Loud, fast, rhythmic music is exciting. It mirrors aspects of human behavior—we are loud and active when excited. Likewise slow, soft, static music mimics how we behave when subdued. That congruence might explain why music affects us as it does. Also, melodies in a major key generally come across as happy; minor melodies are sad. But why those tonalities have their particular emotive effects is not clear.
Now, Duke University neuroscientist Dale Purves, his graduate student Daniel Bowling, and colleagues report that qualities of major- or minor-key melodies also mirror human behavior—specifically, speech—according to the mood of the speaker. One of their analyses focuses on the intervals (tone pairs) implied by melodies. Major-key melodies emphasize the major-third interval, whose two notes have a frequency ratio of about 5:4. Minor-key melodies feature an interval, the minor third, with a 6:5 frequency ratio. How is that interval dichotomy mirrored in speech? The Duke team asked 20 subjects to read a word or short passage in an excited or subdued manner (click the figure below to enlarge). They then analyzed the ratios of the two lowest (and strongest) frequencies of vocal-tract resonance associated with each vowel sound. The prevalence of major-third intervals (5:4 ratios) as compared with minor thirds (6:5) was much greater in excited than in subdued speech. Musically speaking, at least, our thrills are major; our disappointments, minor.(piss)