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Not just humans, but even marmosets seem to use auditory cues. Humans are not the only species to understand the quality of sound or "pitch." Johns Hopkins researchers find that even marmosets use cues that enable them to differentiate between low and high notes.

"Pitch perception is essential to our ability to communicate and make music," said Xiaoqin Wang, Ph.D., a professor of biomedical engineering at the Johns Hopkins University School of Medicine, in a news release, "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."

About ten years ago, the researchers noted that the two species shared a similar brain activity. The nerve cells in the primary auditory cortex of the marmoset brain fired just after it got exposure to sounds with the pitch. Similarly, human brains also displayed similar activity in that area, according to Wang.

But he could not show any evidence that the marmosets reacted to differences in pitch in the same manner that humans do.

Various behavioral tests and electrophysiological devices to record changes in the monkeys' neural activity were documented. Even as the animals were reported to show pitch perception, they seemed to need to display if they carried three specialized human features: the human ability to accurately distinguish low-frequency pitches over high ones, pick out subtle changes in the spread between pitches at low frequencies or hertz, and at high frequencies, locate pitch differences among tones that were played simultaneously. It showed the sensitivity of the human ear to time fluctuations, sound waves and rhythm.

Hearing tests showed that marmosets shared the three features. Human components relating to pitch perception had evolved earlier, the study revealed.

"In addition to the evolutionary implications of this discovery, I'm looking forward to what we will be able to learn about, human pitch perception now that we have a primate relative we can study behaviorally and physiologically," says Wang. "Now we can explore questions about what goes wrong in people who are tone deaf and whether perfect pitch is an inherited or learned trait."

The study is published in the Proceedings of the National Academy of Sciences (PNAS).