Jie Zhang 
Effects of Duration and Sonority on Countour Tone Distribution [PDF ebook] 
A Typological Survey and Formal Analysis

First Published in 2002. Part of the Outstanding Dissertations in Linguistics series, this is an in-depth investigation of the effects of duration and sonority on contour tone distribution. The term "tone language" usually refers to languages in which the pitch of a syllable serves lexical or grammatical functions. In some tone languages, the contrastive functions of pitch are sometimes played by pitch changes within a syllable. Pitch changes of this kind are called contour tones. The distribution of contour tones in a language, are when under what phonological contexts contour tones are more readily realized.