Suprasegmental aspects of phonetic feature representation in human cortex : an fMRI investigation of Cantonese lexical tones

Abstract

This study investigated the neural basis of lexical tone representation in Cantonese, a complex tone language that contrasts pitch height and slope to convey lexical meaning. We used sparse-sampling fMRI to measure brain activity from native Cantonese speakers performing three tasks involving tonal syllables: passive listening, silent repetition, and word identification. Behavioral performance with high identification rates confirmed effective stimulus processing. Group-level activation and multivariate pattern analyses revealed a distributed bilateral network encompassing the bilateral precentral gyri (PrCG), right superior frontal gyrus (RSFG), bilateral superior temporal gyri (STG), left inferior parietal sulcus (LIPS), and bilateral lingual gyri (BiLG), which reliably encoded tone categories. Using dissimilarity matrices constructed from tonal features and neural activation patterns, representational similarity analysis (RSA) showed bilateral STG encoding pitch height and LIPS processing pitch slope. The frontal regions, LIPS, and BiLG contribute to holistic tone processing. This contrasts with the temporal-parietal network identified in previous Mandarin studies, suggesting that Cantonese tones invoke a bilateral and more extended brain network. The inter-subject RSA results revealed significant brain-behavioral correlations in the frontal and parietal regions, suggesting that these regions are closely associated with tone categorization performance. Other regions showed non-significant correlations, indicating their involvement in tone processing but not directly predicting behavioral performance. Together, these findings enhance our understanding of the neural mechanisms underlying tone perception in complex tonal languages and highlight the intricate role of bilateral cortical networks supporting the representation of complex suprasegmental phonetic features.