Modeling L1 Influence on L2 Pronunciation: An MFCC-Based Framework for Explainable Machine Learning and Pedagogical Feedback

This study investigates the extent to which Mel-Frequency Cepstral Coefficients (MFCCs) capture first language (L1) transfer in extended second language (L2) English speech. Speech samples from Mandarin and American English L1 speakers were extracted from the GMU Speech Accent Archive, converted to WAV format, and processed to obtain thirteen MFCCs per speaker. A multi-method analytic framework combining inferential statistics (t-tests, MANOVA, Canonical Discriminant Analysis) and machine learning (Random Forest classification) identified MFCC-1 (broadband energy), MFCC-2 (first formant region), and MFCC-5 (voicing and fricative energy) as the most discriminative features for distinguishing L1 backgrounds. A reduced-feature model using these MFCCs significantly outperformed the full-feature model, as confirmed by McNemar's test and non-overlapping confidence intervals. The findings empirically support the Perceptual Assimilation Model for L2 (PAM-L2) and the Speech Learning Model (SLM), demonstrating that L1-conditioned variation in L2 speech is both perceptually grounded and acoustically quantifiable. Methodologically, the study contributes to applied linguistics and explainable AI by proposing a transparent, data-efficient pipeline for L2 pronunciation modeling. The results also offer pedagogical implications for ESL/EFL instruction by highlighting L1-specific features that can inform intelligibility-oriented instruction, curriculum design, and speech assessment tools.