What are Optical Illusions, and How Do They Work?

Published on
January 5, 2022

We’ve all run into optical or visual illusions at some point, especially in the age of the internet. There are many famous ones which we’d recognize on sight, even if we don’t know their names.

But how do these eye and mind-bending illusions work? Are our eyes the ones being fooled, or is it more the brain & the broader visual system itself?

Here, we’ll look at 3 types of optical illusions

  • Cognitive Illusions
  • Physiological Optical Illusions
  • Literal Optical Illusions

Cognitive Illusions


Cognitive illusions generally show an ambiguous image, and they are caused by a phenomenon known as unconscious inferences, which are made by the brain when looking at ambiguous images. Specifically, with these illusions, the brain infers the presence of an object which doesn’t actually exist.

In one well known example of a cognitive illusion, known as Kanizsa’s Triangle, we perceive a white triangle inside the partial black circles. This is due to the positioning of the pac-man shaped black circles. It looks like a triangle fits in there, and the contrast also implies a bright white triangle, so our brain takes the extra step by actually “seeing” it, inferring its presence despite it not truly being there.

Physiological Optical Illusions


This type of illusion occurs when our eyes take in an excessive amount of visual stimuli for a period of time, and it has an effect on our eyes or brain. Brightness, color, or light flashes can all cause such illusions.

We can illustrate this with the image below. Stare at the image for about 15-20 seconds, then look over at the blank white space while blinking. You’ll see an image there now!

Since we spent a significant amount of time exposing our eyes to the initial images, the photoreceptor cells in the retinas keep sending neural impulses based on that to the brain even once we’ve stopped looking at the image, resulting in what we see in the blank space, known as an afterimage.

You may have experienced something similar if you’ve ever looked at the sun for a moment (try not to do that), or looked at some other very bright light. For a short time afterward, while blinking, you’ll see an object in the shape of that bright light, because your eyes have just been overexposed.

Literal Optical Illusions


Literal optical illusions are when our eyes perceive an image, and our mind fills in gaps in the image which don’t exist. This leads to the creation of an image different from the objects which make up that image, or it focuses in on certain areas of the image, leading to us perceiving something that isn’t truly there.

In the image here, it looks like the elephant has way too many legs. This is because our eyes rely on the edges of objects to distinguish it, and in the example, the shading and especially the lines that make up the elephant confuse our eyes.

This phenomenon is also what leads us to “see” faces in everyday objects, since we’ve also learned to recognize faces, so our brains tend to find them even when they might not actually be present.

These, and other illusions, demonstrate that our brain plays a major role in vision, as it interprets the input that comes from the eyes based on how it’s learned to understand and organize the world around us. And since this is almost entirely done unconsciously, it is susceptible to being fooled or confused when our conscious examination of something conflicts with the brain’s initial assessment.

Unlike some of our senses, vision is very much learned, and studying and experiencing these illusions helps us better understand that process, along with our visual system as a whole.



I haven't actually used the optometrist side, so my review is limited to the vision therapy offered.  This office was recommended by my occupational therapist for the treatment of my double vision following a stroke.

Claire A.

Love this location. I had a brain injury accident from day one one. All the team make you feel you still important and hope in the horizon after when the medical system fell you miserably. Dr. Ikeda very professional and very understanding about your issue. Two tombs up.

Jim K.

My husband and I were immediately impressed with Dr Ikeda. I was hit by a car while cycling which caused broken bones and three brain injuries. The brain injuries caused double vision. Dr. Ikeda examined my eyes and got me started on vision therapy with his occupational therapist who specializes in vision therapy.  She (Chris) is absolutely great.  I am impressed with the array of tools used to help recover my binocular vision.  I am doing things I never thought were possible (balance boards etc).  Chris pushes me and keeps me motivated. I really enjoy my sessions with her.  The office staff is always friendly and they have a wonderful appointment reminder tool that makes it easy to keep my calendar up to date. I am happy the rehab center at Little Co. of Mary recommended them!!

Teresa S.

The Vision Therapy is handled in a separate office through a different door from the shared waiting room. Chris, the vision therapist, has a wide and varied assortment of tools, equipment and resources to best evaluate and treat most vision issues. After just a few visits, my double vision became easier to control, using exercises developed during the therapy process. It was time well-spent.

Joe M.

I have been coming here since I can remember. I love it here. The staff is so amazing and nice. They explain everything they gonna do and never make you feel rushed. Dr. Ikeda has always been my doctor and I would never want another one. He is the doctor for my whole family and is always asking how everyone is doing. I am also so crazy about picking out my frames and have to try so many and each person who helps me take the time and lets me try them all on. I would never want to go anywhere else! I definitely would recommend this office to anyone looking for a great eye doctor.

Kayla W.

This is not for the eye exam but for the frames selection portion. I brought my prescription from Kaiser here with my VSP insurance. The reception staff was very polite and professional.  Manny helped me to pick out frames and explain my coverage.  Very helpful and patient not like the individual at the other place I rated here on Yelp.  I was running late and he still helped me and was not bothered at all.  I am so glad I came here ..........very pleased.

Very professional staff and pleasant.

Daniel G.
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