Synchronizing movements with music is one of the hallmarks of human culture, but its evolutionary and neurobiological origins are unknown. Now, an experimental study goes further and observes in two previously trained macaques their abilities to mark the tempo of a piece of music.
The result contradicts the influential vocal learning hypothesis that holds that beat synchronization is only possible in species with complex vocalizations, such as humans and some songbirds.
Human beings have a unique ability to perceive and move to a constant musical rhythm. It is a skill that develops early in life and requires complex pattern recognition, prediction, and motor coordination.
Outside of humans, the ability to synchronize movement with rhythm is very rare in the animal kingdom and It has only been observed in some birds and in exceptional individuals of other species which leaves a gap in the understanding of its evolutionary and neurobiological roots.
The vocal learning hypothesis suggests that rhythmic synchronization depends on specialized brain circuits that closely link hearing and movement and that evolved to support complex vocal learning.
However, previous research has shown that macaques, despite not being vocal learners, can be trained to synchronize their beats predictively with the ‘beats’ of the metronome, which suggests the neural dynamics necessary for this movement synchrony.
In this study published in the journal Science, Vani Rajendran and his team from the National Autonomous University of Mexico set out to find out if these abilities are extensive to real music in all its acoustic complexity, for which they carried out three experiments.
Surprisingly, both animals—trained to synchronize their movements to the beat of a metronome—developed consistent tapping rhythms across songs, and when the authors varied the tempo of the music, the macaques’ tapping phases also changed.
This showed that they synchronized with the musical structure rather than reflexively responding to experimental cues.
This behavior was observed even when the monkeys were presented with a song they had not heard before and when they were no longer rewarded for beating the rhythm, explains a summary in the magazine.
The work, for which, among others, a fragment of a Backstreet Boys or Barry White song was used, therefore demonstrates, that macaques can detect, anticipate and synchronize to the rhythm of real music.
“Our data reveal that the macaque is able to perceive rhythm and synchronize with music. This reflects greater generalization and flexibility in rhythm perception, beyond what was previously described in the macaque and what was assumed for species that do not learn vocally,” the authors write in their article.
Prudence before the results
In an analysis also published in Science, Asif Ghazanfar and Gavin Steingo, from the University of Priceton (United States), emphasize that the authors They are careful to point out that the skills they observed are not natural behaviors: “they were conditioned through extrinsic rewards, not the apparently intrinsic ones that humans experience when they follow rhythmic beats.”
“A behavior that has been conditioned may not be equivalent to a behavior that arises spontaneously,” they emphasize.
For Miquel Llorente, from the Department of Psychology at the University of Girona (Spain), although the study presents striking results on rhythmic sensitivity in non-human primates, the conclusions should be taken with great caution.
The sample size is extremely small and is based on individuals trained for long periods to perform highly artificial tasks, recalls the expert, who is not participating in the study.
“These types of protocols, even though they are classics in neuroscience, are notably far from the natural repertoire of the species and make it difficult to realistically extrapolate the results,” he tells Science Media Centre, a platform of scientific resources for journalists.
Furthermore, he points out, “the cost of maintaining these animals in such restrictive experimental environments forces us to evaluate whether the scientific benefit outweighs the burden on their well-being.”