Are the balls blue or purple? The optical illusion that is driving the internet crazy

Are the balls blue or purple? The optical illusion that’s driving the internet crazy

From color-changing fire trucks to “The Dress,” many optical illusions have amazed the internet over the years.

Now, a scientist from Harvard Medical School has discovered an illusion that may be the strangest yet.

The illusion, seemingly simple, features nine dots on a simple dark purple background.

But are the dots blue or purple?

Viewers are divided on Reddit, where the illusion has received over 4,900 votes and more than 500 comments.

Some say the dots are “definitely purple”, while others insist they are “all purple”.

One confused commenter wrote: “My eyes are going crazy… I don’t think I’ll sleep tonight. Thank you for sharing this.”

So, what color do you think the dots are?

On social media, commentators were divided between blue and purple.

However, some also noticed an even stranger effect.

One user wrote: “Only one looks purple to me, but it keeps moving.”

Another added: “My perception of color changes depending on whether I focus directly on the point or not.”

And another joked: “How does the purple dot I’m looking at know to change color?”

Although it seems strange, this is exactly the way the illusion’s inventor, Dr Hinnerk Schulz-Hildebrandt, had planned it.

In reality, all the dots are solid purple on a blue-purple background.

But, by holding the phone about 30 cm away from your face and looking at each dot in turn, only the dot in the center of your focus appears purple.

In another variation, 360 purple dots are placed on the same blue background.

By holding the phone about 10 cm away from your face and slowly pulling it further away, you should see more dots transitioning from blue to purple as the field of focus expands.

In a final version, Dr Schulz-Hildebrandt created a “disappearing poem”, using text in the same colour combination.

By holding the phone close to your face and reading carefully, the word you are reading appears purple, while the rest turns blue and fades into the background.

Dr Schulz-Hildebrandt describes this as a “focus- and distance-dependent color illusion.”

He writes: “A pattern of purple objects on a blue background appears purple only where the viewer focuses directly. At the periphery, perception shifts toward blue.”

This illusion works because of the unique way our brain perceives lilac.

In our eyes we have light-sensitive cells called S-cones, M-cones, and L-cones, sensitive to blue, green, and red light.

While some colors like green, yellow, and orange are associated with a specific wavelength of light, purple does not exist in a specific part of the visible spectrum.

In fact, purple is generated in the visual cortex of our brain when L-cones and S-cones combine.

This makes lilac a “fragile and unstable perception,” easily influenced by psychological factors or the surrounding context.

This “color contrast effect” is why many classic optical illusions appear to change color.

For example, lighting or the colors of surrounding objects can make objects that are actually blue and black appear white and gold, as happened with the famous “blue and black dress.”

Also, due to the different distribution of cone cells in the eye, it is easier to see purple in the center of vision than in the periphery.

By placing purple dots on a similar blue background, our brain can generate the correct purple color only for the dots in the spotlight.

This is why the point you see directly appears purple, taking on its true color, while the others appear blue.

WHAT IS THE DELBOEUF ILLUSION?

The Delboeuf illusion is a type of visual illusion where a dot surrounded by a large ring is usually perceived as smaller than a dot of the same size surrounded by a small ring.

This visual trick works because the brain perceives the dot in the context of the outer ring.

It was named after the Belgian philosopher and mathematician Joseph Remi Leopold Delboeuf (1831 – 1896), who created it in 1865.

Regarding plate size, the theory suggests that a smaller plate tricks people into thinking they have more food.

But recent research suggests that when people are hungry, they are able to correctly identify the portion size of food, regardless of how it is served.

However, Delboeuf’s illusion is widely believed to work in other contexts. /GazetaExpress/