Abstract
Humans across cultures show an outstanding capacity to perceive, learn, and synchronise with musical rhythms. These skills rely on mapping the sheer diversity of external rhythms onto sets of internal rhythmic categories. Yet, the nature and neural basis of rhythm categorisation remain largely unknown. Here, we present a novel approach allowing to capture categorical representations of rhythms from neural activity based on a combination of (i) electroencephalography (EEG), (ii) frequency-tagging, and (iii) representational similarity analysis (RSA). Using this approach, we were able to capture first evidence that during movement-free listening, the human brain maps two-interval rhythms onto discrete categories based on small-integer ratios. Importantly, these categorical representations could not be trivially explained by acoustic features of the stimuli, but instead were highly consistent with those found in behaviour when the same adult participants were asked to tap the finger to the same stimuli.
Where in the brain do these categorical representations emerge? It has been proposed that rhythm categorisation could be driven by fundamental low-level physiological properties of neural assemblies, hence, it may occur already in the evolutionary old subcortical parts of the brain. Such neural basis would explain the widespread occurrence of small-integer ratio categories in music around the world. To address this question, we coupled the novel approach with a functional localizer to simultaneously capture activity originating from higher-level cortical vs. subcortical auditory sources, in the form of slow (< 20 Hz) and fast (> 200 Hz) EEG responses. Preliminary results suggest the presence of rudiments of rhythm categorisation in subcortical responses, that are nonetheless markedly different from representational structures found in cortical activity. Together, these findings indicate that rhythm categorisation is further shaped at the cortical level, potentially through connections with higher-level motor and/or associative cortices. These evolutionarily newer plastic networks would thus account for the cross-cultural diversity specific to human rhythm perception and production. We are now investigating these new avenues by comparing neural categorisation of rhythm over development and cultures.
Bio
Francesca Barbero is a postdoctoral research fellow at the Rhythm and Brains Lab led by Prof. Sylvie Nozaradan (UCLouvain, Belgium). She carried her PhD under the supervision of Prof. Olivier Collignon in the Crossmodal Perception and Plasticity Lab (UCLouvain, Belgium), where she investigated voice perception and experience-dependent plasticity associated with the processing of socially relevant sounds. After her PhD, she joined Prof. Nozaradan’s lab, where she is currently working on research projects aimed at better understanding rhythm categorisation in music and how it develops during the lifespan depending on experience. Francesca’s main research interests include understanding how humans make sense of what they hear and how auditory perception is influenced by different sensory-motor experiences and multisensory contexts throughout the lifespan.