Mind-blowing Optical Illusions and the Science Behind Them

The best part of every book fair in grade school was getting your hands on the latest optical illusions book. It almost seemed like magic to pour through the pages and see how static images could come to life and seemingly transform before our very eyes.

If you’ve always wondered how these illusions worked, you’ve come to the right place. Today, we’re looking at some mind-blowing optical illusions and exploring the science behind them, starting with a viral image that flooded newsfeeds in 2015. . .

1) What color is the dress?


Wikimedia Commons. Fair use.

Unless you avoided social media entirely at the end of February in 2015, your newsfeed was probably flooded with images of the dress, the garment that appeared to be different colors to different people. Was it gold and white? Black and blue? Everyone from Anna Kendrick to Kim Kardashian argued about the dress’ true colors.

So, just what was the real color pattern of this fashionable garment?

1.5) Spoiler: It’s black and blue!

Matt Hendrick on Flickr (CC BY-ND 2.0)

No one knows for sure why everyone saw the same dress so differently, even after taking into account different screens and image sizes. Some speculate, though, that whether or not someone is a night owl could be a deciding factor. One study suggests night owls are more likely to see the dress as black and blue. Why? Well, probably because these people are exposed to reddish-tinted artificial lighting more often. So, when they view the original pic of the dress, their eyes may automatically correct for the image’s odd lighting and appear the correct black-and-blue color.

Our next pick also features a color-themed illusion that may leave you wondering HOW?. . .

2) Which square is darker?

Edward H. Adelson and Pbroke13 on Wikimedia COmmons (CC BY-SA 4.0)

Take a gander at this checkerboard. At first glance, it might look like Squares A and B are different shades of gray. But if you were to take a color-dropping tool and select each square, you’d be proven wrong: they’re both the same shade of gray!

How can this be true?

2.5) They’re the same shade of gray!

Adapted from the original on Wikimedia commons.Shades found using Colorpick Eyedropper.

The checkered shadow illusion all has to do with perspective. Part of it has to do with the shadow involved. Since the cylinder casts a shadow over B, B looks comparatively light next to the squares surrounding it, tricking the eyes into thinking that B is therefore darker than A.

Hop on board; our next pick is taking the midnight train to an illusion even more confusing than this one. . .

3) Which line is longer?

Tony Philips/Nasa.

Quick—which line is longer?

Did you say the top line? If so, you’d be wrong. These lines are the same length! Like the checkerboard illusion, this trick of the eye also has to do with perspective. . .

3.5) They’re equal. Did you fall for it?

TONY PHILIPS/NASA.

Named after Mario Ponzo, the Ponzo illusion shown here relies on our mind making associations between the two lines in comparison to the background. The converging upper lines of the “railroad tracks” suggest that the line at the top is farther away. How does this work? Well, we know that objects farther away look smaller, even if they are actually quite large. So, the theory is that our brain interprets the upper line as inherently longer since it appears farther away than the bottom one.

Questioning everything you see yet? Just wait. . .

4) Which circle is larger?

Take a look at the two clusters of circles. Focus on each orange circle in the middle. Which one do you think is larger?

4.5) Trick question.

If you guessed that the two orange circles are the same size, you’d be right.

Known as the Ebbinghaus illusion, this trick is similar to the Ponzo illusion and checkered squares. The extremely large gray circles of the first cluster make the first orange circle look comparatively small. This illusion is exaggerated when placed next to the second cluster. Here, the orange circle is surrounded by smaller gray ones, therefore making the orange dot look much larger than it actually is.

While there’s some stronger evidence to back up theories of the Ebbinghaus illusion, these next few tricks still leave scientists completely puzzled. . .

5) Are these lines the same length?

Here’s another line illusion for you. Some people might initially think that the vertical line is longer than the horizontal line. . .

5.5) Ope. They’re the same length!

But, as this image shows, these lines are the exact same length.

This horizontal-vertical illusion doesn’t work on everyone, and perspective also plays a role in why some people interpret these lines’ lengths differently.

