The Neurolinguistics of Igbo Tonal Processing: An EEG Investigation of Cortical Responses to Tonal Contrasts in Native and Non-Native Speakers

This dissertation presents the first electroencephalography investigation of neural processing responses to lexical tonal contrasts in Igbo among native Igbo speakers and Igbo-learning non-native speakers from Yoruba and Hausa language backgrounds. The neurolinguistic processing of tonal information in non-European languages has expanded significantly as a research domain, but Igbo tonal neurolinguistics remains entirely unstudied. The study recruits thirty native Igbo speakers, twenty Yoruba-background intermediate Igbo learners, and twenty Hausa-background beginner Igbo learners, exposing each group to carefully controlled auditory stimuli including tonal minimal pairs, tonal violations, and semantically congruent and incongruent sentence contexts. EEG data are processed using standard event-related potential analysis pipelines, with particular focus on the N400, P600, and mismatch negativity components as indices of lexical-tonal semantic processing and tonal change detection. Findings reveal that native speakers generate robust mismatch negativity responses to tonal violations with latency profiles consistent with rapid automatic tonal processing. Yoruba-background learners demonstrate intermediate tonal processing speed reflecting positive transfer from Yoruba's own tonal system, while Hausa-background learners show significantly attenuated and delayed neural responses, consistent with the absence of a tonal system in their L1. The dissertation contributes original neurolinguistic data to Igbo linguistics and to cross-linguistic tonal learning research. Keywords: Igbo neurolinguistics, EEG, tonal processing, event-related potentials, second language acquisition.