Marmosets can distinguish between high and low notes -- the sound quality of pitch, a key to music and vocalization -- just as humans do, says new research that may call into question just when pitch perception evolved.
A new study recently published in the journal Proceedings of the National Academy of Sciences by researchers from Johns Hopkins University School of Medicine details behavioral evidence showing that the small monkeys use auditory cues to perceive pitch in the same way humans do.
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"Until now," lead researcher Xiaoqin Wang said in a release, "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 10 years ago, Wang found a region in the marmoset brain that appeared to process pitch, the same region where human brains showed pitch processing activity. But he lacked behavioral evidence showing that the animal perceived it as we do. Now, years and a new battery of tests later, he thinks he's found just that.
Wang and his study colleagues administered hearing tests to a group of marmosets that had been trained to lick a waterspout only after they hear a change in pitch.
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The tests were designed to spot human-like pitch processing. According to the researchers, while other animals had been observed perceiving pitch, none duplicated three features that distinguish human pitch perception:
Better distinguishing of low-frequency pitch differences than high The ability to distinguish subtle shifts in pitch at low frequencies Perception of pitch differences of simultaneous tones played at high frequencies is related to sensitivity to rhythm After testing the animals, Wang and his team concluded that marmosets had those three qualities in their pitch-perception bag of tricks.
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The discovery suggested that the human components for pitch perception may have evolved much earlier than previously thought. Marmosets, very vocal and social animals, are native to South America, and the ancient monkeys were on-board when their home continent split from pre-human Africa some 40 million years ago.
"In addition to the evolutionary implications of this discovery," said Wang, "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."
"Now," he added, "we can explore questions about what goes wrong in people who are tone deaf and whether perfect pitch is an inherited or learned trait."