Perception of musical pitch varies across cultures
The Tsimane people live in a remote area of the Bolivian rainforest, making them of great interest to researchers from a range disciplines, particularly in relation to their health and physical capacity.
Their relative isolation from Western culture also provides a unique opportunity to learn more about how different people understand music. After all, there aren’t many people these days who have never heard a rock song or a classical work.
In 2016 study, a team led by Josh McDermott from the Massachusetts Institute of Technology, US, found that Westerners and Tsimane have different aesthetic reactions to chords or combinations of notes.
To Western ears, the combination of C and F# is grating, but Tsimane listeners rated this chord just as likeable as other chords that Westerners would interpret as more pleasant, such as C and G.
Later, McDermott and Nori Jacoby, now at the Max Planck Institute for Empirical Aesthetics, Germany, found that while both Westerners and Tsimane are drawn to musical rhythms composed of simple integer ratios, the ratios they favour are different, based on which rhythms are more common in the music they listen to.
Now, in a new study published in the journal Current Biology, they and colleagues show that the Tsimane do not perceive the similarities between two versions of the same note played at different registers as do Westerners – or at least those from the US.
And they say this finding suggests that although there is a natural mathematical relationship between the frequencies of every "C," no matter what octave it's played in, the brain only becomes attuned to those similarities after hearing music that is based on octaves.
"It may well be that there is a biological predisposition to favour octave relationships, but it doesn't seem to be realised unless you are exposed to music in an octave-based system," says McDermott.
In the study, Western listeners, especially those who were trained musicians, tended to reproduce the tune an exact number of octaves above or below what they heard, though they were not specifically instructed to do so.
They accurately reproduced sequences such as A-C-A, but in a different register, as though they hear the similarity of notes separated by octaves. However, the Tsimane did not.
"The relative pitch was preserved between notes in the series, but the absolute pitch produced by the Tsimane didn't have any relationship to the absolute pitch of the stimulus," Jacoby says.
"That's consistent with the idea that perceptual similarity is something that we acquire from exposure to Western music, where the octave is structurally very important."
The researchers say their findings also shed light on the upper limits of pitch perception for humans.
Western listeners cannot accurately distinguish pitches above about 4000 hertz (although they can still hear frequencies up to nearly 20,000 hertz) and it has been suggested that the highest note on a traditional piano is about 4100 hertz, because of a fundamental limit on pitch perception.
However, McDermott thought it possible that the opposite was true; that is, that the limit was culturally influenced by the fact that few musical instruments produce frequencies higher than 4000 hertz.
He and his colleagues found that although Tsimane musical instruments usually have upper limits much lower than 4000 hertz, Tsimane listeners could distinguish pitches very well up to about 4000 hertz, as evidenced by accurate sung reproductions of those pitch intervals.
Above that threshold, their perceptions broke down, as was the case with Western listeners.
"It looks almost exactly the same across groups, so we have some evidence for biological constraints on the limits of pitch," Jacoby says.
One possible explanation for this limit, the researchers suggest, is that once frequencies reach about 4000 hertz, the firing rates of the neurons of the inner ear can't keep up and we lose a critical cue with which to distinguish different frequencies.
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