How many times have you wondered about what you see? 😵 💫
Optical illusions are images that challenge our visual perception and they reveal a lot about how the brain processes reality.
In this article, we explore some of our favorite visual illusions - such as the famous white/gold or blue/black dress - and explain what is behind these visual confusions, based on evidence from neuroscience.
An optical illusion consists of Images that are captured by the eyes in a way, but interpreted differently by the brain.
That is, we see something that does not precisely match what is in front of us.
The brain interprets visual stimuli based on previous experiences, context and expectation, and sometimes makes mistakes.
According to an article published in Nature Reviews Neuroscience (2015), these illusions are natural manifestations of “cognitive heuristics”: shortcuts that the brain uses to quickly decipher the environment.
Although these shortcuts work in most situations, they can lead to perceptual distortions.
Let's explore five fascinating visual illusions that show how easily the brain can be deceived:
This image shows an apparently ordinary tree, but with careful attention it's possible to identify several faces between the branches and the trunk.
This type of optical illusion is an example of pareidolia: a psychological phenomenon in which the human brain interprets ambiguous visual stimuli as familiar forms, especially faces.
For example, have you ever looked at the clouds and identified an animal? Or did you notice a wall outlet that seemed to be smiling? 😅 That's pareidolia!
The human brain has an incredible capacity (and a certain tendency) to look for patterns in everything it sees.
When faced with ambiguous or undefined stimuli, it tries to “fill in the blanks” based on its previous experiences. Sometimes it gets it right... other times, it just makes it up.
👉 But let's get to the point, the answer: Although some people report seeing a higher or lower number, the more consensual interpretation indicates that it is possible to identify 10 faces distinct in the image.
Created by Edgar Rubin in 1915, this illusion demonstrates how the brain perceives visual boundaries, alternating between seeing a vase in the foreground or two faces as the background.
Simply put, the brain constantly needs to decide which part of an image represents the main object and which corresponds only to the background.
Researchers at the Salk Institute discovered that neurons in the deeper layers of the visual cortex are the first to assign this border ownership. They function as “central decision-makers”, processing visual information and defining what is a figure and what is a background.
This ability to quickly distinguish objects from the background is essential for our perception and survival. This is what allows us, for example, to differentiate a stone from a simple shadow when driving on a road - something vital to safely interact with the environment around us. ⚠️
In February 2015, this simple photograph shook the internet. For some, it was white and gold. For others, blue and black.
What seemed to be just another viral image became a true case study in the field of vision science.
👉 But then, after all, what is the actual color of the dress? Blue and black.
The author of the image herself confirmed this information by physically showing the dress. And for the more skeptical, it was enough to use design tools to confirm the bluish and brown/black tones of the original image:
The explanation? Our brain is an expert at interpreting the world based on assumptions. When an image has ambiguous lighting (and this one was captured with a phone under uncertain light conditions), the brain has to decide: “Is it in shadow or under direct light?”
Depending on the answer, it compensates the colors differently:
A european study published in the journal Vision Research demonstrated that this variation in color perception is related to individual differences in how we interpret surfaces and lighting. That is, each brain solves the “puzzle” of light in its own way, based on previous visual experiences.
Curiously, other researchers suggest that its biological rhythm may also influence perception: people who wake up early (so-called “larks”) tend to see their clothes as white and gold, while “owls” (more active at night) tend to see blue and black.
Interesting, isn't it?! 🙂
This illusion was first described by the german psychologist Hermann Ebbinghaus at the end of the 19th century and popularized by Edward Titchener (which is why it is also known as the Titchener circle illusion).
At first glance, it seems like a simple observation exercise: two central circles surrounded by other circles of different sizes.
👉 Your brain probably identified the lower black circle as being larger than the upper one. However, we guarantee that both are exactly the same size:
🧠 What happens in the brain? The illusion occurs because our brain interprets size based on comparisons. When a central circle is surrounded by large circles, it appears smaller; when surrounded by small circles, it appears larger.
This phenomenon can be explained by multiple simultaneous mechanisms and, in fact, scientists have not yet reached a definitive consensus:
This is a classic example of how our brain does not evaluate objects absolutely, but rather according to the context!
This classic illusion, originally published in 1915 by cartoonist W.E. Hill, became known as the Boring Illusion after being analyzed by psychologist Edwin Boring in the 1930s.
Some see an elegant young woman in profile, looking at the background of the image; others see an elderly lady looking to the left.
👉 Both interpretations are correct:
What each person sees first depends on their individual perception, and the brain can switch between both versions as it observes the figure, depending on the focus of attention.
This happens because it is a ambiguous stimulus, which can be interpreted in different ways without the physical stimulus changing. 🙃
Although it is still a process without great concrete answers, there are 2 main theories that seek to explain this phenomenon:
Optical illusions show that the reality we perceive is a mental construction, based on expectations and interpretations.
These images not only surprise but also reveal the limits and sophistication of the human brain!
At NeuroImprove Clinic, we use advances in neuroscience to promote brain and psychological health.
If you liked this article, share it with your friends — challenge them to see the world with different eyes! 🧠✨
Liu, J., Li, J., Feng, L., Li, L., Tian, J., & Lee, K. (2014). Seeing Jesus in toast: Neural and behavioral correlates of face pareidolia. Cortex, 53 y.o., 60—77. https://doi.org/10.1016/j.cortex.2014.01.013
Franken, T.P., & Reynolds, J.H. (2021). Columnar processing of border ownership in primate visual cortex. eLife Sciences, 10, and 72573. https://doi.org/10.7554/eLife.72573
Witzel, C., O'Regan, J.K., & Hansmann-Roth, S. (2017). The dress and individual differences in the perception of surface properties. Vision research, 141, 76—94. https://doi.org/10.1016/j.visres.2017.07.015
Wallisch, P. (2023). Here's why people saw “The Dress” differently. Slate. https://slate.com/technology/2017/04/heres-why-people-saw-the-dress-differently.html
Kirsch, W., & Kunde, W. (2021). On the origin of the Ebbinghaus illusion: The role of figural extent and spatial frequency of stimuli. Vision Research, 189, 1—10. https://doi.org/10.1016/j.visres.2021.07.016
Kornmeier, J., & Bach, M. (2012). Ambiguous figures - what happens in the brain when perception changes but not the stimulus. Frontiers in Human Neuroscience, 6, 51. https://doi.org/10.3389/fnhum.2012.00051
