Musical Hierarchy

Previous investigations have established the “bimodal” nature of rhythm perception in which the lower levels of the brain, namely the basal ganglia, is capable of generating a constant and steady “basic beat” either spontaneously or in response to external acoustic stimuli, whereas more complex and irregular rhythmic patterns are processed within higher cortical regions (Snyder and Large 2005; Kung et al. 2013; Cameron and Grahn 2014). According to the Dynamic Attending Theory (DAT) originally developed by Jones (1976), the brain is capable of synchronizing the basic beat with external rhythms through the process of entrainment, which accounts for common physical behaviours such as tapping and clapping along with music (Large and Snyder 2009). While the exact neurological origin of the “basic beat” remains elusive, this process of beat generation appears to be analogous with the various automatic and cyclical phenomena which occur in the human body, from the (self-)depolarization of neurons (occurring at milliseconds) and the sinoatrial (SA) node of the heart (the “pacemaker”; at about 60 beats per minute), ventilation (every 4 seconds), to circadian rhythm (24 hours) and various endocrine cycles lasting for several days to one month (Tagg 1997). The fact that most of these phenomena are driven by electrical and biochemical processes (e.g. via ion channels and messenger proteins) thus provides a link between natural forces and biological periodicities, which is crucial to the establishment of the sense of time. Furthermore, these findings suggest that rhythm is processed and perceived in a “hierarchical” fashion, as the result of the interplay between the lower and upper brain areas (Figure 1):