In the 1970s, psychologist Diana Deutsch was experimenting with a synthesizer, when she heard something strange. “It seemed to me that I’d entered another universe or I’d gone crazy or something…the world had just turned upside down!” Deutsch recalls.Deutsch had stumbled across an illusion in audio form — she called it the “Octave Illusion” and you can listen to it here — and she realized it wasn’t just a quirk. It was telling her something essential about how our brain processes sound.Our brain edits the world we hear. What we hear isn’t a direct real-time feed coming from our ears. It’s our brain’s best guess. “Because the brain doesn’t have direct contact with the physical world,” says professor Dan Polley, “Everything that we perceive as consciousness is constructed from the activity of the brain.”So what are we actually hearing, when we’re hearing? In The Sound Barrier, a special four-part series from Unexplainable, I explore the limits of our sense of hearing and how we can break through. From people trapped by phantom sounds in their heads, to the quest to find out what silence actually sounds like, to astronomers who have figured out a way to listen to space.New episodes will be released every Monday and Wednesday, starting November 3.The Sound Barrier #1: The myth of hearingThe brain’s editing superpower doesn’t just allow us to process the world we hear — it allows people with hearing loss to hear the world again by using a cochlear implant. Noam speaks to someone who lost his hearing and then retrained his brain — using Winnie the Pooh, believe it or not — to relisten to his favorite piece of music, “Bolero.”