ISCA Workshop on Plasticity in Speech Perception (PSP2005)
Senate House, London, UK
Downtrend results in different f0 values for a phonologically equivalent accent/tone (Pierrehumbert 1979, Prieto 1996, 1998, Shih 2000). In a late-occurring position-in-utterance, the phonetic f0 value of an accent is realised lower than in an early-occurring position-in-utterance. In equating different f0 values to the same perceived prominence of an accent, it has been shown that listeners compensate for downtrend with regard to a global reference line (Pierrehumbert 1979, Gussenhoven and Rietveld 1988, Terken 1991, Gussenhoven et al 1997). The current study investigated normalisation of downtrend in a tone language, which allows us to examine which f0 targets in the f0 contour can be employed as a reference frame in normalising for downtrend.
A perception experiment was conducted on Cantonese tones to test whether the listeners compensate for downtrend in tone perception and how different f0 values in different positions-inutterance can be equated to the same tone. Cantonese has two tones - High Mid and Mid Low, which are contrastive in terms of f0 height. With downtrend, a late-occurring High Mid tone is realised with a lower f0 level than an early-occurring High Mid tone. The same is also found for a Mid Low tone. On account of downtrend, it is likely that a lateoccurring High Mid tone will exhibit an f0 value similar to an early-occurring Mid Low tone. Under such scenario, how can the listener decide whether an f0 value belongs to a High Mid tone or a Mid Low tone?
In the first part of the experiment, subjects were instructed to identify a lexical word occurring in different positions-in-utterance. Results showed that a given f0 value in a late-occurring position-inutterance led to more High Level tone responses than in an early-occurring position-in-utterance.
The second part of the experiment was concerned with whether local f0 context was used as a frame of reference in normalising for downtrend. Results showed that more Mid Low tones were perceived in a late-occurring utterance position when the f0 value of an adjacent tone was raised than in the original late-occurring utterance position without any modification of the local f0 context.
The results of the experiment will be discussed in terms of time-dependent downtrend and the primacy of local f0 context as a frame of reference in equating different phonetic f0 values to the same phonological tone in Cantonese.
Bibliographic reference. Yuen, Ivan (2005): "Local context effect on downtrend normalisation in Cantonese", In PSP2005, 64.