Neural mechanisms of the categorical perception of lexical tones in mandarin-speaking adults

Categorical perception (CP) enables listeners to transform continuous acoustic variation into discrete phonological representations, forming a foundation of speech perception. While CP has been extensively studied for segmental phonemes, its neural mechanisms in suprasegmental lexical tones remain less understood. This fMRI study examined the neural substrates and functional connectivity underlying within-category (WC) and across-category (AC) lexical tone perception in native Mandarin speakers. Twenty college students completed a categorical perception task using a nine-step /ba 2 /−/ba 4 / tonal continuum under four conditions: Standard, WC, AC, and Silence Baseline (BL), in a blocked fMRI design. Behavioral results showed high accuracy across conditions, with slightly better performance for AC than WC tones. Neuroimaging analyses revealed that AC > BL activated the left middle temporal gyrus, whereas WC > AC engaged a broader dorsal network including bilateral superior temporal gyri, the left inferior frontal gyrus, and temporal poles. Psychophysiological interaction analyses further demonstrated enhanced functional connectivity among the left inferior frontal gyrus, superior temporal gyri, and temporal poles during WC processing, suggesting increased integration between auditory and articulatory regions. These findings support a dual-stream model of speech perception, in which ventral temporal regions encode categorical phonological information, and dorsal auditory–motor circuits mediate fine-grained acoustic analysis. The results also align with predictive coding accounts, suggesting that within-category ambiguity increases top-down modulation from frontal regions. Collectively, this study advances understanding of the neural architecture underlying categorical tone perception and illustrates how auditory–frontal interactions support language-specific phonological categorization in tone-language speakers.