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Brainworks: Explaining Optical Illusions and Other Mental Tricks


Back during the summer, an early copy of Brainworks showed up in our office. National Geographic was planning to advertise the book in mental_floss magazine (and this was even before we kept popping up on Curb Your Enthusiasm). I got sucked into the optical illusions featured throughout the book and asked if I could reprint a few of the explanations behind them. They agreed. Here you go!

Shepard's Tables

The horizontal/vertical illusion dates to its description in German physiologist Adolf Fick's 1851 doctoral thesis. He demonstrated differences among simple geometrical properties and how they are perceived. These kinds of disparities are called geometrical-optical illusions.

Fick observed that a vertical line looks longer than a horizontal line of the same length. This is easily seen in the letter T when the horizontal and vertical strokes measure precisely the same length, or when two line segments of exactly the same dimension form a right angle with one segment horizontal and the other vertical.
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Another explanation rests on an illusion of perspective. The brain chooses to interpret the drawing as two tables. Applying the rules of perspective it has formed through experience, the brain views the table on the left as receding farther, and being longer, than the one on the right.

The Arrow Illusion

Compare the tables with the Müller-Lyer Illusion (or Arrow Illusion). It is named for Franz Carl Müller-Lyer, a 19th-century German psychiatrist and sociologist. He began his illusion by drawing two parallel lines of the same length. At the ends of one line, he placed two arrowhead shapes with their open ends pointing outward. At the ends of the other line, he placed the same two arrowhead shapes with their open ends pointing inward. The line segment with the arrowheads pointing inward and the ends open to the outside looks significantly longer than its mate. The illusion holds true with the line segments in any orientation.

The Ames Room

American psychologist Adelbert Ames used his background as a painter to create an elaborate trick on the brain: the construction of a distorted room that looks normal when viewed from front and center. The back wall of the room slants away from the viewer instead of lying perpendicular to the viewer's line of sight, but Ames compensated for this by using perspective cues to make the room appear normal. A person who stands at the most distant corner of the sloping wall appears tiny, with plenty of space overhead; the same person standing in the nerer corner crowds the ceiling like a giant. An adult on one side is dwarfed by a child on the other because both appear equidistant from the viewer. The key to this illusion is that perspective and one particular angle make the room appear perfectly rectangular and normal.

If you like this kind of thing, check out the book's site. Here's the description: "You'll see for yourself why these visual illusions and experiments hoodwink the brain. You'll find out how the structure of the eye influences what you see. And you'll think of events that may not have actually happened, in order to learn how the mind can create a false memory."

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Animals
Why Tiny 'Hedgehog Highways' Are Popping Up Around London
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Hedgehogs as pets have gained popularity in recent years, but in many parts of the world, they're still wild animals. That includes London, where close to a million of the creatures roam streets, parks, and gardens, seeking out wood and vegetation to take refuge in. Now, Atlas Obscura reports that animal activists are transforming the city into a more hospitable environment for hedgehogs.

Barnes Hedgehogs, a group founded by Michel Birkenwald in the London neighborhood of Barnes four years ago, is responsible for drilling tiny "hedgehog highways" through walls around London. The passages are just wide enough for the animals to climb through, making it easier for them to travel from one green space to the next.

London's wild hedgehog population has seen a sharp decline in recent decades. Though it's hard to pin down accurate numbers for the elusive animals, surveys have shown that the British population has dwindled by tens of millions since the 1950s. This is due to factors like human development and habitat destruction by farmers who aren't fond of the unattractive shrubs, hedges, and dead wood that hedgehogs use as their homes.

When such environments are left to grow, they can still be hard for hedgehogs to access. Carving hedgehog highways through the stone partitions and wooden fences bordering parks and gardens is one way Barnes Hedgehogs is making life in the big city a little easier for its most prickly residents.

[h/t Atlas Obscura]

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Big Questions
Where Should You Place the Apostrophe in President's Day?
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Happy Presidents’ Day! Or is it President’s Day? Or Presidents Day? What you call the national holiday depends on where you are, who you’re honoring, and how you think we’re celebrating.

Saying "President’s Day" infers that the day belongs to a singular president, such as George Washington or Abraham Lincoln, whose birthdays are the basis for the holiday. On the other hand, referring to it as "Presidents’ Day" means that the day belongs to all of the presidents—that it’s their day collectively. Finally, calling the day "Presidents Day"—plural with no apostrophe—would indicate that we’re honoring all POTUSes past and present (yes, even Andrew Johnson), but that no one president actually owns the day.

You would think that in the nearly 140 years since "Washington’s Birthday" was declared a holiday in 1879, someone would have officially declared a way to spell the day. But in fact, even the White House itself hasn’t chosen a single variation for its style guide. They spelled it “President’s Day” here and “Presidents’ Day” here.


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Maybe that indecision comes from the fact that Presidents Day isn’t even a federal holiday. The federal holiday is technically still called “Washington’s Birthday,” and states can choose to call it whatever they want. Some states, like Iowa, don’t officially acknowledge the day at all. And the location of the punctuation mark is a moot point when individual states choose to call it something else entirely, like “George Washington’s Birthday and Daisy Gatson Bates Day” in Arkansas, or “Birthdays of George Washington/Thomas Jefferson” in Alabama. (Alabama loves to split birthday celebrations, by the way; the third Monday in January celebrates both Martin Luther King, Jr., and Robert E. Lee.)

You can look to official grammar sources to declare the right way, but even they don’t agree. The AP Stylebook prefers “Presidents Day,” while Chicago Style uses “Presidents’ Day.”

The bottom line: There’s no rhyme or reason to any of it. Go with what feels right. And even then, if you’re in one of those states that has chosen to spell it “President’s Day”—Washington, for example—and you use one of the grammar book stylings instead, you’re still technically wrong.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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