Do You See a Mermaid or a Fish? Science Explains Why You Can’t See Both at Once

Date:26 March 2022 Author: Juandre Tags:

An optical illusion claiming to show either a fish or a mermaid is having a viral moment on Twitter, but there’s more to the post than meets the eye.

First, this image—a classic illusion challenging the user to see either a donkey or a seal—dates back to at least 2006, though some accounts place it from as early as the 1960s. Nothing is new under the sun, especially not things shared without credit by some of the biggest names on social media. As the meme goes: “Here’s the attention you ordered.”

We tracked down the recent viral edit posted March 15 on the Facebook page Audrey Loves Paris, which uses an eye-grabbing vaporwave color palette with pinks and teals. The creator also added text combining two of the most tantalizing parts of social media: a dubious claim (“right brain” versus “left brain,” widely acknowledged to be a myth), and a call to action with options people will jump to point out are wrong—the image clearly doesn’t depict a fish or a mermaid. As kids and fishermen agree, this is bait.

People love to be right in public places, which gives them a feeling of clout and importance. These posts combine all three types of people Malcolm Gladwell highlights in his book The Tipping Point: connectors, mavens, and salesmen. By sharing their thoughts online, trying to sound authoritative, and arguing that they’re right, people are doing it all.

The image itself is also interesting. Remember the collective freakout over the white and gold or blue and black dress? That was another case with two equally correct answers that people just enjoyed weighing in on. We love optical illusions that present two different images depending on how you look at it, or what you’re thinking at the time, like the classic duck-rabbit illusion or Rubin’s vase. Another famous one is the Coffer illusion, which was created in 2006.

These images use a psychological trick called a Gestalt switch, which is when our perspective is suddenly altered so that the image is completely changed. With the Coffer illusion, one important factor is corners, which our brains focus on over smooth lines or curves. This also explains a famous illusion where looking at a field of uniformly colored squares creates the appearance of phantom “circles” in the empty space. We perceive the corners to be lighter, which turns the negative space into something more.

rubin's vace optical illusion

An example of the classic Rubin’s vase optical illusion.

NEVIT NEVIT DILMEN – ATATURK.SVG / WIKIMEDIA COMMONS

Illusions like the duck and rabbit or the seal and donkey rely on a similar trick that our eyes play on our brain. In the absence of information, our brains retain the things we’ve already seen and accumulate a picture that can go back as far as 15 seconds, giving us the feeling of seeing something more complete than it really is. Once you see the seal or the donkey, you may find it easy to then see the other one as well, but the visual information being glossed over is then different.

And while this illusion doesn’t have as many squares or corners to study, it does contain something else we’d like to focus on: eyes. In a 2011 study published in the peer-reviewed journal PLoS One, which includes the donkey-seal illusion, scientists found that people’s eyes focused on two areas in the image: the seal face (or the donkey nose) and the donkey’s eye (or the seal’s flipper). When the same viewers saw unambiguous versions of the seal or donkey, they heavily focused on the eyes and ignored almost everything else.

It takes cleverness and talent to choose the right points of overlap to show in order to depict a donkey as well as a seal. We’ll close with another famous illusion from 2015: a photograph that simultaneously depicts Albert Einstein and Marilyn Monroe, two people who are rarely mentioned in the same breath. Indeed, things we look at may have much more in common than we realize at first glance.

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