9 Powerful Tricks of Visual Perception the Eye Plays

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“We see things not as they are but as we are.”

~Immanuel Kant

Can you trust what you see? But forget what you see.. can you trust what you perceive? The answer is no, and you’ll be convinced of that after reading about these 9 tricks of visual perception. In truth, there are very many more too. But first let’s settle what visual perception really is (it’s NOT “what you see”), and some of the history and science leading to the knowledge that what we perceive is not what we see.

In 300 BC, Euclid published Optics, and around 160 AD, Ptolemy published his Optics. Both of these early works postulated that the eyes radiated beams onto objects, enabling sight when bounced back to the eyes. This was wrong in many ways. But it got the discussion popping. And Ptolemy also documented an optical illusion that is still a solid example today – a straw (or stick) in a glass of water.

Between Euclid and Ptolemy, Aristotle published a treatise on sense perception, De Sensu. Aristotle’s take opposed the other two, postulating that eyes themselves took in rays. John Locke was another researcher on that same train of thought. The general consensus state of the mystery of site blended these ideas – “like knows like”. Internal fire of some kind meets external fire and the two come together in sight. Ibn al-Haytham (965-1040), a medieval astronomer from the Islamic Golden age, was the first to propose external light bounced off objects into the eye. He was cited by more famous astronomers like Kepler, Galilei, and even Newton. Newton’s studies on color brought about the fact that color is a character of the objects.

The Umbrella of Visual Perception (it’s not sensation)

There is the act of sensation, the unconscious collection of rays into the eye, but perception happens in the brain. While the sensing organs are responsible for intaking information from the environment, in this case, from the retina to other parts of the brain, their role doesn’t exceed past that. Axons, the branching part of neurons, exit the retina through the optic nerve, and extend to the thalamus and superior colliculus, structures within the brain. The part of the thalamus receiving the visual information (called the lateral geniculate nucleus), processes just 20% of its load from the retina, and the other 80% is modulated by mental states.

All this processing in the brain’s cortex accounts for contrast, color, movement, and more. There are layers of neurons that deal with orientation, textures, distinguishing background and foreground, and identifying objects and position in visual field.

Perception is all in the brain

Visual perception skills include what many would think are purely “brain” tasks. Visual perception includes visual memory, sequential visual memory, telling things apart (form constancy), distinguishing distances, spatial relations, among others.

The sense organs of course, should be at least passing reliable information, and they are developed to do so in non-disordered eyes. The eyes are peculiar in that they are never at rest. The sensing signals come from decreases or increases in the “at rest” continuous firing these neurons experience. The eyes drift even when fixated on something (called ocular drift and microsaccades), automatically cooperate amongst themselves and follow objects in pursuit of motion.

9 Tricks of Visual Perception

I’ve picked out 9 examples of visual perception tricks. Some are entoptic, meaning it comes from within the eye, and others are optical illusions. Through these you will see that we really don’t always see things as they are.

1. In The Shadows – Contrast perception

In the infamous “striped dress” meme of 2015, many found it amusing that different people percieved different colors on the same dress due to the lighting.

There are many such optical illusions where the same color seems different. Here’s a few very blatant ones.

The Adelson illusion is based mainly off of distance perception and patterns. We are already seeing the checkerboard pattern and expect that to repeat. The brain also calls on past experience with distance and shadow to “assume” the details. The shadow of the cylinder makes square A lighter, just outside the shadow, and B lighter, in the cylinder’s shadow, so they are the exact same color. Even though it’s a graphic, this can happen in checkerboard + shadow situations in real life.

The bar is one color throughout. The contrast of the gradient background has us perceiving the color to be darker on the light side and lighter on the dark side.

2. Foehn Fog Moves Mountains

Based on the level of moisture in the atmosphere, mountains can be nearer or farther than they appear. High levels of fog makes the same mountains seem farther away. This effect is greatest when pressure systems rapidly move moisture up and down the atmosphere.

