The Phonology-Morphology Interface in Igbo Verb Morphology: Evidence for Cyclic Spell-Out in Optimality Theory

This study presents a formal analysis of the phonology-morphology interface in Igbo verb morphology, developing an Optimality Theoretic account that deploys cyclic spell-out to explain attested but previously unaccounted-for interactions between tonal morphology and segmental phonological processes at verb stem boundaries. Igbo verb morphology presents a rich array of tonal and segmental phonological changes that are morphologically conditioned, and the formal analysis of these interactions has been a persistent challenge in Igbo phonological theory. The research employs an experimental linguistic methodology to establish empirical adequacy, combining production data from 30 native Igbo speakers in Anambra State through paradigm elicitation with instrumental verification of tonal contours in morphologically complex verbs. The empirical dataset covers 50 verb stems across four morphological construction types, generating a paradigm matrix of 200 morphologically complex forms for analysis. An Optimality Theoretic analysis employing Stratal OT with cyclically evaluated constraint rankings is developed and evaluated against the full paradigm matrix. Findings demonstrate that a two-stratum model with distinct constraint rankings for morphological and phonological levels accounts for 94 percent of the attested surface forms, outperforming a flat (non-stratal) OT analysis. The study makes an original contribution to the formal phonological analysis of Igbo and to the theoretical debate on cyclicity in Optimality Theory, with implications for the typology of phonology-morphology interaction in tonal languages. Keywords: phonology-morphology interface, Igbo, Optimality Theory, tonal morphology, cyclic spell-out.