Evidence of top-down meter representation in infant auditory rhythm perception

• In Event: Poster Session 11
  In Poster Session: PS 11 Topic - Biological Processes: Neuroscience and Genetics

Abstract

Across cultures, infants are exposed to music, and sensitivity to beat and rhythm are present in early development. From rhythmic patterns, people extract the beat – the regular temporal intervals we tap or dance to. Beats can be perceptually grouped into structures called meter. For example, a repeating 6-beat rhythm pattern can be perceived as three 2-beat groups (march meter) or two 3-beat groups (waltz meter; Fig. 1). A previous study from our lab found that without priming, 7-month-olds presented with the repeating ambiguous rhythm of Figure 1 show electroencephalographic (EEG) steady-state responses at all three frequencies present in the stimulus, representing beat, duple and triple levels (Cirelli et al., 2016). However, adults asked to imagine the ambiguous rhythm pattern in one metrical interpretation or another show more energy at frequencies corresponding to their metrical interpretation (Nozaradan et al., 2011). Event-related potentials for rhythm perception have also been studied. Specifically, the mismatch negativity (MMN) is automatically elicited at around 100 - 200 ms after stimulus onset by occasional unexpected ‘deviant’ sounds in a sequence of standard sounds (Näätänen & Alho, 1995). Though the MMN is automatic, it can be modulated by top-down processes, such as internal perceptions of meter. For example, deviants on metrically strong, as opposed to weak beats elicit larger amplitude MMN in infants (Winkler et al., 2009) and adults (Bouwer et al., 2014). Sometimes the MMN response is followed by a positivity called the P3a around 250 ms after stimulus onset, that appears only for awake, attentive participants (Basirat, et al., 2014).
While previous studies show infants can discriminate different metrical structures, it is not known whether they can maintain a metrical interpretation through top-down processes in the case of an ambiguous rhythm. We investigated 6-month-olds’ (N = 24) steady-state and ERP brain responses to the 6-beat rhythm pattern of Figure 1. Thirteen were primed to hear the pattern in duple meter and eleven in triple meter through loudness accents either on every second or every third beat. Periods of priming (4 repetitions of the pattern with accents) were inserted before test trials, which consisted of 16 repetitions of the ambiguous unaccented pattern. To examine MMN, rare pitch deviants occurred on either beat 4 (strong beat in the triple interpretation; weak in triple) or beat 5 (strong in the triple; weak in duple) of the unaccented stimulus. Instead of adult-like MMN, we found a late positive response which, in frontal left sites, was larger for the strong beat vs the weak beat in the duple group. In line with our hypothesis, this shows that some internalization of the duple meter lead to a difference in processing deviants that occur on strong beats. Further, we found that the late positive response was larger overall for those in the duple group compared to the triple group in frontal right sites. These results indicate infants can impose a top-down internally generated metrical structure on ambiguous auditory rhythms, an ability that would aid early language and music learning.

Authors

• Erica Flaten, McMaster University
  Presenting Author

• Laurel Trainor, McMaster University
  Non-Presenting Author