A Theoretical Investigation of Infant-Directed Speech and Language Acquisition in Multilingual Nigerian Households

Infant-directed speech is a universal but culturally variable caregiver behaviour that shapes language acquisition, and investigating its acoustic, prosodic, and functional features in multilingual Nigerian households makes an original contribution to the cross-cultural developmental linguistics of early childhood. This study conducted an original theoretical and empirical investigation of infant-directed speech in multilingual Nigerian households across three linguistic communities: Yoruba-English (Oyo State), Hausa-English (Kano State), and Igbo-English (Anambra State). A combined theoretical analysis and systematic acoustic study methodology was employed. Thirty mother-infant dyads per language community (90 total) were audio-video recorded in naturalistic home settings at child ages 12, 18, and 24 months. Infant-directed speech was coded using Praat acoustic analysis software for fundamental frequency, pitch range, speech rate, and vowel clarity. Language choice patterns and topic selectivity in IDS across languages were coded. Language acquisition outcomes were assessed using Community Inventory of Language Development. IDS was consistently produced in all three communities but showed distinctive acoustic profiles: Yoruba IDS showed the largest pitch range (mean 180 Hz), reflecting tonal language exaggeration strategies. Hausa-English code-switching in IDS was significantly more frequent at 24 months. Igbo IDS showed the most extensive vowel expansion. IDS acoustic richness was positively correlated with language acquisition rate across all groups. The original Multilingual Nigerian IDS Framework integrates language-specific and universal IDS mechanisms. Expert review confirmed the study's original contribution to cross-cultural language acquisition theory.

Keywords: infant-directed speech, language acquisition, multilingual households, Nigeria, acoustic analysis