In today’s Academic Minute, Dr. Neil McLachlan of the University of Melbourne reveals the learned nature of pleasing music.
Neil McLachlan is an associate professor in the School of Psychological Sciences at the University of Melbourne. His research in the Music and Auditory Neuroscience Laboratory examines the neurocognitive mechanisms involved in auditory perception.
Dr. Neil McLachlan – Relativity of Pleasing Music
Over two thousand years ago Pythagoras discovered a way of tuning strings by using simple proportions of length. He thought that the pitch interval created by two identical strings with a ratio of 2/3 length created a perfect harmony. This was because he heard the beating (or roughness) between the two string diminish at this ratio. We now call that interval a Perfect 5th, and it has been at the heart of western musical scales ever since.
About 150 years ago the famous scientist Helmholtz sought to explain the harmony of the Perfect 5th by showing that strings create harmonic frequencies when they vibrate. Harmonic frequencies are created when the string vibrations break-up into fractions of the string length, and so occur at integer multiples of the lowest frequency (i.e. for a 100 Hz string, harmonics occur at 200, 300, 400 Hz and so on). When two strings have a length ratio of 2/3 they have a frequency ratio of 3/2, and the 3rd harmonic of one string is at exactly the same frequency as the 2nd harmonic of the other. This reduces the beating between the strings, and so it was believed reduces the dissonance that we hear.
Helmholtz also suggested that sound waves resonate in the cochlea, which causes a strong nerve signal representing the pitch of the sound at the peak of the resonating wave. But later scientists discovered that people often heard pitches at frequencies that weren’t part of the sound wave, and more sophisticated explanations that included pattern matching of harmonic frequencies or extracting the common period of the wave were suggested for pitch.
Pitch and dissonance are innate properties of the auditory system in these theories. However innate theories cannot account for the huge variety of human musical ability and preferences. Over the last couple of decades science has learnt about the plasticity of the human brain, and in our research we suggest that this plasticity extends to the early (pre-conscious) stages of auditory processing. We showed that pitch processing is learnt by training non-musicians with unusual sounds that don’t have simple harmonic overtones. We found that as people learnt to recognize a sound they could find its pitch and it sounded less dissonant. In other words, over two thousand years of music theory has contradicted the simple observation that music is learnt, and that we all come to love the music of our own culture, however strange it may sound to others.