This next illusion might seem like a no-brainer, but the writing isn’t exactly on the (café) wall. . .

6) Where are these lines going?

Fibonacci on Wikimedia Commons (CC BY-SA 3.0)

As you look at this tricky image, known as the café wall illusion, ask yourself: Are the horizontal lines parallel or will they cross if they went on long enough?

6.5) These lines will never meet.

Modified from the original on Wikimedia Commons.

The horizontal lines are all parallel to each other, despite looking sloped. No one knows exactly why these lines appear to be slanted. But some think this deception likely relies on color contrast and shape placement.

Did you enjoy this trick of the eye? If so, line up for the next few illusions. . .

7) Where is everything going?

FIBONACCI ON WIKIMEDIA COMMONS (CC BY-SA 3.0)

The café wall illusion has nothing on the Zöllner illusion. With lines seemingly going every which way, everything looks like pure chaos., right?

Well, not exactly. . .

7.5) Who thought lines could be so trippy?

Modified from the original on Wikimedia Commons.

The Zöllner illusion likely relies on some of the same tricks as the café wall and Ponzo ones. In short, the placement and angle of the shorter lines contrasted with that of the longer lines creates a sense of depth that isn’t actually there.

As mind-boggling as these illusions are, at least these straight lines look like straight lines. That’s not the case with the next entry. . .

8) Are these straight or curved?

Take a gander at the Hering illusion, a.k.a. the mind-blowing line illusion that will make you question your entire existence. Those vertical lines must be curved. Right? RIGHT?

8.5) Why can’t lines just be lines?

Wrong. Every single line you see? Straight as the edge of a ruler. Once again, placement and angles all work together to confuse your brain into seeing a curve when there aren’t any at all. Silly brain.

Think these past few illusions have been tricky? Just wait. These next few ones are the definition of mind-boggling. . .

9) What in the world is going on?

It’s hard not to look at this object in complete confusion. That’s because, technically, this object cannot exist. This shape is what’s known as an impossible object: a 2D object that looks 3D but can never actually exist in reality as it appears here. This particular example is a Penrose triangle.

What would the Penrose triangle look like if you tried to render it in 3D?. . .

9.5) The triangle does not exist.

Tomruen on Wikimedia Commons (CC-BY SA 4.0)

It would look something like this—not a triangle at all!

Speaking of impossible objects. . .

10) Where do these stairs go?

You’ve probably seen these stairs a time or two, maybe on a poster one of your teachers had up on the wall. It’s a variation of our previous illusion, the Penrose triangle, appropriately named the Penrose stairs.

So, just what makes it so special?

10.5) You’ll never see these stairs in real life.

Chris Dlugosz on Flickr (CC BY 2.0)

Like the Penrose triangle, these stairs cannot be rendered in reality, as a static staircase can’t descend in a repeating clockwise fashion forever.

Think these impossible shapes are incredible? Just wait until you see our next pick, which makes even unicorns seem possible by comparison. . .

11) Is this even a cube?

4C on Wikimedia Commons (CC BY-SA 3.0)

Once again, we have an image that looks to be a simple, perfectly logical cube at first glance. But the more you look at this object, the less logical it appears. It only makes sense that this object is known as an irrational cube.

If you really wanted to make this object a reality, it would look something like this. . .

11.5) Error 404: Cube not found.

Wikimedia Commons.

What you’re looking at is a shape that could exist in 3D, but isn’t actually a cube. But if you move it around and view it at just the right angle, it would look like the irrational cube.

Our next few picks definitely exist in real life, but there’s more than one way to interpret them. . .

12) What do you see?

Brocken Inaglory on Wikimedia Commons (CC-BY SA 3.0)

What do you see when you look at this image?

(Spoiler: There’s more than one correct answer!)

12.5) It’s like an ink blot that won’t tell you about your mother.

Modified from the Original on Wikimedia Commons.

