How Your Brain Creates Reality
BBC Earth|May - June 2021
Do we see the world as it really is, or are we creating our own reality? Here, we delve into the neuroscience behind the world that we experience
Lisa Feldman Barrett

There is a classic Monty Python sketch in which a customer, played by John Cleese, enters a pet shop to buy a cat. The dodgy shopkeeper, played by Michael Palin, whips out a terrier instead and offers to convert the dog surgically into a cat, a budgie, or a fish. “Terriers make lovely fish,” he assures the customer. “I could do that for you straight away. Legs off, fins on, stick a little pipe through the back of its neck so it can breathe, bit of gold paint…” In real life, we often view our pets in terms of other animals, and no scalpel is required. Perhaps you’ve met dogs who are so aloof that they seem like cats, or cats who are so affiliative that they’re more like dogs. My family used to have a pet betta fish named Ariel who seemed more puppy than fish. She’d allow us to pet her without complaint, and when we dropped food in the fish tank she’d nuzzle our fingers.

This topic might seem frivolous, but it reveals a superpower of the human brain. We can consider a physical object, such as a fish, and impose new functions on it that are not part of its physical nature, using only our collective minds. To my family, Ariel was a puppy, even though nothing about her body was dog-like. We simply agreed that Ariel had puppyish qualities, and that agreement became our reality. (The perceptive reader may have noticed that I’ve referred to Ariel as ‘she’, even though the colourful bettas sold in pet shops are always male. Our daughter, who was three at the time and in love with Walt Disney’s The Little Mermaid, informed us in no uncertain terms of Ariel’s preferred pronoun.)

This superpower to modify physical reality is called ‘social reality’. You or I can simply make something up and communicate it to other people, and if they treat it as real, it becomes real. For better or for worse.

Social reality has an astonishing level of influence on our lives. We impose functions on bits of paper and metal and they become money. We draw imaginary lines in the dirt and they become the borders of a country, and the people on opposite sides of those imagined lines transform into citizens with rights, and foreigners without them. Brexit is also social reality. Even your own name is social reality. Someone just made it up, and you and other people treat it as real. In fact, most of us spend most of our time in a real world of serious make-believe.

BRAIN IN A BOX

How do human brains create social reality? To answer this, let’s consider it from a brain’s point of view. For your whole life, your brain is trapped inside a dark, silent box called your skull. Your brain constantly receives data from your eyes, ears, nose, and other sense organs. It also receives a continuous stream of sense data from inside your body as your lungs expand, your heart beats, your temperature changes, and the rest of your insides carry on their symphony of activity.

All this data presents a mystery to your brain-in-a-box. Together, the data represents the end result of some set of causes that are unknown. When something in the world produces a change in air pressure that you hear as a loud bang, some potential causes could be a door slamming, a gunshot, or a fish tank toppling to the floor. When your stomach unleashes a gurgle, the cause might be hunger, indigestion, nervousness, or love. So, your brain has a problem to solve, which philosophers call a ‘reverse inference problem’. Faced with ambiguous data, your brain must somehow guess the causes of that data as it plans what to do next, so it can keep you alive and well.

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