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

Native speakers imitate F0 contours that vary between two lexical tones non-linearly–they do not precisely reproduce the presented F0 features but instead cluster them toward tonal categories, the so-called contrast mediation effect. However, less is known whether non-native speakers who lack the lexical tone phonology will show linear imitation of F0 contours. Addressing this question will deepen our understanding of whether F0 imitation is solely influenced by lexical tone contrasts or also shaped by other sources of non-linearity beyond phonological contrasts. To investigate this, the current study examined 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 two models: a linear regression model, which assumes participants linearly track phonetic cues, and a mixture regression model, which assumes imitation reflects underlying categories. The mixture regression model fit the data better for the Mandarin speakers while the reverse was true for the English speakers, suggesting that Mandarin speakers imitated the F0 contours more categorically than English speakers. However, for both groups, the data was best fit using a weighted combination of both models. For the Mandarin group this result along with additional analyses of duration, F1 and intensity suggest that tone categories involve both phonological and phonetic information and imitation taps both, possibly via hyper- and hypo-articulation. For English participants, the evidence for categorical mediation suggests that imitation is mediated by factors other than lexically contrastive linguistic categories, although the exact nature of the factors is unclear.