Asymmetry in Contextual Tonal Variation in Mandarin

It has been long known that the four lexical tones in Mandarin are subject to contextual variation in connected speech. Most of the contextual tonal variation reported to date (not including phonological variation such as tone sandhi) is assimilatory in nature. In this study, however. both assimilation and dissimilation arc found in contextual tonal variation in Mandarin. Four Mandarin spealcers produced the disyllabic sequences of Imama! with all the sixteen possible bitonal combinations of the four lexical tones of Mandarin in four different carrier sentences. Fo measurements were obtained by measuring the distance between adjacent vocal cycles in the wave form and then transforming the measurements into Fo values. The obtained Fo curves were smoothed and normalized so that comparisons among different tonal contexts would be more straightforward. It was found that carryover contextual effect. i.e~ influence of a tone on the following tone, is assimilatory in nature, whereas the anticipatory effect is mostly dissimilatory. In both cases, the actualization of a tone varies depending on the immediately adjacent tonal values rather than on the entire tone contour of the neighboring tone. While a low ending value in a tone tends to lower the Fo value of the following tone, a low starting value in a tone tends to raise the Fo value of the preceding tone. While the assimilatory tonal variation can be accounted for by coarticulation. the exact mechanism of the anticipatory tonal dissimilation is less clear. Several accounts for the anticipatory tonal dissimilation are discussed, including phonologicai deletion. wide-swing, limit of low pitch register, and counteraction of declination. The data seem to be most in accord with the last two accounts.