Tone differentiation as a means for assessing non-native imitation of Thai tones by Mandarin speakers

Non-native tone production and imitation have been found to be phonetically deviant from native production for some discrete measures. However, it remains unresolved whether nonnative imitation differs from native production in terms of the differentiation of tones in acoustic tone space. 32 native Mandarin speakers who had no experience with Thai imitated five Thai tones, and each participant produced 160 tokens in total under differing memory load and stimulus variability conditions to determine effects of cognitive demands. We calculated two tone differentiation indices (i.e. Index 1: tone differentiation within the tonal space; Index 2: differentiation among tones, both as in Barry & Blamey, 2004) based on F0 onset and F0 offset for Thai tones and the non-native imitations of these Thai tones by Mandarin imitators. There was a significant memory load by vowel variability interaction for Index 1 and a main effect of talker variability and a three-way interaction (memory load ´ talker variability ´ vowel variability) for Index 2, suggesting that tone differentiation is affected by cognitive factors. Nonetheless, non-native tone imitations were not significantly different from native productions on either index, indicating that non-native imitation resembles native production in terms of tone differentiation in an onset-offset F0 space.