The Unexpected Optical Illusion Hidden in a Stack of Chairs

iStock
iStock

When you’re a scientist who studies vision, everything you see is inspiration. Such is the case for Nicholas Scott-Samuel, a researcher at the University of Bristol studying visual perception, whose latest work was inspired by a stack of chairs in an office. As BPS Research Digest reports, his new article in i-PERCEPTION explores an impossible-seeming optical illusion. It's formed by stacks of a certain type of chair with legs that make a square on each side of the chair (meaning the bottoms of the legs are connected by a bar).

A stack of purple chairs in a classroom; a black-and-white drawing of an optical illusion of quadrangles stacked tother
Scott-Samuel et al., i-PERCEPTION (2018)

When you look at it head-on, the stack of squares gives you an illusion of great depth, as if the bottom bars of the chair legs stick out rather than stack vertically, and you may not be able to tell which of the legs is on top and which is on the bottom—especially if you’re looking at the drawing of the illusion, rather than at the photo of the chairs.

To explore why a stack of chairs might look so warped, Scott-Samuel and a few other researchers recruited 40 people on Facebook to ask them whether they found the image visually confusing. They did, but only if the stack contained a certain number of chairs—at nine chairs the illusion held, but any number less than four looked totally normal.

The researchers liken the effect to the Penrose triangle, an impossible shape that’s similar to a Möbius strip. But unlike the Penrose triangle, this one is actually possible, as long as you look at it from the correct angle. As the paper states: “Nick Scott-Samuel (in whose office the illusion was observed) reports that it obtains in real life as well as in images, even when sober.”

The paper is extra-short—the author’s bios are longer than the actual contents of the article—demonstrating that science doesn’t have to be a supremely arduous, heavy endeavor. At least not any heavier than a stack of chairs.

Love optical illusions? Try your eye at this one.

[h/t BPS Research Digest]

These Rugged Steel-Toe Boots Look and Feel Like Summer Sneakers

Indestructible Shoes
Indestructible Shoes

Thanks to new, high-tech materials, our favorite shoes are lighter and more comfortable than ever. Unfortunately, one thing most sneakers are not is durable. They can’t protect your feet from the rain, let alone heavy objects. Luckily, as their name implies, Indestructible Shoes has come up with a line of steel-toe boots that look and feel like regular sneakers.

Made to be incredibly strong but still lightweight, every pair of Indestructible Shoes has steel toes, skid-proof grips, and shock-absorption technology. But they don't look clunky or bulky, which makes them suitable whether you're going to work, the gym, or a family gathering.

The Hummer is Indestructible Shoes’s most well-rounded model. It features European steel toes to protect your feet, while the durable "flymesh" material wicks moisture to keep your feet feeling fresh. The insole features 3D arch support and extra padding in the heel cup. And the outsole features additional padding that distributes weight and helps your body withstand strain.

Indestructible Shoes Hummer.
The Hummer from Indestructible Shoes.
Indestructible Shoes

There’s also the Xciter, Indestructible Shoes’s latest design. The company prioritized comfort for this model, with the same steel toes as the Hummer, but with additional extra-large, no-slip outsoles capable of gripping even smooth, slippery surfaces—like, say, a boat deck. The upper is made of breathable moisture-wicking flymesh to help keep your feet dry in the rain or if you're wearing them on the water.

If you want a more breathable shoe for the peak summer months, there's the Ryder. This shoe is designed to be a stylish solution to the problem of sweaty feet, thanks to a breathable mesh that maximizes airflow and minimizes sweat and odor. Meanwhile, extra padding in the midsole will keep your feet protected.

You can get 44 percent off all styles if you order today.

This article contains affiliate links to products selected by our editors. Mental Floss may receive a commission for purchases made through these links.

No Squawking, Please: A Backyard Bird Library Is the Star of This Livestream

Bird Library, YouTube
Bird Library, YouTube

Many people discovered backyard birding when they were quarantined in their homes at the start of the COVID-19 pandemic. Even if you have a vibrant wildlife population in your area, the Bird Library webcam is worth checking out. As Atlas Obscura reports, the bird feeder at the focus of the livestream resembles a tiny library where feathered guests can misbehave.

Librarian Rebecca Flowers and woodworker Kevin Cwalina were inspired to build the Bird Library in 2015. Located in a backyard in Charlottesville, Virginia, it features a miniature reading chair, bookshelves, and a reception desk. The decorations are even updated to match the seasons; the feeder currently sports a banner that says "Summer Reading." The main differences setting it apart from a real library are the bird seed scattered on the floor and the avian visitors.

The Bird Library attracts a diverse collection of patrons. Sparrows, cardinals, and mourning doves have been recorded perching on the librarian's desk and checking out the reading materials. The occasional squirrel has also been known to stop by.

Live video of the feeder streams on the Bird Library's YouTube page and website 24 hours a day, 7 days a week. You can play the video below to check in on the current guests. If the backyard Bird Library has inspired you to find birds closer to home, here's some gear for beginner naturalists.

[h/t Atlas Obscura]