The Evolution of Rhythmic Cognition: New Perspectives and Technologies in Comparative Research

The Evolution of Rhythmic Cognition: New Perspectives and Technologies in Comparative Research Andrea Ravignani ∗# (andrea.ravignani@univie.ac.at), Bruno Gingras ∗ , Rie Asano † , Ruth Sonnweber ∗ , Vicente Matell´an & W. Tecumseh Fitch ∗ ∗ Department of Cognitive Biology, University of Vienna, Austria Evolution & Computation Research Unit, University of Edinburgh, UK † Department of Musicology, University of Cologne, Germany Robotics Group, University of Le´ on, Spain # Language Abstract Music is a pervasive phenomenon in human culture, and mu- sical rhythm is virtually present in all musical traditions. Re- search on the evolution and cognitive underpinnings of rhythm can benefit from a number of approaches. We outline key con- cepts and definitions, allowing fine-grained analysis of rhyth- mic cognition in experimental studies. We advocate compara- tive animal research as a useful approach to answer questions about human music cognition and review experimental evi- dence from different species. Finally, we suggest future direc- tions for research on the cognitive basis of rhythm. Apart from research in semi-natural setups, possibly allowed by “drum set for chimpanzees” prototypes presented here for the first time, mathematical modeling and systematic use of circular statistics may allow promising advances. Keywords: The evolution of music; primate cognition; animal-machine interaction; chimpanzee drum set; vocal learning; rhythm; entrainment; beat; synchronization; social cognition; comparative cognition. Introduction Evolution of Music and Origins of Rhythm Music as a cognitive system is one of the most prominent and distinctive human features. Since Darwin, the putative role of selection in the emergence of human music has been a topic of great debate. Numerous hypotheses, which attribute an adaptive value to music, have been proposed, all featuring some social component. While hypotheses on music origins are difficult to test directly, the comparative method in cog- nitive biology enables us to investigate the purported human uniqueness of particular musical abilities (Fitch, 2006). In this paper we focus on one aspect of music cognition, namely rhythm, and propose new perspectives and technologies for investigating its evolution. Rhythm and Cognition Rhythm, characterized as a structured pattern of temporal change, plays a central role in music. Beats, defined as points in time occurring in a perceptually periodic way (Patel, 2008), are a basic element of musical rhythm. Grouping and me- ter are subsystems of musical rhythmic organization and are considered the basic structural components of rhythmic pat- terns (Lerdahl & Jackendoff, 1983). Grouping refers to the organization of the musical stream into motives, phrases, and sections. Meter corresponds to a regular pattern of strong and weak beats. In metrical structures, beats are organized hier- archically according to their relative strength. Moreover, the impression of the speed of the performed pattern, the tempo, influences the interpretation and perception of rhythmic struc- tures. According to the tempo, humans may assign different organizations to grouping and metrical hierarchy. Hence, the cognition of musical rhythm should not be investigated solely holistically, but also in terms of beat, grouping, meter, and tempo. These, together, yield the flexibility of human rhyth- mic cognition: humans are able to extract structural proper- ties from music and interpret them in multiple contexts. What are the basic capacities allowing this cognitive flexibility? The metrical hierarchy mentioned above contains a partic- ular hierarchical level called tactus, which listeners perceive as ‘the (primary) beat’ (Lerdahl & Jackendoff, 1983), whose perception is robust to moderate tempo fluctuations (Patel, 2008). It seems that our internal processes underlying rhythm perception can be spontaneously synchronized, entrained, to external regular, periodic sensory cues (Grahn, 2012). In this entrainment model, the relative timing of events is processed by expecting their periods or phase and adjusting the expecta- tions to actual occurrences (Grahn, 2012). This flexible beat processing mechanism is also the basis for synchronizing mo- tor actions to musical stimuli, requiring (i) beat extraction, (ii) synchronization of an internal motor pulse to the inferred au- ditory beat (beat entrainment), and (iii) a motor pattern gen- eration on the basis of the internal pulse (Fitch, 2012). A fundamental requirement of synchronization is hence the ca- pacity to extract the beat, already present in newborns and infants, though not conclusively innate because of possible prenatal learning (Grahn, 2012). The capacity for beat per- ception and synchronization could be shared with other an- imals as an analogous or homologous evolutionary trait. In order to understand the nature and evolution of human cogni- tive capabilities for rhythm, different species must be tested on tasks requiring the three aforementioned skills. Rhythm and Beat Evidence in Non-human Animals Vocal Learning and Dissociation Hypotheses Some non-human animal species have a particularly good control over their vocal tract. Among these, humans, ele- phants, many bird species and some marine mammals are ca- pable of spontaneously imitating sounds which may or may not belong to their natural communication system. A promis- ing hypothesis has been put forward connecting vocal learn- ing and beat-based rhythmic abilities across species (Patel,