The acquisition of implicit regularities in music and language domains during toddlerhood.

Introduction Previous studies have shown that infants can implicitly learn structural regularities from early in development (Bulf et al., 2015; Bettoni et al., 2020, 2021). Building on this evidence, the present study investigates toddlers’ sensitivity to harmonic structures and linguistic rules. Specifically, we examined: (1) spontaneous preference for consonant vs. dissonant isolated chords; (2) implicit learning of harmonic regularities; and (3) implicit learning of morphosyntactic regularities. We further tested whether the ability to extract harmonic rules correlates with learning linguistic rules. Method Sixty toddlers (18–36 months) were recruited across two contexts to maximize ecological validity: laboratory (n = 6) and kindergarten (n = 54). In Task 1, children viewed two visually identical stimuli differing only in harmonic vs. disharmonic isolated chords. In Task 2 Children were exposed to four-chord sequences following Western harmonic rules, which ended with a congruent or incongruent closing chord; and in Task 3 were exposed to grammatically correct or incorrect Italian sentences based on how adjectives adapt to noun based on their gender and number. Ocular behavior (fixations and saccades) was recorded with eye-tracking. The Music@Home questionnaire assessed children’s musical exposure at home to examine its influence on musical and linguistic rule-learning tasks. It also evaluated whether such exposure increases children’s attention and curiosity toward structural novelty. Results No spontaneous preference emerged for consonant vs. dissonant isolated chords (Task 1). By contrast, toddlers successfully extracted both harmonic rules (Task 2) and morphosyntactic regularities (Task 3). Importantly, correlation analyses revealed that children who learned the musical rule were also more likely to learn the linguistic rule, suggesting a shared mechanism for processing structural regularities across domains. Moreover, children more frequently exposed to music, both during pregnancy and in the home environment, showed greater curiosity and attention toward incongruent harmonic endings. Conclusion These findings demonstrate that toddlers’ sensitivity to harmonic structure parallels their capacity to process linguistic regularities. The observed correlation supports the hypothesis that music-based learning can scaffold early language development, highlighting its potential for early interventions in children with primary language impairments.