Music is known to induce terror and tears, as well as inspire dance. Even basic human speech itself is laced with emotional direction: a musical pattern of long drawn out sounds versus short brief ones can be the difference between calming and exciting a child. Might it then be possible for a composer to manipulate an audience's emotions with some carefully chosen notes?

That was the question posed by David Teie, a composer and cellist in the National Symphony Orchestra in Washington, D.C.. Little did he know that the query would lead him to write shrilly monkey music, and open a new door into animal communication and the evolutionary roots of human speech.

Teie did know that seeking an answer from human subjects wouldn't work—children form emotional associations with music early on, which leads to biased responses throughout life. He needed a species that didn't necessarily listen to music, but still had a rich vocal repertoire. The obvious choice: monkeys.

But a problem arose there, too. Monkeys not only don't listen to our music, they seemed to despise it. In fact, prior research had found that cotton-top tamarins, a South American monkey, preferred silence over both German technopop and Mozart.

It was still possible that monkeys did like music, but perhaps just didn't share human tastes. So the musician teamed up with Charles Snowdon, a psychology professor at the University of Wisconsin–Madison, to compose some monkey music and watch to see how tamarins would respond.

"We wanted to have something that wasn't just their calls," says Snowdon, who co-authored a paper with Teie on this topic published in Biology Letters. Just as humans have learned preferences for music or other sounds that we've heard all our lives, monkeys have developed automated responses to their own species' calls. Teie and Snowdon also wanted "something to match human music in terms of duration and complexity," to start to address Teie's initial question.

With the help of some outside musicians, they identified the pitch, tone and tempo of emotional monkey calls—from fearful to soothing—and used these to create 30-second rock and classical music selections with Teie's voice and cello. "To my ears, [the resulting music] is as irritating as I'll get out—it's like fingernails on a chalkboard," Snowdon complained after playing a selection of the new classical over the phone. Indeed, it sounded a bit like the high-pitched screech of a New York City subway car struggling to stop on worn-out brakes.

But the cotton-top tamarins felt otherwise. For five minutes after they heard the affiliative-inspired tunes, the 14 enlisted monkeys displayed calming behaviors, including reduced movement and increased feeding. Fear-based music, on the other hand, heightened the monkeys' movements and other symptoms of anxiety, such as urination.

Compared to Metallica's 200 notes per minute, these anxious tamarin tunes carried about 500 notes per minute.* "It's pushing it for Metallica, but there's no way for me to keep up with the tempo of monkey music," Snowdon says. (He also can't explain why Tool's "The Grudge" and Metallica's "Of Wolf and Man" actually elicited a response in the monkeys similar to that of their own calming classical selections. Of the human music played to them in the experiment, these were the only tunes for which the monkeys showed even the slightest response.)

"If we want to try to affect the emotional state of another species, we need to think about what is appropriate for that species," suggests Snowdon. He highlights the frequency with which radios are played for colonies of monkeys. "If I'm irritated by squealy high-pitched noise that calms them down, what is our music doing to monkeys?"

Also see our podcast on the research.

Picture of cotton-top tamarin by Bryce Richter

*Note (9/2/09): This sentence was changed after publication to correct "notes per second" to "notes per minute."