Top-down Influences On Neural Processing Of Rhythm In Infants And Adults

Abstract

In music, listeners extract the beat and can also group beats, such as duple metre (2-beat groupings) or triple metre (3-beat groupings). This internally derived (top-down) structure can give rise to multiple interpretations of a metrically ambiguous rhythm. Top-down rhythm perception is important for music and language development but has thus far been understudied in infants. In the current thesis, six-month-old infants (Chapters 2 and 4) and adults (Chapter 3) were primed to interpret a metrically ambiguous 6-beat rhythm either in duple or triple metre, by periodically adding loudness accents on beats 1,3 and 5, or on beats 1 and 4, respectively, before hearing the unaccented, ambiguous rhythm. Using electroencephalography (EEG), I examined whether the primed metre influenced participants' predictions of individual beats within the rhythm, indexed by mismatch responses, as well as whether the primed metre improved the brain's overall tracking of the metre frequency, as indexed by neural tracking measures. Infants’ predictions of unexpected pitch changes occurring on beats 4 or 5 were modulated by the primed metre, such that mismatch responses were larger for the strong compared to weak beat position according to the primed metre (Chapter 2), especially in the duple case. Adults (Chapter 3) were comparatively less flexible than infants to being primed, showing a robust bias to the duple metre across EEG measures, although actively attending to the metre improved neural tracking of the primed metre. Further, infants may be limited in their generalizability of a primed metrical structure across different tempos (Chapter 4). Across chapters the results also suggest a duple bias that starts in infancy and is strengthened by musical experience. This thesis provides the first evidence of infants’ top-down maintenance of a structure on an ambiguous rhythm while directly comparing to adults. The work has implications for understanding music and language perception development, and developmental disorders.