By Natalie Wolchover
Life's Little Mysteries

Our brains balk at the thought of four-dimensional hypercubes, quantum mechanics or an infinite universe, and understandably so. But our gray matter is generally adept at processing sensory data from the mundane objects and experiences of daily life. However, there are a few glaring exceptions.

Here are five common things that unexpectedly throw our brains for a loop, revealing some of the bizarre quirks in their structure and function that usually manage to slip under the radar.

Doors
Do you ever walk into a room with some purpose in mind — to get something, perhaps? — only to completely forget what that purpose was?  Turns out, doors themselves are to blame for these strange memory lapses.

Why you forgot what you were just doing

Psychologists at the University of Notre Dame have discovered that passing through a doorway triggers what's known as an "event boundary" in the mind, separating one set of thoughts and memories from the next, just as exiting through a doorway signals the end of a scene in a movie. Your brain files away the thoughts you had in the previous room, and prepares a blank slate for the new locale. Mental event boundaries usually help us organize our thoughts and memories as we move through the continuous and dynamic world, but when we're trying to remember that thing we came in here to do… or get… or maybe find… they can be frustrating indeed.

Beeps
Which bugs you more: the whine of a digital alarm clock, the sound of a truck backing up, or the shrill reminders that your smoke detector is running out of batteries? Fine, they're all terrible. Beeps are practically the soundtrack of the modern world, but they're extremely irritating because each one induces a tiny brain fart.

We didn't evolve hearing beeps, so we struggle to grasp them. Natural sounds are created from a transfer of energy, often from one object striking another, such as a stick hitting a drum. In that case, energy is transferred into the drum and then gradually dissipates, causing the sound to decay over time. Our perceptual system has evolved to use that decay to understand the event — to figure out what made the sound, and where it came from. Beep sounds, on the other hand, are like cars driving at 60 mph then suddenly hitting a wall, as opposed to gradually slowing to a stop. The sound doesn't change over time, and it doesn't fade away, so our brains are baffled about what they are and where they're coming from. 

Photos
Just as we didn't evolve hearing beeps, we also didn't evolve seeing photographs. Like your grandmother learning to use the Internet but never developing an intuitive feel for it, we consciously "get" photographs, but our subconscious brains can't quite separate them from the objects or people pictured.

Case in point: Studies show that people are much less accurate when throwing darts at pictures of JFK, babies, or people they like than when throwing darts at Hitler or their worst enemy. Another study found that people start to sweat profusely when asked to cut up photographs of their cherished childhood possessions. Lacking millions of years of practice, our brains fail when it comes to separating appearance from reality.

Phones
Do you ever feel your phone vibrating in your pocket or purse, only to retrieve it and be met by eerie, black-screened lifelessness? If, like most people, you occasionally experience these "phantom vibrations," it turns out it's because your brain is jumping to wrong conclusions in an attempt to make sense of the chaos that is your life.

Brains are bombarded with sensory data; they must filter out the useless noise, and pick up on the important signals. In prehistoric times we would have constantly misinterpreted curvy sticks in the corny of our vision for snakes. Today, most of us are techno-centric, and so our brains misinterpret everything from the rustle of clothing to the growling of a stomach, jumping to the conclusion that we're getting a call or text, and actually causing us to hallucinate a full-on phone vibration.

Wheels

Ever noticed how car wheels can look like they're spinning backwards in the movies? This is because movie cameras capture still images of a scene at a finite rate, and the brain fills in the gaps between these images by creating the illusion of continuous motion between the similar frames. If the wheel rotates most of the way around between one frame and the next, the most obvious direction of motion for the brain to pick up on is backwards, since this direction suggests the minimal difference between the two frames. [Why It Took so Long to Invent the Wheel]

However, wheels can also appear to spin backwards in real life, too, which is weirder. The leading theory to explain the "continuous wagon wheel illusion," as it is known, holds that the brain's motion perception system samples its input as a series of discrete snapshots, much like a movie camera. So our brains are effectively filming their own movies of the external world, but not always at a fast enough frame rate to perceive the wheels in the scene spinning the right way. 

For scientific explanations of five more brain farts, click here .

More from Life's Little Mysteries:

• 15 Weird Things Humans Do Every Day, and Why
• Top 10 Inventions that Changed the World
• Why Aren't We Smarter?

More from The Body Odd:

• Myth, busted: You only use 10 percent of your brain
• Why it's hard to remember two new things
• Had a Rick Perry moment? What causes memory lapses

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