Abstract: Tone sandhi occurs in Chinese, when two tones are pronounced toge-ther. This phonological rule may give some constraints on the perceptionof tone. 10 subjects took part in a traditional psychophysical experimentto recognize two sets of continua of standard Chinese sounds in whichthe tones of their monosyllables and disyllables Were varied in steps fromthe second tone to the third tone. The experimental results of both setsof continua are similar: when compared with the monosyllable, the pho-neme boundaries between the second tone and the third tone of disyllableare shifted to the end of the second tone. The constraints suggested abo-ve are thus verified.

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