Imitation of F0 tone contours by Mandarin and English speakers is both categorical and continuous

The perception of Mandarin flat-falling tonal contrast has been proposed to be guided by both linguistic categories, expected in native speakers, and psychophysical categories, relevant to all speakers. A recent study has shown that phonetic imitation of Mandarin tones is mediated by categories, but it remains unclear whether this non-linear imitation is mediated by linguistic categories, psychophysical categories, or both. To address this question, the current study investigated the categorization and imitation of a Mandarin flat-falling tonal continuum by both Mandarin speakers and English speakers who were naïve to tonal languages. Imitation distributions were analyzed by comparing the fit of a linear regression model, which assumes participants linearly track phonetic cues, and a Gaussian mixture regression model, which assumes imitation reflects underlying categories. Results revealed that both groups imitated the tonal continuum as a mixture of ‘flat’ and ‘falling’ categories while also tracking some within-category F0 variations. However, Mandarin speakers’ imitation was more categorical than that of the English speakers, and hyper-articulation was elicited only in Mandarin speakers’ imitations. Results suggest that imitation reflects two sources: pre-existing categories and within-category variation in the phonetic cues signaling the category, and that imitation is mediated by not only linguistic categories but also by lower-level psychophysical categories.