The Acquisition of Tonal Grammar by Igbo-Speaking Children in Lagos: A Longitudinal Developmental Study

This study presents a longitudinal investigation of the acquisition of tonal grammar by Igbo-speaking children aged two to six years in Lagos, South West Nigeria, making an original contribution to the sparse literature on tonal language acquisition in West Africa. The acquisition of tone as a grammatical and lexical system presents unique developmental challenges, and the Lagos Igbo-speaking community offers a distinctive context of Igbo tonal acquisition occurring in conditions of Nigerian Pidgin and English contact that may affect the trajectory of tonal development. The research employs a prospective longitudinal design following 30 Igbo-speaking children from age 24 months to 72 months, with data collection points every six months. Data include audio and video recordings of naturalistic parent-child interactions, researcher-led production elicitation tasks for targeted tonal contrasts, and tonal discrimination tasks introduced at age 36 months. The analysis tracks the emergence of lexical tone, grammatical tone morphology including verbal tone alternations, and downstep as developmental milestones. Findings reveal a broadly similar acquisition trajectory to published accounts of tonal acquisition in Mandarin and Yoruba, but document a contact-specific delay in the acquisition of downstep among children in highly Pidgin-dominant households, suggesting tonal input reduction effects. The study makes an original empirical contribution to both Igbo linguistics and first language acquisition theory and recommends bilingual parenting strategies for families seeking to maintain Igbo tonal competence in diaspora urban settings. Keywords: tonal acquisition, Igbo, child language acquisition, Lagos, longitudinal study.