Muse Science Magazine for Kids|January 2022
In the sci-fi movie The Matrix, people lie motionless in pods of nutrients while they "dream” that they are living normal lives in the year 1999.
Carl Zimmer

Their version of reality is being fed into their brains by advanced computers to keep them passive slaves of a malevolent cyber-intelligence. They see what their brains are stimulated to see, not what is there.

Look around you. What do you see? Perhaps a cat sitting in a comfortable chair. But are you sure the cat is really there? Okay, we're teasing you. You're probably not lying in a plastic pod 200 floors up in some alien power station. On the other hand, The Matrix isn't all fantasy. Given sufficient knowledge of the human brain, it would be possible to make people see whatever you wanted them to see, rather than what was in front of their eyes. That's because we see with our brains, not with our eyes. Make the right nerve cells fire in the right order, and we can't tell the difference between a real cat and one that exists only in our minds.

The brain is sometimes compared to a computer that processes input from two cameras (our eyes). In fact, it is a mass of grayish jelly weighing about a kilogram and a half with stalk-like extensions called eyes. You could call it a bio-computer-and it's a powerful one at that. Your bio-computer whips through vision tasks with tremendous speed.

The latest Mars rover, Perseverance, touched down in tricky terrain on Mars in February 2021. For the first time, video cameras were used to help a spacecraft navigate a landing. Like human eyes, its cameras allowed it to understand its position during descent and quickly identify features on the planet's surface. Due to an 11-minute time lag in communicating messages to mission control on Earth, it had to maneuver on its own. Its computer "brain" compared the information from the cameras with examples of surface features that mission team members had uploaded ahead of time. This new navigation system allowed it to avoid the most dangerous spots and land safely, making possible a mission to search for possible signs of ancient microbial life on another planet.

Your brain is even better than this impressive technology. That's because it takes lots of clever shortcuts. It doesn't analyze every bit of light that enters your eyes. Instead it makes hypotheses about what you're seeing, using just a small fraction of the available information. You could think of it as a hyperactive scientist whose job is to make many, many guesses very, very fast.

Your brain's hypotheses are almost always good enough to let you do what you need to do, especially when you're looking at the natural world. Scientists suspect that this is because the brain's skills have been perfected by millions of years of natural selection.

Brains that quickly recognize a hole in the ground allow people to survive and pass on their genes to the next generation. Brains that need an hour to make the same identification leave people at the bottom of the hole.

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