Effect of tempo on newborns' neural processing of auditory rhythm: Emergence of sensitivity to metrical structure

Rhythm perception ability underpins music and language processing, and its developmental origins trace back to the earliest periods of life. While most rhythm patterns contain a variety of inter-onset intervals, listeners typically extract a steady underlying beat periodicity, as well as beat grouping periodicities (groups of two or three beats will be at frequencies 1/2 or 1/3, respectively, of that of the primary beat), forming a metrical hierarchy. While the developing brain can track auditory rhythm before birth, a previous study found that neural sensitivity to faster beat-related periodicities emerges early in third trimester of gestation, whereas encoding of slower metrical structure periodicities only appears closer to term birth. However, as rhythm patterns were only presented at one tempo, neural sensitivity to metrical structure could not be disentangled from sensitivity to tempo during early development. Thus, here we presented auditory rhythmic sequences at two different tempi and used high-resolution electroencephalography to measure neural sensitivity to their encoding in full-term newborns and young adults. Adults demonstrated a similar sensitivity to metrical structure across tempi, with greatest response at the duple metrical frequency regardless of tempo. Newborn neural responses, by contrast, were tempo-dependent, displaying markedly different response patterns across beat and meter frequencies at the different tempi. Together, these results reveal that tempo and metrical structure interact in shaping how the neonatal brain encodes auditory rhythm, suggesting that early neural processing may be constrained in its ability to track slower periodicities, and highlighting a developmental shift in the relative contributions of tempo and metrical structure to rhythmic processing.