Rhesus Monkeys (Macaca mulatta) Detect Rhythmic Groups in Music, but Not the Beat

Abstract

It was recently shown that rhythmic entrainment, long considered a human-specific mechanism, can be demonstrated in a selected group of bird species, and, somewhat surprisingly, not in more closely related species such as nonhuman primates. This observation supports the vocal learning hypothesis that suggests rhythmic entrainment to be a by-product of the vocal learning mechanisms that are shared by several bird and mammal species, including humans, but that are only weakly developed, or missing entirely, in nonhuman primates. To test this hypothesis we measured auditory event-related potentials (ERPs) in two rhesus monkeys (Macaca mulatta), probing a well-documented component in humans, the mismatch negativity (MMN) to study rhythmic expectation. We demonstrate for the first time in rhesus monkeys that, in response to infrequent deviants in pitch that were presented in a continuous sound stream using an oddball paradigm, a comparable ERP component can be detected with negative deflections in early latencies (Experiment 1). Subsequently we tested whether rhesus monkeys can detect gaps (omissions at random positions in the sound stream; Experiment 2) and, using more complex stimuli, also the beat (omissions at the first position of a musical unit, i.e. the ‘downbeat’; Experiment 3). In contrast to what has been shown in human adults and newborns (using identical stimuli and experimental paradigm), the results suggest that rhesus monkeys are not able to detect the beat in music. These findings are in support of the hypothesis that beat induction (the cognitive mechanism that supports the perception of a regular pulse from a varying rhythm) is species-specific and absent in nonhuman primates. In addition, the findings support the auditory timing dissociation hypothesis, with rhesus monkeys being sensitive to rhythmic grouping (detecting the start of a rhythmic group), but not to the induced beat (detecting a regularity from a varying rhythm).

Finding the beat: a neural perspective across humans and non-human primates

“…Similar results were found in newborn infants, but unfortunately the stimuli used with infants confounded MMN responses to beat changes with a general response to a change in the number of instruments sounding [6], so future studies are needed with newborns in order to verify these results. Honing et al [60] also recorded ERPs from the scalp of macaque monkeys. This study demonstrated that an MMN-like ERP component could be measured in rhesus monkeys, both for pitch deviants and unexpected omissions from an isochronous tone sequence.…”

“…virtually any vertebrate species). Why is it that macaques, despite their many similarities with humans, apparently find it so difficult to predictively time their taps to a beat, and show no evidence for grouping events into metrical structures [7,60]? Why is it that the one chimpanzee (out of three tested) who shows any evidence at all for beat perception and synchronization only does so for a single preferred tempo, and does not generalize this behaviour to other tempos [132]?…”

Synchronization and temporal processing

“…To date, only a few species (vocal-learning birds and a sea lion) have been shown to be capable of 'Complex SMS' by synchronizing to the beat of more complex, musical stimuli, indicating a capacity to extract a beat from a complex auditory stimulus, and even to map flexibly to different motor outputs [66,69,76]. Evidence for hierarchical metrical perception or other aspects of rich BPS has not yet adequately been examined in nonhuman animals [77,78].…”

Without it no music: cognition, biology and evolution of musicality

“…They evaluate several brain imaging methods, including functional and electrophysiological techniques, for investigating the underlying mechanisms. The neurophysiology of rhythmic behaviour is also discussed, informed largely by recent findings in monkeys using direct intracortical [71] and non-invasive techniques [72].…”