How often does speech turn into song?

You can make any person's regular speaking voice seem to burst into song with a fairly simple trick. It's called the Speech-to-Song illusion. But can you do it if they're speaking another language? Or if you deliberately tweak their voice? Find out how to make people sing on your iPhone, and how they can make you stop.

Last week I wrote about audio illusions, among them a rather common (if not well-known) Speech-to-Song Illusion. The illusion is simple and often we stumble on it by accident. A recorded speech — not a song — runs into technical error and repeats a few seconds over and over again. As we hear it repeat, it begins to take on a musical tone. When the speech is replayed in full, and we get to those few seconds that we heard so many times, the speaker seems to have suddenly, for a few seconds, started singing.

The discoverer of the illusion, Diana Deutsch, uses one of her speeches as an example. The repeated words are "sometimes behave so strangely," and the tune becomes evident after just a few repetition. Here's a class of grade-schoolers easily singing along moments after the first repetition. If you type the words "sometimes behave so strangely" into YouTube, you can find a host of remixes and songs based on the tune of those words.

People took notice and decided to test out how common this illusion was. Deutsch's voice sounds musical to us, but of course it would. One study took a look at German speakers, and how often they perceive speech as song. It found that the illusion was "robust," in that 60 out of 62 subjects perceived the shift from speech to song. Two thirds of the subjects heard the illusion over 50% of the time. Although that's not overwhelming, consider that most illusions take quite a bit of contriving to make them effective — this one fools most of the people at least half of the time with just a few random words. Another study showed that Mandarin Chinese speakers also hear the illusion, but that there were limitations. Have the person speak too fast, or synthetically accelerate the voice, and suddenly the illusion disappears.

Why do we hear this? Apparently there are eight different areas inside the brain that respond more strongly to musical sounds than to speech. Enough repetition might get those areas engaged. We literally hear that part of the song with a different section of our mind than we hear speech.

[Via On the Speech-to-Song Illusion: Evidence From German, Speech to Song Illusion: Evidence from MC, Speech Versus Song]