Tonal Invariance and Downtrend in Cantonese

Studies of downtrend have reported that accents/tones are realised at progressively lower F0 values during an utterance. Listeners are reported to compensate for such F0 variations over time( Pierrehumbert 1979). Underlying the downtrend studies is the assumption that the phonological categories under investigation are invariant over time and that declination can be factored out of the quantitative characterisation of a given phonological category. In studying Vietnamese tones, Earle (1975) found that variable F0 values for tones can be resolved to distinctive tonal categories in relation to a normalised tonal space: after normalisation, stable and consistent tonal relations were uncovered. The current paper investigates whether such a normalisation is possible as the tonal space changes over time with declination. A production study based on read speech showed first that there is downtrend in Cantonese, and second tonemes exhibit quantitative invariance relative to a locally-determined tonal space.