The internal pulse

From the domain of music and neuroscience, Grahn (2009) provides a comprehensive review of the various research approaches and finding, citing the lack of consensus about timing mechanisms and the problems of comparing neuroscientific findings across different studies. ‘Rhythm’ is defined as the pattern of temporal intervals in a stimulus sequence that can induce an internal pulse (we ‘feel the beat’), and the internal organization of these pulses can lead to the perception of a recurring pattern of relative pulse strengths termed ‘meter’. The process of synchronizing the endogenous pulse with an external rhythm is called ‘entrainment’. In human interaction, this involves the mutual co-adaptation between persons.

Grahn takes us through the ways in which rhythm has been analysed in the brain, forewarning that there is little consensus about the best way to model timing, or how timing is accomplished neurally. ‘Timing has been modelled with neural clock or counter mechanisms, represented as either pulses (firing) or neural oscillations (Buhusi and Meck 2005; Ivry and Richardson 2002), but timing can also be implicit, or an emergent property of movement (Ivry and Spencer 2004)’. Neural oscillator approaches have been more successful in showing how higher-level features of temporal patterns, such as pulse and meter, can arise from the responses of neural non-linear oscillators to rhythmic stimuli (Large 2000, 2008), and this better fits the discussion in this paper on entrainment as coupling in interactional synchrony. Neural oscillation arises from interactions of excitatory and inhibitory neural populations. Through mathematical modelling of these interactions, the universal properties of neural oscillation can be deduced, and these properties examined for features that may correspond to properties of rhythmic behaviour. This ‘neural resonance’ (neural oscillators resonating with rhythmic stimuli) approach gives rise to properties such as pulse and meter, which are aspects of rhythms that have not been easily accounted for by other types of models (Large and Snyder 2009).

Earlier in the paper, we mentioned Winkler et al.’s study (2009) of infants (2 or 3 days old) who are listening to simple rhythms whilst their brain responses are measured using EEG. Every so often, a part of the rhythm was omitted. In some cases, this omission did not disrupt the feel of the beat in the rhythm, but at other times it did. The researchers wanted to know whether the newborns could ‘feel the beat’ and tell when the beat was disrupted. A clear difference was found in their EEG measurements when listening to an omission that disrupted the beat as compared to an omission that did not disrupt the beat. The authors suggest that beat perception may be innate. It has also been found in another study that infants’ rhythm perception is influenced by being ‘bounced’ in time with music (Phillips-Silver and Trainor 2005).

Grahn believes that continued cross-disciplinary endeavours and communication between different fields of music, movement, and language research is needed in neuroscientific research into music. This resonates with Bispham’s call for more understanding on the relationship and differences between the ways entrainment works in music and in language.

Although much of the work in neuroscience is not directly dealing with human interpersonal synchrony, the emerging findings on rhythm and entrainment (perceiving and responding to beat, pulse), and on the mirroring of neural activity of certain motor actions, provide support for findings from studies of interpersonal synchrony that are based on experimental and observation techniques within various disciplines, most significantly music psychology, kinesics, interaction analysis.