Starting with tracking the tone changes in the Bangkok Thai over the past century, a crosslinguistic trend, referred to as “clockwise cycle”, has been revealed. On the other hand, Northern Vietnamese is a quite rare language, which has glottalized tones that are absent in Thai, along with the accumulation of acoustic data in the past 70 years. Therefore, this paper tracks the acoustic data of Northern Vietnamese. As a result, while modal tones exhibit clockwise cycle motivated by the progressive coarticulation effect of fo, non-modal tones may exhibit another changing trend motivated by the regressive coarticulation effect of phonatory characteristics.
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