How the brain builds your world of sound

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 activi