Musical hallucinations are a rare but fascinating condition in which people, most of them with some hearing loss, believe they are hearing music playing pretty much all the time. This is not the same as being unable to get the melody of a catchy song like “Call Me Maybe” out of your head. Now, a new study shows preliminary but promising evidence that understanding such hallucinations might bring deeper insight into how the brain processes the world. If the results are confirmed in larger studies, the researchers argue that they support the theory of the brain as a prediction-generating machine. Carl Zimmer explains in more detail in today’s New York Times.