Humans may not be the only creatures who can enjoy the melodies of a well-crafted pop song—marmosets and other monkeys may also perceive musical pitch like we do. New evidence presented by researchers as Johns Hopkins University suggests that the ability to understand pitch may be a fundamental skill that likely originated early in primate evolution.
While many animals (songbirds, for example) can process pitched sounds, it was thought that only humans were equipped with sound-processing skills as complex as ours. And while our pitch perception is most obviously demonstrated in music, it is also essential for our understanding of speech.
"Pitch perception is essential to our ability to communicate and make music," Johns Hopkins University professor Xiaoqin Wang says, "but until now, we didn’t think any animal species, including monkeys, perceived it the way we do. Now we know that marmosets, and likely other primate ancestors, do."
The newly published paper demonstrates that marmosets, and perhaps other primates, are remarkably similar to us when it comes to decoding complex pitches. In our ears, we have filters that separate incoming signals into "individual frequency channels." These let us detect the harmonics around a fundamental tone. For folks who know about music, we are able to clearly resolve only the lowest 5-10 harmonics—everything above that mixes in with these lower harmonics and adds to their strength. That is, we’re better at separating lower pitches than high—high notes tend to mix in together. Another feature of human hearing is that we are very sensitive to changes in pitch, and at higher frequencies, our sensitivity to the rhythm of the sound affect our pitch perception.
In experiments spanning several years, the marmosets were monitored and trained to lick a water spout when they heard a change in pitch. The result of these studies show that they possess the same wiring as we do. But what’s the point? Why do we—and the marmosets—hear pitch?
"Marmosets have a rich vocal repertoire that contains a variety of harmonic structures," says the report, which suggests that we may be hardwired for subtle vocal communication. So, even though our appreciation for music may be a side effect of our ability to talk to each other, we now know why music is such an important part of human culture. Our bodies and brains are built to listen to it.