Related is the Fata Morgana illusion, responsible for the Flying Dutchman lore. Layers of warmer and cooler air distort the way light passes through it and can act like a refracting lens, producing an inverted and upright image. The result looks like a distorted mirror image of the ship in the horizon. This is a type of mirage and also accounts for some UFO sightings.

fata morgana visual perception
Here is a really clear Fata Morgana image of a cargo ship. It’s not an actual cargo ship, just the image formed in the fog.

3. One Picture, two simultaneous visual perception (ambiguity)

Ambiguous optical illusions create the sensation of the mind switching from one reality to another. There’s more than one way to see things, and if you look for the other way you experience a moment of totally changed perception.

Jasrow’s rabbit-duck. Which do you see first?
Rubin’s vase. Can be seen as a vase on a black background, or 2 faces in silhouette.

The spinning dancer illusion is drawn so that you can see the dancer spinning to either the left or the right. This one is fun because some people have a hard time making her “switch,” and for others she can go back and forth. It’s surprising that it really is the same motion on loop.

4. Distortions in angles and space

These are where objects can seem larger or smaller than they are because of the circumstance. Objects can also distort in orientation. The brain expects something else and makes corrections that are not correct. Here’s some examples.

The lines seem to bulge out but they are not changing at all.

This can happen in real life too, not just graphics, depending on the circumstance and surrounding lines of sight.

5. Paradox in Picture & the upteenth mention of Escher

Paradox is when an image depicts something that is impossible. This is less common in real like but has been depicted a lot by artists like M.C. Escher and Roger Penrose, also a mathematician. (I’ve also mentioned Escher in other blogs, like Hexagonal Art, Types of Symmetry, and Rotational Symmetry in Art)

M.C. Escher, Relativity, 1953
Penrose steps and Penrose triangle, 1930’s.

6. Moire Patterns

Deserving of a whole article of their own, Moire patterns are truly fascinating in that they are not illusions at all, just anomalous optics. They are enlargements or interference patterns of light, studied by quantum scientists beginning with Thomas Young’s diffraction experiment in 1802.

Simply a Moire pattern is produced when a set of lines printed on a semi-transparent sheet is overlaid onto another pattern.

7. Entoptic floaters and Purkinje Trees

Entoptic phenomena are due to images from the eye itself, nothing external. And like hallucinations, the same experience cannot be shared but only described. Floaters are blurry blobs one sees from vitreous humor inside the eyes. Vitreous humor is thick like jelly, and various physical circumstances can cause it to enter where it shouldn’t be.

Purkinje images are another entoptic phenomenon. These are the blood vessels inside the eye refracting off its own lens or cornea. They look like lightning or trees. Purkinje images can be seen if one is in a dark room with one eye closed while moving the other. Thus Purkinje images when viewing a microscope in a dark room are common.

8. Phosphenes

Phosphenes appear with no light needed. They are the spontaneous and hard to describe swirls behind your eyelids. Phosphenes come from mechanical pressure or electromagnetic stimuli, as well as the random at-rest firing of retinal neurons I’ve referred to. I also have discussed the use of phosphenes to help induce lucid dreams.

visual perception
Newton’s lab notebook in which phosphenes are mentioned.

9. Illusory Palinopsia

Palinopsia means “seeing again.’ It is the persistence of an image after the stimulus is removed. Palinopsia creates the sensation that an image is “burned” into your eyes. Migraines and other disorders can cause palinopsia. But it can be induced by high contrast images on fixates on.

Stare at the dot for 445 seconds, then at a white piece of paper, to experience palinopsia and see the flag in different colors.

Seeing is Perceiving

Seeing is not perceiving. Our processing centers do the best they can to serve us, but unexpected visual stimuli causes us to be incorrect in perceiving what we see. Luckily, artists have made this an enjoyable experience for us.

You may also be interested in knowing that we don’t see colors the same way either, even if you aren’t color blind. Our lexicon actually limits shades of color we see too. Read about color perception based on language and culture.

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