Duke University neuroscientists have shown new evidence that a deep biological link exists between human music and speech.
In two new studies, researchers found that the musical scales most commonly used over the centuries are those that come closest to mimicking the physics of the human voice.
They also said that we understand emotions expressed through music because the music mimics the way emotions are expressed in speech.
Composers have long exploited the perception of minor chord music as sad and major chord music as happy, and it is now that the researchers led by Dale Purves, a professor of neurobiology, found that sad or happy speech can be categorized in major and minor intervals, just as music can.
In the second study, Kamraan Gill, another member of the team, found the most commonly used musical scales are also based on the physics of the vocal tones humans produce.
"There is a strong biological basis to the aesthetics of sound. Humans prefer tone combinations that are similar to those found in speech," said Purves.
And the evidence suggests that the main biological reason we appreciate music is because it mimics speech, which has been critical to our evolutionary success, said Purves.
To study the emotional content of music, the researchers collected a database of major and minor melodies from about 1,000 classical music compositions and more than 6,000 folk songs and then analysed their tonal qualities.
They also had 10 people speak a series of single words with 10 different vowel sounds in either excited or subdued voices, as well as short monologues.
The team then compared the tones that distinguished the major and minor melodies with the tones of speech uttered in the different emotional states.
They found that the sound spectra of the speech tones could be sorted the same way as the music, with excited speech exhibiting more major musical intervals and subdued speech more minor ones.
The tones in speech are a series of harmonic frequencies, whose relative power distinguishes the different vowels. Vowels are produced by the physics of air moving through the vocal cords; consonants are produced by other parts of the vocal tract.
In the second paper, researchers argued that the harmonic structure of vowel tones forms the basis of the musical scales we find most appealing.
They showed that the popularity of musical scales could be predicted based on how well they match up with the series of harmonics characteristic of vowels in speech.
The first study has been published in the Journal of the Acoustical Society of America (JASA), while the second appears in the online journal PLOS One.