Some people might see a vase, represented by the white space. Others might notice two people staring at each other, represented by the black spaces.

The sharp contrast between the white and black in this image? It lets our brains interpret the picture in such a way that we can distinctly see more than just one thing. What you see depends on what you consider the figure (object) and the ground (background). Whatever you see as the ground will help give shape to the figure.

If this illusion wasn't all it seemed quacked up to be, try checking out this next picture. . .

13) What mystery animal is that?

Another ambiguous image, you’ve probably seen this little guy before. Depending on how you look at it, this animal could be a duck or a rabbit. Some people can see both!

How does this work, though?

13.5) Rabbit or duck? YOU DECIDE.

Once again, context likely plays a part. One study showed that children were more likely to initially see a rabbit when it was Easter.

Older research from psychologist Joseph Jastrow suggests that highly creative people are able to quickly switch back and forth between viewing the rabbit and the duck. So, perception might be more nuanced than we thought! That’s right: perception is a mental process as much as it is “just” viewing something.

But wait, there's more!

14) Physicist or movie star?

Who do you see? A famed physicist or iconic movie star?

The answer is a bit more complicated than you might think. . .

14.5) It depends where you’re at.

If you are close to your screen, you probably see the famed physicist Albert Einstein. If you are farther away, you probably see the iconic Marilyn Monroe laughing. You see, the previous image is actually a composite of these two shown above; this composite picture is known as a hybrid image.

A hybrid image superimposes a low-pass filtered image (the blurry one) onto a high-pass filtered one (the sharper-looking image). The closer you get to a hybrid image, the more likely you are to notice the sharper looking image. The farther away, the opposite is true.

Can you face the next illusion? . . .

15) Is there more to this than meets the eye?

At first glance, this image looks like a cliffside community. But there’s more to this image than what first meets the eye. . .

15.5) Man oh man, did that trip us up.

The artist carefully arranged the landscape in such a way that it should resemble the side view of a man’s head.

But if you think that this face-based image is confusing, wait until you see what’s next. . .

16) Front-facing or profile view?

Pinterest.

There’s a lot going on here. Depending on how you look at this man’s face, you may think you’re looking at a cropped front-facing photo or a very warped profile.

Now, you may be wondering how these images are created. . .

16.5) Face the facts: This is weird.

Pinterest.

These images are compiled from two separate photos of the same person with the same expression. To create one, both front and profile photos are needed. Part of the front-facing image is carved away to serve as the base. Then, parts of the profile are added, such as the nose and forehead.

While these results are unsettling, they still won’t leave your head spinning like these next few illusions. . .

17) What can you see from this gif?

Stare at this gif. . .

17.5) Psyche!

Fiestoforo on Wikimedia Commons (CC BY 3.0)

This actually isn’t a gif, but an unmoving picture.

This motion illusion relies both on shapes and colors to trick the eyes and mind into seeing movement when there isn’t any. Both the placement of the circles and the contrast of all the colors fire certain neurons in such a way that the brain mistakenly interprets what the eyes see as movement.

Our next illusion does actually rely on movement. . .

18) Will this illusion stay with you?

No tricks here. What you’re looking at really is a moving object. In order to see the magic, though, you’ll need to do a little bit of work.

Watch the video for about a minute, then look away.

18.5) It’s all in the neurons, baby.

Did things look a little distorted for a few seconds after watching that video? If so, you’ve just experienced the power of motion aftereffect. How does this work?

It’s believed to be the result of neural adaptation, or our neurons getting used to the motion of the video. When neurons are continually exposed to a certain movement, their responses are reduced. This is why there’s a tiny bit of a “lag” when you suddenly break away from the video and look at something stationary.

Is your mind sufficiently blown?. . .

Decoding Your Favorite Optical Illusions

While science may not have come to any definitive conclusions about why certain images look bizarre at first glance, there’s no doubt that the human mind is amazing.

Did any of our top picks stump you? Or did you see right past the smoke and mirrors?

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