Test your brain and mind with these nine classic optical Illusions

Are the two orange cir­cles of the same size? 

One way to learn more about our brains and minds is to look at how we can trick them–that is, to see how we react to brain teasers and visu­al illusions.

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

Below are 9 opti­cal illu­sions that com­bine fun and learn­ing about our visu­al sys­tem. We know you know there is a trick since these are illu­sions… but don’t try to be smarter than your brain. Enjoy being surprised!

(You’ll find answers and expla­na­tions at the end of the article)

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

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2. Are the horizontal lines straight or crooked? 

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3. Are the circles static or moving?

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4. How many legs does this elephant have?

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

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

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

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8. Does Lincoln’s face look normal?

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9. Where is the baby?

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ANSWERS AND EXPLANATIONS

Con­trast your answers with the ones below, and learn about what was going on in your brain and mind while you expe­ri­enced each of these clas­sic opti­cal 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. 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–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.

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5. 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.

6. 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.

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7. 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).

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8. 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 to spe­cial­ize in pro­cess­ing faces. And 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 in face recog­ni­tion. As a con­se­quence, they (we) do not respond to face dis­tor­tions as well. This explains why we miss the weird eyes when the face is invert­ed..

This is how the orig­i­nal image looked like:

9. Where is the 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..

–> To keep learn­ing about your brain and mind, check out these Top 25 Brain Teasers, Games and Illu­sions, for Teens and Adults of Any Age.