The effect of lexical frequency and Lombard reflex on tone hyperarticulation

Among the many factors that affect phonetic variation, two of them, low word frequency and speech in noise (Lombard speech), are linked to stronger or fuller realizations of segments. Noise and low usage frequency are both factors that may lead to perceptual difficulty suggesting that the strengthening due to these two factors may be related. To understand how these two factors relate to each other and to see if they play a similar role with respect to suprasegmental phenomena like tone, we investigated the effect of ambient noise and word usage frequency on tone production in Cantonese. We recorded Cantonese monosyllabic words of high and low usage frequency in both normal and Lombard speech styles, controlling for segmental and other factors and measured f0. We found that both ambient noise and lexical frequency influence tonal production. All six tones are produced with higher f0 in the presence of noise. Usage frequency affects f0 realization as well, but only for words with mid-range (mid-level or mid-rising) tones. Low-frequency words with mid-range tones are produced with higher f0 than frequent words. Extending earlier work showing greater vowel-space dispersion in less frequent words, we also found that the f0 trajectories of less frequent words are more dispersed than that of their more frequent counterparts, especially for mid–low tones. This dispersion does not occur for Lombard speech. Our results suggest that different aspects of speech production may account for the strengthening of speech in noise and in low-frequency words.