Metronome-trained monkeys can tap to the beat of human music

(Press-News.org) Macaques can tap along to a musical beat, according to a new study – findings that upend the assumption that only animals with vocal-learning abilities can find and move to a groove. According to the authors, the discovery offers fresh insights that suggest the roots of rhythm may run far deeper in our evolutionary past than previously believed. Humans have a unique ability to perceive and move in time to a steady musical beat. 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 to rhythm – isochronicity – is strikingly rare in the animal kingdom and has only been observed in some birds and exceptional individuals of other species, leaving a gap in our understanding of its evolutionary and neurobiological roots. One powerful leading theory, the vocal-learning hypothesis, suggests that rhythmic synchronization depends on specialized brain circuits that tightly link hearing and movement, which evolved to support complex vocal learning. However, previous research shows that macaques, despite not being vocal learners, can be trained to synchronize their taps predictively with metronome beats, hinting at the neural dynamics required for isochronicity.

 

In this study, Vani Rajendran and colleagues investigated whether macaques trained to synchronize their taps with metronome beats could extend their metronome-tapping skills to real music in all its acoustic complexity. Rajendran et al. observed that two metronome-trained macaques independently initiated experimental trials in which they heard one of three human-selected songs and were rewarded when they tapped in time to each song’s tempo. Remarkably, both animals developed consistent tapping rhythms across all songs, and when the authors shifted the music’s tempo, the macaques’ tapping phases shifted as well, demonstrating that they were synchronizing to musical structure rather than responding reflexively to experimental cues. This behavior was observed even when the monkeys were presented with a song they had not yet heard before and when they were no longer rewarded for tapping to the beat. According to the authors, the findings suggest that, although monkeys do not experience music as fully as humans do and require substantial training, beat perception may span a broader evolutionary continuum than previously believed; it is not just restricted to vocal-learning species. “Rajendran et al. are careful to note that the abilities they observed are not natural behaviors: They were conditioned through extrinsic rewards, not the seemingly intrinsic ones that humans experience when they follow rhythmic beats,” write Asif Ghazanfar and Gavin Steingo in a related Perspective that highlights the study’s caveats. “A behavior that has been conditioned may not be equivalent to a behavior that emerges spontaneously.”

 

Podcast: A segment of Science's weekly podcast with Vani Rajendran, related to this research, will be available on the Science.org podcast landing page after the embargo lifts. Reporters are free to make use of the segments for broadcast purposes and/or quote from them – with appropriate attribution (i.e., cite "Science podcast"). Please note that the file itself should not be posted to any other Web site.

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