The effects of lexical frequency and homophone neighborhood density on incomplete tonal neutralization

We investigated the effects of lexical frequency and homophone neighborhood density on the acoustic realization of two neutralizing falling tones in Dalian Mandarin Chinese. Monosyllabic morphemes containing the target tones (Tone 1 and Tone 4) were produced by 60 native speakers from two generations (middle-aged vs. young). The duration of tone-bearing syllable rhymes, as well as the F0 curves and velocity profiles of the lexical tones were quantitatively analyzed via linear mixed-effects modeling and functional data analysis. Results showed no durational difference between T1 and T4. However, the F0 contours of the two falling tones were incompletely neutralized for both young and middle-aged speakers. Lexical frequency showed little effect on the incomplete tonal neutralization; there were significant differences in the turning point of the two falling tones in syllables with both high and low lexical frequency. However, homophone neighborhood density showed an effect on the incomplete neutralization between the two falling tones, reflected in significant differences in the slope and turning point of the F0 velocity profiles between the two tones carried by syllables with low density but not with high density. Moreover, homophone neighborhood density also affected the duration, the turning point of F0 curves, and velocity profiles of the T1- and T4-syllables. These results are discussed with consideration of social phonetic variations, the theory of Hypo- and Hyper-articulation (H&H), the Neighborhood Activation Model, and communication-based information-theoretic accounts. Collectively, these results broaden our understanding of the effects that lexical properties have on the acoustic details of lexical tone production and tonal sound changes.