Test your Brain with these 10 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.

Here are 10 visual illusions to combine fun and learning about the visual system.

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

To go beyond the illusions, read about what happens in your brain while you experience them.

1. Can you put the fish in the fishbowl?

Stare at the yel­low stripe in the mid­dle of the fish in the pic­ture below for about 10–20 sec. Then move your gaze to the fish bowl.



2. Are the squares inside the blue and yel­low squares all the same color?


3. Are the hor­i­zon­tal lines straight or crooked?


4. Are the cir­cles sta­tic or moving?


5. How many legs does this elephant have?


6. Are the two hor­i­zon­tal lines of the same length?


7. Do you see gray dots at the inter­sec­tions of the white lines?


8. Are the two orange cir­cles of the same size?


9. Does Lincoln’s face look normal?


10. Can you see a baby?



Check your answers and learn about what was going on in your brain while you expe­ri­enced each of these illusions:

  1. Can you put the fish in the fishbowl?

Did you see a fish of a dif­fer­ent color in the bowl? You have just expe­ri­enced an after­im­age.
In the retina of your eyes, there are three types of color recep­tors (cones) that are most sen­si­tive to either red, blue or green. When you stare at a par­tic­u­lar color for too long, these recep­tors get “fatigued.” When you then look at a dif­fer­ent back­ground, the recep­tors that are tired do not work as well. There­fore, the infor­ma­tion from all of the dif­fer­ent color recep­tors is not in bal­ance. This will cre­ate the color “afterimages.”

  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).

  1. Café Wall Illusion

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

  1. 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.

  1. How many legs does this ele­phant have?

Tricky, isn’t it?!This pic­ture is an impos­si­ble pic­ture that also con­tains some sub­jec­tive con­tours, such as the Kanizsa Tri­an­gle below: A white tri­an­gle (point­ing down) can be seen in this fig­ure even though no tri­an­gle is actu­ally drawn. This effect is known as a sub­jec­tive or illu­sory con­tour. The con­tour of the tri­an­gle is cre­ated by the shapes around it.


  1. 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.

  1. 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).

  1. 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.

  1. 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.


  1. 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.


I hope you had fun and learned inter­est­ing facts about your brain!

Leave a Comment