Music Appreciation for Monkeys

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Class of ’68 | Dr. Charles Snowdon Gr’68 had studied cotton-top tamarins for almost four decades. The Hilldale Professor of Psychology and Zoology at the University of Wisconsin-Madison knew which treats the monkeys in his laboratory colony liked best (Apple Newtons), what put them in the mood to mate (plenty of privacy), and what kinds of calls they made when calm or frightened. (The shrillest trills came during visits from the vet.) He didn’t know much, however, about their tastes in music.

That changed when Snowdon got an email from David Teie, a cellist with the National Symphony Orchestra. Teie, who serves on the music faculty at the University of Maryland, sought the help of Snowdon and his monkeys to test some theories about how music conveys emotions.

“One of the problems about testing music on humans is that we all grow up with a lot of exposure” to it, Snowdon explains. “By the time we reach adulthood, we have our own genres and preferences selected”—variables that can skew research results. Testing music on a species without any favorites on their iPods seemed like a viable alternative.

“I thought it was an intriguing idea,” recalls Snowdon, who used to sing in a choir himself. “Do animals … respond to music?” (His tamarins had not been exposed to any, though a previous study on the same species suggested that the monkeys were not big fans of the sounds one might hear over the radio or in the concert hall. When given the choice, they selected Mozart over rock, and silence over Mozart.) But how would they respond to music made especially for monkeys? Snowdon and Teie decided to find out.

Snowdon became curious about how animals communicate while studying behavioral neuroscience at Penn in the 1960s and working under biology professor W. John Smith to decode the calls of chickadees. At Wisconsin Snowdon opened his own primate lab, where he began to explore the meaning of different vocalizations—particularly among cotton-top tamarins. These animals, so named for their rock-star manes of white hair, were declared endangered in 1971; as few as 1,000 still live in the wild. They are cooperative breeders, with fathers and older siblings helping to take care of the youngest, and are among the few nonhuman primates who live only in family groups.

One of the challenges Snowdon faced when he began his colony of 11 cotton-top tamarins in 1978 was to boost the animals’ chances of breeding in captivity. Adult monkeys weigh just a pound, but they need space for their families and to avoid stressful run-ins with their neighbors. So Snowdon gave each family group a room-sized cage with branches and ropes to simulate their natural environment as well as visual barriers for privacy. The colony had “excellent reproductive success” and swelled to 75 monkeys; over the years, Snowdon gave 150 to zoos and other educational institutions around the country.

To start their music study, Snowdon emailed Teie sound files of snow-top tamarin calls, slowed down for human ears. Teie listened and correctly guessed the emotional context of each kind of call. Then Teie got several other musicians to group tamarin calls into clusters based on their musical structure. (For example, did the notes travel up or down the scale? What was the duration of each note?) The musicians didn’t know if a grooming session was underway, if one monkey was about to mount another for sex, or if the veterinarian had just been spotted, but their clusters corresponded with five different social contexts, ranging from positive social interactions to high fear.

Human speech contains some of the same structural features as you see in monkey calls, Snowdon points out. People use descending notes, for example, when they want to calm an infant or a pet: “Awww. I’m sor-ry,” he intones. “You use this motherese—or parentese it should be called. You manipulate your pitch to induce an emotional behavior.”

On the other hand, people start with a low pitch and move to a higher pitch, using short staccato notes, to get a child or pet to move,” Snowdon says. “‘Yeeess! Come on!’ It gets people aroused and active.”

Interestingly, among adult tamarins, ascending notes (along with long, tonal notes) are associated more with affiliation. Downward notes (as well as short, fast, and dissonant sequences) are associated with threats and fear, though the monkeys also use descending notes when retrieving infants. 

Teie used some of the features in these clusters to compose fear/threat- and affiliation-based music on his 250-year-old Italian cello. His fear music featured a rapid tempo of nine notes per second, descending intervals, and the dissonance of two lines played at one time. Teie also added harshness to the sound by playing up on the bridge of the cello.

In contrast, his affiliative music slowed down to one note per second and had clear musical intervals. After he created two samples of each, it was time to see if he could find an appreciative audience among Snowdon’s monkeys.

This quest was not as simple as throwing a concert and counting the number of lighters held in the air. Snowdon didn’t want the animals to habituate to the music, so he had to limit their exposure to one 30-second sound clip per week. The researchers also needed something to compare their response to, so they added some human music to the playlist.

Barber’s “Adagio for Strings” got no reaction from the monkeys. Neither did a soft piano piece from the rock band Nine Inch Nails. A sound clip that combined the heavy-metal guitar licks of Metallica and Tool had a slight, but strangely soothing, effect on its listeners. “We have no explanation for that at all,” Snowdon admits. 

The biggest response, however, came from Teie’s monkey-oriented compositions, which were transposed to a higher pitch during playback. When the affiliation music was played, the animals became even calmer than they had been in their relaxed, baseline conditions. They moved less and started eating more. “You have to be a relaxed monkey to eat,” Snowdon explains.

In response to the fear music, the monkeys showed many more anxiety behaviors, such as scratching themselves, sticking out their tongues, and shaking their heads. Both effects lasted up to five minutes after the song had stopped. 

The tamarins’ responses to the monkey-based songs provide interesting insights into communication. While animal vocalizations are usually thought to provide information about the animal making them, Snowdon notes, this study suggests that tamarins may be using their own calls unconsciously to induce an emotional state in their listeners. Snowdon’s and Teie’s findings appeared in the September issue of the journal Biology Letters.

Since the study was conducted, funding cuts have forced Snowdon to close his primate lab, donate his remaining 75 monkeys to zoos, and shift his focus to human research. He has transferred an interest in animal pair-bonding, for example, to a study on hormonal levels in couples.

“I miss the animals, but I don’t miss the bureaucracy of keeping a lab going,” Snowdon says. “I do have all sorts of questions that the music study has raised that I’d like to pursue, but I can’t. It’s sad, but it’s been more than 40 years since I left Penn with a PhD, so maybe it’s time to look for other things.”

—Susan Frith

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