Science

Test Your Brain With These Visual Illusions

The brain has two hemispheres, each divided into four lobes. Each lobe is responsible for different functions. For instance the frontal cortex (in blue below) is responsible for decision making and planning; the temporal lobe (in green) for language and memory; and the parietal lobe (in yellow) for spatial skills. The occipital lobe (in red) is entirely devoted to vision: It is thus the place where visual illusions happen.

The frontal lobe represents around 41% of total cerebral cortex volume; the temporal lobe 22%; the parietal lobe 19%; and the occipital lobe 18%. How the visual system processes shapes, colors, sizes, etc. has been researched for decades. One way to understand more about this system is to look at how we can trick it, that is, to look at how the brain reacts to visual illusions.

Following are some visual illusions to combine fun and learning about the visual system (You’ll find answers and explanations at the end).

We know you know there is a trick since these are illusions… but don’t try to be smarter than your brain, just enjoy being tricked!

1. Are The Squares Inside The Blue And Yellow Squares All the Same Color?

Are The Squares Inside The Blue And Yellow Squares All the Same Color?

2. Are The Horizontal Lines Straight Or Crooked?

Are The Horizontal Lines Straight Or Crooked?

3. Are The Circles Static Or Moving?

Are The Circles Static Or Moving?

4. Are The Two Horizontal Lines Of The Same Length?

Are The Two Horizontal Lines Of The Same Length?

5. Do You See Gray Dots At The Intersections Of The White Lines?

Do You See Gray Dots At The Intersections Of The White Lines?

6. Are The Two Orange Circles Of The Same Size?

Are The Two Orange Circles Of The Same Size?

7. Does Lincoln’s Face Look Normal?

Does Lincoln’s Face Look Normal?

8. Can You See A Baby?

Can You See A Baby?

 

Answers and explanations: Contrast your answers with the ones below, and learn about what was going on in your brain while you experienced each of these illusions:

 

1. Bezold Effect

The smaller squares inside the blue and yellow squares are all the same color. They seem different (magenta and orange) because a color is perceived differently depending on its relation to adjacent colors (here blue or yellow depending on the outer square).

2. Café Wall Illusion

The horizontal lines are straight, even though they do not seem straight. In this illusion, the vertical zigzag patterns disrupt our horizontal perception.

3. Illusory Motion

The circles do appear to be moving even though they are static. This is due to the cognitive effects of interacting color contrasts and shape position.

 

4. The Mueller-Lyer Illusion

The two horizontal lines are of the same length, even though the one at the bottom seems longer. As you know, the visual angle gets smaller with distance, so the brain automatically perceives objects at farther distances to be bigger.

In general, lines that have inward flaps, such as corner of a building, are relatively the nearest points of the overall object. Similarly, lines with outward flaps are found at the longer distance, as the farthest corner of a room. So in the Mueller-Lyer illusion, the brain perceives the line with outward flaps to be at a farther point as compared to the line with inward flaps. Consequently, the brain perceives the line with outward flaps to be longer.

5. Hermann Grid Illusion

There are not gray dots in this grid. However “ghostlike” gray blobs are perceived at the intersections of the white lines. The gray dots disappear when looking directly at an intersection. This illusion can be explained by a neural process happening in the visual system called lateral inhibition (the capacity of an active neuron to reduce the activity of its neighbors).

6. The Ebbinghaus Illusion

The two orange circles are exactly the same size,even though the one on the left seems smaller. This size distortion may be caused by the size of the surrounding circles or by their distance to the center circle.

7. Does Lincoln’s Face Look Normal?

It seems normal but now, look at it upright: Lincoln’s eyes do not look quite right!

Some neurons in the brain seem specialized in processing faces. Faces are usually seen upright. When presented upside down, the brain no longer recognizes a picture of a face as a face but rather as an object. Neurons processing objects are different from those processing faces and not as specialized. As a consequence these neurons do not respond to face distortions as well. This explains why we miss the weird eyes when the face is inverted.

8. Can You See A Baby?

Another great example of an illusory contour! The baby’s head is on the left, the baby’s feet are against the trunk of the tree on the right.