Just listen to this radio clip. It's only takes 50 seconds for the Franklin Institute's chief bioscientist, Jayatri Das, to demonstrate something fundamental about your brain.
She starts with a clip that's been digitally altered to sound like jibberish. On first listen, to my ears, it was entirely meaningless. Next, Das plays the original, unaltered clip: a woman's voice saying, "The Constitution Center is at the next stop." Then we hear the jibberish clip again, and woven inside what had sounded like nonsense, we hear "The Constitution Center is at the next stop."
The point is: When our brains know what to expect to hear, they do, even if, in reality, it is impossible. Not one person could decipher that clip without knowing what they were hearing, but with the prompt, it's impossible not to hear the message in the jibberish.
This is a wonderful audio illusion.
The reason is that we still think of our senses—sight, hearing, touch—as reflecting the outside world, purely. But they don't. They provide us with a mixture of the world out there and our own expectations.
We explored this in the visual realm a few weeks ago, playing with images that you "can't unsee," which flip your perception of a phenomenon. The first example that I came across was that the World Cup logo looks like someone executing the maneuver known as the facepalm.
Now that you've been tuned to look for this meaning in the World Cup logo, it will be difficult not to see this alternate meaning for what is supposed to be a soccer ball trophy thing.
Surveying the latest evidence about how our brains work, a philosopher at the University of Edinburgh, Andy Clark summed it up: "All this makes the line between perception and cognition fuzzy, perhaps even vanishing."
Hearing, itself, is thinking. Which makes it subject to the machinations of the rest of the brain, which are constantly priming the ears about what they should be expecting.
Back to the clip at the top, come back to this story in a day or two, and I bet you'll find that even on the first listen to the jibberish sound, you'll perceive some meaning. You'll pick up a hint of one of the words in the sentence, and you'll detect the rhythm of the sentence.
There is meaning in the noise precisely to the degree that I can remember what to expect it to be.
That's the power of cognitive expectation, and it's working at a level beyond (or maybe the word is underneath) your conscious control.