Turn your speakers on and listen up – it's experiment time. Sometimes, the only thing separating speech from music is repetition, and the speech-to-song illusion proves it. In an outstanding feature published over atAeon, Elizabeth Hellmuth Margulis – director of the music cognition lab at the University of Arkansas – explores why humans so enjoy listening to our favorite music over and over and over again. According to Margulis, what governs our affinity for auditory repetition extends far beyond the "mere exposure effect" (a well-documented tendency for people to prefer things they've been exposed to before – their reflections, for instance). "Repetition is a startlingly prevalent feature of music, real and imagined," Margulis writes. "In fact, repetition is so powerfully linked with musicality that its applications can dramatically transform apparently non-musical materials into song." The effect she's talking about is the speech-to-song illusion, discovered by UC San Diego psychologist Diana Deutsch in 1995. You can try it for yourself here. First, listen to the this sound demo all the way through. When you're finished, listen to the second sound demo. Pretty incredible, no? "When the listener reaches the phrase that was looped, it seems as if the speaker has broken into song, Disney-style," writes Margulis. She continues: The transformation is truly bizarre. You'd think that listening to someone speak and listening to someone sing were separate things, distinguished by the objective characteristics of the sound itself. It seems obvious: I hear someone speak when she's speaking, and sing when she's singing. But the speech-to-song illusion reveals that the exact same sequence of sounds can seem either like speech or like music, depending only on whether it has been repeated. Repetition can actually shift your perceptual circuitry such that the segment of sound is heard as music: not thought about as similar to music, or contemplated in reference to music, but actually experienced as if the words were being sung. Margulis doesn't get into this in her piece, but I imagine the illusion must be amplified when looped speech is backed by music (i.e. what we typically think of as music). If you're a fan of electronic music, or any other genre that relies heavily on sampling, you've almost certainly experienced this before. One of the best examples I can think of – an example that popped into my mind somewhere around the third repetition of Deutsch's sometimes behave so strangely –is "Frontier Psychiatrist," by The Avalanches: The rest of Margulis' feature is equally fascinating, delving into the neuroscienceand psychology of sound and repetition. It's a fantastic read, so definitely check it out atAeon. Also: if this kind of thing interests you, I highly recommend checking out theIllusion Songs tumblr, a collection of auditory illusions found in indigenous folk practices, popular music, and scientific research by sound artist and educator Meara O'Reilly.