Does vowel intrinsic f0 affect lexical tone?

Diachronic change has often been linked with synchronic instability and the realignment of phonological categories according to fine phonetic detail. For example, the development of tones in some languages is widely believed to have been the result of coarticulatory influences of onset obstruent voicing contrasts on the fundamental frequency (f0) of the following vowel. This is just one example of a phenomenon known as intrinsic f0. Our goal was to investigate whether lexical tone can be influenced by vowel intrinsic f0 effects. In a study of Hong Kong Cantonese, we found that f0 is significantly affected by both lexical tone and vowel openness. Vowel intrinsic f0 effects caused substantial overlap between the tones. We thus find evidence of synchronic instability leading to overlap between distinct phonological categories. These findings may contribute greatly to our understanding of the phonetic precursors to sound change.