definite or constant shape, size, and brightness. Even when there is a change in the stimulus, this perception does not change. For example, you are on a train and going towards a city with high-raised buildings. From far those buildings appear to be a tiny dot which you can cover with your palm. But as you are moving towards the buildings, they appear to be bigger in size and your palm cannot cover them anymore. But you know that the buildings have not gone taller. They have consistency in their size, shape, and brightness. And you know this because of perceptual constancy. So size, shape, and brightness are the three constancies of perception.

Size constancy: It is the tendency to interpret an object of having the same actual size always, regardless of its distance.

Shape constancy: It is the tendency to interpret an object of having a constant shape, even when its shape changes in the retina.

Brightness constancy: It is the tendency to perceive an object having the same apparent brightness, even when the light conditions change.

Difference between Perception and Perspective

Perception: Perception is what you interpret through the ability to see, hearing, or becoming aware of something through the senses. Perception does not develop overnight. It is based on our beliefs which we keep as a reference to perceive something.

Perspective: Perspective is basically our “point of view” – the way we see or think about something logically. And this perspective comes from our perception.

Perception can change your Perspective

It is true that your change in perception can literally change the way you see or think about something. For example, it is said that success is the core of all joy. So most of the people think that if you are successful in your life you will have all the happiness. Now, what happens when you want to change your perception of this saying? You believe that it is happiness which is the key to a successful life. Now since your perception is changed, you now think if you stay happy you can do anything to become successful in your life.

Monocular cues

The cues that are used to perceive depth using the vision of only one eye are called monocular cues. They are also known as pictorial depth cues because artists sometimes use these cues to create the illusion of depth in paintings and drawings. The following are the monocular cues-

Linear perspective:

It is the tendency to visualize parallel lines appearing to be converged on each other. For example, when you look down at a long highway, the two sides of the road appear to join together.

Relative size:

It is the perception that occurs when people expect a certain size of objects but they appear to be small. Hence, it is assumed that the objects are far away from them. Filmmakers use this technique to make their small casts look bigger and in the distance.


It is the assumption that an object blocked by another object is behind the second one and much far away. It is also called interposition.

Aerial perspective:

It is the haziness surrounding the objects that are farther away from the viewer. Therefore, the viewer perceives the distance to be greater. Because of this, mountains in the distance look fuzzy and buildings blurry.

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Texture gradient:

Textured surfaces appear to be smaller and smoother as the distance between the viewer and the surface increases. This tendency is called a textured gradient. When you walk on a pebble or brick covered street, the rocks and bricks closer to you appear to be distinctive. But as you look into the distance, you can see that the surface has become smaller and finer.

Motion parallax:

The perception of an object’s motion in which close objects seem to move faster than the objects in the distance. When you travel by car or a bus, you can see that the vehicles closer to you are moving quicker than the ones far away from you.


It is not one of the pictorial cues. Here, the brain uses the information of the changing shape or thickness of the eyes’ lens in response to the objects that are near or far away from the viewer. It is also known as a muscular cue.

Binocular cues
The cues that are used to perceive the depth using both the eyes are called binocular cues. Such cues are –

Convergence: It is the rotation of the two eyes in their sockets to focus on a single object. This results in closer objects to have greater convergence and far objects to have lesser. If you hold your finger in front of your nose and move it back and forth, the feeling that you get in the eye muscle is the convergence.

Binocular disparity: It is the difference in images between the two eyes, which appears to be greater for closer objects and smaller for objects that are far away. You can notice this difference by holding an object close to your nose. Close one of the eyes and mark the position of the object. Then open the eye and close the other one. There should be a significant difference in the views.

How far can the Human eyes see?

It has been thought that people can see the flame of a burning candle from up to 30 miles away. But new research by astronomers Professor Kevin Krisciunas and Don Carona has discovered that the burning candle will only be visible to our naked eyes up to a distance of 2.576 meters or 1.6 miles. At this distance, the brightness of the candle would be as much as that of the faintest star which has a magnitude of 6.

In other research, it has been found that our ability to see the farthest object depends on the health of our eyes and the place from where we are looking. Since the earth is curved, if we stand on a flat surface having our eyes 5 feet off the ground, the farthest edge that our eyes can see is around 3 miles away. So, if the earth was not curved, then we might have been able to see objects from hundreds of miles away. The depth perception test can give us an appropriate result about the distance cues.

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