Variation in the formant dynamics of southeastern Nigerian English diphthongs

This study investigates the phonetic realization of diphthongs in southeastern Nigerian English (sNigE) to focus on the influence of gender and regional variation and the role of formant trajectories in vowel identity. Building on prior claims that sNigE exhibits monophthongal realizations and reduced diphthongal contrasts (e.g., Jowitt, 2018), this study applies dynamic acoustic methods to reassess vowel patterns in the variety. We sampled data from sNigE from the five states in the region to extract F1 and F2 formants at normalized timepoints and analysed them via generalized additive mixed models (GAMMs). The results revealed significant variation in diphthong realization across lexical sets, with many vowels exhibiting spectral shifts inconsistent with canonical RP diphthongs. Even diphthongs that were monophthongized (e.g., [a:], [a], and [e]) showed temporal movement, aligning with the Vowel-Inherent Spectral Change (VISC) framework. Gender significantly influenced vowel height (F1), whereas vowel frontness (F2) remained relatively consistent, likely because of the shared Igbo L1 across the region. These findings support a gradient view of vowel identity in sNigE and underscore the need to reevaluate Nigerian English phonology through dynamic, trajectory-based analyses.