An Empirical Study of Vowel Harmony Violations in Yoruba Child Language Acquisition

Child language acquisition in tone languages with vowel harmony systems requires learners to simultaneously master multiple interacting phonological constraints, providing important data for theories of phonological development. This study empirically investigates vowel harmony violations in Yoruba child language acquisition, examining how and when Yoruba-acquiring children master the advanced tongue root vowel harmony system. Longitudinal speech samples were collected from 20 Yoruba-acquiring children aged between two and four years from monolingual Yoruba-speaking families in Ibadan, Oyo State, South West Nigeria, over a twelve-month period. Acoustic phonetic analysis was conducted on vowel productions to identify harmony violations, error patterns, and developmental trajectories. The study draws on phonological acquisition theory, specifically Optimality Theory developmental models and the Feature Geometry approach to vowel harmony acquisition. Existing research on Yoruba phonological acquisition has addressed tonal development, with the acquisition of advanced tongue root vowel harmony being empirically underdocumented in the developmental literature. This study addresses that acquisition data gap. The research investigates the order in which harmony constraints are acquired, whether harmony violations occur more frequently in specific morphological environments, and whether children's harmony error patterns reflect the underlying phonological structure predicted by adult grammar models. Findings are expected to reveal a staged acquisition trajectory in which harmony in lexical roots precedes harmony across morpheme boundaries, consistent with optimality theoretic developmental predictions. Recommendations will address Yoruba phonological acquisition research methodology and early childhood speech assessment protocols for Yoruba-speaking children. Keywords: vowel harmony, Yoruba, child language acquisition, phonological development, acoustic phonetics.