A female rhesus macaque monkey in Himachal Pradesh, India. Credit: Timothy Gonsalves/CC BY-SA 4.0.
Like humans, monkeys have an innate sense of rhythm. But unlike humans, they appear to have little or no sense of melody, according to an Italian-led research collaboration.
Musical sensitivity has been a feature of all cultures through the ages and can be seen in the response of newborn babies to lullabies and other music, indicating that this is an innate human quality. But Giacomo Novembre and Roberta Bianco, neuroscientists at the Italian Institute of Technology (IIT) in Rome, argue that our apparent predisposition for music could be partly acquired in the early stages of life.
To remove at least some of the doubt, Novembre and Bianco, with colleagues in Rome, the United Kingdom, and the Netherlands, investigated the behaviour of two rhesus monkeys that had never heard music. The idea was to establish whether the primates could spontaneously anticipate what might follow specific sequences of notes, contained in several of Bach's violin sonatas and flute partitas.
They did this by first using a computer simulation to model the monkeys' neural response, calculating how surprised they were likely to be by each new note, given the series of notes they had already heard. Then the researchers placed electrodes on the monkeys' heads and monitored the electrical activity of the animals' brains while listening to the music – both Bach's unadulterated pieces and distorted versions of them that contained the same notes in a different order.
As they report1 in Current Biology, Bianco and colleagues found that the real music generated a bigger voltage gap between the most and least surprising notes, indicating, they say, “optimized detection of unexpected events within structured contexts” – in other words, sensitivity to music.
However, that musical appreciation was incomplete. While humans are sensitive to both the timing of notes (rhythm) and their pitch (melody), that was not the case with the monkeys. Bianco and co-workers tweaked their models to predict the monkeys' brain signals when responding either to unusually-timed notes or to out-of-place pitches, but not both. They found that only the temporal-based model yielded good predictions.
The researchers argue that these results sugest humans have an inherited sense of rhythm from their genetic forebears, but then develop a distinctive appreciation for melody. As to why this difference came about, Bianco suggests that only those species using modulations in pitch to communicate are likely to have developed an ear for such variations.
The group plans to carry out two further strands of research. One will involve the same test of pitch vs. timing recognition in babies just 48 hours old, and the other will see monkeys exposed to music over longer periods of time – just in case they can learn to appreciate melody.
