These optical illusions are images that the brain predicts in advance…
Optical illusions are known as images that deceive the eyes. However, they actually carry a different meaning; they are images that the brain “predicts.”
When the retina receives light, the brain takes about 1/10 of a second to process and convert the signals. According to neuroscientist Mark Changizi, this 1/10 second delay is the time it takes for the brain to form “predictions” about what images may occur next.
The brain’s ability to “predict” plays a crucial role in keeping us safe from fast-moving objects (like cars on the highway) or rapidly moving predators. Through this, it gives us a clearer insight into this special capability of the brain.
1. Ebbinghaus Illusion
When you look at the image below, you might say that the orange circle on the left is much smaller than the one on the right?
In reality, they are the same size. The reason is that the size and distance of the surrounding circles relative to the central circle deceive the brain regarding the size and width of the two orange circles.
2. Blurred Lines
Try looking closely at the image and then gradually pull your gaze away, repeating this several times; you will see the blurred lines in the image moving according to the distance between your eyes and the picture.
This phenomenon is explained by the fact that as you look at the picture while changing your viewing distance, the retina receives multiple images, activating the brain’s neurons. Subsequently, the brain predicts the subsequent images. With so many images appearing, the last thing we see are the blurred lines.
Continuously, as each object appears, the brain focuses on determining the direction of the object’s movement, helping to predict what that object will look like immediately afterward, resulting in the appearance of blurred lines.
3. Herring Illusion
Do you see that the two red lines appear to be curved?
In fact, these two red lines are parallel to each other.
While our brain is “disagreeing,” the spoked lines “pull” our gaze, creating the illusion that our eyes are directed towards a central point. In other words, our eyes are seeing these lines radiate in depth, giving the impression of movement, causing the two parallel lines to appear curved.
The “curved” appearance of the two lines is what the brain predicts about how the lines should look when the line of sight is following the “direction” of the spoked lines toward the center point.
The brain assumes that the center of the two lines “must” extend further and that the distance between the two lines “must” be wider at the center. All of this happens in just 1/10 of a second. Subsequent illusions arise due to changes in perspective, color contrast, and the spatial arrangement of objects.
This Herring illusion is named after the German physicist Ewald Hering.
4. Pink Dots
The image above consists of light pink dots arranged in a circle with a cross in the center on a gray background. However, if you focus on the cross, the pink dots will disappear, leaving a gray rectangle.
This is also known as the “Troxler fading” phenomenon, discovered by Swiss physicist Ignaz Paul Vital Troxler in 1804.
When the human eye focuses on one point, we tend to keep our gaze still. At this moment, the light pink dots are in the peripheral view of our eyes, as the gaze is directed at the black cross. These light pink dots are present, but they do not sufficiently stimulate the neurons to maintain their image, causing them to gradually disappear.
5. Scintillating Grid Illusion
The scintillating grid illusion is created by white dots at the intersections of gray lines on a black background. The black dots constantly flicker around the grid, hence the name “scintillating.”
Similar to the pink dot illusion, the black dots only appear at the periphery of the retina, insufficient to stimulate the neurons to maintain their image continuously, causing them to “vanish and reappear” at times.
6. Café Wall Illusion
You may see these black and white lines as “misaligned,” but in reality, they are parallel straight lines.
This illusion was discovered by British psychologist Richard Gregory when he accidentally saw a café wall in the city of Bristol.
Scientists have demonstrated that the spacing between the tiles and the rows of bricks, along with the contrast between the two colors black and white, are the reasons behind this phenomenon.
7. Rotating Snake Illusion
When you look at the image below, you will see the circles appearing to be moving, but in fact, they are stationary.
A Japanese professor, Akiyoshi Kitaoka, also refers to this as the “retinal peripheral illusion”—the motion illusions occurring at the edge of vision. When looking at the sides of the image, this illusion becomes more pronounced.
Previous research suggested that this illusion was triggered by slow eye movements while observing the picture. However, in 2012, neuroscientist Susana Martinez proved the opposite, indicating it is caused by rapid eye movements.
8. Contrasting Rectangles
This is an illusion created by color contrast. Do you see that the gray rectangles between the black bars appear darker than those between the white bars?
In reality, they are the same color. The greater the color contrast of the surrounding environment, the smaller the contrast of the object. This has led our eyes to perceive these rectangles as having contrasting colors.
